Optical Detection in Ultrafast Short Wavelength Science

International Nuclear Information System (INIS)

Fullagar, Wilfred K.; Hall, Chris J.

2010-01-01

A new approach to coherent detection of ionising radiation is briefly motivated and recounted. The approach involves optical scattering of coherent light fields by colour centres in transparent solids. It has significant potential for diffractive imaging applications that require high detection dynamic range from pulsed high brilliance short wavelength sources. It also motivates new incarnations of Bragg's X-ray microscope for pump-probe studies of ultrafast molecular structure-dynamics.

Phase-controlled coherent population trapping in superconducting quantum circuits

International Nuclear Information System (INIS)

Cheng Guang-Ling; Wang Yi-Ping; Chen Ai-Xi

2015-01-01

We investigate the influences of the-applied-field phases and amplitudes on the coherent population trapping behavior in superconducting quantum circuits. Based on the interactions of the microwave fields with a single Δ-type three-level fluxonium qubit, the coherent population trapping could be obtainable and it is very sensitive to the relative phase and amplitudes of the applied fields. When the relative phase is tuned to 0 or π, the maximal atomic coherence is present and coherent population trapping occurs. While for the choice of π/2, the atomic coherence becomes weak. Meanwhile, for the fixed relative phase π/2, the value of coherence would decrease with the increase of Rabi frequency of the external field coupled with two lower levels. The responsible physical mechanism is quantum interference induced by the control fields, which is indicated in the dressed-state representation. The microwave coherent phenomenon is present in our scheme, which will have potential applications in optical communication and nonlinear optics in solid-state devices. (paper)

Coherent dynamics in semiconductors

DEFF Research Database (Denmark)

Hvam, Jørn Märcher

1998-01-01

enhanced in quantum confined lower-dimensional systems, where exciton and biexciton effects dominate the spectra even at room temperature. The coherent dynamics of excitons are at modest densities well described by the optical Bloch equations and a number of the dynamical effects known from atomic......Ultrafast nonlinear optical spectroscopy is used to study the coherent dynamics of optically excited electron-hole pairs in semiconductors. Coulomb interaction implies that the optical inter-band transitions are dominated, at least at low temperatures, by excitonic effects. They are further...... and molecular systems are found and studied in the exciton-biexciton system of semiconductors. At densities where strong exciton interactions, or many-body effects, become dominant, the semiconductor Bloch equations present a more rigorous treatment of the phenomena Ultrafast degenerate four-wave mixing is used...

Influence of temporal–spectral effects on ultrafast fiber coherent polarization beam combining system

International Nuclear Information System (INIS)

Yu, H L; Ma, P F; Wang, X L; Su, R T; Zhou, P; Chen, J B

2015-01-01

The active coherent polarization beam combining (CPBC) technique has been experimentally proved to be a promising approach for the energy and power scaling of ultrashort laser pulses, despite the tremendous challenge in temporal synchronization, dispersion management and nonlinearity control. In order to develop a comprehensive theoretical model to investigate the influence of temporal–spectral effects on ultrafast fiber active CPBC systems, a generalized nonlinear Schrödinger equation carrying spectral factors is used to depict the propagation of ultrashort pulses in fiber amplifier channels and ultrashort-pulsed Gaussian beams (PGBs) carrying temporal–spatial factors are utilized to picture the propagation of ultrashort pulses in the free space. To the best of our knowledge, the influence of different temporal–spectral effects has been segregated for the first time and corresponding analytical equations have been strictly derived to link the combining efficiency with specific factors. Based on our analysis, the optical path difference (OPD) has the most detrimental impact on the combining efficiency because of the high controlling accuracy and anti-interference requirements. For instance, the OPD must be controlled in ∼  ±14 μm to achieve a combining efficiency of above 95% for combining ultrashort laser pulses with a 3 dB spectral bandwidth of 13 nm centered at 1064 nm. Besides, the analytical expression also demonstrates that the impact of self-phase modulation on the combining efficiency has no dependence on spectral bandwidth and only depends on the B integral difference if neglecting the direct influence of the peak power difference. Our analysis also indicates that the group velocity dispersion has relatively small influence on the combining efficiency. These formulas can be used to diagnose the influence of temporal–spectral effects and provide useful guidelines for the design or optimization of the active CPBC system of ultrafast

Coherent secondary emission from resonantly excited two-exciton states

DEFF Research Database (Denmark)

Birkedal, Dan

2000-01-01

The coherent interaction of light and the electronic states of semiconductors near the fundamental bandgap has been a very active topic of research since the advent of ultrafast lasers. While many of the ultrafast nonlinear properties of semiconductors have been well explained within mean field...

The separation of vibrational coherence from ground- and excited-electronic states in P3HT film

KAUST Repository

Song, Yin

2015-06-07

© 2015 AIP Publishing LLC. Concurrence of the vibrational coherence and ultrafast electron transfer has been observed in polymer/fullerene blends. However, it is difficult to experimentally investigate the role that the excited-state vibrational coherence plays during the electron transfer process since vibrational coherence from the ground- and excited-electronic states is usually temporally and spectrally overlapped. Here, we performed 2-dimensional electronic spectroscopy (2D ES) measurements on poly(3-hexylthiophene) (P3HT) films. By Fourier transforming the whole 2D ES datasets (S (λ 1, T∼ 2, λ 3)) along the population time (T∼ 2) axis, we develop and propose a protocol capable of separating vibrational coherence from the ground- and excited-electronic states in 3D rephasing and nonrephasing beating maps (S (λ 1, ν∼ 2, λ 3)). We found that the vibrational coherence from pure excited electronic states appears at positive frequency (+ ν∼ 2) in the rephasing beating map and at negative frequency (- ν∼ 2) in the nonrephasing beating map. Furthermore, we also found that vibrational coherence from excited electronic state had a long dephasing time of 244 fs. The long-lived excited-state vibrational coherence indicates that coherence may be involved in the electron transfer process. Our findings not only shed light on the mechanism of ultrafast electron transfer in organic photovoltaics but also are beneficial for the study of the coherence effect on photoexcited dynamics in other systems.

The separation of vibrational coherence from ground- and excited-electronic states in P3HT film

International Nuclear Information System (INIS)

Song, Yin; Hellmann, Christoph; Stingelin, Natalie; Scholes, Gregory D.

2015-01-01

Concurrence of the vibrational coherence and ultrafast electron transfer has been observed in polymer/fullerene blends. However, it is difficult to experimentally investigate the role that the excited-state vibrational coherence plays during the electron transfer process since vibrational coherence from the ground- and excited-electronic states is usually temporally and spectrally overlapped. Here, we performed 2-dimensional electronic spectroscopy (2D ES) measurements on poly(3-hexylthiophene) (P3HT) films. By Fourier transforming the whole 2D ES datasets (S(λ 1 ,T ~ 2 ,λ 3 )) along the population time (T ~ 2 ) axis, we develop and propose a protocol capable of separating vibrational coherence from the ground- and excited-electronic states in 3D rephasing and nonrephasing beating maps (S(λ 1 ,ν ~ 2 ,λ 3 )). We found that the vibrational coherence from pure excited electronic states appears at positive frequency (+ν ~ 2 ) in the rephasing beating map and at negative frequency (−ν ~ 2 ) in the nonrephasing beating map. Furthermore, we also found that vibrational coherence from excited electronic state had a long dephasing time of 244 fs. The long-lived excited-state vibrational coherence indicates that coherence may be involved in the electron transfer process. Our findings not only shed light on the mechanism of ultrafast electron transfer in organic photovoltaics but also are beneficial for the study of the coherence effect on photoexcited dynamics in other systems

Modelling multi-pulse population dynamics from ultrafast spectroscopy.

Directory of Open Access Journals (Sweden)

Luuk J G W van Wilderen

2011-03-01

Full Text Available Current advanced laser, optics and electronics technology allows sensitive recording of molecular dynamics, from single resonance to multi-colour and multi-pulse experiments. Extracting the occurring (bio- physical relevant pathways via global analysis of experimental data requires a systematic investigation of connectivity schemes. Here we present a Matlab-based toolbox for this purpose. The toolbox has a graphical user interface which facilitates the application of different reaction models to the data to generate the coupled differential equations. Any time-dependent dataset can be analysed to extract time-independent correlations of the observables by using gradient or direct search methods. Specific capabilities (i.e. chirp and instrument response function for the analysis of ultrafast pump-probe spectroscopic data are included. The inclusion of an extra pulse that interacts with a transient phase can help to disentangle complex interdependent pathways. The modelling of pathways is therefore extended by new theory (which is included in the toolbox that describes the finite bleach (orientation effect of single and multiple intense polarised femtosecond pulses on an ensemble of randomly oriented particles in the presence of population decay. For instance, the generally assumed flat-top multimode beam profile is adapted to a more realistic Gaussian shape, exposing the need for several corrections for accurate anisotropy measurements. In addition, the (selective excitation (photoselection and anisotropy of populations that interact with single or multiple intense polarised laser pulses is demonstrated as function of power density and beam profile. Using example values of real world experiments it is calculated to what extent this effectively orients the ensemble of particles. Finally, the implementation includes the interaction with multiple pulses in addition to depth averaging in optically dense samples. In summary, we show that mathematical

Modelling multi-pulse population dynamics from ultrafast spectroscopy.

Science.gov (United States)

van Wilderen, Luuk J G W; Lincoln, Craig N; van Thor, Jasper J

2011-03-21

Current advanced laser, optics and electronics technology allows sensitive recording of molecular dynamics, from single resonance to multi-colour and multi-pulse experiments. Extracting the occurring (bio-) physical relevant pathways via global analysis of experimental data requires a systematic investigation of connectivity schemes. Here we present a Matlab-based toolbox for this purpose. The toolbox has a graphical user interface which facilitates the application of different reaction models to the data to generate the coupled differential equations. Any time-dependent dataset can be analysed to extract time-independent correlations of the observables by using gradient or direct search methods. Specific capabilities (i.e. chirp and instrument response function) for the analysis of ultrafast pump-probe spectroscopic data are included. The inclusion of an extra pulse that interacts with a transient phase can help to disentangle complex interdependent pathways. The modelling of pathways is therefore extended by new theory (which is included in the toolbox) that describes the finite bleach (orientation) effect of single and multiple intense polarised femtosecond pulses on an ensemble of randomly oriented particles in the presence of population decay. For instance, the generally assumed flat-top multimode beam profile is adapted to a more realistic Gaussian shape, exposing the need for several corrections for accurate anisotropy measurements. In addition, the (selective) excitation (photoselection) and anisotropy of populations that interact with single or multiple intense polarised laser pulses is demonstrated as function of power density and beam profile. Using example values of real world experiments it is calculated to what extent this effectively orients the ensemble of particles. Finally, the implementation includes the interaction with multiple pulses in addition to depth averaging in optically dense samples. In summary, we show that mathematical modelling is

Hotspot-mediated non-dissipative and ultrafast plasmon passage

Science.gov (United States)

Roller, Eva-Maria; Besteiro, Lucas V.; Pupp, Claudia; Khorashad, Larousse Khosravi; Govorov, Alexander O.; Liedl, Tim

2017-08-01

Plasmonic nanoparticles hold great promise as photon handling elements and as channels for coherent transfer of energy and information in future all-optical computing devices. Coherent energy oscillations between two spatially separated plasmonic entities via a virtual middle state exemplify electron-based population transfer, but their realization requires precise nanoscale positioning of heterogeneous particles. Here, we show the assembly and optical analysis of a triple-particle system consisting of two gold nanoparticles with an inter-spaced silver island. We observe strong plasmonic coupling between the spatially separated gold particles, mediated by the connecting silver particle, with almost no dissipation of energy. As the excitation energy of the silver island exceeds that of the gold particles, only quasi-occupation of the silver transfer channel is possible. We describe this effect both with exact classical electrodynamic modelling and qualitative quantum-mechanical calculations. We identify the formation of strong hotspots between all particles as the main mechanism for the lossless coupling and thus coherent ultrafast energy transfer between the remote partners. Our findings could prove useful for quantum gate operations, as well as for classical charge and information transfer processes.

Coherent imaging at FLASH

International Nuclear Information System (INIS)

Chapman, H N; Bajt, S; Duesterer, S; Treusch, R; Barty, A; Benner, W H; Bogan, M J; Frank, M; Hau-Riege, S P; Woods, B W; Boutet, S; Cavalleri, A; Hajdu, J; Iwan, B; Seibert, M M; Timneanu, N; Marchesini, S; Sakdinawat, A; Sokolowski-Tinten, K

2009-01-01

We have carried out high-resolution single-pulse coherent diffractive imaging at the FLASH free-electron laser. The intense focused FEL pulse gives a high-resolution low-noise coherent diffraction pattern of an object before that object turns into a plasma and explodes. In particular we are developing imaging of biological specimens beyond conventional radiation damage resolution limits, developing imaging of ultrafast processes, and testing methods to characterize and perform single-particle imaging.

Coherent captivity of population in gas of excited atoms

International Nuclear Information System (INIS)

Anisimov, P.M.; Akhmedzhanov, R.A.; Zelenskij, I.V.; Kolesov, R.L.; Kuznetsova, E.A.

2003-01-01

The coherent captivity of the population in the gaseous discharge on the transitions between the neon atoms excited levels is studied. The resonances, corresponding to the origination of the population coherent captivity in the Λ- and V-schemes on the Zeeman sublevels of the low and upper working states, were observed in the presence of the longitudinal magnetic field. The effect of the nonlinear rotation of the polarization plane under the conditions of the population coherent captivity was studied. The possibility of applying the results of the work for the diagnostics of the local magnetic fields and other plasma parameters in the gaseous discharges is considered [ru

Subwavelength atom localization via coherent population trapping

International Nuclear Information System (INIS)

Agarwal, G S; Kapale, K T

2006-01-01

We present an atom localization scheme based on coherent population trapping. We consider atomic transitions in a Lambda configuration where the control field is a standing-wave field. The probe field and the control field produce coherence between the two ground states and prepare the atom in a pure state. We show that the population in one of the ground states has the same fringe pattern as produced by a Fabry-Perot interferometer and thus measurement of this population would localize the atom. Interestingly enough the role of the cavity finesse is played by the ratio of the intensities of the pump and probe. This is in fact the reason for obtaining extreme subwavelength localization

Optical laser systems at the Linac Coherent Light Source

Energy Technology Data Exchange (ETDEWEB)

Minitti, Michael P.; Robinson, Joseph S.; Coffee, Ryan N.; Edstrom, Steve; Gilevich, Sasha; Glownia, James M.; Granados, Eduardo; Hering, Philippe; Hoffmann, Matthias C.; Miahnahri, Alan; Milathianaki, Despina; Polzin, Wayne; Ratner, Daniel; Tavella, Franz; Vetter, Sharon; Welch, Marc; White, William E.; Fry, Alan R., E-mail: alanfry@slac.stanford.edu [Linac Coherent Light Source, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025 (United States)

2015-04-22

This manuscript serves as a reference to describe the optical laser sources and capabilities at the Linac Coherent Light Source. Ultrafast optical lasers play an essential role in exploiting the unique capabilities of recently commissioned X-ray free-electron laser facilities such as the Linac Coherent Light Source (LCLS). Pump–probe experimental techniques reveal ultrafast dynamics in atomic and molecular processes and reveal new insights in chemistry, biology, material science and high-energy-density physics. This manuscript describes the laser systems and experimental methods that enable cutting-edge optical laser/X-ray pump–probe experiments to be performed at LCLS.

Attosecond electron pulse trains and quantum state reconstruction in ultrafast transmission electron microscopy

Science.gov (United States)

Priebe, Katharina E.; Rathje, Christopher; Yalunin, Sergey V.; Hohage, Thorsten; Feist, Armin; Schäfer, Sascha; Ropers, Claus

2017-12-01

Ultrafast electron and X-ray imaging and spectroscopy are the basis for an ongoing revolution in the understanding of dynamical atomic-scale processes in matter. The underlying technology relies heavily on laser science for the generation and characterization of ever shorter pulses. Recent findings suggest that ultrafast electron microscopy with attosecond-structured wavefunctions may be feasible. However, such future technologies call for means to both prepare and fully analyse the corresponding free-electron quantum states. Here, we introduce a framework for the preparation, coherent manipulation and characterization of free-electron quantum states, experimentally demonstrating attosecond electron pulse trains. Phase-locked optical fields coherently control the electron wavefunction along the beam direction. We establish a new variant of quantum state tomography—`SQUIRRELS'—for free-electron ensembles. The ability to tailor and quantitatively map electron quantum states will promote the nanoscale study of electron-matter entanglement and new forms of ultrafast electron microscopy down to the attosecond regime.

Gain with and without population inversion via vacuum-induced coherence in a V-type atom without external coherent driving

International Nuclear Information System (INIS)

Xu Weihua; Wu Jinhui; Gao Jinyue

2006-01-01

In a three-level V-type atomic system without any external coherent driving, owing to the coherence that results from the vacuum of the radiation field, both the probe gain with and without population inversion can be achieved with very weak incoherent pumping. The gain is achieved in the absence of any external coherent driving field, so it is different from the gain without inversion in ordinary laser-driven schemes where a coherent driving field is necessary to create the coherence. The gain is also different from the conventional lasing gain because the population inversion is achieved via vacuum-induced coherence, which is dependent on the atomic coherence

Ultrafast surface-enhanced Raman spectroscopy.

Science.gov (United States)

Keller, Emily L; Brandt, Nathaniel C; Cassabaum, Alyssa A; Frontiera, Renee R

2015-08-07

Ultrafast surface-enhanced Raman spectroscopy (SERS) with pico- and femtosecond time resolution has the ability to elucidate the mechanisms by which plasmons mediate chemical reactions. Here we review three important technological advances in these new methodologies, and discuss their prospects for applications in areas including plasmon-induced chemistry and sensing at very low limits of detection. Surface enhancement, arising from plasmonic materials, has been successfully incorporated with stimulated Raman techniques such as femtosecond stimulated Raman spectroscopy (FSRS) and coherent anti-Stokes Raman spectroscopy (CARS). These techniques are capable of time-resolved measurement on the femtosecond and picosecond time scale and can be used to follow the dynamics of molecules reacting near plasmonic surfaces. We discuss the potential application of ultrafast SERS techniques to probe plasmon-mediated processes, such as H2 dissociation and solar steam production. Additionally, we discuss the possibilities for high sensitivity SERS sensing using these stimulated Raman spectroscopies.

Population and coherence dynamics in light harvesting complex II (LH2).

Science.gov (United States)

Yeh, Shu-Hao; Zhu, Jing; Kais, Sabre

2012-08-28

The electronic excitation population and coherence dynamics in the chromophores of the photosynthetic light harvesting complex 2 (LH2) B850 ring from purple bacteria (Rhodopseudomonas acidophila) have been studied theoretically at both physiological and cryogenic temperatures. Similar to the well-studied Fenna-Matthews-Olson (FMO) protein, oscillations of the excitation population and coherence in the site basis are observed in LH2 by using a scaled hierarchical equation of motion approach. However, this oscillation time (300 fs) is much shorter compared to the FMO protein (650 fs) at cryogenic temperature. Both environment and high temperature are found to enhance the propagation speed of the exciton wave packet yet they shorten the coherence time and suppress the oscillation amplitude of coherence and the population. Our calculations show that a long-lived coherence between chromophore electronic excited states can exist in such a noisy biological environment.

Inhibitory coherence in a heterogeneous population of subthreshold and suprathreshold type-I neurons

International Nuclear Information System (INIS)

Kim, Sang-Yoon; Hong, Duk-Geun; Kim, Jean; Lim, Woochang

2012-01-01

We study inhibitory coherence (i.e. collective coherence by synaptic inhibition) in a population of globally coupled type-I neurons, which can fire at arbitrarily low frequency. No inhibitory coherence is observed in a homogeneous population composed of only subthreshold neurons, which exhibit noise-induced firings. In addition to subthreshold neurons, there exist spontaneously firing suprathreshold neurons in a noisy environment of a real brain. To take into consideration the effect of suprathreshold neurons on inhibitory coherence, we consider a heterogeneous population of subthreshold and suprathreshold neurons and investigate the inhibitory coherence by increasing the fraction of suprathreshold neurons P supra . As P supra passes a threshold P* supra , suprathreshold neurons begin to synchronize and play the role of coherent inhibitors for the emergence of inhibitory coherence. Thus, regularly oscillating population-averaged global potential appears for P supra > P* supra . For this coherent case, suprathreshold neurons exhibit sparse spike synchronization (i.e. individual potentials of suprathreshold neurons consist of coherent sparse spikings and coherent subthreshold small-amplitude hoppings). By virtue of their coherent inhibition, sparsely synchronized suprathreshold neurons suppress the noisy activity of subthreshold neurons. Thus, subthreshold neurons exhibit hopping synchronization (i.e. only coherent subthreshold hopping oscillations without spikings appear in the individual potentials of subthreshold neurons). We also characterize the inhibitory coherence in terms of the ‘statistical-mechanical’ spike-based and correlation-based measures, which quantify the average contributions of the microscopic individual spikes and individual potentials to the macroscopic global potential. Finally, the effect of sparse randomness of synaptic connectivity on the inhibitory coherence is briefly discussed. (paper)

Optical Coherence Tomography

DEFF Research Database (Denmark)

Fercher, A.F.; Andersen, Peter E.

2017-01-01

Optical coherence tomography (OCT) is a technique that is used to peer inside a body noninvasively. Tissue structure defined by tissue absorption and scattering coefficients, and the speed of blood flow, are derived from the characteristics of light remitted by the body. Singly backscattered light...... detected by partial coherence interferometry (PCI) is used to synthesize the tomographic image coded in false colors. A prerequisite of this technique is a low time-coherent but high space-coherent light source, for example, a superluminescent diode or a supercontinuum source. Alternatively, the imaging...... technique can be realized by using ultrafast wavelength scanning light sources. For tissue imaging, the light source wavelengths are restricted to the red and near-infrared (NIR) region from about 600 to 1300 nm, the so-called therapeutic window, where absorption (μa ≈ 0.01 mm−1) is small enough. Transverse...

Population dynamics of graphene driven by a few-cycle laser pulse

Science.gov (United States)

Ding, Chunling; Yu, Rong; Hao, Xiangying; Zhang, Duo; Zu, Fengxia

2017-06-01

We study the time evolution of the populations in a two-dimensional (2D) graphene system by employing a few-cycle laser pulse with a linear polarization. Specifically, we present a comparative numerical analysis of the population dynamics of graphene in three different model configurations. Our results show that the Rabi-like oscillations and intraband population inversion can be observed in the population spectrum, which originated from the periodicity of a few-cycle laser pulse and the intraband Coulomb scattering. Also, coherent population oscillations are produced across the Dirac point when the Rabi frequency of the laser field which is used to couple the interband transition is much larger than that couples the intraband transition, and vice versa. These investigations may be helpful to enhance the performance of graphene-based ultrafast electronic and optoelectronic devices, including light-emitting devices, touch screens, photodetectors, and ultrafast lasers.

Ultrafast spectral interferometry of resonant secondary emmission from semiconductor quantum wells

DEFF Research Database (Denmark)

Birkedal, Dan; Shah, Jagdeep

1999-01-01

Recent investigations of secondary emission from quantum well excitons follwing resonant excitation have demonstrated an intricate interplay of coherent Rayleigh scattering and incoherent luminescence. We have very recently demonstrated that it is possible to isolate and time resolve the coherent...... field associated with the Rayleigh component using ultrafast spectral interferometry, thus, obtaining substantial and new information of the nature of resonant secondary emission. Our findings demonstrate that Rayleigh scattering from static disorder is inherently a non-ergodic process invalidating...

Influence of the Chemical Design on the Coherent Photoisomerization of Biomimetic Molecular Switches

Directory of Open Access Journals (Sweden)

Olivucci Massimo

2013-03-01

Full Text Available Ultrafast transient absorption spectroscopy reveals the effect of chemical substitutions on the photoreaction kinetics of biomimetic photoswitches displaying coherent dynamics. Ground state vibrational coherences are no longer observed when the excited state lifetime exceeds 300fs.

Femtosecond X-Ray Scattering Study of Ultrafast Photoinduced Structural Dynamics in Solvated [Co(terpy)2]2+

DEFF Research Database (Denmark)

Biasin, Elisa; Brandt van Driel, Tim; Kjær, Kasper Skov

2016-01-01

We study the structural dynamics of photoexcited [Co(terpy)2]2+ in an aqueous solution with ultrafast x-ray diffuse scattering experiments conducted at the Linac Coherent Light Source. Through direct comparisons with density functional theory calculations, our analysis shows that the photoexcitat......We study the structural dynamics of photoexcited [Co(terpy)2]2+ in an aqueous solution with ultrafast x-ray diffuse scattering experiments conducted at the Linac Coherent Light Source. Through direct comparisons with density functional theory calculations, our analysis shows...... find that the equilibrium bond-elongated structure of the high spin state is established on a single-picosecond time scale and that this state has a lifetime of ∼7 ps....

Strategies to improve phase-stability of ultrafast swept source optical coherence tomography for single shot imaging of transient mechanical waves at 16 kHz frame rate

Energy Technology Data Exchange (ETDEWEB)

Song, Shaozhen; Wei, Wei; Hsieh, Bao-Yu; Pelivanov, Ivan; O' Donnell, Matthew [Department of Bioengineering, University of Washington, Seattle, Washington 98195 (United States); Shen, Tueng T.; Wang, Ruikang K., E-mail: wangrk@uw.edu [Department of Bioengineering, University of Washington, Seattle, Washington 98195 (United States); Department of Ophthalmology, University of Washington, Seattle, Washington 98104 (United States)

2016-05-09

We present single-shot phase-sensitive imaging of propagating mechanical waves within tissue, enabled by an ultrafast optical coherence tomography (OCT) system powered by a 1.628 MHz Fourier domain mode-locked (FDML) swept laser source. We propose a practical strategy for phase-sensitive measurement by comparing the phases between adjacent OCT B-scans, where the B-scan contains a number of A-scans equaling an integer number of FDML buffers. With this approach, we show that micro-strain fields can be mapped with ∼3.0 nm sensitivity at ∼16 000 fps. The system's capabilities are demonstrated on porcine cornea by imaging mechanical wave propagation launched by a pulsed UV laser beam, promising non-contact, real-time, and high-resolution optical coherence elastography.

Ultrafast Ultrasound Imaging With Cascaded Dual-Polarity Waves.

Science.gov (United States)

Zhang, Yang; Guo, Yuexin; Lee, Wei-Ning

2018-04-01

Ultrafast ultrasound imaging using plane or diverging waves, instead of focused beams, has advanced greatly the development of novel ultrasound imaging methods for evaluating tissue functions beyond anatomical information. However, the sonographic signal-to-noise ratio (SNR) of ultrafast imaging remains limited due to the lack of transmission focusing, and thus insufficient acoustic energy delivery. We hereby propose a new ultrafast ultrasound imaging methodology with cascaded dual-polarity waves (CDWs), which consists of a pulse train with positive and negative polarities. A new coding scheme and a corresponding linear decoding process were thereby designed to obtain the recovered signals with increased amplitude, thus increasing the SNR without sacrificing the frame rate. The newly designed CDW ultrafast ultrasound imaging technique achieved higher quality B-mode images than coherent plane-wave compounding (CPWC) and multiplane wave (MW) imaging in a calibration phantom, ex vivo pork belly, and in vivo human back muscle. CDW imaging shows a significant improvement in the SNR (10.71 dB versus CPWC and 7.62 dB versus MW), penetration depth (36.94% versus CPWC and 35.14% versus MW), and contrast ratio in deep regions (5.97 dB versus CPWC and 5.05 dB versus MW) without compromising other image quality metrics, such as spatial resolution and frame rate. The enhanced image qualities and ultrafast frame rates offered by CDW imaging beget great potential for various novel imaging applications.

Vibrational energy on surfaces: Ultrafast flash-thermal conductance of molecular monolayers

Science.gov (United States)

Dlott, Dana

2008-03-01

Vibrational energy flow through molecules remains a perennial problem in chemical physics. Usually vibrational energy dynamics are viewed through the lens of time-dependent level populations. This is natural because lasers naturally pump and probe vibrational transitions, but it is also useful to think of vibrational energy as being conducted from one location in a molecule to another. We have developed a new technique where energy is driven into a specific part of molecules adsorbed on a metal surface, and ultrafast nonlinear coherent vibrational spectroscopy is used to watch the energy arrive at another part. This technique is the analog of a flash thermal conductance apparatus, except it probes energy flow with angstrom spatial and femtosecond temporal resolution. Specific examples to be presented include energy flow along alkane chains, and energy flow into substituted benzenes. Ref: Z. Wang, J. A. Carter, A. Lagutchev, Y. K. Koh, N.-H. Seong, D. G. Cahill, and D. D. Dlott, Ultrafast flash thermal conductance of molecular chains, Science 317, 787-790 (2007). This material is based upon work supported by the National Science Foundation under award DMR 0504038 and the Air Force Office of Scientific Research under award FA9550-06-1-0235.

Optimal control of population and coherence in three-level Λ systems

Science.gov (United States)

Kumar, Praveen; Malinovskaya, Svetlana A.; Malinovsky, Vladimir S.

2011-08-01

Optimal control theory (OCT) implementations for an efficient population transfer and creation of maximum coherence in a three-level system are considered. We demonstrate that the half-stimulated Raman adiabatic passage scheme for creation of the maximum Raman coherence is the optimal solution according to the OCT. We also present a comparative study of several implementations of OCT applied to the complete population transfer and creation of the maximum coherence. Performance of the conjugate gradient method, the Zhu-Rabitz method and the Krotov method has been analysed.

Optimal control of population and coherence in three-level Λ systems

International Nuclear Information System (INIS)

Kumar, Praveen; Malinovskaya, Svetlana A; Malinovsky, Vladimir S

2011-01-01

Optimal control theory (OCT) implementations for an efficient population transfer and creation of maximum coherence in a three-level system are considered. We demonstrate that the half-stimulated Raman adiabatic passage scheme for creation of the maximum Raman coherence is the optimal solution according to the OCT. We also present a comparative study of several implementations of OCT applied to the complete population transfer and creation of the maximum coherence. Performance of the conjugate gradient method, the Zhu-Rabitz method and the Krotov method has been analysed.

Simple and robust generation of ultrafast laser pulse trains using polarization-independent parallel-aligned thin films

Science.gov (United States)

Wang, Andong; Jiang, Lan; Li, Xiaowei; Wang, Zhi; Du, Kun; Lu, Yongfeng

2018-05-01

Ultrafast laser pulse temporal shaping has been widely applied in various important applications such as laser materials processing, coherent control of chemical reactions, and ultrafast imaging. However, temporal pulse shaping has been limited to only-in-lab technique due to the high cost, low damage threshold, and polarization dependence. Herein we propose a novel design of ultrafast laser pulse train generation device, which consists of multiple polarization-independent parallel-aligned thin films. Various pulse trains with controllable temporal profile can be generated flexibly by multi-reflections within the splitting films. Compared with other pulse train generation techniques, this method has advantages of compact structure, low cost, high damage threshold and polarization independence. These advantages endow it with high potential for broad utilization in ultrafast applications.

Complete elimination of nonlinear light-matter interactions with broadband ultrafast laser pulses

DEFF Research Database (Denmark)

Shu, Chuan-Cun; Dong, Daoyi; Petersen, Ian R.

2017-01-01

optical effects, however, the probability of pure single-photon absorption is usually very low, which is particularly pertinent in the case of strong ultrafast laser pulses with broad bandwidth. Here we demonstrate theoretically a counterintuitive coherent single-photon absorption scheme by eliminating...... nonlinear interactions of ultrafast laser pulses with quantum systems. That is, a completely linear response of the system with respect to the spectral energy density of the incident light at the transition frequency can be obtained for all transition probabilities between 0 and 100% in multilevel quantum...... systems. To that end, a multiobjective optimization algorithm is developed to find an optimal spectral phase of an ultrafast laser pulse, which is capable of eliminating all possible nonlinear optical responses while maximizing the probability of single-photon absorption between quantum states. This work...

Correlation between photoeletron and photoion in ultrafast multichannel photoionization of Ar

International Nuclear Information System (INIS)

Itakura, R.; Fushitani, M.; Hishikawa, A.; Sako, T.

2015-01-01

We theoretically investigate coherent dynamics of ions created through ultrafast multichannel photoionization from a viewpoint of photoelectron-photoion correlation. The model calculation on single-photon ionization of Ar reveals that the coherent hole dynamics in Ar + associated with a superposition of the spin-orbit states 2 PJ (J = 3/2 and 1/2) can be identified by monitoring only the photoion created by a Fourier-transform limited extreme ultraviolet (EUV) pulse with the fs pulse duration, while the coherence is lost by a chirped EUV pulse. It is demonstrated that by coincidence detection of the photoelectron and photoion the coherent hole dynamics can be extracted even in the case of ionization by a chirped EUV pulse with the sufficiently wide bandwidth

Ultrafast dynamics of Coulomb correlated excitons in GaAs quantum wells

Energy Technology Data Exchange (ETDEWEB)

Mycek, M.A. [Univ. of California, Berkeley, CA (United States). Dept. of Physics]|[Lawrence Berkeley National Lab., CA (United States). Materials Sciences Div.

1995-12-01

The author measures the transient nonlinear optical response of room temperature excitons in gallium arsenide quantum wells via multi-wave mixing experiments. The dynamics of the resonantly excited excitons is directly reflected by the ultrafast decay of the induced nonlinear polarization, which radiates the detected multi-wave mixing signal. She characterizes this ultrafast coherent emission in both amplitude and phase, using time- and frequency-domain measurement techniques, to better understand the role of Coulomb correlation in these systems. To interpret the experimental results, the nonlinear optical response of a dense medium is calculated using a model including Coulomb interaction. She contributes three new elements to previous theoretical and experimental studies of these systems. First, surpassing traditional time-integrated measurements, she temporally resolves the amplitude of the ultrafast coherent emission. Second, in addition to measuring the third-order four-wave mixing signal, she also investigates the fifth-order six-wave mixing response. Third, she characterizes the ultrafast phase dynamics of the nonlinear emission using interferometric techniques with an unprecedented resolution of approximately 140 attoseconds. The author finds that effects arising from Coulomb correlation dominate the nonlinear optical response when the density of excitons falls below 3 {times} 10{sup 11} cm{sup {minus}2}, the saturation density. These signatures of Coulomb correlation are investigated for increasing excitation density to gradually screen the interactions and test the validity of the model for dense media. The results are found to be qualitatively consistent with both the predictions of the model and with numerical solutions to the semiconductor Bloch equations. Importantly, the results also indicate current experimental and theoretical limitations, which should be addressed in future research.

Ultrafast coherent diffractive imaging of nanoparticles using X-ray free-electron laser radiation

International Nuclear Information System (INIS)

Kassemeyer, Stephan

2014-01-01

Coherent diffractive imaging with X-ray free-electron lasers (X-FEL) promises high-resolution structure determination of single microscopic particles without the need for crystallization. The diffraction signal of small samples can be very weak, a difficulty that can not be countered by merely increasing the number of photons because the sample would be damaged by a high absorbed radiation dose. Traditional X-ray crystallography avoids this problem by bringing many sample particles into a periodic arrangement, which amplifies the individual signals while distributing the absorbed dose. Depending on the sample, however, crystallization can be very difficult or even impossible. This thesis presents algorithms for a new imaging approach using X-FEL radiation that works with single, non-crystalline sample particles. X-FELs can deliver X-rays with a peak brilliance many orders of magnitude higher than conventional X-ray sources, compensating for their weak interaction cross sections. At the same time, FELs can produce ultra-short pulses down to a few femtoseconds. In this way it is possible to perform ultra-fast imaging, essentially ''freezing'' the atomic positions in time and terminating the imaging process before the sample is destroyed by the absorbed radiation. This thesis primarily focuses on the three-dimensional reconstruction of single (and not necessarily crystalline) particles using coherent diffractive imaging at X-FELs: in order to extract three-dimensional information from scattering data, two-dimensional diffraction patterns from many different viewing angles must be combined. Therefore, the diffraction signal of many identical sample copies in random orientations is measured. The main result of this work is a globally optimal algorithm that can recover the sample orientations solely based on the diffraction signal, enabling three-dimensional imaging for arbitrary samples. The problem of finding three-dimensional orientations is

Ultrafast optical generation of squeezed magnon states and long lifetime coherent LO phonons

Science.gov (United States)

Zhao, Jimin

2005-12-01

Ultrafast optical pulses have been used to generate, probe, and control low-energy elementary excitations in crystals. In particular, we report the first experimental demonstration of the generation of quantum squeezed states of magnons (collective spin-wave excitations) in a magnetic material, and new progress in experimental investigation of anharmonic interactions in a semiconductor. The mechanism for the magnon squeezing is two-magnon impulsive stimulated Raman scattering (ISRS). Femtosecond laser pulses have been used to coherently correlate degenerate counter-propagating magnons in the antiferromagnetic insulator MnF2. In the squeezed state, fluctuations of the magnetization of a crystallographic unit cell vary periodically in time and are reduced below that of the ground-state quantum noise. Similar experiments were also performed in another antiferromagnetic insulator, FeF2, for which the squeezing effect is one order of magnitude larger. We have also investigated the anharmonic interaction of the low-frequency E2 phonon in ZnO through ISRS. Temperature dependence of the linewidth and frequency indicates that the two-phonon up-conversion process is the dominant decay channel and isotopic disorder may be the main limit on the lifetime at low temperature. We have observed the longest lifetime of an optical phonon mode in a solid (211 ps at 5 K). And we have found that pump-probe experiments, compared with spontaneous Raman spectroscopy, have extremely high accuracy in determining the frequency of a low-lying excitation.

Ultrafast lattice dynamics in photoexcited nanostructures. Femtosecond X-ray diffraction with optimized evaluation schemes

International Nuclear Information System (INIS)

Schick, Daniel

2013-01-01

Within the course of this thesis, I have investigated the complex interplay between electron and lattice dynamics in nanostructures of perovskite oxides. Femtosecond hard X-ray pulses were utilized to probe the evolution of atomic rearrangement directly, which is driven by ultrafast optical excitation of electrons. The physics of complex materials with a large number of degrees of freedom can be interpreted once the exact fingerprint of ultrafast lattice dynamics in time-resolved X-ray diffraction experiments for a simple model system is well known. The motion of atoms in a crystal can be probed directly and in real-time by femtosecond pulses of hard X-ray radiation in a pump-probe scheme. In order to provide such ultrashort X-ray pulses, I have built up a laser-driven plasma X-ray source. The setup was extended by a stable goniometer, a two-dimensional X-ray detector and a cryogen-free cryostat. The data acquisition routines of the diffractometer for these ultrafast X-ray diffraction experiments were further improved in terms of signal-to-noise ratio and angular resolution. The implementation of a high-speed reciprocal-space mapping technique allowed for a two-dimensional structural analysis with femtosecond temporal resolution. I have studied the ultrafast lattice dynamics, namely the excitation and propagation of coherent phonons, in photoexcited thin films and superlattice structures of the metallic perovskite SrRuO 3 . Due to the quasi-instantaneous coupling of the lattice to the optically excited electrons in this material a spatially and temporally well-defined thermal stress profile is generated in SrRuO 3 . This enables understanding the effect of the resulting coherent lattice dynamics in time-resolved X-ray diffraction data in great detail, e.g. the appearance of a transient Bragg peak splitting in both thin films and superlattice structures of SrRuO 3 . In addition, a comprehensive simulation toolbox to calculate the ultrafast lattice dynamics and the

Resonances of coherent population trapping in samarium vapours

International Nuclear Information System (INIS)

Kolachevsky, Nikolai N; Akimov, A V; Kiselev, N A; Papchenko, A A; Sorokin, Vadim N; Kanorskii, S I

2001-01-01

Resonances of coherent population trapping were detected in atomic vapours of the rare-earth element samarium. The coherent population trapping was produced by two external-cavity diode lasers (672 and 686 nm) in a Λ-system formed by the three levels of 154 Sm: the 4f 6 6s 2 ( 7 F 0 ) ground state, the first fine-structure 4f 6 6s 2 ( 7 F 1 ) sublevel of the ground state and the 4f 6 ( 7 F)6s6p( 3 P o ) 9 F o 1 upper level. The dependence of the spectral shapes and resonance contrasts on the polarisation of the laser beams and the direction of the applied magnetic field was studied. The obtained results were analysed. (nonlinear optical phenomena)

A coherent modified Redfield theory for excitation energy transfer in molecular aggregates

Energy Technology Data Exchange (ETDEWEB)

Hwang-Fu, Yu-Hsien; Chen, Wei; Cheng, Yuan-Chung, E-mail: yuanchung@ntu.edu.tw

2015-02-02

Highlights: • A CMRT method for coherent energy transfer in molecular aggregates was developed. • Applicability of the method was verified in two-site systems with various parameters. • CMRT accurately describes population dynamics in the FMO-complex. • The method is accurate in a large parameter space and computationally efficient. - Abstract: Excitation energy transfer (EET) is crucial in photosynthetic light harvesting, and quantum coherence has been recently proven to be a ubiquitous phenomenon in photosynthetic EET. In this work, we derive a coherent modified Redfield theory (CMRT) that generalizes the modified Redfield theory to treat coherence dynamics. We apply the CMRT method to simulate the EET in a dimer system and compare the results with those obtained from numerically exact path integral calculations. The comparison shows that CMRT provides excellent computational efficiency and accuracy within a large EET parameter space. Furthermore, we simulate the EET dynamics in the FMO complex at 77 K using CMRT. The results show pronounced non-Markovian effects and long-lasting coherences in the ultrafast EET, in excellent agreement with calculations using the hierarchy equation of motion approach. In summary, we have successfully developed a simple yet powerful framework for coherent EET dynamics in photosynthetic systems and organic materials.

Quantum modeling of ultrafast photoinduced charge separation

Science.gov (United States)

Rozzi, Carlo Andrea; Troiani, Filippo; Tavernelli, Ivano

2018-01-01

Phenomena involving electron transfer are ubiquitous in nature, photosynthesis and enzymes or protein activity being prominent examples. Their deep understanding thus represents a mandatory scientific goal. Moreover, controlling the separation of photogenerated charges is a crucial prerequisite in many applicative contexts, including quantum electronics, photo-electrochemical water splitting, photocatalytic dye degradation, and energy conversion. In particular, photoinduced charge separation is the pivotal step driving the storage of sun light into electrical or chemical energy. If properly mastered, these processes may also allow us to achieve a better command of information storage at the nanoscale, as required for the development of molecular electronics, optical switching, or quantum technologies, amongst others. In this Topical Review we survey recent progress in the understanding of ultrafast charge separation from photoexcited states. We report the state-of-the-art of the observation and theoretical description of charge separation phenomena in the ultrafast regime mainly focusing on molecular- and nano-sized solar energy conversion systems. In particular, we examine different proposed mechanisms driving ultrafast charge dynamics, with particular regard to the role of quantum coherence and electron-nuclear coupling, and link experimental observations to theoretical approaches based either on model Hamiltonians or on first principles simulations.

Ultrafast Laser-Based Spectroscopy and Sensing: Applications in LIBS, CARS, and THz Spectroscopy

Science.gov (United States)

Leahy-Hoppa, Megan R.; Miragliotta, Joseph; Osiander, Robert; Burnett, Jennifer; Dikmelik, Yamac; McEnnis, Caroline; Spicer, James B.

2010-01-01

Ultrafast pulsed lasers find application in a range of spectroscopy and sensing techniques including laser induced breakdown spectroscopy (LIBS), coherent Raman spectroscopy, and terahertz (THz) spectroscopy. Whether based on absorption or emission processes, the characteristics of these techniques are heavily influenced by the use of ultrafast pulses in the signal generation process. Depending on the energy of the pulses used, the essential laser interaction process can primarily involve lattice vibrations, molecular rotations, or a combination of excited states produced by laser heating. While some of these techniques are currently confined to sensing at close ranges, others can be implemented for remote spectroscopic sensing owing principally to the laser pulse duration. We present a review of ultrafast laser-based spectroscopy techniques and discuss the use of these techniques to current and potential chemical and environmental sensing applications. PMID:22399883

Ultrafast Laser-Based Spectroscopy and Sensing: Applications in LIBS, CARS, and THz Spectroscopy

Directory of Open Access Journals (Sweden)

Megan R. Leahy-Hoppa

2010-04-01

Full Text Available Ultrafast pulsed lasers find application in a range of spectroscopy and sensing techniques including laser induced breakdown spectroscopy (LIBS, coherent Raman spectroscopy, and terahertz (THz spectroscopy. Whether based on absorption or emission processes, the characteristics of these techniques are heavily influenced by the use of ultrafast pulses in the signal generation process. Depending on the energy of the pulses used, the essential laser interaction process can primarily involve lattice vibrations, molecular rotations, or a combination of excited states produced by laser heating. While some of these techniques are currently confined to sensing at close ranges, others can be implemented for remote spectroscopic sensing owing principally to the laser pulse duration. We present a review of ultrafast laser-based spectroscopy techniques and discuss the use of these techniques to current and potential chemical and environmental sensing applications.

Role of coherence and delocalization in photo-induced electron transfer at organic interfaces

Science.gov (United States)

Abramavicius, V.; Pranculis, V.; Melianas, A.; Inganäs, O.; Gulbinas, V.; Abramavicius, D.

2016-09-01

Photo-induced charge transfer at molecular heterojunctions has gained particular interest due to the development of organic solar cells (OSC) based on blends of electron donating and accepting materials. While charge transfer between donor and acceptor molecules can be described by Marcus theory, additional carrier delocalization and coherent propagation might play the dominant role. Here, we describe ultrafast charge separation at the interface of a conjugated polymer and an aggregate of the fullerene derivative PCBM using the stochastic Schrödinger equation (SSE) and reveal the complex time evolution of electron transfer, mediated by electronic coherence and delocalization. By fitting the model to ultrafast charge separation experiments, we estimate the extent of electron delocalization and establish the transition from coherent electron propagation to incoherent hopping. Our results indicate that even a relatively weak coupling between PCBM molecules is sufficient to facilitate electron delocalization and efficient charge separation at organic interfaces.

Population coherent control of Rydberg potassium atom via adiabatic passage

International Nuclear Information System (INIS)

Jiang Li-Juan; Zhang Xian-Zhou; Jia Guang-Rui; Zhang Yong-Hui; Xia Li-Hua

2013-01-01

The time-dependent multilevel approach (TDMA) and B-spline expansion technique are used to study the coherent population transfer between the quantum states of a potassium atom by a single frequency-chirped microwave pulse. The Rydberg potassium atom energy levels of n = 6–15, l = 0–5 states in zero field are calculated and the results are in good agreement with other theoretical values. The time evolutions of the population transfer of the six states from n = 70 to n = 75 in different microwave fields are obtained. The results show that the coherent control of the population transfer from the lower states to the higher ones can be accomplished by optimizing the microwave pulse parameters. (atomic and molecular physics)

Progress in Ultrafast Intense Laser Science Volume V

CERN Document Server

Yamanouchi, Kaoru; Ledingham, Kenneth

2010-01-01

The PUILS series delivers up-to-date reviews of progress in Ultrafast Intense Laser Science, a newly emerging interdisciplinary research field spanning atomic and molecular physics, molecular science, and optical science, which has been stimulated by the recent developments in ultrafast laser technologies. Each volume compiles peer-reviewed articles authored by researchers at the forefront of each their own subfields of UILS. Every chapter opens with an overview of the topics to be discussed, so that researchers unfamiliar to the subfield, as well as graduate students, can grasp the importance and attractions of the research topic at hand; these are followed by reports of cutting-edge discoveries. This fifth volume covers a broad range of topics from this interdisciplinary research field, focusing on coherent responses of gaseous and condensed matter to ultrashort intense laser pulses, propagation of intense laser pulses, and laser-plasma interaction and its applications.

Carrier dynamics in graphene. Ultrafast many-particle phenomena

Energy Technology Data Exchange (ETDEWEB)

Malic, E.; Brem, S.; Jago, R. [Department of Physics, Chalmers University of Technology, Goeteborg (Sweden); Winzer, T.; Wendler, F.; Knorr, A. [Institut fuer Theoretische Physik, Technische Universitaet Berlin (Germany); Mittendorff, M.; Koenig-Otto, J.C.; Schneider, H.; Helm, M.; Winnerl, S. [Helmholtz-Zentrum Dresden-Rossendorf, Dresden (Germany); Ploetzing, T.; Neumaier, D. [Advanced Microelectronic Center Aachen, AMO GmbH, Aachen (Germany)

2017-11-15

Graphene is an ideal material to study fundamental Coulomb- and phonon-induced carrier scattering processes. Its remarkable gapless and linear band structure opens up new carrier relaxation channels. In particular, Auger scattering bridging the valence and the conduction band changes the number of charge carriers and gives rise to a significant carrier multiplication - an ultrafast many-particle phenomenon that is promising for the design of highly efficient photodetectors. Furthermore, the vanishing density of states at the Dirac point combined with ultrafast phonon-induced intraband scattering results in an accumulation of carriers and a population inversion suggesting the design of graphene-based terahertz lasers. Here, we review our work on the ultrafast carrier dynamics in graphene and Landau-quantized graphene is presented providing a microscopic view on the appearance of carrier multiplication and population inversion. (copyright 2017 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Ultrafast dynamics during the photoinduced phase transition in VO2

Science.gov (United States)

Wegkamp, Daniel; Stähler, Julia

2015-12-01

The phase transition of VO2 from a monoclinic insulator to a rutile metal, which occurs thermally at TC = 340 K, can also be driven by strong photoexcitation. The ultrafast dynamics during this photoinduced phase transition (PIPT) have attracted great scientific attention for decades, as this approach promises to answer the question of whether the insulator-to-metal (IMT) transition is caused by electronic or crystallographic processes through disentanglement of the different contributions in the time domain. We review our recent results achieved by femtosecond time-resolved photoelectron, optical, and coherent phonon spectroscopy and discuss them within the framework of a selection of latest, complementary studies of the ultrafast PIPT in VO2. We show that the population change of electrons and holes caused by photoexcitation launches a highly non-equilibrium plasma phase characterized by enhanced screening due to quasi-free carriers and followed by two branches of non-equilibrium dynamics: (i) an instantaneous (within the time resolution) collapse of the insulating gap that precedes charge carrier relaxation and significant ionic motion and (ii) an instantaneous lattice potential symmetry change that represents the onset of the crystallographic phase transition through ionic motion on longer timescales. We discuss the interconnection between these two non-thermal pathways with particular focus on the meaning of the critical fluence of the PIPT in different types of experiments. Based on this, we conclude that the PIPT threshold identified in optical experiments is most probably determined by the excitation density required to drive the lattice potential change rather than the IMT. These considerations suggest that the IMT can be driven by weaker excitation, predicting a transiently metallic, monoclinic state of VO2 that is not stabilized by the non-thermal structural transition and, thus, decays on ultrafast timescales.

Advanced Instrumentation for Ultrafast Science at the LCLS

Energy Technology Data Exchange (ETDEWEB)

Berrah, Nora [Univ. of Connecticut, Storrs, CT (United States)

2015-10-13

This grant supported a Single Investigator and Small Group Research (SISGR) application to enable multi-user research in Ultrafast Science using the Linac Coherent Light Source (LCLS), the world’s first hard x-ray free electron laser (FEL) which lased for the first time at 1.5 Å on April 20, 2009. The goal of our proposal was to enable a New Era of Science by requesting funds to purchase and build Advanced Instrumentation for Ultrafast Science (AIUS), to utilize the intense, short x-ray pulses produced by the LCLS. The proposed instrumentation will allow peer review selected users to probe the ultrasmall and capture the ultrafast. These tools will expand on the investment already made in the construction of the light source and its instrumentation in both the LCLS and LUSI projects. The AIUS will provide researchers in the AMO, Chemical, Biological and Condensed Matter communities with greater flexibility in defining their scientific agenda at the LCLS. The proposed instrumentation will complement and significantly augment the present AMO instrument (funded through the LCLS project) through detectors and capabilities not included in the initial suite of instrumentation at the facility. We have built all of the instrumentations and they have been utilized by scientists. Please see report attached.

Ultrafast dynamics of correlated electrons

International Nuclear Information System (INIS)

Rettig, Laurenz

2012-01-01

This work investigates the ultrafast electron dynamics in correlated, low-dimensional model systems using femtosecond time- and angle-resolved photoemission spectroscopy (trARPES) directly in the time domain. In such materials, the strong electron-electron (e-e) correlations or coupling to other degrees of freedom such as phonons within the complex many-body quantum system lead to new, emergent properties that are characterized by phase transitions into broken-symmetry ground states such as magnetic, superconducting or charge density wave (CDW) phases. The dynamical processes related to order like transient phase changes, collective excitations or the energy relaxation within the system allow deeper insight into the complex physics governing the emergence of the broken-symmetry state. In this work, several model systems for broken-symmetry ground states and for the dynamical charge balance at interfaces have been studied. In the quantum well state (QWS) model system Pb/Si(111), the charge transfer across the Pb/Si interface leads to an ultrafast energetic stabilization of occupied QWSs, which is the result of an increase of the electronic confinement to the metal film. In addition, a coherently excited surface phonon mode is observed. In antiferromagnetic (AFM) Fe pnictide compounds, a strong momentum-dependent asymmetry of electron and hole relaxation rates allows to separate the recovery dynamics of the AFM phase from electron-phonon (e-ph) relaxation. The strong modulation of the chemical potential by coherent phonon modes demonstrates the importance of e-ph coupling in these materials. However, the average e-ph coupling constant is found to be small. The investigation of the excited quasiparticle (QP) relaxation dynamics in the high-T c 4 superconductor Bi 2 Sr 2 CaCu 2 O 8+δ reveals a striking momentum and fluence independence of the QP life times. In combination with the momentum-dependent density of excited QPs, this demonstrates the suppression of momentum

Ultrafast Coherent Diffraction Imaging with X-ray Free-Electron Lasers

International Nuclear Information System (INIS)

Chapman, H N; Bajt, S; Barty, A; Benner, W; Bogan, M; Frank, M; Hau-Riege, S; London, R; Marchesini, S; Spiller, E; Szoke, A; Woods, B; Boutet, S; Hodgson, K; Hajdu, J; Bergh, M; Burmeister, F; Caleman, C; Huldt, G; Maia, F; Seibert, M M; der Spoel, D v

2006-01-01

The ultrafast pulses from X-ray free-electron lasers will enable imaging of non-periodic objects at near-atomic resolution [1, Neutze]. These objects could include single molecules, protein complexes, or virus particles. The specimen would be completely destroyed by the pulse in a Coulomb explosion, but that destruction will only happen after the pulse. The scattering from the sample will give structural information about the undamaged object. There are many technical challenges that must be addressed before carrying out such experiments at an XFEL, which we are doing so with experiments at FLASH, the soft-X-ray FEL at DESY

Testing ultrafast mode-locking at microhertz relative optical linewidth.

Science.gov (United States)

Martin, Michael J; Foreman, Seth M; Schibli, T R; Ye, Jun

2009-01-19

We report new limits on the phase coherence of the ultrafast mode-locking process in an octave-spanning Ti:sapphire comb.We find that the mode-locking mechanism correlates optical phase across a full optical octave with less than 2.5 microHZ relative linewidth. This result is at least two orders of magnitude below recent predictions for quantum-limited individual comb-mode linewidths, verifying that the mode-locking mechanism strongly correlates quantum noise across the comb spectrum.

Testing ultrafast mode-locking at microhertz relative optical linewidth

OpenAIRE

Martin, Michael J.; Foreman, Seth M.; Schibli, T. R.; Ye, Jun

2008-01-01

We report new limits on the phase coherence of the ultrafast mode-locking process in an octave-spanning Ti:sapphire comb. We find that the mode-locking mechanism correlates optical phase across a full optical octave with less than 2.5 micro Hz relative linewidth. This result is at least two orders of magnitude below recent predictions for quantum-limited individual comb-mode linewidths, verifying that the mode-locking mechanism strongly correlates quantum noise across the comb spectrum.

A Recirculating Linac-Based Facility for Ultrafast X-Ray Science

International Nuclear Information System (INIS)

Corlett, J. N.; Barletta, W. A.; DeSantis, S.; Doolittle, L.; Fawley, W. M.; Green, M.A.; Heimann, P.; Leone, S.; Lidia, S.; Li, D.; Ratti, A.; Robinson, K.; Schoenlein, R.; Staples, J.; Wan, W.; Wells, R.; Wolski, A.; Zholents, A.; Parmigiani, F.; Placidi, M.; Pirkl, W.; Rimmer, R. A.; Wang, S.

2003-01-01

We present an updated design for a proposed source of ultra-fast synchrotron radiation pulses based on a recirculating superconducting linac [1,2], in particular the incorporation of EUV and soft x-ray production. The project has been named LUX--Linac-based Ultrafast X-ray facility. The source produces intense x-ray pulses with duration of 10-100 fs at a 10 kHz repetition rate, with synchronization of 10's fs, optimized for the study of ultra-fast dynamics. The photon range covers the EUV to hard x-ray spectrum by use of seeded harmonic generation in undulators, and a specialized technique for ultra-short pulse photon production in the 1-10 keV range. High brightness rf photocathodes produce electron bunches which are optimized either for coherent emission in free electron lasers, or to provide a large x/y emittance ration and small vertical emittance which allows for manipulation to produce short-pulse hard x-rays. An injector linac accelerates the beam to 120 MeV, and is followed by f our passes through a 600-720 MeV recirculating linac. We outline the major technical components of the proposed facility

Coherent multi-octave spanning supercontinuum in tapered sulphide fibres

DEFF Research Database (Denmark)

Kubat, Irnis; Mägi, Eric; Hu, Tomonori

A novel frequency comb design is proposed based on a newly developed ultrafast 3µm mid-infrared laser in conjunction with micro-taper chalcogenide fibre. The novel design allows for an all-fibre laser source yielding up to three octave coherent supercontinuum. The design is the first step in real...

Ultrafast Optical Modulation of Second- and Third-Harmonic Generation from Cut-Disk-Based Metasurfaces

KAUST Repository

Sartorello, Giovanni

2016-06-06

We design and fabricate a metasurface composed of gold cut-disk resonators that exhibits a strong coherent nonlinear response. We experimentally demonstrate all-optical modulation of both second- and third-harmonic signals on a subpicosecond time scale. Pump-probe experiments and numerical models show that the observed effects are due to the ultrafast response of the electronic excitations in the metal under external illumination. These effects pave the way for the development of novel active nonlinear metasurfaces with controllable and switchable coherent nonlinear response. © 2016 American Chemical Society.

Nonlinear Optical Spectroscopy in the Time Domain: Studies of Ultrafast Molecular Processes in the Condensed Phase.

Science.gov (United States)

Joo, Taiha

Ultrafast molecular processes in the condensed phase at room temperature are studied in the time domain by four wave mixing spectroscopy. The structure/dynamics of various quantum states can be studied by varying the time ordering of the incident fields, their polarization, their colors, etc. In one, time-resolved coherent Stokes Raman spectroscopy of benzene is investigated at room temperature. The reorientational correlation time of benzene as well as the T_2 time of the nu _1 ring-breathing mode have been measured by using two different polarization geometries. Bohr frequency difference beats have also been resolved between the nu_1 modes of ^ {12}C_6H_6 and ^{12}C_5^{13 }CH_6.. The dephasing dynamics of the nu _1 ring-breathing mode of neat benzene is studied by time-resolved coherent anti-Stokes Raman scattering. Ultrafast time resolution reveals deviation from the conventional exponential decay. The correlation time, tau _{rm c}, and the rms magnitude, Delta, of the Bohr frequency modulation are determined for the process responsible for the vibrational dephasing by Kubo dephasing function analysis. The electronic dephasing of two oxazine dyes in ethylene glycol at room temperature is investigated by photon echo experiments. It was found that at least two stochastic processes are responsible for the observed electronic dephasing. Both fast (homogeneous) and slow (inhomogeneous) dynamics are recovered using Kubo line shape analysis. Moreover, the slow dynamics is found to spectrally diffuse over the inhomogeneous distribution on the time scale around a picosecond. Time-resolved degenerate four wave mixing signal of dyes in a population measurement geometry is reported. The vibrational coherences both in the ground and excited electronic states produced strong oscillations in the signal together with the usual population decay from the excited electronic state. Absolute frequencies and their dephasing times of the vibrational modes at ~590 cm^{-1} are obtained

Synchronous Measurement of Ultrafast Anisotropy Decay of the B850 in Bacterial LH2 Complex

International Nuclear Information System (INIS)

Wang Yun-Peng; Du Lu-Chao; Zhu Gang-Bei; Wang Zhuan; Weng Yu-Xiang

2015-01-01

Ultrafast anisotropic decay is a prominent parameter revealing ultrafast energy and electron transfer; however, it is difficult to be determined reliably owing to the requirement of a simultaneous availability of the parallel and perpendicular polarized decay kinetics. Nowadays, any measurement of anisotropic decay is a kind of approach to the exact simultaneity. Here we report a novel method for a synchronous ultrafast anisotropy decay measurement, which can well determine the anisotropy, even at a very early time, as the rising phase of the excitation laser pulse. The anisotropic decay of the B850 in bacterial light harvesting antenna complex LH2 of Rhodobacter sphaeroides in solution at room temperature with coherent excitation is detected by this method, which shows a polarization response time of 30 fs, and the energy transfer from the initial excitation to the bacteriochlorophylls in B850 ring takes about 70 fs. The anisotropic decay that is probed at the red side of the absorption spectrum, such as 880 nm, has an initial value of 0.4, corresponding to simulated emission, while the blue side with an anisotropy of 0.1 contributes to the ground-state bleaching. Our results show that the coherent excitation covering the whole ring might not be realized owing to the symmetry breaking of LH2: from C_9 symmetry in membrane to C_2 symmetry in solution. (atomic and molecular physics)

Synchronous Measurement of Ultrafast Anisotropy Decay of the B850 in Bacterial LH2 Complex

Science.gov (United States)

Wang, Yun-Peng; Du, Lu-Chao; Zhu, Gang-Bei; Wang, Zhuan; Weng, Yu-Xiang

2015-02-01

Ultrafast anisotropic decay is a prominent parameter revealing ultrafast energy and electron transfer; however, it is difficult to be determined reliably owing to the requirement of a simultaneous availability of the parallel and perpendicular polarized decay kinetics. Nowadays, any measurement of anisotropic decay is a kind of approach to the exact simultaneity. Here we report a novel method for a synchronous ultrafast anisotropy decay measurement, which can well determine the anisotropy, even at a very early time, as the rising phase of the excitation laser pulse. The anisotropic decay of the B850 in bacterial light harvesting antenna complex LH2 of Rhodobacter sphaeroides in solution at room temperature with coherent excitation is detected by this method, which shows a polarization response time of 30 fs, and the energy transfer from the initial excitation to the bacteriochlorophylls in B850 ring takes about 70 fs. The anisotropic decay that is probed at the red side of the absorption spectrum, such as 880 nm, has an initial value of 0.4, corresponding to simulated emission, while the blue side with an anisotropy of 0.1 contributes to the ground-state bleaching. Our results show that the coherent excitation covering the whole ring might not be realized owing to the symmetry breaking of LH2: from C9 symmetry in membrane to C2 symmetry in solution.

Portable atomic frequency standard based on coherent population trapping

Science.gov (United States)

Shi, Fan; Yang, Renfu; Nian, Feng; Zhang, Zhenwei; Cui, Yongshun; Zhao, Huan; Wang, Nuanrang; Feng, Keming

2015-05-01

In this work, a portable atomic frequency standard based on coherent population trapping is designed and demonstrated. To achieve a portable prototype, in the system, a single transverse mode 795nm VCSEL modulated by a 3.4GHz RF source is used as a pump laser which generates coherent light fields. The pump beams pass through a vapor cell containing atom gas and buffer gas. This vapor cell is surrounded by a magnetic shield and placed inside a solenoid which applies a longitudinal magnetic field to lift the Zeeman energy levels' degeneracy and to separate the resonance signal, which has no first-order magnetic field dependence, from the field-dependent resonances. The electrical control system comprises two control loops. The first one locks the laser wavelength to the minimum of the absorption spectrum; the second one locks the modulation frequency and output standard frequency. Furthermore, we designed the micro physical package and realized the locking of a coherent population trapping atomic frequency standard portable prototype successfully. The short-term frequency stability of the whole system is measured to be 6×10-11 for averaging times of 1s, and reaches 5×10-12 at an averaging time of 1000s.

Reversible ultrafast melting in bulk CdSe

International Nuclear Information System (INIS)

Wu, Wenzhi; He, Feng; Wang, Yaguo

2016-01-01

In this work, transient reflectivity changes in bulk CdSe have been measured with two-color femtosecond pump-probe spectroscopy under a wide range of pump fluences. Three regions of reflectivity change with pump fluences have been consistently revealed for excited carrier density, coherent phonon amplitude, and lattice temperature. For laser fluences from 13 to 19.3 mJ/cm 2 , ultrafast melting happens in first several picoseconds. This melting process is purely thermal and reversible. A complete phase transformation in bulk CdSe may be reached when the absorbed laser energy is localized long enough, as observed in nanocrystalline CdSe

Ultrafast dynamics of correlated electrons

Energy Technology Data Exchange (ETDEWEB)

Rettig, Laurenz

2012-07-09

This work investigates the ultrafast electron dynamics in correlated, low-dimensional model systems using femtosecond time- and angle-resolved photoemission spectroscopy (trARPES) directly in the time domain. In such materials, the strong electron-electron (e-e) correlations or coupling to other degrees of freedom such as phonons within the complex many-body quantum system lead to new, emergent properties that are characterized by phase transitions into broken-symmetry ground states such as magnetic, superconducting or charge density wave (CDW) phases. The dynamical processes related to order like transient phase changes, collective excitations or the energy relaxation within the system allow deeper insight into the complex physics governing the emergence of the broken-symmetry state. In this work, several model systems for broken-symmetry ground states and for the dynamical charge balance at interfaces have been studied. In the quantum well state (QWS) model system Pb/Si(111), the charge transfer across the Pb/Si interface leads to an ultrafast energetic stabilization of occupied QWSs, which is the result of an increase of the electronic confinement to the metal film. In addition, a coherently excited surface phonon mode is observed. In antiferromagnetic (AFM) Fe pnictide compounds, a strong momentum-dependent asymmetry of electron and hole relaxation rates allows to separate the recovery dynamics of the AFM phase from electron-phonon (e-ph) relaxation. The strong modulation of the chemical potential by coherent phonon modes demonstrates the importance of e-ph coupling in these materials. However, the average e-ph coupling constant is found to be small. The investigation of the excited quasiparticle (QP) relaxation dynamics in the high-T{sub c}4 superconductor Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+δ} reveals a striking momentum and fluence independence of the QP life times. In combination with the momentum-dependent density of excited QPs, this demonstrates the

Femtosecond spectroscopy in semiconductors: a key to coherences, correlations and quantum kinetics

International Nuclear Information System (INIS)

Axt, V M; Kuhn, T

2004-01-01

The application of femtosecond spectroscopy to the study of ultrafast dynamics in semiconductor materials and nanostructures is reviewed with particular emphasis on the physics that can be learned from it. Excitation with ultrashort optical pulses in general results in the creation of coherent superpositions and correlated many-particle states. The review comprises a discussion of the dynamics of this correlated many-body system during and after pulsed excitation as well as its analysis by means of refined measurements and advanced theories. After an introduction of basic concepts-such as coherence, correlation and quantum kinetics-a brief overview of the most important experimental techniques and theoretical approaches is given. The remainder of this paper is devoted to specific results selected in order to highlight how femtosecond spectroscopy gives access to the physics of coherences, correlations and quantum kinetics involving charge, spin and lattice degrees of freedom. First examples deal with the dynamics of basic laser-induced coherences that can be observed, e.g. in quantum beat spectroscopy, in coherent control measurements or in experiments using few-cycle pulses. The phenomena discussed here are basic in the sense that they can be understood to a large extent on the mean-field level of the theory. Nevertheless, already on this level it is found that semiconductors behave substantially differently from atomic systems. Subsequent sections report on the occurrence of coherences and correlations beyond the mean-field level that are mediated either by carrier-phonon or carrier-carrier interactions. The corresponding analysis gives deep insight into fundamental issues such as the energy-time uncertainty, pure dephasing in quantum dot structures, the role of two-pair or even higher correlations and the build-up of screening. Finally results are presented concerning the ultrafast dynamics of resonantly coupled excitations, where a combination of different

Coherent control of atto-second emission from aligned molecules

Energy Technology Data Exchange (ETDEWEB)

Boutu, W; Haessler, S; Merdji, H; Breger, P; Monchicourt, P; Carre, B; Salieres, P [CEA Saclay, DSM, Serv Photons Atomes Mol, F-91191 Gif Sur Yvette, (France); Waters, G [Univ Reading, JJ Thomson Phys Lab, Reading RG6 6AF, Berks, (United Kingdom); Stankiewicz, M [Jagiellonian Univ, Inst Phys, PL-30059 Krakow, (Poland); Frasinski, L J [Univ London Imperial Coll Sci Technol and Med, Blackett Lab, London SW7 2BW, (United Kingdom); Taieb, R; Caillat, J; Maquet, A [Univ Paris 06, UMR 7614, Lab Chim Phys Matiere Rayonnement, F-75231 Paris 05, (France); Taieb, R; Caillat, J; Maquet, A [LCPMR, UMR 7614, CNRS, F-75005 Paris, (France)

2008-07-01

Controlling atto-second electron wave packets and soft X-ray pulses represents a formidable challenge of general implication to many areas of science. A strong laser field interacting with atoms or molecules drives ultrafast intra-atomic/molecular electron wave packets on a sub femtosecond timescale, resulting in the emission of atto-second bursts of extreme-ultraviolet light. Controlling the intra-atomic/molecular electron dynamics enables steering of the atto-second emission. Here, we carry out a coherent control in linear molecules, where the interaction of the laser-driven electron wave packet with the core leads to quantum interferences. We demonstrate that these interferences can be finely controlled by turning the molecular axis relative to the laser polarization, that is, changing the electron re-collision angle. The wave-packet coulombic distortion modifies the spectral phase jump measured in the extreme-ultraviolet emission. Our atto-second control of the interference results in atto-second pulse shaping, useful for future applications in ultrafast coherent control of atomic and molecular processes. (authors)

An ultrafast nanotip electron gun triggered by grating-coupled surface plasmons

Energy Technology Data Exchange (ETDEWEB)

Schröder, Benjamin; Sivis, Murat; Bormann, Reiner; Schäfer, Sascha; Ropers, Claus, E-mail: cropers@gwdg.de [4th Physical Institute - Solids and Nanostructures, University of Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen (Germany)

2015-12-07

We demonstrate multiphoton photoelectron emission from gold nanotips induced by nanofocusing surface plasmons, resonantly excited on the tip shaft by a grating coupler. The tip is integrated into an electron gun assembly, which facilitates control over the spatial emission sites and allows us to disentangle direct grating emission from plasmon-triggered apex emission. The nanoscale source size of this electron gun concept enables highly coherent electron pulses with applications in ultrafast electron imaging and diffraction.

Multiplane wave imaging increases signal-to-noise ratio in ultrafast ultrasound imaging

International Nuclear Information System (INIS)

Tiran, Elodie; Deffieux, Thomas; Correia, Mafalda; Maresca, David; Osmanski, Bruno-Felix; Pernot, Mathieu; Tanter, Mickael; Sieu, Lim-Anna; Bergel, Antoine; Cohen, Ivan

2015-01-01

Ultrafast imaging using plane or diverging waves has recently enabled new ultrasound imaging modes with improved sensitivity and very high frame rates. Some of these new imaging modalities include shear wave elastography, ultrafast Doppler, ultrafast contrast-enhanced imaging and functional ultrasound imaging. Even though ultrafast imaging already encounters clinical success, increasing even more its penetration depth and signal-to-noise ratio for dedicated applications would be valuable.Ultrafast imaging relies on the coherent compounding of backscattered echoes resulting from successive tilted plane waves emissions; this produces high-resolution ultrasound images with a trade-off between final frame rate, contrast and resolution. In this work, we introduce multiplane wave imaging, a new method that strongly improves ultrafast images signal-to-noise ratio by virtually increasing the emission signal amplitude without compromising the frame rate. This method relies on the successive transmissions of multiple plane waves with differently coded amplitudes and emission angles in a single transmit event. Data from each single plane wave of increased amplitude can then be obtained, by recombining the received data of successive events with the proper coefficients.The benefits of multiplane wave for B-mode, shear wave elastography and ultrafast Doppler imaging are experimentally demonstrated. Multiplane wave with 4 plane waves emissions yields a 5.8  ±  0.5 dB increase in signal-to-noise ratio and approximately 10 mm in penetration in a calibrated ultrasound phantom (0.7 d MHz −1 cm −1 ). In shear wave elastography, the same multiplane wave configuration yields a 2.07  ±  0.05 fold reduction of the particle velocity standard deviation and a two-fold reduction of the shear wave velocity maps standard deviation. In functional ultrasound imaging, the mapping of cerebral blood volume results in a 3 to 6 dB increase of the contrast-to-noise ratio in

Picosecond phase-velocity dispersion of hypersonic phonons imaged with ultrafast electron microscopy

International Nuclear Information System (INIS)

Cremons, Daniel R.; Du, Daniel X.; Flannigan, David J.

2017-01-01

We describe the direct imaging—with four-dimensional ultrafast electron microscopy—of the emergence, evolution, dispersion, and decay of photoexcited, hypersonic coherent acoustic phonons in nanoscale germanium wedges. Coherent strain waves generated via ultrafast in situ photoexcitation were imaged propagating with initial phase velocities of up to 35 km/s across discrete micrometer-scale crystal regions. We then observe that, while each wave front travels at a constant velocity, the entire wave train evolves with a time-varying phase-velocity dispersion, displaying a single-exponential decay to the longitudinal speed of sound (5 km/s) and with a mean lifetime of 280 ps. We also find that the wave trains propagate along a single in-plane direction oriented parallel to striations introduced during specimen preparation, independent of crystallographic direction. Elastic-plate modeling indicates the dynamics arise from excitation of a single, symmetric (dilatational) guided acoustic mode. Further, by precisely determining the experiment time-zero position with a plasma-lensing method, we find that wave-front emergence occurs approximately 100 ps after femtosecond photoexcitation, which matches well with Auger recombination times in germanium. We conclude by discussing the similarities between the imaged hypersonic strain-wave dynamics and electron/hole plasma-wave dynamics in strongly photoexcited semiconductors.

Picosecond phase-velocity dispersion of hypersonic phonons imaged with ultrafast electron microscopy

Science.gov (United States)

Cremons, Daniel R.; Du, Daniel X.; Flannigan, David J.

2017-12-01

Here, we describe the direct imaging—with four-dimensional ultrafast electron microscopy—of the emergence, evolution, dispersion, and decay of photoexcited, hypersonic coherent acoustic phonons in nanoscale germanium wedges. Coherent strain waves generated via ultrafast in situ photoexcitation were imaged propagating with initial phase velocities of up to 35 km/s across discrete micrometer-scale crystal regions. We observe that, while each wave front travels at a constant velocity, the entire wave train evolves with a time-varying phase-velocity dispersion, displaying a single-exponential decay to the longitudinal speed of sound (5 km/s) and with a mean lifetime of 280 ps. We also find that the wave trains propagate along a single in-plane direction oriented parallel to striations introduced during specimen preparation, independent of crystallographic direction. Elastic-plate modeling indicates the dynamics arise from excitation of a single, symmetric (dilatational) guided acoustic mode. Further, by precisely determining the experiment time-zero position with a plasma-lensing method, we find that wave-front emergence occurs approximately 100 ps after femtosecond photoexcitation, which matches well with Auger recombination times in germanium. We conclude by discussing the similarities between the imaged hypersonic strain-wave dynamics and electron/hole plasma-wave dynamics in strongly photoexcited semiconductors.

Nuclear spin cooling by electric dipole spin resonance and coherent population trapping

Science.gov (United States)

Li, Ai-Xian; Duan, Su-Qing; Zhang, Wei

2017-09-01

Nuclear spin fluctuation suppression is a key issue in preserving electron coherence for quantum information/computation. We propose an efficient way of nuclear spin cooling in semiconductor quantum dots (QDs) by the coherent population trapping (CPT) and the electric dipole spin resonance (EDSR) induced by optical fields and ac electric fields. The EDSR can enhance the spin flip-flop rate and may bring out bistability under certain conditions. By tuning the optical fields, we can avoid the EDSR induced bistability and obtain highly polarized nuclear spin state, which results in long electron coherence time. With the help of CPT and EDSR, an enhancement of 1500 times of the electron coherence time can been obtained after a 500 ns preparation time.

Coherent dynamics of plasma mirrors

Energy Technology Data Exchange (ETDEWEB)

Thaury, C; George, H; Quere, F; Monot, P; Martin, Ph [CEA, DSM, IRAMIS, Serv Photons Atomes and Mol, F-91191 Gif Sur Yvette, (France); Loch, R [Univ Twente, Laser Phys and Nonlinear Opt Grp, Fac Sci and Technol, MESA Inst Nanotechnol, NL-7500 AE Enschede, (Netherlands); Geindre, J P [Ecole Polytech, Lab Pour Utilisat Lasers Intenses, CNRS, F-91128 Palaiseau, (France)

2008-07-01

Coherent ultrashort X-ray pulses provide new ways to probe matter and its ultrafast dynamics. One of the promising paths to generate these pulses consists of using a nonlinear interaction with a system to strongly and periodically distort the waveform of intense laser fields, and thus produce high-order harmonics. Such distortions have so far been induced by using the nonlinear polarizability of atoms, leading to the production of atto-second light bursts, short enough to study the dynamics of electrons in matter. Shorter and more intense atto-second pulses, together with higher harmonic orders, are expected by reflecting ultra intense laser pulses on a plasma mirror - a dense (approximate to 10{sup 23} electrons cm{sup -3}) plasma with a steep interface. However, short-wavelength-light sources produced by such plasmas are known to generally be incoherent. In contrast, we demonstrate that like in usual low-intensity reflection, the coherence of the light wave is preserved during harmonic generation on plasma mirrors. We then exploit this coherence for interferometric measurements and thus carry out a first study of the laser-driven coherent dynamics of the plasma electrons. (authors)

Ultrafast generation of pseudo-magnetic field for valley excitons in WSe2 monolayers

KAUST Repository

Kim, J.

2014-12-04

The valley pseudospin is a degree of freedom that emerges in atomically thin two-dimensional transition metal dichalcogenides (MX2). The capability to manipulate it, in analogy to the control of spin in spintronics, can open up exciting opportunities. Here, we demonstrate that an ultrafast and ultrahigh valley pseudo-magnetic field can be generated by using circularly polarized femtosecond pulses to selectively control the valley degree of freedom in monolayer MX2. Using ultrafast pump-probe spectroscopy, we observed a pure and valley-selective optical Stark effect in WSe2 monolayers from the nonresonant pump, resulting in an energy splitting of more than 10 milli-electron volts between the K and K′ valley exciton transitions. Our study opens up the possibility to coherently manipulate the valley polarization for quantum information applications.

Ultrafast generation of pseudo-magnetic field for valley excitons in WSe2 monolayers

KAUST Repository

Kim, J.; Hong, X.; Jin, C.; Shi, S.-F.; Chang, C.-Y. S.; Chiu, Ming-Hui; Li, Lain-Jong; Wang, F.

2014-01-01

The valley pseudospin is a degree of freedom that emerges in atomically thin two-dimensional transition metal dichalcogenides (MX2). The capability to manipulate it, in analogy to the control of spin in spintronics, can open up exciting opportunities. Here, we demonstrate that an ultrafast and ultrahigh valley pseudo-magnetic field can be generated by using circularly polarized femtosecond pulses to selectively control the valley degree of freedom in monolayer MX2. Using ultrafast pump-probe spectroscopy, we observed a pure and valley-selective optical Stark effect in WSe2 monolayers from the nonresonant pump, resulting in an energy splitting of more than 10 milli-electron volts between the K and K′ valley exciton transitions. Our study opens up the possibility to coherently manipulate the valley polarization for quantum information applications.

Manipulation of Zeeman coherence in solids at room temperature: Ramsey interference in the coherent-population-trapping spectrum of ruby

International Nuclear Information System (INIS)

Kolesov, Roman; Scully, Marlan O.; Kocharovskaya, Olga

2006-01-01

Coherent population trapping (CPT) in a three-level atomic medium pumped by two subsequent short optical pulses is considered under the condition of negligible population decay from the excited optical state. It is shown that the amount of atomic population transferred to the excited state by the combined action of the pulses strongly depends on the phase of the ground-state coherence excited by the first pulse at the arrival time of the second pulse. Oscillatory behavior of optical excitation efficiency on the time delay between the pulses is predicted. It is also shown that saturating optical pulses can produce population inversion in a resonantly pumped quasi-two-level system. A class of solid materials in which the predicted phenomena can be observed at room temperature is found. It includes some rare-earth and transition-metal doped dielectric crystals where Orbach relaxation between ground-state Zeeman states is suppressed: ruby, alexandrite, and several others. On the basis of the theoretical predictions, experimental observation of Ramsey fringes in CPT spectrum of ruby is reported

PREFACE: Ultrafast and nonlinear optics in carbon nanomaterials

Science.gov (United States)

Kono, Junichiro

2013-02-01

Carbon-based nanomaterials—single-wall carbon nanotubes (SWCNTs) and graphene, in particular—have emerged in the last decade as novel low-dimensional systems with extraordinary properties. Because they are direct-bandgap systems, SWCNTs are one of the leading candidates to unify electronic and optical functions in nanoscale circuitry; their diameter-dependent bandgaps can be utilized for multi-wavelength devices. Graphene's ultrahigh carrier mobilities are promising for high-frequency electronic devices, while, at the same time, it is predicted to have ideal properties for terahertz generation and detection due to its unique zero-gap, zero-mass band structure. There have been a large number of basic optical studies on these materials, but most of them were performed in the weak-excitation, quasi-equilibrium regime. In order to probe and assess their performance characteristics as optoelectronic materials under device-operating conditions, it is crucial to strongly drive them and examine their optical properties in highly non-equilibrium situations and with ultrashot time resolution. In this section, the reader will find the latest results in this rapidly growing field of research. We have assembled contributions from some of the leading experts in ultrafast and nonlinear optical spectroscopy of carbon-based nanomaterials. Specific topics featured include: thermalization, cooling, and recombination dynamics of photo-generated carriers; stimulated emission, gain, and amplification; ultrafast photoluminescence; coherent phonon dynamics; exciton-phonon and exciton-plasmon interactions; exciton-exciton annihilation and Auger processes; spontaneous and stimulated emission of terahertz radiation; four-wave mixing and harmonic generation; ultrafast photocurrents; the AC Stark and Franz-Keldysh effects; and non-perturbative light-mater coupling. We would like to express our sincere thanks to those who contributed their latest results to this special section, and the

The separation of vibrational coherence from ground- and excited-electronic states in P3HT film

KAUST Repository

Song, Yin; Hellmann, Christoph; Stingelin, Natalie; Scholes, Gregory D.

2015-01-01

© 2015 AIP Publishing LLC. Concurrence of the vibrational coherence and ultrafast electron transfer has been observed in polymer/fullerene blends. However, it is difficult to experimentally investigate the role that the excited-state vibrational

Population branching in the conical intersection of the retinal chromophore revealed by multipulse ultrafast optical spectroscopy.

Science.gov (United States)

Zgrablić, Goran; Novello, Anna Maria; Parmigiani, Fulvio

2012-01-18

The branching ratio of the excited-state population at the conical intersection between the S(1) and S(0) energy surfaces (Φ(CI)) of a protonated Schiff base of all-trans retinal in protic and aprotic solvents was studied by multipulse ultrafast transient absorption spectroscopy. In particular, pump-dump-probe experiments allowed to isolate the S(1) reactive state and to measure the photoisomerization time constant with unprecedented precision. Starting from these results, we demonstrate that the polarity of the solvent is the key factor influencing the Φ(CI) and the photoisomerization yield. © 2011 American Chemical Society

The Coherent X-ray Imaging (CXI) Instrument at the Linac Coherent Light Source (LCLS)

International Nuclear Information System (INIS)

Boutet, Sebastien

2011-01-01

The Linac Coherent Light Source (LCLS) has become the first ever operational hard X-ray Free Electron Laser in 2009. It will operate as a user facility capable of delivering unique research opportunities in multiple fields of science. The LCLS and the LCLS Ultrafast Science Instruments (LUSI) construction projects are developing instruments designed to make full use of the capabilities afforded by the LCLS beam. One such instrument is being designed to utilize the LCLS coherent beam to image with high resolution any sub-micron object. This instrument is called the Coherent X-ray Imaging (CXI) instrument. This instrument will provide a flexible optical system capable of tailoring key beam parameters for the users. A suite of shot-to-shot diagnostics will also be provided to characterize the beam on every pulse. The provided instrumentation will include multi-purpose sample environments, sample delivery and a custom detector capable of collecting 2D data at 120 Hz. In this article, the LCLS will be briefly introduced along with the technique of Coherent X-ray Diffractive Imaging (CXDI). A few examples of scientific opportunities using the CXI instrument will be described. Finally, the conceptual layout of the instrument will be presented along with a description of the key requirements for the overall system and specific devices required.

Ultrafast electric phase control of a single exciton qubit

Science.gov (United States)

Widhalm, Alex; Mukherjee, Amlan; Krehs, Sebastian; Sharma, Nandlal; Kölling, Peter; Thiede, Andreas; Reuter, Dirk; Förstner, Jens; Zrenner, Artur

2018-03-01

We report on the coherent phase manipulation of quantum dot excitons by electric means. For our experiments, we use a low capacitance single quantum dot photodiode which is electrically controlled by a custom designed SiGe:C BiCMOS chip. The phase manipulation is performed and quantified in a Ramsey experiment, where ultrafast transient detuning of the exciton energy is performed synchronous to double pulse π/2 ps laser excitation. We are able to demonstrate electrically controlled phase manipulations with magnitudes up to 3π within 100 ps which is below the dephasing time of the quantum dot exciton.

Fourteenth International Conference on Ultrafast Phenomena

CERN Document Server

Kobayashi, Takayoshi; Kobayashi, Tetsuro; Nelson, Keith A; Silvestri, Sandro; Ultrafast Phenomena XIV

2005-01-01

Ultrafast Phenomena XIV presents the latest advances in ultrafast science, including ultrafast laser and measurement technology as well as studies of ultrafast phenomena. Pico-, femto-, and atosecond processes relevant in physics, chemistry, biology and engineering are presented. Ultrafast technology is now having a profound impact within a wide range of applications, among them imaging, material diagnostics, and transformation and high-speed optoelectronics. This book summarizes results presented at the 14th Ultrafast Phenomena Conference and reviews the state of the art in this important and rapidly advancing field.

Sixteenth International Conference on Ultrafast Phenomena

CERN Document Server

Corkum, Paul; Nelson, Keith A; Riedle, Eberhard; Schoenlein, Robert W; Ultrafast Phenomena XVI

2009-01-01

Ultrafast Phenomena XVI presents the latest advances in ultrafast science, including both ultrafast optical technology and the study of ultrafast phenomena. It covers picosecond, femtosecond and attosecond processes relevant to applications in physics, chemistry, biology, and engineering. Ultrafast technology has a profound impact in a wide range of applications, amongst them biomedical imaging, chemical dynamics, frequency standards, material processing, and ultrahigh speed communications. This book summarizes the results presented at the 16th International Conference on Ultrafast Phenomena and provides an up-to-date view of this important and rapidly advancing field.

Interpretation of photocurrent correlation measurements used for ultrafast photoconductive switch characterization

DEFF Research Database (Denmark)

Jacobsen, R. H.; Birkelund, Karen; Holst, T.

1996-01-01

of the switch. By using both photocurrent measurements and terahertz spectroscopy we verify the importance of space-charge effects on the carrier dynamics. Photocurrent nonlinearities and coherent effects are discussed as they appear in the correlation signals. An analysis based on a simple model allows......Photocurrent correlation measurements used for the characterization of ultrafast photoconductive switches based on GaAs and silicon-on-sapphire are demonstrated. The correlation signal arises from the interplay of the photoexcited carriers, the dynamics of the bias field and a subsequent recharging...

Coherent radiation spectrum measurements at KEK LUCX facility

Energy Technology Data Exchange (ETDEWEB)

Shevelev, M., E-mail: mishe@post.kek.jp [KEK: High Energy Accelerator Research Organization, 1-1 Oho, Tsukuba, Ibaraki 305-0801 (Japan); Aryshev, A., E-mail: alar@post.kek.jp [KEK: High Energy Accelerator Research Organization, 1-1 Oho, Tsukuba, Ibaraki 305-0801 (Japan); Araki, S.; Fukuda, M. [KEK: High Energy Accelerator Research Organization, 1-1 Oho, Tsukuba, Ibaraki 305-0801 (Japan); Karataev, P. [John Adams Institute at Royal Holloway, University of London, Egham, Surrey TW20 0EX (United Kingdom); Terunuma, N.; Urakawa, J. [KEK: High Energy Accelerator Research Organization, 1-1 Oho, Tsukuba, Ibaraki 305-0801 (Japan)

2015-01-21

This paper demonstrates the detailed design concept, alignment, and initial testing of a Michelson interferometer for the THz spectral range. We present the first results on the measurement of a coherent transition radiation spectrum and describe the performance of a pair of ultra-fast broadband room temperature Schottky barrier diode detectors. We discuss the main criteria of interferometer beam splitter optimization, the alignment technique, the high-precision calibration and linearity check of the motion system.

Coherent phonon dynamics in micro- and nanocrystalline diamond

Czech Academy of Sciences Publication Activity Database

Kozák, M.; Trojánek, F.; Galář, P.; Varga, Marián; Kromka, Alexander; Malý, P.

2013-01-01

Roč. 21, č. 25 (2013), s. 31521-31529 ISSN 1094-4087 R&D Projects: GA ČR(CZ) GAP108/11/0794; GA ČR GA13-12386S Institutional support: RVO:68378271 Keywords : optical nonlinearities of condensed matter * spectroscopy * coherent anti-Stokes Raman scattering * ultrafast spectroscopy * nanomaterials Subject RIV: BH - Optics, Masers, Lasers Impact factor: 3.525, year: 2013 http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-25-31521

Roadmap of ultrafast x-ray atomic and molecular physics

Science.gov (United States)

Young, Linda; Ueda, Kiyoshi; Gühr, Markus; Bucksbaum, Philip H.; Simon, Marc; Mukamel, Shaul; Rohringer, Nina; Prince, Kevin C.; Masciovecchio, Claudio; Meyer, Michael; Rudenko, Artem; Rolles, Daniel; Bostedt, Christoph; Fuchs, Matthias; Reis, David A.; Santra, Robin; Kapteyn, Henry; Murnane, Margaret; Ibrahim, Heide; Légaré, François; Vrakking, Marc; Isinger, Marcus; Kroon, David; Gisselbrecht, Mathieu; L'Huillier, Anne; Wörner, Hans Jakob; Leone, Stephen R.

2018-02-01

X-ray free-electron lasers (XFELs) and table-top sources of x-rays based upon high harmonic generation (HHG) have revolutionized the field of ultrafast x-ray atomic and molecular physics, largely due to an explosive growth in capabilities in the past decade. XFELs now provide unprecedented intensity (1020 W cm-2) of x-rays at wavelengths down to ˜1 Ångstrom, and HHG provides unprecedented time resolution (˜50 attoseconds) and a correspondingly large coherent bandwidth at longer wavelengths. For context, timescales can be referenced to the Bohr orbital period in hydrogen atom of 150 attoseconds and the hydrogen-molecule vibrational period of 8 femtoseconds; wavelength scales can be referenced to the chemically significant carbon K-edge at a photon energy of ˜280 eV (44 Ångstroms) and the bond length in methane of ˜1 Ångstrom. With these modern x-ray sources one now has the ability to focus on individual atoms, even when embedded in a complex molecule, and view electronic and nuclear motion on their intrinsic scales (attoseconds and Ångstroms). These sources have enabled coherent diffractive imaging, where one can image non-crystalline objects in three dimensions on ultrafast timescales, potentially with atomic resolution. The unprecedented intensity available with XFELs has opened new fields of multiphoton and nonlinear x-ray physics where behavior of matter under extreme conditions can be explored. The unprecedented time resolution and pulse synchronization provided by HHG sources has kindled fundamental investigations of time delays in photoionization, charge migration in molecules, and dynamics near conical intersections that are foundational to AMO physics and chemistry. This roadmap coincides with the year when three new XFEL facilities, operating at Ångstrom wavelengths, opened for users (European XFEL, Swiss-FEL and PAL-FEL in Korea) almost doubling the present worldwide number of XFELs, and documents the remarkable progress in HHG capabilities since

Locking Lasers to RF in an Ultrafast FEL

International Nuclear Information System (INIS)

Wilcox, R.; Huang, G.; Doolittle, L.; White, W.; Frisch, J.; Coffee, R.

2010-01-01

Using a novel, phase-stabilized RF-over-fiber scheme, they transmit 3GHz over 300m with 27fs RMS error in 250kHz bandwidth over 12 hours, and phase lock a laser to enable ultrafast pump-probe experiments. Free-electron lasers (FELs) are capable of producing short-duration (< 10fs), high-energy X-ray pulses for a range of scientific applications. The recently activated Linac Coherent Light Source (LCLS) FEL facility at SLAC will support experiments which require synchronized light pulses for pump-probe schemes. They developed and operated a fiber optic RF transmission system to synchronize lasers to the emitted X-ray pulses, which was used to enable the first pump-probe experiments at the LCLS.

Spin squeezing and light entanglement in Coherent Population Trapping

DEFF Research Database (Denmark)

Dantan, Aurelien Romain; Cviklinski, Jean; Giacobino, Elisabeth

2006-01-01

We show that strong squeezing and entanglement can be generated at the output of a cavity containing atoms interacting with two fields in a coherent population trapping situation, on account of a nonlinear Faraday effect experienced by the fields close to a dark-state resonance in a cavity....... Moreover, the cavity provides a feedback mechanism allowing to reduce the quantum fluctuations of the ground state spin, resulting in strong steady state spin squeezing....

Coherent Control of Four-Wave Mixing

CERN Document Server

Zhang, Yanpeng; Xiao, Min

2011-01-01

"Coherent Control of Four-Wave Mixing" discusses the frequency, temporal and spatial domain interplays of four-wave mixing (FWM) processes induced by atomic coherence in multi-level atomic systems. It covers topics in five major areas: the ultrafast FWM polarization beats due to interactions between multi-color laser beams and multi-level media; coexisting Raman-Rayleigh-Brillouin-enhanced polarization beats due to color-locking noisy field correlations; FWM processes with different kinds of dual-dressed schemes in ultra-thin, micrometer and long atomic cells; temporal and spatial interference between FWM and six-wave mixing (SWM) signals in multi-level electromagnetically induced transparency (EIT) media; spatial displacements and splitting of the probe and generated FWM beams, as well as the observations of gap soliton trains, vortex solitons, and stable multicomponent vector solitons in the FWM signals. The book is intended for scientists, researchers, advanced undergraduate and graduate students in Nonlin...

The importance of the reference populations for coherent mortality forecasting models

DEFF Research Database (Denmark)

Kjærgaard, Søren; Canudas-Romo, Vladimir; Vaupel, James W.

-population mortality models aiming to find the optimal of the set of countries to use as reference population and analyse the importance of the selection of countries. The two multi-population mortality models used are the Li-Lee model and the Double-Gap life expectancy forecasting model. The reference populations......Coherent forecasting models that take into consideration mortality changes observed in different countries are today among the essential tools for demographers, actuaries and other researchers interested in forecasts. Medium and long term life expectancy forecasts are compared for two multi...... is calculated taking into account all the possible combinations of a set of 20 industrialized countries. The different reference populations possibilities are compared by their forecast performance. The results show that the selection of countries for multi-population mortality models has a significant effect...

Coherence and population dynamics of chlorophyll excitations in FCP complex: Two-dimensional spectroscopy study

Energy Technology Data Exchange (ETDEWEB)

Butkus, Vytautas; Gelzinis, Andrius; Valkunas, Leonas [Department of Theoretical Physics, Faculty of Physics, Vilnius University, Sauletekio Ave. 9-III, 10222 Vilnius (Lithuania); Center for Physical Sciences and Technology, Savanoriu Ave. 231, 02300 Vilnius (Lithuania); Augulis, Ramūnas [Center for Physical Sciences and Technology, Savanoriu Ave. 231, 02300 Vilnius (Lithuania); Gall, Andrew; Robert, Bruno [Institut de Biologie et Technologies de Saclay, Bât 532, Commissariat à l’Energie Atomique Saclay, 91191 Gif sur Yvette (France); Büchel, Claudia [Institut für Molekulare Biowissenschaften, Universität Frankfurt, Max-von-Laue-Straße 9, Frankfurt (Germany); Zigmantas, Donatas [Department of Chemical Physics, Lund University, P.O. Box 124, 22100 Lund (Sweden); Abramavicius, Darius, E-mail: darius.abramavicius@ff.vu.lt [Department of Theoretical Physics, Faculty of Physics, Vilnius University, Sauletekio Ave. 9-III, 10222 Vilnius (Lithuania)

2015-06-07

Energy transfer processes and coherent phenomena in the fucoxanthin–chlorophyll protein complex, which is responsible for the light harvesting function in marine algae diatoms, were investigated at 77 K by using two-dimensional electronic spectroscopy. Experiments performed on femtosecond and picosecond timescales led to separation of spectral dynamics, witnessing evolutions of coherence and population states of the system in the spectral region of Q{sub y} transitions of chlorophylls a and c. Analysis of the coherence dynamics allowed us to identify chlorophyll (Chl) a and fucoxanthin intramolecular vibrations dominating over the first few picoseconds. Closer inspection of the spectral region of the Q{sub y} transition of Chl c revealed previously not identified, mutually non-interacting chlorophyll c states participating in femtosecond or picosecond energy transfer to the Chl a molecules. Consideration of separated coherent and incoherent dynamics allowed us to hypothesize the vibrations-assisted coherent energy transfer between Chl c and Chl a and the overall spatial arrangement of chlorophyll molecules.

Anomalous Phase Change in [(GeTe)2/(Sb2Te3)]20 Superlattice Observed by Coherent Phonon Spectroscopy

Science.gov (United States)

Makino, K.; Saito, Y.; Mitrofanov, K.; Tominaga, J.; Kolobov, A. V.; Nakano, T.; Fons, P.; Hase, M.

The temperature-dependent ultrafast coherent phonon dynamics of topological (GeTe)2/(Sb2Te3) super lattice phase change memory material was investigated. By comparing with Ge-Sb-Te alloy, a clear contrast suggesting the unique phase change behavior was found.

Ultrafast MR Imaging in Pediatric Neuroradiology

International Nuclear Information System (INIS)

Singh, R.K.; Smith, J.T.; Wilkinson, I.D.; Griffiths, P.D.

2003-01-01

Purpose: To compare the diagnostic information obtained from ultrafast MR imaging with standard MR imaging techniques in pediatric neuroradiology. The goal was to judge whether ultrafast methods can be used to replace standard methods and reduce the need for sedation or general anesthesia as a result of the considerably shorter scan times. Material and Methods: Our prospective study involved 125 patients. Routine clinical imaging was performed along with two ultrafast methods. Single shot fast spin echo (SSFSE) was used to give T2-weighted images and an echo planar imaging (EPI) sequence to provide a T1-weighted images. The ultrafast images were presented to an experienced neuro radiologist who was also given the information present on the initial referral card. These reports based on the ultrafast images were then compared with the formal radiologic report made solely on the basis of the standard imaging. Results: The overall sensitivity and specificity for ultrafast imaging when compared to the reference standard were 78% and 98% with positive and negative predictive values of 98% and 76%. Pathologies characterized by small areas of subtle T2 prolongation were difficult or impossible to see on the ultrafast images but otherwise they provided reliable information. Conclusions: This paper demonstrates that ultrafast MR imaging can diagnose many pediatric intracranial abnormalities as well as standard methods. Anatomic resolution limits its capacity to define subtle developmental anomalies and contrast resolution limitations of the ultrafast methods reduce the detection of pathology characterized by subtle T2 prolongation

Ultrafast gain recovery and modulation limitations in self-assembled quantum-dot devices

DEFF Research Database (Denmark)

Berg, Tommy Winther; Bischoff, Svend; Magnúsdóttir, Ingibjörg

2001-01-01

Measurements of ultrafast gain recovery in self-assembled InAs quantum-dot (QD) amplifiers are explained by a comprehensive numerical model. The on excited state carriers are found to act as a reservoir for the optically active ground state carriers resulting in an ultrafast gain recovery as long...... as the excited state is well populated. However, when pulses are injected into the device at high-repetition frequencies, the response of a on amplifier is found to be limited by the wetting-layer dynamics....

Time resolved 3D momentum imaging of ultrafast dynamics by coherent VUV-XUV radiation

Energy Technology Data Exchange (ETDEWEB)

Sturm, F. P., E-mail: fpsturm@lbl.gov [Ultrafast X-Ray Science Lab, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Institut für Kernphysik, Universität Frankfurt, Max-von-Laue Str. 1, D-60438 Frankfurt (Germany); Wright, T. W.; Ray, D.; Zalyubovskaya, I.; Shivaram, N.; Slaughter, D. S.; Belkacem, A.; Weber, Th. [Ultrafast X-Ray Science Lab, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Ranitovic, P. [Ultrafast X-Ray Science Lab, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); ELI-ALPS, ELI-Hu Nkft, Dugonics ter 13, Szeged H6720 (Hungary)

2016-06-15

We present a new experimental setup for measuring ultrafast nuclear and electron dynamics of molecules after photo-excitation and ionization. We combine a high flux femtosecond vacuum ultraviolet (VUV) and extreme ultraviolet (XUV) source with an internally cold molecular beam and a 3D momentum imaging particle spectrometer to measure electrons and ions in coincidence. We describe a variety of tools developed to perform pump-probe studies in the VUV-XUV spectrum and to modify and characterize the photon beam. First benchmark experiments are presented to demonstrate the capabilities of the system.

Dynamics of plasmonic field polarization induced by quantum coherence in quantum dot-metallic nanoshell structures.

Science.gov (United States)

Sadeghi, S M

2014-09-01

When a hybrid system consisting of a semiconductor quantum dot and a metallic nanoparticle interacts with a laser field, the plasmonic field of the metallic nanoparticle can be normalized by the quantum coherence generated in the quantum dot. In this Letter, we study the states of polarization of such a coherent-plasmonic field and demonstrate how these states can reveal unique aspects of the collective molecular properties of the hybrid system formed via coherent exciton-plasmon coupling. We show that transition between the molecular states of this system can lead to ultrafast polarization dynamics, including sudden reversal of the sense of variations of the plasmonic field and formation of circular and elliptical polarization.

Ultrafast ultrasound localization microscopy for deep super-resolution vascular imaging

Science.gov (United States)

Errico, Claudia; Pierre, Juliette; Pezet, Sophie; Desailly, Yann; Lenkei, Zsolt; Couture, Olivier; Tanter, Mickael

2015-11-01

Non-invasive imaging deep into organs at microscopic scales remains an open quest in biomedical imaging. Although optical microscopy is still limited to surface imaging owing to optical wave diffusion and fast decorrelation in tissue, revolutionary approaches such as fluorescence photo-activated localization microscopy led to a striking increase in resolution by more than an order of magnitude in the last decade. In contrast with optics, ultrasonic waves propagate deep into organs without losing their coherence and are much less affected by in vivo decorrelation processes. However, their resolution is impeded by the fundamental limits of diffraction, which impose a long-standing trade-off between resolution and penetration. This limits clinical and preclinical ultrasound imaging to a sub-millimetre scale. Here we demonstrate in vivo that ultrasound imaging at ultrafast frame rates (more than 500 frames per second) provides an analogue to optical localization microscopy by capturing the transient signal decorrelation of contrast agents—inert gas microbubbles. Ultrafast ultrasound localization microscopy allowed both non-invasive sub-wavelength structural imaging and haemodynamic quantification of rodent cerebral microvessels (less than ten micrometres in diameter) more than ten millimetres below the tissue surface, leading to transcranial whole-brain imaging within short acquisition times (tens of seconds). After intravenous injection, single echoes from individual microbubbles were detected through ultrafast imaging. Their localization, not limited by diffraction, was accumulated over 75,000 images, yielding 1,000,000 events per coronal plane and statistically independent pixels of ten micrometres in size. Precise temporal tracking of microbubble positions allowed us to extract accurately in-plane velocities of the blood flow with a large dynamic range (from one millimetre per second to several centimetres per second). These results pave the way for deep non

Tracking the ultrafast motion of a single molecule by femtosecond orbital imaging

Science.gov (United States)

Cocker, Tyler L.; Peller, Dominik; Yu, Ping; Repp, Jascha; Huber, Rupert

2016-11-01

Watching a single molecule move on its intrinsic timescale has been one of the central goals of modern nanoscience, and calls for measurements that combine ultrafast temporal resolution with atomic spatial resolution. Steady-state experiments access the requisite spatial scales, as illustrated by direct imaging of individual molecular orbitals using scanning tunnelling microscopy or the acquisition of tip-enhanced Raman and luminescence spectra with sub-molecular resolution. But tracking the intrinsic dynamics of a single molecule directly in the time domain faces the challenge that interactions with the molecule must be confined to a femtosecond time window. For individual nanoparticles, such ultrafast temporal confinement has been demonstrated by combining scanning tunnelling microscopy with so-called lightwave electronics, which uses the oscillating carrier wave of tailored light pulses to directly manipulate electronic motion on timescales faster even than a single cycle of light. Here we build on ultrafast terahertz scanning tunnelling microscopy to access a state-selective tunnelling regime, where the peak of a terahertz electric-field waveform transiently opens an otherwise forbidden tunnelling channel through a single molecular state. It thereby removes a single electron from an individual pentacene molecule’s highest occupied molecular orbital within a time window shorter than one oscillation cycle of the terahertz wave. We exploit this effect to record approximately 100-femtosecond snapshot images of the orbital structure with sub-ångström spatial resolution, and to reveal, through pump/probe measurements, coherent molecular vibrations at terahertz frequencies directly in the time domain. We anticipate that the combination of lightwave electronics and the atomic resolution of our approach will open the door to visualizing ultrafast photochemistry and the operation of molecular electronics on the single-orbital scale.

Coherent Femtosecond Spectroscopy and Nonlinear Optical Imaging on the Nanoscale

Science.gov (United States)

Kravtsov, Vasily

four-wave mixing response from the tip apex and investigate its microscopic mechanism. Our results reveal a significant contribution to the third order nonlinearity of plasmonic structures due to large near-field gradients associated with nanofocused plasmons. In combination with scanning probe imaging and femtosecond pulse shaping, the nanofocused four-wave mixing response provides a basis for a novel type of ultrafast optical microscopy on the nanoscale. We demonstrate its capabilities by nano-imaging the coherent dynamics of localized plasmonic modes in a rough gold film edge with simultaneous sub-50 nm spatial and sub-5 fs temporal resolution. We capture the coherent decay and extract the dephasing times of individual plasmonic modes. Lastly, we apply our technique to study nanoscale spatial heterogeneity of the nonlinear optical response in novel two-dimensional materials: monolayer and few-layer graphene. An enhanced four-wave mixing signal is revealed on the edges of graphene flakes. We investigate the mechanism of this enhancement by performing nano-imaging on a graphene field-effect transistor with the variable carrier density controlled by electrostatic gating.

Ultrafast Graphene Photonics and Optoelectronics

Science.gov (United States)

2017-04-14

AFRL-AFOSR-JP-TR-2017-0032 Ultrafast Graphene Photonics and Optoelectronics Kuang-Hsiung Wu National Chiao Tung University Final Report 04/14/2017...DATES COVERED (From - To) 18 Apr 2013 to 17 Apr 2016 4. TITLE AND SUBTITLE Ultrafast Graphene Photonics and Optoelectronics 5a.  CONTRACT NUMBER 5b...Prescribed by ANSI Std. Z39.18 Final Report for AOARD Grant FA2386-13-1-4022 “Ultrafast Graphene Photonics and Optoelectronics” Date May 23th, 2016

Tracking ultrafast relaxation dynamics of furan by femtosecond photoelectron imaging

International Nuclear Information System (INIS)

Liu, Yuzhu; Knopp, Gregor; Qin, Chaochao; Gerber, Thomas

2015-01-01

Graphical abstract: - Highlights: • Relaxation dynamics of furan are tracked by femtosecond photoelectron imaging. • The mechanism for ultrafast formation of α-carbene and β-carbene is proposed. • Ultrafast internal conversion from S 2 to S 1 is observed. • The transient characteristics of the fragment ions are obtained. • Single-color multi-photon ionization dynamics at 800 nm are also studied. - Abstract: Ultrafast internal conversion dynamics of furan has been studied by femtosecond photoelectron imaging (PEI) coupled with photofragmentation (PF) spectroscopy. Photoelectron imaging of single-color multi-photon ionization and two-color pump–probe ionization are obtained and analyzed. Photoelectron bands are assigned to the related states. The time evolution of the photoelectron signal by pump–probe ionization can be well described by a biexponential decay: two rapid relaxation pathways with time constants of ∼15 fs and 85 (±11) fs. The rapid relaxation is ascribed to the ultrafast internal conversion (IC) from the S 2 state to the vibrationally hot S 1 state. The second relaxation process is attributed to the redistributions and depopulation of secondarily populated high vibronic S 1 state and the formation of α-carbene and β-carbene by H immigration. Additionally, the transient characteristics of the fragment ions are also measured and discussed as a complementary understanding

Multiobjective optimizations of a novel cryocooled dc gun based ultrafast electron diffraction beam line

Directory of Open Access Journals (Sweden)

Colwyn Gulliford

2016-09-01

Full Text Available We present the results of multiobjective genetic algorithm optimizations of a single-shot ultrafast electron diffraction beam line utilizing a 225 kV dc gun with a novel cryocooled photocathode system and buncher cavity. Optimizations of the transverse projected emittance as a function of bunch charge are presented and discussed in terms of the scaling laws derived in the charge saturation limit. Additionally, optimization of the transverse coherence length as a function of final rms bunch length at the sample location have been performed for three different sample radii: 50, 100, and 200  μm, for two final bunch charges: 10^{5} electrons (16 fC and 10^{6} electrons (160 fC. Example optimal solutions are analyzed, and the effects of disordered induced heating estimated. In particular, a relative coherence length of L_{c,x}/σ_{x}=0.27  nm/μm was obtained for a final bunch charge of 10^{5} electrons and final bunch length of σ_{t}≈100  fs. For a final charge of 10^{6} electrons the cryogun produces L_{c,x}/σ_{x}≈0.1  nm/μm for σ_{t}≈100–200  fs and σ_{x}≥50  μm. These results demonstrate the viability of using genetic algorithms in the design and operation of ultrafast electron diffraction beam lines.

Ultrafast population transfer in a Λ-configuration level system driven by few-cycle laser pulses

International Nuclear Information System (INIS)

Zhang Wen-Jing; Xie Xiao-Tao; Jin Lu-Ling; Bai Jin-Tao

2013-01-01

The feasibility of population transfer from a populated level via an intermediate state to the target level driven by few-cycle pulses is theoretically discussed. The processes of on- or far-resonance stimulated Raman scattering with sequential or simultaneous ultrashort pulses are investigated respectively. We find that the ultrashort pulses with about two optical cycles can be used to realize the population operation. This suggests that the population transfer can be completed in the femtosecond time scale. At the same time, our simulation shows that the signal of the carrier-envelope-phase-dependent effect can be enlarged due to quantum interference in some conditions. Our theoretic study may promote the research on the coherent control via ultrashort pulses in the related fields

Ultrafast Hierarchical OTDM/WDM Network

Directory of Open Access Journals (Sweden)

Hideyuki Sotobayashi

2003-12-01

Full Text Available Ultrafast hierarchical OTDM/WDM network is proposed for the future core-network. We review its enabling technologies: C- and L-wavelength-band generation, OTDM-WDM mutual multiplexing format conversions, and ultrafast OTDM wavelengthband conversions.

Wavelet analysis of molecular dynamics: Efficient extraction of time-frequency information in ultrafast optical processes

International Nuclear Information System (INIS)

Prior, Javier; Castro, Enrique; Chin, Alex W.; Almeida, Javier; Huelga, Susana F.; Plenio, Martin B.

2013-01-01

New experimental techniques based on nonlinear ultrafast spectroscopies have been developed over the last few years, and have been demonstrated to provide powerful probes of quantum dynamics in different types of molecular aggregates, including both natural and artificial light harvesting complexes. Fourier transform-based spectroscopies have been particularly successful, yet “complete” spectral information normally necessitates the loss of all information on the temporal sequence of events in a signal. This information though is particularly important in transient or multi-stage processes, in which the spectral decomposition of the data evolves in time. By going through several examples of ultrafast quantum dynamics, we demonstrate that the use of wavelets provide an efficient and accurate way to simultaneously acquire both temporal and frequency information about a signal, and argue that this greatly aids the elucidation and interpretation of physical process responsible for non-stationary spectroscopic features, such as those encountered in coherent excitonic energy transport

Understanding strong-field coherent control: Measuring single-atom versus collective dynamics

International Nuclear Information System (INIS)

Trallero-Herrero, Carlos; Weinacht, Thomas; Spanner, Michael

2006-01-01

We compare the results of two strong field coherent control experiments: one which optimizes multi-photon population transfer in atomic sodium (from the 3s to the 4s state, measured by spontaneous emission from the 3p-3s transition) with one that optimizes stimulated emission on the 3p-3s transition in an ensemble of sodium atoms. Both experiments make use of intense, shaped ultrafast laser pulses discovered by a Genetic Algorithm inside a learning control loop. Optimization leads to improvements in the spontaneous and stimulated emission yields of about 4 and 10 4 , respectively, over an unshaped pulse. We interpret these results by modeling both the single atom dynamics as well as the stimulated emission buildup through numerical integration of Schroedinger's and Maxwell's equations. Our interpretation leads to the conclusion that modest yields for controlling single quantum systems can lead to dramatic effects whenever an ensemble of such systems acts collectively following controlled impulsive excitation

Tracking ultrafast relaxation dynamics of furan by femtosecond photoelectron imaging

Energy Technology Data Exchange (ETDEWEB)

Liu, Yuzhu, E-mail: yuzhu.liu@gmail.com [School of Physics and Optoelectronic Engineering, Nanjing University of Information Science and Technology, Nanjing 210044 (China); Knopp, Gregor [Paul Scherrer Institute, Villigen 5232 (Switzerland); Qin, Chaochao [Department of Physics, Henan Normal University, Xinxiang 453007 (China); Gerber, Thomas [Paul Scherrer Institute, Villigen 5232 (Switzerland)

2015-01-13

Graphical abstract: - Highlights: • Relaxation dynamics of furan are tracked by femtosecond photoelectron imaging. • The mechanism for ultrafast formation of α-carbene and β-carbene is proposed. • Ultrafast internal conversion from S{sub 2} to S{sub 1} is observed. • The transient characteristics of the fragment ions are obtained. • Single-color multi-photon ionization dynamics at 800 nm are also studied. - Abstract: Ultrafast internal conversion dynamics of furan has been studied by femtosecond photoelectron imaging (PEI) coupled with photofragmentation (PF) spectroscopy. Photoelectron imaging of single-color multi-photon ionization and two-color pump–probe ionization are obtained and analyzed. Photoelectron bands are assigned to the related states. The time evolution of the photoelectron signal by pump–probe ionization can be well described by a biexponential decay: two rapid relaxation pathways with time constants of ∼15 fs and 85 (±11) fs. The rapid relaxation is ascribed to the ultrafast internal conversion (IC) from the S{sub 2} state to the vibrationally hot S{sub 1} state. The second relaxation process is attributed to the redistributions and depopulation of secondarily populated high vibronic S{sub 1} state and the formation of α-carbene and β-carbene by H immigration. Additionally, the transient characteristics of the fragment ions are also measured and discussed as a complementary understanding.

Avant-Garde Ultrafast Laser Writing

Directory of Open Access Journals (Sweden)

Kazansky P. G.

2013-11-01

Full Text Available Ultrafast laser processing of transparent materials reveals new phenomena. Reviewed, are recent demonstrations of 5D optical memory, vortex polarization and Airy beam converters employing self-assembled nanostructuring, ultrafast laser calligraphy and polarization writing control using pulses with tilted front.

Ultrafast nonlinear optics

CERN Document Server

Leburn, Christopher; Reid, Derryck

2013-01-01

The field of ultrafast nonlinear optics is broad and multidisciplinary, and encompasses areas concerned with both the generation and measurement of ultrashort pulses of light, as well as those concerned with the applications of such pulses. Ultrashort pulses are extreme events – both in terms of their durations, and also the high peak powers which their short durations can facilitate. These extreme properties make them powerful experiment tools. On one hand, their ultrashort durations facilitate the probing and manipulation of matter on incredibly short timescales. On the other, their ultrashort durations can facilitate high peak powers which can drive highly nonlinear light-matter interaction processes. Ultrafast Nonlinear Optics covers a complete range of topics, both applied and fundamental in nature, within the area of ultrafast nonlinear optics. Chapters 1 to 4 are concerned with the generation and measurement of ultrashort pulses. Chapters 5 to 7 are concerned with fundamental applications of ultrasho...

All optical quantum control of a spin-quantum state and ultrafast transduction into an electric current.

Science.gov (United States)

Müller, K; Kaldewey, T; Ripszam, R; Wildmann, J S; Bechtold, A; Bichler, M; Koblmüller, G; Abstreiter, G; Finley, J J

2013-01-01

The ability to control and exploit quantum coherence and entanglement drives research across many fields ranging from ultra-cold quantum gases to spin systems in condensed matter. Transcending different physical systems, optical approaches have proven themselves to be particularly powerful, since they profit from the established toolbox of quantum optical techniques, are state-selective, contact-less and can be extremely fast. Here, we demonstrate how a precisely timed sequence of monochromatic ultrafast (~ 2-5 ps) optical pulses, with a well defined polarisation can be used to prepare arbitrary superpositions of exciton spin states in a semiconductor quantum dot, achieve ultrafast control of the spin-wavefunction without an applied magnetic field and make high fidelity read-out the quantum state in an arbitrary basis simply by detecting a strong (~ 2-10 pA) electric current flowing in an external circuit. The results obtained show that the combined quantum state preparation, control and read-out can be performed with a near-unity (≥97%) fidelity.

Multidimensional Quantum Mechanical Modeling of Electron Transfer and Electronic Coherence in Plant Cryptochromes: The Role of Initial Bath Conditions.

Science.gov (United States)

Mendive-Tapia, David; Mangaud, Etienne; Firmino, Thiago; de la Lande, Aurélien; Desouter-Lecomte, Michèle; Meyer, Hans-Dieter; Gatti, Fabien

2018-01-11

A multidimensional quantum mechanical protocol is used to describe the photoinduced electron transfer and electronic coherence in plant cryptochromes without any semiempirical, e.g., experimentally obtained, parameters. Starting from a two-level spin-boson Hamiltonian we look at the effect that the initial photoinduced nuclear bath distribution has on an intermediate step of this biological electron transfer cascade for two idealized cases. The first assumes a slow equilibration of the nuclear bath with respect to the previous electron transfer step that leads to an ultrafast decay with little temperature dependence; while the second assumes a prior fast bath equilibration on the donor potential energy surface leading to a much slower decay, which contrarily displays a high temperature dependence and a better agreement with previous theoretical and experimental results. Beyond Marcus and semiclassical pictures these results unravel the strong impact that the presence or not of equilibrium initial conditions has on the electronic population and coherence dynamics at the quantum dynamics level in this and conceivably in other biological electron transfer cascades.

Observing Structure and Motion in Molecules with Ultrafast Strong Field and Short Wavelength Laser Radiation

Energy Technology Data Exchange (ETDEWEB)

Bucksbaum, Philip H

2011-04-13

The term "molecular movie" has come to describe efforts to track and record Angstrom-scale coherent atomic and electronic motion in a molecule. The relevant time scales for this range cover several orders of magnitude, from sub-femtosecond motion associated with electron-electron correlations, to 100-fs internal vibrations, to multi-picosecond motion associated with the dispersion and quantum revivals of molecular reorientation. Conventional methods of cinematography do not work well in this ultrafast and ultrasmall regime, but stroboscopic "pump and probe" techniques can reveal this motion with high fidelity. This talk will describe some of the methods and recent progress in exciting and controlling this motion, using both laboratory lasers and the SLAC Linac Coherent Light Source x-ray free electron laser, and will further try to relate the date to the goal of molecular movies.

Phase-coherence transitions and communication in the gamma range between delay-coupled neuronal populations.

Directory of Open Access Journals (Sweden)

Alessandro Barardi

2014-07-01

Full Text Available Synchronization between neuronal populations plays an important role in information transmission between brain areas. In particular, collective oscillations emerging from the synchronized activity of thousands of neurons can increase the functional connectivity between neural assemblies by coherently coordinating their phases. This synchrony of neuronal activity can take place within a cortical patch or between different cortical regions. While short-range interactions between neurons involve just a few milliseconds, communication through long-range projections between different regions could take up to tens of milliseconds. How these heterogeneous transmission delays affect communication between neuronal populations is not well known. To address this question, we have studied the dynamics of two bidirectionally delayed-coupled neuronal populations using conductance-based spiking models, examining how different synaptic delays give rise to in-phase/anti-phase transitions at particular frequencies within the gamma range, and how this behavior is related to the phase coherence between the two populations at different frequencies. We have used spectral analysis and information theory to quantify the information exchanged between the two networks. For different transmission delays between the two coupled populations, we analyze how the local field potential and multi-unit activity calculated from one population convey information in response to a set of external inputs applied to the other population. The results confirm that zero-lag synchronization maximizes information transmission, although out-of-phase synchronization allows for efficient communication provided the coupling delay, the phase lag between the populations, and the frequency of the oscillations are properly matched.

Coherent structural trapping through wave packet dispersion during photoinduced spin state switching

DEFF Research Database (Denmark)

Lemke, Henrik T.; Kjær, Kasper Skov; Hartsock, Robert

2017-01-01

The description of ultrafast nonadiabatic chemical dynamics during molecular photo-transformations remains challenging because electronic and nuclear configurations impact each other and cannot be treated independently. Here we gain experimental insights, beyond the Born-Oppenheimer approximation...... is distinguished from the structural trapping dynamics, which launches a coherent oscillating wave packet (265 fs period), clearly identified as molecular breathing. Throughout the structural trapping, the dispersion of the wave packet along the reaction coordinate reveals details of intramolecular vibronic...

Extreme sub-wavelength atom localization via coherent population trapping

OpenAIRE

Agarwal, Girish S.; Kapale, Kishore T.

2005-01-01

We demonstrate an atom localization scheme based on monitoring of the atomic coherences. We consider atomic transitions in a Lambda configuration where the control field is a standing wave field. The probe field and the control field produce coherence between the two ground states. We show that this coherence has the same fringe pattern as produced by a Fabry-Perot interferometer and thus measurement of the atomic coherence would localize the atom. Interestingly enough the role of the cavity ...

Harmonic Quantum Coherence of Multiple Excitons in PbS/CdS Core-Shell Nanocrystals

Science.gov (United States)

Tahara, Hirokazu; Sakamoto, Masanori; Teranishi, Toshiharu; Kanemitsu, Yoshihiko

2017-12-01

The generation and recombination dynamics of multiple excitons in nanocrystals (NCs) have attracted much attention from the viewpoints of fundamental physics and device applications. However, the quantum coherence of multiple exciton states in NCs still remains unclear due to a lack of experimental support. Here, we report the first observation of harmonic dipole oscillations in PbS/CdS core-shell NCs using a phase-locked interference detection method for transient absorption. From the ultrafast coherent dynamics and excitation-photon-fluence dependence of the oscillations, we found that multiple excitons cause the harmonic dipole oscillations with ω , 2 ω , and 3 ω oscillations, even though the excitation pulse energy is set to the exciton resonance frequency, ω . This observation is closely related to the quantum coherence of multiple exciton states in NCs, providing important insights into multiple exciton generation mechanisms.

Ultrafast THz saturable absorption in doped semiconductors at room temperature

DEFF Research Database (Denmark)

Turchinovich, Dmitry; Hoffmann, M. V.

2011-01-01

Ultrafast Phenomena XVII presents the latest advances in ultrafast science, including both ultrafast optical technology and the study of ultrafast phenomena. It covers picosecond, femtosecond and attosecond processes relevant to applications in physics, chemistry, biology, and engineering. Ultraf...

From Computational Photobiology to the Design of Vibrationally Coherent Molecular Devices and Motors

Science.gov (United States)

Olivucci, Massimo

2014-03-01

In the past multi-configurational quantum chemical computations coupled with molecular mechanics force fields have been employed to investigate spectroscopic, thermal and photochemical properties of visual pigments. Here we show how the same computational technology can nowadays be used to design, characterize and ultimately, prepare light-driven molecular switches which mimics the photophysics of the visual pigment bovine rhodopsin (Rh). When embedded in the protein cavity the chromophore of Rh undergoes an ultrafast and coherent photoisomerization. In order to design a synthetic chromophore displaying similar properties in common solvents, we recently focused on indanylidene-pyrroline (NAIP) systems. We found that these systems display light-induced ground state coherent vibrational motion similar to the one detected in Rh. Semi-classical trajectories provide a mechanistic description of the structural changes associated to the observed coherent motion which is shown to be ultimately due to periodic changes in the π-conjugation.

Coherent Phonon Dynamics in Short-Period InAs/GaSb Superlattices

OpenAIRE

Noe, G. T.; Haugan, H. J.; Brown, G. J.; Sanders, G. D.; Stanton, C. J.; Kono, J.

2011-01-01

We have performed ultrafast pump-probe spectroscopy studies on a series of InAs/GaSb-based short-period superlattice (SL) samples with periods ranging from 46 \\AA to 71 \\AA. We observe two types of oscillations in the differential reflectivity with fast ($\\sim$ 1- 2 ps) and slow ($\\sim$ 24 ps) periods. The period of the fast oscillations changes with the SL period and can be explained as coherent acoustic phonons generated from carriers photoexcited within the SL. This mode provides an accura...

Quantum coherent π-electron rotations in a non-planar chiral molecule induced by using a linearly polarized UV laser pulse

Science.gov (United States)

Mineo, Hirobumi; Fujimura, Yuichi

2015-06-01

We propose an ultrafast quantum switching method of π-electron rotations, which are switched among four rotational patterns in a nonplanar chiral aromatic molecule (P)-2,2’- biphenol and perform the sequential switching among four rotational patterns which are performed by the overlapped pump-dump laser pulses. Coherent π-electron dynamics are generated by applying the linearly polarized UV pulse laser to create a pair of coherent quasidegenerated excited states. We also plot the time-dependent π-electron ring current, and discussed ring current transfer between two aromatic rings.

Ultrafast dynamic ellipsometry and spectroscopy of laser shocked materials

Energy Technology Data Exchange (ETDEWEB)

Mcgrane, Shawn David [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Bolme, Cindy B [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Whitley, Von H [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Moore, David S [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

2010-01-01

Shock waves create extreme states of matter with very high pressures, temperatures, and volumetric compressions, at an exceedingly rapid rate of change. We review how to use a beamsplitter and a note card to turn a typical chirp pulse amplified femtosecond laser system into an ultrafast shock dynamics machine. Open scientific questions that can be addressed with such an apparatus are described. We report on the development of several single shot time resolved diagnostics needed to answer these questions. These single shot diagnostics are expected to be broadly applicable to other types of laser ablation experiments. Experimental results measured from shocked material dynamics of several systems are detailed. Finally, we report on progress towards using transient absorption as a measure of electronic excitation and coherent Raman as a picosecond probe of temperature in shock compressed condensed matter.

Theory of coherent resonance energy transfer

International Nuclear Information System (INIS)

Jang, Seogjoo; Cheng, Y.-C.; Reichman, David R.; Eaves, Joel D.

2008-01-01

A theory of coherent resonance energy transfer is developed combining the polaron transformation and a time-local quantum master equation formulation, which is valid for arbitrary spectral densities including common modes. The theory contains inhomogeneous terms accounting for nonequilibrium initial preparation effects and elucidates how quantum coherence and nonequilibrium effects manifest themselves in the coherent energy transfer dynamics beyond the weak resonance coupling limit of the Foerster and Dexter (FD) theory. Numerical tests show that quantum coherence can cause significant changes in steady state donor/acceptor populations from those predicted by the FD theory and illustrate delicate cooperation of nonequilibrium and quantum coherence effects on the transient population dynamics.

Probing Photoinduced Structural Phase Transitions by Fast or Ultra-Fast Time-Resolved X-Ray Diffraction

Science.gov (United States)

Cailleau, Hervé Collet, Eric; Buron-Le Cointe, Marylise; Lemée-Cailleau, Marie-Hélène Koshihara, Shin-Ya

molecules transform in an independent way each other. Actually the photoinduced phase transition with the establishment of the new electronic and structural oscopic order is preceded by precursor co-operative phenomena due to the formation of nano-scale correlated objects. These are the counterpart of pre-transitional fluctuations at thermal equilibrium which take place above the transition temperature (short range order preceding long range one). Moreover ultra-fast X-ray scattering will play a central role within the fascinating field of manipulating coherence, for instance to directly observe coherent atomic motions induced by a light pulse, such as optical phonons. In the first part of this contribution we present what experimental features are accessible by X-ray scattering to describe the physical picture for a photoinduced structural phase transition. The second part shows how a time-resolved X-ray scattering experiment can be performed with regards to the different pulsed X-ray sources. The first time-resolved X-ray diffraction experiments on photoinduced phase transitions are described and discussed in the third part. Finally some challenges for future are briefly indicated in the conclusion.

Ultrafast molecular dynamics illuminated with synchrotron radiation

International Nuclear Information System (INIS)

Bozek, John D.; Miron, Catalin

2015-01-01

Highlights: • Ultrafast molecular dynamics probed with synchrotron radiation. • Core-excitation as probe of ultrafast dynamics through core-hole lifetime. • Review of experimental and theoretical methods in ultrafast dynamics using core-level excitation. - Abstract: Synchrotron radiation is a powerful tool for studying molecular dynamics in small molecules in spite of the absence of natural matching between the X-ray pulse duration and the time scale of nuclear motion. Promoting core level electrons to unoccupied molecular orbitals simultaneously initiates two ultrafast processes, nuclear dynamics on the potential energy surfaces of the highly excited neutral intermediate state of the molecule on the one hand and an ultrafast electronic decay of the intermediate excited state to a cationic final state, characterized by a core hole lifetime. The similar time scales of these processes enable core excited pump-probe-type experiments to be performed with long duration X-ray pulses from a synchrotron source. Recent results obtained at the PLIEADES beamline concerning ultrafast dissociation of core excited states and molecular potential energy curve mapping facilitated by changes in the geometry of the short-lived intermediate core excited state are reviewed. High brightness X-ray beams combined with state-of-the art electron and ion-electron coincidence spectrometers and highly sophisticated theoretical methods are required to conduct these experiments and to achieve a full understanding of the experimental results.

Ultrafast laser based coherent control methods for explosives detection

Energy Technology Data Exchange (ETDEWEB)

Moore, David Steven [Los Alamos National Laboratory

2010-12-06

The detection of explosives is a notoriously difficult problem, especially at stand-off, due to their (generally) low vapor pressure, environmental and matrix interferences, and packaging. We are exploring Optimal Dynamic Detection of Explosives (ODD-Ex), which exploits the best capabilities of recent advances in laser technology and recent discoveries in optimal shaping of laser pulses for control of molecular processes to significantly enhance the standoff detection of explosives. The core of the ODD-Ex technique is the introduction of optimally shaped laser pulses to simultaneously enhance sensitivity to explosives signatures while dramatically improving specificity, particularly against matrix materials and background interferences. These goals are being addressed by operating in an optimal non-linear fashion, typically with a single shaped laser pulse inherently containing within it coherently locked control and probe subpulses. Recent results will be presented.

New photonic devices for ultrafast pulse processing operating on the basis of the diffraction-dispersion analogy

Energy Technology Data Exchange (ETDEWEB)

Torres-Company, Victor; Minguez-Vega, Gladys; Climent, Vicent; Lands, Jesus [GROC-UJI, Departament de Fisica, Universitat Jaume I, 12080 Castello (Spain); Andres, Pedro [Departament d' Optica, Universitat de Valencia, 46100 Burjassot (Spain)], E-mail: lancis@fca.uji.es

2008-11-01

The space-time analogy is a well-known topic within wave optics that brings together some results from beam diffraction and pulse dispersion. On the above basis, and taking as starting point some classical concepts in Optics, several photonic devices have been proposed during the last few years with application in rapidly evolving fields such as ultrafast (femtosecond) optics or RF and microwave signal processing. In this contribution, we briefly review the above ideas with particular emphasis in the generation of trains of ultrafast pulses from periodic modulation of the phase of a CW laser source. This is the temporal analogue of Fresnel diffraction by a pure phase grating. Finally, we extend the analogy to the partially coherent case, what enables us to design an original technique for wavelength-to-time mapping of the spectrum of a temporally stationary source. Results of laboratory experiments concerning the generation of user-defined radio-frequency waveforms and filtering of microwave signals will be shown. The devices are operated with low-cost incoherent sources.

High-speed optical coherence tomography by circular interferometric ranging

Science.gov (United States)

Siddiqui, Meena; Nam, Ahhyun S.; Tozburun, Serhat; Lippok, Norman; Blatter, Cedric; Vakoc, Benjamin J.

2018-02-01

Existing three-dimensional optical imaging methods excel in controlled environments, but are difficult to deploy over large, irregular and dynamic fields. This means that they can be ill-suited for use in areas such as material inspection and medicine. To better address these applications, we developed methods in optical coherence tomography to efficiently interrogate sparse scattering fields, that is, those in which most locations (voxels) do not generate meaningful signal. Frequency comb sources are used to superimpose reflected signals from equispaced locations through optical subsampling. This results in circular ranging, and reduces the number of measurements required to interrogate large volumetric fields. As a result, signal acquisition barriers that have limited speed and field in optical coherence tomography are avoided. With a new ultrafast, time-stretched frequency comb laser design operating with 7.6 MHz to 18.9 MHz repetition rates, we achieved imaging of multi-cm3 fields at up to 7.5 volumes per second.

Characterization of Cs vapor cell coated with octadecyltrichlorosilane using coherent population trapping spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Hafiz, Moustafa Abdel; Maurice, Vincent; Chutani, Ravinder; Passilly, Nicolas; Gorecki, Christophe; Boudot, Rodolphe [FEMTO-ST, CNRS, UFC, 26 Chemin de l' Epitaphe, 25030 Besançon Cedex (France); Guérandel, Stéphane; Clercq, Emeric de [LNE-SYRTE, Observatoire de Paris, CNRS, UPMC, 61 avenue de l' Observatoire, 75014 Paris (France)

2015-05-14

We report the realization and characterization using coherent population trapping (CPT) spectroscopy of an octadecyltrichlorosilane (OTS)-coated centimeter-scale Cs vapor cell. The dual-structure of the resonance lineshape, with presence of a narrow structure line at the top of a Doppler-broadened structure, is clearly observed. The linewidth of the narrow resonance is compared to the linewidth of an evacuated Cs cell and of a buffer gas Cs cell of similar size. The Cs-OTS adsorption energy is measured to be (0.42 ± 0.03) eV, leading to a clock frequency shift rate of 2.7 × 10{sup −9}/K in fractional unit. A hyperfine population lifetime, T{sub 1}, and a microwave coherence lifetime, T{sub 2}, of 1.6 and 0.5 ms are reported, corresponding to about 37 and 12 useful bounces, respectively. Atomic-motion induced Ramsey narrowing of dark resonances is observed in Cs-OTS cells by reducing the optical beam diameter. Ramsey CPT fringes are detected using a pulsed CPT interrogation scheme. Potential applications of the Cs-OTS cell to the development of a vapor cell atomic clock are discussed.

Characterization of Cs vapor cell coated with octadecyltrichlorosilane using coherent population trapping spectroscopy

International Nuclear Information System (INIS)

Hafiz, Moustafa Abdel; Maurice, Vincent; Chutani, Ravinder; Passilly, Nicolas; Gorecki, Christophe; Boudot, Rodolphe; Guérandel, Stéphane; Clercq, Emeric de

2015-01-01

We report the realization and characterization using coherent population trapping (CPT) spectroscopy of an octadecyltrichlorosilane (OTS)-coated centimeter-scale Cs vapor cell. The dual-structure of the resonance lineshape, with presence of a narrow structure line at the top of a Doppler-broadened structure, is clearly observed. The linewidth of the narrow resonance is compared to the linewidth of an evacuated Cs cell and of a buffer gas Cs cell of similar size. The Cs-OTS adsorption energy is measured to be (0.42 ± 0.03) eV, leading to a clock frequency shift rate of 2.7 × 10 −9 /K in fractional unit. A hyperfine population lifetime, T 1 , and a microwave coherence lifetime, T 2 , of 1.6 and 0.5 ms are reported, corresponding to about 37 and 12 useful bounces, respectively. Atomic-motion induced Ramsey narrowing of dark resonances is observed in Cs-OTS cells by reducing the optical beam diameter. Ramsey CPT fringes are detected using a pulsed CPT interrogation scheme. Potential applications of the Cs-OTS cell to the development of a vapor cell atomic clock are discussed

Uncondensed atoms in the regime of velocity-selective coherent population trapping

International Nuclear Information System (INIS)

Il’ichov, L. V.; Tomilin, V. A.

2016-01-01

We consider the model of a Bose condensate in the regime of velocity-selective coherent population trapping. As a result of interaction between particles, some fraction of atoms is outside the condensate, remaining in the coherent trapping state. These atoms are involved in brief events of intense interaction with external resonant electromagnetic fields. Intense induced and spontaneous transitions are accompanied by the exchange of momenta between atoms and radiation, which is manifested as migration of atoms in the velocity space. The rate of such migration is calculated. A nonlinear kinetic equation for the many-particle statistical operator for uncondensed atoms is derived under the assumption that correlations of atoms with different momenta are insignificant. The structure of its steady-state solution leads to certain conclusions about the above-mentioned migration pattern taking the Bose statistics into consideration. With allowance for statistical effects, we derive nonlinear integral equations for frequencies controlling the migration. The results of numerical solution of these equations are represented in the weak interatomic interaction approximation.

Coherent population trapping magnetometer by differential detecting magneto–optic rotation effect

International Nuclear Information System (INIS)

Zhang Fan; Tian Yuan; Zhang Yi; Gu Si-Hong

2016-01-01

A pocket coherent population trapping (CPT) atomic magnetometer scheme that uses a vertical cavity surface emitting laser as a light source is proposed and experimentally investigated. Using the differential detecting magneto–optic rotation effect, a CPT spectrum with the background canceled and a high signal-to-noise ratio is obtained. The experimental results reveal that the sensitivity of the proposed scheme can be improved by half an order, and the ability to detect weak magnetic fields is extended one-fold. Therefore, the proposed scheme is suited to realize a pocket-size CPT magnetometer. (paper)

Coherent population transfer in multilevel systems with magnetic sublevels. II. Algebraic analysis

International Nuclear Information System (INIS)

Martin, J.; Shore, B.W.; Bergmann, K.

1995-01-01

We extend previous theoretical work on coherent population transfer by stimulated Raman adiabatic passage for states involving nonzero angular momentum. The pump and Stokes fields are either copropagating or counterpropagating with the corresponding linearly polarized electric-field vectors lying in a common plane with the magnetic-field direction. Zeeman splitting lifts the magnetic sublevel degeneracy. We present an algebraic analysis of dressed-state properties to explain the behavior noted in numerical studies. In particular, we discuss conditions which are likely to lead to a failure of complete population transfer. The applied strategy, based on simple methods of linear algebra, will also be successful for other types of discrete multilevel systems, provided the rotating-wave and adiabatic approximation are valid

Coherent population transfer in multilevel systems with magnetic sublevels. II. Algebraic analysis

Science.gov (United States)

Martin, J.; Shore, B. W.; Bergmann, K.

1995-07-01

We extend previous theoretical work on coherent population transfer by stimulated Raman adiabatic passage for states involving nonzero angular momentum. The pump and Stokes fields are either copropagating or counterpropagating with the corresponding linearly polarized electric-field vectors lying in a common plane with the magnetic-field direction. Zeeman splitting lifts the magnetic sublevel degeneracy. We present an algebraic analysis of dressed-state properties to explain the behavior noted in numerical studies. In particular, we discuss conditions which are likely to lead to a failure of complete population transfer. The applied strategy, based on simple methods of linear algebra, will also be successful for other types of discrete multilevel systems, provided the rotating-wave and adiabatic approximation are valid.

Optical pulse shaping approaches to coherent control

International Nuclear Information System (INIS)

Goswami, Debabrata

2003-01-01

The last part of the twentieth century has experienced a huge resurge of activity in the field of coherent light-matter interaction, more so in attempting to exert control over such interactions. Birth of coherent control was originally spurred by the theoretical understanding of the quantum interferences that lead to energy randomization and experimental developments in ultrafast laser spectroscopy. The theoretical predictions on control of reaction channels or energy randomization processes are still more dramatic than the experimental demonstrations, though this gap between the two is consistently reducing over the recent years with realistic theoretical models and technological developments. Experimental demonstrations of arbitrary optical pulse shaping have made some of the previously impracticable theoretical predictions possible to implement. Starting with the simple laser modulation schemes to provide proof-of-the-principle demonstrations, feedback loop pulse shaping systems have been developed that can actively manipulate some atomic and molecular processes. This tremendous experimental boost of optical pulse shaping developments has prospects and implications into many more new directions, such as quantum computing and terabit/sec data communications. This review captures certain aspects and impacts of optical pulse shaping into the fast developing areas of coherent control and other related fields. Currently available reviews focus on one or the other detailed aspects of coherent control, and the reader will be referred to such details as and when necessary for issues that are dealt in brief here. We will focus on the current issues including control of intramolecular dynamics and make connections to the future concepts, such as, quantum computation, biomedical applications, etc

State-Resolved Metal Nanoparticle Dynamics Viewed through the Combined Lenses of Ultrafast and Magneto-optical Spectroscopies.

Science.gov (United States)

Zhao, Tian; Herbert, Patrick J; Zheng, Hongjun; Knappenberger, Kenneth L

2018-05-08

Electronic carrier dynamics play pivotal roles in the functional properties of nanomaterials. For colloidal metals, the mechanisms and influences of these dynamics are structure dependent. The coherent carrier dynamics of collective plasmon modes for nanoparticles (approximately 2 nm and larger) determine optical amplification factors that are important to applied spectroscopy techniques. In the nanocluster domain (sub-2 nm), carrier coupling to vibrational modes affects photoluminescence yields. The performance of photocatalytic materials featuring both nanoparticles and nanoclusters also depends on the relaxation dynamics of nonequilibrium charge carriers. The challenges for developing comprehensive descriptions of carrier dynamics spanning both domains are multifold. Plasmon coherences are short-lived, persisting for only tens of femtoseconds. Nanoclusters exhibit discrete carrier dynamics that can persist for microseconds in some cases. On this time scale, many state-dependent processes, including vibrational relaxation, charge transfer, and spin conversion, affect carrier dynamics in ways that are nonscalable but, rather, structure specific. Hence, state-resolved spectroscopy methods are needed for understanding carrier dynamics in the nanocluster domain. Based on these considerations, a detailed understanding of structure-dependent carrier dynamics across length scales requires an appropriate combination of spectroscopic methods. Plasmon mode-specific dynamics can be obtained through ultrafast correlated light and electron microscopy (UCLEM), which pairs interferometric nonlinear optical (INLO) with electron imaging methods. INLO yields nanostructure spectral resonance responses, which capture the system's homogeneous line width and coherence dynamics. State-resolved nanocluster dynamics can be obtained by pairing ultrafast with magnetic-optical spectroscopy methods. In particular, variable-temperature variable-field (VTVH) spectroscopies allow quantification

Communication: Coherences observed in vivo in photosynthetic bacteria using two-dimensional electronic spectroscopy

International Nuclear Information System (INIS)

Dahlberg, Peter D.; Norris, Graham J.; Wang, Cheng; Viswanathan, Subha; Singh, Ved P.; Engel, Gregory S.

2015-01-01

Energy transfer through large disordered antenna networks in photosynthetic organisms can occur with a quantum efficiency of nearly 100%. This energy transfer is facilitated by the electronic structure of the photosynthetic antennae as well as interactions between electronic states and the surrounding environment. Coherences in time-domain spectroscopy provide a fine probe of how a system interacts with its surroundings. In two-dimensional electronic spectroscopy, coherences can appear on both the ground and excited state surfaces revealing detailed information regarding electronic structure, system-bath coupling, energy transfer, and energetic coupling in complex chemical systems. Numerous studies have revealed coherences in isolated photosynthetic pigment-protein complexes, but these coherences have not been observed in vivo due to the small amplitude of these signals and the intense scatter from whole cells. Here, we present data acquired using ultrafast video-acquisition gradient-assisted photon echo spectroscopy to observe quantum beating signals from coherences in vivo. Experiments were conducted on isolated light harvesting complex II (LH2) from Rhodobacter sphaeroides, whole cells of R. sphaeroides, and whole cells of R. sphaeroides grown in 30% deuterated media. A vibronic coherence was observed following laser excitation at ambient temperature between the B850 and the B850 ∗ states of LH2 in each of the 3 samples with a lifetime of ∼40-60 fs

Communication: Coherences observed in vivo in photosynthetic bacteria using two-dimensional electronic spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Dahlberg, Peter D. [Graduate Program in the Biophysical Sciences, Institute for Biophysical Dynamics, and The James Franck Institute, The University of Chicago, Chicago, Illinois 60637 (United States); Norris, Graham J.; Wang, Cheng; Viswanathan, Subha; Singh, Ved P.; Engel, Gregory S., E-mail: gsengel@uchicago.edu [Department of Chemistry, Institute for Biophysical Dynamics, and The James Franck Institute, The University of Chicago, Chicago, Illinois 60637 (United States)

2015-09-14

Energy transfer through large disordered antenna networks in photosynthetic organisms can occur with a quantum efficiency of nearly 100%. This energy transfer is facilitated by the electronic structure of the photosynthetic antennae as well as interactions between electronic states and the surrounding environment. Coherences in time-domain spectroscopy provide a fine probe of how a system interacts with its surroundings. In two-dimensional electronic spectroscopy, coherences can appear on both the ground and excited state surfaces revealing detailed information regarding electronic structure, system-bath coupling, energy transfer, and energetic coupling in complex chemical systems. Numerous studies have revealed coherences in isolated photosynthetic pigment-protein complexes, but these coherences have not been observed in vivo due to the small amplitude of these signals and the intense scatter from whole cells. Here, we present data acquired using ultrafast video-acquisition gradient-assisted photon echo spectroscopy to observe quantum beating signals from coherences in vivo. Experiments were conducted on isolated light harvesting complex II (LH2) from Rhodobacter sphaeroides, whole cells of R. sphaeroides, and whole cells of R. sphaeroides grown in 30% deuterated media. A vibronic coherence was observed following laser excitation at ambient temperature between the B850 and the B850{sup ∗} states of LH2 in each of the 3 samples with a lifetime of ∼40-60 fs.

A passion for precision - from the ultrafast to the ultraslow

International Nuclear Information System (INIS)

Haensch, T.W.

2005-01-01

Full text: Femtosecond laser optical frequency comb synthesizers have become the established tool for measuring the frequency of light with extreme precision. By permitting phase-coherent comparisons of optical and microwave frequencies, they can serve as the clockwork for ultraprecise optical atomic clocks. Applications to laser spectroscopy of atomic hydrogen permit stringent tests of basic laws of quantum physics. Such experiments can yield accurate values of fundamental constants, and they may reveal slow changes of fundamental constants with the evolution of the universe. Laser frequency comb techniques can also control the light phase of femtosecond laser pulses, thus advancing the frontier of ultrafast science from the femtosecond to the attosecond regime. High harmonic generation with intense femtosecond pulses may extend frequency comb techniques to the extreme ultraviolet and soft x-ray regime, conquering new territory for precision laser spectroscopy and fundamental measurements. (author)

Control of ultrafast pulses in a hydrogen-filled hollow-core photonic-crystal fiber by Raman coherence

Science.gov (United States)

Belli, F.; Abdolvand, A.; Travers, J. C.; Russell, P. St. J.

2018-01-01

We present the results of an experimental and numerical investigation into temporally nonlocal coherent interactions between ultrashort pulses, mediated by Raman coherence, in a gas-filled kagome-style hollow-core photonic-crystal fiber. A pump pulse first sets up the Raman coherence, creating a refractive index spatiotemporal grating in the gas that travels at the group velocity of the pump pulse. Varying the arrival time of a second, probe, pulse allows a high degree of control over its evolution as it propagates along the fiber through the grating. Of particular interest are soliton-driven effects such as self-compression and dispersive wave (DW) emission. In the experiments reported, a DW is emitted at ˜300 nm and exhibits a wiggling effect, with its central frequency oscillating periodically with pump-probe delay. The results demonstrate that a strong Raman coherence, created in a broadband guiding gas-filled kagome photonic-crystal fiber, can be used to control the nonlinear dynamics of ultrashort probe pulses, even in difficult-to-access spectral regions such as the deep and vacuum ultraviolet.

Beam properties of fully optimized, table-top, coherent source at 30 nm

Czech Academy of Sciences Publication Activity Database

Jakubczak, Krzysztof; Mocek, Tomáš; Rus, Bedřich; Polan, Jiří; Hřebíček, Jan; Sawicka, Magdalena; Sikocinski, Pawel; Sobota, Jaroslav; Fořt, Tomáš; Pína, L.

2011-01-01

Roč. 19, č. 2 (2011), s. 169-175 ISSN 1230-3402 R&D Projects: GA AV ČR KAN300100702; GA MŠk(CZ) LC528; GA ČR GC202/07/J008 Grant - others:AV ČR(CZ) M100100911 Institutional research plan: CEZ:AV0Z10100523; CEZ:AV0Z20650511 Keywords : laser applications * high−order harmonic generation * coherent extreme ultraviolet radiation * ultrafast optics Subject RIV: BH - Optics, Masers, Lasers Impact factor: 0.966, year: 2011 http://www.springerlink.com/content/y0057067wvw03234/

Observation of antiphase coherent phonons in the warped Dirac cone of Bi2Te3

Science.gov (United States)

Golias, E.; Sánchez-Barriga, J.

2016-10-01

In this Rapid Communication we investigate the coupling between excited electrons and phonons in the highly anisotropic electronic structure of the prototypical topological insulator Bi2Te3 . Using time- and angle-resolved photoemission spectroscopy we are able to identify the emergence and ultrafast temporal evolution of the longitudinal-optical A1 g coherent-phonon mode in Bi2Te3 . We observe an antiphase behavior in the onset of the coherent-phonon oscillations between the Γ K ¯ and the Γ M ¯ high-symmetry directions that is consistent with warping. The qualitative agreement between our density-functional theory calculations and the experimental results reveals the critical role of the anisotropic coupling between Dirac fermions and phonon modes in the topological insulator Bi2Te3 .

High peak power THz source for ultrafast electron diffraction

Directory of Open Access Journals (Sweden)

Shengguang Liu

2018-01-01

Full Text Available Terahertz (THz science and technology have already become the research highlight at present. In this paper, we put forward a device setup to carry out ultrafast fundamental research. A photocathode RF gun generates electron bunches with ∼MeV energy, ∼ps bunch width and about 25pC charge. The electron bunches inject the designed wiggler, the coherent radiation at THz spectrum emits from these bunches and increases rapidly until the saturation at ∼MW within a short wiggler. THz pulses can be used as pump to stimulate an ultra-short excitation in some kind of sample. Those electron bunches out of wiggler can be handled into bunches with ∼1pC change, small beam spot and energy spread to be probe. Because the pump and probe comes from the same electron source, synchronization between pump and probe is inherent. The whole facility can be compacted on a tabletop.

Phase-controlled all-optical switching based on coherent population oscillation in a two-level system

International Nuclear Information System (INIS)

Liao, Ping; Yu, Song; Luo, Bin; Shen, Jing; Gu, Wanyi; Guo, Hong

2011-01-01

We theoretically propose a scheme of phase-controlled all-optical switching due to the effect of degenerate four-wave mixing (FWM) and coherent population oscillation (CPO) in a two-level system driven by a strong coupling field and two weak symmetrically detuned fields. The results show that the phase of the FWM field can be utilized to switch between constructive and destructive interference, which can lead to the transmission or attenuation of the probe field and thus switch the field on or off. We also find the intensity of the coupling field and the propagation distance have great influence on the performance of the switching. In our scheme, due to the quick response in semiconductor systems, a fast all-optical switching can be realized at low light level. -- Highlights: ► We study a new all-optical switching based on coherent population oscillation. ► The phase of the FWM field can be utilized to switch the probe field on or off. ► A fast and low-light-level switching can be realized in semiconductors.

Study on the coherence degree of magnetization reversal in Permalloy single-domain nano-ellipses

Energy Technology Data Exchange (ETDEWEB)

Júnior, D.S. Vieira [Departamento Acadêmico de Matemática, Física, e Estatística, Instituto Federal de Educação, Ciência e Tecnologia do Sudeste de Minas Gerais – Campus Rio Pomba, Rio Pomba, Minas Gerais 36180-000 (Brazil); Leonel, S.A. [Departamento de Física, Laboratório de Simulação Computacional, Universidade Federal de Juiz de Fora, Juiz de Fora, Minas Gerais 36036-330 (Brazil); Toscano, D., E-mail: danilotoscano@fisica.ufjf.br [Departamento de Física, Laboratório de Simulação Computacional, Universidade Federal de Juiz de Fora, Juiz de Fora, Minas Gerais 36036-330 (Brazil); Sato, F.; Coura, P.Z.; Dias, R.A. [Departamento de Física, Laboratório de Simulação Computacional, Universidade Federal de Juiz de Fora, Juiz de Fora, Minas Gerais 36036-330 (Brazil)

2017-03-15

Numerical simulations have been performed to study the magnetization reversal in Permalloy nano-ellipses, under combined in-plane magnetic fields along the longitudinal and the transverse directions. We have considered nano-ellipses with two different aspect ratios and five thicknesses: 220×80×t nm{sup 3} and 70×50×t nm{sup 3}, where t ranging from 5 to 25 nm in steps of 5 nm. We found that the mechanism of magnetization reversal is not only dependent on the parameters of the magnetic field pulse but also related to the ellipse dimensions. It is known that the reversal time is related to the mechanism behind the magnetization reversal. In particular, ultrafast magnetization reversals occur by coherent rotation, when applying a field oriented mainly perpendicular to the initial magnetization. In order to evaluate the degree of coherence of the magnetization reversal we have introduced a quantity called “coherence index”. Besides complementing the previous studies by including the effect of the thickness on the magnetization reversal, our results indicate that it is possible to obtain magnetization reversals with high degree of coherence in small nano-ellipses by adjusting the geometric factors of the ellipse and the parameters of the magnetic field pulse simultaneously. - Highlights: • Magnetization reversals in single-domain nano-ellipses were investigated. • A parameter to evaluate the degree of coherence of the magnetization reversal was proposed. • A higher coherence index indicates a complete, coherent, rotation of the magnetization.

Ultrafast surface carrier dynamics in the topological insulator Bi₂Te₃.

Science.gov (United States)

Hajlaoui, M; Papalazarou, E; Mauchain, J; Lantz, G; Moisan, N; Boschetto, D; Jiang, Z; Miotkowski, I; Chen, Y P; Taleb-Ibrahimi, A; Perfetti, L; Marsi, M

2012-07-11

We discuss the ultrafast evolution of the surface electronic structure of the topological insulator Bi(2)Te(3) following a femtosecond laser excitation. Using time and angle-resolved photoelectron spectroscopy, we provide a direct real-time visualization of the transient carrier population of both the surface states and the bulk conduction band. We find that the thermalization of the surface states is initially determined by interband scattering from the bulk conduction band, lasting for about 0.5 ps; subsequently, few picoseconds are necessary for the Dirac cone nonequilibrium electrons to recover a Fermi-Dirac distribution, while their relaxation extends over more than 10 ps. The surface sensitivity of our measurements makes it possible to estimate the range of the bulk-surface interband scattering channel, indicating that the process is effective over a distance of 5 nm or less. This establishes a correlation between the nanoscale thickness of the bulk charge reservoir and the evolution of the ultrafast carrier dynamics in the surface Dirac cone.

Electron diffraction using ultrafast electron bunches from a laser-wakefield accelerator at kHz repetition rate

Science.gov (United States)

He, Z.-H.; Thomas, A. G. R.; Beaurepaire, B.; Nees, J. A.; Hou, B.; Malka, V.; Krushelnick, K.; Faure, J.

2013-02-01

We show that electron bunches in the 50-100 keV range can be produced from a laser wakefield accelerator using 10 mJ, 35 fs laser pulses operating at 0.5 kHz. It is shown that using a solenoid magnetic lens, the electron bunch distribution can be shaped. The resulting transverse and longitudinal coherence is suitable for producing diffraction images from a polycrystalline 10 nm aluminum foil. The high repetition rate, the stability of the electron source, and the fact that its uncorrelated bunch duration is below 100 fs make this approach promising for the development of sub-100 fs ultrafast electron diffraction experiments.

Electron diffraction using ultrafast electron bunches from a laser-wakefield accelerator at kHz repetition rate

Energy Technology Data Exchange (ETDEWEB)

He, Z.-H.; Thomas, A. G. R.; Nees, J. A.; Hou, B.; Krushelnick, K. [Center for Ultrafast Optical Science, University of Michigan, Ann Arbor, Michigan 48106-2099 (United States); Beaurepaire, B.; Malka, V.; Faure, J. [Laboratoire d' Optique Appliquee, ENSTA-CNRS-Ecole Polytechnique, UMR 7639, 91761 Palaiseau (France)

2013-02-11

We show that electron bunches in the 50-100 keV range can be produced from a laser wakefield accelerator using 10 mJ, 35 fs laser pulses operating at 0.5 kHz. It is shown that using a solenoid magnetic lens, the electron bunch distribution can be shaped. The resulting transverse and longitudinal coherence is suitable for producing diffraction images from a polycrystalline 10 nm aluminum foil. The high repetition rate, the stability of the electron source, and the fact that its uncorrelated bunch duration is below 100 fs make this approach promising for the development of sub-100 fs ultrafast electron diffraction experiments.

Diffraction contrast as a sensitive indicator of femtosecond sub-nanoscale motion in ultrafast transmission electron microscopy

Science.gov (United States)

Cremons, Daniel R.; Schliep, Karl B.; Flannigan, David J.

2013-09-01

With ultrafast transmission electron microscopy (UTEM), access can be gained to the spatiotemporal scales required to directly visualize rapid, non-equilibrium structural dynamics of materials. This is achieved by operating a transmission electron microscope (TEM) in a stroboscopic pump-probe fashion by photoelectrically generating coherent, well-timed electron packets in the gun region of the TEM. These probe photoelectrons are accelerated down the TEM column where they travel through the specimen before reaching a standard, commercially-available CCD detector. A second laser pulse is used to excite (pump) the specimen in situ. Structural changes are visualized by varying the arrival time of the pump laser pulse relative to the probe electron packet at the specimen. Here, we discuss how ultrafast nanoscale motions of crystalline materials can be visualized and precisely quantified using diffraction contrast in UTEM. Because diffraction contrast sensitively depends upon both crystal lattice orientation as well as incoming electron wavevector, minor spatial/directional variations in either will produce dynamic and often complex patterns in real-space images. This is because sections of the crystalline material that satisfy the Laue conditions may be heterogeneously distributed such that electron scattering vectors vary over nanoscale regions. Thus, minor changes in either crystal grain orientation, as occurs during specimen tilting, warping, or anisotropic expansion, or in the electron wavevector result in dramatic changes in the observed diffraction contrast. In this way, dynamic contrast patterns observed in UTEM images can be used as sensitive indicators of ultrafast specimen motion. Further, these motions can be spatiotemporally mapped such that direction and amplitude can be determined.

An injector for the proposed Berkeley Ultrafast X-Ray Light Source

International Nuclear Information System (INIS)

Lidia, Steven; Corlett, John; Pusina, Jan; Staples, John; Zholents, Alexander

2003-01-01

Berkeley Lab has proposed to build a recirculating linac based X-ray source for ultra-fast dynamic studies [1]. This machine requires a flat electron beam with a small vertical emittance and large x/y emittance ratio to allow for compression of spontaneous undulator emission of soft and hard x-ray pulses, and a low-emittance, round electron beam for coherent emission of soft x-rays via the FEL process based on cascaded harmonic generation [2]. We propose an injector system consisting of two high gradient high repetition rate photo cathode guns [3] (one for each application), an ∼120 MeV super conducting linear accelerator, a 3rd harmonic cavity for linearization of the longitudinal phase space, and a bunch compressor. We present details of the design and the results of particle tracking studies using several computer codes

Progress in ultrafast laser processing and future prospects

Science.gov (United States)

Sugioka, Koji

2017-03-01

The unique characteristics of ultrafast lasers have rapidly revolutionized materials processing after their first demonstration in 1987. The ultrashort pulse width of the laser suppresses heat diffusion to the surroundings of the processed region, which minimizes the formation of a heat-affected zone and thereby enables ultrahigh precision micro- and nanofabrication of various materials. In addition, the extremely high peak intensity can induce nonlinear multiphoton absorption, which extends the diversity of materials that can be processed to transparent materials such as glass. Nonlinear multiphoton absorption enables three-dimensional (3D) micro- and nanofabrication by irradiation with tightly focused femtosecond laser pulses inside transparent materials. Thus, ultrafast lasers are currently widely used for both fundamental research and practical applications. This review presents progress in ultrafast laser processing, including micromachining, surface micro- and nanostructuring, nanoablation, and 3D and volume processing. Advanced technologies that promise to enhance the performance of ultrafast laser processing, such as hybrid additive and subtractive processing, and shaped beam processing are discussed. Commercial and industrial applications of ultrafast laser processing are also introduced. Finally, future prospects of the technology are given with a summary.

Perspective: Ultrafast magnetism and THz spintronics

Energy Technology Data Exchange (ETDEWEB)

Walowski, Jakob; Münzenberg, Markus [Institut für Physik, Ernst-Moritz-Arndt-Universität Greifswald, 17489 Greifswald (Germany)

2016-10-14

This year the discovery of femtosecond demagnetization by laser pulses is 20 years old. For the first time, this milestone work by Bigot and coworkers gave insight directly into the time scales of microscopic interactions that connect the spin and electron system. While intense discussions in the field were fueled by the complexity of the processes in the past, it now became evident that it is a puzzle of many different parts. Rather than providing an overview that has been presented in previous reviews on ultrafast processes in ferromagnets, this perspective will show that with our current depth of knowledge the first applications are developed: THz spintronics and all-optical spin manipulation are becoming more and more feasible. The aim of this perspective is to point out where we can connect the different puzzle pieces of understanding gathered over 20 years to develop novel applications. Based on many observations in a large number of experiments. Differences in the theoretical models arise from the localized and delocalized nature of ferromagnetism. Transport effects are intrinsically non-local in spintronic devices and at interfaces. We review the need for multiscale modeling to address the processes starting from electronic excitation of the spin system on the picometer length scale and sub-femtosecond time scale, to spin wave generation, and towards the modeling of ultrafast phase transitions that altogether determine the response time of the ferromagnetic system. Today, our current understanding gives rise to the first usage of ultrafast spin physics for ultrafast magnetism control: THz spintronic devices. This makes the field of ultrafast spin-dynamics an emerging topic open for many researchers right now.

Perspective: Ultrafast magnetism and THz spintronics

International Nuclear Information System (INIS)

Walowski, Jakob; Münzenberg, Markus

2016-01-01

This year the discovery of femtosecond demagnetization by laser pulses is 20 years old. For the first time, this milestone work by Bigot and coworkers gave insight directly into the time scales of microscopic interactions that connect the spin and electron system. While intense discussions in the field were fueled by the complexity of the processes in the past, it now became evident that it is a puzzle of many different parts. Rather than providing an overview that has been presented in previous reviews on ultrafast processes in ferromagnets, this perspective will show that with our current depth of knowledge the first applications are developed: THz spintronics and all-optical spin manipulation are becoming more and more feasible. The aim of this perspective is to point out where we can connect the different puzzle pieces of understanding gathered over 20 years to develop novel applications. Based on many observations in a large number of experiments. Differences in the theoretical models arise from the localized and delocalized nature of ferromagnetism. Transport effects are intrinsically non-local in spintronic devices and at interfaces. We review the need for multiscale modeling to address the processes starting from electronic excitation of the spin system on the picometer length scale and sub-femtosecond time scale, to spin wave generation, and towards the modeling of ultrafast phase transitions that altogether determine the response time of the ferromagnetic system. Today, our current understanding gives rise to the first usage of ultrafast spin physics for ultrafast magnetism control: THz spintronic devices. This makes the field of ultrafast spin-dynamics an emerging topic open for many researchers right now.

A versatile setup for ultrafast broadband optical spectroscopy of coherent collective modes in strongly correlated quantum systems

Directory of Open Access Journals (Sweden)

Edoardo Baldini

2016-11-01

Full Text Available A femtosecond pump-probe setup is described that is optimised for broadband transient reflectivity experiments on solid samples over a wide temperature range. By combining high temporal resolution and a broad detection window, this apparatus can investigate the interplay between coherent collective modes and high-energy electronic excitations, which is a distinctive characteristic of correlated electron systems. Using a single-shot readout array detector at frame rates of 10 kHz allows resolving coherent oscillations with amplitudes <10−4. We demonstrate its operation on the charge-transfer insulator La2CuO4, revealing coherent phonons with frequencies up to 13 THz and providing access into their Raman matrix elements.

Coherent generation of symmetry-forbidden phonons by light-induced electron-phonon interactions in magnetite

Science.gov (United States)

Borroni, S.; Baldini, E.; Katukuri, V. M.; Mann, A.; Parlinski, K.; Legut, D.; Arrell, C.; van Mourik, F.; Teyssier, J.; Kozlowski, A.; Piekarz, P.; Yazyev, O. V.; Oleś, A. M.; Lorenzana, J.; Carbone, F.

2017-09-01

Symmetry breaking across phase transitions often causes changes in selection rules and emergence of optical modes which can be detected via spectroscopic techniques or generated coherently in pump-probe experiments. In second-order or weakly first-order transitions, fluctuations of the ordering field are present above the ordering temperature, giving rise to intriguing precursor phenomena, such as critical opalescence. Here, we demonstrate that in magnetite (Fe3O4 ) light excitation couples to the critical fluctuations of the charge order and coherently generates structural modes of the ordered phase above the critical temperature of the Verwey transition. Our findings are obtained by detecting coherent oscillations of the optical constants through ultrafast broadband spectroscopy and analyzing their dependence on temperature. To unveil the coupling between the structural modes and the electronic excitations, at the origin of the Verwey transition, we combine our results from pump-probe experiments with spontaneous Raman scattering data and theoretical calculations of both the phonon dispersion curves and the optical constants. Our methodology represents an effective tool to study the real-time dynamics of critical fluctuations across phase transitions.

Bright broadband coherent fiber sources emitting strongly blue-shifted resonant dispersive wave pulses

DEFF Research Database (Denmark)

Tu, Haohua; Lægsgaard, Jesper; Zhang, Rui

2013-01-01

We predict and realize the targeted wavelength conversion from the 1550-nm band of a fs Er:fiber laser to an isolated band inside 370-850 nm, corresponding to a blue-shift of 700-1180 nm. The conversion utilizes resonant dispersive wave generation in widely available optical fibers with good...... efficiency (~7%). The converted band has a large pulse energy (~1 nJ), high spectral brightness (~1 mW/nm), and broad Gaussian-like spectrum compressible to clean transform-limited ~17 fs pulses. The corresponding coherent fiber sources open up portable applications of optical parametric oscillators and dual......-output synchronized ultrafast lasers....

Advancing non-equilibrium ARPES experiments by a 9.3 eV coherent ultrafast photon source

Energy Technology Data Exchange (ETDEWEB)

Cilento, F., E-mail: federico.cilento@elettra.eu [Elettra – Sincrotrone Trieste S.C.p.A., Strada Statale 14, km 163.5, Trieste 34149 (Italy); C.N.R. – I.O.M., Strada Statale 14, km 163.5, Trieste 34149 (Italy); Crepaldi, A. [Elettra – Sincrotrone Trieste S.C.p.A., Strada Statale 14, km 163.5, Trieste 34149 (Italy); Manzoni, G.; Sterzi, A. [Universitá degli Studi di Trieste, Via A. Valerio 2, Trieste 34127 (Italy); Zacchigna, M. [C.N.R. – I.O.M., Strada Statale 14, km 163.5, Trieste 34149 (Italy); Bugnon, Ph.; Berger, H. [Institute of Condensed Matter Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne (Switzerland); Parmigiani, F. [Elettra – Sincrotrone Trieste S.C.p.A., Strada Statale 14, km 163.5, Trieste 34149 (Italy); Universitá degli Studi di Trieste, Via A. Valerio 2, Trieste 34127 (Italy); International Faculty, University of Köln, 50937 Köln (Germany)

2016-02-15

The quest for investigating the non-equilibrium dynamics of the band structure of strongly-correlated materials over their entire Brillouin zone is a primary objective. However, the actual ultrafast UV light sources are not suitable for addressing several critical questions in the field. Here we report on a novel light source generating sub-250 fs, 9.3 eV photon energy light pulses at 250 kHz repetition rate, obtained via third-harmonic generation in Xe of frequency-doubled 50 fs laser pulses at 1.55 eV. By reporting the measured band dispersion of a Cu(111) crystal and the non-equilibrium dynamics of the Bi{sub 2}Se{sub 3} topological insulator, we prove that this source is suitable for studying the non-equilibrium dynamics of the entire Fermi surface of several complex materials, with high signal statistics and limited space-charge effect.

Generalization of fewest-switches surface hopping for coherences

Science.gov (United States)

Tempelaar, Roel; Reichman, David R.

2018-03-01

Fewest-switches surface hopping (FSSH) is perhaps the most widely used mixed quantum-classical approach for the modeling of non-adiabatic processes, but its original formulation is restricted to (adiabatic) population terms of the quantum density matrix, leaving its implementations with an inconsistency in the treatment of populations and coherences. In this article, we propose a generalization of FSSH that treats both coherence and population terms on equal footing and which formally reduces to the conventional FSSH algorithm for the case of populations. This approach, coherent fewest-switches surface hopping (C-FSSH), employs a decoupling of population relaxation and pure dephasing and involves two replicas of the classical trajectories interacting with two active surfaces. Through extensive benchmark calculations of a spin-boson model involving a Debye spectral density, we demonstrate the potential of C-FSSH to deliver highly accurate results for a large region of parameter space. Its uniform description of populations and coherences is found to resolve incorrect behavior observed for conventional FSSH in various cases, in particular at low temperature, while the parameter space regions where it breaks down are shown to be quite limited. Its computational expenses are virtually identical to conventional FSSH.

Ultrafast pulse generation in integrated arrays of anapole nanolasers

KAUST Repository

Gongora, J. S. Totero

2017-11-02

One of the main challenges in photonics is the integration of ultrafast coherent sources in silicon compatible platforms at the nanoscale [1]. Generally, the emission of ultra-short pulses is achieved by synchronizing the cavity modes of the system via external active components, such as, e.g., Q-switch or saturable absorbers. Consequently, the required optical setups are complex and difficult to integrate on-chip. To address these difficulties, we propose a novel type of integrated source based on the spontaneous synchronization of several near-field nanolasers. We design our near-field lasers by considering the nonlinear amplification of non-radiating Anapole modes [2]. Anapoles represent an intriguing non-conventional state of radiation, whose excitation is responsible for the formation of scattering suppression states in dielectric nanostructures [3]. Due to their inherent near-field emission properties, an ensemble of anapole-based nanolasers represent an ideal candidate to investigate and tailor spontaneous synchronization phenomena in a silicon-compatible framework. Additionally, their mutual non-linear interaction can be precisely controlled within standard nanofabrication tolerances.

Ultrafast photoinduced structure phase transition in antimony single crystals

NARCIS (Netherlands)

Fausti, Daniele; Misochko, Oleg V.; van Loosdrecht, Paul H. M.

2009-01-01

Picosecond Raman scattering is used to study the photoinduced ultrafast dynamics in Peierls distorted antimony. We find evidence for an ultrafast nonthermal reversible structural phase transition. Most surprisingly, we find evidence that this transition evolves toward a lower symmetry in contrast to

Direct Characterization of Ultrafast Energy-Time Entangled Photon Pairs.

Science.gov (United States)

MacLean, Jean-Philippe W; Donohue, John M; Resch, Kevin J

2018-02-02

Energy-time entangled photons are critical in many quantum optical phenomena and have emerged as important elements in quantum information protocols. Entanglement in this degree of freedom often manifests itself on ultrafast time scales, making it very difficult to detect, whether one employs direct or interferometric techniques, as photon-counting detectors have insufficient time resolution. Here, we implement ultrafast photon counters based on nonlinear interactions and strong femtosecond laser pulses to probe energy-time entanglement in this important regime. Using this technique and single-photon spectrometers, we characterize all the spectral and temporal correlations of two entangled photons with femtosecond resolution. This enables the witnessing of energy-time entanglement using uncertainty relations and the direct observation of nonlocal dispersion cancellation on ultrafast time scales. These techniques are essential to understand and control the energy-time degree of freedom of light for ultrafast quantum optics.

Progress in ultrafast intense laser science

CERN Document Server

Yamanouchi, Kaoru; Mathur, Deepak

2014-01-01

The PUILS series delivers up-to-date reviews of progress in Ultrafast Intense Laser Science, a newly emerging interdisciplinary research field spanning atomic and molecular physics, molecular science, and optical science, which has been stimulated by the recent developments in ultrafast laser technologies. Each volume compiles peer-reviewed articles authored by researchers at the forefront of each their own subfields of UILS. Every chapter opens with an overview of the topics to be discussed, so that researchers unfamiliar to the subfield, as well as graduate students, can grasp the importance

Relaxation dynamics and coherent energy exchange in coupled vibration-cavity polaritons (Conference Presentation)

Science.gov (United States)

Simpkins, Blake S.; Fears, Kenan P.; Dressick, Walter J.; Dunkelberger, Adam D.; Spann, Bryan T.; Owrutsky, Jeffrey C.

2016-09-01

Coherent coupling between an optical transition and confined optical mode have been investigated for electronic-state transitions, however, only very recently have vibrational transitions been considered. Here, we demonstrate both static and dynamic results for vibrational bands strongly coupled to optical cavities. We experimentally and numerically describe strong coupling between a Fabry-Pérot cavity and carbonyl stretch ( 1730 cm 1) in poly-methylmethacrylate and provide evidence that the mixed-states are immune to inhomogeneous broadening. We investigate strong and weak coupling regimes through examination of cavities loaded with varying concentrations of a urethane monomer. Rabi splittings are in excellent agreement with an analytical description using no fitting parameters. Ultrafast pump-probe measurements reveal transient absorption signals over a frequency range well-separated from the vibrational band, as well as drastically modified relaxation rates. We speculate these modified kinetics are a consequence of the energy proximity between the vibration-cavity polariton modes and excited state transitions and that polaritons offer an alternative relaxation path for vibrational excitations. Varying the polariton energies by angle-tuning yields transient results consistent with this hypothesis. Furthermore, Rabi oscillations, or quantum beats, are observed at early times and we see evidence that these coherent vibration-cavity polariton excitations impact excited state population through cavity losses. Together, these results indicate that cavity coupling may be used to influence both excitation and relaxation rates of vibrations. Opening the field of polaritonic coupling to vibrational species promises to be a rich arena amenable to a wide variety of infrared-active bonds that can be studied in steady state and dynamically.

Arbitrarily shaped high-coherence electron bunches from cold atoms

Science.gov (United States)

McCulloch, A. J.; Sheludko, D. V.; Saliba, S. D.; Bell, S. C.; Junker, M.; Nugent, K. A.; Scholten, R. E.

2011-10-01

Ultrafast electron diffractive imaging of nanoscale objects such as biological molecules and defects in solid-state devices provides crucial information on structure and dynamic processes: for example, determination of the form and function of membrane proteins, vital for many key goals in modern biological science, including rational drug design. High brightness and high coherence are required to achieve the necessary spatial and temporal resolution, but have been limited by the thermal nature of conventional electron sources and by divergence due to repulsive interactions between the electrons, known as the Coulomb explosion. It has been shown that, if the electrons are shaped into ellipsoidal bunches with uniform density, the Coulomb explosion can be reversed using conventional optics, to deliver the maximum possible brightness at the target. Here we demonstrate arbitrary and real-time control of the shape of cold electron bunches extracted from laser-cooled atoms. The ability to dynamically shape the electron source itself and to observe this shape in the propagated electron bunch provides a remarkable experimental demonstration of the intrinsically high spatial coherence of a cold-atom electron source, and the potential for alleviation of electron-source brightness limitations due to Coulomb explosion.

Observation of coherent population transfer in a four-level tripod system with a rare-earth-metal-ion-doped crystal

International Nuclear Information System (INIS)

Goto, Hayato; Ichimura, Kouichi

2007-01-01

Coherent population transfer in a laser-driven four-level system in a tripod configuration is experimentally investigated with a rare-earth-metal-ion-doped crystal (Pr 3+ :Y 2 SiO 5 ). The population transfers observed here indicate that a main process inducing them is not optical pumping, which is an incoherent process inducing population transfer. Moreover, numerical simulation, which well reproduces the experimental results, also shows that the process inducing the observed population transfers is similar to stimulated Raman adiabatic passage (STIRAP) in the sense that this process possesses characteristic features of STIRAP

Ultrafast THz Saturable Absorption in Doped Semiconductors

DEFF Research Database (Denmark)

Turchinovich, Dmitry; Hoffmann, Matthias C.

2011-01-01

We demonstrate ultrafast THz saturable absorption in n-doped semiconductors by nonlinear THz time-domain spectroscopy. This effect is caused by the semiconductor conductivity modulation due to electron heating and satellite-valley scattering in strong THz fields.......We demonstrate ultrafast THz saturable absorption in n-doped semiconductors by nonlinear THz time-domain spectroscopy. This effect is caused by the semiconductor conductivity modulation due to electron heating and satellite-valley scattering in strong THz fields....

Coherent population dynamics of a three-level atom in spacetime

International Nuclear Information System (INIS)

Netz, R.; Sauerbrey, R.; Feurer, T.; Roberts, G.

2002-01-01

This work explores temporal and spatial aspects of coherent population transfer in a three-level atom through a synergic combination of experimental measurements and theoretical calculations. Experimental measurements exploit the broad bandwidth of a femtosecond laser pulse to initiate simultaneous excitation of the 5p 2 P 1/2 2 S 1/2 and 5p 2 P 3/2 2 S 1/2 components of the doublet line of atomic rubidium. By adjusting positive or negative frequency sweeps the pump pulse favors either one of the two transitions and eventually even decouples the two excited states. The population of the excited spin-orbit levels is monitored in real time by stimulated emission probing under conditions of different intensity, chirp, and pulse width of the driving field, giving detailed information on the coupling between the three levels and their interactions with the driving and probe fields at different points in spacetime. Both pump and probe pulses are carefully characterized after the interaction region by frequency-resolved optical gating. In order to interpret and understand the experimental results it is essential to consider the close relationship between pulse propagation and time evolution of the atomic system via the coupled Maxwell-Bloch equations. This analysis highlights the importance of spatial propagation of the light fields, as well as their temporal dependence, in understanding the dynamical population evolution, and quantitatively reproduces all aspects of the experimental measurements

Imaging ultrafast excited state pathways in transition metal complexes by X-ray transient absorption and scattering using X-ray free electron laser source

DEFF Research Database (Denmark)

Chen, Lin X; Shelby, Megan L; Lestrange, Patrick J

2016-01-01

This report will describe our recent studies of transition metal complex structural dynamics on the fs and ps time scales using an X-ray free electron laser source, Linac Coherent Light Source (LCLS). Ultrafast XANES spectra at the Ni K-edge of nickel(ii) tetramesitylporphyrin (NiTMP) were measured...... on the low-energy shoulder of the edge, which is aided by the computation of X-ray transitions for postulated excited electronic states. The observed and computed inner shell to valence orbital transition energies demonstrate and quantify the influence of the electronic configuration on specific metal...

Generation of ultrafast pulse via combined effects of stimulated

Indian Academy of Sciences (India)

A project of ultrafast pulse generation has been presented and demonstrated by utilizing the combined nonlinear effects of stimulated Raman scattering (SRS) and non-degenerate two-photon absorption (TPA) based on silicon nanophotonic chip, in which a continuous wave (CW) and an ultrafast dark pulse are ...

Ultrashort and coherent single-electron pulses for diffraction at ultimate resolutions

International Nuclear Information System (INIS)

Kirchner, Friedrich Oscar

2013-01-01

Ultrafast electron diffraction is a powerful tool for studying structural dynamics with femtosecond temporal and sub-aangstroem spatial resolutions. It benefits from the high scattering cross-sections of electrons compared X-rays and allows the examination of thin samples, surfaces and gases. One of the main challenges in ultrafast electron diffraction is the generation of electron pulses with a short duration and a large transverse coherence. The former limits the temporal resolution of the experiment while the latter determines the maximum size of the scattering structures that can be studied. In this work, we strive to push the limits of electron diffraction towards higher temporal and spatial resolutions. The decisive step in our approach is to eliminate all detrimental effects caused by Coulomb repulsion between the electrons by reducing the number of electrons per pulse to one. In this situation, the electrons' longitudinal and transverse velocity distributions are determined solely by the photoemission process. By reducing the electron source size on the photocathode, we make use of the small transverse velocity spread to produce electron pulses with a transverse coherence length of 20 nm, which is about an order of magnitude larger than the reported values for comparable experiments. The energy distribution of an ensemble of single-electron pulses from a photoemission source is directly linked to the mismatch between the photon energy and the cathode's work function. This excess energy can be reduced by using a photon energy close to the material's work function. Using a tunable source of ultraviolet pulses, we demonstrate the reduction of the velocity spread of the electrons, resulting in a shorter duration of the electron pulses. The reduced electron pulse durations achieved by a tunable excitation or by other approaches require new characterization techniques for electron pulses. We developed a novel method for the characterization of electron pulses at

Ultrafast Time-Resolved Photoluminescence Studies of Gallium-Arsenide

Science.gov (United States)

Johnson, Matthew Bruce

This thesis concerns the study of ultrafast phenomena in GaAs using time-resolved photoluminescence (PL). The thesis consists of five chapters. Chapter one is an introduction, which discusses the study of ultrafast phenomena in semiconductors. Chapter two is a description of the colliding-pulse mode-locked (CPM) ring dye laser, which is at the heart of the experimental apparatus used in this thesis. Chapter three presents a detailed experimental and theoretical investigation of photoluminescence excitation correlation spectroscopy (PECS), the novel technique which is used to time-resolve ultrafast PL phenomena. Chapters 4 and 5 discuss two applications of the PECS technique. In Chapter 4 the variation of PL intensity in In-alloyed GaAs substrate material is studied, while Chapter 5 discusses the variation of carrier lifetimes in ion-damaged GaAs used in photo-conductive circuit elements (PCEs). PECS is a pulse-probe technique that measures the cross correlation of photo-excited carrier populations. The theoretical model employed in this thesis is based upon the rate equation for a simple three-level system consisting of valence and conduction bands and a single trap level. In the limit of radiative band-to-band dominated recombination, no PECS signal should be observed; while in the capture -dominated recombination limit, the PECS signal from the band-to-band PL measures the cross correlation of the excited electron and hole populations and thus, the electron and hole lifetimes. PECS is experimentally investigated using a case study of PL in semi-insulating (SI) GaAs and In -alloyed GaAs. At 77 K, the PECS signal is characteristic of a capture-dominated system, yielding an electron-hole lifetime of about 200 ps. However, at 5 K the behavior is more complicated and shows saturation effects due to the C acceptor level, which is un-ionized at 5 K. As a first application, PECS is used to investigate the large band-to-band PL contrast observed near dislocations in In

Dynamical model of coherent circularly polarized optical pulse interactions with two-level quantum systems

International Nuclear Information System (INIS)

Slavcheva, G.; Hess, O.

2005-01-01

We propose and develop a method for theoretical description of circularly (elliptically) polarized optical pulse resonant coherent interactions with two-level atoms. The method is based on the time-evolution equations of a two-level quantum system in the presence of a time-dependent dipole perturbation for electric dipole transitions between states with total angular-momentum projection difference (ΔJ z =±1) excited by a circularly polarized electromagnetic field [Feynman et al., J. Appl. Phys. 28, 49 (1957)]. The adopted real-vector representation approach allows for coupling with the vectorial Maxwell's equations for the optical wave propagation and thus the resulting Maxwell pseudospin equations can be numerically solved in the time domain without any approximations. The model permits a more exact study of the ultrafast coherent pulse propagation effects taking into account the vector nature of the electromagnetic field and hence the polarization state of the optical excitation. We demonstrate self-induced transparency effects and formation of polarized solitons. The model represents a qualitative extension of the well-known optical Maxwell-Bloch equations valid for linearly polarized light and a tool for studying coherent quantum control mechanisms

Feed-forward motor control of ultrafast, ballistic movements.

Science.gov (United States)

Kagaya, K; Patek, S N

2016-02-01

To circumvent the limits of muscle, ultrafast movements achieve high power through the use of springs and latches. The time scale of these movements is too short for control through typical neuromuscular mechanisms, thus ultrafast movements are either invariant or controlled prior to movement. We tested whether mantis shrimp (Stomatopoda: Neogonodactylus bredini) vary their ultrafast smashing strikes and, if so, how this control is achieved prior to movement. We collected high-speed images of strike mechanics and electromyograms of the extensor and flexor muscles that control spring compression and latch release. During spring compression, lateral extensor and flexor units were co-activated. The strike initiated several milliseconds after the flexor units ceased, suggesting that flexor activity prevents spring release and determines the timing of strike initiation. We used linear mixed models and Akaike's information criterion to serially evaluate multiple hypotheses for control mechanisms. We found that variation in spring compression and strike angular velocity were statistically explained by spike activity of the extensor muscle. The results show that mantis shrimp can generate kinematically variable strikes and that their kinematics can be changed through adjustments to motor activity prior to the movement, thus supporting an upstream, central-nervous-system-based control of ultrafast movement. Based on these and other findings, we present a shishiodoshi model that illustrates alternative models of control in biological ballistic systems. The discovery of feed-forward control in mantis shrimp sets the stage for the assessment of targets, strategic variation in kinematics and the role of learning in ultrafast animals. © 2016. Published by The Company of Biologists Ltd.

Review of chip-scale atomic clocks based on coherent population trapping

International Nuclear Information System (INIS)

Wang Zhong

2014-01-01

Research on chip-scale atomic clocks (CSACs) based on coherent population trapping (CPT) is reviewed. The background and the inspiration for the research are described, including the important schemes proposed to improve the CPT signal quality, the selection of atoms and buffer gases, and the development of micro-cell fabrication. With regard to the reliability, stability, and service life of the CSACs, the research regarding the sensitivity of the CPT resonance to temperature and laser power changes is also reviewed, as well as the CPT resonance's collision and light of frequency shifts. The first generation CSACs have already been developed but its characters are still far from our expectations. Our conclusion is that miniaturization and power reduction are the most important aspects calling for further research. (review)

Ultrafast Nonlinear Signal Processing in Silicon Waveguides

DEFF Research Database (Denmark)

Oxenløwe, Leif Katsuo; Mulvad, Hans Christian Hansen; Hu, Hao

2012-01-01

We describe recent demonstrations of exploiting highly nonlinear silicon waveguides for ultrafast optical signal processing. We describe wavelength conversion and serial-to-parallel conversion of 640 Gbit/s data signals and 1.28 Tbit/s demultiplexing and all-optical sampling.......We describe recent demonstrations of exploiting highly nonlinear silicon waveguides for ultrafast optical signal processing. We describe wavelength conversion and serial-to-parallel conversion of 640 Gbit/s data signals and 1.28 Tbit/s demultiplexing and all-optical sampling....

Optimization and practical implementation of ultrafast 2D NMR experiments

Energy Technology Data Exchange (ETDEWEB)

Queiroz Junior, Luiz H. K., E-mail: professorkeng@gmail.com [Universidade Federal de Sao Carlos (UFSC), SP (Brazil). Departamento de Quimica; Universidade Federal de Goias (UFGO), Goiania, GO (Brazil). Inst. de Quimica; Ferreira, Antonio G. [Universidade Federal de Sao Carlos (UFSC), SP (Brazil). Departamento de Quimica; Giraudeau, Patrick [Universite de Nantes (France). CNRS, Chimie et Interdisciplinarite: Synthese, Analyse, Modelisation

2013-09-01

Ultrafast 2D NMR is a powerful methodology that allows recording of a 2D NMR spectrum in a fraction of second. However, due to the numerous non-conventional parameters involved in this methodology its implementation is no trivial task. Here, an optimized experimental protocol is carefully described to ensure efficient implementation of ultrafast NMR. The ultrafast spectra resulting from this implementation are presented based on the example of two widely used 2D NMR experiments, COSY and HSQC, obtained in 0.2 s and 41 s, respectively. (author)

All-optical temporal integration of ultrafast pulse waveforms.

Science.gov (United States)

Park, Yongwoo; Ahn, Tae-Jung; Dai, Yitang; Yao, Jianping; Azaña, José

2008-10-27

An ultrafast all-optical temporal integrator is experimentally demonstrated. The demonstrated integrator is based on a very simple and practical solution only requiring the use of a widely available all-fiber passive component, namely a reflection uniform fiber Bragg grating (FBG). This design allows overcoming the severe speed (bandwidth) limitations of the previously demonstrated photonic integrator designs. We demonstrate temporal integration of a variety of ultrafast optical waveforms, including Gaussian, odd-symmetry Hermite Gaussian, and (odd-)symmetry double pulses, with temporal features as fast as ~6-ps, which is about one order of magnitude faster than in previous photonic integration demonstrations. The developed device is potentially interesting for a multitude of applications in all-optical computing and information processing, ultrahigh-speed optical communications, ultrafast pulse (de-)coding, shaping and metrology.

First-Principles Quantum Dynamics of Singlet Fission: Coherent versus Thermally Activated Mechanisms Governed by Molecular π Stacking

Science.gov (United States)

Tamura, Hiroyuki; Huix-Rotllant, Miquel; Burghardt, Irene; Olivier, Yoann; Beljonne, David

2015-09-01

Singlet excitons in π -stacked molecular crystals can split into two triplet excitons in a process called singlet fission that opens a route to carrier multiplication in photovoltaics. To resolve controversies about the mechanism of singlet fission, we have developed a first principles nonadiabatic quantum dynamical model that reveals the critical role of molecular stacking symmetry and provides a unified picture of coherent versus thermally activated singlet fission mechanisms in different acenes. The slip-stacked equilibrium packing structure of pentacene derivatives is found to enhance ultrafast singlet fission mediated by a coherent superexchange mechanism via higher-lying charge transfer states. By contrast, the electronic couplings for singlet fission strictly vanish at the C2 h symmetric equilibrium π stacking of rubrene. In this case, singlet fission is driven by excitations of symmetry-breaking intermolecular vibrations, rationalizing the experimentally observed temperature dependence. Design rules for optimal singlet fission materials therefore need to account for the interplay of molecular π -stacking symmetry and phonon-induced coherent or thermally activated mechanisms.

Triplet exciton dissociation and electron extraction in graphene-templated pentacene observed with ultrafast spectroscopy.

Science.gov (United States)

McDonough, Thomas J; Zhang, Lushuai; Roy, Susmit Singha; Kearns, Nicholas M; Arnold, Michael S; Zanni, Martin T; Andrew, Trisha L

2017-02-08

We compare the ultrafast dynamics of singlet fission and charge generation in pentacene films grown on glass and graphene. Pentacene grown on graphene is interesting because it forms large crystals with the long axis of the molecules "lying-down" (parallel to the surface). At low excitation fluence, spectra for pentacene on graphene contain triplet absorptions at 507 and 545 nm and no bleaching at 630 nm, which we show is due to the orientation of the pentacene molecules. We perform the first transient absorption anisotropy measurements on pentacene, observing negative anisotropy of the 507 and 545 nm peaks, consistent with triplet absorption. A broad feature at 853 nm, observed on both glass and graphene, is isotropic, suggesting hole absorption. At high fluence, there are additional features, whose kinetics and anisotropies are not explained by heating, that we assign to charge generation; we propose a polaron pair absorption at 614 nm. The lifetimes are shorter at high fluence for both pentacene on glass and graphene, indicative of triplet-triplet annihilation that likely enhances charge generation. The anisotropy decays more slowly for pentacene on graphene than on glass, in keeping with the smaller domain size observed via atomic force microscopy. Coherent acoustic phonons are observed for pentacene on graphene, which is a consequence of more homogeneous domains. Measuring the ultrafast dynamics of pentacene as a function of molecular orientation, fluence, and polarization provides new insight to previous spectral assignments.

Spectrally- and Time-Resolved Sum Frequency Generation (STiR-SFG): a new tool for ultrafast hydrogen bond dynamics at interfaces.

Science.gov (United States)

Benderskii, Alexander; Bordenyuk, Andrey; Weeraman, Champika

2006-03-01

The recently developed spectrally- and time-resolved Sum Frequency Generation (STiR-SFG) is a surface-selective 3-wave mixing (IR+visible) spectroscopic technique capable of measuring ultrafast spectral evolution of vibrational coherences. A detailed description of this measurement will be presented, and a noniterative method or deconvolving the laser pulses will be introduced to obtain the molecular response function. STiR-SFG, combined with the frequency-domain SFG spectroscopy, was applied to study hydrogen bonding dynamics at aqueous interfaces (D2O/CaF2). Spectral dynamics of the OD-stretch on the 50-150 fs time scale provides real-time observation of ultrafast H-bond rearrangement. Tuning the IR wavelength to the blue or red side of the OD-stretch transition, we selectively monitor the dynamics of different sub-ensembles in the distribution of the H-bond structures. The blue-side excitation (weaker H-bonding) shows monotonic red-shift of the OD-frequency. In contrast, the red-side excitation (stronger H-bonding structures) produces a blue-shift and a recursion, which may indicate the presence of an underdamped intermolecular mode of interfacial water. Effect of electrolyte concentration on the H-bond dynamics will be discussed.

Ultrafast electron diffraction studies of optically excited thin bismuth films

International Nuclear Information System (INIS)

Rajkovic, Ivan

2008-01-01

This thesis contains work on the design and the realization of an experimental setup capable of providing sub-picosecond electron pulses for ultrafast electron diffraction experiments, and performing the study of ultrafast dynamics in bismuth after optical excitation using this setup. (orig.)

Ultrafast electron diffraction studies of optically excited thin bismuth films

Energy Technology Data Exchange (ETDEWEB)

Rajkovic, Ivan

2008-10-21

This thesis contains work on the design and the realization of an experimental setup capable of providing sub-picosecond electron pulses for ultrafast electron diffraction experiments, and performing the study of ultrafast dynamics in bismuth after optical excitation using this setup. (orig.)

Tracking of the nuclear wavepacket motion in cyanine photoisomerization by ultrafast pump-dump-probe spectroscopy.

Science.gov (United States)

Wei, Zhengrong; Nakamura, Takumi; Takeuchi, Satoshi; Tahara, Tahei

2011-06-01

Understanding ultrafast reactions, which proceed on a time scale of nuclear motions, requires a quantitative characterization of the structural dynamics. To track such structural changes with time, we studied a nuclear wavepacket motion in photoisomerization of a prototype cyanine dye, 1,1'-diethyl-4,4'-cyanine, by ultrafast pump-dump-probe measurements in solution. The temporal evolution of wavepacket motion was examined by monitoring the efficiency of stimulated emission dumping, which was obtained from the recovery of a ground-state bleaching signal. The dump efficiency versus pump-dump delay exhibited a finite rise time, and it became longer (97 fs → 330 fs → 390 fs) as the dump pulse was tuned to longer wavelengths (690 nm → 950 nm → 1200 nm). This result demonstrates a continuous migration of the leading edge of the wavepacket on the excited-state potential from the Franck-Condon region toward the potential minimum. A slowly decaying feature of the dump efficiency indicated a considerable broadening of the wavepacket over a wide range of the potential, which results in the spread of a population distribution on the flat S(1) potential energy surface. The rapid migration as well as broadening of the wavepacket manifests a continuous nature of the structural dynamics and provides an intuitive visualization of this ultrafast reaction. We also discussed experimental strategies to evaluate reliable dump efficiencies separately from other ultrafast processes and showed a high capability and possibility of the pump-dump-probe method for spectroscopic investigation of unexplored potential regions such as conical intersections. © 2011 American Chemical Society

Understanding the features in the ultrafast transient absorption spectra of CdSe quantum dots

Energy Technology Data Exchange (ETDEWEB)

Zhang, Cheng; Do, Thanh Nhut [Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371 (Singapore); Ong, Xuanwei [Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543 (Singapore); Chan, Yinthai [Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543 (Singapore); Institute of Materials Research & Engineering, A*STAR, 2 Fusionopolis Way, Innovis, Singapore 138634 (Singapore); Tan, Howe-Siang, E-mail: howesiang@ntu.edu.sg [Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371 (Singapore)

2016-12-20

We describe a model to explain the features of the ultrafast transient absorption (TA) spectra of CdSe core type quantum dots (QDs). The measured TA spectrum consists of contributions by the ground state bleach (GSB), stimulated emission (SE) and excited state absorption (ESA) processes associated with the three lowest energy transition of the QDs. We model the shapes of the GSB, SE and ESA spectral components after fits to the linear absorption. The spectral positions of the ESA components take into account the biexcitonic binding energy. In order to obtain the correct weightage of the GSB, SE and ESA components to the TA spectrum, we enumerate the set of coherence transfer pathways associated with these processes. From our fits of the experimental TA spectra of 65 Å diameter QDs, biexcitonic binding energies for the three lowest energy transitions are obtained.

A new coupling mechanism between two graphene electron waveguides for ultrafast switching

Science.gov (United States)

Huang, Wei; Liang, Shi-Jun; Kyoseva, Elica; Ang, Lay Kee

2018-03-01

In this paper, we report a novel coupling between two graphene electron waveguides, in analogy the optical waveguides. The design is based on the coherent quantum mechanical tunneling of Rabi oscillation between the two graphene electron waveguides. Based on this coupling mechanism, we propose that it can be used as an ultrafast electronic switching device. Based on a modified coupled mode theory, we construct a theoretical model to analyze the device characteristics, and predict that the switching speed is faster than 1 ps and the on-off ratio exceeds 106. Due to the long mean free path of electrons in graphene at room temperature, the proposed design avoids the limitation of low temperature operation required in the traditional design by using semiconductor quantum-well structure. The layout of our design is similar to that of a standard complementary metal-oxide-semiconductor transistor that should be readily fabricated with current state-of-art nanotechnology.

Globally Stable Microresonator Turing Pattern Formation for Coherent High-Power THz Radiation On-Chip

Science.gov (United States)

Huang, Shu-Wei; Yang, Jinghui; Yang, Shang-Hua; Yu, Mingbin; Kwong, Dim-Lee; Zelevinsky, T.; Jarrahi, Mona; Wong, Chee Wei

2017-10-01

In nonlinear microresonators driven by continuous-wave (cw) lasers, Turing patterns have been studied in the formalism of the Lugiato-Lefever equation with emphasis on their high coherence and exceptional robustness against perturbations. Destabilization of Turing patterns and the transition to spatiotemporal chaos, however, limit the available energy carried in the Turing rolls and prevent further harvest of their high coherence and robustness to noise. Here, we report a novel scheme to circumvent such destabilization, by incorporating the effect of local mode hybridizations, and we attain globally stable Turing pattern formation in chip-scale nonlinear oscillators with significantly enlarged parameter space, achieving a record-high power-conversion efficiency of 45% and an elevated peak-to-valley contrast of 100. The stationary Turing pattern is discretely tunable across 430 GHz on a THz carrier, with a fractional frequency sideband nonuniformity measured at 7.3 ×10-14 . We demonstrate the simultaneous microwave and optical coherence of the Turing rolls at different evolution stages through ultrafast optical correlation techniques. The free-running Turing-roll coherence, 9 kHz in 200 ms and 160 kHz in 20 minutes, is transferred onto a plasmonic photomixer for one of the highest-power THz coherent generations at room temperature, with 1.1% optical-to-THz power conversion. Its long-term stability can be further improved by more than 2 orders of magnitude, reaching an Allan deviation of 6 ×10-10 at 100 s, with a simple computer-aided slow feedback control. The demonstrated on-chip coherent high-power Turing-THz system is promising to find applications in astrophysics, medical imaging, and wireless communications.

Progress in ultrafast intense laser science XI

CERN Document Server

Yamanouchi, Kaoru; Martin, Philippe

2014-01-01

The PUILS series delivers up-to-date reviews of progress in Ultrafast Intense Laser Science, a newly emerging interdisciplinary research field spanning atomic and molecular physics, molecular science and optical science, which has been stimulated by the recent developments in ultrafast laser technologies. Each volume compiles peer-reviewed articles authored by researchers at the forefront of each their own subfields of UILS. Every chapter opens with an overview of the topics to be discussed, so that researchers unfamiliar to the subfield, as well as graduate students, can grasp the importance

Progress in Ultrafast Intense Laser Science II

CERN Document Server

Yamanouchi, Kaoru; Agostini, Pierre; Ferrante, Gaetano

2007-01-01

This book series addresses a newly emerging interdisciplinary research field, Ultrafast Intense Laser Science, spanning atomic and molecular physics, molecular science, and optical science. Its progress is being stimulated by the recent development of ultrafast laser technologies. Highlights of this second volume include Coulomb explosion and fragmentation of molecules, control of chemical dynamics, high-order harmonic generation, propagation and filamentation, and laser-plasma interaction. All chapters are authored by foremost experts in their fields and the texts are written at a level accessible to newcomers and graduate students, each chapter beginning with an introductory overview.

Mega-electron-volt ultrafast electron diffraction at SLAC National Accelerator Laboratory

Energy Technology Data Exchange (ETDEWEB)

Weathersby, S. P.; Brown, G.; Chase, T. F.; Coffee, R.; Corbett, J.; Eichner, J. P.; Frisch, J. C.; Fry, A. R.; Gühr, M.; Hartmann, N.; Hast, C.; Hettel, R.; Jobe, R. K.; Jongewaard, E. N.; Lewandowski, J. R.; Li, R. K., E-mail: lrk@slac.stanford.edu; Lindenberg, A. M.; Makasyuk, I.; May, J. E.; McCormick, D. [SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); and others

2015-07-15

Ultrafast electron probes are powerful tools, complementary to x-ray free-electron lasers, used to study structural dynamics in material, chemical, and biological sciences. High brightness, relativistic electron beams with femtosecond pulse duration can resolve details of the dynamic processes on atomic time and length scales. SLAC National Accelerator Laboratory recently launched the Ultrafast Electron Diffraction (UED) and microscopy Initiative aiming at developing the next generation ultrafast electron scattering instruments. As the first stage of the Initiative, a mega-electron-volt (MeV) UED system has been constructed and commissioned to serve ultrafast science experiments and instrumentation development. The system operates at 120-Hz repetition rate with outstanding performance. In this paper, we report on the SLAC MeV UED system and its performance, including the reciprocal space resolution, temporal resolution, and machine stability.

WE-B-210-02: The Advent of Ultrafast Imaging in Biomedical Ultrasound

International Nuclear Information System (INIS)

Tanter, M.

2015-01-01

In the last fifteen years, the introduction of plane or diverging wave transmissions rather than line by line scanning focused beams has broken the conventional barriers of ultrasound imaging. By using such large field of view transmissions, the frame rate reaches the theoretical limit of physics dictated by the ultrasound speed and an ultrasonic map can be provided typically in tens of micro-seconds (several thousands of frames per second). Interestingly, this leap in frame rate is not only a technological breakthrough but it permits the advent of completely new ultrasound imaging modes, including shear wave elastography, electromechanical wave imaging, ultrafast doppler, ultrafast contrast imaging, and even functional ultrasound imaging of brain activity (fUltrasound) introducing Ultrasound as an emerging full-fledged neuroimaging modality. At ultrafast frame rates, it becomes possible to track in real time the transient vibrations – known as shear waves – propagating through organs. Such “human body seismology” provides quantitative maps of local tissue stiffness whose added value for diagnosis has been recently demonstrated in many fields of radiology (breast, prostate and liver cancer, cardiovascular imaging, …). Today, Supersonic Imagine company is commercializing the first clinical ultrafast ultrasound scanner, Aixplorer with real time Shear Wave Elastography. This is the first example of an ultrafast Ultrasound approach surpassing the research phase and now widely spread in the clinical medical ultrasound community with an installed base of more than 1000 Aixplorer systems in 54 countries worldwide. For blood flow imaging, ultrafast Doppler permits high-precision characterization of complex vascular and cardiac flows. It also gives ultrasound the ability to detect very subtle blood flow in very small vessels. In the brain, such ultrasensitive Doppler paves the way for fUltrasound (functional ultrasound imaging) of brain activity with unprecedented

WE-B-210-02: The Advent of Ultrafast Imaging in Biomedical Ultrasound

Energy Technology Data Exchange (ETDEWEB)

Tanter, M. [Laboratoire Ondes et Acoustique (France)

2015-06-15

In the last fifteen years, the introduction of plane or diverging wave transmissions rather than line by line scanning focused beams has broken the conventional barriers of ultrasound imaging. By using such large field of view transmissions, the frame rate reaches the theoretical limit of physics dictated by the ultrasound speed and an ultrasonic map can be provided typically in tens of micro-seconds (several thousands of frames per second). Interestingly, this leap in frame rate is not only a technological breakthrough but it permits the advent of completely new ultrasound imaging modes, including shear wave elastography, electromechanical wave imaging, ultrafast doppler, ultrafast contrast imaging, and even functional ultrasound imaging of brain activity (fUltrasound) introducing Ultrasound as an emerging full-fledged neuroimaging modality. At ultrafast frame rates, it becomes possible to track in real time the transient vibrations – known as shear waves – propagating through organs. Such “human body seismology” provides quantitative maps of local tissue stiffness whose added value for diagnosis has been recently demonstrated in many fields of radiology (breast, prostate and liver cancer, cardiovascular imaging, …). Today, Supersonic Imagine company is commercializing the first clinical ultrafast ultrasound scanner, Aixplorer with real time Shear Wave Elastography. This is the first example of an ultrafast Ultrasound approach surpassing the research phase and now widely spread in the clinical medical ultrasound community with an installed base of more than 1000 Aixplorer systems in 54 countries worldwide. For blood flow imaging, ultrafast Doppler permits high-precision characterization of complex vascular and cardiac flows. It also gives ultrasound the ability to detect very subtle blood flow in very small vessels. In the brain, such ultrasensitive Doppler paves the way for fUltrasound (functional ultrasound imaging) of brain activity with unprecedented

Earle K. Plyler Prize Lecture: The Three Pillars of Ultrafast Molecular Science - Time, Phase, Intensity

Science.gov (United States)

Stolow, Albert

We discuss the probing and control of molecular wavepacket dynamics in the context of three main `pillars' of light-matter interaction: time, phase, intensity. Time: Using short, coherent laser pulses and perturbative matter-field interactions, we study molecular wavepackets with a focus on the ultrafast non-Born-Oppenheimer dynamics, that is, the coupling of electronic and nuclear motions. Time-Resolved Photoelectron Spectroscopy (TRPES) is a powerful ultrafast probe of these processes in polyatomic molecules because it is sensitive both electronic and vibrational dynamics. Ideally, one would like to observe these ultrafast processes from the molecule's point of view - the Molecular Frame - thereby avoiding loss of information due to orientational averaging. This can be achieved by Time-Resolved Coincidence Imaging Spectroscopy (TRCIS) which images 3D recoil vectors of both photofragments and photoelectrons, in coincidence and as a function of time, permitting direct Molecular Frame imaging of valence electronic dynamics during a molecular dynamics. Phase: Using intermediate strength non-perturbative interactions, we apply the second order (polarizability) Non-Resonant Dynamic Stark Effect (NRDSE) to control molecular dynamics without any net absorption of light. NRDSE is also the interaction underlying molecular alignment and applies to field-free 1D of linear molecules and field-free 3D alignment of general (asymmetric) molecules. Using laser alignment, we can transiently fix a molecule in space, yielding a more general approach to direct Molecular Frame imaging of valence electronic dynamics during a chemical reaction. Intensity: In strong (ionizing) laser fields, a new laser-matter physics emerges for polyatomic systems wherein both the single active electron picture and the adiabatic electron response, both implicit in the standard 3-step models, can fail dramatically. This has important consequences for all attosecond strong field spectroscopies of

Ultrafast optical signal processing using semiconductor quantum dot amplifiers

DEFF Research Database (Denmark)

Berg, Tommy Winther; Mørk, Jesper

2002-01-01

The linear and nonlinear properties of quantum dot amplifiers are discussed on the basis of an extensive theoretical model. These devices show great potential for linear amplification as well as ultrafast signal processing.......The linear and nonlinear properties of quantum dot amplifiers are discussed on the basis of an extensive theoretical model. These devices show great potential for linear amplification as well as ultrafast signal processing....

Ultrafast dynamics in CeTe{sub 3} near the pressure-induced charge-density-wave transition

Energy Technology Data Exchange (ETDEWEB)

Tauch, Jonas; Obergfell, Manuel [Department of Physics and Center for Applied Photonics, University of Konstanz (Germany); Schaefer, Hanjo [Department of Physics and Center for Applied Photonics, University of Konstanz (Germany); Institute of Physics, Ilmenau University of Technology (Germany); Demsar, Jure [Department of Physics and Center for Applied Photonics, University of Konstanz (Germany); Institute of Physics, Ilmenau University of Technology (Germany); Institute of Physics, Johannes Gutenberg-University Mainz (Germany); Giraldo, Paula; Fisher, Ian R. [Geballe Laboratory for Advanced Materials and Department of Applied Physics, Stanford University (United States); Pashkin, Alexej [Department of Physics and Center for Applied Photonics, University of Konstanz (Germany); Helmholtz-Zentrum Dresden-Rossendorf (Germany)

2015-07-01

Femtosecond pump-probe spectroscopy is an efficient tool for studying ultrafast dynamics in strongly correlated electronic systems, in particular, compounds with a charge-density-wave (CDW) order. Application of external pressure often leads to a suppression of a CDW state due to an impairment of the Fermi surface nesting. We combine time-resolved optical spectroscopy and diamond anvil cell technology to study electron and lattice dynamics in tri-telluride compound CeTe{sub 3}. Around pressures of 4 GPa we observe a gradual vanishing of the relaxation process related to the recombination of the photoexcited quasiparticles. The coherent oscillations of the phonon modes coupled to the CDW order parameter demonstrate even more dramatic suppression with increasing pressure. These observations clearly indicate a transition into the metallic state of CeTe{sub 3} induced by the external pressure.

Ultrafast Thermal Transport at Interfaces

Energy Technology Data Exchange (ETDEWEB)

Cahill, David [Univ. of Illinois, Champaign, IL (United States); Murphy, Catherine [Univ. of Illinois, Champaign, IL (United States); Martin, Lane [Univ. of Illinois, Champaign, IL (United States)

2014-10-21

Our research program on Ultrafast Thermal Transport at Interfaces advanced understanding of the mesoscale science of heat conduction. At the length and time scales of atoms and atomic motions, energy is transported by interactions between single-particle and collective excitations. At macroscopic scales, entropy, temperature, and heat are the governing concepts. Key gaps in fundamental knowledge appear at the transitions between these two regimes. The transport of thermal energy at interfaces plays a pivotal role in these scientific issues. Measurements of heat transport with ultrafast time resolution are needed because picoseconds are the fundamental scales where the lack of equilibrium between various thermal excitations becomes a important factor in the transport physics. A critical aspect of our work has been the development of experimental methods and model systems that enabled more precise and sensitive investigations of nanoscale thermal transport.

Determination of hot carrier energy distributions from inversion of ultrafast pump-probe reflectivity measurements.

Science.gov (United States)

Heilpern, Tal; Manjare, Manoj; Govorov, Alexander O; Wiederrecht, Gary P; Gray, Stephen K; Harutyunyan, Hayk

2018-05-10

Developing a fundamental understanding of ultrafast non-thermal processes in metallic nanosystems will lead to applications in photodetection, photochemistry and photonic circuitry. Typically, non-thermal and thermal carrier populations in plasmonic systems are inferred either by making assumptions about the functional form of the initial energy distribution or using indirect sensors like localized plasmon frequency shifts. Here we directly determine non-thermal and thermal distributions and dynamics in thin films by applying a double inversion procedure to optical pump-probe data that relates the reflectivity changes around Fermi energy to the changes in the dielectric function and in the single-electron energy band occupancies. When applied to normal incidence measurements our method uncovers the ultrafast excitation of a non-Fermi-Dirac distribution and its subsequent thermalization dynamics. Furthermore, when applied to the Kretschmann configuration, we show that the excitation of propagating plasmons leads to a broader energy distribution of electrons due to the enhanced Landau damping.

Ultrafast vibrations of gold nanorings

DEFF Research Database (Denmark)

Kelf, T; Tanaka, Y; Matsuda, O

2011-01-01

We investigate the vibrational modes of gold nanorings on a silica substrate with an ultrafast optical technique. By comparison with numerical simulations, we identify several resonances in the gigahertz range associated with axially symmetric deformations of the nanoring and substrate. We...

Ultrafast Spectroscopy of Semiconductor Devices

DEFF Research Database (Denmark)

Borri, Paola; Langbein, Wolfgang; Hvam, Jørn Marcher

1999-01-01

In this work we present an experimental technique for investigating ultrafast carrier dynamics in semiconductor optical amplifiers at room temperature. These dynamics, influenced by carrier heating, spectral hole-burning and two-photon absorption, are very important for device applications in inf...

Electrically-driven GHz range ultrafast graphene light emitter (Conference Presentation)

Science.gov (United States)

Kim, Youngduck; Gao, Yuanda; Shiue, Ren-Jye; Wang, Lei; Aslan, Ozgur Burak; Kim, Hyungsik; Nemilentsau, Andrei M.; Low, Tony; Taniguchi, Takashi; Watanabe, Kenji; Bae, Myung-Ho; Heinz, Tony F.; Englund, Dirk R.; Hone, James

2017-02-01

Ultrafast electrically driven light emitter is a critical component in the development of the high bandwidth free-space and on-chip optical communications. Traditional semiconductor based light sources for integration to photonic platform have therefore been heavily studied over the past decades. However, there are still challenges such as absence of monolithic on-chip light sources with high bandwidth density, large-scale integration, low-cost, small foot print, and complementary metal-oxide-semiconductor (CMOS) technology compatibility. Here, we demonstrate the first electrically driven ultrafast graphene light emitter that operate up to 10 GHz bandwidth and broadband range (400 1600 nm), which are possible due to the strong coupling of charge carriers in graphene and surface optical phonons in hBN allow the ultrafast energy and heat transfer. In addition, incorporation of atomically thin hexagonal boron nitride (hBN) encapsulation layers enable the stable and practical high performance even under the ambient condition. Therefore, electrically driven ultrafast graphene light emitters paves the way towards the realization of ultrahigh bandwidth density photonic integrated circuits and efficient optical communications networks.

Ultrafast demagnetisation dependence on film thickness: A TDDFT calculation

Science.gov (United States)

Singh, N.; Sharma, S.

2018-04-01

Ferromagnetic materials when subjected to intense laser pulses leads to reduction of their magnetisation on an ultrafast scale. Here, we perform an ab-initio calculation to study the behavior of ultrafast demagnetisation as a function of film thickness for Nickel as compared to the bulk of the material. In thin films surface formation results in amplification of demagnetisation with the percentage of demagnetisation depending upon the film thickness.

Evaluating Extensions to Coherent Mortality Forecasting Models

Directory of Open Access Journals (Sweden)

Syazreen Shair

2017-03-01

Full Text Available Coherent models were developed recently to forecast the mortality of two or more sub-populations simultaneously and to ensure long-term non-divergent mortality forecasts of sub-populations. This paper evaluates the forecast accuracy of two recently-published coherent mortality models, the Poisson common factor and the product-ratio functional models. These models are compared to each other and the corresponding independent models, as well as the original Lee–Carter model. All models are applied to age-gender-specific mortality data for Australia and Malaysia and age-gender-ethnicity-specific data for Malaysia. The out-of-sample forecast error of log death rates, male-to-female death rate ratios and life expectancy at birth from each model are compared and examined across groups. The results show that, in terms of overall accuracy, the forecasts of both coherent models are consistently more accurate than those of the independent models for Australia and for Malaysia, but the relative performance differs by forecast horizon. Although the product-ratio functional model outperforms the Poisson common factor model for Australia, the Poisson common factor is more accurate for Malaysia. For the ethnic groups application, ethnic-coherence gives better results than gender-coherence. The results provide evidence that coherent models are preferable to independent models for forecasting sub-populations’ mortality.

Ultrafast magnetodynamics with free-electron lasers

Science.gov (United States)

Malvestuto, Marco; Ciprian, Roberta; Caretta, Antonio; Casarin, Barbara; Parmigiani, Fulvio

2018-02-01

The study of ultrafast magnetodynamics has entered a new era thanks to the groundbreaking technological advances in free-electron laser (FEL) light sources. The advent of these light sources has made possible unprecedented experimental schemes for time-resolved x-ray magneto-optic spectroscopies, which are now paving the road for exploring the ultimate limits of out-of-equilibrium magnetic phenomena. In particular, these studies will provide insights into elementary mechanisms governing spin and orbital dynamics, therefore contributing to the development of ultrafast devices for relevant magnetic technologies. This topical review focuses on recent advancement in the study of non-equilibrium magnetic phenomena from the perspective of time-resolved extreme ultra violet (EUV) and soft x-ray spectroscopies at FELs with highlights of some important experimental results.

Femtochemistry and femtobiology ultrafast dynamics in molecular science

CERN Document Server

Douhal, Abderrazzak

2002-01-01

This book contains important contributions from top international scientists on the-state-of-the-art of femtochemistry and femtobiology at the beginning of the new millennium. It consists of reviews and papers on ultrafast dynamics in molecular science.The coverage of topics highlights several important features of molecular science from the viewpoint of structure (space domain) and dynamics (time domain). First of all, the book presents the latest developments, such as experimental techniques for understanding ultrafast processes in gas, condensed and complex systems, including biological mol

Ultrafast spectroscopy of biological photoreceptors

NARCIS (Netherlands)

Kennis, J.T.M.; Groot, M.L.

2007-01-01

We review recent new insights on reaction dynamics of photoreceptors proteins gained from ultrafast spectroscopy. In Blue Light sensing Using FAD (BLUF) domains, a hydrogen-bond rearrangement around the flavin chromophore proceeds through a radical-pair mechanism, by which light-induced electron and

Ultrafast vibrations of gold nanorings

DEFF Research Database (Denmark)

Kelf, T; Tanaka, Y; Matsuda, O

2011-01-01

We investigate the vibrational modes of gold nanorings on a silica substrate with an ultrafast optical technique. By comparison with numerical simulations, we identify several resonances in the gigahertz range associated with axially symmetric deformations of the nanoring and substrate. We elucid...

Ultrafast gas switching experiments

International Nuclear Information System (INIS)

Frost, C.A.; Martin, T.H.; Patterson, P.E.; Rinehart, L.F.; Rohwein, G.J.; Roose, L.D.; Aurand, J.F.; Buttram, M.T.

1993-01-01

We describe recent experiments which studied the physics of ultrafast gas breakdown under the extreme overvoltages which occur when a high pressure gas switch is pulse charged to hundreds of kV in 1 ns or less. The highly overvolted peaking gaps produce powerful electromagnetic pulses with risetimes Khz at > 100 kV/m E field

Ultrafast magnetization dynamics

OpenAIRE

Woodford, Simon

2008-01-01

This thesis addresses ultrafast magnetization dynamics from a theoretical perspective. The manipulation of magnetization using the inverse Faraday effect has been studied, as well as magnetic relaxation processes in quantum dots. The inverse Faraday effect – the generation of a magnetic field by nonresonant, circularly polarized light – offers the possibility to control and reverse magnetization on a timescale of a few hundred femtoseconds. This is important both for the technological advant...

Coherent Sources of XUV Radiation Soft X-Ray Lasers and High-Order Harmonic Generation

CERN Document Server

Jaeglé, Pierre

2006-01-01

Extreme ultraviolet radiation, also referred to as soft X-rays or XUV, offers very special optical properties. The X-UV refractive index of matter is such that normal reflection cannot take place on polished surfaces whereas beam transmission through one micrometer of almost all materials reduces to zero. Therefore, it has long been a difficult task to imagine and to implement devices designed for complex optics experiments in this wavelength range. Thanks to new sources of coherent radiation - XUV-lasers and High Order Harmonics - the use of XUV radiation, for interferometry, holography, diffractive optics, non-linear radiation-matter interaction, time-resolved study of fast and ultrafast phenomena and many other applications, including medical sciences, is ubiquitous.

Tissue strain rate estimator using ultrafast IQ complex data

OpenAIRE

TERNIFI , Redouane; Elkateb Hachemi , Melouka; Remenieras , Jean-Pierre

2012-01-01

International audience; Pulsatile motion of brain parenchyma results from cardiac and breathing cycles. In this study, transient motion of brain tissue was estimated using an Aixplorer® imaging system allowing an ultrafast 2D acquisition mode. The strain was computed directly from the ultrafast IQ complex data using the extended autocorrelation strain estimator (EASE), which provides great SNRs regardless of depth. The EASE first evaluates the autocorrelation function at each depth over a set...

Patellofemoral joint motion: Evaluation by ultrafast computed tomography

International Nuclear Information System (INIS)

Stanford, W.; Phelan, J.; Kathol, M.H.; Rooholamini, S.A.; El-Khoury, G.Y.; Palutsis, G.R.; Albright, J.P.

1988-01-01

Patellofemoral maltracking is a recognized cause of peripatellar pain. Clinicians currently rely on observation, palpation, and static radiographic images to evaluate the symptomatic patient. Ultrafast computed tomography (ultrafast CT) offers objective observations of the dynamic influences of muscle contraction on the patellofemoral joint as the knee is actively moved through a range of motion from 90 0 C flexion of full extension. This study reports our initial observations and establishes a range of normal values so that patients with a clinical suspicion of patellar maltracking may be evaluated. (orig./GDG)

Patellofemoral joint motion: Evaluation by ultrafast computed tomography

Energy Technology Data Exchange (ETDEWEB)

Stanford, W.; Phelan, J.; Kathol, M.H.; Rooholamini, S.A.; El-Khoury, G.Y.; Palutsis, G.R.; Albright, J.P.

1988-10-01

Patellofemoral maltracking is a recognized cause of peripatellar pain. Clinicians currently rely on observation, palpation, and static radiographic images to evaluate the symptomatic patient. Ultrafast computed tomography (ultrafast CT) offers objective observations of the dynamic influences of muscle contraction on the patellofemoral joint as the knee is actively moved through a range of motion from 90/sup 0/C flexion of full extension. This study reports our initial observations and establishes a range of normal values so that patients with a clinical suspicion of patellar maltracking may be evaluated. (orig./GDG).

Coherent quantum dynamics launched by incoherent relaxation in a quantum circuit simulator of a light-harvesting complex

Science.gov (United States)

Chin, A. W.; Mangaud, E.; Atabek, O.; Desouter-Lecomte, M.

2018-06-01

Engineering and harnessing coherent excitonic transport in organic nanostructures has recently been suggested as a promising way towards improving manmade light-harvesting materials. However, realizing and testing the dissipative system-environment models underlying these proposals is presently very challenging in supramolecular materials. A promising alternative is to use simpler and highly tunable "quantum simulators" built from programmable qubits, as recently achieved in a superconducting circuit by Potočnik et al. [A. Potočnik et al., Nat. Commun. 9, 904 (2018), 10.1038/s41467-018-03312-x]. We simulate the real-time dynamics of an exciton coupled to a quantum bath as it moves through a network based on the quantum circuit of Potočnik et al. Using the numerically exact hierarchical equations of motion to capture the open quantum system dynamics, we find that an ultrafast but completely incoherent relaxation from a high-lying "bright" exciton into a doublet of closely spaced "dark" excitons can spontaneously generate electronic coherences and oscillatory real-space motion across the network (quantum beats). Importantly, we show that this behavior also survives when the environmental noise is classically stochastic (effectively high temperature), as in present experiments. These predictions highlight the possibilities of designing matched electronic and spectral noise structures for robust coherence generation that do not require coherent excitation or cold environments.

Silicon based ultrafast optical waveform sampling

DEFF Research Database (Denmark)

Ji, Hua; Galili, Michael; Pu, Minhao

2010-01-01

A 300 nmx450 nmx5 mm silicon nanowire is designed and fabricated for a four wave mixing based non-linear optical gate. Based on this silicon nanowire, an ultra-fast optical sampling system is successfully demonstrated using a free-running fiber laser with a carbon nanotube-based mode-locker as th......A 300 nmx450 nmx5 mm silicon nanowire is designed and fabricated for a four wave mixing based non-linear optical gate. Based on this silicon nanowire, an ultra-fast optical sampling system is successfully demonstrated using a free-running fiber laser with a carbon nanotube-based mode......-locker as the sampling source. A clear eye-diagram of a 320 Gbit/s data signal is obtained. The temporal resolution of the sampling system is estimated to 360 fs....

Ultra-fast framing camera tube

Science.gov (United States)

Kalibjian, Ralph

1981-01-01

An electronic framing camera tube features focal plane image dissection and synchronized restoration of the dissected electron line images to form two-dimensional framed images. Ultra-fast framing is performed by first streaking a two-dimensional electron image across a narrow slit, thereby dissecting the two-dimensional electron image into sequential electron line images. The dissected electron line images are then restored into a framed image by a restorer deflector operated synchronously with the dissector deflector. The number of framed images on the tube's viewing screen is equal to the number of dissecting slits in the tube. The distinguishing features of this ultra-fast framing camera tube are the focal plane dissecting slits, and the synchronously-operated restorer deflector which restores the dissected electron line images into a two-dimensional framed image. The framing camera tube can produce image frames having high spatial resolution of optical events in the sub-100 picosecond range.

Ultrafast Saturation of Electronic-Resonance-Enhanced Coherent Anti-Stokes Raman Scattering and Comparison for Pulse Durations in the Nanosecond to Femtosecond Regime

Science.gov (United States)

2016-02-05

near sat- uration limit of the probe intensity [16]. In such spectro - scopic techniques, while it is important to obtain spec- trum of the intended...There are a few literature that exist on the ultrafast UV -laser excitation of NO, e.g., Lopez-Marten et al. have shown that the laser intensi- ties in...observe ac-Stark shift (see Ref. [40]). Though, to the best of our knowledge, no study has been reported for ionization of NO by UV pulse of 236 nm at 10

Coherence Phenomena in Coupled Optical Resonators

Science.gov (United States)

Smith, D. D.; Chang, H.

2004-01-01

We predict a variety of photonic coherence phenomena in passive and active coupled ring resonators. Specifically, the effective dispersive and absorptive steady-state response of coupled resonators is derived, and used to determine the conditions for coupled-resonator-induced transparency and absorption, lasing without gain, and cooperative cavity emission. These effects rely on coherent photon trapping, in direct analogy with coherent population trapping phenomena in atomic systems. We also demonstrate that the coupled-mode equations are formally identical to the two-level atom Schrodinger equation in the rotating-wave approximation, and use this result for the analysis of coupled-resonator photon dynamics. Notably, because these effects are predicted directly from coupled-mode theory, they are not unique to atoms, but rather are fundamental to systems of coherently coupled resonators.

Short-Range Electron Transfer in Reduced Flavodoxin: Ultrafast Nonequilibrium Dynamics Coupled with Protein Fluctuations.

Science.gov (United States)

Kundu, Mainak; He, Ting-Fang; Lu, Yangyi; Wang, Lijuan; Zhong, Dongping

2018-05-03

Short-range electron transfer (ET) in proteins is an ultrafast process on the similar timescales as local protein-solvent fluctuations thus the two dynamics are coupled. Here, we use semiquinone flavodoxin and systematically characterized the photoinduced redox cycle with eleven mutations of different aromatic electron donors (tryptophan and tyrosine) and local residues to change redox properties. We observed the forward and backward ET dynamics in a few picoseconds, strongly following a stretched behavior resulting from a coupling between local environment relaxations and these ET processes. We further observed the hot vibrational-state formation through charge recombination and the subsequent cooling dynamics also in a few picoseconds. Combined with the ET studies in oxidized flavodoxin, these results coherently reveal the evolution of the ET dynamics from single to stretched exponential behaviors and thus elucidate critical timescales for the coupling. The observed hot vibration-state formation is robust and should be considered in all photoinduced back ET processes in flavoproteins.

Real-time control of ultrafast laser micromachining by laser-induced breakdown spectroscopy

International Nuclear Information System (INIS)

Tong Tao; Li Jinggao; Longtin, Jon P.

2004-01-01

Ultrafast laser micromachining provides many advantages for precision micromachining. One challenging problem, however, particularly for multilayer and heterogeneous materials, is how to prevent a given material from being ablated, as ultrafast laser micromachining is generally material insensitive. We present a real-time feedback control system for an ultrafast laser micromachining system based on laser-induced breakdown spectroscopy (LIBS). The characteristics of ultrafast LIBS are reviewed and discussed so as to demonstrate the feasibility of the technique. Comparison methods to identify the material emission patterns are developed, and several of the resulting algorithms were implemented into a real-time computer control system. LIBS-controlled micromachining is demonstrated for the fabrication of microheater structures on thermal sprayed materials. Compared with a strictly passive machining process without any such feedback control, the LIBS-based system provides several advantages including less damage to the substrate layer, reduced machining time, and more-uniform machining features

Spin-controlled ultrafast vertical-cavity surface-emitting lasers

Science.gov (United States)

Höpfner, Henning; Lindemann, Markus; Gerhardt, Nils C.; Hofmann, Martin R.

2014-05-01

Spin-controlled semiconductor lasers are highly attractive spintronic devices providing characteristics superior to their conventional purely charge-based counterparts. In particular, spin-controlled vertical-cavity surface emitting lasers (spin-VCSELs) promise to offer lower thresholds, enhanced emission intensity, spin amplification, full polarization control, chirp control and ultrafast dynamics. Most important, the ability to control and modulate the polarization state of the laser emission with extraordinarily high frequencies is very attractive for many applications like broadband optical communication and ultrafast optical switches. We present a novel concept for ultrafast spin-VCSELs which has the potential to overcome the conventional speed limitation for directly modulated lasers by the relaxation oscillation frequency and to reach modulation frequencies significantly above 100 GHz. The concept is based on the coupled spin-photon dynamics in birefringent micro-cavity lasers. By injecting spin-polarized carriers in the VCSEL, oscillations of the coupled spin-photon system can by induced which lead to oscillations of the polarization state of the laser emission. These oscillations are decoupled from conventional relaxation oscillations of the carrier-photon system and can be much faster than these. Utilizing these polarization oscillations is thus a very promising approach to develop ultrafast spin-VCSELs for high speed optical data communication in the near future. Different aspects of the spin and polarization dynamics, its connection to birefringence and bistability in the cavity, controlled switching of the oscillations, and the limitations of this novel approach will be analysed theoretically and experimentally for spin-polarized VCSELs at room temperature.

Ultrafast Terahertz Conductivity of Photoexcited Nanocrystalline Silicon

DEFF Research Database (Denmark)

Cooke, David; MacDonald, A. Nicole; Hryciw, Aaron

2007-01-01

The ultrafast transient ac conductivity of nanocrystalline silicon films is investigated using time-resolved terahertz spectroscopy. While epitaxial silicon on sapphire exhibits a free carrier Drude response, silicon nanocrystals embedded in glass show a response that is best described by a class...... in the silicon nanocrystal films is dominated by trapping at the Si/SiO2 interface states, occurring on a 1–100 ps time scale depending on particle size and hydrogen passivation......The ultrafast transient ac conductivity of nanocrystalline silicon films is investigated using time-resolved terahertz spectroscopy. While epitaxial silicon on sapphire exhibits a free carrier Drude response, silicon nanocrystals embedded in glass show a response that is best described...

Development of Scanning Ultrafast Electron Microscope Capability.

Energy Technology Data Exchange (ETDEWEB)

Collins, Kimberlee Chiyoko [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Talin, Albert Alec [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Chandler, David W. [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Michael, Joseph R. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

2016-11-01

Modern semiconductor devices rely on the transport of minority charge carriers. Direct examination of minority carrier lifetimes in real devices with nanometer-scale features requires a measurement method with simultaneously high spatial and temporal resolutions. Achieving nanometer spatial resolutions at sub-nanosecond temporal resolution is possible with pump-probe methods that utilize electrons as probes. Recently, a stroboscopic scanning electron microscope was developed at Caltech, and used to study carrier transport across a Si p-n junction [ 1 , 2 , 3 ] . In this report, we detail our development of a prototype scanning ultrafast electron microscope system at Sandia National Laboratories based on the original Caltech design. This effort represents Sandia's first exploration into ultrafast electron microscopy.

Development of fiber lasers and devices for coherent Raman scattering microscopy

Science.gov (United States)

Lamb, Erin Stranford

As ultrafast laser technology has found expanding application in machining, spectroscopy, microscopy, surgery, and numerous other areas, the desire for inexpensive and robust laser sources has grown. Until recently, nonlinear effects in fiber systems due to the tight confinement of the light in the core have limited their performance. However, with advances in managing nonlinearity through pulse propagation physics and the use of large core fibers, the performance of fiber lasers can compete with that of their solid-state counterparts. As specific applications, such as coherent Raman scattering microscopy, emerge that stand to benefit from fiber technology, new performance challenges in areas such as laser noise are anticipated. This thesis studies nonlinear pulse propagation in fiber lasers and fiber parametric devices. Applications of dissipative solitons and self-similar pulse propagation to low-repetition rate oscillators that have the potential to simplify short-pulse amplification schemes will be examined. The rest of this thesis focuses on topics relevant to fiber laser development for coherent Raman scattering microscopy sources. Coherent pulse division and recombination inside the laser cavity will be introduced as an energy-scaling mechanism and demonstrated for a fiber soliton laser. The relative intensity noise properties of mode-locked fiber lasers, with a particular emphasis on normal dispersion lasers, will be explored in simulation and experiment. A fiber optical parametric oscillator will be studied in detail for low noise frequency conversion of picosecond pulses, and its utility for coherent Raman imaging will be demonstrated. Spectral compression of femtosecond pulses is used to generate picosecond pulses to pump this device, and this technique provides a route to future noise reduction in the system. Furthermore, this device forms a multimodal source capable of providing the picosecond pulses for coherent Raman scattering microscopy and the

Chirped pulse digital holography for measuring the sequence of ultrafast optical wavefronts

Science.gov (United States)

Karasawa, Naoki

2018-04-01

Optical setups for measuring the sequence of ultrafast optical wavefronts using a chirped pulse as a reference wave in digital holography are proposed and analyzed. In this method, multiple ultrafast object pulses are used to probe the temporal evolution of ultrafast phenomena and they are interfered with a chirped reference wave to record a digital hologram. Wavefronts at different times can be reconstructed separately from the recorded hologram when the reference pulse can be treated as a quasi-monochromatic wave during the pulse width of each object pulse. The feasibility of this method is demonstrated by numerical simulation.

9th International Symposium on Ultrafast Processes in Spectroscopy

CERN Document Server

Silvestri, S; Denardo, G

1996-01-01

This volume is a collection of papers presented at the Ninth International Symposium on "Ultrafast Processes in Spectroscopy" (UPS '95) held at the International Centre for Theo­ retical Physics (ICTP), Trieste (Italy), October 30 -November 3, 1995. These meetings have become recognized as the major forum in Europe for discussion of new work in this rapidly moving field. The UPS'95 Conference in Trieste brought together a multidisciplinary group of researchers sharing common interests in the generation of ultrashort optical pulses and their application to studies of ultrafast phenomena in physics, chemistry, material science, electronics, and biology. It was attended by approximately 250 participants from 20 countries and the five-day program comprises more than 200 papers. The progress of both technology and applications in the field of ultrafast processes during these last years is truly remarkable. The advent of all solid state femtosecond lasers and the extension of laser wavelengths by frequency convers...

Ultrafast Spectroscopic Noninvasive Probe of Vertical Carrier Transport in Heterostructure Devices

Science.gov (United States)

2016-03-01

ARL-TR-7618 ● MAR 2016 US Army Research Laboratory Ultrafast Spectroscopic Noninvasive Probe of Vertical Carrier Transport in...US Army Research Laboratory Ultrafast Spectroscopic Noninvasive Probe of Vertical Carrier Transport in Heterostructure Devices by Blair C...Spectroscopic Noninvasive Probe of Vertical Carrier Transport in Heterostructure Devices 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT

Progress in Ultrafast Intense Laser Science

CERN Document Server

Yamanouchi, Kaoru; Li, Ruxin; Chin, See Leang

2009-01-01

The PUILS series presents Progress in Ultrafast Intense Laser Science, a newly emerging interdisciplinary research field spanning atomic and molecular physics, molecular science, and optical science. PUILS has been stimulated by the recent development of ultrafast laser technologies. Each volume contains approximately 15 chapters, authored by researchers at the forefront. Each chapter opens with an overview of the topics to be discussed, so that researchers, who are not experts in the specific topics, as well as graduate students can grasp the importance and attractions of this sub-field of research, and these are followed by reports of cutting-edge discoveries. This fourth volume covers a broad range of topics from this interdisciplinary research field, focusing on strong field ionization of atoms; excitation, ionization and fragmentation of molecules; nonlinear intense optical phenomena and attosecond pulses; and laser - solid interactions and photoemission.

Pump polarization insensitive and efficient laser-diode pumped Yb:KYW ultrafast oscillator.

Science.gov (United States)

Wang, Sha; Wang, Yan-Biao; Feng, Guo-Ying; Zhou, Shou-Huan

2016-02-01

We theoretically and experimentally report and evaluate a novel split laser-diode (LD) double-end pumped Yb:KYW ultrafast oscillator aimed at improving the performance of an ultrafast laser. Compared to a conventional unpolarized single-LD end-pumped ultrafast laser system, we improve the laser performance such as absorption efficiency, slope efficiency, cw mode-locking threshold, and output power by this new structure LD-pumped Yb:KYW ultrafast laser. Experiments were carried out with a 1 W output fiber-coupled LD. Experimental results show that the absorption increases from 38.7% to 48.4%, laser slope efficiency increases from 18.3% to 24.2%, cw mode-locking threshold decreases 12.7% from 630 to 550 mW in cw mode-locking threshold, and maximum output-power increases 28.5% from 158.4 to 221.5 mW when we switch the pump scheme from an unpolarized single-end pumping structure to a split LD double-end pumping structure.

Loop-locked coherent population trapping magnetometer based on a fiber electro-optic modulator.

Science.gov (United States)

Hu, Yong; Feng, Y Y; Xu, Chi; Xue, H B; Sun, Li

2014-04-01

We have set up a coherent population trapping (CPT)-based magnetometer prototype with the D1 line of ⁸⁷Rb atoms. The dichromatic light field is derived from a fiber electro-optic modulator (FEOM) connected to an external cavity laser diode. A CPT resonance signal with a 516 Hz linewidth is observed. By feeding back the derivative of the resonance curve to the FEOM with a proportional integral controller, of which the voltage output is directly converted to the measured magnetic field intensity, the resonance peak is locked to the environmental magnetic field. The measurement data we have achieved are well matched with the data measured by a commercial fluxgate magnetometer within 2 nT, and the sensitivity is better than 8 pT/√Hz in a parallel B field.

Coherent Diffractive Imaging at LCLS

Science.gov (United States)

Schulz, Joachim

2010-03-01

Soft x-ray FEL light sources produce ultrafast x-ray pulses with outstanding high peak brilliance. This might enable the structure determination of proteins that cannot be crystallized. The deposited energy would destroy the molecules completely, but owing to the short pulses the destruction will ideally only happen after the termination of the pulse. In order to address the many challenges that we face in attempting molecular diffraction, we have carried out experiments in coherent diffraction from protein nanocrystals at the Linac Coherent Light Source (LCLS) at SLAC. The periodicity of these objects gives us much higher scattering signals than uncrystallized proteins would. The crystals are filtered to sizes less than 2 micron, and delivered to the pulsed X-ray beam in a liquid jet. The effects of pulse duration and fluence on the high-resolution structure of the crystals have been studied. Diffraction patterns are recorded at a repetition rate of 30 Hz with pnCCD detectors. This allows us to take 108,000 images per hour. With 2-mega-pixel-detectors this gives a data-rate of more than 400 GB per hour. The automated sorting and evaluation of hundreds of thousands images is another challenge of this kind of experiments. Preliminary results will be presented on our first LCLS experiments. This work was carried out as part of a collaboration, for which Henry Chapman is the spokesperson. The collaboration consists of CFEL DESY, Arizona State University, SLAC, Uppsala University, LLNL, The University of Melbourne, LBNL, the Max Planck Institute for Medical Research, and the Max Planck Advanced Study Group (ASG) at the CFEL. The experiments were carried out using the CAMP apparatus, which was designed and built by the Max Planck ASG at CFEL. The LCLS is operated by Stanford University on behalf of the U.S. Department of Energy, Office of Basic Energy Sciences.

Collision-induced coherence

International Nuclear Information System (INIS)

Bloembergen, N.

1985-01-01

Collision-induced coherence is based on the elimination of phase correlations between coherent Feynman-type pathways which happen to interfere destructively in the absence of damping for certain nonlinear processes. One consequence is the appearance of the extra resonances in four-wave light mixing experiments, for which the intensity increases with increasing buffer gas pressure. These resonances may occur between a pair of initially unpopulated excited states, or between a pair of initially equally populated ground states. The pair of levels may be Zeeman substrates which became degenerate in zero magnetic field. The resulting collision-enhanced Hanle resonances can lead to very sharp variations in the four-wave light mixing signal as the external magnetic field passes through zero. The theoretical description in terms of a coherence grating between Zeeman substrates is equivalent to a description in terms of a spin polarization grating obtained by collision-enhanced transverse optical pumping. The axis of quantization in the former case is taken perpendicular to the direction of the light beams; in the latter case is taken parallel to this direction

Fast MR imaging and ultrafast MR imaging of fetal central nervous system abnormalities

Energy Technology Data Exchange (ETDEWEB)

Shakudo, Miyuki; Manabe, Takao; Murata, Katsuko; Matsuo, Ryoichi; Oda, Junro [Osaka City General Hospital (Japan); Inoue, Yuichi; Mochizuki, Kunizo; Yamada, Ryusaku

2001-12-01

The aims of this study were two: to compare the efficacy of fast MRI (breath-hold fast spin-echo T2-weighted and fast gradient-echo T1-weighted sequence) and ultrafast MRI (half-Fourier acquisition single-shot turbo spin-echo sequence) in evaluation of fetal central nervous system (CNS) abnormalities at late gestational age, and to compare the capability of fast MRI and ultrafast MRI to assess fetal CNS abnormalities with that of prenatal ultrasonography (US). Forty-nine women with fetuses at gestational ages of 26-39 weeks underwent fast MRI (29 patients) or ultrafast MRI (20 patients). In detection of motion artifact, visualization of the lateral and 4th ventricles, and differentiation between gray and white matter in cerebral hemispheres, ultrafast MRI was significantly superior to fast MRI (p<0.0001, Mann-Whitney U test). In 25 of 43 cases, US and MR diagnoses were the same and consistent with postnatal diagnosis. In 10 of 43 cases, MRI demonstrated findings additional to or different from those of US, and MR findings were confirmed postnatally. MRI, particularly ultrafast MRI, is useful for demonstrating CNS abnormalities in situations in which US is suggestive but not definitive. (author)

Ultrafast biophotonics

CERN Document Server

Vasa, P

2016-01-01

This book presents emerging contemporary optical techniques of ultrafast science which have opened entirely new vistas for probing biological entities and processes. The spectrum reaches from time-resolved imaging and multiphoton microscopy to cancer therapy and studies of DNA damage. The book displays interdisciplinary research at the interface of physics and biology. Emerging topics on the horizon are also discussed, like the use of squeezed light, frequency combs and terahertz imaging as the possibility of mimicking biological systems. The book is written in a manner to make it readily accessible to researchers, postgraduate biologists, chemists, engineers, and physicists and students of optics, biomedical optics, photonics and biotechnology.

Ultrafast photoelectron spectroscopy of small molecule organic films

Science.gov (United States)

Read, Kendall Laine

As research in the field of ultrafast optics has produced shorter and shorter pulses, at an ever-widening range of frequencies, ultrafast spectroscopy has grown correspondingly. In particular, ultrafast photoelectron spectroscopy allows direct observation of electrons in transient or excited states, regardless of the eventual relaxation mechanisms. High-harmonic conversion of 800nm, femtosecond, Ti:sapphire laser pulses allows excite/probe spectroscopy down into atomic core level states. To this end, an ultrafast, X-UV photoelectron spectroscopic system is described, including design considerations for the high-harmonic generation line, the time of flight detector, and the subsequent data collection electronics. Using a similar experimental setup, I have performed several ultrafast, photoelectron excited state decay studies at the IBM, T. J. Watson Research Center. All of the observed materials were electroluminescent thin film organics, which have applications as the emitter layer in organic light emitting devices. The specific materials discussed are: Alq, BAlq, DPVBi, and Alq doped with DCM or DMQA. Alq:DCM is also known to lase at low photoexcitation thresholds. A detailed understanding of the involved relaxation mechanisms is beneficial to both applications. Using 3.14 eV excite, and 26.7 eV probe, 90 fs laser pulses, we have observed the lowest unoccupied molecular orbital (LUMO) decay rate over the first 200 picoseconds. During this time, diffusion is insignificant, and all dynamics occur in the absence of electron transport. With excitation intensities in the range of 100μJ/cm2, we have modeled the Alq, BAlq, and DPVBi decays via bimolecular singlet-singlet annihilation. At similar excitations, we have modeled the Alq:DCM decay via Förster transfer, stimulated emission, and excimeric formation. Furthermore, the Alq:DCM occupied to unoccupied molecular orbital energy gap was seen to shrink as a function of excite-to-probe delay, in accordance with the

Ultrafast Holographic Image Recording by Single Shot Femtosecond Spectral Hole Burning

National Research Council Canada - National Science Library

Rebane, Aleksander

2001-01-01

.... This allowed us to record image holograms with 150-fs duration pulses without need to accumulate the SHB effect from many exposures. Results of this research show that it is possible to perform optical recording of data in frequency-domain on ultrafast time scale. These results can be used also as a new diagnostic tool for femtosecond dynamics in various ultrafast optical interactions.

Ultra-fast ipsilateral DPOAE adaptation not modulated by attention?

Science.gov (United States)

Dalhoff, Ernst; Zelle, Dennis; Gummer, Anthony W.

2018-05-01

Efferent stimulation of outer hair cells is supposed to attenuate cochlear amplification of sound waves and is accompanied by reduced DPOAE amplitudes. Recently, a method using two subsequent f2 pulses during presentation of a longer f1 pulse was introduced to measure fast ipsilateral adaptation effects on separated DPOAE components. Compensating primary-tone onsets for their latencies at the f2-tonotopic place, the average adaptation measured in four normal-hearing subjects was 5.0 dB with a time constant below 5 ms. In the present study, two experiments were performed to determine the origin of this ultra-fast ipsilateral adaptation effect. The first experiment measured ultra-fast ipsilateral adaptation using a two-pulse paradigm at three frequencies in the four subjects, while controlling for visual attention of the subjects. The other experiment also controlled for visual attention, but utilized a sequence of f2 short pulses in the presence of a continuous f1 tone to sample ipsilateral adaptation effects with longer time constants in eight subjects. In the first experiment, no significant change in the ultra-fast adaptation between non-directed attention and visual attention could be detected. In contrast, the second experiment revealed significant changes in the magnitude of the slower ipsilateral adaptation in the visual-attention condition. In conclusion, the lack of an attentional influence indicates that the ultra-fast ipsilateral DPOAE adaptation is not solely mediated by the medial olivocochlear reflex.

Nano structured materials studied by coherent X-ray diffraction

International Nuclear Information System (INIS)

Gulden, Johannes

2013-03-01

following chapter focuses on experiments carried out at synchrotron sources showing the potential of applying SAB-CDI to colloidal crystals. An experiment on GaAs nanowires proves the prospects of this method for other nano structured materials. To investigate dynamics, especially on the ultrafast time scale, FEL sources are needed. The next chapter therefore presents two experiments performed at the FLASH facility in Hamburg, showing that SAB-CDI can also be applied at FELs on an artificial crystal and an experiment performed on colloidal crystals to investigate the ultra fast dynamics with a pump-probe experiment. The technical advances in synchrotron radiation creation have opened the field to applications with the coherent part of the X-rays. The combination of iterative phase retrieval methods with crystallographic methods yields the unique opportunity to measure the internal structure of nano structured samples. This thesis gives an introduction into this exciting new field.

Nano structured materials studied by coherent X-ray diffraction

Energy Technology Data Exchange (ETDEWEB)

Gulden, Johannes

2013-03-15

following chapter focuses on experiments carried out at synchrotron sources showing the potential of applying SAB-CDI to colloidal crystals. An experiment on GaAs nanowires proves the prospects of this method for other nano structured materials. To investigate dynamics, especially on the ultrafast time scale, FEL sources are needed. The next chapter therefore presents two experiments performed at the FLASH facility in Hamburg, showing that SAB-CDI can also be applied at FELs on an artificial crystal and an experiment performed on colloidal crystals to investigate the ultra fast dynamics with a pump-probe experiment. The technical advances in synchrotron radiation creation have opened the field to applications with the coherent part of the X-rays. The combination of iterative phase retrieval methods with crystallographic methods yields the unique opportunity to measure the internal structure of nano structured samples. This thesis gives an introduction into this exciting new field.

Phosphorene in ultrafast laser field

Science.gov (United States)

Nematollahi, Fatemeh; Apalkov, Vadym; Stockman, Mark I.

2018-01-01

We study numerically interaction of phosphorene monolayer with a strong femtosecond-long optical pulse. For such a short pulse, the electron dynamics is coherent and can be described by the time-dependent Schrödinger equation. Strong optical field of the pulse causes redistribution of electrons between the conduction and valence bands. Such interband dynamics is highly irreversible, i.e., the conduction band population after the pulse is large and comparable to the maximum conduction band during the pulse. The conduction band population distribution in the reciprocal space shows high contrast hot spots, which are due to large interband coupling at the Γ point. The optical pulse also causes the net charge transfer through the phosphorene monolayer. The direction of the transfer is the same as the direction of the field maximum.

Advanced ultrafast fiber laser sources enabled by fiber nonlinearities

International Nuclear Information System (INIS)

Liu, Wei

2017-05-01

Development of high power/energy ultrafast fiber lasers for scientific research and industrial applications is one of the most exciting fields in ultrafast optics. This thesis demonstrated new means to improve two essential properties - which are indispensable for novel applications such as high-harmonic generation (HHG) and multiphoton microscopy (MPM) - of an ultrafast fiber laser system: energy scaling capability and wavelength tunability. High photon-flux extreme ultraviolet sources enabled by HHG desire high power (>100 W), high repetition-rate (>1 MHz) ultrafast driving laser sources. We have constructed from scratch a high-power Yb-fiber laser system using the well-known chirped-pulse amplification (CPA) technique. Such a CPA system capable of producing ∝200-W average power consists of a monolithic Yb-fiber oscillator, an all-fiber stretcher, a pre-amplifier chain, a main amplifier constructed from rode-type large pitch fiber, and a diffraction-grating based compressor. To increase the HHG efficiency, ultrafast pulses with duration 130-W average power. The amplified pulses are compressed to 60-fs pulses with 100-W average power, constituting a suitable HHG driving source. MPM is a powerful biomedical imaging tool, featuring larger penetration depth while providing the capability of optical sectioning. Although femtosecond solid-state lasers have been widely accepted as the standard option as MPM driving sources, fiber-based sources have received growing research efforts due to their superior performance. In the second part of this thesis, we both theoretically and experimentally demonstrated a new method of producing wavelength widely tunable femtosecond pulses for driving MPM. We employed self-phase modulation to broaden a narrowband spectrum followed by bandpass filters to select the rightmost/leftmost spectral lobes. Widely tunable in 820-1225 nm, the resulting sources generated nearly transform-limited, ∝100 fs pulses. Using short fibers with large

Combined passive detection and ultrafast active imaging of cavitation events induced by short pulses of high-intensity ultrasound.

Science.gov (United States)

Gateau, Jérôme; Aubry, Jean-François; Pernot, Mathieu; Fink, Mathias; Tanter, Mickaël

2011-03-01

The activation of natural gas nuclei to induce larger bubbles is possible using short ultrasonic excitations of high amplitude, and is required for ultrasound cavitation therapies. However, little is known about the distribution of nuclei in tissues. Therefore, the acoustic pressure level necessary to generate bubbles in a targeted zone and their exact location are currently difficult to predict. To monitor the initiation of cavitation activity, a novel all-ultrasound technique sensitive to single nucleation events is presented here. It is based on combined passive detection and ultrafast active imaging over a large volume using the same multi-element probe. Bubble nucleation was induced using a focused transducer (660 kHz, f-number = 1) driven by a high-power electric burst (up to 300 W) of one to two cycles. Detection was performed with a linear array (4 to 7 MHz) aligned with the single-element focal point. In vitro experiments in gelatin gel and muscular tissue are presented. The synchronized passive detection enabled radio-frequency data to be recorded, comprising high-frequency coherent wave fronts as signatures of the acoustic emissions linked to the activation of the nuclei. Active change detection images were obtained by subtracting echoes collected in the unnucleated medium. These indicated the appearance of stable cavitating regions. Because of the ultrafast frame rate, active detection occurred as quickly as 330 μs after the high-amplitude excitation and the dynamics of the induced regions were studied individually.

Octave-Spanning Mid-IR Supercontinuum Generation with Ultrafast Cascaded Nonlinearities

DEFF Research Database (Denmark)

Zhou, Binbin; Guo, Hairun; Liu, Xing

2014-01-01

An octave-spanning mid-IR supercontinuum is observed experimentally using ultrafast cascaded nonlinearities in an LiInS2 quadratic nonlinear crystal pumped with 70 fs energetic mid-IR pulses and cut for strongly phase-mismatched second-harmonic generation.......An octave-spanning mid-IR supercontinuum is observed experimentally using ultrafast cascaded nonlinearities in an LiInS2 quadratic nonlinear crystal pumped with 70 fs energetic mid-IR pulses and cut for strongly phase-mismatched second-harmonic generation....

Coherent phonon excitation and linear thermal expansion in structural dynamics and ultrafast electron diffraction of laser-heated metals.

Science.gov (United States)

Tang, Jau

2008-04-28

In this study, we examine the ultrafast structural dynamics of metals induced by a femtosecond laser-heating pulse as probed by time-resolved electron diffraction. Using the two-temperature model and the Grüneisen relationship we calculate the electron temperature, phonon temperature, and impulsive force at each atomic site in the slab. Together with the Fermi-Pasta-Ulam anharmonic chain model we calculate changes of bond distance and the peak shift of Bragg spots or Laue rings. A laser-heated thin slab is shown to exhibit "breathing" standing-wave behavior, with a period equal to the round-trip time for sound wave and a wavelength twice the slab thickness. The peak delay time first increases linearly with the thickness (linear thermal expansion due to lattice temperature jump are shown to contribute to the overall structural changes. Differences between these two mechanisms and their dependence on film thickness and other factors are discussed.

Mapping momentum-dependent electron-phonon coupling and nonequilibrium phonon dynamics with ultrafast electron diffuse scattering

Science.gov (United States)

Stern, Mark J.; René de Cotret, Laurent P.; Otto, Martin R.; Chatelain, Robert P.; Boisvert, Jean-Philippe; Sutton, Mark; Siwick, Bradley J.

2018-04-01

Despite their fundamental role in determining material properties, detailed momentum-dependent information on the strength of electron-phonon and phonon-phonon coupling (EPC and PPC, respectively) across the entire Brillouin zone has remained elusive. Here we demonstrate that ultrafast electron diffuse scattering (UEDS) directly provides such information. By exploiting symmetry-based selection rules and time resolution, scattering from different phonon branches can be distinguished even without energy resolution. Using graphite as a model system, we show that UEDS patterns map the relative EPC and PPC strength through their profound sensitivity to photoinduced changes in phonon populations. We measure strong EPC to the K -point TO phonon of A1' symmetry (K -A1' ) and along the entire TO branch between Γ -K , not only to the Γ -E2 g phonon. We also determine that the subsequent phonon relaxation of these strongly coupled optical phonons involve three stages: decay via several identifiable channels to TA and LA phonons (1 -2 ps), intraband thermalization of the non-equilibrium TA/LA phonon populations (30 -40 ps) and interband relaxation of the TA/LA modes (115 ps). Combining UEDS with ultrafast angle-resolved photoelectron spectroscopy will yield a complete picture of the dynamics within and between electron and phonon subsystems, helping to unravel complex phases in which the intertwined nature of these systems has a strong influence on emergent properties.

Ultrafast excited state relaxation in long-chain polyenes

International Nuclear Information System (INIS)

Antognazza, Maria Rosa; Lueer, Larry; Polli, Dario; Christensen, Ronald L.; Schrock, Richard R.; Lanzani, Guglielmo; Cerullo, Giulio

2010-01-01

Graphical abstract: Excited state dynamics of a long-chain polyene studied by femtosecond pump-probe spectroscopy. - Abstract: We present a comprehensive study, by femtosecond pump-probe spectroscopy, of excited state dynamics in a polyene that approaches the infinite chain limit. By excitation with sub-10-fs pulses resonant with the 0-0 S 0 → S 2 transition, we observe rapid loss of stimulated emission from the bright excited state S 2 , followed by population of the hot S 1 state within 150 fs. Vibrational cooling of S 1 takes place within 500 fs and is followed by decay back to S 0 with 1 ps time constant. By excitation with excess vibrational energy we also observe the ultrafast formation of a long-living absorption, that is assigned to the triplet state generated by singlet fission.

Coherence enhanced quantum metrology in a nonequilibrium optical molecule

Science.gov (United States)

Wang, Zhihai; Wu, Wei; Cui, Guodong; Wang, Jin

2018-03-01

We explore the quantum metrology in an optical molecular system coupled to two environments with different temperatures, using a quantum master equation beyond secular approximation. We discover that the steady-state coherence originating from and sustained by the nonequilibrium condition can enhance quantum metrology. We also study the quantitative measures of the nonequilibrium condition in terms of the curl flux, heat current and entropy production at the steady state. They are found to grow with temperature difference. However, an apparent paradox arises considering the contrary behaviors of the steady-state coherence and the nonequilibrium measures in relation to the inter-cavity coupling strength. This paradox is resolved by decomposing the heat current into a population part and a coherence part. Only the latter, the coherence part of the heat current, is tightly connected to the steady-state coherence and behaves similarly with respect to the inter-cavity coupling strength. Interestingly, the coherence part of the heat current flows from the low-temperature reservoir to the high-temperature reservoir, opposite to the direction of the population heat current. Our work offers a viable way to enhance quantum metrology for open quantum systems through steady-state coherence sustained by the nonequilibrium condition, which can be controlled and manipulated to maximize its utility. The potential applications go beyond quantum metrology and extend to areas such as device designing, quantum computation and quantum technology in general.

Photonic-assisted ultrafast THz wireless access

DEFF Research Database (Denmark)

Yu, Xianbin; Chen, Ying; Galili, Michael

THz technology has been considered feasible for ultrafast wireless data communi- cation, to meet the increasing demand on next-generation fast wireless access, e.g., huge data file transferring and fast mobile data stream access. This talk reviews recent progress in high-speed THz wireless...

Discrete decoding based ultrafast multidimensional nuclear magnetic resonance spectroscopy

International Nuclear Information System (INIS)

Wei, Zhiliang; Lin, Liangjie; Ye, Qimiao; Li, Jing; Cai, Shuhui; Chen, Zhong

2015-01-01

The three-dimensional (3D) nuclear magnetic resonance (NMR) spectroscopy constitutes an important and powerful tool in analyzing chemical and biological systems. However, the abundant 3D information arrives at the expense of long acquisition times lasting hours or even days. Therefore, there has been a continuous interest in developing techniques to accelerate recordings of 3D NMR spectra, among which the ultrafast spatiotemporal encoding technique supplies impressive acquisition speed by compressing a multidimensional spectrum in a single scan. However, it tends to suffer from tradeoffs among spectral widths in different dimensions, which deteriorates in cases of NMR spectroscopy with more dimensions. In this study, the discrete decoding is proposed to liberate the ultrafast technique from tradeoffs among spectral widths in different dimensions by focusing decoding on signal-bearing sites. For verifying its feasibility and effectiveness, we utilized the method to generate two different types of 3D spectra. The proposed method is also applicable to cases with more than three dimensions, which, based on the experimental results, may widen applications of the ultrafast technique

Discrete decoding based ultrafast multidimensional nuclear magnetic resonance spectroscopy

Science.gov (United States)

Wei, Zhiliang; Lin, Liangjie; Ye, Qimiao; Li, Jing; Cai, Shuhui; Chen, Zhong

2015-07-01

The three-dimensional (3D) nuclear magnetic resonance (NMR) spectroscopy constitutes an important and powerful tool in analyzing chemical and biological systems. However, the abundant 3D information arrives at the expense of long acquisition times lasting hours or even days. Therefore, there has been a continuous interest in developing techniques to accelerate recordings of 3D NMR spectra, among which the ultrafast spatiotemporal encoding technique supplies impressive acquisition speed by compressing a multidimensional spectrum in a single scan. However, it tends to suffer from tradeoffs among spectral widths in different dimensions, which deteriorates in cases of NMR spectroscopy with more dimensions. In this study, the discrete decoding is proposed to liberate the ultrafast technique from tradeoffs among spectral widths in different dimensions by focusing decoding on signal-bearing sites. For verifying its feasibility and effectiveness, we utilized the method to generate two different types of 3D spectra. The proposed method is also applicable to cases with more than three dimensions, which, based on the experimental results, may widen applications of the ultrafast technique.

Ultrafast photocurrents in monolayer MoS2

Science.gov (United States)

Parzinger, Eric; Wurstbauer, Ursula; Holleitner, Alexander W.

Two-dimensional transition metal dichalcogenides such as MoS2 have emerged as interesting materials for optoelectronic devices. In particular, the ultrafast dynamics and lifetimes of photoexcited charge carriers have attracted great interest during the last years. We investigate the photocurrent response of monolayer MoS2 on a picosecond time scale utilizing a recently developed pump-probe spectroscopy technique based on coplanar striplines. We discuss the ultrafast dynamics within MoS2 including photo-thermoelectric currents and the impact of built-in fields due to Schottky barriers as well as the Fermi level pinning at the contact region. We acknowledge support by the ERC via Project 'NanoREAL', the DFG via excellence cluster 'Nanosystems Initiative Munich' (NIM), and through the TUM International Graduate School of Science and Engineering (IGSSE) and BaCaTeC.

Coherent dynamics and terahertz emission in an asymmetric quantum well coupled to broadband infrared pulses

International Nuclear Information System (INIS)

Wu, B H; Cao, J C

2004-01-01

A selected intersubband transition in the asymmetric quantum well is theoretically proposed by using the superposition of two identical time delayed and phase shifted broadband pulses. Three conduction subbands in the semiconductor quantum well structure are optically coupled with the ultrafast infrared pulses. By adjusting the delay between these two pulses, the carriers at ground level can be selectively pumped to one of the upper levels, while the other upper level remains unoccupied. Thus selective transitions in the three level model can be manipulated by optical interference. At the same time, terahertz radiation will be emitted by coherent controlled charge oscillations. The phase and amplitude of THz radiation is found to be sensitive to the optical interference of the coupling pulses

Ultrafast spectroscopy of model biological membranes

NARCIS (Netherlands)

Ghosh, Avishek

2009-01-01

In this PhD thesis, I have described the novel time-resolved sum-frequency generation (TR-SFG) spectroscopic technique that I developed during the course of my PhD research and used it study the ultrafast vibrational, structural and orientational dynamics of water molecules at model biological

Effect of ballistic electrons on ultrafast thermomechanical responses of a thin metal film

International Nuclear Information System (INIS)

Xiong Qi-lin; Tian Xin

2017-01-01

The ultrafast thermomechanical coupling problem in a thin gold film irradiated by ultrashort laser pulses with different electron ballistic depths is investigated via the ultrafast thermoelasticity model. The solution of the problem is obtained by solving finite element governing equations. The comparison between the results of ultrafast thermomechanical coupling responses with different electron ballistic depths is made to show the ballistic electron effect. It is found that the ballistic electrons have a significant influence on the ultrafast thermomechanical coupling behaviors of the gold thin film and the best laser micromachining results can be achieved by choosing the specific laser technology (large or small ballistic range). In addition, the influence of simplification of the ultrashort laser pulse source on the results is studied, and it is found that the simplification has a great influence on the thermomechanical responses, which implies that care should be taken when the simplified form of the laser source term is applied as the Gaussian heat source. (paper)

Electromagnetically induced transparency and absorption due to optical and ground-state coherences in 6Li

International Nuclear Information System (INIS)

Fuchs, J; Duffy, G J; Rowlands, W J; Lezama, A; Hannaford, P; Akulshin, A M

2007-01-01

We present an experimental study of sub-natural width resonances in fluorescence from a collimated beam of 6 Li atoms excited on the D 1 and D 2 lines by a bichromatic laser field. We show that in addition to ground-state Zeeman coherence, coherent population oscillations between ground and excited states contribute to the sub-natural resonances. High-contrast resonances of electromagnetically induced transparency and electromagnetically induced absorption due to both effects, i.e., ground-state Zeeman coherence and coherent population oscillations, are observed

Dynamic regime of coherent population trapping and optimization of frequency modulation parameters in atomic clocks.

Science.gov (United States)

Yudin, V I; Taichenachev, A V; Basalaev, M Yu; Kovalenko, D V

2017-02-06

We theoretically investigate the dynamic regime of coherent population trapping (CPT) in the presence of frequency modulation (FM). We have formulated the criteria for quasi-stationary (adiabatic) and dynamic (non-adiabatic) responses of atomic system driven by this FM. Using the density matrix formalism for Λ system, the error signal is exactly calculated and optimized. It is shown that the optimal FM parameters correspond to the dynamic regime of atomic-field interaction, which significantly differs from conventional description of CPT resonances in the frame of quasi-stationary approach (under small modulation frequency). Obtained theoretical results are in good qualitative agreement with different experiments. Also we have found CPT-analogue of Pound-Driver-Hall regime of frequency stabilization.

Communication: Fully coherent quantum state hopping

Energy Technology Data Exchange (ETDEWEB)

Martens, Craig C., E-mail: cmartens@uci.edu [University of California, Irvine, California 92697-2025 (United States)

2015-10-14

In this paper, we describe a new and fully coherent stochastic surface hopping method for simulating mixed quantum-classical systems. We illustrate the approach on the simple but unforgiving problem of quantum evolution of a two-state quantum system in the limit of unperturbed pure state dynamics and for dissipative evolution in the presence of both stationary and nonstationary random environments. We formulate our approach in the Liouville representation and describe the density matrix elements by ensembles of trajectories. Population dynamics are represented by stochastic surface hops for trajectories representing diagonal density matrix elements. These are combined with an unconventional coherent stochastic hopping algorithm for trajectories representing off-diagonal quantum coherences. The latter generalizes the binary (0,1) “probability” of a trajectory to be associated with a given state to allow integers that can be negative or greater than unity in magnitude. Unlike existing surface hopping methods, the dynamics of the ensembles are fully entangled, correctly capturing the coherent and nonlocal structure of quantum mechanics.

Cutting-Edge High-Power Ultrafast Thin Disk Oscillators

Directory of Open Access Journals (Sweden)

Thomas Südmeyer

2013-04-01

Full Text Available A growing number of applications in science and industry are currently pushing the development of ultrafast laser technologies that enable high average powers. SESAM modelocked thin disk lasers (TDLs currently achieve higher pulse energies and average powers than any other ultrafast oscillator technology, making them excellent candidates in this goal. Recently, 275 W of average power with a pulse duration of 583 fs were demonstrated, which represents the highest average power so far demonstrated from an ultrafast oscillator. In terms of pulse energy, TDLs reach more than 40 μJ pulses directly from the oscillator. In addition, another major milestone was recently achieved, with the demonstration of a TDL with nearly bandwidth-limited 96-fs long pulses. The progress achieved in terms of pulse duration of such sources enabled the first measurement of the carrier-envelope offset frequency of a modelocked TDL, which is the first key step towards full stabilization of such a source. We will present the key elements that enabled these latest results, as well as an outlook towards the next scaling steps in average power, pulse energy and pulse duration of such sources. These cutting-edge sources will enable exciting new applications, and open the door to further extending the current performance milestones.

Ultrafast photoinduced charge separation in metal-semiconductor nanohybrids.

Science.gov (United States)

Mongin, Denis; Shaviv, Ehud; Maioli, Paolo; Crut, Aurélien; Banin, Uri; Del Fatti, Natalia; Vallée, Fabrice

2012-08-28

Hybrid nano-objects formed by two or more disparate materials are among the most promising and versatile nanosystems. A key parameter in their properties is interaction between their components. In this context we have investigated ultrafast charge separation in semiconductor-metal nanohybrids using a model system of gold-tipped CdS nanorods in a matchstick architecture. Experiments are performed using an optical time-resolved pump-probe technique, exciting either the semiconductor or the metal component of the particles, and probing the light-induced change of their optical response. Electron-hole pairs photoexcited in the semiconductor part of the nanohybrids are shown to undergo rapid charge separation with the electron transferred to the metal part on a sub-20 fs time scale. This ultrafast gold charging leads to a transient red-shift and broadening of the metal surface plasmon resonance, in agreement with results for free clusters but in contrast to observation for static charging of gold nanoparticles in liquid environments. Quantitative comparison with a theoretical model is in excellent agreement with the experimental results, confirming photoexcitation of one electron-hole pair per nanohybrid followed by ultrafast charge separation. The results also point to the utilization of such metal-semiconductor nanohybrids in light-harvesting applications and in photocatalysis.

Feasibility of UltraFast Doppler in Post-operative Evaluation of Hepatic Artery in Recipients following Liver Transplantation.

Science.gov (United States)

Kim, Se-Young; Kim, Kyoung Won; Choi, Sang Hyun; Kwon, Jae Hyun; Song, Gi-Won; Kwon, Heon-Ju; Yun, Young Ju; Lee, Jeongjin; Lee, Sung-Gyu

2017-11-01

To determine the feasibility of using UltraFast Doppler in post-operative evaluation of the hepatic artery (HA) after liver transplantation (LT), we evaluated 283 simultaneous conventional and UltraFast Doppler sessions in 126 recipients over a 2-mo period after LT, using an Aixplorer scanner The Doppler indexes of the HA (peak systolic velocity [PSV], end-diastolic velocity [EDV], resistive index [RI] and systolic acceleration time [SAT]) by retrospective analysis of retrieved waves from UltraFast Doppler clips were compared with those obtained by conventional spectral Doppler. Correlation, performance in diagnosing the pathologic wave, examination time and reproducibility were evaluated. The PSV, EDV, RI and SAT of spectral and UltraFast Doppler measurements exhibited excellent correlation with favorable diagnostic performance. During the bedside examination, the mean time spent for UltraFast clip storing was significantly shorter than that for conventional Doppler US measurements. Both conventional and UltraFast Doppler exhibited good to excellent inter-analysis consistency. In conclusion, compared with conventional spectral Doppler, UltraFast Doppler values correlated excellently and yielded acceptable pathologic wave diagnostic performance with reduced examination time at the bedside and excellent reproducibility. Copyright © 2017 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

High-speed ultrafast laser machining with tertiary beam positioning (Conference Presentation)

Science.gov (United States)

Yang, Chuan; Zhang, Haibin

2017-03-01

For an industrial laser application, high process throughput and low average cost of ownership are critical to commercial success. Benefiting from high peak power, nonlinear absorption and small-achievable spot size, ultrafast lasers offer advantages of minimal heat affected zone, great taper and sidewall quality, and small via capability that exceeds the limits of their predecessors in via drilling for electronic packaging. In the past decade, ultrafast lasers have both grown in power and reduced in cost. For example, recently, disk and fiber technology have both shown stable operation in the 50W to 200W range, mostly at high repetition rate (beyond 500 kHz) that helps avoid detrimental nonlinear effects. However, to effectively and efficiently scale the throughput with the fast-growing power capability of the ultrafast lasers while keeping the beneficial laser-material interactions is very challenging, mainly because of the bottleneck imposed by the inertia-related acceleration limit and servo gain bandwidth when only stages and galvanometers are being used. On the other side, inertia-free scanning solutions like acoustic optics and electronic optical deflectors have small scan field, and therefore not suitable for large-panel processing. Our recent system developments combine stages, galvanometers, and AODs into a coordinated tertiary architecture for high bandwidth and meanwhile large field beam positioning. Synchronized three-level movements allow extremely fast local speed and continuous motion over the whole stage travel range. We present the via drilling results from such ultrafast system with up to 3MHz pulse to pulse random access, enabling high quality low cost ultrafast machining with emerging high average power laser sources.

An improved ultrafast 2D NMR experiment: Towards atom-resolved real-time studies of protein kinetics at multi-Hz rates

International Nuclear Information System (INIS)

Gal, Maayan; Kern, Thomas; Schanda, Paul; Frydman, Lucio; Brutscher, Bernhard

2009-01-01

Multidimensional NMR spectroscopy is a well-established technique for the characterization of structure and fast-time-scale dynamics of highly populated ground states of biological macromolecules. The investigation of short-lived excited states that are important for molecular folding, misfolding and function, however, remains a challenge for modern biomolecular NMR techniques. Off-equilibrium real-time kinetic NMR methods allow direct observation of conformational or chemical changes by following peak positions and intensities in a series of spectra recorded during a kinetic event. Because standard multidimensional NMR methods required to yield sufficient atom-resolution are intrinsically time-consuming, many interesting phenomena are excluded from real-time NMR analysis. Recently, spatially encoded ultrafast 2D NMR techniques have been proposed that allow one to acquire a 2D NMR experiment within a single transient. In addition, when combined with the SOFAST technique, such ultrafast experiments can be repeated at high rates. One of the problems detected for such ultrafast protein NMR experiments is related to the heteronuclear decoupling during detection with interferences between the pulses and the oscillatory magnetic field gradients arising in this scheme. Here we present a method for improved ultrafast data acquisition yielding higher signal to noise and sharper lines in single-scan 2D NMR spectra. In combination with a fast-mixing device, the recording of 1 H- 15 N correlation spectra with repetition rates of up to a few Hertz becomes feasible, enabling real-time studies of protein kinetics occurring on time scales down to a few seconds

Face to phase: pitfalls in time delay estimation from coherency phase

NARCIS (Netherlands)

Campfens, S.F.; van der Kooij, Herman; Schouten, Alfred Christiaan

2014-01-01

Coherency phase is often interpreted as a time delay reflecting a transmission delay between spatially separated neural populations. However, time delays estimated from corticomuscular coherency are conflicting and often shorter than expected physiologically. Recent work suggests that

Ultrafast Photoinduced Electron Transfer in a π-Conjugated Oligomer/Porphyrin Complex

KAUST Repository

Aly, Shawkat Mohammede

2014-10-02

Controlling charge transfer (CT), charge separation (CS), and charge recombination (CR) at the donor-acceptor interface is extremely important to optimize the conversion efficiency in solar cell devices. In general, ultrafast CT and slow CR are desirable for optimal device performance. In this Letter, the ultrafast excited-state CT between platinum oligomer (DPP-Pt(acac)) as a new electron donor and porphyrin as an electron acceptor is monitored for the first time using femtosecond (fs) transient absorption (TA) spectroscopy with broad-band capability and 120 fs temporal resolution. Turning the CT on/off has been shown to be possible either by switching from an organometallic oligomer to a metal-free oligomer or by controlling the charge density on the nitrogen atom of the porphyrin meso unit. Our time-resolved data show that the CT and CS between DPP-Pt(acac) and cationic porphyrin are ultrafast (approximately 1.5 ps), and the CR is slow (ns time scale), as inferred from the formation and the decay of the cationic and anionic species. We also found that the metallic center in the DPP-Pt(acac) oligomer and the positive charge on the porphyrin are the keys to switching on/off the ultrafast CT process.

Manipulating Quantum Coherence in Solid State Systems

CERN Document Server

Flatté, Michael E; The NATO Advanced Study Institute "Manipulating Quantum Coherence in Solid State Systems"

2007-01-01

The NATO Advanced Study Institute "Manipulating Quantum Coherence in Solid State Systems", in Cluj-Napoca, Romania, August 29-September 9, 2005, presented a fundamental introduction to solid-state approaches to achieving quantum computation. This proceedings volume describes the properties of quantum coherence in semiconductor spin-based systems and the behavior of quantum coherence in superconducting systems. Semiconductor spin-based approaches to quantum computation have made tremendous advances in the past several years. Coherent populations of spins can be oriented, manipulated and detected experimentally. Rapid progress has been made towards performing the same tasks on individual spins (nuclear, ionic, or electronic) with all-electrical means. Superconducting approaches to quantum computation have demonstrated single qubits based on charge eigenstates as well as flux eigenstates. These topics have been presented in a pedagogical fashion by leading researchers in the fields of semiconductor-spin-based qu...

Progress in ultrafast intense laser science XIII

CERN Document Server

III, Wendell; Paulus, Gerhard

2017-01-01

This thirteenth volume covers a broad range of topics from this interdisciplinary research field, focusing on atoms, molecules, and clusters interacting in intense laser field and high-order harmonics generation and their applications. The PUILS series delivers up-to-date reviews of progress in Ultrafast Intense Laser Science, the interdisciplinary research field spanning atomic and molecular physics, molecular science, and optical science, which has been stimulated by the recent developments in ultrafast laser technologies. Each volume compiles peer-reviewed articles authored by researchers at the forefront of each their own subfields of UILS. Every chapter opens with an overview of the topics to be discussed, so that researchers unfamiliar to the subfield, as well as graduate students, can grasp the importance and attractions of the research topic at hand; these are followed by reports of cutting-edge discoveries.   .

Progress in ultrafast intense laser science XII

CERN Document Server

Roso, Luis; Li, Ruxin; Mathur, Deepak; Normand, Didier

2015-01-01

This  volume covers a broad range of topics focusing on atoms, molecules, and clusters interacting in intense laser field, laser induced filamentation, and laser plasma interaction and application. The PUILS series delivers up-to-date reviews of progress in Ultrafast Intense Laser Science, a newly emerging interdisciplinary research field spanning atomic and molecular physics, molecular science, and optical science, which has been stimulated by the recent developments in ultrafast laser technologies. Each volume compiles peer-reviewed articles authored by researchers at the forefront of each their own subfields of UILS. Every chapter opens with an overview of the topics to be discussed, so that researchers unfamiliar to the subfield, as well as graduate students, can grasp the importance and attractions of the research topic at hand; these are followed by reports of cutting-edge discoveries. .

Watching ultrafast responses of structure and magnetism in condensed matter with momentum-resolved probes

Directory of Open Access Journals (Sweden)

S. L. Johnson

2017-11-01

Full Text Available We present a non-comprehensive review of some representative experimental studies in crystalline condensed matter systems where the effects of intense ultrashort light pulses are probed using x-ray diffraction and photoelectron spectroscopy. On an ultrafast (sub-picosecond time scale, conventional concepts derived from the assumption of thermodynamic equilibrium must often be modified in order to adequately describe the time-dependent changes in material properties. There are several commonly adopted approaches to this modification, appropriate in different experimental circumstances. One approach is to treat the material as a collection of quasi-thermal subsystems in thermal contact with each other in the so-called “N-temperature” models. On the other extreme, one can also treat the time-dependent changes as fully coherent dynamics of a sometimes complex network of excitations. Here, we present examples of experiments that fall into each of these categories, as well as experiments that partake of both models. We conclude with a discussion of the limitations and future potential of these concepts.

Ultrafast electron diffraction with megahertz MeV electron pulses from a superconducting radio-frequency photoinjector

Energy Technology Data Exchange (ETDEWEB)

Feng, L. W.; Lin, L.; Huang, S. L.; Quan, S. W.; Hao, J. K.; Zhu, F.; Wang, F.; Liu, K. X., E-mail: kxliu@pku.edu.cn [Institute of Heavy Ion Physics and State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871 (China); Jiang, T.; Zhu, P. F.; Fu, F.; Wang, R.; Zhao, L.; Xiang, D., E-mail: dxiang@sjtu.edu.cn [Key Laboratory for Laser Plasmas (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); IFSA Collaborative Innovation Center, Shanghai Jiao Tong University, Shanghai 200240 (China)

2015-11-30

We report ultrafast relativistic electron diffraction operating at the megahertz repetition rate where the electron beam is produced in a superconducting radio-frequency (rf) photoinjector. We show that the beam quality is sufficiently high to provide clear diffraction patterns from gold and aluminium samples. With the number of electrons, several orders of magnitude higher than that from a normal conducting photocathode rf gun, such high repetition rate ultrafast MeV electron diffraction may open up many new opportunities in ultrafast science.

Advanced ultrafast fiber laser sources enabled by fiber nonlinearities

Energy Technology Data Exchange (ETDEWEB)

Liu, Wei

2017-05-15

Development of high power/energy ultrafast fiber lasers for scientific research and industrial applications is one of the most exciting fields in ultrafast optics. This thesis demonstrated new means to improve two essential properties - which are indispensable for novel applications such as high-harmonic generation (HHG) and multiphoton microscopy (MPM) - of an ultrafast fiber laser system: energy scaling capability and wavelength tunability. High photon-flux extreme ultraviolet sources enabled by HHG desire high power (>100 W), high repetition-rate (>1 MHz) ultrafast driving laser sources. We have constructed from scratch a high-power Yb-fiber laser system using the well-known chirped-pulse amplification (CPA) technique. Such a CPA system capable of producing ∝200-W average power consists of a monolithic Yb-fiber oscillator, an all-fiber stretcher, a pre-amplifier chain, a main amplifier constructed from rode-type large pitch fiber, and a diffraction-grating based compressor. To increase the HHG efficiency, ultrafast pulses with duration <60 fs are highly desired. We proposed and demonstrated a novel amplification technique, named as pre-chirp managed amplification (PCMA). We successfully constructed an Yb-fiber based PCMA system that outputs 75-MHz spectrally broadened pulses with >130-W average power. The amplified pulses are compressed to 60-fs pulses with 100-W average power, constituting a suitable HHG driving source. MPM is a powerful biomedical imaging tool, featuring larger penetration depth while providing the capability of optical sectioning. Although femtosecond solid-state lasers have been widely accepted as the standard option as MPM driving sources, fiber-based sources have received growing research efforts due to their superior performance. In the second part of this thesis, we both theoretically and experimentally demonstrated a new method of producing wavelength widely tunable femtosecond pulses for driving MPM. We employed self-phase modulation

Fast and ultrafast MR-imaging of the heart

International Nuclear Information System (INIS)

Schulthess, G.K. von; Davis, C.P.; Debatin, J.F.; McKinnon, G.C.

1995-01-01

MRI has been hampered by long image acquisition times. This combined with its non-realtime nature and the limited spatial resolution has made it difficult to extend MRT to the study of small cardiac structures. Recent technical improvements have made breath-held or realtime MRI feasible and thus laid the foundations for further applications in the field of cardiovascular imaging, notably MR coronary angiography, imaging of cardiac valve leaflets, as well as firstpass perfusion studies. Moreover ultrafast MR techniques may eventually replace conventional data acquisition strategies and thus drastically increase patient throughput by shortening acquisition time. This article provides an overview of the technical advances in MRI and their application to the cardiovascular system and discusses possibilities of combined ultrafast and interventional strategies. (orig.) [de

Quantum Computation with Ultrafast Laser Pulse Shaping

Indian Academy of Sciences (India)

Home; Journals; Resonance – Journal of Science Education; Volume 10; Issue 6. Quantum Computation with Ultrafast Laser Pulse Shaping. Debabrata Goswami. General Article Volume 10 Issue 6 June 2005 pp 8-14. Fulltext. Click here to view fulltext PDF. Permanent link:

Photoisomerization around a fulvene double bond: coherent population transfer to the electronic ground state?

Science.gov (United States)

Ioffe, Ilya; Dobryakov, Alexander L; Granovsky, Alexander A; Ernsting, Nikolaus P; Lustres, J Luis Pérez

2011-07-11

Photoisomerization around a central fulvene-type double bond is known to proceed through a conical intersection at the perpendicular geometry. The process is studied with an indenylidene-dihydropyridine model compound, allowing the use of visible excitation pulses. Transient absorption shows that 1) stimulated emission shifts to the red and loses oscillator strength on a 50 fs timescale, and 2) bleach recovery is highly nonexponential and not affected by solvent viscosity or methyl substitution at the dihydropyridine ring. Quantum-chemical calculations are used to explain point 1 as a result of initial elongation of the central C=C bond with mixing of S(2) and S(1) states. From point 2 it is concluded that internal conversion of S(1)→S(0) does not require torsional motion to the fully perpendicular state. The S(1) population appears to encounter a sink on the torsional coordinate before the conical intersection is reached. Rate equations cannot model the observed ground-state recovery adequately. Instead the dynamics are best described with a strongly damped oscillatory contribution, which could indicate coherent S(1)-S(0) population transfer. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Detection of coronary calcification in ultrafast CT compared to coronary angiography

International Nuclear Information System (INIS)

Koesling, S.; Hoffmann, U.; Rother, T.; Lieberenz, S.; Heywang-Koebrunner, S.H.; Schulz, H.G.

1994-01-01

The angiographical findings of 24 patients with coronary artery disease were compared with qualitative and quantitative detection of coronary calcification by ultrafast CT. Doubts concerning the capabilities of the ultrafast CT for a screening of coronary artery disease arise when the results of one third false positive and fase negative findings are considered. Variations in the quantification of coronary calcification were too great to allow a realistic assessment of the degree of stenosis of the coronary arteries. (orig.) [de

Propagation of complex shaped ultrafast pulses in highly optically dense samples

International Nuclear Information System (INIS)

Davis, J. C.; Fetterman, M. R.; Warren, W. S.; Goswami, D.

2008-01-01

We examine the propagation of shaped (amplitude- and frequency-modulated) ultrafast laser pulses through optically dense rubidium vapor. Pulse reshaping, stimulated emission dynamics, and residual electronic excitation all strongly depend on the laser pulse shape. For example, frequency swept pulses, which produce adiabatic passage in the optically thin limit (independent of the sign of the frequency sweep), behave unexpectedly in optically dense samples. Paraxial Maxwell optical Bloch equations can model our ultrafast pulse propagation results well and provide insight

Vibronic coupling explains the ultrafast carotenoid-to-bacteriochlorophyll energy transfer in natural and artificial light harvesters

Energy Technology Data Exchange (ETDEWEB)

Perlík, Václav; Seibt, Joachim; Šanda, František; Mančal, Tomáš [Institute of Physics, Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 5, Prague 121 16 (Czech Republic); Cranston, Laura J.; Cogdell, Richard J. [Institute of Molecular Cell and System Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow Biomedical Research Centre, 120 University Place, Glasgow G12 8TA, Scotland (United Kingdom); Lincoln, Craig N.; Hauer, Jürgen, E-mail: juergen.hauer@tuwien.ac.at [Photonics Institute, Vienna University of Technology, Gusshausstrasse 27, 1040 Vienna (Austria); Savolainen, Janne [Department of Physical Chemistry II, Ruhr-University Bochum, 44780 Bochum (Germany)

2015-06-07

The initial energy transfer steps in photosynthesis occur on ultrafast timescales. We analyze the carotenoid to bacteriochlorophyll energy transfer in LH2 Marichromatium purpuratum as well as in an artificial light-harvesting dyad system by using transient grating and two-dimensional electronic spectroscopy with 10 fs time resolution. We find that Förster-type models reproduce the experimentally observed 60 fs transfer times, but overestimate coupling constants, which lead to a disagreement with both linear absorption and electronic 2D-spectra. We show that a vibronic model, which treats carotenoid vibrations on both electronic ground and excited states as part of the system’s Hamiltonian, reproduces all measured quantities. Importantly, the vibronic model presented here can explain the fast energy transfer rates with only moderate coupling constants, which are in agreement with structure based calculations. Counterintuitively, the vibrational levels on the carotenoid electronic ground state play the central role in the excited state population transfer to bacteriochlorophyll; resonance between the donor-acceptor energy gap and the vibrational ground state energies is the physical basis of the ultrafast energy transfer rates in these systems.

Vibronic coupling explains the ultrafast carotenoid-to-bacteriochlorophyll energy transfer in natural and artificial light harvesters

International Nuclear Information System (INIS)

Perlík, Václav; Seibt, Joachim; Šanda, František; Mančal, Tomáš; Cranston, Laura J.; Cogdell, Richard J.; Lincoln, Craig N.; Hauer, Jürgen; Savolainen, Janne

2015-01-01

The initial energy transfer steps in photosynthesis occur on ultrafast timescales. We analyze the carotenoid to bacteriochlorophyll energy transfer in LH2 Marichromatium purpuratum as well as in an artificial light-harvesting dyad system by using transient grating and two-dimensional electronic spectroscopy with 10 fs time resolution. We find that Förster-type models reproduce the experimentally observed 60 fs transfer times, but overestimate coupling constants, which lead to a disagreement with both linear absorption and electronic 2D-spectra. We show that a vibronic model, which treats carotenoid vibrations on both electronic ground and excited states as part of the system’s Hamiltonian, reproduces all measured quantities. Importantly, the vibronic model presented here can explain the fast energy transfer rates with only moderate coupling constants, which are in agreement with structure based calculations. Counterintuitively, the vibrational levels on the carotenoid electronic ground state play the central role in the excited state population transfer to bacteriochlorophyll; resonance between the donor-acceptor energy gap and the vibrational ground state energies is the physical basis of the ultrafast energy transfer rates in these systems

Novel coherent supercontinuum light sources based on all-normal dispersion fibers

Energy Technology Data Exchange (ETDEWEB)

Heidt, Alexander

2011-07-05

The concept of broadband coherent supercontinuum (SC) generation in all-normal dispersion (ANDi) fibers in the near-infrared, visible and ultraviolet (UV) spectral regions is introduced and investigated in detail. In numerical studies, explicit design criteria are established for ANDi photonic crystal fiber (PCF) designs that allow the generation of flat and smooth ultrabroad spectral profiles without significant fine structure and with excellent stability and coherence properties. The key benefit of SC generation in ANDi fibers is the conservation of a single ultrashort pulse in the time domain with smooth and recompressible phase distribution. In the numerical investigation of the SC generation dynamics self-phase modulation and optical wave breaking are identified as the dominant nonlinear effects responsible for the nonlinear spectral broadening. It is further demonstrated that coherence properties, spectral bandwidth and temporal compressibility are independent of input pulse duration for constant peak power. The numerical predictions are in excellent agreement with experimental results obtained in two realizations of ANDi PCF optimized for the near-infrared and visible spectral region. In these experiments, the broadest SC spectrum generated in the normal dispersion regime of an optical fiber to date is achieved. The exceptional temporal properties of the generated SC pulses are verified experimentally and their applicability for the time-resolved study of molecular dynamics in ultrafast transient absorption spectroscopy is demonstrated. In an additional nonlinear pulse compression experiment, the SC pulses obtained in a short piece of ANDi PCF could be temporally recompressed to sub-two cycle durations by linear chirp compensation. Numerical simulations show that even shorter pulse durations with excellent quality can be achieved by full phase compensation. The concept is further extended into the UV spectral regime by considering tapered optical fibers with

OSA Trends in Optics and Photonics Series. Volume 13: Ultrafast Electronics and Optoelectronics

Science.gov (United States)

1997-01-01

tomography. Many materials such as plastics, cardboard, wood and rubber have good transparency in the terahertz frequency range. Hence, this new...Ultrafast processes in semiconductors. Introduction Nonlinear Bragg reflector ( NBR ) consists of periodically distributed optical nonlinearity coexisting...with multiple reflection and group-delay dispersion. Recent theoretical analyses showed the potential of NBR in ultrafast optoelectronics such as all

Ultrafast optical pump terahertz-probe spectroscopy of strongly correlated electron materials

International Nuclear Information System (INIS)

Averitt, R.D.; Taylor, Antoinette J.; Thorsmolle, V.K.; Jia, Quanxi; Lobad, A.I.; Trugman, S.A.

2001-01-01

We have used optical-pump far-infrared probe spectroscopy to probe the low energy electron dynamics of high temperature superconductors and colossal magnetoresistance manganites. For the superconductor YBa2Cu3O7, picosecond conductivity measurements probe the interplay between Cooper-pairs and quasiparticles. In optimally doped films, the recovery time for long-range phase-coherent pairing increases from ∼1.5 ps at 4K to ∼3.5 ps near Tc, consistent with the closing of the superconducting gap. For underdoped films, the measured recovery time is temperature independent (3.5 ps) in accordance with the presence of a pseudogap. Ultrafast picosecond measurements of optically induced changes in the absolute conductivity of La0:7M0:3MnO3 thin films (M = Ca, Sr) from 10K to ∼0.9Tc reveal a two-component relaxation. A fast, ∼2 ps, conductivity decrease arises from optically induced modification of the effective phonon temperature. The slower component, related to spin-lattice relaxation, has a lifetime that increases upon approaching Tc from below in accordance with an increasing spin specific heat. Our results indicate that for T<< Tc, the conductivity is determined by incoherent phonons while spin fluctuations dominate near Tc.

Progress in Ultrafast Intense Laser Science III

CERN Document Server

Yamanouchi, Kaoru; Agostini, Pierre; Ferrante, Gaetano

2008-01-01

The PUILS series presents Progress in Ultrafast Intense Laser Science, a newly emerging interdisciplinary research field spanning atomic and molecular physics, molecular science, and optical science. PUILS has been stimulated by the recent development of ultrafast laser technologies. Each volume contains approximately 15 chapters, authored by researchers at the forefront. Each chapter opens with an overview of the topics to be discussed, so that researchers, who are not experts in the specific topics, as well as graduate students can grasp the importance and attractions of this sub-field of research, and these are followed by reports of cutting-edge discoveries. This third volume covers a diverse range of disciplines, focusing on such topics as strong field ionization of atoms, ionization and fragmentation of molecules and clusters, generation of high-order harmonics and attosecond pulses, filamentation and laser plasma interaction, and the development of ultrashort and ultrahigh-intensity light sources.

Progress in Ultrafast Intense Laser Science VIII

CERN Document Server

Nisoli, Mauro; Hill, Wendell; III, III

2012-01-01

The PUILS series delivers up-to-date reviews of progress in Ultrafast Intense Laser Science, a newly emerging interdisciplinary research field spanning atomic and molecular physics, molecular science and optical science which has been stimulated by the recent developments in ultrafast laser technologies. Each volume compiles peer-reviewed articles authored by researchers at the forefront of each their own subfields of UILS. Every chapter opens with an overview of the topics to be discussed, so that researchers unfamiliar to the subfield as well as graduate students can grasp the importance and attractions of the research topic at hand. These are followed by reports of cutting-edge discoveries. This eighth volume covers a broad range of topics from this interdisciplinary research field, focusing on molecules interacting with ultrashort and intense laser fields, advanced technologies for the characterization of ultrashort laser pulses and their applications, laser plasma formation and laser acceleration.

Progress in Ultrafast Intense Laser Science VI

CERN Document Server

Yamanouchi, Kaoru; Bandrauk, André D

2010-01-01

The PUILS series delivers up-to-date reviews of progress in Ultrafast Intense Laser Science, a newly emerging interdisciplinary research field spanning atomic and molecular physics, molecular science, and optical science, which has been stimulated by the recent developments in ultrafast laser technologies. Each volume compiles peer-reviewed articles authored by researchers at the forefront of each their own subfields of UILS. Every chapter opens with an overview of the topics to be discussed, so that researchers unfamiliar to the subfield, as well as graduate students, can grasp the importance and attractions of the research topic at hand; these are followed by reports of cutting-edge discoveries. This sixth volume covers a broad range of topics from this interdisciplinary research field, focusing on responses of molecules to ultrashort intense laser pulses, generation and characterization of attosecond pulses and high-order harmonics, and filamentation and laser-plasma interaction.

Ultrafast time-resolved spectroscopy of xanthophylls at low temperature.

Science.gov (United States)

Cong, Hong; Niedzwiedzki, Dariusz M; Gibson, George N; Frank, Harry A

2008-03-20

Many of the spectroscopic features and photophysical properties of xanthophylls and their role in energy transfer to chlorophyll can be accounted for on the basis of a three-state model. The characteristically strong visible absorption of xanthophylls is associated with a transition from the ground state S0 (1(1)Ag-) to the S2 (1(1)Bu+) excited state. The lowest lying singlet state denoted S1 (2(1)Ag-), is a state into which absorption from the ground state is symmetry forbidden. Ultrafast optical spectroscopic studies and quantum computations have suggested the presence of additional excited singlet states in the vicinity of S1 (2(1)Ag-) and S2 (1(1)Bu+). One of these is denoted S* and has been suggested in previous work to be associated with a twisted molecular conformation of the molecule in the S1 (2(1)Ag-) state. In this work, we present the results of a spectroscopic investigation of three major xanthophylls from higher plants: violaxanthin, lutein, and zeaxanthin. These molecules have systematically increasing extents of pi-electron conjugation from nine to eleven conjugated carbon-carbon double bonds. All-trans isomers of the molecules were purified by high-performance liquid chromatography (HPLC) and studied by steady-state and ultrafast time-resolved optical spectroscopy at 77 K. Analysis of the data using global fitting techniques has revealed the inherent spectral properties and ultrafast dynamics of the excited singlet states of each of the molecules. Five different global fitting models were tested, and it was found that the data are best explained using a kinetic model whereby photoexcitation results in the promotion of the molecule into the S2 (1(1)Bu+) state that subsequently undergoes decay to a vibrationally hot S1 (1(1)Ag-) state and with the exception of violaxanthin also to the S* state. The vibrationally hot S1 (1(1)Ag-) state then cools to a vibrationally relaxed S1 (2(1)Ag-) state in less than a picosecond. It was also found that a portion

New ultrafast X-ray sources and their applications. Coherent ultrashort X UV emission by harmonic generation

International Nuclear Information System (INIS)

Salieres, P.; Le deroff, L.; Hergott, J.F.; Merdji, H.; Carre, B.

2000-01-01

By focusing an intense short-pulse laser into a rare gas jet, high-order harmonics of the laser frequency are generated. Considerable progress have been made in the last few years, with the observation of harmonic orders higher that 200, extending the emission down to 3 nm. Besides its fundamental interest, this XUV emission represents a new source with unique properties of coherence and ultrashort (femtosecond) duration. A growing number of applications are reported, ranging from atomic and molecular spectroscopy to solid-state and plasma physics. (authors)

Ultrafast comparison of personal genomes

OpenAIRE

Mauldin, Denise; Hood, Leroy; Robinson, Max; Glusman, Gustavo

2017-01-01

We present an ultra-fast method for comparing personal genomes. We transform the standard genome representation (lists of variants relative to a reference) into 'genome fingerprints' that can be readily compared across sequencing technologies and reference versions. Because of their reduced size, computation on the genome fingerprints is fast and requires little memory. This enables scaling up a variety of important genome analyses, including quantifying relatedness, recognizing duplicative s...

Parametric spectro-temporal analyzer (PASTA) for ultrafast optical performance monitoring

Science.gov (United States)

Zhang, Chi; Wong, Kenneth K. Y.

2013-12-01

Ultrafast optical spectrum monitoring is one of the most challenging tasks in observing ultrafast phenomena, such as the spectroscopy, dynamic observation of the laser cavity, and spectral encoded imaging systems. However, conventional method such as optical spectrum analyzer (OSA) spatially disperses the spectrum, but the space-to-time mapping is realized by mechanical rotation of a grating, so are incapable of operating at high speed. Besides the spatial dispersion, temporal dispersion provided by dispersive fiber can also stretches the spectrum in time domain in an ultrafast manner, but is primarily confined in measuring short pulses. In view of these constraints, here we present a real-time spectrum analyzer called parametric spectro-temporal analyzer (PASTA), which is based on the time-lens focusing mechanism. It achieves a 100-MHz frame rate and can measure arbitrary waveforms. For the first time, we observe the dynamic spectrum of an ultrafast swept-source: Fourier domain mode-locked (FDML) laser, and the spectrum evolution of a laser cavity during its stabilizing process. In addition to the basic single-lens structure, the multi-lens configurations (e.g. telescope or wide-angle scope) will provide a versatile operating condition, which can zoom in to achieve 0.05-nm resolution and zoom out to achieve 10-nm observation range, namely 17 times zoom in/out ratio. In view of the goal of achieving spectrum analysis with fine accuracy, PASTA provides a promising path to study the real-time spectrum of some dynamic phenomena and non-repetitive events, with orders of magnitude enhancement in the frame rate over conventional OSAs.

SAR image effects on coherence and coherence estimation.

Energy Technology Data Exchange (ETDEWEB)

Bickel, Douglas Lloyd

2014-01-01

Radar coherence is an important concept for imaging radar systems such as synthetic aperture radar (SAR). This document quantifies some of the effects in SAR which modify the coherence. Although these effects can disrupt the coherence within a single SAR image, this report will focus on the coherence between separate images, such as for coherent change detection (CCD) processing. There have been other presentations on aspects of this material in the past. The intent of this report is to bring various issues that affect the coherence together in a single report to support radar engineers in making decisions about these matters.

All-optical devices for ultrafast packet switching

DEFF Research Database (Denmark)

Dorren, H.J.S.; HerreraDorren, J.; Raz, O.

2007-01-01

We discuss integrated devices for all-optical packet switching. We focus on monolithically integrated all-optical flip-flops, ultra-fast semiconductor based wavelength converters and explain the operation principles. Finally, a 160 Gb/s all-optical packet switching experiment over 110 km of field...

rf streak camera based ultrafast relativistic electron diffraction.

Science.gov (United States)

Musumeci, P; Moody, J T; Scoby, C M; Gutierrez, M S; Tran, T

2009-01-01

We theoretically and experimentally investigate the possibility of using a rf streak camera to time resolve in a single shot structural changes at the sub-100 fs time scale via relativistic electron diffraction. We experimentally tested this novel concept at the UCLA Pegasus rf photoinjector. Time-resolved diffraction patterns from thin Al foil are recorded. Averaging over 50 shots is required in order to get statistics sufficient to uncover a variation in time of the diffraction patterns. In the absence of an external pump laser, this is explained as due to the energy chirp on the beam out of the electron gun. With further improvements to the electron source, rf streak camera based ultrafast electron diffraction has the potential to yield truly single shot measurements of ultrafast processes.

Real-time visualization of soliton molecules with evolving behavior in an ultrafast fiber laser

Science.gov (United States)

Liu, Meng; Li, Heng; Luo, Ai-Ping; Cui, Hu; Xu, Wen-Cheng; Luo, Zhi-Chao

2018-03-01

Ultrafast fiber lasers have been demonstrated to be great platforms for the investigation of soliton dynamics. The soliton molecules, as one of the most fascinating nonlinear phenomena, have been a hot topic in the field of nonlinear optics in recent years. Herein, we experimentally observed the real-time evolving behavior of soliton molecule in an ultrafast fiber laser by using the dispersive Fourier transformation technology. Several types of evolving soliton molecules were obtained in our experiments, such as soliton molecules with monotonically or chaotically evolving phase, flipping and hopping phase. These results would be helpful to the communities interested in soliton nonlinear dynamics as well as ultrafast laser technologies.

Ultrafast quenching of tryptophan fluorescence in proteins: Interresidue and intrahelical electron transfer

Energy Technology Data Exchange (ETDEWEB)

Qiu Weihong; Li Tanping; Zhang Luyuan; Yang Yi; Kao Yating; Wang Lijuan [Department of Physics, Chemistry, and Biochemistry, Program of Biophysics, Chemical Physics, and Biochemistry, Ohio State University, Columbus, OH 43210 (United States); Zhong Dongping [Department of Physics, Chemistry, and Biochemistry, Program of Biophysics, Chemical Physics, and Biochemistry, Ohio State University, Columbus, OH 43210 (United States)], E-mail: dongping@mps.ohio-state.edu

2008-06-23

Quenching of tryptophan fluorescence in proteins has been critical to the understanding of protein dynamics and enzyme reactions using tryptophan as a molecular optical probe. We report here our systematic examinations of potential quenching residues with more than 40 proteins. With site-directed mutation, we placed tryptophan to desired positions or altered its neighboring residues to screen quenching groups among 20 amino acid residues and of peptide backbones. With femtosecond resolution, we observed the ultrafast quenching dynamics within 100 ps and identified two ultrafast quenching groups, the carbonyl- and sulfur-containing residues. The former is glutamine and glutamate residues and the later is disulfide bond and cysteine residue. The quenching by the peptide-bond carbonyl group as well as other potential residues mostly occurs in longer than 100 ps. These ultrafast quenching dynamics occur at van der Waals distances through intraprotein electron transfer with high directionality. Following optimal molecular orbital overlap, electron jumps from the benzene ring of the indole moiety in a vertical orientation to the LUMO of acceptor quenching residues. Molecular dynamics simulations were invoked to elucidate various correlations of quenching dynamics with separation distances, relative orientations, local fluctuations and reaction heterogeneity. These unique ultrafast quenching pairs, as recently found to extensively occur in high-resolution protein structures, may have significant biological implications.

Characterization of irradiation damage distribution near TiO2/SrTiO3 interfaces using coherent acoustic phonon interferometry

International Nuclear Information System (INIS)

Yarotski, Dmitry; Yan Li; Jia Quanxi; Taylor, Antoinette J.; Fu Engang; Wang Yongqiang; Uberuaga, Blas P.

2012-01-01

We apply ultrafast coherent acoustic phonon interferometry to characterize the distribution of the radiation damage near the TiO 2 /SrTiO 3 interfaces. We show that the optical and mechanical properties of anatase TiO 2 remain unaffected by the radiation dosages in the 0.1÷5 dpa (displacements per atom) range, while the degraded optical response indicates a significant defect accumulation in the interfacial region of SrTiO 3 at 0.1 dpa and subsequent amorphization at 3 dpa. Comparison between the theoretical simulations and the experimental results reveals an almost threefold reduction of the sound velocity in the irradiated SrTiO 3 layer with peak damage levels of 3 and 5 dpa.

Electromagnetically induced absorption due to transfer of coherence and to transfer of population

International Nuclear Information System (INIS)

Goren, C.; Rosenbluh, M.; Wilson-Gordon, A.D.; Friedmann, H.

2003-01-01

The absorption spectrum of a weak probe, interacting with a driven degenerate two-level atomic system, whose ground and excited hyperfine states are F g,e , can exhibit narrow peaks at line center. When the pump and probe polarizations are different, F e =F g +1 and F g >0, the electromagnetically induced absorption (EIA) peak has been shown to be due to the transfer of coherence (TOC) between the excited and ground states via spontaneous decay. We give a detailed explanation of why the TOC that leads to EIA (EIA-TOC) can only take place when ground-state population trapping does not occur, that is, when F e =F g +1. We also explain why EIA-TOC is observed in open systems. We show that EIA can also occur when the pump and probe polarizations are identical and F e =F g +1. This EIA is analogous to an effect that occurs in simple two-level systems when the collisional transfer of population (TOP) from the ground state to a reservoir is greater than that from the excited state. For a degenerate two-level system, the reservoir consists of the Zeeman sublevels of the ground hyperfine state, and of other nearby hyperfine states that do not interact with the pump. We will also discuss the four-wave mixing spectrum under the conditions where EIA-TOC and EIA-TOP occur

Tracking Ultrafast Carrier Dynamics in Single Semiconductor Nanowire Heterostructures

Directory of Open Access Journals (Sweden)

Taylor A.J.

2013-03-01

Full Text Available An understanding of non-equilibrium carrier dynamics in silicon (Si nanowires (NWs and NW heterostructures is very important due to their many nanophotonic and nanoelectronics applications. Here, we describe the first measurements of ultrafast carrier dynamics and diffusion in single heterostructured Si nanowires, obtained using ultrafast optical microscopy. By isolating individual nanowires, we avoid complications resulting from the broad size and alignment distribution in nanowire ensembles, allowing us to directly probe ultrafast carrier dynamics in these quasi-one-dimensional systems. Spatially-resolved pump-probe spectroscopy demonstrates the influence of surface-mediated mechanisms on carrier dynamics in a single NW, while polarization-resolved femtosecond pump-probe spectroscopy reveals a clear anisotropy in carrier lifetimes measured parallel and perpendicular to the NW axis, due to density-dependent Auger recombination. Furthermore, separating the pump and probe spots along the NW axis enabled us to track space and time dependent carrier diffusion in radial and axial NW heterostructures. These results enable us to reveal the influence of radial and axial interfaces on carrier dynamics and charge transport in these quasi-one-dimensional nanosystems, which can then be used to tailor carrier relaxation in a single nanowire heterostructure for a given application.

The Ultrafast Wolff Rearrangement in the Gas Phase

Science.gov (United States)

Steinbacher, Andreas; Roeding, Sebastian; Brixner, Tobias; Nuernberger, Patrick

The Wolff rearrangement of gas-phase 5-diazo Meldrum's acid is disclosed with femtosecond ion spectroscopy. Distinct differences are found for 267 nm and 200 nm excitation, the latter leading to even two ultrafast rearrangement reactions.

Proposal to DOE Basic Energy Sciences Ultrafast X-ray science facility at the Advanced Light Source

CERN Document Server

Schönlein, R W; Alivisatos, A P; Belkacem, A; Berrah, N; Bozek, J; Bressler, C; Cavalleri, A; Chang, Z; Chergui, M; Falcone, R W; Glover, T E; Heimann, P A; Hepburn, J; Larsson, J; Lee, R W; McCusker, J; Padmore, H A; Pattison, P; Pratt, S T; Robin, D W; Schlüter, Ross D; Shank, C V; Wark, J; Zholents, A A; Zolotorev, M S

2001-01-01

We propose to develop a true user facility for ultrafast x-ray science at the Advanced Light Source. This facility will be unique in the world, and will fill a critical need for the growing ultrafast x-ray research community. The development of this facility builds upon the expertise from long-standing research efforts in ultrafast x-ray spectroscopy and the development of femtosecond x-ray sources and techniques at both the Lawrence Berkeley National Laboratory and at U.C. Berkeley. In particular, the technical feasibility of a femtosecond x-ray beamline at the ALS has already been demonstrated, and existing ultrafast laser technology will enable such a beamline to operate near the practical limit for femtosecond x-ray flux and brightness from a 3rd generation synchrotron.

Proposal to DOE Basic Energy Sciences: Ultrafast X-ray science facility at the Advanced Light Source

Energy Technology Data Exchange (ETDEWEB)

Schoenlein, Robert W.; Falcone, Roger W.; Abela, R.; Alivisatos, A.P.; Belkacem, A.; Berrah, N.; Bozek, J.; Bressler, C.; Cavalleri, A.; Chergui, M.; Glover, T.E.; Heimann, P.A.; Hepburn, J.; Larsson, J.; Lee, R.W.; McCusker, J.; Padmore, H.A.; Pattison, P.; Pratt, S.T.; Shank, C.V.; Wark, J.; Chang, Z.; Robin, D.W.; Schlueter, R.D.; Zholents, A.A.; Zolotorev, M.S.

2001-12-12

We propose to develop a true user facility for ultrafast x-ray science at the Advanced Light Source. This facility will be unique in the world, and will fill a critical need for the growing ultrafast x-ray research community. The development of this facility builds upon the expertise from long-standing research efforts in ultrafast x-ray spectroscopy and the development of femtosecond x-ray sources and techniques at both the Lawrence Berkeley National Laboratory and at U.C. Berkeley. In particular, the technical feasibility of a femtosecond x-ray beamline at the ALS has already been demonstrated, and existing ultrafast laser technology will enable such a beamline to operate near the practical limit for femtosecond x-ray flux and brightness from a 3rd generation synchrotron.

Proposal to DOE Basic Energy Sciences: Ultrafast X-ray science facility at the Advanced Light Source

International Nuclear Information System (INIS)

Schoenlein, Robert W.; Falcone, Roger W.; Abela, R.; Alivisatos, A.P.; Belkacem, A.; Berrah, N.; Bozek, J.; Bressler, C.; Cavalleri, A.; Chergui, M.; Glover, T.E.; Heimann, P.A.; Hepburn, J.; Larsson, J.; Lee, R.W.; McCusker, J.; Padmore, H.A.; Pattison, P.; Pratt, S.T.; Shank, C.V.; Wark, J.; Chang, Z.; Robin, D.W.; Schlueter, R.D.; Zholents, A.A.; Zolotorev, M.S.

2001-01-01

We propose to develop a true user facility for ultrafast x-ray science at the Advanced Light Source. This facility will be unique in the world, and will fill a critical need for the growing ultrafast x-ray research community. The development of this facility builds upon the expertise from long-standing research efforts in ultrafast x-ray spectroscopy and the development of femtosecond x-ray sources and techniques at both the Lawrence Berkeley National Laboratory and at U.C. Berkeley. In particular, the technical feasibility of a femtosecond x-ray beamline at the ALS has already been demonstrated, and existing ultrafast laser technology will enable such a beamline to operate near the practical limit for femtosecond x-ray flux and brightness from a 3rd generation synchrotron

Ultrafast X-Ray Spectroscopy of Conical Intersections

Science.gov (United States)

Neville, Simon P.; Chergui, Majed; Stolow, Albert; Schuurman, Michael S.

2018-06-01

Ongoing developments in ultrafast x-ray sources offer powerful new means of probing the complex nonadiabatically coupled structural and electronic dynamics of photoexcited molecules. These non-Born-Oppenheimer effects are governed by general electronic degeneracies termed conical intersections, which play a key role, analogous to that of a transition state, in the electronic-nuclear dynamics of excited molecules. Using high-level ab initio quantum dynamics simulations, we studied time-resolved x-ray absorption (TRXAS) and photoelectron spectroscopy (TRXPS) of the prototypical unsaturated organic chromophore, ethylene, following excitation to its S2(π π*) state. The TRXAS, in particular, is highly sensitive to all aspects of the ensuing dynamics. These x-ray spectroscopies provide a clear signature of the wave packet dynamics near conical intersections, related to charge localization effects driven by the nuclear dynamics. Given the ubiquity of charge localization in excited state dynamics, we believe that ultrafast x-ray spectroscopies offer a unique and powerful route to the direct observation of dynamics around conical intersections.

A PSF-shape-based beamforming strategy for robust 2D motion estimation in ultrafast data

NARCIS (Netherlands)

Saris, Anne E.C.M.; Fekkes, Stein; Nillesen, Maartje; Hansen, Hendrik H.G.; de Korte, Chris L.

2018-01-01

This paper presents a framework for motion estimation in ultrafast ultrasound data. It describes a novel approach for determining the sampling grid for ultrafast data based on the system's point-spread-function (PSF). As a consequence, the cross-correlation functions (CCF) used in the speckle

Hilbert-Schmidt quantum coherence in multi-qudit systems

Science.gov (United States)

Maziero, Jonas

2017-11-01

Using Bloch's parametrization for qudits ( d-level quantum systems), we write the Hilbert-Schmidt distance (HSD) between two generic n-qudit states as an Euclidean distance between two vectors of observables mean values in R^{Π_{s=1}nds2-1}, where ds is the dimension for qudit s. Then, applying the generalized Gell-Mann's matrices to generate SU(ds), we use that result to obtain the Hilbert-Schmidt quantum coherence (HSC) of n-qudit systems. As examples, we consider in detail one-qubit, one-qutrit, two-qubit, and two copies of one-qubit states. In this last case, the possibility for controlling local and non-local coherences by tuning local populations is studied, and the contrasting behaviors of HSC, l1-norm coherence, and relative entropy of coherence in this regard are noticed. We also investigate the decoherent dynamics of these coherence functions under the action of qutrit dephasing and dissipation channels. At last, we analyze the non-monotonicity of HSD under tensor products and report the first instance of a consequence (for coherence quantification) of this kind of property of a quantum distance measure.

Ultrafast optical responses of {beta}-carotene and lycopene probed by sub-20-fs time-resolved coherent spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Fujiwara, M.; Sugisaki, M. [CREST-JST and Department of Physics, Osaka City University, Osaka 558-8585 (Japan); Gall, A.; Robert, B. [CEA, Institut de Biologie et Technologies de Saclay, and CNRS, Gif-sur-Yvette F-91191 (France); Cogdell, R.J. [IBLS, Glasgow Biomedical Research Centre, University of Glasgow, Glasgow G12 8QQ, Scotland (United Kingdom); Hashimoto, H., E-mail: hassy@sci.osaka-cu.ac.j [CREST-JST and Department of Physics, Osaka City University, Osaka 558-8585 (Japan)

2009-12-15

We investigate how structural distortions in carotenoid cause decoherences of its high-frequency vibrational modes by applying the sub-20-fs time-resolved transient grating spectroscopy to {beta}-carotene and lycopene. The results indicate that the C=C central stretching mode shows significant loss of coherence under the effects of the steric hindrance between {beta}-ionone ring and polyene backbone, whereas the other high-frequency modes do not show such dependency on the structural distortions.

Ultrafast optical responses of β-carotene and lycopene probed by sub-20-fs time-resolved coherent spectroscopy

International Nuclear Information System (INIS)

Fujiwara, M.; Sugisaki, M.; Gall, A.; Robert, B.; Cogdell, R.J.; Hashimoto, H.

2009-01-01

We investigate how structural distortions in carotenoid cause decoherences of its high-frequency vibrational modes by applying the sub-20-fs time-resolved transient grating spectroscopy to β-carotene and lycopene. The results indicate that the C=C central stretching mode shows significant loss of coherence under the effects of the steric hindrance between β-ionone ring and polyene backbone, whereas the other high-frequency modes do not show such dependency on the structural distortions.

Fusion of Ultraviolet-Visible and Infrared Transient Absorption Spectroscopy Data to Model Ultrafast Photoisomerization.

Science.gov (United States)

Debus, Bruno; Orio, Maylis; Rehault, Julien; Burdzinski, Gotard; Ruckebusch, Cyril; Sliwa, Michel

2017-08-03

Ultrafast photoisomerization reactions generally start at a higher excited state with excess of internal vibrational energy and occur via conical intersections. This leads to ultrafast dynamics which are difficult to investigate with a single transient absorption spectroscopy technique, be it in the ultraviolet-visible (UV-vis) or infrared (IR) domain. On one hand, the information available in the UV-vis domain is limited as only slight spectral changes are observed for different isomers. On the other hand, the interpretation of vibrational spectra is strongly hindered by intramolecular relaxation and vibrational cooling. These limitations can be circumvented by fusing UV-vis and IR transient absorption spectroscopy data in a multiset multivariate curve resolution analysis. We apply this approach to describe the spectrodynamics of the ultrafast cis-trans photoisomerization around the C-N double bond observed for aromatic Schiff bases. Twisted intermediate states could be elucidated, and isomerization was shown to occur through a continuous complete rotation. More broadly, data fusion can be used to rationalize a vast range of ultrafast photoisomerization processes of interest in photochemistry.

High speed fluorescence imaging with compressed ultrafast photography

Science.gov (United States)

Thompson, J. V.; Mason, J. D.; Beier, H. T.; Bixler, J. N.

2017-02-01

Fluorescent lifetime imaging is an optical technique that facilitates imaging molecular interactions and cellular functions. Because the excited lifetime of a fluorophore is sensitive to its local microenvironment,1, 2 measurement of fluorescent lifetimes can be used to accurately detect regional changes in temperature, pH, and ion concentration. However, typical state of the art fluorescent lifetime methods are severely limited when it comes to acquisition time (on the order of seconds to minutes) and video rate imaging. Here we show that compressed ultrafast photography (CUP) can be used in conjunction with fluorescent lifetime imaging to overcome these acquisition rate limitations. Frame rates up to one hundred billion frames per second have been demonstrated with compressed ultrafast photography using a streak camera.3 These rates are achieved by encoding time in the spatial direction with a pseudo-random binary pattern. The time domain information is then reconstructed using a compressed sensing algorithm, resulting in a cube of data (x,y,t) for each readout image. Thus, application of compressed ultrafast photography will allow us to acquire an entire fluorescent lifetime image with a single laser pulse. Using a streak camera with a high-speed CMOS camera, acquisition rates of 100 frames per second can be achieved, which will significantly enhance our ability to quantitatively measure complex biological events with high spatial and temporal resolution. In particular, we will demonstrate the ability of this technique to do single-shot fluorescent lifetime imaging of cells and microspheres.

Ultrafast terahertz electrodynamics of photonic and electronic nanostructures

Energy Technology Data Exchange (ETDEWEB)

Luo, Liang [Iowa State Univ., Ames, IA (United States)

2015-01-01

This thesis summarizes my work on using ultrafast laser pulses to study Terahertz (THz) electrodynamics of photonic and electronic nanostructures and microstructures. Ultrafast timeresolved (optical, NIR, MIR, THz) pump-probe spectroscopy setup has been successfully built, which enables me to perform a series of relevant experiments. Firstly, a novel high e ciency and compact THz wave emitter based on split-ring-resonators has been developed and characterized. The emitter can be pumped at any wavelength by tailoring the magnetic resonance and could generate gapless THz waves covering the entire THz band. Secondly, two kinds of new photonic structures for THz wave manipulation have been successfully designed and characterized. One is based on the 1D and 2D photo-imprinted di ractive elements. The other is based on the photoexcited double-split-ring-resonator metamaterials. Both structures are exible and can modulate THz waves with large tunability. Thirdly, the dark excitons in semiconducting singlewalled carbon nanotubes are studied by optical pump and THz probe spectroscopy, which provides the rst insights into the THz responses of nonequilibrium excitonic correlations and dynamics from the dark ground states in carbon nanotubes. Next, several on-going projects are brie y presented such as the study of ultrafast THz dynamics of Dirac fermions in topological insulator Bi₂Se₃ with Mid-infrared excitation. Finally, the thesis ends with a summary of the completed experiments and an outlook of the future plan.

Demonstration of Ultra-Fast Switching in Nano metallic Resistive Switching Memory Devices

International Nuclear Information System (INIS)

Yang, Y.

2016-01-01

Interdependency of switching voltage and time creates a dilemma/obstacle for most resistive switching memories, which indicates low switching voltage and ultra-fast switching time cannot be simultaneously achieved. In this paper, an ultra-fast (sub-100 ns) yet low switching voltage resistive switching memory device (“nano metallic ReRAM”) was demonstrated. Experimental switching voltage is found independent of pulse width (intrinsic device property) when the pulse is long but shows abrupt time dependence (“cliff”) as pulse width approaches characteristic RC time of memory device (extrinsic device property). Both experiment and simulation show that the onset of cliff behavior is dependent on physical device size and parasitic resistance, which is expected to diminish as technology nodes shrink down. We believe this study provides solid evidence that nano metallic resistive switching memory can be reliably operated at low voltage and ultra-fast regime, thus beneficial to future memory technology.

Real-time observation of ultrafast electron injection at graphene–Zn porphyrin interfaces

KAUST Repository

Masih, Dilshad

2015-02-25

We report on the ultrafast interfacial electron transfer ( ET) between zinc( II) porphyrin ( ZnTMPyP) and negatively charged graphene carboxylate ( GC) using state- of- the- art femtosecond laser spectroscopy with broadband capabilities. The steady- state interaction between GC and ZnTMPyP results in a red- shifted absorption spectrum, providing a clear indication for the binding affinity between ZnTMPyP and GC via electrostatic and p- p stacking interactions. Ultrafast transient absorption ( TA) spectra in the absence and presence of three different GC concentrations reveal ( i) the ultrafast formation of singlet excited ZnTMPyP*, which partially relaxes into a long- lived triplet state, and ( ii) ET from the singlet excited ZnTMPyP* to GC, forming ZnTMPyP + and GC , as indicated by a spectral feature at 650- 750 nm, which is attributed to a ZnTMPyP radical cation resulting from the ET process.

Four-Dimensional Ultrafast Electron Microscopy: Insights into an Emerging Technique

KAUST Repository

Adhikari, Aniruddha

2016-12-15

Four-dimensional ultrafast electron microscopy (4D-UEM) is a novel analytical technique that aims to fulfill the long-held dream of researchers to investigate materials at extremely short spatial and temporal resolutions by integrating the excellent spatial resolution of electron microscopes with the temporal resolution of ultrafast femtosecond laser-based spectroscopy. The ingenious use of pulsed photoelectrons to probe surfaces and volumes of materials enables time-resolved snapshots of the dynamics to be captured in a way hitherto impossible by other conventional techniques. The flexibility of 4D-UEM lies in the fact that it can be used in both the scanning (S-UEM) and transmission (UEM) modes depending upon the type of electron microscope involved. While UEM can be employed to monitor elementary structural changes and phase transitions in samples using real-space mapping, diffraction, electron energy-loss spectroscopy, and tomography, S-UEM is well suited to map ultrafast dynamical events on materials surfaces in space and time. This review provides an overview of the unique features that distinguish these techniques and also illustrates the applications of both S-UEM and UEM to a multitude of problems relevant to materials science and chemistry.

Ultrafast Control of Magnetism in Ferromagnetic Semiconductors via Photoexcited Transient Carriers

Energy Technology Data Exchange (ETDEWEB)

Cotoros, Ingrid A. [Univ. of California, Berkeley, CA (United States)

2008-12-01

The field of spintronics offers perspectives for seamless integration of coupled and inter-tunable electrical and magnetic properties in a single device. For integration of the spin degree of freedom with current electronic technology, new semiconductors are needed that show electrically-tunable magnetic properties at room temperature and above. Dilute magnetic semiconductors derived from III-V compounds, like GaMnAs and InMnAs, show coupled and tunable magnetic, transport, and optical properties, due to the fact that their ferromagnetism is hole-mediated. These unconventional materials are ideal systems for manipulating the magnetic order by changing the carrier polarization, population density, and energy band distribution of the complementary subsystem of holes. This is the main theme we cover in this thesis. In particular, we develop a unique setup by use of ultraviolet pump, near-infrared probe femtosecond laser pulses, that allows for magneto-optical Kerr effect (MOKE) spectroscopy experiments. We photo-excite transient carriers in our samples, and measure the induced transient magnetization dynamics. One set of experiments performed allowed us to observe for the first time enhancement of the ferromagnetic order in GaMnAs, on an ultrafast time scale of hundreds of picoseconds. The corresponding transient increase of Curie temperature (Tc, the temperature above which a ferromagnetic material loses its permanent magnetism) of about 1 K for our experimental conditions is a very promising result for potential spintronics applications, especially since it is seconded by observation of an ultrafast ferromagnetic to paramagnetic phase transition above Tc. In a different set of experiments, we "write" the magnetization in a particular orientation in the sample plane. Using an ultrafast scheme, we alter the distribution of holes in the system and detect signatures of the particular memory state in the subsequent magnetization dynamics, with unprecedented hundreds of

Microwave-controlled ultrafast synthesis of uniform silver nanocubes and nanowires

Science.gov (United States)

Zhao, Tian; Fan, Jun-Bing; Cui, Jing; Liu, Jin-Hua; Xu, Xiao-Bo; Zhu, Ming-Qiang

2011-01-01

Synthesis of well-defined silver nanostructure in terms of size and shape has been strongly motivated by the requirements to their size- and shape-dependent optical properties which achieve their practical applications ranging from biosensing to catalysis and optics. In this Letter, an ultrafast synthetic process for the well-defined Ag nanocubes and nanowires have been developed, which simply involve the microwave-mediated polyol reduction of silver nitrate in ethylene glycol by adding different amount sodium sulfide (Na2S) into the solution. The possible growth and evolution process of the Ag nanocubes and nanowires involves the microwave ultrafast nucleation and growth followed by oxidative etching of Ag nanocrystals.

An ultrafast study of Zinc Phthalocyanine in DMSO

CSIR Research Space (South Africa)

Ombinda-Lemboumba, Saturnin

2010-10-01

Full Text Available The ultrafast dynamics of Zinc Phthalocyanine was studied using trasient absorption pump probe spectroscopy. Zinc Phthalocyanine was excited (pumped) at 672nm and probed by a white light continuum. The pump-probe technique used in this study...

Ultrafast Structural Dynamics in InSb Probed by Time-Resolved X-Ray Diffraction

International Nuclear Information System (INIS)

Chin, A.H.; Shank, C.V.; Chin, A.H.; Schoenlein, R.W.; Shank, C.V.; Glover, T.E.; Leemans, W.P.; Balling, P.

1999-01-01

Ultrafast structural dynamics in laser-perturbed InSb are studied using time-resolved x-ray diffraction with a novel femtosecond x-ray source. We report the first observation of a delay in the onset of lattice expansion, which we attribute to energy relaxation processes and lattice strain propagation. In addition, we observe direct indications of ultrafast disordering on a subpicosecond time scale. copyright 1999 The American Physical Society

Ultrafast, 2 min synthesis of monolayer-protected gold nanoclusters (d < 2 nm)

Science.gov (United States)

Martin, Matthew N.; Li, Dawei; Dass, Amala; Eah, Sang-Kee

2012-06-01

An ultrafast synthesis method is presented for hexanethiolate-coated gold nanoclusters (d gold nanoclusters are separated from the reaction byproducts fast and easily without any need for post-synthesis cleaning.An ultrafast synthesis method is presented for hexanethiolate-coated gold nanoclusters (d gold nanoclusters are separated from the reaction byproducts fast and easily without any need for post-synthesis cleaning. Electronic supplementary information (ESI) available: Experimental details of gold nanocluster synthesis and mass-spectrometry. See DOI: 10.1039/c2nr30890h

Dependence of adiabatic population transfer on pulse profile

Indian Academy of Sciences (India)

Control of population transfer by rapid adiabatic passage has been an established technique wherein the exact amplitude profile of the shaped pulse is considered to be insignificant. We study the effect of ultrafast shaped pulses for two-level systems, by density-matrix approach. However, we find that adiabaticity depends ...

Imaging nanoscale spatial modulation of a relativistic electron beam with a MeV ultrafast electron microscope

Science.gov (United States)

Lu, Chao; Jiang, Tao; Liu, Shengguang; Wang, Rui; Zhao, Lingrong; Zhu, Pengfei; Liu, Yaqi; Xu, Jun; Yu, Dapeng; Wan, Weishi; Zhu, Yimei; Xiang, Dao; Zhang, Jie

2018-03-01

An accelerator-based MeV ultrafast electron microscope (MUEM) has been proposed as a promising tool to the study structural dynamics at the nanometer spatial scale and the picosecond temporal scale. Here, we report experimental tests of a prototype MUEM where high quality images with nanoscale fine structures were recorded with a pulsed ˜3 MeV picosecond electron beam. The temporal and spatial resolutions of the MUEM operating in the single-shot mode are about 4 ps (FWHM) and 100 nm (FWHM), corresponding to a temporal-spatial resolution of 4 × 10-19 s m, about 2 orders of magnitude higher than that achieved with state-of-the-art single-shot keV UEM. Using this instrument, we offer the demonstration of visualizing the nanoscale periodic spatial modulation of an electron beam, which may be converted into longitudinal density modulation through emittance exchange to enable production of high-power coherent radiation at short wavelengths. Our results mark a great step towards single-shot nanometer-resolution MUEMs and compact intense x-ray sources that may have widespread applications in many areas of science.

Localized vibrations in superconducting YB a2C u3O7 revealed by ultrafast optical coherent spectroscopy

Science.gov (United States)

Novelli, Fabio; Giovannetti, Gianluca; Avella, Adolfo; Cilento, Federico; Patthey, Luc; Radovic, Milan; Capone, Massimo; Parmigiani, Fulvio; Fausti, Daniele

2017-05-01

The interaction between phonons and high-energy excitations of electronic origin in cuprates and their role in the superconducting mechanisms is still controversial. Here we use coherent vibrational time-domain spectroscopy together with density functional and dynamical mean-field theory calculations to establish a direct link between the c -axis phonon modes and the in-plane electronic charge excitations in optimally doped YB a2C u3O7 . The nonequilibrium Raman tensor is measured by means of the broadband "coherent-phonon" response in pump-probe experiments and is qualitatively described by our model using density functional theory in the frozen-phonon approximation plus single-band dynamical mean-field theory to account for the electronic correlations. The major outcome of our experimental and theoretical study is to establish the link between out-of-plane copper ion displacements and the in-plane electronic correlations, and to estimate at a few unit cells the correlation length of the associated phonon mode. The approach introduced here could help in revealing the complex interplay between fluctuations of different nature and spatial correlation in several strongly correlated materials.

"Ultra"-Fast Fracture Strength of Advanced Structural Ceramic Materials Studied at Elevated Temperatures

Science.gov (United States)

Choi, Sung R.; Gyekenyesi, John P.

1999-01-01

The accurate determination of inert strength is important in reliable life prediction of structural ceramic components. At ambient temperature, the inert strength of a brittle material is typically regarded as free of the effects of slow crack growth due to stress corrosion. Therefore, the inert strength can be determined either by eliminating active species, especially moisture, with an appropriate inert medium, or by using a very high test rate. However, at elevated temperatures, the concept or definition of the inert strength of brittle ceramic materials is not clear, since temperature itself is a degrading environment, resulting in strength degradation through slow crack growth and/or creep. Since the mechanism to control strength is rate-dependent viscous flow, the only conceivable way to determine the inert strength at elevated temperatures is to utilize a very fast test rate that either minimizes the time for or eliminates slow crack growth. Few experimental studies have measured the elevated-temperature, inert (or "ultra"-fast fracture) strength of advanced ceramics. At the NASA Lewis Research Center, an experimental study was initiated to better understand the "ultra"-fast fracture strength behavior of advanced ceramics at elevated temperatures. Fourteen advanced ceramics - one alumina, eleven silicon nitrides, and two silicon carbides - have been tested using constant stress-rate (dynamic fatigue) testing in flexure with a series of stress rates including the "ultra"-fast stress rate of 33 000 MPa/sec with digitally controlled test frames. The results for these 14 advanced ceramics indicate that, notwithstanding possible changes in flaw populations as well as flaw configurations because of elevated temperatures, the strength at 33 000 MPa/sec approached the room-temperature strength or reached a higher value than that determined at the conventional test rate of 30 MPa/sec. On the basis of the experimental data, it can be stated that the elevated

Ultrafast scanning tunneling microscopy

Energy Technology Data Exchange (ETDEWEB)

Botkin, D.A. [California Univ., Berkeley, CA (United States). Dept. of Physics]|[Lawrence Berkeley Lab., CA (United States)

1995-09-01

I have developed an ultrafast scanning tunneling microscope (USTM) based on uniting stroboscopic methods of ultrafast optics and scanned probe microscopy to obtain nanometer spatial resolution and sub-picosecond temporal resolution. USTM increases the achievable time resolution of a STM by more than 6 orders of magnitude; this should enable exploration of mesoscopic and nanometer size systems on time scales corresponding to the period or decay of fundamental excitations. USTM consists of a photoconductive switch with subpicosecond response time in series with the tip of a STM. An optical pulse from a modelocked laser activates the switch to create a gate for the tunneling current, while a second laser pulse on the sample initiates a dynamic process which affects the tunneling current. By sending a large sequence of identical pulse pairs and measuring the average tunnel current as a function of the relative time delay between the pulses in each pair, one can map the time evolution of the surface process. USTM was used to measure the broadband response of the STM`s atomic size tunnel barrier in frequencies from tens to hundreds of GHz. The USTM signal amplitude decays linearly with the tunnel junction conductance, so the spatial resolution of the time-resolved signal is comparable to that of a conventional STM. Geometrical capacitance of the junction does not appear to play an important role in the measurement, but a capacitive effect intimately related to tunneling contributes to the measured signals and may limit the ultimate resolution of the USTM.

Experiments with trapped ions and ultrafast laser pulses

Science.gov (United States)

Johnson, Kale Gifford

Since the dawn of quantum information science, laser-cooled trapped atomic ions have been one of the most compelling systems for the physical realization of a quantum computer. By applying qubit state dependent forces to the ions, their collective motional modes can be used as a bus to realize entangling quantum gates. Ultrafast state-dependent kicks [1] can provide a universal set of quantum logic operations, in conjunction with ultrafast single qubit rotations [2], which uses only ultrafast laser pulses. This may present a clearer route to scaling a trapped ion processor [3]. In addition to the role that spin-dependent kicks (SDKs) play in quantum computation, their utility in fundamental quantum mechanics research is also apparent. In this thesis, we present a set of experiments which demonstrate some of the principle properties of SDKs including ion motion independence (we demonstrate single ion thermometry from the ground state to near room temperature and the largest Schrodinger cat state ever created in an oscillator), high speed operations (compared with conventional atom-laser interactions), and multi-qubit entanglement operations with speed that is not fundamentally limited by the trap oscillation frequency. We also present a method to provide higher stability in the radial mode ion oscillation frequencies of a linear radiofrequency (rf) Paul trap-a crucial factor when performing operations on the rf-sensitive modes. Finally, we present the highest atomic position sensitivity measurement of an isolated atom to date of 0.5 nm Hz. (-1/2) with a minimum uncertaintyof 1.7 nm using a 0.6 numerical aperature (NA) lens system, along with a method to correct aberrations and a direct position measurement of ion micromotion (the inherent oscillations of an ion trapped in an oscillating rf field). This development could be used to directly image atom motion in the quantum regime, along with sensing forces at the yoctonewton [10. (-24) N)] scale forgravity sensing

Ultrafast terahertz scanning tunneling microscopy with atomic resolution

DEFF Research Database (Denmark)

Jelic, Vedran; Iwaszczuk, Krzysztof; Nguyen, Peter H.

2016-01-01

We demonstrate that ultrafast terahertz scanning tunneling microscopy (THz-STM) can probe single atoms on a silicon surface with simultaneous sub-nanometer and sub-picosecond spatio-temporal resolution. THz-STM is established as a new technique for exploring high-field non-equilibrium tunneling...

Ultrafast collinear scattering and carrier multiplication in graphene.

Science.gov (United States)

Brida, D; Tomadin, A; Manzoni, C; Kim, Y J; Lombardo, A; Milana, S; Nair, R R; Novoselov, K S; Ferrari, A C; Cerullo, G; Polini, M

2013-01-01

Graphene is emerging as a viable alternative to conventional optoelectronic, plasmonic and nanophotonic materials. The interaction of light with charge carriers creates an out-of-equilibrium distribution, which relaxes on an ultrafast timescale to a hot Fermi-Dirac distribution, that subsequently cools emitting phonons. Although the slower relaxation mechanisms have been extensively investigated, the initial stages still pose a challenge. Experimentally, they defy the resolution of most pump-probe setups, due to the extremely fast sub-100 fs carrier dynamics. Theoretically, massless Dirac fermions represent a novel many-body problem, fundamentally different from Schrödinger fermions. Here we combine pump-probe spectroscopy with a microscopic theory to investigate electron-electron interactions during the early stages of relaxation. We identify the mechanisms controlling the ultrafast dynamics, in particular the role of collinear scattering. This gives rise to Auger processes, including charge multiplication, which is key in photovoltage generation and photodetectors.

Ultrafast dynamics and laser action of organic semiconductors

CERN Document Server

Vardeny, Zeev Valy

2009-01-01

Spurred on by extensive research in recent years, organic semiconductors are now used in an array of areas, such as organic light emitting diodes (OLEDs), photovoltaics, and other optoelectronics. In all of these novel applications, the photoexcitations in organic semiconductors play a vital role. Exploring the early stages of photoexcitations that follow photon absorption, Ultrafast Dynamics and Laser Action of Organic Semiconductors presents the latest research investigations on photoexcitation ultrafast dynamics and laser action in pi-conjugated polymer films, solutions, and microcavities.In the first few chapters, the book examines the interplay of charge (polarons) and neutral (excitons) photoexcitations in pi-conjugated polymers, oligomers, and molecular crystals in the time domain of 100 fs-2 ns. Summarizing the state of the art in lasing, the final chapters introduce the phenomenon of laser action in organics and cover the latest optoelectronic applications that use lasing based on a variety of caviti...

Ultrafast optical ranging using microresonator soliton frequency combs

Science.gov (United States)

Trocha, P.; Karpov, M.; Ganin, D.; Pfeiffer, M. H. P.; Kordts, A.; Wolf, S.; Krockenberger, J.; Marin-Palomo, P.; Weimann, C.; Randel, S.; Freude, W.; Kippenberg, T. J.; Koos, C.

2018-02-01

Light detection and ranging is widely used in science and industry. Over the past decade, optical frequency combs were shown to offer advantages in optical ranging, enabling fast distance acquisition with high accuracy. Driven by emerging high-volume applications such as industrial sensing, drone navigation, or autonomous driving, there is now a growing demand for compact ranging systems. Here, we show that soliton Kerr comb generation in integrated silicon nitride microresonators provides a route to high-performance chip-scale ranging systems. We demonstrate dual-comb distance measurements with Allan deviations down to 12 nanometers at averaging times of 13 microseconds along with ultrafast ranging at acquisition rates of 100 megahertz, allowing for in-flight sampling of gun projectiles moving at 150 meters per second. Combining integrated soliton-comb ranging systems with chip-scale nanophotonic phased arrays could enable compact ultrafast ranging systems for emerging mass applications.

Ultrafast electron microscopy: Instrument response from the single-electron to high bunch-charge regimes

Science.gov (United States)

Plemmons, Dayne A.; Flannigan, David J.

2017-09-01

We determine the instrument response of an ultrafast electron microscope equipped with a conventional thermionic electron gun and absent modifications beyond the optical ports. Using flat, graphite-encircled LaB6 cathodes, we image space-charge effects as a function of photoelectron-packet population and find that an applied Wehnelt bias has a negligible effect on the threshold levels (>103 electrons per pulse) but does appear to suppress blurring at the upper limits (∼105 electrons). Using plasma lensing, we determine the instrument-response time for 700-fs laser pulses and find that single-electron packets are laser limited (1 ps), while broadening occurs well below the space-charge limit.

Ultrafast dynamic ellipsometry and spectroscopies of laser shocked materials

Energy Technology Data Exchange (ETDEWEB)

Mcgrane, Shawn David [Los Alamos National Laboratory; Bolme, Cindy B [Los Alamos National Laboratory; Whitley, Von H [Los Alamos National Laboratory; Moore, David S [Los Alamos National Laboratory

2010-01-01

Ultrafast ellipsometry and transient absorption spectroscopies are used to measure material dynamics under extreme conditions of temperature, pressure, and volumetric compression induced by shock wave loading with a chirped, spectrally clipped shock drive pulse.

Compression of Ultrafast Laser Beams

Science.gov (United States)

2016-03-01

Copyright 2003, AIP Publishing LLC. DOI: http://dx.doi.org/10.1063/1.1611998.) When designing the pulse shaper, the laser beam must completely fill the...for the design of future versions of this device. The easiest way to align the pulse shaper is to use the laser beam that will be shaped, without...Afterward, an ultrafast thin beam splitter is placed into the system after the diameter of the laser beam is reduced; this is done to monitor the beam

Coherence between harvest and habitat management -- Joint venture perspectives

Science.gov (United States)

Baxter, C.K.; Nelson, J.W.; Reinecke, K.J.; Stephens, S.E.

2006-01-01

Introduction: In recent months, an ad hoc group of waterfowl scientists, representing the International Association of Fish and Wildlife Agencies (IAFWA) Adaptive Harvest Management (ARM) Task Force and the North American Waterfowl Management Plan (NAWMP) Committee, have collaborated as a Joint Task Group (JTG) to assess options for unifying the population goals guiding waterfowl harvest management and habitat management. The JTG has been charged with bringing coherence to the population goals of the two programs. Characterizing the problem as one of coherence indicates value judgments exist regarding its significance or perhaps existence. For purposes of this paper, we characterize the lack of coherence as the absence of consistent population goals in the two related components of waterfowl conservation habitat and harvest management. Our purpose is to support continued dialogue on the respective goals of these programs and the possible implications of discordant goals to habitat joint ventures. Our objectives are two-fold: (1) illustrate how NAWMP habitat management goals and strategies have been interpreted and pursued in both breeding and wintering areas, and (2) provide perspectives on the linkages between regional habitat management programs and harvest management. The Lower Mississippi Valley and the Prairie Pothole joint ventures (LMVJV and PPJV, respectively) will be used as examples.

Ultrafast Dynamics of Quantum-Dot Semiconductor Optical Amplifiers

DEFF Research Database (Denmark)

Poel, Mike van der; Hvam, Jørn Märcher

2007-01-01

We report on a series of experiments on the dynamical properties of quantum-dot semiconductor optical amplifiers. We show how the amplifier responds to one or several ultrafast (170 fs) pulses in rapid succession and our results demonstrate applicability and ultimate limitations to application...

Partially coherent imaging and spatial coherence wavelets

International Nuclear Information System (INIS)

Castaneda, Roman

2003-03-01

A description of spatially partially coherent imaging based on the propagation of second order spatial coherence wavelets and marginal power spectra (Wigner distribution functions) is presented. In this dynamics, the spatial coherence wavelets will be affected by the system through its elementary transfer function. The consistency of the model with the both extreme cases of full coherent and incoherent imaging was proved. In the last case we obtained the classical concept of optical transfer function as a simple integral of the elementary transfer function. Furthermore, the elementary incoherent response function was introduced as the Fourier transform of the elementary transfer function. It describes the propagation of spatial coherence wavelets form each object point to each image point through a specific point on the pupil planes. The point spread function of the system was obtained by a simple integral of the elementary incoherent response function. (author)

Functional MRI of the patellofemoral joint: comparison of ultrafast MRI, motion-triggered cine MRI and static MRI

Energy Technology Data Exchange (ETDEWEB)

Muhle, C. [Klinik fuer Radiologische Diagnostik, Univ. Kiel (Germany); Brossmann, J. [Klinik fuer Radiologische Diagnostik, Univ. Kiel (Germany); Melchert, U.H. [Klinik fuer Radiologische Diagnostik, Univ. Kiel (Germany); Schroeder, C. [Radiologische Abt., Universitaets-Kinderklinik, Christian-Albrechts-Universitaet, Kiel (Germany); Boer, R. de [Philips Medical Systems, Best (Netherlands); Spielmann, R.P. [Klinik fuer Radiologische Diagnostik, Univ. Kiel (Germany); Heller, M. [Klinik fuer Radiologische Diagnostik, Univ. Kiel (Germany)

1995-12-31

To evaluate the feasibility and usefulness of ultrafast MRI (u), patellar tracking from 30 of flexion to knee extension (0 ) was analysed and compared with motion-triggered cine MRI (m) and a static MRI technique (s). The different imaging methods were compared in respect of the patellofemoral relationship, the examination time and image quality. Eight healthy subjects and four patients (in total 18 joints) with patellar subluxation or luxation were examined. Significant differences between the static MRI series without quadriceps contraction and the functional MRI studies (motion-triggered cine MRI and ultrafast MRI) were found for the patellar tilt angle. In the dynamic joint studies there was no statistical difference of the regression coefficients between the motion-triggered cine MRI studies and the ultrafast MRI studies. The findings of the functional MRI studies compared with the static MRI images were significantly different for the lateralisation of the patella, expressed by the lateral patellar displacement and bisect offset. No significant differences in patellar lateralisation were found between motion-triggered cine MRI and ultrafast MRI. Ultrafast MRI was superior to motion-triggered cine MRI in terms of the reduction in imaging time and improvement of the image quality. (orig.)

Functional MRI of the patellofemoral joint: comparison of ultrafast MRI, motion-triggered cine MRI and static MRI

International Nuclear Information System (INIS)

Muhle, C.; Brossmann, J.; Melchert, U.H.; Schroeder, C.; Boer, R. de; Spielmann, R.P.; Heller, M.

1995-01-01

To evaluate the feasibility and usefulness of ultrafast MRI (u), patellar tracking from 30 of flexion to knee extension (0 ) was analysed and compared with motion-triggered cine MRI (m) and a static MRI technique (s). The different imaging methods were compared in respect of the patellofemoral relationship, the examination time and image quality. Eight healthy subjects and four patients (in total 18 joints) with patellar subluxation or luxation were examined. Significant differences between the static MRI series without quadriceps contraction and the functional MRI studies (motion-triggered cine MRI and ultrafast MRI) were found for the patellar tilt angle. In the dynamic joint studies there was no statistical difference of the regression coefficients between the motion-triggered cine MRI studies and the ultrafast MRI studies. The findings of the functional MRI studies compared with the static MRI images were significantly different for the lateralisation of the patella, expressed by the lateral patellar displacement and bisect offset. No significant differences in patellar lateralisation were found between motion-triggered cine MRI and ultrafast MRI. Ultrafast MRI was superior to motion-triggered cine MRI in terms of the reduction in imaging time and improvement of the image quality. (orig.)

Time-resolved single-shot terahertz time-domain spectroscopy for ultrafast irreversible processes

Science.gov (United States)

Zhai, Zhao-Hui; Zhong, Sen-Cheng; Li, Jun; Zhu, Li-Guo; Meng, Kun; Li, Jiang; Liu, Qiao; Peng, Qi-Xian; Li, Ze-Ren; Zhao, Jian-Heng

2016-09-01

Pulsed terahertz spectroscopy is suitable for spectroscopic diagnostics of ultrafast events. However, the study of irreversible or single shot ultrafast events requires ability to record transient properties at multiple time delays, i.e., time resolved at single shot level, which is not available currently. Here by angular multiplexing use of femtosecond laser pulses, we developed and demonstrated a time resolved, transient terahertz time domain spectroscopy technique, where burst mode THz pulses were generated and then detected in a single shot measurement manner. The burst mode THz pulses contain 2 sub-THz pulses, and the time gap between them is adjustable up to 1 ns with picosecond accuracy, thus it can be used to probe the single shot event at two different time delays. The system can detect the sub-THz pulses at 0.1 THz-2.5 THz range with signal to noise ratio (SNR) of ˜400 and spectrum resolution of 0.05 THz. System design was described here, and optimizations of single shot measurement of THz pulses were discussed in detail. Methods to improve SNR were also discussed in detail. A system application was demonstrated where pulsed THz signals at different time delays of the ultrafast process were successfully acquired within single shot measurement. This time resolved transient terahertz time domain spectroscopy technique provides a new diagnostic tool for irreversible or single shot ultrafast events where dynamic information can be extracted at terahertz range within one-shot experiment.

Impact of local order and stoichiometry on the ultrafast magnetization dynamics of Heusler compounds

International Nuclear Information System (INIS)

Steil, Daniel; Schmitt, Oliver; Fetzer, Roman; Aeschlimann, Martin; Cinchetti, Mirko; Kubota, Takahide; Naganuma, Hiroshi; Oogane, Mikihiko; Ando, Yasuo; Rodan, Steven; Blum, Christian G F; Wurmehl, Sabine; Balke, Benjamin

2015-01-01

Nowadays, a wealth of information on ultrafast magnetization dynamics of thin ferromagnetic films exists in the literature. Information is, however, scarce on bulk single crystals, which may be especially important for the case of multi-sublattice systems. In Heusler compounds, representing prominent examples for such multi-sublattice systems, off-stoichiometry and degree of order can significantly change the magnetic properties of thin films, while bulk single crystals may be generally produced with a much more well-defined stoichiometry and a higher degree of ordering. A careful characterization of the local structure of thin films versus bulk single crystals combined with ultrafast demagnetization studies can, thus, help to understand the impact of stoichiometry and order on ultrafast spin dynamics.Here, we present a comparative study of the structural ordering and magnetization dynamics for thin films and bulk single crystals of the family of Heusler alloys with composition Co 2 Fe 1 − x Mn x Si. The local ordering is studied by 59 Co nuclear magnetic resonance (NMR) spectroscopy, while the time-resolved magneto-optical Kerr effect gives access to the ultrafast magnetization dynamics. In the NMR studies we find significant differences between bulk single crystals and thin films, both regarding local ordering and stoichiometry. The ultrafast magnetization dynamics, on the other hand, turns out to be mostly unaffected by the observed structural differences, especially on the time scale of some hundreds of femtoseconds. These results confirm hole-mediated spin-flip processes as the main mechanism for ultrafast demagnetization and the robustness of this demagnetization channel against defect states in the minority band gap as well as against the energetic position of the band gap with respect to the Fermi energy. The very small differences observed in the magnetization dynamics on the picosecond time-scale, on the other hand, can be explained by considering the

Ultrafast, laser-based, x-ray science: the dawn of atomic-scale cinematography

International Nuclear Information System (INIS)

Barty, C.P.J.

2000-01-01

The characteristics of ultrafast chirped pulse amplification systems are reviewed. Application of ultrafast chirped pulse amplification to the generation of femtosecond, incoherent, 8-keV line radiation is outlined and the use of femtosecond laser-based, x-rays for novel time-resolved diffraction studies of crystalline dynamics with sub-picosecond temporal resolution and sub-picometer spatial resolution is reviewed in detail. Possible extensions of laser-based, x-ray technology and evaluation of alternative x-ray approaches for time-resolved studies of the atomic scale dynamics are given. (author)

Ultrafast, laser-based, x-ray science: the dawn of atomic-scale cinematography

Energy Technology Data Exchange (ETDEWEB)

Barty, C.P.J. [University of California, Department of Applied Mechanics and Engineering Science, Urey Hall, Mali Code 0339, San Diego, La Jolla, CA (United States)

2000-03-01

The characteristics of ultrafast chirped pulse amplification systems are reviewed. Application of ultrafast chirped pulse amplification to the generation of femtosecond, incoherent, 8-keV line radiation is outlined and the use of femtosecond laser-based, x-rays for novel time-resolved diffraction studies of crystalline dynamics with sub-picosecond temporal resolution and sub-picometer spatial resolution is reviewed in detail. Possible extensions of laser-based, x-ray technology and evaluation of alternative x-ray approaches for time-resolved studies of the atomic scale dynamics are given. (author)

Ultrafast quantum control of ionization dynamics in krypton.

Science.gov (United States)

Hütten, Konrad; Mittermair, Michael; Stock, Sebastian O; Beerwerth, Randolf; Shirvanyan, Vahe; Riemensberger, Johann; Duensing, Andreas; Heider, Rupert; Wagner, Martin S; Guggenmos, Alexander; Fritzsche, Stephan; Kabachnik, Nikolay M; Kienberger, Reinhard; Bernhardt, Birgitta

2018-02-19

Ultrafast spectroscopy with attosecond resolution has enabled the real time observation of ultrafast electron dynamics in atoms, molecules and solids. These experiments employ attosecond pulses or pulse trains and explore dynamical processes in a pump-probe scheme that is selectively sensitive to electronic state of matter via photoelectron or XUV absorption spectroscopy or that includes changes of the ionic state detected via photo-ion mass spectrometry. Here, we demonstrate how the implementation of combined photo-ion and absorption spectroscopy with attosecond resolution enables tracking the complex multidimensional excitation and decay cascade of an Auger auto-ionization process of a few femtoseconds in highly excited krypton. In tandem with theory, our study reveals the role of intermediate electronic states in the formation of multiply charged ions. Amplitude tuning of a dressing laser field addresses different groups of decay channels and allows exerting temporal and quantitative control over the ionization dynamics in rare gas atoms.

The effect of solvent relaxation time constants on free energy gap law for ultrafast charge recombination following photoinduced charge separation.

Science.gov (United States)

Mikhailova, Valentina A; Malykhin, Roman E; Ivanov, Anatoly I

2018-05-16

To elucidate the regularities inherent in the kinetics of ultrafast charge recombination following photoinduced charge separation in donor-acceptor dyads in solutions, the simulations of the kinetics have been performed within the stochastic multichannel point-transition model. Increasing the solvent relaxation time scales has been shown to strongly vary the dependence of the charge recombination rate constant on the free energy gap. In slow relaxing solvents the non-equilibrium charge recombination occurring in parallel with solvent relaxation is very effective so that the charge recombination terminates at the non-equilibrium stage. This results in a crucial difference between the free energy gap laws for the ultrafast charge recombination and the thermal charge transfer. For the thermal reactions the well-known Marcus bell-shaped dependence of the rate constant on the free energy gap is realized while for the ultrafast charge recombination only a descending branch is predicted in the whole area of the free energy gap exceeding 0.2 eV. From the available experimental data on the population kinetics of the second and first excited states for a series of Zn-porphyrin-imide dyads in toluene and tetrahydrofuran solutions, an effective rate constant of the charge recombination into the first excited state has been calculated. The obtained rate constant being very high is nearly invariable in the area of the charge recombination free energy gap from 0.2 to 0.6 eV that supports the theoretical prediction.

Robust Stacking-Independent Ultrafast Charge Transfer in MoS2/WS2 Bilayers.

Science.gov (United States)

Ji, Ziheng; Hong, Hao; Zhang, Jin; Zhang, Qi; Huang, Wei; Cao, Ting; Qiao, Ruixi; Liu, Can; Liang, Jing; Jin, Chuanhong; Jiao, Liying; Shi, Kebin; Meng, Sheng; Liu, Kaihui

2017-12-26

Van der Waals-coupled two-dimensional (2D) heterostructures have attracted great attention recently due to their high potential in the next-generation photodetectors and solar cells. The understanding of charge-transfer process between adjacent atomic layers is the key to design optimal devices as it directly determines the fundamental response speed and photon-electron conversion efficiency. However, general belief and theoretical studies have shown that the charge transfer behavior depends sensitively on interlayer configurations, which is difficult to control accurately, bringing great uncertainties in device designing. Here we investigate the ultrafast dynamics of interlayer charge transfer in a prototype heterostructure, the MoS 2 /WS 2 bilayer with various stacking configurations, by optical two-color ultrafast pump-probe spectroscopy. Surprisingly, we found that the charge transfer is robust against varying interlayer twist angles and interlayer coupling strength, in time scale of ∼90 fs. Our observation, together with atomic-resolved transmission electron characterization and time-dependent density functional theory simulations, reveals that the robust ultrafast charge transfer is attributed to the heterogeneous interlayer stretching/sliding, which provides additional channels for efficient charge transfer previously unknown. Our results elucidate the origin of transfer rate robustness against interlayer stacking configurations in optical devices based on 2D heterostructures, facilitating their applications in ultrafast and high-efficient optoelectronic and photovoltaic devices in the near future.

Ultra-Fast Low Energy Switching Using an InP Photonic Crystal H0 Nanocavity

DEFF Research Database (Denmark)

Yu, Yi; Palushani, Evarist; Heuck, Mikkel

2013-01-01

Pump-probe measurements on InP photonic crystal H0 nanocavities show large-contrast ultrafast switching at low pulse energy. For large pulse energies, high-frequency carrier density oscillations are induced, leading to pulsesplitting.......Pump-probe measurements on InP photonic crystal H0 nanocavities show large-contrast ultrafast switching at low pulse energy. For large pulse energies, high-frequency carrier density oscillations are induced, leading to pulsesplitting....

Theory of coherent Stark nonlinear spectroscopy in a three-level system

International Nuclear Information System (INIS)

Loiko, Yurii; Serrat, Carles

2007-01-01

Coherent Stark nonlinear spectroscopy (CSNS) is a spectroscopic tool based on the cancellation of the phase sensitivity at frequency 5ω in the ultrafast four-wave mixing (FWM) of two-color pulses with frequencies ω and 3ω. We develop a theory for CSNS in three-level V-type systems, and reveal that the mechanism for the phase sensitivity at 5ω is the quantum interference between the two primary paths in the FWM of the ω and 3ω fields. We find that the cancellation phenomenon occurs when the probability amplitude of one of these two primary pathways becomes equal to zero due to the competition effect between the two allowed transitions in the V-type system. The analytical expressions that describe the phase-sensitivity phenomenon and the conditions for its cancellation have been derived on the basis of perturbation theory, and are confirmed by numerical integration of the density matrix and Maxwell equations. We argue that CSNS can be utilized, in particular, for the investigation of optically dense media

Lasing cavities and ultra-fast switch based on self-collimation of photonic crystal

International Nuclear Information System (INIS)

Zhao Deyin; Zhou Chuanhong; Gong Qian; Jiang Xunya

2008-01-01

The lasing cavities and ultra-fast switch based on the self-collimation (SC) of photonic crystal have been studied in this work. Some special properties of these devices are demonstrated, such as the higher quality factors and concise integration of the lasing cavities, the tolerance of the non-parallel reflectors in Fabry-Perot cavities. With nonlinearity, the ultra-fast switch can also be realized around the SC frequency. All these functional devices are designed based on the strong beam confinement of SC

Lasing cavities and ultra-fast switch based on self-collimation of photonic crystal

Energy Technology Data Exchange (ETDEWEB)

Zhao Deyin; Zhou Chuanhong; Gong Qian; Jiang Xunya [State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050 (China)], E-mail: xyjiang@mit.edu

2008-06-07

The lasing cavities and ultra-fast switch based on the self-collimation (SC) of photonic crystal have been studied in this work. Some special properties of these devices are demonstrated, such as the higher quality factors and concise integration of the lasing cavities, the tolerance of the non-parallel reflectors in Fabry-Perot cavities. With nonlinearity, the ultra-fast switch can also be realized around the SC frequency. All these functional devices are designed based on the strong beam confinement of SC.

Measuring and understanding ultrafast phenomena using X-rays

DEFF Research Database (Denmark)

Haldrup, Kristoffer; Nielsen, Martin Meedom

2014-01-01

Within the last decade, significant advances in X-ray sources and instrumentation as well as simultaneous developments in analysis methodology has allowed the field of fast- and ultrafast time-resolved X-ray studies of solution-state systems to truly come of age. We here describe some aspects of ...

An electronically tunable ultrafast laser source applied to fluorescence imaging and fluorescence lifetime imaging microscopy

International Nuclear Information System (INIS)

Dunsby, C; Lanigan, P M P; McGinty, J; Elson, D S; Requejo-Isidro, J; Munro, I; Galletly, N; McCann, F; Treanor, B; Oenfelt, B; Davis, D M; Neil, M A A; French, P M W

2004-01-01

Fluorescence imaging is used widely in microscopy and macroscopic imaging applications for fields ranging from biomedicine to materials science. A critical component for any fluorescence imaging system is the excitation source. Traditionally, wide-field systems use filtered thermal or arc-generated white light sources, while point scanning confocal microscope systems require spatially coherent (point-like) laser sources. Unfortunately, the limited range of visible wavelengths available from conventional laser sources constrains the design and usefulness of fluorescent probes in confocal microscopy. A 'hands-off' laser-like source, electronically tunable across the visible spectrum, would be invaluable for fluorescence imaging and provide new opportunities, e.g. automated excitation fingerprinting and in situ measurement of excitation cross-sections. Yet more information can be obtained using fluorescence lifetime imaging (FLIM), which requires that the light source be pulsed or rapidly modulated. We show how a white light continuum, generated by injecting femtosecond optical radiation into a micro-structured optical fibre, coupled with a simple prism-based tunable filter arrangement, can fulfil all these roles as a continuously electronically tunable (435-1150 nm) visible ultrafast light source in confocal, wide-field and FLIM systems

Ultrafast Non-Thermal Electron Dynamics in Single Layer Graphene

Directory of Open Access Journals (Sweden)

Novoselov K.S.

2013-03-01

Full Text Available We study the ultrafast dynamics of non-thermal electron relaxation in graphene upon impulsive excitation. The 10-fs resolution two color pump-probe allows us to unveil the non-equilibrium electron gas decay at early times.

Ultrafast Photovoltaic Response in Ferroelectric Nanolayers

Science.gov (United States)

2016-04-19

the free energy of the system [3,4,8]. Intensive research has been aimed at bypassing the intrinsic size limits imposed by the depolarization field...Page 1 of 21   Ultrafast photovoltaic response in ferroelectric nanolayers Dan Daranciang1,2, Matthew J. Highland3, Haidan Wen4, Steve M. Young5...ferroelectric PbTiO3 via direct coupling to its intrinsic photovoltaic response. Using time-resolved x-ray scattering to visualize atomic displacements on

Large lateral photovoltaic effect with ultrafast relaxation time in SnSe/Si junction

Energy Technology Data Exchange (ETDEWEB)

Wang, Xianjie; Zhao, Xiaofeng; Hu, Chang; Zhang, Yang; Song, Bingqian; Zhang, Lingli; Liu, Weilong; Lv, Zhe; Zhang, Yu; Sui, Yu, E-mail: suiyu@hit.edu.cn [Department of Physics, Harbin Institute of Technology, Harbin 150001 (China); Tang, Jinke [Department of Physics and Astronomy, University of Wyoming, Laramie, Wyoming 82071 (United States); Song, Bo, E-mail: songbo@hit.edu.cn [Department of Physics, Harbin Institute of Technology, Harbin 150001 (China); Academy of Fundamental and Interdisciplinary Sciences, Harbin Institute of Technology, Harbin 150001 (China)

2016-07-11

In this paper, we report a large lateral photovoltaic effect (LPE) with ultrafast relaxation time in SnSe/p-Si junctions. The LPE shows a linear dependence on the position of the laser spot, and the position sensitivity is as high as 250 mV mm{sup −1}. The optical response time and the relaxation time of the LPE are about 100 ns and 2 μs, respectively. The current-voltage curve on the surface of the SnSe film indicates the formation of an inversion layer at the SnSe/p-Si interface. Our results clearly suggest that most of the excited-electrons diffuse laterally in the inversion layer at the SnSe/p-Si interface, which results in a large LPE with ultrafast relaxation time. The high positional sensitivity and ultrafast relaxation time of the LPE make the SnSe/p-Si junction a promising candidate for a wide range of optoelectronic applications.

Ultrafast Charge Photogeneration in MEH-PPV Charge-Transfer Complexes

NARCIS (Netherlands)

Bakulin, Artem A.; Paraschuk, Dmitry Yu; Pshenichnikov, Maxim S.; van Loosdrecht, Paul H. M.; Corkum, P; DeSilvestri, S; Nelson, KA; Riedle, E; Schoenlein, RW

2009-01-01

Visible-pump - IR-probe spectroscopy is used to study the ultrafast charge dynamics in MEH-PPV based charge-transfer complexes and donor-acceptor blends. Transient anisotropy of the polymer polaron band provides invaluable insights into excitation localisation and charge-transfer pathways.

Intensified CCD for ultrafast diagnostics

International Nuclear Information System (INIS)

Cheng, J.; Tripp, G.; Coleman, L.

1978-01-01

Many of the present laser fusion diagnostics are recorded on either ultrafast streak cameras or on oscilloscopes. For those experiments in which a large volume of data is accumulated, direct computer processing of the information becomes important. We describe an approach which uses a RCA 52501 back-thinned CCD sensor to obtain direct electron readouts for both the streak camera and the CRT. Performance of the 100 GHz streak camera and the 4 GHz CRT are presented. Design parameters and computer interfacing for both systems are described in detail

Aneurysmatic dissection of an aberrant right subclavian artery; Disseziierendes Aneurysma einer aberranten Arteria subclavia dextra: Diagnose mittels Ultrafast-CT

Energy Technology Data Exchange (ETDEWEB)

Reittner, P. [Universitaetsklinik fuer Radiologie, Graz (Austria). Abt. fuer Allgemeine Radiologie; Stacher, R. [Universitaetsklinik fuer Radiologie, Graz (Austria). Abt. fuer Allgemeine Radiologie

1996-01-01

Diagnosis with Ultrafast-CT: An aneurysm of an aberrant right subclavian artery is a very rare cause for dysphagia. We describe such a case in a 67-year-old patient, diagnosed with Ultrafast-CT and discuss it together in concert with the embryology and the radiological findings. (orig.) [Deutsch] Eine aberrierende Arteria subclavia dextra ist eine seltene Ursache fuer Dysphagie. Anhand eines 67jaehrigen Patienten werden Embryologie und radiologische Charakteristika, diagnostiziert mittels Ultrafast-CT, diskutiert. (orig.)

Evaluation of the product ratio coherent model in forecasting mortality rates and life expectancy at births by States

Science.gov (United States)

Shair, Syazreen Niza; Yusof, Aida Yuzi; Asmuni, Nurin Haniah

2017-05-01

Coherent mortality forecasting models have recently received increasing attention particularly in their application to sub-populations. The advantage of coherent models over independent models is the ability to forecast a non-divergent mortality for two or more sub-populations. One of the coherent models was recently developed by [1] known as the product-ratio model. This model is an extension version of the functional independent model from [2]. The product-ratio model has been applied in a developed country, Australia [1] and has been extended in a developing nation, Malaysia [3]. While [3] accounted for coherency of mortality rates between gender and ethnic group, the coherency between states in Malaysia has never been explored. This paper will forecast the mortality rates of Malaysian sub-populations according to states using the product ratio coherent model and its independent version— the functional independent model. The forecast accuracies of two different models are evaluated using the out-of-sample error measurements— the mean absolute forecast error (MAFE) for age-specific death rates and the mean forecast error (MFE) for the life expectancy at birth. We employ Malaysian mortality time series data from 1991 to 2014, segregated by age, gender and states.

Multilayer-WS2:ferroelectric composite for ultrafast tunable metamaterial-induced transparency applications

Science.gov (United States)

Yang, Xiaoyu; Yang, Jinghuan; Hu, Xiaoyong; Zhu, Yu; Yang, Hong; Gong, Qihuang

2015-08-01

An ultrafast and low-power all-optical tunable metamaterial-induced transparency is realized, using polycrystalline barium titanate doped gold nanoparticles and multilayer tungsten disulfide microsheets as nonlinear optical materials. Large nonlinearity enhancement is obtained associated with quantum confinement effect, local-field effect, and reinforced interaction between light and multilayer tungsten disulfide. Low threshold pump intensity of 20 MW/cm2 is achieved. An ultrafast response time of 85 ps is maintained because of fast carrier relaxation dynamics in nanoscale crystal grains of polycrystalline barium titanate. This may be useful for the study of integrated photonic devices based on two-dimensional materials.

Multilayer-WS2:ferroelectric composite for ultrafast tunable metamaterial-induced transparency applications

International Nuclear Information System (INIS)

Yang, Xiaoyu; Yang, Jinghuan; Zhu, Yu; Yang, Hong; Hu, Xiaoyong; Gong, Qihuang

2015-01-01

An ultrafast and low-power all-optical tunable metamaterial-induced transparency is realized, using polycrystalline barium titanate doped gold nanoparticles and multilayer tungsten disulfide microsheets as nonlinear optical materials. Large nonlinearity enhancement is obtained associated with quantum confinement effect, local-field effect, and reinforced interaction between light and multilayer tungsten disulfide. Low threshold pump intensity of 20 MW/cm 2 is achieved. An ultrafast response time of 85 ps is maintained because of fast carrier relaxation dynamics in nanoscale crystal grains of polycrystalline barium titanate. This may be useful for the study of integrated photonic devices based on two-dimensional materials

Theory of pump–probe ultrafast photoemission and X-ray absorption spectra

Energy Technology Data Exchange (ETDEWEB)

Fujikawa, Takashi, E-mail: tfujikawa@faculty.chiba-u.jp; Niki, Kaori

2016-01-15

Highlights: • Pump–probe ultrafast XAFS and XPS spectra are theoretically studied. • Keldysh Green's function theory is applied. • Important many-body effects are explicitly included. - Abstract: Keldysh Green's function approach is extensively used in order to derive practical formulas to analyze pump–probe ultrafast photoemission and X-ray absorption spectra. Here the pump pulse is strong enough whereas the probe X-ray pulse can be treated by use of a perturbation theory. We expand full Green's function in terms of renormalized Green's function without the interaction between electrons and probe pulse. The present theoretical formulas allow us to handle the intrinsic and extrinsic losses, and furthermore resonant effects in X-ray Absorption Fine Structures (XAFS). To understand the radiation field screening in XPS spectra, we have to use more sophisticated theoretical approach. In the ultrafast XPS and XAFS analyses the intrinsic and extrinsic loss effects can interfere as well. In the XAFS studies careful analyses are necessary to handle extrinsic losses in terms of damped photoelectron propagation. The nonequilibrium dynamics after the pump pulse irradiation is well described by use of the time-dependent Dyson orbitals. Well above the edge threshold, ultrafast photoelectron diffraction and extended X-ray absorption fine structure (EXAFS) provide us with transient structural change after the laser pump excitations. In addition to these slow processes, the rapid oscillation in time plays an important role related to pump electronic excitations. Near threshold detailed information could be obtained for the combined electronic and structural dynamics. In particular high-energy photoemission and EXAFS are not so influenced by the details of excited states by pump pulse. Random-Phase Approximation (RPA)-boson approach is introduced to derive some practical formulas for time-dependent intrinsic amplitudes.

Hot-electrons-induced ultrafast demagnitization in Co/Pt multilayers

NARCIS (Netherlands)

Bergeard, N.; Hehn, M.; Mangin, S.; Lengaigne, G.; Montaigne, F.; Lalieu, M. L. M.; Koopmans, B.; Malinowski, G.

2016-01-01

Using specially engineered structures to tailor the optical absorption in a metallic multilayer, we analyze the magnetization dynamics of a Co/Pt multilayer buried below a thick Cu layer. We demonstrate that hot electrons alone can very efficiently induce ultrafast demagnetization. Simulations based

Field transients of coherent terahertz synchrotron radiation accessed via time-resolving and correlation techniques

Energy Technology Data Exchange (ETDEWEB)

Pohl, A.; Hübers, H.-W. [Humboldt-Universität zu Berlin, Institute of Physics, Newtonstraße 15, 12489 Berlin (Germany); Institute of Optical Sensor Systems, German Aerospace Center (DLR), Rutherfordstrasse 29, 12489 Berlin (Germany); Semenov, A. [Institute of Optical Sensor Systems, German Aerospace Center (DLR), Rutherfordstrasse 29, 12489 Berlin (Germany); Hoehl, A.; Ulm, G. [Physikalisch-Technische Bundesanstalt (PTB), Abbestraße 2-12, 10587 Berlin (Germany); Ries, M.; Wüstefeld, G. [Helmholz-Zentrum Berlin, Albert-Einstein-Str. 15, 12489 Berlin (Germany); Ilin, K.; Thoma, P.; Siegel, M. [Institute of Micro- and Nanoelectronic Systems, Karlsruhe Institute of Technology (KIT), Hertzstrasse 16, 76187 Karlsruhe (Germany)

2016-03-21

Decaying oscillations of the electric field in repetitive pulses of coherent synchrotron radiation in the terahertz frequency range was evaluated by means of time-resolving and correlation techniques. Comparative analysis of real-time voltage transients of the electrical response and interferograms, which were obtained with an ultrafast zero-bias Schottky diode detector and a Martin-Puplett interferometer, delivers close values of the pulse duration. Consistent results were obtained via the correlation technique with a pair of Golay Cell detectors and a pair of resonant polarisation-sensitive superconducting detectors integrated on one chip. The duration of terahertz synchrotron pulses does not closely correlate with the duration of single-cycle electric field expected for the varying size of electron bunches. We largely attribute the difference to the charge density oscillations in electron bunches and to the low-frequency spectral cut-off imposed by both the synchrotron beamline and the coupling optics of our detectors.

A spectroelectrochemical cell for ultrafast two-dimensional infrared spectroscopy

Energy Technology Data Exchange (ETDEWEB)

El Khoury, Youssef; Van Wilderen, Luuk J. G. W.; Vogt, Tim; Winter, Ernst; Bredenbeck, Jens, E-mail: bredenbeck@biophysik.uni-frankfurt.org, E-mail: bredenbeck@biophysik.uni-frankfurt.de [Institut für Biophysik, Johann Wolfgang Goethe-Universität, Max-von-Laue-Strasse 1, 60438 Frankfurt (Germany)

2015-08-15

A spectroelectrochemical cell has been designed to combine electrochemistry and ultrafast two-dimensional infrared (2D-IR) spectroscopy, which is a powerful tool to extract structure and dynamics information on the femtosecond to picosecond time scale. Our design is based on a gold mirror with the dual role of performing electrochemistry and reflecting IR light. To provide the high optical surface quality required for laser spectroscopy, the gold surface is made by electron beam evaporation on a glass substrate. Electrochemical cycling facilitates in situ collection of ultrafast dynamics of redox-active molecules by means of 2D-IR. The IR beams are operated in reflection mode so that they travel twice through the sample, i.e., the signal size is doubled. This methodology is optimal for small sample volumes and successfully tested with the ferricyanide/ferrocyanide redox system of which the corresponding electrochemically induced 2D-IR difference spectrum is reported.

Various manifestations of hypertrophic cardiomyopathy on ultrafast computed tomography

International Nuclear Information System (INIS)

Sekiya, Tohru; Karikomi, Masahito; Ohshiro, Masaya; Iwakami, Masayoshi; Takamoto, Toshihiko; Sakamoto, Tsuguya

1992-01-01

Ultrafast computed tomography was performed in 30 patients with hypertrophic cardiomyopathy and images were assessed on variability of left ventricular hypertrophy, the pattern of left ventricular contraction, right ventricular hypertrophy, dilatation of the left atrium, and thickening of the mitral valve. Fifteen (50.0%) of 30 patients had asymmetric septal hypertrophy, six (20.0%) had diffuse hypertrophy, and nine (30.0%) had apical hypertrophy. In eleven patients with asymmetric septal hypertrophy and two with apical hypertrophy, non-hypertrophied segments in end-diastole showed vigorous contraction. Sixteen patients showed homogeneous left ventricular contraction and one showed partial apical contraction. Right ventricular hypertrophy was noted in 12 patients (40.0%), dilatation of the left atrium in 13 patients (43.3%), and mitral valve thickening in three (10.0%). Ultrafast computed tomography was useful in the evaluation of apical hypertrophy and right ventricular hypertrophy, which could be difficult to obtain by echocardiography. (author)

A spectroelectrochemical cell for ultrafast two-dimensional infrared spectroscopy

International Nuclear Information System (INIS)

El Khoury, Youssef; Van Wilderen, Luuk J. G. W.; Vogt, Tim; Winter, Ernst; Bredenbeck, Jens

2015-01-01

A spectroelectrochemical cell has been designed to combine electrochemistry and ultrafast two-dimensional infrared (2D-IR) spectroscopy, which is a powerful tool to extract structure and dynamics information on the femtosecond to picosecond time scale. Our design is based on a gold mirror with the dual role of performing electrochemistry and reflecting IR light. To provide the high optical surface quality required for laser spectroscopy, the gold surface is made by electron beam evaporation on a glass substrate. Electrochemical cycling facilitates in situ collection of ultrafast dynamics of redox-active molecules by means of 2D-IR. The IR beams are operated in reflection mode so that they travel twice through the sample, i.e., the signal size is doubled. This methodology is optimal for small sample volumes and successfully tested with the ferricyanide/ferrocyanide redox system of which the corresponding electrochemically induced 2D-IR difference spectrum is reported

Bunch evolution study in optimization of MeV ultrafast electron diffraction

International Nuclear Information System (INIS)

Lu Xianhai; Du Yingchao; Huang Wenhui; Tang Chuanxiang

2014-01-01

transverse ultrafast electron diffraction (UED) is a promising detection tool for ultrafast processes. The quality of diffraction image is determined by the transverse evolution of the probe bunch. In this paper, we study the contributing terms of the emittance and space charge effects to the bunch evolution in the MeV UED scheme, employing a mean-field model with an ellipsoidal distribution as well as particle tracking simulation. The small transverse dimension of the drive laser is found to be critical to improve the reciprocal resolution, exploiting both smaller emittance and larger transverse bunch size before the solenoid. The degradation of the reciprocal spatial resolution caused by the space charge effects should be carefully controlled. (authors)

Bunch evolution study in optimization of MeV ultrafast electron diffraction

Science.gov (United States)

Lu, Xian-Hai; Du, Ying-Chao; Huang, Wen-Hui; Tang, Chuan-Xiang

2014-12-01

Megaelectronvolt ultrafast electron diffraction (UED) is a promising detection tool for ultrafast processes. The quality of diffraction image is determined by the transverse evolution of the probe bunch. In this paper, we study the contributing terms of the emittance and space charge effects to the bunch evolution in the MeV UED scheme, employing a mean-field model with an ellipsoidal distribution as well as particle tracking simulation. The small transverse dimension of the drive laser is found to be critical to improve the reciprocal resolution, exploiting both smaller emittance and larger transverse bunch size before the solenoid. The degradation of the reciprocal spatial resolution caused by the space charge effects should be carefully controlled.

Case study on the dynamics of ultrafast laser heating and ablation of gold thin films by ultrafast pump-probe reflectometry and ellipsometry

Science.gov (United States)

Pflug, T.; Wang, J.; Olbrich, M.; Frank, M.; Horn, A.

2018-02-01

To increase the comprehension of ultrafast laser ablation, the ablation process has to be portrayed with sufficient temporal resolution. For example, the temporal modification of the complex refractive index {\\tilde{n}} and the relative reflectance of a sample material after irradiation with ultrafast single-pulsed laser radiation can be measured with a pump-probe setup. This work describes the construction and validation of a pump-probe setup enabling spatially, temporally, and spectroscopically resolved Brewster angle microscopy, reflectometry, ellipsometry, and shadow photography. First pump-probe reflectometry and ellipsometry measurements are performed on gold at λ _{probe}= 440 nm and three fluences of the single-pulsed pump radiation at λ _{pump}= 800 nm generating no, gentle, and strong ablation. The relative reflectance overall increases at no and gentle ablation. At strong ablation, the relative reflectance locally decreases, presumable caused by emitted thermal electrons, ballistic electrons, and ablating material. The refractive index n is slightly decreasing after excitation, while the extinction coefficient k is increasing.

Applanation optical coherence elastography: noncontact measurement of intraocular pressure, corneal biomechanical properties, and corneal geometry with a single instrument

Science.gov (United States)

Singh, Manmohan; Han, Zhaolong; Nair, Achuth; Schill, Alexander; Twa, Michael D.; Larin, Kirill V.

2017-02-01

Current clinical tools provide critical information about ocular health such as intraocular pressure (IOP). However, they lack the ability to quantify tissue material properties, which are potent markers for ocular tissue health and integrity. We describe a single instrument to measure the eye-globe IOP, quantify corneal biomechanical properties, and measure corneal geometry with a technique termed applanation optical coherence elastography (Appl-OCE). An ultrafast OCT system enabled visualization of corneal dynamics during noncontact applanation tonometry and direct measurement of micro air-pulse induced elastic wave propagation. Our preliminary results show that the proposed Appl-OCE system can be used to quantify IOP, corneal biomechanical properties, and corneal geometry, which builds a solid foundation for a unique device that can provide a more complete picture of ocular health.

Quantum Coherent Dynamics Enhanced by Synchronization with Nonequilibrium Environments

Science.gov (United States)

Ishikawa, Akira; Okada, Ryo; Uchiyama, Kazuharu; Hori, Hirokazu; Kobayashi, Kiyoshi

2018-05-01

We report the discovery of the anomalous enhancement of quantum coherent dynamics (CD) due to a non-Markovian mechanism originating from not thermal-equilibrium phonon baths but nonequilibrium coherent phonons. CD is an elementary process for quantum phenomena in nanosystems, such as excitation transfer (ET) in semiconductor nanostructures and light-harvesting systems. CD occurs in homogeneous nanosystems because system inhomogeneity typically destroys coherence. In real systems, however, nanosystems behave as open systems surrounded by environments such as phonon systems. Typically, CD in inhomogeneous nanosystems is enhanced by the absorption and emission of thermal-equilibrium phonons, and the enhancement is described by the conventional master equation. On the other hand, CD is also enhanced by synchronization between population dynamics in nanosystems and coherent phonons; namely, coherent phonons, which are self-consistently induced by phase matching with Rabi oscillation, are fed back to enhance CD. This anomalous enhancement of CD essentially originates from the nonequilibrium and dynamical non-Markovian nature of coherent phonon environments, and the enhancement is firstly predicted by applying time-dependent projection operators to nonequilibrium and dynamical environments. Moreover, CD is discussed by considering ET from a donor to an acceptor. It is found that the enhancement of ET by synchronization with coherent phonons depends on the competition between the output time from a system to an acceptor and the formation time of coherent phonons. These findings in this study will stimulate the design and manipulation of CD via structured environments from the viewpoint of application to nano-photoelectronic devices.

Theory and Modelling of Ultrafast X-ray Imaging of Dynamical Non-equilibrium Systems

DEFF Research Database (Denmark)

Lorenz, Ulf

Over the next few years, a new generation of x-ray sources is going online. These freeelectron lasers will provide extremely bright subpicosecond x-ray pulses. Traditionally, x-ray diraction has the advantage of directly determining the atomic positions within a sample. With these new machines......, it becomes feasible to exploit this concept for ultrafast processes; in eect, we can study chemical reactions as they occur. This thesis deals with theoretical aspect of ultrafast time-resolved x-ray diraction (TRXD).We derive general formulas for calculating the diraction signal that are closely related...

Ultrafast Plasmonic Electron Emission from Ag Nanolayers with Different Roughness

Czech Academy of Sciences Publication Activity Database

Márton, I.; Ayadi, V.; Rácz, P.; Stefaniuk, T.; Wróbel, Piotr; Földi, P.; Dombi, P.

2016-01-01

Roč. 11, č. 3 (2016), s. 811-816 ISSN 1557-1955 Institutional support: RVO:67985882 Keywords : Nanoparticles * Ultrafast phenomena * Electron emission Subject RIV: JA - Electronics ; Optoelectronics, Electrical Engineering Impact factor: 2.139, year: 2016

Tunable soliton-induced resonant radiation by three-wave mixing

DEFF Research Database (Denmark)

Zhou, B. B.; Liu, X.; Guo, H. R.

2017-01-01

A remarkable feature about the temporal optical soliton is that it can be phase-matched to new frequencies, emitting so-called resonant radiation (RR). This constitutes an efficient source of ultrafast pulses in emerging wavelength regimes, and plays a vital role in coherently extending the super......A remarkable feature about the temporal optical soliton is that it can be phase-matched to new frequencies, emitting so-called resonant radiation (RR). This constitutes an efficient source of ultrafast pulses in emerging wavelength regimes, and plays a vital role in coherently extending...

Development of Ultrafast Indirect Flash Heating Methods for RDX

Science.gov (United States)

2014-02-01

8 1 1. Introduction The mission of the Multiscale Response of Energetic Materials program is to establish...vinyl nitrate ) Films. J. Phys. Chem. A 2004, 108 (43), 9342–9347. 11 12. Gottfried, J. L.; de Lucia, F. C., Jr.; Piraino, S. M. Ultrafast Laser

Checklist for One Health Epidemiological Reporting of Evidence (COHERE

Directory of Open Access Journals (Sweden)

Meghan F. Davis

2017-12-01

Full Text Available One Health is defined as the intersection and integration of knowledge regarding humans, animals, and the environment, yet as the One Health scientific literature expands, there is considerable heterogeneity of approach and quality of reporting in One Health studies. In addition, many researchers who publish such studies do not include or integrate data from all three domains of human, animal, and environmental health. This points to a critical need to unify guidelines for One Health studies. This report details the Checklist for One Health Epidemiological Reporting of Evidence (COHERE to guide the design and publication format of future One Health studies. COHERE was developed by a core writing team and international expert review group that represents multiple disciplines, including human medicine, veterinary medicine, public health, allied professionals, clinical laboratory science, epidemiology, the social sciences, ecohealth and environmental health. The twin aims of the COHERE standards are to 1 improve the quality of reporting of observational or interventional epidemiological studies that collect and integrate data from humans, animals and/or vectors, and their environments; and 2 promote the concept that One Health studies should integrate knowledge from these three domains. The 19 standards in the COHERE checklist address descriptions of human populations, animal populations, environmental assessment, spatial and temporal relationships of data from the three domains, integration of analyses and interpretation, and inclusion of expertise in the research team from disciplines related to human health, animal health, and environmental health.

Two-Dimensional Resonance Raman Signatures of Vibronic Coherence Transfer in Chemical Reactions.

Science.gov (United States)

Guo, Zhenkun; Molesky, Brian P; Cheshire, Thomas P; Moran, Andrew M

2017-11-02

Two-dimensional resonance Raman (2DRR) spectroscopy has been developed for studies of photochemical reaction mechanisms and structural heterogeneity in condensed phase systems. 2DRR spectroscopy is motivated by knowledge of non-equilibrium effects that cannot be detected with traditional resonance Raman spectroscopy. For example, 2DRR spectra may reveal correlated distributions of reactant and product geometries in systems that undergo chemical reactions on the femtosecond time scale. Structural heterogeneity in an ensemble may also be reflected in the 2D spectroscopic line shapes of both reactive and non-reactive systems. In this chapter, these capabilities of 2DRR spectroscopy are discussed in the context of recent applications to the photodissociation reactions of triiodide. We show that signatures of "vibronic coherence transfer" in the photodissociation process can be targeted with particular 2DRR pulse sequences. Key differences between the signal generation mechanisms for 2DRR and off-resonant 2D Raman spectroscopy techniques are also addressed. Overall, recent experimental developments and applications of the 2DRR method suggest that it will be a valuable tool for elucidating ultrafast chemical reaction mechanisms.

Out-and-back {sup 13}C-{sup 13}C scalar transfers in protein resonance assignment by proton-detected solid-state NMR under ultra-fast MAS

Energy Technology Data Exchange (ETDEWEB)

Barbet-Massin, Emeline; Pell, Andrew J. [University of Lyon, CNRS/ENS Lyon/UCB Lyon 1, Centre de RMN a Tres Hauts Champs (France); Jaudzems, Kristaps [Latvian Institute of Organic Synthesis (Latvia); Franks, W. Trent; Retel, Joren S. [Leibniz-Institut fuer Molekulare Pharmakologie (Germany); Kotelovica, Svetlana; Akopjana, Inara; Tars, Kaspars [Biomedical Research and Study Center (Latvia); Emsley, Lyndon [University of Lyon, CNRS/ENS Lyon/UCB Lyon 1, Centre de RMN a Tres Hauts Champs (France); Oschkinat, Hartmut [Leibniz-Institut fuer Molekulare Pharmakologie (Germany); Lesage, Anne; Pintacuda, Guido, E-mail: guido.pintacuda@ens-lyon.fr [University of Lyon, CNRS/ENS Lyon/UCB Lyon 1, Centre de RMN a Tres Hauts Champs (France)

2013-08-15

We present here {sup 1}H-detected triple-resonance H/N/C experiments that incorporate CO-CA and CA-CB out-and-back scalar-transfer blocks optimized for robust resonance assignment in biosolids under ultra-fast magic-angle spinning (MAS). The first experiment, (H)(CO)CA(CO)NH, yields {sup 1}H-detected inter-residue correlations, in which we record the chemical shifts of the CA spins in the first indirect dimension while during the scalar-transfer delays the coherences are present only on the longer-lived CO spins. The second experiment, (H)(CA)CB(CA)NH, correlates the side-chain CB chemical shifts with the NH of the same residue. These high sensitivity experiments are demonstrated on both fully-protonated and 100 %-H{sup N} back-protonated perdeuterated microcrystalline samples of Acinetobacter phage 205 (AP205) capsids at 60 kHz MAS.

An ultrafast electron microscope gun driven by two-photon photoemission from a nanotip cathode

International Nuclear Information System (INIS)

Bormann, Reiner; Strauch, Stefanie; Schäfer, Sascha; Ropers, Claus

2015-01-01

We experimentally and numerically investigate the performance of an advanced ultrafast electron source, based on two-photon photoemission from a tungsten needle cathode incorporated in an electron microscope gun geometry. Emission properties are characterized as a function of the electrostatic gun settings, and operating conditions leading to laser-triggered electron beams of very low emittance (below 20 nm mrad) are identified. The results highlight the excellent suitability of optically driven nano-cathodes for the further development of ultrafast transmission electron microscopy

Cohering power of quantum operations

Energy Technology Data Exchange (ETDEWEB)

Bu, Kaifeng, E-mail: bkf@zju.edu.cn [School of Mathematical Sciences, Zhejiang University, Hangzhou 310027 (China); Kumar, Asutosh, E-mail: asukumar@hri.res.in [Harish-Chandra Research Institute, Chhatnag Road, Jhunsi, Allahabad 211019 (India); Homi Bhabha National Institute, Anushaktinagar, Mumbai 400094 (India); Zhang, Lin, E-mail: linyz@zju.edu.cn [Institute of Mathematics, Hangzhou Dianzi University, Hangzhou 310018 (China); Wu, Junde, E-mail: wjd@zju.edu.cn [School of Mathematical Sciences, Zhejiang University, Hangzhou 310027 (China)

2017-05-18

Highlights: • Quantum coherence. • Cohering power: production of quantum coherence by quantum operations. • Study of cohering power and generalized cohering power, and their comparison for differentmeasures of quantum coherence. • Operational interpretation of cohering power. • Bound on cohering power of a generic quantum operation. - Abstract: Quantum coherence and entanglement, which play a crucial role in quantum information processing tasks, are usually fragile under decoherence. Therefore, the production of quantum coherence by quantum operations is important to preserve quantum correlations including entanglement. In this paper, we study cohering power–the ability of quantum operations to produce coherence. First, we provide an operational interpretation of cohering power. Then, we decompose a generic quantum operation into three basic operations, namely, unitary, appending and dismissal operations, and show that the cohering power of any quantum operation is upper bounded by the corresponding unitary operation. Furthermore, we compare cohering power and generalized cohering power of quantum operations for different measures of coherence.

Four-Dimensional Ultrafast Electron Microscopy: Insights into an Emerging Technique

KAUST Repository

Adhikari, Aniruddha; Eliason, Jeffrey K.; Sun, Jingya; Bose, Riya; Flannigan, David J.; Mohammed, Omar F.

2016-01-01

Four-dimensional ultrafast electron microscopy (4D-UEM) is a novel analytical technique that aims to fulfill the long-held dream of researchers to investigate materials at extremely short spatial and temporal resolutions by integrating the excellent

Ultrafast Non-thermal Response of Plasmonic Resonance in Gold Nanoantennas

Science.gov (United States)

Soavi, Giancarlo; Valle, Giuseppe Della; Biagioni, Paolo; Cattoni, Andrea; Longhi, Stefano; Cerullo, Giulio; Brida, Daniele

Ultrafast thermalization of electrons in metal nanostructures is studied by means of pump-probe spectroscopy. We track in real-time the plasmon resonance evolution, providing a tool for understanding and controlling gold nanoantennas non-linear optical response.

Measurements of ultrafast spin-profiles and spin-diffusion properties in the domain wall area at a metal/ferromagnetic film interface.

Science.gov (United States)

Sant, T; Ksenzov, D; Capotondi, F; Pedersoli, E; Manfredda, M; Kiskinova, M; Zabel, H; Kläui, M; Lüning, J; Pietsch, U; Gutt, C

2017-11-08

Exciting a ferromagnetic material with an ultrashort IR laser pulse is known to induce spin dynamics by heating the spin system and by ultrafast spin diffusion processes. Here, we report on measurements of spin-profiles and spin diffusion properties in the vicinity of domain walls in the interface region between a metallic Al layer and a ferromagnetic Co/Pd thin film upon IR excitation. We followed the ultrafast temporal evolution by means of an ultrafast resonant magnetic scattering experiment in surface scattering geometry, which enables us to exploit the evolution of the domain network within a 1/e distance of 3 nm to 5 nm from the Al/FM film interface. We observe a magnetization-reversal close to the domain wall boundaries that becomes more pronounced closer to the Al/FM film interface. This magnetization-reversal is driven by the different transport properties of majority and minority carriers through a magnetically disordered domain network. Its finite lateral extension has allowed us to measure the ultrafast spin-diffusion coefficients and ultrafast spin velocities for majority and minority carriers upon IR excitation.

Ultrafast Digital Printing toward 4D Shape Changing Materials.

Science.gov (United States)

Huang, Limei; Jiang, Ruiqi; Wu, Jingjun; Song, Jizhou; Bai, Hao; Li, Bogeng; Zhao, Qian; Xie, Tao

2017-02-01

Ultrafast 4D printing (printing converts the structure into 3D. An additional dimension can be incorporated by choosing the printing precursors. The process overcomes the speed limiting steps of typical 3D (4D) printing. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Tunable third-harmonic probe for non-degenerate ultrafast pump ...

Indian Academy of Sciences (India)

2014-02-12

Feb 12, 2014 ... 413–417. Tunable third-harmonic probe for non-degenerate ultrafast ... A beam splitter was used to split the beam into two with the power ratio of ... Now polarization of the 800-nm beam is made to be parallel with the 400-nm.

Ultrafast phenomena in molecular sciences femtosecond physics and chemistry

CERN Document Server

Bañares, Luis

2014-01-01

This book presents the latest developments in Femtosecond Chemistry and Physics for the study of ultrafast photo-induced molecular processes. Molecular systems, from the simplest H2 molecule to polymers or biological macromolecules, constitute central objects of interest for Physics, Chemistry and Biology, and despite the broad range of phenomena that they exhibit, they share some common behaviors. One of the most significant of those is that many of the processes involving chemical transformation (nuclear reorganization, bond breaking, bond making) take place in an extraordinarily short time, in or around the femtosecond temporal scale (1 fs = 10-15 s). A number of experimental approaches - very particularly the developments in the generation and manipulation of ultrashort laser pulses - coupled with theoretical progress, provide the ultrafast scientist with powerful tools to understand matter and its interaction with light, at this spatial and temporal scale. This book is an attempt to reunite some of the ...

Phosphorene quantum dot saturable absorbers for ultrafast fiber lasers

Science.gov (United States)

Du, J.; Zhang, M.; Guo, Z.; Chen, J.; Zhu, X.; Hu, G.; Peng, P.; Zheng, Z.; Zhang, H.

2017-01-01

We fabricate ultrasmall phosphorene quantum dots (PQDs) with an average size of 2.6 ± 0.9 nm using a liquid exfoliation method involving ultrasound probe sonication followed by bath sonication. By coupling the as-prepared PQDs with microfiber evanescent light field, the PQD-based saturable absorber (SA) device exhibits ultrafast nonlinear saturable absorption property, with an optical modulation depth of 8.1% at the telecommunication band. With the integration of the all-fiber PQD-based SA, a continuous-wave passively mode-locked erbium-doped (Er-doped) laser cavity delivers stable, self-starting pulses with a pulse duration of 0.88 ps and at the cavity repetition rate of 5.47 MHz. Our results contribute to the growing body of work studying the nonlinear optical properties of ultrasmall PQDs that present new opportunities of this two-dimensional (2D) nanomaterial for future ultrafast photonic technologies. PMID:28211471

Precision machining of pig intestine using ultrafast laser pulses

Science.gov (United States)

Beck, Rainer J.; Góra, Wojciech S.; Carter, Richard M.; Gunadi, Sonny; Jayne, David; Hand, Duncan P.; Shephard, Jonathan D.

2015-07-01

Endoluminal surgery for the treatment of early stage colorectal cancer is typically based on electrocautery tools which imply restrictions on precision and the risk of harm through collateral thermal damage to the healthy tissue. As a potential alternative to mitigate these drawbacks we present laser machining of pig intestine by means of picosecond laser pulses. The high intensities of an ultrafast laser enable nonlinear absorption processes and a predominantly nonthermal ablation regime. Laser ablation results of square cavities with comparable thickness to early stage colorectal cancers are presented for a wavelength of 1030 nm using an industrial picosecond laser. The corresponding histology sections exhibit only minimal collateral damage to the surrounding tissue. The depth of the ablation can be controlled precisely by means of the pulse energy. Overall, the application of ultrafast lasers to ablate pig intestine enables significantly improved precision and reduced thermal damage to the surrounding tissue compared to conventional techniques.

Ultrafast dissociation: An unexpected tool for probing molecular dynamics

International Nuclear Information System (INIS)

Morin, Paul; Miron, Catalin

2012-01-01

Highlights: ► Ultrafast dissociation has been investigated by means of XPS and mass spectrometry. ► The interplay between electron relaxation and molecular dynamics is evidenced. ► Extension toward polyatomics, clusters, adsorbed molecules is considered. ► Quantum effects (spectral hole, angular effects) evidence the molecular field anisotropy. -- Abstract: Ultrafast dissociation following core–shell excitation into an antibonding orbital led to the early observation in HBr of atomic Auger lines associated to the decay of dissociated excited atoms. The purpose of this article is to review the very large variety of systems where such a situation has been encountered, extending from simple diatomic molecules toward more complex systems like polyatomics, clusters, or adsorbed molecules. Interestingly, this phenomenon has revealed an extremely rich and powerful tool for probing nuclear dynamics and its subtle interplay with electron relaxation occurring on a comparable time scale. Consequently this review covers a surprisingly large period, starting in 1986 and still ongoing.

Morphological changes in ultrafast laser ablation plumes with varying spot size.

Science.gov (United States)

Harilal, S S; Diwakar, P K; Polek, M P; Phillips, M C

2015-06-15

We investigated the role of spot size on plume morphology during ultrafast laser ablation of metal targets. Our results show that the spatial features of fs LA plumes are strongly dependent on the focal spot size. Two-dimensional self-emission images showed that the shape of the ultrafast laser ablation plumes changes from spherical to cylindrical with an increasing spot size from 100 to 600 μm. The changes in plume morphology and internal structures are related to ion emission dynamics from the plasma, where broader angular ion distribution and faster ions are noticed for the smallest spot size used. The present results clearly show that the morphological changes in the plume with spot size are independent of laser pulse width.

Development of an Ultrafast Scanning Tunneling Microscope for Dynamic Surface Studies

National Research Council Canada - National Science Library

Nunes

1999-01-01

.... The microscope has demonstrated atomic resolution. We have a femtosecond laser system, optics for delivering ultrafast laser pulses to the STM, and a computer controlled delay line for time-resolved measurements...

Observation of an octave-spanning supercontinuum in the mid-infrared using ultrafast cascaded nonlinearities

DEFF Research Database (Denmark)

Bache, Morten; Liu, Xing; Zhou, Binbin

2014-01-01

An octave-spanning mid-IR supercontinuum is observed experimentally using ultrafast cascaded nonlinearities in an LiInS2 quadratic nonlinear crystal pumped with 70 fs energetic mid-IR pulses and cut for strongly phase-mismatched second-harmonic generation. ©OSA 2014.......An octave-spanning mid-IR supercontinuum is observed experimentally using ultrafast cascaded nonlinearities in an LiInS2 quadratic nonlinear crystal pumped with 70 fs energetic mid-IR pulses and cut for strongly phase-mismatched second-harmonic generation. ©OSA 2014....

Adlayer structure dependent ultrafast desorption dynamics in carbon monoxide adsorbed on Pd (111)

Energy Technology Data Exchange (ETDEWEB)

Hong, Sung-Young; Camillone, Nina R.; Camillone, Nicholas, E-mail: nicholas@bnl.gov [Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973 (United States); Xu, Pan [Department of Chemistry, Stony Brook University, Stony Brook, New York 11794 (United States); White, Michael G. [Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973 (United States); Department of Chemistry, Stony Brook University, Stony Brook, New York 11794 (United States)

2016-07-07

We report our ultrafast photoinduced desorption investigation of the coverage dependence of substrate–adsorbate energy transfer in carbon monoxide adlayers on the (111) surface of palladium. As the CO coverage is increased, the adsorption site population shifts from all threefold hollows (up to 0.33 ML), to bridge and near bridge (>0.5 to 0.6 ML) and finally to mixed threefold hollow plus top site (at saturation at 0.75 ML). We show that between 0.24 and 0.75 ML this progression of binding site motifs is accompanied by two remarkable features in the ultrafast photoinduced desorption of the adsorbates: (i) the desorption probability increases roughly two orders magnitude, and (ii) the adsorbate–substrate energy transfer rate observed in two-pulse correlation experiments varies nonmonotonically, having a minimum at intermediate coverages. Simulations using a phenomenological model to describe the adsorbate–substrate energy transfer in terms of frictional coupling indicate that these features are consistent with an adsorption-site dependent electron-mediated energy coupling strength, η{sub el}, that decreases with binding site in the order: three-fold hollow > bridge and near bridge > top site. This weakening of η{sub el} largely counterbalances the decrease in the desorption activation energy that accompanies this progression of adsorption site motifs, moderating what would otherwise be a rise of several orders of magnitude in the desorption probability. Within this framework, the observed energy transfer rate enhancement at saturation coverage is due to interadsorbate energy transfer from the copopulation of molecules bound in three-fold hollows to their top-site neighbors.

Ultrafast demagnetization enhancement in CoFeB/MgO/CoFeB magnetic tunneling junction driven by spin tunneling current.

Science.gov (United States)

He, Wei; Zhu, Tao; Zhang, Xiang-Qun; Yang, Hai-Tao; Cheng, Zhao-Hua

2013-10-07

The laser-induced ultrafast demagnetization of CoFeB/MgO/CoFeB magnetic tunneling junction is exploited by time-resolved magneto-optical Kerr effect (TRMOKE) for both the parallel state (P state) and the antiparallel state (AP state) of the magnetizations between two magnetic layers. It was observed that the demagnetization time is shorter and the magnitude of demagnetization is larger in the AP state than those in the P state. These behaviors are attributed to the ultrafast spin transfer between two CoFeB layers via the tunneling of hot electrons through the MgO barrier. Our observation indicates that ultrafast demagnetization can be engineered by the hot electrons tunneling current. It opens the door to manipulate the ultrafast spin current in magnetic tunneling junctions.

Update on The Ultra-Fast Flash Observatory (UFFO) Pathfinder

DEFF Research Database (Denmark)

Grossan, B.; Brandt, Søren; Budtz-Jørgensen, Carl

2011-01-01

The Ultra-Fast Flash Observatory (UFFO) uses an X/gamma and an optical/UV instrument to observe gamma-ray bursts (GRB) starting milliseconds after burst trigger and location. The X/gamma instrument, a standard coded-mask camera, locates the GRB and triggers the system. The optical/UV instrument, ...

Dissociation dynamics of 3- and 4-nitrotoluene radical cations: Coherently driven C-NO2 bond homolysis

Science.gov (United States)

Ampadu Boateng, Derrick; Gutsev, Gennady L.; Jena, Puru; Tibbetts, Katharine Moore

2018-04-01

Monosubstituted nitrotoluenes serve as important model compounds for nitroaromatic energetic molecules such as trinitrotoluene. This work investigates the ultrafast nuclear dynamics of 3- and 4-nitrotoluene radical cations using femtosecond pump-probe measurements and the results of density functional theory calculations. Strong-field adiabatic ionization of 3- and 4-nitrotoluene using 1500 nm, 18 fs pulses produces radical cations in the ground electronic state with distinct coherent vibrational excitations. In both nitrotoluene isomers, a one-photon excitation with the probe pulse results in NO2 loss to form C7H7+, which exhibits out-of-phase oscillations in yield with the parent molecular ion. The oscillations in 4-nitrotoluene with a period of 470 fs are attributed to the torsional motion of the NO2 group based on theoretical results showing that the dominant relaxation pathway in 4-nitrotoluene radical cations involves the rotation of the NO2 group away from the planar geometry. The distinctly faster oscillation period of 216 fs in 3-nitrotoluene is attributed to an in-plane bending motion of the NO2 and CH3 moieties based on analysis of the normal modes. These results demonstrate that coherent nuclear motions determine the probability of C-NO2 homolysis in the nitrotoluene radical cations upon optical excitation within several hundred femtoseconds of the initial ionization event.

Ultrafast Nonradiative Decay and Excitation Energy Transfer by Carotenoids in Photosynthetic Light-Harvesting Proteins

Science.gov (United States)

Ghosh, Soumen

This dissertation investigates the photophysical and structural dynamics that allow carotenoids to serve as efficient excitation energy transfer donor to chlorophyll acceptors in photosynthetic light harvesting proteins. Femtosecond transient grating spectroscopy with optical heterodyne detection has been employed to follow the nonradiative decay pathways of carotenoids and excitation energy transfer to chlorophylls. It was found that the optically prepared S2 (11Bu+) state of beta-carotene decays in 12 fs fs to populate an intermediate electronic state, Sx, which then decays nonradiatively to the S 1 state. The ultrafast rise of the dispersion component of the heterodyne transient grating signal reports the formation of Sx intermediate since the rise of the dispersion signal is controlled by the loss of stimulated emission from the S2 state. These findings were extended to studies of peridinin, a carbonyl substituted carotenoid that serves as a photosynthetic light-harvesting chromophore in dinoflagellates. Numerical simulations using nonlinear response formalism and the multimode Brownian oscillator model assigned the Sx intermediate to a torsionally distorted structure evolving on the S2 potential surface. The decay of the Sx state is promoted by large amplitude out-of-plane torsional motions and is significantly retarded by solvent friction owing to the development of an intramolecular charge transfer character in peridinin. The slowing of the nonradiative decay allows the Sx state to transfer significant portion of the excitation energy to chlorophyll a acceptors in the peridinin-chlorophyll a protein. The results of heterodyne transient grating study on peridinin-chlorophyll a protein suggests two distinct energy transfer channels from peridinin to chlorophyll a: a 30 fs process involving quantum coherence and delocalized peridinin-Chl states and an incoherent, 2.5 ps process involving the distorted S2 state of peridinin. The torsional evolution on the S2

Relaxation process of coherent transients in the presence of an adjacent strongly driven transition

International Nuclear Information System (INIS)

Feng Xiaomin; Yang Lijun; Li Xiaoli; Zhang Lianshui; Han Li; Guo Qinglin; Fu Guangsheng

2007-01-01

Coherent transient occurs when a two-level transition is subjected to pulsed laser excitation. The relaxation process of coherent transient depends on both the longitudinal and transverse relaxation parameters of the two-level transition, which is related to the population and coherence decay rates. In this paper we study relaxation process of a new type coherent transients observed by applying a pulsed laser excitation to a two-level transition in the presence of a second strong continuous-wave (cw) coherent field coupling one of the two levels to a third level, that is, in a three-level double-resonance configuration. The relaxation process of coherent transients is studied as a function of relaxation parameters of both the two-level transition excited by the pulsed laser field and the transition coupled by the cw laser field. It is shown that by involving a third level with coherent field the relaxation process of coherent transients of a two-level transition can be modified. Our study illustrates a new way of controlling relaxation process of coherent transients in a two-level transition by a second coherent laser and this has important implication for quantum information storage and quantum computing

A US Based Ultrafast Interdisciplinary Research Facility

Science.gov (United States)

Gueye, Paul; Hill, Wendell; Johnson, Anthony

2006-10-01

The US scientific competitiveness on the world arena has substantially decreased due to the lack of funding and training of qualified personnel. Most of the potential workforce found in higher education is composed of foreign students and post-docs. In the specific field of low- and high-field science, the European and Asian communities are rapidly catching-up with the US, even leading in some areas. To remain the leader in ultrafast science and technology, new visions and commitment must be embraced. For that reason, an international effort of more than 70 countries for a US-based interdisciplinary research facility using ultrafast laser technology is under development. It will provide research and educational training, as well as new venues for a strong collaboration between the fields of astrophysics, nuclear/high energy physics, plasma physics, optical sciences, biological and medical physics. This facility will consist of a uniquely designed high contrast multi-lines concept housing twenty experimental rooms shared between four beams:[0.1 TW, 1 kHz], [10 TW, 9 kHz], [100-200 TW, 10 Hz] and [500 TW, 10 Hz]. The detail schematic of this multi-laser system, foreseen research and educational programs, and organizational structure of this facility will be presented.

Ultra-fast relaxation kinetics in semiconductors

International Nuclear Information System (INIS)

Luzzi, R.

1983-01-01

It is presented a brief description of relaxation processes in highly excited semiconductor plasmas (HESP). Comparison with experimental data obtained by means of ultra-fast laser light spectroscopy (UFLS) is made. Some aspects of response funtion theory in systems far-from-equilibrium are reviewed in Section II. In Section III we present some comments on the question of nonequilibrium thermodynamics relevant to the problem to be considered. In last section we present a brief summary of the different aspects of the subject. (author) [pt

Ultra-fast relaxation kinetics in semiconductors

International Nuclear Information System (INIS)

Luzzi, R.

1983-01-01

It is presented a brief description of relaxation processes in highly excited semiconductor plasmas (HESP). Comparison with experimental data obtained by means of ultra-fast laser light spectroscopy (UFLS) is made. Some aspects of response function theory in systems far-from-equilibrium are reviewed in Section II. In Section III some comments on the question of nonequilibrium thermodynamics relevant to the problem to be considered are presented. In last Section a brief summary of the different aspects of the subject is also presented. (Author) [pt

Ultrafast Ge-Te bond dynamics in a phase-change superlattice

NARCIS (Netherlands)

Malvestuto, Marco; Caretta, Antonio; Casarin, Barbara; Cilento, Federico; Dell'Angela, Martina; Fausti, Daniele; Calarco, Raffaella; Kooi, Bart J.; Varesi, Enrico; Robertson, John; Parmigiani, Fulvio

2016-01-01

A long-standing question for avant-garde data storage technology concerns the nature of the ultrafast photoinduced phase transformations in the wide class of chalcogenide phase-change materials (PCMs). Overall, a comprehensive understanding of the microstructural evolution and the relevant kinetics

A PSF-Shape-Based Beamforming Strategy for Robust 2D Motion Estimation in Ultrafast Data

OpenAIRE

Anne E. C. M. Saris; Stein Fekkes; Maartje M. Nillesen; Hendrik H. G. Hansen; Chris L. de Korte

2018-01-01

This paper presents a framework for motion estimation in ultrafast ultrasound data. It describes a novel approach for determining the sampling grid for ultrafast data based on the system’s point-spread-function (PSF). As a consequence, the cross-correlation functions (CCF) used in the speckle tracking (ST) algorithm will have circular-shaped peaks, which can be interpolated using a 2D interpolation method to estimate subsample displacements. Carotid artery wall motion and parabolic blood flow...

Direct measurement of exciton valley coherence in monolayer WSe2

KAUST Repository

Hao, Kai

2016-02-29

In crystals, energy band extrema in momentum space can be identified by a valley index. The internal quantum degree of freedom associated with valley pseudospin indices can act as a useful information carrier, analogous to electronic charge or spin. Interest in valleytronics has been revived in recent years following the discovery of atomically thin materials such as graphene and transition metal dichalcogenides. However, the valley coherence time—a crucial quantity for valley pseudospin manipulation—is difficult to directly probe. In this work, we use two-dimensional coherent spectroscopy to resonantly generate and detect valley coherence of excitons (Coulomb-bound electron–hole pairs) in monolayer WSe₂ (refs ,). The imposed valley coherence persists for approximately one hundred femtoseconds. We propose that the electron–hole exchange interaction provides an important decoherence mechanism in addition to exciton population recombination. This work provides critical insight into the requirements and strategies for optical manipulation of the valley pseudospin for future valleytronics applications.

Ultrafast spontaneous emission modulation of graphene quantum dots interacting with Ag nanoparticles in solution

Energy Technology Data Exchange (ETDEWEB)

Zhao, Jianwei [Department of Physics, Shanghai University, Shanghai 200444 (China); Research Center of Quantum Macro-Phenomenon and Application, Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201210 (China); Lu, Jian, E-mail: luj@sari.ac.cn; Wang, Zhongyang, E-mail: wangzy@sari.ac.cn [Research Center of Quantum Macro-Phenomenon and Application, Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201210 (China); Wang, Liang [School of Environmental and Chemical Engineering, Shanghai University, Shanghai 200444 (China); Institute of Nanochemistry and Nanobiology, Shanghai University, Shanghai 200444 (China); Tian, Linfan [Research Center of Quantum Macro-Phenomenon and Application, Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201210 (China); School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210 (China); Deng, Xingxia [Research Center of Quantum Macro-Phenomenon and Application, Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201210 (China); School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Tian, Lijun [Department of Physics, Shanghai University, Shanghai 200444 (China); Pan, Dengyu [School of Environmental and Chemical Engineering, Shanghai University, Shanghai 200444 (China)

2016-07-11

We investigated the strong interaction between graphene quantum dots and silver nanoparticles in solution using time-resolved photoluminescence techniques. In solution, the silver nanoparticles are surrounded by graphene quantum dots and interacted with graphene quantum dots through exciton-plasmon coupling. An ultrafast spontaneous emission process (lifetime 27 ps) was observed in such a mixed solution. This ultrafast lifetime corresponds to the emission rate exceeding 35 GHz, with the purcell enhancement by a factor of ∼12. These experiment results pave the way for the realization of future high speed light sources applications.

Quantification of retinal nerve fiber layer thickness using spectral domain optical coherence tomography in normal Indian population

Directory of Open Access Journals (Sweden)

Tarannum Mansoori

2012-01-01

Full Text Available The purpose of this study was to measure peripapillary retinal nerve fiber layer thickness (RNFLT using spectral domain optical coherence tomography (SD-OCT in normal Indian eyes, for which, 210 normal volunteers were recruited. One eye of each subject underwent RNFL scanning at 3.4 mm circle diameter around optic nerve using SD OCT. The data were analyzed to determine RNFLT in the sample population and its variation with age and gender. The average peripapillary RNFLT was 114.03 ± 9.59 μm. There was no effect of gender on RNFLT parameters. Age had significant negative correlation with average (P = 0.005, superior (P = 0.04, temporal (P = 0.049, and nasal quadrants (P = 0.01 RNFLT. Inferior quadrant RNFLT also had a negative correlation with age, but it was not statistically significant (P = 0.15.

Ultrafast dynamic computed tomography myelography for the precise identification of high-flow cerebrospinal fluid leaks caused by spiculated spinal osteophytes.

Science.gov (United States)

Thielen, Kent R; Sillery, John C; Morris, Jonathan M; Hoxworth, Joseph M; Diehn, Felix E; Wald, John T; Rosebrock, Richard E; Yu, Lifeng; Luetmer, Patrick H

2015-03-01

Precise localization and understanding of the origin of spontaneous high-flow spinal CSF leaks is required prior to targeted treatment. This study demonstrates the utility of ultrafast dynamic CT myelography for the precise localization of high-flow CSF leaks caused by spiculated spinal osteophytes. This study reports a series of 14 patients with high-flow CSF leaks caused by spiculated spinal osteophytes who underwent ultrafast dynamic CT myelography between March 2009 and December 2010. There were 10 male and 4 female patients, with an average age of 49 years (range 37-74 years). The value of ultrafast dynamic CT myelography in depicting the CSF leak site was qualitatively assessed. In all 14 patients, ultrafast dynamic CT myelography was technically successful at precisely demonstrating the site of the CSF leak, the causative spiculated osteophyte piercing the dura, and the relationship of the implicated osteophyte to adjacent structures. Leak sites included 3 cervical, 11 thoracic, and 0 lumbar levels, with 86% of the leaks occurring from C-5 to T-7. Information obtained from the ultrafast dynamic CT myelogram was considered useful in all treated CSF leaks. Spinal osteophytes piercing the dura are a more frequent cause of high-flow CSF leaks than previously recognized. Ultrafast dynamic CT myelography adds value beyond standard dynamic myelography or digital subtraction myelography in the diagnosis and anatomical characterization of high-flow spinal CSF leaks caused by these osteophytes. This information allows for appropriate planning for percutaneous or surgical treatment.

Coherent Control of Nanoscale Ballistic Currents in Transition Metal Dichalcogenide ReS2.

Science.gov (United States)

Cui, Qiannan; Zhao, Hui

2015-04-28

Transition metal dichalcogenides are predicted to outperform traditional semiconductors in ballistic devices with nanoscale channel lengths. So far, experimental studies on charge transport in transition metal dichalcogenides are limited to the diffusive regime. Here we show, using ReS2 as an example, all-optical injection, detection, and coherent control of ballistic currents. By utilizing quantum interference between one-photon and two-photon interband transition pathways, ballistic currents are injected in ReS2 thin film samples by a pair of femtosecond laser pulses. We find that the current decays on an ultrafast time scale, resulting in an electron transport of only a fraction of one nanometer. Following the relaxation of the initially injected momentum, backward motion of the electrons for about 1 ps is observed, driven by the Coulomb force from the oppositely moved holes. We also show that the injected current can be controlled by the phase of the laser pulses. These results demonstrate a new platform to study ballistic transport of nonequilibrium carriers in transition metal dichalcogenides.

Coherent spin-rotational dynamics of oxygen superrotors

Science.gov (United States)

Milner, Alexander A.; Korobenko, Aleksey; Milner, Valery

2014-09-01

We use state- and time-resolved coherent Raman spectroscopy to study the rotational dynamics of oxygen molecules in ultra-high rotational states. While it is possible to reach rotational quantum numbers up to N≈ 50 by increasing the gas temperature to 1500 K, low population levels and gas densities result in correspondingly weak optical response. By spinning {{O}2} molecules with an optical centrifuge, we efficiently excite extreme rotational states with N≤slant 109 in high-density room temperature ensembles. Fast molecular rotation results in the enhanced robustness of the created rotational wave packets against collisions, enabling us to observe the effects of weak spin-rotation coupling in the coherent rotational dynamics of oxygen. The decay rate of spin-rotational coherence due to collisions is measured as a function of the molecular angular momentum and its dependence on the collisional adiabaticity parameter is discussed. We find that at high values of N, the rotational decoherence of oxygen is much faster than that of the previously studied non-magnetic nitrogen molecules, pointing at the effects of spin relaxation in paramagnetic gases.

Silicon nanowires for ultra-fast and ultrabroadband optical signal processing

DEFF Research Database (Denmark)

Ji, Hua; Hu, Hao; Pu, Minhao

2015-01-01

In this paper, we present recent research on silicon nanowires for ultra-fast and ultra-broadband optical signal processing at DTU Fotonik. The advantages and limitations of using silicon nanowires for optical signal processing are revealed through experimental demonstrations of various optical...

Multiphoton microscopy in every lab: the promise of ultrafast semiconductor disk lasers

Science.gov (United States)

Emaury, Florian; Voigt, Fabian F.; Bethge, Philipp; Waldburger, Dominik; Link, Sandro M.; Carta, Stefano; van der Bourg, Alexander; Helmchen, Fritjof; Keller, Ursula

2017-07-01

We use an ultrafast diode-pumped semiconductor disk laser (SDL) to demonstrate several applications in multiphoton microscopy. The ultrafast SDL is based on an optically pumped Vertical External Cavity Surface Emitting Laser (VECSEL) passively mode-locked with a semiconductor saturable absorber mirror (SESAM) and generates 170-fs pulses at a center wavelength of 1027 nm with a repetition rate of 1.63 GHz. We demonstrate the suitability of this laser for structural and functional multiphoton in vivo imaging in both Drosophila larvae and mice for a variety of fluorophores (including mKate2, tdTomato, Texas Red, OGB-1, and R-CaMP1.07) and for endogenous second-harmonic generation in muscle cell sarcomeres. We can demonstrate equivalent signal levels compared to a standard 80-MHz Ti:Sapphire laser when we increase the average power by a factor of 4.5 as predicted by theory. In addition, we compare the bleaching properties of both laser systems in fixed Drosophila larvae and find similar bleaching kinetics despite the large difference in pulse repetition rates. Our results highlight the great potential of ultrafast diode-pumped SDLs for creating a cost-efficient and compact alternative light source compared to standard Ti:Sapphire lasers for multiphoton imaging.

Ultrafast-laser-inscribed 3D integrated photonics: challenges and emerging applications

Directory of Open Access Journals (Sweden)

Gross S.

2015-11-01

Full Text Available Since the discovery that tightly focused femtosecond laser pulses can induce a highly localised and permanent refractive index modification in a large number of transparent dielectrics, the technique of ultrafast laser inscription has received great attention from a wide range of applications. In particular, the capability to create three-dimensional optical waveguide circuits has opened up new opportunities for integrated photonics that would not have been possible with traditional planar fabrication techniques because it enables full access to the many degrees of freedom in a photon. This paper reviews the basic techniques and technological challenges of 3D integrated photonics fabricated using ultrafast laser inscription as well as reviews the most recent progress in the fields of astrophotonics, optical communication, quantum photonics, emulation of quantum systems, optofluidics and sensing.

Ultrafast Ge-Te bond dynamics in a phase-change superlattice

Science.gov (United States)

Malvestuto, Marco; Caretta, Antonio; Casarin, Barbara; Cilento, Federico; Dell'Angela, Martina; Fausti, Daniele; Calarco, Raffaella; Kooi, Bart J.; Varesi, Enrico; Robertson, John; Parmigiani, Fulvio

2016-09-01

A long-standing question for avant-garde data storage technology concerns the nature of the ultrafast photoinduced phase transformations in the wide class of chalcogenide phase-change materials (PCMs). Overall, a comprehensive understanding of the microstructural evolution and the relevant kinetics mechanisms accompanying the out-of-equilibrium phases is still missing. Here, after overheating a phase-change chalcogenide superlattice by an ultrafast laser pulse, we indirectly track the lattice relaxation by time resolved x-ray absorption spectroscopy (tr-XAS) with a sub-ns time resolution. The approach to the tr-XAS experimental results reported in this work provides an atomistic insight of the mechanism that takes place during the cooling process; meanwhile a first-principles model mimicking the microscopic distortions accounts for a straightforward representation of the observed dynamics. Finally, we envisage that our approach can be applied in future studies addressing the role of dynamical structural strain in PCMs.

Structural Transformation of LiFePO4 during Ultrafast Delithiation.

Science.gov (United States)

Kuss, Christian; Trinh, Ngoc Duc; Andjelic, Stefan; Saulnier, Mathieu; Dufresne, Eric M; Liang, Guoxian; Schougaard, Steen B

2017-12-21

The prolific lithium battery electrode material lithium iron phosphate (LiFePO 4 ) stores and releases lithium ions by undergoing a crystallographic phase change. Nevertheless, it performs unexpectedly well at high rate and exhibits good cycling stability. We investigate here the ultrafast charging reaction to resolve the underlying mechanism while avoiding the limitations of prevailing electrochemical methods by using a gaseous oxidant to deintercalate lithium from the LiFePO 4 structure. Oxidizing LiFePO 4 with nitrogen dioxide gas reveals structural changes through in situ synchrotron X-ray diffraction and electronic changes through in situ UV/vis reflectance spectroscopy. This study clearly shows that ultrahigh rates reaching 100% state of charge in 10 s does not lead to a particle-wide union of the olivine and heterosite structures. An extensive solid solution phase is therefore not a prerequisite for ultrafast charge/discharge.

Imacon 600 ultrafast streak camera evaluation

International Nuclear Information System (INIS)

Owen, T.C.; Coleman, L.W.

1975-01-01

The Imacon 600 has a number of designed in disadvantages for use as an ultrafast diagnostic instrument. The unit is physically large (approximately 5' long) and uses an external power supply rack for the image intensifier. Water cooling is required for the intensifier; it is quiet but not conducive to portability. There is no interlock on the cooling water. The camera does have several switch selectable sweep speeds. This is desirable if one is working with both slow and fast events. The camera can be run in a framing mode. (MOW)

Ultrafast Photoinduced Electron Transfer in a π-Conjugated Oligomer/Porphyrin Complex

KAUST Repository

Aly, Shawkat Mohammede; Goswami, Subhadip; Alsulami, Qana; Schanze, Kirk S.; Mohammed, Omar F.

2014-01-01

Controlling charge transfer (CT), charge separation (CS), and charge recombination (CR) at the donor-acceptor interface is extremely important to optimize the conversion efficiency in solar cell devices. In general, ultrafast CT and slow CR

Lifetime broadening of atomic lines produced upon ultrafast dissociation of HCl and HBr

Energy Technology Data Exchange (ETDEWEB)

Lablanquie, P., E-mail: pascal.lablanquie@upmc.fr [Sorbonne Universités, UPMC Univ Paris 06, LCPMR, 11 rue Pierre et Marie Curie, 75231 Paris Cedex 05 (France); CNRS, LCPMR (UMR 7614), 11 rue Pierre et Marie Curie, 75231 Paris Cedex 05 (France); Iwayama, H. [UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585 (Japan); Penent, F. [Sorbonne Universités, UPMC Univ Paris 06, LCPMR, 11 rue Pierre et Marie Curie, 75231 Paris Cedex 05 (France); CNRS, LCPMR (UMR 7614), 11 rue Pierre et Marie Curie, 75231 Paris Cedex 05 (France); Soejima, K. [Department of Environmental Science, Niigata University, Niigata 950-2181 (Japan); Shigemasa, E. [UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585 (Japan)

2014-08-15

Highlights: • Ultrafast dissociation of HCl is triggered by 2p{sub 3/2} → σ* excitation. • Ultrafast dissociation of HBr is triggered by 3d{sub 5/2} → σ* excitation. • Photoelectron spectroscopy reveals sharp vibrational molecular lines and broad atomic lines. • The profiles of the atomic lines are analyzed in detail. • We extract the lifetime of the inner shell hole in the neutral atomic fragment. - Abstract: Ultrafast dissociation of the HCl and HBr molecules excited respectively to the 2p{sub 3/2} → σ* and 3d{sub 5/2} → σ* resonances are studied with high resolution photoelectron spectroscopy. Sharp vibrational molecular lines and broad atomic lines are observed. The analysis of the profile of the atomic lines gives access to the lifetimes of the inner shell 2p{sub 3/2} hole in the Cl* (2p{sub 3/2}){sup −1} 3s{sup 2}3p{sup 6} configuration, and the inner shell 3d{sub 5/2} hole in the Br* (3d{sub 5/2}){sup −1} 4s{sup 2}4p{sup 6} configuration.

Partial coherence with application to the monotonicity problem of coherence involving skew information

Science.gov (United States)

Luo, Shunlong; Sun, Yuan

2017-08-01

Quantifications of coherence are intensively studied in the context of completely decoherent operations (i.e., von Neuamnn measurements, or equivalently, orthonormal bases) in recent years. Here we investigate partial coherence (i.e., coherence in the context of partially decoherent operations such as Lüders measurements). A bona fide measure of partial coherence is introduced. As an application, we address the monotonicity problem of K -coherence (a quantifier for coherence in terms of Wigner-Yanase skew information) [Girolami, Phys. Rev. Lett. 113, 170401 (2014), 10.1103/PhysRevLett.113.170401], which is introduced to realize a measure of coherence as axiomatized by Baumgratz, Cramer, and Plenio [Phys. Rev. Lett. 113, 140401 (2014), 10.1103/PhysRevLett.113.140401]. Since K -coherence fails to meet the necessary requirement of monotonicity under incoherent operations, it is desirable to remedy this monotonicity problem. We show that if we modify the original measure by taking skew information with respect to the spectral decomposition of an observable, rather than the observable itself, as a measure of coherence, then the problem disappears, and the resultant coherence measure satisfies the monotonicity. Some concrete examples are discussed and related open issues are indicated.

Measuring coherence with entanglement concurrence

Science.gov (United States)

Qi, Xianfei; Gao, Ting; Yan, Fengli

2017-07-01

Quantum coherence is a fundamental manifestation of the quantum superposition principle. Recently, Baumgratz et al (2014 Phys. Rev. Lett. 113 140401) presented a rigorous framework to quantify coherence from the view of theory of physical resource. Here we propose a new valid quantum coherence measure which is a convex roof measure, for a quantum system of arbitrary dimension, essentially using the generalized Gell-Mann matrices. Rigorous proof shows that the proposed coherence measure, coherence concurrence, fulfills all the requirements dictated by the resource theory of quantum coherence measures. Moreover, strong links between the resource frameworks of coherence concurrence and entanglement concurrence is derived, which shows that any degree of coherence with respect to some reference basis can be converted to entanglement via incoherent operations. Our work provides a clear quantitative and operational connection between coherence and entanglement based on two kinds of concurrence. This new coherence measure, coherence concurrence, may also be beneficial to the study of quantum coherence.

Laser selective cutting of biological tissues by impulsive heat deposition through ultrafast vibrational excitations.

Science.gov (United States)

Franjic, Kresimir; Cowan, Michael L; Kraemer, Darren; Miller, R J Dwayne

2009-12-07

Mechanical and thermodynamic responses of biomaterials after impulsive heat deposition through vibrational excitations (IHDVE) are investigated and discussed. Specifically, we demonstrate highly efficient ablation of healthy tooth enamel using 55 ps infrared laser pulses tuned to the vibrational transition of interstitial water and hydroxyapatite around 2.95 microm. The peak intensity at 13 GW/cm(2) was well below the plasma generation threshold and the applied fluence 0.75 J/cm(2) was significantly smaller than the typical ablation thresholds observed with nanosecond and microsecond pulses from Er:YAG lasers operating at the same wavelength. The ablation was performed without adding any superficial water layer at the enamel surface. The total energy deposited per ablated volume was several times smaller than previously reported for non-resonant ultrafast plasma driven ablation with similar pulse durations. No micro-cracking of the ablated surface was observed with a scanning electron microscope. The highly efficient ablation is attributed to an enhanced photomechanical effect due to ultrafast vibrational relaxation into heat and the scattering of powerful ultrafast acoustic transients with random phases off the mesoscopic heterogeneous tissue structures.

Ultrafast excited-state deactivation of 9-methylhypoxanthine in aqueous solution: A QM/MM MD study.

Science.gov (United States)

Guo, Xugeng; Yuan, Huijuan; An, Beibei; Zhu, Qiuling; Zhang, Jinglai

2016-04-21

Photoinduced ultrafast non-adiabatic decay of 9-methylhypoxanthine (9MHPX) in aqueous solution was investigated by ab initio surface-hopping dynamics calculations using a combined quantum mechanical/molecular mechanical approach. The absorption spectra of 9MHPX in aqueous solution were also explored by the hybrid cluster-continuum model at the level of time-dependent density functional theory along with the polarizable continuum model (PCM). The static electronic-structure calculations indicate that the absorption spectra of 9MHPX simulated by TD-B3LYP/PCM and TD-X3LYP/PCM can reproduce very well the experimental findings, with the accuracy of about 0.20 eV. According to dynamics simulations, irradiation of 9MHPX populates the bright excited singlet S1 state, which may undergo an ultrafast non-radiative deactivation to the S0 state. The lifetime of the S1 state of 9MHPX in aqueous solution is predicted to be 115.6 fs, slightly longer than that in the gas phase (88.8 fs), suggesting that the solventwater has no significant influence on the excited-state lifetime of 9MHPX. Such a behavior in 9MHPX is distinctly different from its parent hypoxanthine keto-N9H tautomer in which the excited-state lifetime of the latter in watersolution was remarkably enhanced as compared to the gas phase. The significant difference of the photodynamical behaviors between 9MHPX and keto-N9H can be ascribed to their different hydrogen bond environment in aqueous solution.

Generation of mega-electron-volt electron beams by an ultrafast intense laser pulse

International Nuclear Information System (INIS)

Wang Xiaofang; Saleh, Ned; Krishnan, Mohan; Wang Haiwen; Backus, Sterling; Murnane, Margaret; Kapteyn, Henry; Umstadter, Donald; Wang Quandong; Shen Baifei

2003-01-01

Mega-electron-volt (MeV) electron emission from the interaction of an ultrafast (τ∼29 fs), intense (>10 18 W/cm 2 ) laser pulse with underdense plasmas has been studied. A beam of MeV electrons with a divergence angle as small as 1 deg. is observed in the forward direction, which is correlated with relativistic filamentation of the laser pulse in plasmas. A novel net-energy-gain mechanism is proposed for electron acceleration resulting from the relativistic filamentation and beam breakup. These results suggest an approach for generating a beam of femtosecond, MeV electrons at a kilohertz repetition rate with a compact ultrafast intense laser system

Self-induced coherence in a single pair of quantum dots

Energy Technology Data Exchange (ETDEWEB)

Sitek, Anna; Machnikowski, Pawel [Institute of Physics, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw (Poland)

2011-04-15

We study self-induced coherence (SIC) in a system composed of two coupled quantum dots (QDs). SIC consists in a coherent transfer of excitation between two systems (atoms or QDs) resulting from their collective interaction with the quantum electromagnetic vacuum. This leads to population trapping in a delocalized, optically inactive state. We focus on the effect of a difference in transition energies and coupling between the two emitters on the evolution of exciton occupation in the two QD system. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Novel Electrosorption-Enhanced Solid-Phase Microextraction Device for Ultrafast In Vivo Sampling of Ionized Pharmaceuticals in Fish.

Science.gov (United States)

Qiu, Junlang; Wang, Fuxin; Zhang, Tianlang; Chen, Le; Liu, Yuan; Zhu, Fang; Ouyang, Gangfeng

2018-01-02

Decreasing the tedious sample preparation duration is one of the most important concerns for the environmental analytical chemistry especially for in vivo experiments. However, due to the slow mass diffusion paths for most of the conventional methods, ultrafast in vivo sampling remains challenging. Herein, for the first time, we report an ultrafast in vivo solid-phase microextraction (SPME) device based on electrosorption enhancement and a novel custom-made CNT@PPY@pNE fiber for in vivo sampling of ionized acidic pharmaceuticals in fish. This sampling device exhibited an excellent robustness, reproducibility, matrix effect-resistant capacity, and quantitative ability. Importantly, the extraction kinetics of the targeted ionized pharmaceuticals were significantly accelerated using the device, which significantly improved the sensitivity of the SPME in vivo sampling method (limits of detection ranged from 0.12 ng·g -1 to 0.25 ng·g -1 ) and shorten the sampling time (only 1 min). The proposed approach was successfully applied to monitor the concentrations of ionized pharmaceuticals in living fish, which demonstrated that the device and fiber were suitable for ultrafast in vivo sampling and continuous monitoring. In addition, the bioconcentration factor (BCF) values of the pharmaceuticals were derived in tilapia (Oreochromis mossambicus) for the first time, based on the data of ultrafast in vivo sampling. Therefore, we developed and validated an effective and ultrafast SPME sampling device for in vivo sampling of ionized analytes in living organisms and this state-of-the-art method provides an alternative technique for future in vivo studies.

Radiomics for ultrafast dynamic contrast-enhanced breast MRI in the diagnosis of breast cancer: a pilot study

Science.gov (United States)

Drukker, Karen; Anderson, Rachel; Edwards, Alexandra; Papaioannou, John; Pineda, Fred; Abe, Hiroyuke; Karzcmar, Gregory; Giger, Maryellen L.

2018-02-01

Radiomics for dynamic contrast-enhanced (DCE) breast MRI have shown promise in the diagnosis of breast cancer as applied to conventional DCE-MRI protocols. Here, we investigate the potential of using such radiomic features in the diagnosis of breast cancer applied on ultrafast breast MRI in which images are acquired every few seconds. The dataset consisted of 64 lesions (33 malignant and 31 benign) imaged with both `conventional' and ultrafast DCE-MRI. After automated lesion segmentation in each image sequence, we calculated 38 radiomic features categorized as describing size, shape, margin, enhancement-texture, kinetics, and enhancement variance kinetics. For each feature, we calculated the 95% confidence interval of the area under the ROC curve (AUC) to determine whether the performance of each feature in the task of distinguishing between malignant and benign lesions was better than random guessing. Subsequently, we assessed performance of radiomic signatures in 10-fold cross-validation repeated 10 times using a support vector machine with as input all the features as well as features by category. We found that many of the features remained useful (AUC>0.5) for the ultrafast protocol, with the exception of some features, e.g., those designed for latephase kinetics such as the washout rate. For ultrafast MRI, the radiomics enhancement-texture signature achieved the best performance, which was comparable to that of the kinetics signature for `conventional' DCE-MRI, both achieving AUC values of 0.71. Radiomic developed for `conventional' DCE-MRI shows promise for translation to the ultrafast protocol, where enhancement texture appears to play a dominant role.

Self-consistent Maxwell-Bloch theory of quantum-dot-population switching in photonic crystals

International Nuclear Information System (INIS)

Takeda, Hiroyuki; John, Sajeev

2011-01-01

We theoretically demonstrate the population switching of quantum dots (QD's), modeled as two-level atoms in idealized one-dimensional (1D) and two-dimensional (2D) photonic crystals (PC's) by self-consistent solution of the Maxwell-Bloch equations. In our semiclassical theory, energy states of the electron are quantized, and electron dynamics is described by the atomic Bloch equation, while electromagnetic waves satisfy the classical Maxwell equations. Near a waveguide cutoff in a photonic band gap, the local electromagnetic density of states (LDOS) and spontaneous emission rates exhibit abrupt changes with frequency, enabling large QD population inversion driven by both continuous and pulsed optical fields. We recapture and generalize this ultrafast population switching using the Maxwell-Bloch equations. Radiative emission from the QD is obtained directly from the surrounding PC geometry using finite-difference time-domain simulation of the electromagnetic field. The atomic Bloch equations provide a source term for the electromagnetic field. The total electromagnetic field, consisting of the external input and radiated field, drives the polarization components of the atomic Bloch vector. We also include a microscopic model for phonon dephasing of the atomic polarization and nonradiative decay caused by damped phonons. Our self-consistent theory captures stimulated emission and coherent feedback effects of the atomic Mollow sidebands, neglected in earlier treatments. This leads to remarkable high-contrast QD-population switching with relatively modest (factor of 10) jump discontinuities in the electromagnetic LDOS. Switching is demonstrated in three separate models of QD's placed (i) in the vicinity of a band edge of a 1D PC, (ii) near a cutoff frequency in a bimodal waveguide channel of a 2D PC, and (iii) in the vicinity of a localized defect mode side coupled to a single-mode waveguide channel in a 2D PC.

Linear and ultrafast nonlinear plasmonics of single nano-objects

Science.gov (United States)

Crut, Aurélien; Maioli, Paolo; Vallée, Fabrice; Del Fatti, Natalia

2017-03-01

Single-particle optical investigations have greatly improved our understanding of the fundamental properties of nano-objects, avoiding the spurious inhomogeneous effects that affect ensemble experiments. Correlation with high-resolution imaging techniques providing morphological information (e.g. electron microscopy) allows a quantitative interpretation of the optical measurements by means of analytical models and numerical simulations. In this topical review, we first briefly recall the principles underlying some of the most commonly used single-particle optical techniques: near-field, dark-field, spatial modulation and photothermal microscopies/spectroscopies. We then focus on the quantitative investigation of the surface plasmon resonance (SPR) of metallic nano-objects using linear and ultrafast optical techniques. While measured SPR positions and spectral areas are found in good agreement with predictions based on Maxwell’s equations, SPR widths are strongly influenced by quantum confinement (or, from a classical standpoint, surface-induced electron scattering) and, for small nano-objects, cannot be reproduced using the dielectric functions of bulk materials. Linear measurements on single nano-objects (silver nanospheres and gold nanorods) allow a quantification of the size and geometry dependences of these effects in confined metals. Addressing the ultrafast response of an individual nano-object is also a powerful tool to elucidate the physical mechanisms at the origin of their optical nonlinearities, and their electronic, vibrational and thermal relaxation processes. Experimental investigations of the dynamical response of gold nanorods are shown to be quantitatively modeled in terms of modifications of the metal dielectric function enhanced by plasmonic effects. Ultrafast spectroscopy can also be exploited to unveil hidden physical properties of more complex nanosystems. In this context, two-color femtosecond pump-probe experiments performed on individual

Ultrafast electron microscopy in materials science, biology, and chemistry

International Nuclear Information System (INIS)

King, Wayne E.; Campbell, Geoffrey H.; Frank, Alan; Reed, Bryan; Schmerge, John F.; Siwick, Bradley J.; Stuart, Brent C.; Weber, Peter M.

2005-01-01

The use of pump-probe experiments to study complex transient events has been an area of significant interest in materials science, biology, and chemistry. While the emphasis has been on laser pump with laser probe and laser pump with x-ray probe experiments, there is a significant and growing interest in using electrons as probes. Early experiments used electrons for gas-phase diffraction of photostimulated chemical reactions. More recently, scientists are beginning to explore phenomena in the solid state such as phase transformations, twinning, solid-state chemical reactions, radiation damage, and shock propagation. This review focuses on the emerging area of ultrafast electron microscopy (UEM), which comprises ultrafast electron diffraction (UED) and dynamic transmission electron microscopy (DTEM). The topics that are treated include the following: (1) The physics of electrons as an ultrafast probe. This encompasses the propagation dynamics of the electrons (space-charge effect, Child's law, Boersch effect) and extends to relativistic effects. (2) The anatomy of UED and DTEM instruments. This includes discussions of the photoactivated electron gun (also known as photogun or photoelectron gun) at conventional energies (60-200 keV) and extends to MeV beams generated by rf guns. Another critical aspect of the systems is the electron detector. Charge-coupled device cameras and microchannel-plate-based cameras are compared and contrasted. The effect of various physical phenomena on detective quantum efficiency is discussed. (3) Practical aspects of operation. This includes determination of time zero, measurement of pulse-length, and strategies for pulse compression. (4) Current and potential applications in materials science, biology, and chemistry. UEM has the potential to make a significant impact in future science and technology. Understanding of reaction pathways of complex transient phenomena in materials science, biology, and chemistry will provide fundamental

Ultrafast photon counting applied to resonant scanning STED microscopy.

Science.gov (United States)

Wu, Xundong; Toro, Ligia; Stefani, Enrico; Wu, Yong

2015-01-01

To take full advantage of fast resonant scanning in super-resolution stimulated emission depletion (STED) microscopy, we have developed an ultrafast photon counting system based on a multigiga sample per second analogue-to-digital conversion chip that delivers an unprecedented 450 MHz pixel clock (2.2 ns pixel dwell time in each scan). The system achieves a large field of view (∼50 × 50 μm) with fast scanning that reduces photobleaching, and advances the time-gated continuous wave STED technology to the usage of resonant scanning with hardware-based time-gating. The assembled system provides superb signal-to-noise ratio and highly linear quantification of light that result in superior image quality. Also, the system design allows great flexibility in processing photon signals to further improve the dynamic range. In conclusion, we have constructed a frontier photon counting image acquisition system with ultrafast readout rate, excellent counting linearity, and with the capacity of realizing resonant-scanning continuous wave STED microscopy with online time-gated detection. © 2014 The Authors Journal of Microscopy © 2014 Royal Microscopical Society.

Ultrafast Bessel beams: advanced tools for laser materials processing

Science.gov (United States)

Stoian, Razvan; Bhuyan, Manoj K.; Zhang, Guodong; Cheng, Guanghua; Meyer, Remy; Courvoisier, Francois

2018-05-01

Ultrafast Bessel beams demonstrate a significant capacity of structuring transparent materials with a high degree of accuracy and exceptional aspect ratio. The ability to localize energy on the nanometer scale (bypassing the 100-nm milestone) makes them ideal tools for advanced laser nanoscale processing on surfaces and in the bulk. This allows to generate and combine micron and nano-sized features into hybrid structures that show novel functionalities. Their high aspect ratio and the accurate location can equally drive an efficient material modification and processing strategy on large dimensions. We review, here, the main concepts of generating and using Bessel non-diffractive beams and their remarkable features, discuss general characteristics of their interaction with matter in ablation and material modification regimes, and advocate their use for obtaining hybrid micro and nanoscale structures in two and three dimensions (2D and 3D) performing complex functions. High-throughput applications are indicated. The example list ranges from surface nanostructuring and laser cutting to ultrafast laser welding and the fabrication of 3D photonic systems embedded in the volume.

Ultrafast CT in the diagnosis of sleep apnea during awake tidal breathing

International Nuclear Information System (INIS)

Galvin, J.R.; Rooholamini, S.A.; Stanford, W.

1988-01-01

With sleep there is normally a decrease in neural output to upper airway muscles. If this decrease is superimposed on a structurally abnormal airway, then sleep apnea may result. Ultrafast CT axially images the upper airway in near real time. The authors compared 11 awake patients with sleep apnea with 24 healthy volunteers during quiet tidal breathing. They found that apneic patients have a small oropharyngeal airway (31.3 mm 2 +- 30.2 vs 134.2 mm 2 +- 46.6[P=<.0001]). Apneic patients also have significant collapsibility of the nasopharynx (75% +- 18% vs 27% +- 14% [P=<.0001]). Ultrafast CT gives dynamic anatomic definition of the upper airway and provides a means to eulcidate further the pathogenesis of sleep apnea

Characterization of Nanostructured Semiconductors by Ultrafast Luminescence Imaging

Science.gov (United States)

Blake, Jolie

Single nanostructures are predicted to be the building blocks of next generation devices and have already been incorporated into prototypes for solar cells, biomedical devices and lasers. Their role in such applications requires a fundamental understanding of their opto-electronic properties and in particular the charge carrier dynamics occurring on an ultrafast timescale. Luminescence detection is a common approach used to investigate electronic properties of nanostructures because of the contact-less nature of these methods. They are, however, often not equipped to efficiently measure multiple single nanostructures nor do they have the temporal resolution necessary for observing femtosecond dynamics. This dissertation intends to address this paucity of techniques available for the contact-less measurement of single nanostructures through the development of an ultrafast wide-field Kerr-gated microscope system and measurement technique. The setup, operational in both the steady state and transient mode and capable of microscopic and spectroscopic measurements, was developed to measure the transient luminescence of single semiconductor nanostructures. With sub micron spatial resolution and the potential to achieve a temporal resolution greater than 90 fs, the system was used to probe the charge carrier dynamics at multiple discrete locations on single nanowires exhibiting amplified spontaneous emission. Using a rate model for amplified spontaneous emission, the transient emission data was fitted to extract the values of the competing Shockley-Read-Hall, non-geminate and Auger recombination constants. The capabilities of the setup were first demonstrated in the visible detection range, where single nanowires of the ternary alloy CdS x Se1-x were measured. The temporal emission dynamics at two separate locations were compared and calculation of the Langevin mobility revealed that the large carrier densities generated in the nanowire allows access to non

Ultrafast nonlinear response of silicon carbide to intense THz fields

DEFF Research Database (Denmark)

Tarekegne, Abebe Tilahun; Iwaszczuk, Krzysztof; Kaltenecker, Korbinian J.

2017-01-01

We demonstrate ultrafast nonlinear absorption induced by strong, single-cycle THz fields in bulk, lightly doped 4H silicon carbide. A combination of Zener tunneling and intraband transitions makes the effect as at least as fast as the excitation pulse. The sub-picosecond recovery time makes...

Quantitative shear wave imaging optical coherence tomography for noncontact mechanical characterization of myocardium

Science.gov (United States)

Wang, Shang; Lopez, Andrew L.; Morikawa, Yuka; Tao, Ge; Li, Jiasong; Larina, Irina V.; Martin, James F.; Larin, Kirill V.

2015-03-01

Optical coherence elastography (OCE) is an emerging low-coherence imaging technique that provides noninvasive assessment of tissue biomechanics with high spatial resolution. Among various OCE methods, the capability of quantitative measurement of tissue elasticity is of great importance for tissue characterization and pathology detection across different samples. Here we report a quantitative OCE technique, termed quantitative shear wave imaging optical coherence tomography (Q-SWI-OCT), which enables noncontact measurement of tissue Young's modulus based on the ultra-fast imaging of the shear wave propagation inside the sample. A focused air-puff device is used to interrogate the tissue with a low-pressure short-duration air stream that stimulates a localized displacement with the scale at micron level. The propagation of this tissue deformation in the form of shear wave is captured by a phase-sensitive OCT system running with the scan of the M-mode imaging over the path of the wave propagation. The temporal characteristics of the shear wave is quantified based on the cross-correlation of the tissue deformation profiles at all the measurement locations, and linear regression is utilized to fit the data plotted in the domain of time delay versus wave propagation distance. The wave group velocity is thus calculated, which results in the quantitative measurement of the Young's modulus. As the feasibility demonstration, experiments are performed on tissuemimicking phantoms with different agar concentrations and the quantified elasticity values with Q-SWI-OCT agree well with the uniaxial compression tests. For functional characterization of myocardium with this OCE technique, we perform our pilot experiments on ex vivo mouse cardiac muscle tissues with two studies, including 1) elasticity difference of cardiac muscle under relaxation and contract conditions and 2) mechanical heterogeneity of the heart introduced by the muscle fiber orientation. Our results suggest the

Spectroscopic Investigation of the Ultrafast Photoinduced Dynamics in pi-Conjugated Terpyridines

NARCIS (Netherlands)

Siebert, R.; Akimov, D.; Schmitt, M.; Winter, A.; Schubert, U.S.; Dietzek, B.; Popp, J.

2009-01-01

Time-resolved spectroscopy is applied to investigate the ultrafast relaxation dynamics of several pi-conjugated mono-, bis-, tris- and tetrakis(terpyridine) derivs. This particular series of structurally closely related systems was prepd. applying efficient synthetic strategies and resembles key

Ultrafast measurements of chlorine dioxide photochemistry

Energy Technology Data Exchange (ETDEWEB)

Ludowise, P.D.

1997-08-01

Time-resolved mass spectrometry and time-resolved photoelectron spectroscopy are used to study the ultrafast photodissociation dynamics of chlorine dioxide, an important constituent in stratospheric ozone depletion. Chapter 1 introduces these pump/probe techniques, in which a femtosecond pump pulse excites a molecule to a dissociative state. At a later time, a second femtosecond probe pulse ionizes the molecule. The resulting mass and photoelectron spectra are acquired as a function of the delay between the pump and probe pulses, which follows the evolution of the molecule on the excited state. A comparison to other techniques used to study reaction dynamics is discussed. Chapter 2 includes a detailed description of the design and construction of the experimental apparatus, which consists of a femtosecond laser system, a molecular beam time-of-flight spectrometer, and a data acquisition system. The time-of-flight spectrometer is specifically designed to have a short flight distance to maximize the photoelectron collection efficiency without degrading the resolution, which is limited by the bandwidth of the femtosecond laser system. Typical performance of the apparatus is demonstrated in a study of the time-resolved photoelectron spectroscopy of nitric oxide. The results of the time-resolved mass spectrometry experiments of chlorine dioxide are presented in Chapter 3. Upon excitation to the A {sup 2}A{sub 2} state near 3.2 eV, the molecule dissociates through an indirect two-step mechanism. The direct dissociation channel has been predicted to be open, but is not observed. A quantum beat is observed in the OClO{sup +} species, which is described as a vibrational coherence of the optically prepared A {sup 2}A{sub 2} state. Chapter 4 presents the results of the time-resolved photoelectron experiments of chlorine dioxide. At short delay time, the quantum beat of the OClO{sup +} species is observed in the X {sup 1}A{sub 1} state of the ion. At infinite delay, the signal

Femtosecond Coherent Spectroscopy at 800nm: MI-FROG Measures High-Field Ionization Rates in Gases

International Nuclear Information System (INIS)

Siders, C.W.; Siders, J.L.W.; Taylor, A.J.

1999-01-01

The authors report the first quantitative phase-sensitive measurement of ultrafast ionization rates in gases using Multi-phase Interferometric Frequency-Resolved Optical Gating. Ultrafast probe depletion via frequency mixing in the ionization front is observed

Quantum coherence: Reciprocity and distribution

Energy Technology Data Exchange (ETDEWEB)

Kumar, Asutosh, E-mail: asukumar@hri.res.in [Harish-Chandra Research Institute, Allahabad-211019 (India); Homi Bhabha National Institute, Anushaktinagar, Mumbai 400094 (India)

2017-03-18

Quantum coherence is the outcome of the superposition principle. Recently, it has been theorized as a quantum resource, and is the premise of quantum correlations in multipartite systems. It is therefore interesting to study the coherence content and its distribution in a multipartite quantum system. In this work, we show analytically as well as numerically the reciprocity between coherence and mixedness of a quantum state. We find that this trade-off is a general feature in the sense that it is true for large spectra of measures of coherence and of mixedness. We also study the distribution of coherence in multipartite systems by looking at monogamy-type relation–which we refer to as additivity relation–between coherences of different parts of the system. We show that for the Dicke states, while the normalized measures of coherence violate the additivity relation, the unnormalized ones satisfy the same. - Highlights: • Quantum coherence. • Reciprocity between quantum coherence and mixedness. • Distribution of quantum coherence in multipartite quantum systems. • Additivity relation for distribution of quantum coherence in Dicke and “X” states.

Photonic crystal fiber technology for compact fiber-delivered high-power ultrafast fiber lasers

Science.gov (United States)

Triches, Marco; Michieletto, Mattia; Johansen, Mette M.; Jakobsen, Christian; Olesen, Anders S.; Papior, Sidsel R.; Kristensen, Torben; Bondue, Magalie; Weirich, Johannes; Alkeskjold, Thomas T.

2018-02-01

Photonic crystal fiber (PCF) technology has radically impacted the scientific and industrial ultrafast laser market. Reducing platform dimensions are important to decrease cost and footprint while maintaining high optical efficiency. We present our recent work on short 85 μm core ROD-type fiber amplifiers that maintain single-mode performance and excellent beam quality. Robust long-term performance at 100 W average power and 250 kW peak power in 20 ps pulses at 1030 nm wavelength is presented, exceeding 500 h with stable performance in terms of both polarization and power. In addition, we present our recent results on hollow-core ultrafast fiber delivery maintaining high beam quality and polarization purity.

Vibrational imaging and microspectroscopies based on coherent anti-Stokes Raman scattering microscopy

International Nuclear Information System (INIS)

Volkmer, Andreas

2005-01-01

For noninvasive characterization of chemical species or biological components within a complex heterogeneous system, their intrinsic molecular vibrational properties can be used in contrast mechanisms in optical microscopy. A series of recent advances have made coherent anti-Stokes Raman scattering (CARS) microscopy a powerful technique that allows vibrational imaging with high sensitivity, high spectral resolution and three-dimensional sectioning capability. In this review, we discuss theoretical and experimental aspects of CARS microscopy in a collinear excitation beam geometry. Particular attention is given to the underlying physical principles behind the new features of CARS signal generation under tight focusing conditions. We provide a brief overview of the instrumentation of CARS microscopy and its experimental characterization by means of imaging of model systems and live unstained cells. CARS microscopy offers the possibility of spatially resolved vibrational spectroscopy, providing chemical and physical structure information of molecular specimens on the sub-micrometre length scale. We review multiplex CARS microspectroscopy allowing fast acquisition of frequency-resolved CARS spectra, time-resolved CARS microspectroscopy recording ultrafast Raman free induction decays and CARS correlation spectroscopy probing dynamical processes with chemical selectivity. (topical review)

Coherent quantum dynamics of excitons in monolayer transition metal dichalcogenides

KAUST Repository

Moody, Galan

2016-03-14

Transition metal dichalcogenides (TMDs) have garnered considerable interest in recent years owing to their layer thickness-dependent optoelectronic properties. In monolayer TMDs, the large carrier effective masses, strong quantum confinement, and reduced dielectric screening lead to pronounced exciton resonances with remarkably large binding energies and coupled spin and valley degrees of freedom (valley excitons). Coherent control of valley excitons for atomically thin optoelectronics and valleytronics requires understanding and quantifying sources of exciton decoherence. In this work, we reveal how exciton-exciton and exciton-phonon scattering influence the coherent quantum dynamics of valley excitons in monolayer TMDs, specifically tungsten diselenide (WSe2), using two-dimensional coherent spectroscopy. Excitation-density and temperature dependent measurements of the homogeneous linewidth (inversely proportional to the optical coherence time) reveal that exciton-exciton and exciton-phonon interactions are significantly stronger compared to quasi-2D quantum wells and 3D bulk materials. The residual homogeneous linewidth extrapolated to zero excitation density and temperature is ~1:6 meV (equivalent to a coherence time of 0.4 ps), which is limited only by the population recombination lifetime in this sample. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Coherent quantum dynamics of excitons in monolayer transition metal dichalcogenides

KAUST Repository

Moody, Galan; Hao, Kai; Dass, Chandriker Kavir; Singh, Akshay; Xu, Lixiang; Tran, Kha; Chen, Chang-Hsiao; Li, Ming-yang; Li, Lain-Jong; Clark, Genevieve; Bergh ä user, Gunnar; Malic, Ermin; Knorr, Andreas; Xu, Xiaodong; Li, Xiaoqin

2016-01-01

Transition metal dichalcogenides (TMDs) have garnered considerable interest in recent years owing to their layer thickness-dependent optoelectronic properties. In monolayer TMDs, the large carrier effective masses, strong quantum confinement, and reduced dielectric screening lead to pronounced exciton resonances with remarkably large binding energies and coupled spin and valley degrees of freedom (valley excitons). Coherent control of valley excitons for atomically thin optoelectronics and valleytronics requires understanding and quantifying sources of exciton decoherence. In this work, we reveal how exciton-exciton and exciton-phonon scattering influence the coherent quantum dynamics of valley excitons in monolayer TMDs, specifically tungsten diselenide (WSe2), using two-dimensional coherent spectroscopy. Excitation-density and temperature dependent measurements of the homogeneous linewidth (inversely proportional to the optical coherence time) reveal that exciton-exciton and exciton-phonon interactions are significantly stronger compared to quasi-2D quantum wells and 3D bulk materials. The residual homogeneous linewidth extrapolated to zero excitation density and temperature is ~1:6 meV (equivalent to a coherence time of 0.4 ps), which is limited only by the population recombination lifetime in this sample. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

The scaup conservation action plan: working toward coherence

Science.gov (United States)

Austin, Jane E.

2010-01-01

The last in a series of three workshops to develop a decision framework for the scaup conservation action plan was conducted in September 2009. Fifteen waterfowl biologists and managers met in Memphis, Tennessee at the Ducks Unlimited Headquarters to review and refine the decision statement, objectives, and prototype model for the continental scaup population, with a special focus on vital rate parameters that are affected during migration and winter. In a significant step toward coherence, the participants also developed models for incorporating human dimensions – hunters – into the decision framework, and to link the population of diving duck hunters with the continental scaup population.

Vacuum-induced coherence in quantum dot systems

Science.gov (United States)

Sitek, Anna; Machnikowski, Paweł

2012-11-01

We present a theoretical study of vacuum-induced coherence in a pair of vertically stacked semiconductor quantum dots. The process consists in a coherent excitation transfer from a single-exciton state localized in one dot to a delocalized state in which the exciton occupation gets trapped. We study the influence of the factors characteristic of quantum dot systems (as opposed to natural atoms): energy mismatch, coupling between the single-exciton states localized in different dots, and different and nonparallel dipoles due to sub-band mixing, as well as coupling to phonons. We show that the destructive effect of the energy mismatch can be overcome by an appropriate interplay of the dipole moments and coupling between the dots which allows one to observe the trapping effect even in a structure with technologically realistic energy splitting of the order of milli-electron volts. We also analyze the impact of phonon dynamics on the occupation trapping and show that phonon effects are suppressed in a certain range of system parameters. This analysis shows that the vacuum-induced coherence effect and the associated long-living trapped excitonic population can be achieved in quantum dots.

Observation of coherent optical phonons excited by femtosecond laser radiation in Sb films by ultrafast electron diffraction method

Energy Technology Data Exchange (ETDEWEB)

Mironov, B. N.; Kompanets, V. O.; Aseev, S. A., E-mail: isanfemto@yandex.ru [Russian Academy of Sciences, Institute of Spectroscopy (Russian Federation); Ischenko, A. A. [Moscow Technological University, Institute of High Chemical Technologies (Russian Federation); Kochikov, I. V. [Moscow State University (Russian Federation); Misochko, O. V. [Russian Academy of Sciences, Institute of Solid State Physics (Russian Federation); Chekalin, S. V.; Ryabov, E. A. [Russian Academy of Sciences, Institute of Spectroscopy (Russian Federation)

2017-03-15

The generation of coherent optical phonons in a polycrystalline antimony film sample has been investigated using femtosecond electron diffraction method. Phonon vibrations have been induced in the Sb sample by the main harmonic of a femtosecond Ti:Sa laser (λ = 800 nm) and probed by a pulsed ultrashort photoelectron beam synchronized with the pump laser. The diffraction patterns recorded at different times relative to the pump laser pulse display oscillations of electron diffraction intensity corresponding to the frequencies of vibrations of optical phonons: totally symmetric (A{sub 1g}) and twofold degenerate (E{sub g}) phonon modes. The frequencies that correspond to combinations of these phonon modes in the Sb sample have also been experimentally observed.

Beating Darwin-Bragg losses in lab-based ultrafast x-ray experiments

Directory of Open Access Journals (Sweden)

Wilfred K. Fullagar

2017-07-01

Full Text Available The use of low temperature thermal detectors for avoiding Darwin-Bragg losses in lab-based ultrafast experiments has begun. An outline of the background of this new development is offered, showing the relevant history and initiative taken by this work.

On nonequilibrium many-body systems V: ultrafast transport phenomena

International Nuclear Information System (INIS)

Freire, V.N.; Vasconcellos, A.R.; Luzzi, R.

1989-01-01

The monequilibrium statistical operator method and its accompanying nonlinear quantum transport theory, are used to perform an analytical study of the ultrafast mobility transient of central-valley photoinjected carriers in direct-gap polar semiconductors. Expressions for the time-resolved mobility of the hot carriers are derived. A brief discussion of the carriers' diffusion coefficient is done. (A.C.A.S.) [pt

New Aspects of Photocurrent Generation at Graphene pn Junctions Revealed by Ultrafast Optical Measurements

Science.gov (United States)

Aivazian, Grant; Sun, Dong; Jones, Aaron; Ross, Jason; Yao, Wang; Cobden, David; Xu, Xiaodong

2012-02-01

The remarkable electrical and optical properties of graphene make it a promising material for new optoelectronic applications. However, one important, but so far unexplored, property is the role of hot carriers in charge and energy transport at graphene interfaces. Here we investigate the photocurrent (PC) dynamics at a tunable graphene pn junction using ultrafast scanning PC microscopy. Pump-probe measurements show a temperature dependent relaxation time of photogenerated carriers that increases from 1.5ps at 290K to 4ps at 20K; while the amplitude of the PC is independent of the lattice temperature. These observations imply that it is hot carriers, not phonons, which dominate ultrafast energy transport. Gate dependent measurements show many interesting features such as pump induced saturation, enhancement, and sign reversal of probe generated PC. These observations reveal that the underlying PC mechanism is a combination of the thermoelectric and built-in electric field effects. Our results enhance the understanding of non-equilibrium electron dynamics, electron-electron interactions, and electron-phonon interactions in graphene. They also determine fundamental limits on ultrafast device operation speeds (˜500 GHz) for graphene-based photodetectors.

Ultrafast release and capture of carriers in InGaAs/GaAs quantum dots observed by time-resolved terahertz spectroscopy

DEFF Research Database (Denmark)

Porte, Henrik; Jepsen, Peter Uhd; Daghestani, N.

2009-01-01

We observe ultrafast release and capture of charge carriers in InGaAs/GaAs quantum dots in a room-temperature optical pump-terahertz probe experiment sensitive to the population dynamics of conducting states. In case of resonant excitation of the quantum dot ground state, the maximum conductivity...... is achieved at approximately 35 ps after photoexcitation, which is assigned to release of carriers from the quantum dots. When exciting carriers into the conduction band of the barriers, depletion of the conductivity via carrier capture into the quantum dots with a few picosecond pump fluence-dependent time...

Concept and design of a beam blanker with integrated photoconductive switch for ultrafast electron microscopy.

Science.gov (United States)

Weppelman, I G C; Moerland, R J; Hoogenboom, J P; Kruit, P

2018-01-01

We present a new method to create ultrashort electron pulses by integrating a photoconductive switch with an electrostatic deflector. This paper discusses the feasibility of such a system by analytical and numerical calculations. We argue that ultrafast electron pulses can be achieved for micrometer scale dimensions of the blanker, which are feasible with MEMS-based fabrication technology. According to basic models, the design presented in this paper is capable of generating 100 fs electron pulses with spatial resolutions of less than 10 nm. Our concept for an ultrafast beam blanker (UFB) may provide an attractive alternative to perform ultrafast electron microscopy, as it does not require modification of the microscope nor realignment between DC and pulsed mode of operation. Moreover, only low laser pulse energies are required. Due to its small dimensions the UFB can be inserted in the beam line of a commercial microscope via standard entry ports for blankers or variable apertures. The use of a photoconductive switch ensures minimal jitter between laser and electron pulses. Copyright © 2017 Elsevier B.V. All rights reserved.

Ultrafast cavitation induced by an X-ray laser in water drops

Science.gov (United States)

Stan, Claudiu; Willmott, Philip; Stone, Howard; Koglin, Jason; Liang, Mengning; Aquila, Andrew; Robinson, Joseph; Gumerlock, Karl; Blaj, Gabriel; Sierra, Raymond; Boutet, Sebastien; Guillet, Serge; Curtis, Robin; Vetter, Sharon; Loos, Henrik; Turner, James; Decker, Franz-Josef

2016-11-01

Cavitation in pure water is determined by an intrinsic heterogeneous cavitation mechanism, which prevents in general the experimental generation of large tensions (negative pressures) in bulk liquid water. We developed an ultrafast decompression technique, based on the reflection of shock waves generated by an X-ray laser inside liquid drops, to stretch liquids to large negative pressures in a few nanoseconds. Using this method, we observed cavitation in liquid water at pressures below -100 MPa. These large tensions exceed significantly those achieved previously, mainly due to the ultrafast decompression. The decompression induced by shock waves generated by an X-ray laser is rapid enough to continue to stretch the liquid phase after the heterogeneous cavitation occurs in water, despite the rapid growth of cavitation nanobubbles. We developed a nucleation-and-growth hydrodynamic cavitation model that explains our results and estimates the concentration of heterogeneous cavitation nuclei in water.

Femtosecond laser studies of ultrafast intramolecular processes

Energy Technology Data Exchange (ETDEWEB)

Hayden, C. [Sandia National Laboratories, Livermore, CA (United States)

1993-12-01

The goal of this research is to better understand the detailed mechanisms of chemical reactions by observing, directly in time, the dynamics of fundamental chemical processes. In this work femtosecond laser pulses are used to initiate chemical processes and follow the progress of these processes in time. The authors are currently studying ultrafast internal conversion and subsequent intramolecular relaxation in unsaturated hydrocarbons. In addition, the authors are developing nonlinear optical techniques to prepare and monitor the time evolution of specific vibrational motions in ground electronic state molecules.

Ultrafast carrier dynamics in band edge and broad deep defect emission ZnSe nanowires

Science.gov (United States)

Othonos, Andreas; Lioudakis, Emmanouil; Philipose, U.; Ruda, Harry E.

2007-12-01

Ultrafast carrier dynamics of ZnSe nanowires grown under different growth conditions have been studied. Transient absorption measurements reveal the dependence of the competing effects of state filling and photoinduced absorption on the probed energy states. The relaxation of the photogenerated carriers occupying defect states in the stoichiometric and Se-rich samples are single exponentials with time constants of 3-4ps. State filling is the main contribution for probe energies below 1.85eV in the Zn-rich grown sample. This ultrafast carrier dynamics study provides an important insight into the role that intrinsic point defects play in the observed photoluminescence from ZnSe nanowires.

Observation and control of coherent torsional dynamics in a quinquethiophene molecule.

Science.gov (United States)

Cirmi, Giovanni; Brida, Daniele; Gambetta, Alessio; Piacenza, Manuel; Della Sala, Fabio; Favaretto, Laura; Cerullo, Giulio; Lanzani, Guglielmo

2010-07-28

By applying femtosecond pump-probe spectroscopy to a substituted quinquethiophene molecule in solution, we observe in the time domain the coherent torsional dynamics that drives planarization of the excited state. Our interpretation is based on numerical modeling of the ground and excited state potential energy surfaces and simulation of wavepacket dynamics, which reveals two symmetric excited state deactivation pathways per oscillation period. We use the acquired knowledge on torsional dynamics to coherently control the excited state population with a pump-dump scheme, exploiting the non-stationary Franck-Condon overlap between ground and excited states.

Coherent hybrid electromagnetic field imaging

Science.gov (United States)

Cooke, Bradly J [Jemez Springs, NM; Guenther, David C [Los Alamos, NM

2008-08-26

An apparatus and corresponding method for coherent hybrid electromagnetic field imaging of a target, where an energy source is used to generate a propagating electromagnetic beam, an electromagnetic beam splitting means to split the beam into two or more coherently matched beams of about equal amplitude, and where the spatial and temporal self-coherence between each two or more coherently matched beams is preserved. Two or more differential modulation means are employed to modulate each two or more coherently matched beams with a time-varying polarization, frequency, phase, and amplitude signal. An electromagnetic beam combining means is used to coherently combine said two or more coherently matched beams into a coherent electromagnetic beam. One or more electromagnetic beam controlling means are used for collimating, guiding, or focusing the coherent electromagnetic beam. One or more apertures are used for transmitting and receiving the coherent electromagnetic beam to and from the target. A receiver is used that is capable of square-law detection of the coherent electromagnetic beam. A waveform generator is used that is capable of generation and control of time-varying polarization, frequency, phase, or amplitude modulation waveforms and sequences. A means of synchronizing time varying waveform is used between the energy source and the receiver. Finally, a means of displaying the images created by the interaction of the coherent electromagnetic beam with target is employed.

Detection of coronary artery calcification by ultrafast CT and correlation with angiography

International Nuclear Information System (INIS)

Zhang Shaoxiong; Dai Ruping; Lu Bin

1997-01-01

To investigate the relationship between coronary calcification and significant coronary stenosis ninety patients including 81 men and 9 women were studied asithage ranging from 27∼72 years (mean, 58 years). All patients had both ultrafast CT (UFCT) examination and coronary angiography within one month. Single slice mode with ECG gating and thickness of 3 mm were used in UFCT scan. Selected coronary angiography was performed by the Judkins technique. Among 160 vessels in which coronary calcifications were identified, 74% had significant coronary stenosis (>50% stenosis), and 77% of 154 vessels with significant coronary stenosis had calcification demonstrable by UFCT. In the younger age group the sensitivity of calcification for evaluating stenosis of coronary artery was lower and the specificity was generally higher than those in the elderly group. UFCT is a promising procedure for detecting coronary arterial disease, since this examination has high sensitivity and specificity, easy to conduct, noninvasive, and widely applicable for screening a large population

Ultrafast optical switching in three-dimensional photonic crystals

OpenAIRE

Mazurenko, D.A.

2004-01-01

The rapidly expanding research on photonic crystals is driven by potential applications in all-optical switches, optical computers, low-threshold lasers, and holographic data storage. The performance of such devices might surpass the speed of traditional electronics by several orders of magnitude and may result in a true revolution in nanotechnology. The heart of such devices would likely be an optical switching element. This thesis analyzes different regimes of ultrafast all-optical switchin...

Pump-probe study of the formation of rubidium molecules by ultrafast photoassociation of ultracold atoms

Science.gov (United States)

McCabe, David J.; England, Duncan G.; Martay, Hugo E. L.; Friedman, Melissa E.; Petrovic, Jovana; Dimova, Emiliya; Chatel, Béatrice; Walmsley, Ian A.

2009-09-01

An experimental pump-probe study of the photoassociative creation of translationally ultracold rubidium molecules is presented together with numerical simulations of the process. The formation of loosely bound excited-state dimers is observed as a first step toward a fully coherent pump-dump approach to the stabilization of Rb2 into its lowest ground vibrational states. The population that contributes to the pump-probe process is characterized and found to be distinct from a background population of preassociated molecules.

Ultrafast and ultrasensitive dielectric liquids/mixtures: Basic measurements and applications

International Nuclear Information System (INIS)

Christophorou, L.G.; Faidas, H.; McCorkle, D.L.; Tennessee Univ., Knoxville, TN

1989-01-01

Basic properties of cryogenic and room temperature dielectric liquids/mixtures with high electron yields (under irradiation by ionizing particles) and high excess electron drift velocities are discussed. A number of ultrafast and ultrasensitive liquid media -- appropriate for possible use in liquid-filled radiation detectors and other applications -- are identified. 44 refs., 12 figs

Ultra-fast repair of single-strand breaks in DNA of. gamma. -irradiated Chinese hamster cells

Energy Technology Data Exchange (ETDEWEB)

Leontjeva, G A; Mantzighin, Yu A; Gaziev, A I [AN SSSR, Pushchino-na-Oke. Inst. Biologicheskoj Fiziki

1976-12-01

Studies of the effect of thermal treatment of Chinese hamster cells on sedimentation of DNA in the alkaline sucrose gradient showed that heating the cells to 68/sup 0/C for 15 min caused the same degradation as ..gamma..-irradiation with 5 to 7 krad at 37/sup 0/C. The inhibition of cellular repair enzymes by heating was therefore unacceptable. The process of ultra-fast repair is essentially determined by the DNA-ligase reaction, which is activated in the presence of Mg ions, and inhibited in mammalian cells in the presence of EDTA and pyrophosphate. Sedimentation profiles were therefore measured for the DNA of Chinese hamster cells ..gamma..-irradiated (5 krad) at 0/sup 0/C or 22/sup 0/C in the presence of Mg/sup + +/, or EDTA and pyrophosphate, and the results demonstrated ultra-fast repair only at 20 to 37/sup 0/C, in contrast to bacteria. A study was made of the temperature dependence of the activity of the DNA ligases isolated from E.coli and rabbit bone marrow. The NAD-dependent bacterial DNA ligase was active at temperatures from 0 to 40/sup 0/C, whereas ATP-dependent DNA ligase of mammals only showed activity in the range 15 to 40/sup 0/C. The differing temperature dependences of ultra-fast repair in bacterial and mammalian cells are in agreement with the temperature dependences of the activities of isolated enzymes, and the results suggest that the process of ultra-fast repair of single-strand breaks of DNA takes place in both bacterial and mammalian cells.

Ordering states with various coherence measures

Science.gov (United States)

Yang, Long-Mei; Chen, Bin; Fei, Shao-Ming; Wang, Zhi-Xi

2018-04-01

Quantum coherence is one of the most significant theories in quantum physics. Ordering states with various coherence measures is an intriguing task in quantification theory of coherence. In this paper, we study this problem by use of four important coherence measures—the l_1 norm of coherence, the relative entropy of coherence, the geometric measure of coherence and the modified trace distance measure of coherence. We show that each pair of these measures give a different ordering of qudit states when d≥3. However, for single-qubit states, the l_1 norm of coherence and the geometric coherence provide the same ordering. We also show that the relative entropy of coherence and the geometric coherence give a different ordering for single-qubit states. Then we partially answer the open question proposed in Liu et al. (Quantum Inf Process 15:4189, 2016) whether all the coherence measures give a different ordering of states.

Ultrafast characterization of optoelectronic devices and systems

Science.gov (United States)

Zheng, Xuemei

The recent fast growth in high-speed electronics and optoelectronics has placed demanding requirements on testing tools. Electro-optic (EO) sampling is a well-established technique for characterization of high-speed electronic and optoelectronic devices and circuits. However, with the progress in device miniaturization, lower power consumption (smaller signal), and higher throughput (higher clock rate), EO sampling also needs to be updated, accordingly, towards better signal-to-noise ratio (SNR) and sensitivity, without speed sacrifice. In this thesis, a novel EO sampler with a single-crystal organic 4-dimethylamino-N-methy-4-stilbazolium tosylate (DAST) as the EO sensor is developed. The system exhibits sub-picosecond temporal resolution, sub-millivolt sensitivity, and a 10-fold improvement on SNR, compared with its LiTaO3 counterpart. The success is attributed to the very high EO coefficient, the very low dielectric constant, and the fast response, coming from the major contribution of the pi-electrons in DAST. With the advance of ultrafast laser technology, low-noise and compact femtosecond fiber lasers have come to maturation and become light-source options for ultrafast metrology systems. We have successfully integrated a femtosecond erbium-doped-fiber laser into an EO sampler, making the system compact and very reliable. The fact that EO sampling is essentially an impulse-response measurement process, requires integration of ultrashort (sub-picosecond) impulse generation network with the device under test. We have implemented a reliable lift-off and transfer technique in order to obtain epitaxial-quality freestanding low-temperature-grown GaAs (LT-GaAs) thin-film photo-switches, which can be integrated with many substrates. The photoresponse of our freestanding LT-GaAs devices was thoroughly characterized with the help of our EO sampler. As fast as 360 fs full-width-at-half-maximum (FWHM) and >1 V electrical pulses were obtained, with quantum efficiency

Oxygen Activated, Palladium Nanoparticle Catalyzed, Ultrafast Cross-Coupling of Organolithium Reagents

NARCIS (Netherlands)

Heijnen, Dorus; Tosi, Filippo; Vila, Carlos; Stuart, Marc C. A.; Elsinga, Philip H.; Szymanski, Wiktor; Feringa, Ben L.

2017-01-01

The discovery of an ultrafast cross-coupling of alkyland aryllithium reagents with a range of aryl bromides is presented. The essential role of molecular oxygen to form the active palladium catalyst was established; palladium nanoparticles that are highly active in cross-coupling reactions with

Ultrafast signal processing in quantum dot amplifiers through effective spectral holeburning

DEFF Research Database (Denmark)

Berg, Tommy Winther; Mørk, Jesper; Uskov, A. V.

2002-01-01

suitable for ultrafast signal processing. The basis of this property is that the process of spectral hole burning (SHB) can become very effective. We consider a traveling wave optical amplifier consisting of the dot states, which interact with the optical signal (no inhomogeneous broadening included...

Scalable coherent interface

International Nuclear Information System (INIS)

Alnaes, K.; Kristiansen, E.H.; Gustavson, D.B.; James, D.V.

1990-01-01

The Scalable Coherent Interface (IEEE P1596) is establishing an interface standard for very high performance multiprocessors, supporting a cache-coherent-memory model scalable to systems with up to 64K nodes. This Scalable Coherent Interface (SCI) will supply a peak bandwidth per node of 1 GigaByte/second. The SCI standard should facilitate assembly of processor, memory, I/O and bus bridge cards from multiple vendors into massively parallel systems with throughput far above what is possible today. The SCI standard encompasses two levels of interface, a physical level and a logical level. The physical level specifies electrical, mechanical and thermal characteristics of connectors and cards that meet the standard. The logical level describes the address space, data transfer protocols, cache coherence mechanisms, synchronization primitives and error recovery. In this paper we address logical level issues such as packet formats, packet transmission, transaction handshake, flow control, and cache coherence. 11 refs., 10 figs

Cladding-like waveguide fabricated by cooperation of ultrafast laser writing and ion irradiation: characterization and laser generation.

Science.gov (United States)

Lv, Jinman; Shang, Zhen; Tan, Yang; Vázquez de Aldana, Javier Rodríguez; Chen, Feng

2017-08-07

We report the surface cladding-like waveguide fabricated by the cooperation of the ultrafast laser writing and the ion irradiation. The ultrafast laser writes tracks near the surface of the Nd:YAG crystal, constructing a semi-circle columnar structure with a decreased refractive index of - 0.00208. Then, the Nd:YAG crystal is irradiated by the Carbon ion beam, forming an enhanced-well in the semi-circle columnar with an increased refractive index of + 0.0024. Tracks and the enhanced-well consisted a surface cladding-like waveguide. Utilizing this cladding-like waveguide as the gain medium for the waveguide lasing, optimized characterizations were observed compared with the monolayer waveguide. This work demonstrates the refractive index of the Nd:YAG crystal can be well tailored by the cooperation of the ultrafast laser writing and the ion irradiation, which provides an convenient way to fabricate the complex and multilayered photonics devices.

Ultrafast Microscopy of Energy and Charge Transport

Science.gov (United States)

Huang, Libai

The frontier in solar energy research now lies in learning how to integrate functional entities across multiple length scales to create optimal devices. Advancing the field requires transformative experimental tools that probe energy transfer processes from the nano to the meso lengthscales. To address this challenge, we aim to understand multi-scale energy transport across both multiple length and time scales, coupling simultaneous high spatial, structural, and temporal resolution. In my talk, I will focus on our recent progress on visualization of exciton and charge transport in solar energy harvesting materials from the nano to mesoscale employing ultrafast optical nanoscopy. With approaches that combine spatial and temporal resolutions, we have recently revealed a new singlet-mediated triplet transport mechanism in certain singlet fission materials. This work demonstrates a new triplet exciton transport mechanism leading to favorable long-range triplet exciton diffusion on the picosecond and nanosecond timescales for solar cell applications. We have also performed a direct measurement of carrier transport in space and in time by mapping carrier density with simultaneous ultrafast time resolution and 50 nm spatial precision in perovskite thin films using transient absorption microscopy. These results directly visualize long-range carrier transport of 220nm in 2 ns for solution-processed polycrystalline CH3NH3PbI3 thin films. The spatially and temporally resolved measurements reported here underscore the importance of the local morphology and establish an important first step towards discerning the underlying transport properties of perovskite materials.

Ultrafast laser pump/x-ray probe experiments

International Nuclear Information System (INIS)

Larsson, J.; Judd, E.; Schuck, P.J.

1997-01-01

In an ongoing project aimed at probing solids using x-rays obtained at the ALS synchrotron with a sub-picosecond time resolution following interactions with a 100 fs laser pulse, the authors have successfully performed pump-probe experiments limited by the temporal duration of ALS-pulse. They observe a drop in the diffraction efficiency following laser heating. They can attribute this to a disordering of the crystal. Studies with higher temporal resolution are required to determine the mechanism. The authors have also incorporated a low-jitter streakcamera as a diagnostic for observing time-dependant x-ray diffraction. The streakcamera triggered by a photoconductive switch was operated at kHz repetition rates. Using UV-pulses, the authors obtain a temporal response of 2 ps when averaging 5000 laser pulses. They demonstrate the ability to detect monochromatized x-ray radiation from a bend-magnet with the streak camera by measuring the pulse duration of a x-ray pulse to 70 ps. In conclusion, the authors show a rapid disordering of an InSb crystal. The resolution was determined by the duration of the ALS pulse. They also demonstrate that they can detect x-ray radiation from a synchrotron source with a temporal resolution of 2ps, by using an ultrafast x-ray streak camera. Their set-up will allow them to pursue laser pump/x-ray probe experiments to monitor structural changes in materials with ultrafast time resolution

Nanoparticle size and morphology control using ultrafast laser induced forward transfer of Ni thin films

Energy Technology Data Exchange (ETDEWEB)

Murphy, Ryan D. [Applied Physics Program, University of Michigan, Ann Arbor, Michigan 48109 (United States); Abere, Michael J.; Schrider, Keegan J.; Yalisove, Steven M. [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109 (United States); Torralva, Ben [Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor, Michigan 48109 (United States)

2013-08-26

We have developed a nanoparticle (NP) printing technique using Ni thin film lift-off from glass substrates after ultrafast irradiation in air. Unique interactions of ultrafast laser pulses with thin films allow for control over NP faceting and size distributions. Control is achieved by changing the laser fluence, film thickness, and film-substrate distance. We demonstrate 20 nm Ni film removal from substrates and rapid NP printing, with size distributions centered at a 6 nm diameter. When the Ni film thickness is lowered to 10 nm, NPs are printed with distributions peaked at a 2 nm diameter.

Coherent detectors

International Nuclear Information System (INIS)

Lawrence, C R; Church, S; Gaier, T; Lai, R; Ruf, C; Wollack, E

2009-01-01

Coherent systems offer significant advantages in simplicity, testability, control of systematics, and cost. Although quantum noise sets the fundamental limit to their performance at high frequencies, recent breakthroughs suggest that near-quantum-limited noise up to 150 or even 200 GHz could be realized within a few years. If the demands of component separation can be met with frequencies below 200 GHz, coherent systems will be strong competitors for a space CMB polarization mission. The rapid development of digital correlator capability now makes space interferometers with many hundreds of elements possible. Given the advantages of coherent interferometers in suppressing systematic effects, such systems deserve serious study.

Coherent detectors

Energy Technology Data Exchange (ETDEWEB)

Lawrence, C R [M/C 169-327, Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Church, S [Room 324 Varian Physics Bldg, 382 Via Pueblo Mall, Stanford, CA 94305-4060 (United States); Gaier, T [M/C 168-314, Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Lai, R [Northrop Grumman Corporation, Redondo Beach, CA 90278 (United States); Ruf, C [1533 Space Research Building, The University of Michigan, Ann Arbor, MI 48109-2143 (United States); Wollack, E, E-mail: charles.lawrence@jpl.nasa.go [NASA/GSFC, Code 665, Observational Cosmology Laboratory, Greenbelt, MD 20771 (United States)

2009-03-01

Coherent systems offer significant advantages in simplicity, testability, control of systematics, and cost. Although quantum noise sets the fundamental limit to their performance at high frequencies, recent breakthroughs suggest that near-quantum-limited noise up to 150 or even 200 GHz could be realized within a few years. If the demands of component separation can be met with frequencies below 200 GHz, coherent systems will be strong competitors for a space CMB polarization mission. The rapid development of digital correlator capability now makes space interferometers with many hundreds of elements possible. Given the advantages of coherent interferometers in suppressing systematic effects, such systems deserve serious study.

Left ventricular ejection fraction and volumes as measured by 3D echocardiography and ultrafast computed tomography

International Nuclear Information System (INIS)

Vieira, Marcelo Luiz Campos; Nomura, Cesar H.; Tranchesi Junior, Bernardino; Oliveira, Wercules A. de; Naccarato, Gustavo; Serpa, Bruna S.; Passos, Rodrigo B.D.; Funari, Marcelo B. G.; Fischer, Claudio H.; Morhy, Samira S.

2009-01-01

Background: Real-time three-dimensional echocardiography (RT-3D-Echo) and ultrafast computed tomography (CT) are two novel methods for the analysis of LV ejection fraction and volumes. Objective: To compare LVEF and volume measurements as obtained using RT-3D-Echo and ultrafast CT. Methods: Thirty nine consecutive patients (27 men, mean age of 57+- 12 years) were studied using RT-3D-Echo and 64-slice ultrafast CT. LVEF and LV volumes were analyzed. Statistical analysis: coefficient of correlation (r: Pearson), Bland-Altman analysis, linear regression analysis, 95% CI, p 5 .58)%; end-diastolic volume ranged from 49.6 to 178.2 (87+-27.8) ml; end-systolic volume ranged from 11.4 to 78 (33.1+-13.6) ml. CT scan measurements: LVEF ranged from 53 to 86% (67.8+-7.78); end-diastolic volume ranged from 51 to 186 (106.5+-30.3) ml; end-systolic volume ranged from 7 to 72 (35.5+-13.4)ml. Correlations between RT-3D-Echo and CT were: LVEF (r: 0.7888, p<0.0001, 95% CI 0.6301 to 0.8843); end-diastolic volume (r: 0.7695, p<0.0001, 95% CI 0.5995 to 0.8730); end-systolic volume (r: 0.8119, p<0.0001, 95% CI 0.6673 to 0.8975). Conclusion: Good correlation between LVEF and ventricular volume parameters as measured by RT-3D-Echo and 64-slice ultrafast CT was found in the present case series. (author)

Ultrafast carrier dynamics in tetrahedral amorphous carbon: carrier trapping versus electron-hole recombination

International Nuclear Information System (INIS)

Carpene, E; Mancini, E; Dallera, C; Schwen, D; Ronning, C; Silvestri, S De

2007-01-01

We report the investigation of the ultrafast carrier dynamics in thin tetrahedral amorphous carbon films by means of femtosecond time-resolved reflectivity. We estimated the electron-phonon relaxation time of a few hundred femtoseconds and we observed that under low optical excitation photo-generated carriers decay according to two distinct mechanisms attributed to trapping by defect states and direct electron-hole recombination. With high excitation, when photo-carrier and trap densities are comparable, a unique temporal evolution develops, as the time dependence of the trapping process becomes degenerate with the electron-hole recombination. This experimental evidence highlights the role of defects in the ultrafast electronic dynamics and is not specific to this particular form of carbon, but has general validity for amorphous and disordered semiconductors

Coherent population transfer and superposition of atomic states via stimulated Raman adiabatic passage using an excited-doublet four-level atom

International Nuclear Information System (INIS)

Jin Shiqi; Gong Shangqing; Li Ruxin; Xu Zhizhan

2004-01-01

Coherent population transfer and superposition of atomic states via a technique of stimulated Raman adiabatic passage in an excited-doublet four-level atomic system have been analyzed. It is shown that the behavior of adiabatic passage in this system depends crucially on the detunings between the laser frequencies and the corresponding atomic transition frequencies. Particularly, if both the fields are tuned to the center of the two upper levels, the four-level system has two degenerate dark states, although one of them contains the contribution from the excited atomic states. The nonadiabatic coupling of the two degenerate dark states is intrinsic, it originates from the energy difference of the two upper levels. An arbitrary superposition of atomic states can be prepared due to such nonadiabatic coupling effect

Unlocking the Constraints of Cyanobacterial Productivity: Acclimations Enabling Ultrafast Growth

Energy Technology Data Exchange (ETDEWEB)

Bernstein, Hans C.; McClure, Ryan S.; Hill, Eric A.; Markillie, Lye Meng; Chrisler, William B.; Romine, Margie F.; McDermott, Jason E.; Posewitz, Matthew C.; Bryant, Donald A.; Konopka, Allan E.; Fredrickson, James K.; Beliaev, Alexander S.

2016-07-26

Harnessing the metabolic potential of photosynthetic microbes for next-generation biotechnology objectives requires detailed scientific understanding of the physiological constraints and regulatory controls affecting carbon partitioning between biomass, metabolite storage pools, and bioproduct synthesis. We dissected the cellular mechanisms underlying the remarkable physiological robustness of the euryhaline unicellular cyanobacteriumSynechococcussp. strain PCC 7002 (Synechococcus7002) and identify key mechanisms that allow cyanobacteria to achieve unprecedented photoautotrophic productivities (~2.5-h doubling time). Ultrafast growth ofSynechococcus7002 was supported by high rates of photosynthetic electron transfer and linked to significantly elevated transcription of precursor biosynthesis and protein translation machinery. Notably, no growth or photosynthesis inhibition signatures were observed under any of the tested experimental conditions. Finally, the ultrafast growth inSynechococcus7002 was also linked to a 300% expansion of average cell volume. We hypothesize that this cellular adaptation is required at high irradiances to support higher cell division rates and reduce deleterious effects, corresponding to high light, through increased carbon and reductant sequestration.

IMPORTANCEEfficient coupling between photosynthesis and productivity is central to the development of biotechnology based on solar energy. Therefore, understanding the factors constraining maximum rates of carbon processing is necessary to identify regulatory mechanisms and devise strategies to overcome productivity constraints. Here, we interrogate the molecular mechanisms that operate at a systems level to allow cyanobacteria to achieve ultrafast growth. This was done by considering growth and photosynthetic kinetics with global transcription patterns. We have delineated

Teleportation of a Coherent Superposition State Via a nonmaximally Entangled Coherent Xhannel

Institute of Scientific and Technical Information of China (English)

无

2002-01-01

@@ We investigate the problemm of teleportation of a superposition coherent state with nonmaximally entangled coherent channel. Two strategies are considered to complete the task. The first one uses entanglement concentration to purify the channel to a maximally entangled one. The second one teleports the state through the nonmaximally entangled coherent channel directly. We find that the probabilities of successful teleportations for the two strategies are depend on the amplitudes of the coherent states and the mean fidelity of teleportation using the first strategy is always less than that of the second strategy.

Ultra-fast boriding of metal surfaces for improved properties

Science.gov (United States)

Timur, Servet; Kartal, Guldem; Eryilmaz, Osman L.; Erdemir, Ali

2015-02-10

A method of ultra-fast boriding of a metal surface. The method includes the step of providing a metal component, providing a molten electrolyte having boron components therein, providing an electrochemical boriding system including an induction furnace, operating the induction furnace to establish a high temperature for the molten electrolyte, and boriding the metal surface to achieve a boride layer on the metal surface.

Laser pulses for coherent xuv Raman excitation

Science.gov (United States)

Greenman, Loren; Koch, Christiane P.; Whaley, K. Birgitta

2015-07-01

We combine multichannel electronic structure theory with quantum optimal control to derive femtosecond-time-scale Raman pulse sequences that coherently populate a valence excited state. For a neon atom, Raman target populations of up to 13% are obtained. Superpositions of the ground and valence Raman states with a controllable relative phase are found to be reachable with up to 4.5% population and arbitrary phase control facilitated by the pump pulse carrier-envelope phase. Analysis of the optimized pulse structure reveals a sequential mechanism in which the valence excitation is reached via a fast (femtosecond) population transfer through an intermediate resonance state in the continuum rather than avoiding intermediate-state population with simultaneous or counterintuitive (stimulated Raman adiabatic passage) pulse sequences. Our results open a route to coupling valence excitations and core-hole excitations in molecules and aggregates that locally address specific atoms and represent an initial step towards realization of multidimensional spectroscopy in the xuv and x-ray regimes.

q-deformed charged fermion coherent states and SU(3) charged, Hyper-charged fermion coherent states

International Nuclear Information System (INIS)

Hao Sanru; Li Guanghua; Long Junyan

1994-01-01

By virtue of the algebra of the q-deformed fermion oscillators, the q-deformed charged fermion coherent states and SU(3) charged, hyper-charged fermion coherent states are discussed. The explicit forms of the two kinds of coherent states mentioned above are obtained by making use of the completeness of base vectors in the q-fermion Fock space. By comparing the q-deformed results with the ordinary results, it is found that the q-deformed charged fermion coherent states and SU(3) charged, hyper-charged fermion coherent states are automatically reduced to the ordinary charged fermion coherent states and SU(3) charged hyper-charged fermion coherent states if the deformed parameter q→1

Proposal for arbitrary-order temporal integration of ultrafast optical signals using a single uniform-period fiber Bragg grating.

Science.gov (United States)

Asghari, Mohammad H; Azaña, José

2008-07-01

A simple and practical all-fiber design for implementing arbitrary-order temporal integration of ultrafast optical waveforms is proposed and numerically investigated. We demonstrate that an ultrafast photonics integrator of any desired integration order can be implemented using a uniform-period fiber Bragg grating (FBG) with a properly designed amplitude-only grating apodization profile. In particular, the grating coupling strength must vary according to the (N-1) power of the fiber distance for implementing an Nth-order photonics integrator (N=1,2,...). This approach requires the same level of practical difficulty for realizing any given integration order. The proposed integration devices operate over a limited time window, which is approximately fixed by the round-trip propagation time in the FBG. Ultrafast arbitrary-order all-optical integrators capable of accurate operation over nanosecond time windows can be implemented using readily feasible FBGs.

Sensors for ultra-fast silicon detectors

Energy Technology Data Exchange (ETDEWEB)

Sadrozinski, H.F.-W., E-mail: hartmut@scipp.ucsc.edu [Santa Cruz Institute for Particle Physics, UC Santa Cruz, Santa Cruz, CA 95064 (United States); Baselga, M.; Ely, S.; Fadeyev, V.; Galloway, Z.; Ngo, J.; Parker, C.; Schumacher, D.; Seiden, A.; Zatserklyaniy, A. [Santa Cruz Institute for Particle Physics, UC Santa Cruz, Santa Cruz, CA 95064 (United States); Cartiglia, N. [INFN Torino, Torino (Italy); Pellegrini, G.; Fernández-Martínez, P.; Greco, V.; Hidalgo, S.; Quirion, D. [Centro Nacional de Microelectrónica, IMB-CNM-CSIC, Barcelona (Spain)

2014-11-21

We report on electrical and charge collection tests of silicon sensors with internal gain as part of our development of ultra-fast silicon detectors. Using C–V and α TCT measurements, we investigate the non-uniform doping profile of so-called low-gain avalanche detectors (LGAD). These are n-on-p pad sensors with charge multiplication due to the presence of a thin, low-resistivity diffusion layer below the junction, obtained with a highly doped implant. We compare the bias dependence of the pulse shapes of traditional sensors and of LGAD sensors with different dopant density of the diffusion layer, and extract the internal gain.

Sensors for ultra-fast silicon detectors

International Nuclear Information System (INIS)

Sadrozinski, H.F.-W.; Baselga, M.; Ely, S.; Fadeyev, V.; Galloway, Z.; Ngo, J.; Parker, C.; Schumacher, D.; Seiden, A.; Zatserklyaniy, A.; Cartiglia, N.; Pellegrini, G.; Fernández-Martínez, P.; Greco, V.; Hidalgo, S.; Quirion, D.

2014-01-01

We report on electrical and charge collection tests of silicon sensors with internal gain as part of our development of ultra-fast silicon detectors. Using C–V and α TCT measurements, we investigate the non-uniform doping profile of so-called low-gain avalanche detectors (LGAD). These are n-on-p pad sensors with charge multiplication due to the presence of a thin, low-resistivity diffusion layer below the junction, obtained with a highly doped implant. We compare the bias dependence of the pulse shapes of traditional sensors and of LGAD sensors with different dopant density of the diffusion layer, and extract the internal gain

Ultrafast photoconductor detector-laser-diode transmitter

International Nuclear Information System (INIS)

Wang, C.L.; Davis, B.A.; Davies, T.J.; Nelson, M.A.; Thomas, M.C.; Zagarino, P.A.

1987-01-01

We report the results of an experiment in which we used an ultrafast, photoconductive, radiation detector to drive a fast laser-diode transmitter. When we irradiated the neutron-damaged Cr-doped GaAs detector with 17-MeV electron beams, the temporal response was measured to be less than 30 ps. The pulses from this detector modulated a fast GaAlAs laser diode to transmit the laser output through 30- and 1100-m optical fibers. Preliminary results indicate that 50- and 80-ps time resolutions, respectively, are obtainable with these fibers. We are now working to integrate the photoconductive detector and the laser diode transmitter into a single chip

Quantum interference and coherent control in dissipative atomic systems

International Nuclear Information System (INIS)

Paspalakis, E.

1999-01-01

In this thesis we study the effects of quantum interference arising from dissipative processes in atomic systems. First, we identify quantum interference phenomena arising from decay mechanisms. Second, we use dynamical methods (the properties of laser fields) to obtain a tailored response of systems in which such interferences are present. We are mainly concerned with two dissipative processes: spontaneous emission and ionization. First, we study the effects of quantum interference arising from spontaneous emission on the population dynamics and the spontaneous emission spectrum of several multi-level systems. Coherent 'phase' control methods for manipulating the response of systems involving spontaneous emission interference are also proposed. Several interesting phenomena are identified such as partial and total quenching of spontaneous emission, phase dependent population dynamics and coherent population trapping. Next, we consider the process of laser-induced continuum structure, where an atom is coupled by two laser fields to the same electronic continuum. An {it ab initio}, non-perturbative study of this process in helium using the R-Matrix Floquet theory is presented. The results of our numerical calculations are compared with those obtained by simple perturbative models and with recent experimental results. The possibility of coherent population transfer via a continuum of states is then analyzed. We study two distinct atomic systems. A laser-induced continuum structure scheme (unstructured continuum) and a bichromatically driven autoionizing scheme (structured continuum). We find that the same conditions which lead to 'dark' states in these systems lead to efficient population transfer. We also identify parameters detrimental to the transfer efficiency and propose methods to overcome them. Finally, we study short pulse propagation in systems involving interfering dissipation mechanisms. We show that the existence of dark states can lead to loss-free and

Probing Ultrafast Electron Dynamics at Surfaces Using Soft X-Ray Transient Reflectivity Spectroscopy

Science.gov (United States)

Baker, L. Robert; Husek, Jakub; Biswas, Somnath; Cirri, Anthony

The ability to probe electron dynamics with surface sensitivity on the ultrafast time scale is critical for understanding processes such as charge separation, injection, and surface trapping that mediate efficiency in catalytic and energy conversion materials. Toward this goal, we have developed a high harmonic generation (HHG) light source for femtosecond soft x-ray reflectivity. Using this light source we investigated the ultrafast carrier dynamics at the surface of single crystalline α-Fe2O3, polycrystalline α-Fe2O3, and the mixed metal oxide, CuFeO2. We have recently demonstrated that CuFeO2 in particular is a selective catalyst for photo-electrochemical CO2 reduction to acetate; however, the role of electronic structure and charge carrier dynamics in mediating catalytic selectivity has not been well understood. Soft x-ray reflectivity measurements probe the M2,3, edges of the 3d transition metals, which provide oxidation and spin state resolution with element specificity. In addition to chemical state specificity, these measurements are also surface sensitive, and by independently simulating the contributions of the real and imaginary components of the complex refractive index, we can differentiate between surface and sub-surface contributions to the excited state spectrum. Accordingly, this work demonstrates the ability to probe ultrafast carrier dynamics in catalytic materials with element and chemical state specificity and with surface sensitivity.

Ultrafast geometric control of a single qubit using chirped pulses

International Nuclear Information System (INIS)

Hawkins, Patrick E; Malinovskaya, Svetlana A; Malinovsky, Vladimir S

2012-01-01

We propose a control strategy to perform arbitrary unitary operations on a single qubit based solely on the geometrical phase that the qubit state acquires after cyclic evolution in the parameter space. The scheme uses ultrafast linearly chirped pulses and provides the possibility of reducing the duration of a single-qubit operation to a few picoseconds.

Ultrafast terahertz control of extreme tunnel currents through single atoms on a silicon surface

DEFF Research Database (Denmark)

Jelic, Vedran; Iwaszczuk, Krzysztof; Nguyen, Peter H.

2017-01-01

scanning tunnelling microscopy (THz-STM) in ultrahigh vacuum as a new platform for exploring ultrafast non-equilibrium tunnelling dynamics with atomic precision. Extreme terahertz-pulse-driven tunnel currents up to 10(7) times larger than steady-state currents in conventional STM are used to image...... terahertz-induced band bending and non-equilibrium charging of surface states opens new conduction pathways to the bulk, enabling extreme transient tunnel currents to flow between the tip and sample.......Ultrafast control of current on the atomic scale is essential for future innovations in nanoelectronics. Extremely localized transient electric fields on the nanoscale can be achieved by coupling picosecond duration terahertz pulses to metallic nanostructures. Here, we demonstrate terahertz...

Excited-state intramolecular proton transfer of 2-acetylindan-1,3-dione studied by ultrafast absorption and fluorescence spectroscopy

Directory of Open Access Journals (Sweden)

Pramod Kumar Verma

2016-03-01

Full Text Available We employ transient absorption from the deep-UV to the visible region and fluorescence upconversion to investigate the photoinduced excited-state intramolecular proton-transfer dynamics in a biologically relevant drug molecule, 2-acetylindan-1,3-dione. The molecule is a ß-diketone which in the electronic ground state exists as exocyclic enol with an intramolecular H-bond. Upon electronic excitation at 300 nm, the first excited state of the exocyclic enol is initially populated, followed by ultrafast proton transfer (≈160 fs to form the vibrationally hot endocyclic enol. Subsequently, solvent-induced vibrational relaxation takes place (≈10 ps followed by decay (≈390 ps to the corresponding ground state.

Infrared studies of impurity states and ultrafast carrier dynamics in semiconductor quantum structures

Energy Technology Data Exchange (ETDEWEB)

Stehr, D.

2007-12-28

This thesis deals with infrared studies of impurity states, ultrafast carrier dynamics as well as coherent intersubband polarizations in semiconductor quantum structures such as quantum wells and superlattices, based on the GaAs/AlGaAs material system. In the first part it is shown that the 2p{sub z} confined impurity state of a semiconductor quantum well develops into an excited impurity band in the case of a superlattice. This is studied by following theoretically the transition from a single to a multiple quantum well or superlattice by exactly diagonalizing the three-dimensional Hamiltonian for a quantum well system with random impurities. These results also require reinterpretation of previous experimental data. The relaxation dynamics of interminiband transitions in doped GaAs/AlGaAs superlattices in the mid-IR are studied. This involves single-color pump-probe measurements to explore the dynamics at different wavelengths, which is performed with the Rossendorf freeelectron laser (FEL), providing picosecond pulses in a range from 3-200 {mu}m and are used for the first time within this thesis. In these experiments, a fast bleaching of the interminiband transition is observed followed by thermalization and subsequent relaxation, whose time constants are determined to be 1-2 picoseconds. This is followed by an additional component due to carrier cooling in the lower miniband. In the second part, two-color pump-probe measurements are performed, involving the FEL as the pump source and a table-top broad-band tunable THz source for probing the transmission changes. In addition, the dynamics of excited electrons within the minibands is explored and their contribution quantitatively extracted from the measurements. Intersubband absorption experiments of photoexcited carriers in single quantum well structures, measured directly in the time-domain, i.e. probing coherently the polarization between the first and the second subband, are presented. By varying the carrier

Spatio-temporal imaging of voltage pulses with an ultrafast scanning tunneling microscope

DEFF Research Database (Denmark)

Jensen, Jacob Riis; Keil, Ulrich Dieter Felix; Hvam, Jørn Märcher

1997-01-01

Measurements on an ultrafast scanning tunneling microscope with simultaneous spatial and temporal resolution are presented. We show images of picosecond pulses propagating on a coplanar waveguide and resolve their mode structures. The influence of transmission line discontinuities on the mode...

Topological Properties of Spatial Coherence Function

International Nuclear Information System (INIS)

Ji-Rong, Ren; Tao, Zhu; Yi-Shi, Duan

2008-01-01

The topological properties of the spatial coherence function are investigated rigorously. The phase singular structures (coherence vortices) of coherence function can be naturally deduced from the topological current, which is an abstract mathematical object studied previously. We find that coherence vortices are characterized by the Hopf index and Brouwer degree in topology. The coherence flux quantization and the linking of the closed coherence vortices are also studied from the topological properties of the spatial coherence function

Blockage of ultrafast and directional diffusion of Li atoms on phosphorene with intrinsic defects.

Science.gov (United States)

Zhang, Ruiqi; Wu, Xiaojun; Yang, Jinlong

2016-02-21

The diffusion of Li in electrode materials is a key factor for the charging/discharging rate capacity of a Li-ion battery (LIB). Recently, two-dimensional phosphorene has been proposed as a very promising electrode material due to its ultrafast and directional lithium diffusion, as well as large energy capacity. Herein, on the basis of density functional theory, we report that intrinsic point defects, including vacancy and stone-wales defects, will block the directional ultrafast diffusion of lithium in phosphorene. On the defect-free phosphorene, diffusion of Li along the zig-zag lattice direction is 1.6 billion times faster than along the armchair lattice direction, and 260 times faster than that in graphite. After introducing intrinsic vacancy and stone-wales defect, the diffusion energy barrier of Li along the zig-zag lattice direction increases sharply to the range of 0.17-0.49 eV, which blocks the ultrafast migration of lithium along the zig-zag lattice direction. Moreover, the open circuit voltage increases with the emergence of defects, which is not suitable for anode materials. In addition, the formation energies of the defects in phosphorene are considerably lower than those in graphene and silicene sheet; therefore, it is highly important to generate defect-free phosphorene for LIB applications.