WorldWideScience

Sample records for phonon laser action

  1. Nonequilibrium phonon effects in midinfrared quantum cascade lasers

    Shi, Y. B., E-mail: yshi9@wisc.edu; Knezevic, I., E-mail: knezevic@engr.wisc.edu [Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706-1691 (United States)

    2014-09-28

    We investigate the effects of nonequilibrium phonon dynamics on the operation of a GaAs-based midinfrared quantum cascade laser over a range of temperatures (77–300 K) via a coupled ensemble Monte Carlo simulation of electron and optical-phonon systems. Nonequilibrium phonon effects are shown to be important below 200 K. At low temperatures, nonequilibrium phonons enhance injection selectivity and efficiency by drastically increasing the rate of interstage electron scattering from the lowest injector state to the next-stage upper lasing level via optical-phonon absorption. As a result, the current density and modal gain at a given field are higher and the threshold current density lower and considerably closer to experiment than results obtained with thermal phonons. By amplifying phonon absorption, nonequilibrium phonons also hinder electron energy relaxation and lead to elevated electronic temperatures.

  2. LO-phonon assisted polariton laser

    Maragkou, M.; Grundy, A. J. D.; Ostatnický, T.; Lagoudakis, P. G.

    2010-01-01

    We demonstrate the role of LO-phonon assisted polariton relaxation in reducing the stimulation threshold in strongly coupled microcavities. When the energy of the relaxation bottleneck is one LO-phonon above the ground polariton state, we observe a ten-fold improvement of the polariton relaxation rate in the linear regime, and a two-fold reduction of the threshold to the non-linear polariton lasing regime.

  3. Dynamics of a vertical cavity quantum cascade phonon laser structure

    Maryam, W.; Akimov, A. V.; Campion, R. P.; Kent, Anthony

    2013-01-01

    Driven primarily by scientific curiosity, but also by the potential applications of intense sources of coherent sound, researchers have targeted the phonon laser (saser) since the invention of the optical laser over 50 years ago. Here we fabricate a vertical cavity structure designed to operate as a saser oscillator device at a frequency of 325 GHz. It is based on a semiconductor superlattice gain medium, inside a multimode cavity between two acoustic Bragg reflectors. We measure the acoustic...

  4. Dynamics of a vertical cavity quantum cascade phonon laser structure

    Maryam, W.; Akimov, A. V.; Campion, R. P.; Kent, A. J.

    2013-01-01

    Driven primarily by scientific curiosity, but also by the potential applications of intense sources of coherent sound, researchers have targeted the phonon laser (saser) since the invention of the optical laser over 50 years ago. Here we fabricate a vertical cavity structure designed to operate as a saser oscillator device at a frequency of 325 GHz. It is based on a semiconductor superlattice gain medium, inside a multimode cavity between two acoustic Bragg reflectors. We measure the acoustic output of the device as a function of time after applying electrical pumping. The emission builds in intensity reaching a steady state on a timescale of order 0.1 μs. We show that the results are consistent with a model of the dynamics of a saser cavity exactly analogous to the models used for describing laser dynamics. We also obtain estimates for the gain coefficient, steady-state acoustic power output and efficiency of the device. PMID:23884078

  5. Multi-phonon-assisted absorption and emission in semiconductors and its potential for laser refrigeration

    Khurgin, Jacob B

    2014-01-01

    Laser cooling of semiconductors has been an elusive goal for many years, and while attempts to cool the narrow gap semiconductors such as GaAs are yet to succeed, recently, net cooling has been attained in a wider gap CdS. This raises the question of whether wider gap semiconductors with higher phonon energies and stronger electron-phonon coupling are better suitable for laser cooling. In this work we develop a straightforward theory of phonon-assisted absorption and photoluminescence of semiconductors that involves more than one phonon and use to examine wide gap materials, such as GaN and CdS and compare them with GaAs. The results indicate that while strong electron-phonon coupling in both GaN and CdS definitely improves the prospects of laser cooling, large phonon energy in GaN may be a limitation, which makes CdS a better prospect for laser cooling.

  6. Laser structuring for control of coupling between THz light and phonon modes

    Wang, X W; Balcytis, A; Kasalynas, I; Jakstas, V; Janonis, V; Venckevicius, R; Buividas, R; Appadoo, D; Valusis, G; Juodkazis, S

    2016-01-01

    Modification of surface and volume of sapphire is shown to affect reflected and transmitted light at THz spectral range. Structural modifications were made using ultra-short 230 fs laser pulses at 1030 nm and 257.5 nm wavelengths forming surface ripples of ~250 nm and 60 nm period, respectively. Softening of the transverse optical phonon TO1 mode due to disorder was the most pronounced in reflection from laser ablated surface. It is shown that sub-surface periodic patterns of laser damage sites have also modified reflection spectrum due to coupling of THz radiation with phonons. Application potential of laser structuring and disordering for phononic engineering is discussed.

  7. Inter-Landau level scattering and LO-phonon emission in Terahertz quantum cascade laser

    Péré-Laperne, Nicolas; De Vaulchier, Louis-Anne; Guldner, Yves; Bastard, Gérald; Scalari, Giacomo; Giovannini, Marcella; Faist, Jérôme; Vasanelli, Angela; Dhillon, Sukhdeep; Sirtori, Carlo

    2007-01-01

    A Terahertz Quantum Cascade Laser (THz QCL) structure based on a bound to continuum and LO-phonon extraction stage is studied under a strong magnetic field. Two series of power oscillations as a function of magnetic field are observed. Comprehensive simulations of the lifetimes allow the first series to be assigned to interface roughness (elastic) and the second to LO phonon scattering (inelastic) of hot carriers in an excited Landau level, previously unobserved in terahertz QCL. We demonstra...

  8. Low phonon energy Nd:LaF3 channel waveguide lasers fabricated by molecular beam epitaxy

    Bhutta, T.; Chardon, A.M.; Shepherd, D. P.; Daran, E.; Serrano, C.; Munoz-Yague, A.

    2001-01-01

    We report the first fabrication and laser operation of channel waveguides based on LaF3 planar thin films grown by molecular beam epitaxy. To our knowledge, this is the lowest phonon energy dielectric material to have shown guided-wave laser operation to date. A full characterization, in terms of spectroscopy, laser results, and propagation losses, is given for the planar thin films upon which the channel waveguides are based. Two channel-fabrication methods are then described, the first invo...

  9. Ultrafast electron diffraction from non-equilibrium phonons in femtosecond laser heated Au films

    We use ultrafast electron diffraction to detect the temporal evolution of non-equilibrium phonons in femtosecond laser-excited ultrathin single-crystalline gold films. From the time-dependence of the Debye-Waller factor, we extract a 4.7 ps time-constant for the increase in mean-square atomic displacements. The observed increase in the diffuse scattering intensity demonstrates that the energy transfer from laser-heated electrons to phonon modes near the X and K points in the Au fcc Brillouin zone proceeds with timescales of 2.3 and 2.9 ps, respectively, faster than the Debye-Waller average mean-square displacement

  10. Ultrafast electron diffraction from non-equilibrium phonons in femtosecond laser heated Au films

    Chase, T. [Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Department of Applied Physics, Stanford University, Stanford, California 94305 (United States); Trigo, M.; Reid, A. H.; Dürr, H. A. [Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Li, R.; Vecchione, T.; Shen, X.; Weathersby, S.; Coffee, R.; Hartmann, N.; Wang, X. J. [SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Reis, D. A. [Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Department of Applied Physics, Stanford University, Stanford, California 94305 (United States); PULSE Institute, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States)

    2016-01-25

    We use ultrafast electron diffraction to detect the temporal evolution of non-equilibrium phonons in femtosecond laser-excited ultrathin single-crystalline gold films. From the time-dependence of the Debye-Waller factor, we extract a 4.7 ps time-constant for the increase in mean-square atomic displacements. The observed increase in the diffuse scattering intensity demonstrates that the energy transfer from laser-heated electrons to phonon modes near the X and K points in the Au fcc Brillouin zone proceeds with timescales of 2.3 and 2.9 ps, respectively, faster than the Debye-Waller average mean-square displacement.

  11. Effect of Pulse Width and Fluence of Femtosecond Laser on Electron-Phonon Relaxation Time

    FANG Ran-Ran; ZHANG Duan-Ming; WEI Hua; LI Zhi-Hua; YANG Feng-Xia; TAN Xin-Yu

    2008-01-01

    The electron-phonon relaxation time as functions of pulse width and fluence of femtosecond laser is studied based on the two-temperature model. The two-temperature model is solved using a finite difference method for copper target. The temperature distribution of the electron and the lattice along with space and time for a certain laser fluence is presented. The time-dependence of lattice and electron temperature of the surface for different pulse width and different laser fluence are also performed, respectively. Moreover, the variation of heat-affected zone per pulse with laser fluence is obtained. The satisfactory agreement between our numerical results and experimental data indicates that the electron-phonon relaxation time is reasonably accurate with the influences of pulse width and fluence of femtosecond laser.

  12. Structural transformations in silicon under exposure by femtosecond laser pulse: role of electron-hole plasma and phonon-phonon anharmonism

    It is experimentally shown for the first time that by the effect of the feed-up laser pulse of 100 fs duration on the silicon target the consecutive structural transitions of the substance into the new crystalline and liquid metallic phase occur both during the laser pulse feed-up and after 0.1-103 ps, depending on the material excitation conditions. The thresholds of the observed structural transitions are determined and the phonon nodes, responsible for therefore, are identified. The structural transitions dynamics in the silicon by the 01.-103 ps times is described within the frames of the model of the phonon modes instability, originating due to the plasma electron-hole effect and also due to the intra- and intermode phonon-phonon anharmonic interactions

  13. Highly Efficient Lasing Action of Nd3+- and Cr3+-Doped Yttrium Aluminum Garnet Ceramics Based on Phonon-Assisted Cross-Relaxation Using Solar Light Source

    Saiki, Taku; Nakatsuka, Masahiro; Imasaki, Kazuo

    2010-08-01

    We constructed a theory to explain the mechanism of laser generation with a high optical-optical conversion efficiency for Nd3+- and Cr3+-doped yttrium aluminum ceramics when sunlight or lamplight sources are used for pumping. As a result, a unique mechanism of laser action was found where the solar or lamp-light power could be converted to laser power with a high efficiency close to 80%, which has not previously been observed. The high conversion efficiency was not only considered to be based on one-to-one photon conversion but on two-photon excitation by a single photon with phonon assistance. Thus, the mechanism of lasing action should include a process where thermal energy is converted to photon energy. The theoretical results we obtained were consistent with those of the experiments.

  14. A phonon scattering assisted injection and extraction based terahertz quantum cascade laser

    Dupont, E; Fathololoumi, S; Wasilewski, Z. R.; Aers, G.; Laframboise, S. R.; Lindskog, M; Wacker, A.; Ban, D.; Liu, H. C.

    2012-01-01

    A novel lasing scheme for terahertz quantum cascade lasers, based on consecutive phonon-photon-phonon emissions per module, is proposed and experimentally demonstrated. The charge transport of the proposed structure is modeled using a rate equation formalism. An optimization code based on a genetic algorithm was developed to find a four-well design in the $\\mathrm{GaAs/Al_{0.25}Ga_{0.75}As}$ material system that maximizes the product of population inversion and oscillator strength at 150 K. T...

  15. Rapid phase change induced by double picosecond laser pulses and the dynamics of acoustic phonons

    For a given phase change material and composition, the double laser pulses better than a single pulse for the crystallization process. We investigated the crystallization process in Si15Sb85 thin films induced by double picosecond pulses with constant fluence and variable intervals. The crystallization degree is a function of the intervals of double pump laser pulses. The crystallization time decreased with the increasing of the intervals of the pump pulses. We believe that acoustic phonons play a key role in the crystallization process. - Highlights: • The double pulse crystallization is easier than the single pulse crystallization. • The crystallization is a function of the intervals of double pump laser pulses. • The crystallization time decreases with the increase of the pump pulse intervals. • Acoustic phonons play a key role in the crystallization process

  16. Experimental Study of Photon-Phonon Interactions in an Explosive by Laser Probe Mass Spectrography

    Eloy, J.; Delpuech, A.

    1995-01-01

    We have shown in a series of previous papers the part of the molecular electronic structure played in the decomposition process of an explosive submitted to a shock wave. This part is important especially as regards energy transfer properties. This work is intented to investigate the process of these transfers by the study of photon-phonon interactions in this type of material. The experimental technique used for this purpose is laser probe mass spectrography. The first tested explosives are ...

  17. Enhanced performance of thin-disk lasers by pumping into the zero-phonon line.

    Weichelt, Birgit; Voss, Andreas; Abdou Ahmed, Marwan; Graf, Thomas

    2012-08-01

    Pumping Yb:YAG or Yb:LuAG into the zero-phonon line at 969 nm instead of using the common pump wavelength of 940 nm reduces the heat generation by 32%. In addition to the 3% increase of the Stokes efficiency, this significantly reduces the diffraction losses caused by the thermally induced phase distortions leading to a remarkable increase of the overall efficiency especially of fundamental-mode thin-disk lasers. Using this pumping scheme in an Yb:LuAG thin-disk laser, we achieved 742 W of nearly diffraction limited (M2≈1.5) output power at an unprecedented high optical efficiency of 58.5%. For multimode operation (M2≈15) the maximum optical efficiency of an Yb:YAG thin-disk laser was increased to 72%. PMID:22859080

  18. Temperature performance of terahertz quantum-cascade lasers with resonant-phonon active-regions

    Significant progress has recently been made toward improving the power output, beam quality and spectral characteristics of terahertz quantum cascade lasers (QCLs). However, the maximum operating temperature of the best-performing devices has become relatively stagnant and is in the range of 150–200 K for QCLs designed to emit in the frequency range of 2–4 THz. Such QCLs are primarily designed with resonant-phonon depopulation schemes. The requirement to cryogenically cool terahertz QCLs leads to stringent limitations on their use for various applications. Although significant advances have been made to model quantum transport in quantum cascade superlattices, the relative role of various electron transport mechanisms as a function of temperature is not clear. This article discusses temperature behavior of resonant-phonon terahertz QCLs with respect to a variety of active-region design schemes, and argues that precise understanding of high-temperature transport remains elusive for terahertz QCLs. The role of electron–phonon scattering, collisional-broadening, thermal leakage, and interface-roughness scattering towards the degradation of intersubband optical gain at higher temperatures is discussed for the popular terahertz QCL designs. (special issue article)

  19. Influence of screening on longitudinal-optical phonon scattering in quantum cascade lasers

    We theoretically investigate the influence of screening on electron-longitudinal optical phonon scattering in quantum cascade lasers. By employing ensemble Monte Carlo simulations, an advanced screening model based on the random-phase approximation is compared to the more elementary Thomas-Fermi and Debye models. For mid-infrared structures, and to a lesser extent also for terahertz designs, the inclusion of screening is shown to affect the simulated current and optical output power. Furthermore, it is demonstrated that by using the electron temperature rather than the lattice temperature, the Debye model can be significantly improved

  20. Influence of screening on longitudinal-optical phonon scattering in quantum cascade lasers

    Ezhov, Ivan; Jirauschek, Christian, E-mail: jirauschek@tum.de [Institute for Nanoelectronics, Technical University of Munich (TUM), D-80333 Munich (Germany)

    2016-01-21

    We theoretically investigate the influence of screening on electron-longitudinal optical phonon scattering in quantum cascade lasers. By employing ensemble Monte Carlo simulations, an advanced screening model based on the random-phase approximation is compared to the more elementary Thomas-Fermi and Debye models. For mid-infrared structures, and to a lesser extent also for terahertz designs, the inclusion of screening is shown to affect the simulated current and optical output power. Furthermore, it is demonstrated that by using the electron temperature rather than the lattice temperature, the Debye model can be significantly improved.

  1. Influence of screening on longitudinal-optical phonon scattering in quantum cascade lasers

    Ezhov, Ivan; Jirauschek, Christian

    2016-01-01

    We theoretically investigate the influence of screening on electron-longitudinal optical phonon scattering in quantum cascade lasers. By employing ensemble Monte Carlo simulations, an advanced screening model based on the random-phase approximation is compared to the more elementary Thomas-Fermi and Debye models. For mid-infrared structures, and to a lesser extent also for terahertz designs, the inclusion of screening is shown to affect the simulated current and optical output power. Furthermore, it is demonstrated that by using the electron temperature rather than the lattice temperature, the Debye model can be significantly improved.

  2. Terahertz lasers and amplifiers based on resonant optical phonon scattering to achieve population inversion

    Hu, Qing (Inventor); Williams, Benjamin S. (Inventor)

    2009-01-01

    The present invention provides quantum cascade lasers and amplifier that operate in a frequency range of about 1 Terahertz to about 10 Terahertz. In one aspect, a quantum cascade laser of the invention includes a semiconductor heterostructure that provides a plurality of lasing modules connected in series. Each lasing module includes a plurality of quantum well structure that collectively generate at least an upper lasing state, a lower lasing state, and a relaxation state such that the upper and the lower lasing states are separated by an energy corresponding to an optical frequency in a range of about 1 to about 10 Terahertz. The lower lasing state is selectively depopulated via resonant LO-phonon scattering of electrons into the relaxation state.

  3. High-gain KY(WO4)2:Yb3+ planar waveguide laser at the zero-phonon line

    Geskus, D.; Aravazhi, S.; Wörhoff, K.; Pollnau, M.

    2010-01-01

    When pumping at a short wavelength of 932 nm, the high gain obtained at the 981-nm zero-phonon line of a KY(WO4)2:Gd3+, Lu3+, Yb3+ planar waveguide resulted in efficient laser emission in an open cavity configuration.

  4. Time-Resolved X-Ray Diffraction from Coherent Phonons during a Laser-Induced Phase Transition

    Time-resolved x-ray diffraction with picosecond temporal resolution is used to observe scattering from impulsively generated coherent acoustic phonons in laser-excited InSb crystals. The observed frequencies and damping rates are in agreement with a model based on dynamical diffraction theory coupled to analytic solutions for the laser-induced strain profile. The results are consistent with a 12 ps thermal electron-acoustic phonon coupling time together with an instantaneous component from the deformation-potential interaction. Above a critical laser fluence, we show that the first step in the transition to a disordered state is the excitation of large amplitude, coherent atomic motion. (c) 1999 The American Physical Society

  5. Experimental demonstration of mode-selective phonon excitation of 6H-SiC by a mid-infrared laser with anti-Stokes Raman scattering spectroscopy

    Yoshida, Kyohei; Hachiya, Kan; Okumura, Kensuke; Mishima, Kenta; Inukai, Motoharu; Torgasin, Konstantin; Omer, Mohamed [Graduate School of Energy Science, Kyoto University, Yoshida-honmachi, Sakyo-ku, Kyoto 606-8501 (Japan); Sonobe, Taro [Kyoto University Research Administration Office, Kyoto University, Yoshida-honmachi, Sakyo-ku, Kyoto 606-8501 (Japan); Zen, Heishun; Negm, Hani; Kii, Toshiteru; Masuda, Kai; Ohgaki, Hideaki [Institute of Advanced Energy, Kyoto University, Gokasyo, Uji, Kyoto 611-0011 (Japan)

    2013-10-28

    Mode-selective phonon excitation by a mid-infrared laser (MIR-FEL) is demonstrated via anti-Stokes Raman scattering measurements of 6H-silicon carbide (SiC). Irradiation of SiC with MIR-FEL and a Nd-YAG laser at 14 K produced a peak where the Raman shift corresponds to a photon energy of 119 meV (10.4 μm). This phenomenon is induced by mode-selective phonon excitation through the irradiation of MIR-FEL, whose photon energy corresponds to the photon-absorption of a particular phonon mode.

  6. Ballistic phonon and thermal radiation transport across a minute vacuum gap in between aluminum and silicon thin films: Effect of laser repetitive pulses on transport characteristics

    Yilbas, B. S.; Ali, H.

    2016-08-01

    Short-pulse laser heating of aluminum and silicon thin films pair with presence of a minute vacuum gap in between them is considered and energy transfer across the thin films pair is predicted. The frequency dependent Boltzmann equation is used to predict the phonon intensity distribution along the films pair for three cycles of the repetitive short-pulse laser irradiation on the aluminum film surface. Since the gap size considered is within the Casimir limit, thermal radiation and ballistic phonon contributions to energy transfer across the vacuum gap is incorporated. The laser irradiated field is formulated in line with the Lambert's Beer law and it is considered as the volumetric source in the governing equations of energy transport. In order to assess the phonon intensity distribution in the films pair, equivalent equilibrium temperature is introduced. It is demonstrated that thermal separation of electron and lattice sub-systems in the aluminum film, due to the short-pulse laser irradiation, takes place and electron temperature remains high in the aluminum film while equivalent equilibrium temperature for phonons decays sharply in the close region of the aluminum film interface. This behavior is attributed to the phonon boundary scattering at the interface and the ballistic phonon transfer to the silicon film across the vacuum gap. Energy transfer due to the ballistic phonon contribution is significantly higher than that of the thermal radiation across the vacuum gap.

  7. Dynamical Phenomena in an Optical-Wavelength Phonon Laser (Phaser): Nonlinear Resonances and Self-Organized Mode Alternation

    Makovetskii, D N

    2011-01-01

    This is a part of an overview of my early studies on nonlinear spin-phonon dynamics in solid state optical-wavelength phonon lasers (phasers) started in 1984. The main goal of this work is a short description and a qualitative analysis of experimental data on low-frequency nonlinear resonances revealed in a nonautonomous ruby phaser. Under phaser pumping modulation near these resonances, an unusual kind of self-organized motions in the ruby spin-phonon system was observed by me in 1984 for the first time. The original technique of optical-wavelength microwave-frequency acoustic stimulated emission (SE) detection and microwave-frequency power spectra (MFPS) analysis was used in these experiments (description of the technique see: D.N.Makovetskii, Cand. Sci. Diss., Kharkov, 1983). The real time evolution of MFPS was studied using this technique at scales up to several hours. The phenomenon of the self-organized periodic alternation of SE phonon modes was experimentally revealed at hyperlow frequencies from abou...

  8. Band structure of cavity-type hypersonic phononic crystals fabricated by femtosecond laser-induced two-photon polymerization

    Rakhymzhanov, A. M.; Gueddida, A.; Alonso-Redondo, E.; Utegulov, Z. N.; Perevoznik, D.; Kurselis, K.; Chichkov, B. N.; El Boudouti, E. H.; Djafari-Rouhani, B.; Fytas, G.

    2016-05-01

    The phononic band diagram of a periodic square structure fabricated by femtosecond laser pulse-induced two photon polymerization is recorded by Brillouin light scattering (BLS) at hypersonic (GHz) frequencies and computed by finite element method. The theoretical calculations along the two main symmetry directions quantitatively capture the band diagrams of the air- and liquid-filled structure and moreover represent the BLS intensities. The theory helps identify the observed modes, reveals the origin of the observed bandgaps at the Brillouin zone boundaries, and unravels direction dependent effective medium behavior.

  9. PHONON IMAGING

    Eisenmenger, W.

    1981-01-01

    Investigations of phonon propagation and scattering in solids use either coherent microwave phonons or incoherent phonons in the form of heat pulses1 generated by current flow through thin metallic films and bolometer detection, or monochromatic incoherent phonons generated and detected with superconducting tunneling junctions2. Applying these techniques to a perfect single crystal, quantitative measurements require knowledge on phonon propagation in anisotropic media. In contrast to optic pr...

  10. Random laser action from flexible biocellulose-based device

    dos Santos, Molíria V.; Dominguez, Christian T.; Schiavon, João V.; Barud, Hernane S.; de Melo, Luciana S. A.; Ribeiro, Sidney J. L.; Gomes, Anderson S. L.; de Araújo, Cid B.

    2014-02-01

    We demonstrate random lasing action in flexible bacterial cellulose (BC) membrane containing a laser-dye and either dielectric or metallic nanoparticles (NPs). The novel random laser system consists of BC nanofibers attached with Rhodamine 6G molecules and having incorporated either silica or silver NPs. The laser action was obtained by excitation of the samples with a 6 ns pulsed laser at 532 nm. Minimum laser threshold of ≈0.7 mJ/pulse was measured for the samples with silica NPs, whereas a laser threshold of 2.5 mJ/pulse for a system based on silver NPs was obtained. In both cases a linewidth narrowing from ≈50 to ≈4 nm was observed. Potential applications in biophotonics and life sciences are discussed for this proof-of-concept device.

  11. Phonon engineering for nanostructures.

    Aubry, Sylvie (Stanford University); Friedmann, Thomas Aquinas; Sullivan, John Patrick; Peebles, Diane Elaine; Hurley, David H. (Idaho National Laboratory); Shinde, Subhash L.; Piekos, Edward Stanley; Emerson, John Allen

    2010-01-01

    Understanding the physics of phonon transport at small length scales is increasingly important for basic research in nanoelectronics, optoelectronics, nanomechanics, and thermoelectrics. We conducted several studies to develop an understanding of phonon behavior in very small structures. This report describes the modeling, experimental, and fabrication activities used to explore phonon transport across and along material interfaces and through nanopatterned structures. Toward the understanding of phonon transport across interfaces, we computed the Kapitza conductance for {Sigma}29(001) and {Sigma}3(111) interfaces in silicon, fabricated the interfaces in single-crystal silicon substrates, and used picosecond laser pulses to image the thermal waves crossing the interfaces. Toward the understanding of phonon transport along interfaces, we designed and fabricated a unique differential test structure that can measure the proportion of specular to diffuse thermal phonon scattering from silicon surfaces. Phonon-scale simulation of the test ligaments, as well as continuum scale modeling of the complete experiment, confirmed its sensitivity to surface scattering. To further our understanding of phonon transport through nanostructures, we fabricated microscale-patterned structures in diamond thin films.

  12. Laser Incident Lessons Learned and Action List

    Yarotski, Dmitry Anatolievitch [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2016-02-29

    On Thursday November 19, 2015, LANL postdoc received an eye injury from a reflected, nonvisible laser beam (Class 4, pulsed, wavelength 800 nanometer). The setup is configured to split the laser output into two work areas in which qualified operators conduct research experiments. During this incident, the laser output beam was being projected to both experimental work areas, although only one experimental area was actively being used. The second laser beam directed to the second work area was blocked by an inappropriate device (Plexiglas, reflective, non-normal incidence) that reflected substantial portion of the beam toward the first setup. In preparation for the measurements, worker stepped on the stepstool and decided to remove the laser goggles to better see the micrometer readings which were difficult to see due to insufficient lighting. Immediately, he noticed a flash of light in his eye. The operator quickly replaced the laser eye-wear and then, using an infrared viewer, located a stray laser beam being reflected from the plexiglas beam block. The operator did not think he had sustained any injury and continued working. Later that day, however, he noticed a blurry spot in the vision of his left eye. He notified his supervisor on Friday morning, November 20, 2015, and was taken by CINT management to Sandia National Laboratories (SNL) medical facility for evaluation. SNL Medical did not find any abnormalities, but referred the operator to a local ophthalmologist for further evaluation. Further evaluations by the ophthalmologist on November 21 and November 23 identified a small spot of inflammation near the fovea on the retina in his left eye. The ophthalmologist stated that this spot would most likely heal on its own and that the blurry spot on the operator's vision would go away. A follow-up visit was scheduled. The employee was released back to work without restrictions.

  13. Ultrafast dynamics and laser action of organic semiconductors

    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...

  14. Bound-to-continuum terahertz quantum cascade laser with a single-quantum-well phonon extraction/injection stage

    A terahertz quantum cascade laser design that combines a wide gain bandwidth, large photon-driven transport and good high-temperature characteristics is presented. It relies on a diagonal transition between a bound state and doublet of states tunnel coupled to the upper state of a phonon extraction stage. The high optical efficiency of this design enables the observation of photon-driven transport over a wide current density range. The relative tolerance of the design to small variations in the barrier thicknesses made it suitable for testing different growth techniques and materials. In particular, we compared the performances of devices grown using molecular-beam epitaxy with those achieved using organometallic chemical vapor deposition. The low-threshold current density and the high slope efficiency makes this device an attractive active region for the development of single-mode quantum cascade lasers based on third-order-distributed feedback structures. Single-mode, high power was achieved with good continuous and pulsed wave operation.

  15. Bound-to-continuum terahertz quantum cascade laser with a single-quantum-well phonon extraction/injection stage

    Amanti, Maria I; Scalari, Giacomo; Terazzi, Romain; Fischer, Milan; Beck, Mattias; Faist, Jerome [Institute of Quantum Electronics, ETH Zurich (Switzerland); Rudra, Alok; Gallo, Pascal; Kapon, Eli [Laboratory of Physics of Nanostructures, Ecole Polytechnique Federale de Lausanne (EPFL) (Switzerland)], E-mail: jerome.faist@phys.ethz.ch

    2009-12-15

    A terahertz quantum cascade laser design that combines a wide gain bandwidth, large photon-driven transport and good high-temperature characteristics is presented. It relies on a diagonal transition between a bound state and doublet of states tunnel coupled to the upper state of a phonon extraction stage. The high optical efficiency of this design enables the observation of photon-driven transport over a wide current density range. The relative tolerance of the design to small variations in the barrier thicknesses made it suitable for testing different growth techniques and materials. In particular, we compared the performances of devices grown using molecular-beam epitaxy with those achieved using organometallic chemical vapor deposition. The low-threshold current density and the high slope efficiency makes this device an attractive active region for the development of single-mode quantum cascade lasers based on third-order-distributed feedback structures. Single-mode, high power was achieved with good continuous and pulsed wave operation.

  16. Femtosecond laser-induced crystallization of amorphous Sb{sub 2}Te{sub 3} film and coherent phonon spectroscopy characterization and optical injection of electron spins

    Li Simian [State Key Laboratory of Optoelectronic Materials and Technology, School of Physics and Engineering, Sun Yat-Sen University, Guangzhou 510275 (China); Hebei Key Laboratory of Optoelectronic Information and Geo-detection Technology Shijiazhuang University of Economics, Shijiazhuang 050031 (China); Huang Huan; Wang Yang; Wu Yiqun; Gan Fuxi [Key Laboratory of High Power Laser Materials, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800 (China); Zhu Weiling; Wang Wenfang; Chen Ke; Yao Daoxin; Lai Tianshu [State Key Laboratory of Optoelectronic Materials and Technology, School of Physics and Engineering, Sun Yat-Sen University, Guangzhou 510275 (China)

    2011-09-01

    A femtosecond laser-irradiated crystallizing technique is tried to convert amorphous Sb{sub 2}Te{sub 3} film into crystalline film. Sensitive coherent phonon spectroscopy (CPS) is used to monitor the crystallization of amorphous Sb{sub 2}Te{sub 3} film at the original irradiation site. The CPS reveals that the vibration strength of two phonon modes that correspond to the characteristic phonon modes (A{sub 1g}{sup 1} and E{sub g}) of crystalline Sb{sub 2}Te{sub 3} enhances with increasing laser irradiation fluence (LIF), showing the rise of the degree of crystallization with LIF and that femtosecond laser irradiation is a good post-treatment technique. Time-resolved circularly polarized pump-probe spectroscopy is used to investigate electron spin relaxation dynamics of the laser-induced crystallized Sb{sub 2}Te{sub 3} film. Spin relaxation process indeed is observed, confirming the theoretical predictions on the validity of spin-dependent optical transition selection rule and the feasibility of transient spin-grating-based optical detection scheme of spin-plasmon collective modes in Sb{sub 2}Te{sub 3}-like topological insulators.

  17. Laser air-jet engine: the action of shock waves at low laser pulse repetition rates

    The impact and thermal action of laser sparks on the reflector of a laser engine in which the propulsion is produced by repetitively pulsed radiation is estimated. It is shown that for a low pulse repetition rate, the thermal contact of a plasma with the reflector and strong dynamic resonance loads are inevitable. These difficulties can be surmounted by using the method based on the merging of shock waves at a high pulse repetition rate. (laser applications)

  18. Enhanced laser action of Perylene-Red doped polymeric materials

    Garcia-Moreno, I.; Costela, A.; Pintado-Sierra, Mercedes; Martin, Virginia; Sastre, Roberto

    2009-01-01

    The laser action of Perylene-Red doped in linear, crosslinked, fluorinated and sililated polymeric materials is reported. The purity of dye was found to be a key factor to enhance its solid-state laser behaviour. The samples were transversely pumped at 532 nm, with 5.5 mJ/pulse and 10 Hz repetition rate. Perylene-Red doped copolymers of methyl methacrylate with a 10 vol% proportion of 2,2,2-trifluoroethyl-methacrylate exhibited a lasing efficiency of 26% with a high photosta...

  19. Textural Properties of Silicon Materials Produced by Laser Action

    Dřínek, Vladislav; Fajgar, Radek; Schneider, Petr; Šnajdaufová, Hana; Šolcová, Olga

    Marseille : MADIREL, 2005. s.50. [International Symposium on the Characterisation of Porous Solids COPS VII /7./. 25.05.2005-28.05.2005, Aix-en-Provence] R&D Projects: GA ČR(CZ) GA104/04/0963; GA ČR(CZ) GD203/03/H140 Institutional research plan: CEZ:AV0Z40720504 Keywords : textural properties * laser action * experiments Subject RIV: CF - Physical ; Theoretical Chemistry

  20. Phonon-phonon interactions in photoexcited graphite studied by ultrafast electron diffraction

    Harb, M.; Enquist, H.; Jurgilaitis, A.; Tuyakova, F. T.; Obraztsov, A. N.; Larsson, J.

    2016-03-01

    We investigated phonon-phonon interactions in photoexcited single-crystalline graphite by ultrafast electron diffraction. Transient electron diffraction profiles from a 35 nm graphite film were observed following laser excitation. Changes in intensities of diffraction spots revealed a two-exponential relaxation process with decay of strongly coupled optical phonons, and the slow relaxation process to redistribution of phonon energy to the equilibrium thermal distribution.

  1. Surface phonons

    Wette, Frederik

    1991-01-01

    In recent years substantial progress has been made in the detection of surface phonons owing to considerable improvements in inelastic rare gas scattering tech­ niques and electron energy loss spectroscopy. With these methods it has become possible to measure surface vibrations in a wide energy range for all wave vectors in the two-dimensional Brillouin zone and thus to deduce the complete surface phonon dispersion curves. Inelastic atomic beam scattering and electron energy loss spectroscopy have started to play a role in the study of surface phonons similar to the one played by inelastic neutron scattering in the investigation of bulk phonons in the last thirty years. Detailed comparison between experimen­ tal results and theoretical studies of inelastic surface scattering and of surface phonons has now become feasible. It is therefore possible to test and to improve the details of interaction models which have been worked out theoretically in the last few decades. At this point we felt that a concise, co...

  2. Phonons with orbital angular momentum

    Ion accoustic waves or phonon modes are studied with orbital angular momentum (OAM) in an unmagnetized collissionless uniform plasma, whose constituents are the Boltzmann electrons and inertial ions. For this purpose, we have employed the fluid equations to obtain a paraxial equation in terms of ion density perturbations and discussed its Gaussian beam and Laguerre-Gauss (LG) beam solutions. Furthermore, an approximate solution for the electrostatic potential problem is presented, allowing to express the components of the electric field in terms of LG potential perturbations. The energy flux due to phonons is also calculated and the corresponding OAM is derived. Numerically, it is shown that the parameters such as azimuthal angle, radial and angular mode numbers, and beam waist, strongly modify the profiles of the phonon LG potential. The present results should be helpful in understanding the phonon mode excitations produced by Brillouin backscattering of laser beams in a uniform plasma.

  3. Phonons with orbital angular momentum

    Ayub, M. K. [Theoretical Plasma Physics Division, PINSTECH, P. O. Nilore, Islamabad (Pakistan); National Centre for Physics, Shahdra Valley Road, Quaid-i-Azam University Campus, Islamabad 44000 (Pakistan); Ali, S. [National Centre for Physics, Shahdra Valley Road, Quaid-i-Azam University Campus, Islamabad 44000 (Pakistan); Mendonca, J. T. [IPFN, Instituto Superior Tecnico, Av. Rovisco Pais 1, 1049-001 Lisboa (Portugal)

    2011-10-15

    Ion accoustic waves or phonon modes are studied with orbital angular momentum (OAM) in an unmagnetized collissionless uniform plasma, whose constituents are the Boltzmann electrons and inertial ions. For this purpose, we have employed the fluid equations to obtain a paraxial equation in terms of ion density perturbations and discussed its Gaussian beam and Laguerre-Gauss (LG) beam solutions. Furthermore, an approximate solution for the electrostatic potential problem is presented, allowing to express the components of the electric field in terms of LG potential perturbations. The energy flux due to phonons is also calculated and the corresponding OAM is derived. Numerically, it is shown that the parameters such as azimuthal angle, radial and angular mode numbers, and beam waist, strongly modify the profiles of the phonon LG potential. The present results should be helpful in understanding the phonon mode excitations produced by Brillouin backscattering of laser beams in a uniform plasma.

  4. "Social Laser": Action Amplification by Stimulated Emission of Social Energy

    Khrennikov, Andrei

    2015-01-01

    The problem of the "explanation" of recent social explosions, especially in the Middle East, but also in Southern Europe and the USA, have been debated actively in the social and political literature. We can mention the contributions of P. Mason, F. Fukuyama, E. Schmidt and J. Cohen, I. Krastev to this debate. We point out that the diversity of opinions and conclusions is really amazing. At the moment, there is no consistent and commonly acceptable theory of these phenomena. We present a model of social explosions based on a novel approach for the description of social processes, namely, the quantum-like approach. Here quantum theory is treated simply as an operational formalism - without any direct relation to physics. We explore the quantum-like laser model to describe the possibility of Action Amplification by Stimulated Emission of Social Energy (ASE).

  5. Phonon manipulation with phononic crystals.

    Kim Bongsang; Hopkins, Patrick Edward; Leseman, Zayd C.; Goettler, Drew F.; Su, Mehmet F. (University of New Mexico, Albuquerque, NM); El-Kady, Ihab Fathy; Reinke, Charles M.; Olsson, Roy H., III

    2012-01-01

    In this work, we demonstrated engineered modification of propagation of thermal phonons, i.e. at THz frequencies, using phononic crystals. This work combined theoretical work at Sandia National Laboratories, the University of New Mexico, the University of Colorado Boulder, and Carnegie Mellon University; the MESA fabrication facilities at Sandia; and the microfabrication facilities at UNM to produce world-leading control of phonon propagation in silicon at frequencies up to 3 THz. These efforts culminated in a dramatic reduction in the thermal conductivity of silicon using phononic crystals by a factor of almost 30 as compared with the bulk value, and about 6 as compared with an unpatterned slab of the same thickness. This work represents a revolutionary advance in the engineering of thermoelectric materials for optimal, high-ZT performance. We have demonstrated the significant reduction of the thermal conductivity of silicon using phononic crystal structuring using MEMS-compatible fabrication techniques and in a planar platform that is amenable to integration with typical microelectronic systems. The measured reduction in thermal conductivity as compared to bulk silicon was about a factor of 20 in the cross-plane direction [26], and a factor of 6 in the in-plane direction. Since the electrical conductivity was only reduced by a corresponding factor of about 3 due to the removal of conductive material (i.e., porosity), and the Seebeck coefficient should remain constant as an intrinsic material property, this corresponds to an effective enhancement in ZT by a factor of 2. Given the number of papers in literature devoted to only a small, incremental change in ZT, the ability to boost the ZT of a material by a factor of 2 simply by reducing thermal conductivity is groundbreaking. The results in this work were obtained using silicon, a material that has benefitted from enormous interest in the microelectronics industry and that has a fairly large thermoelectric power

  6. Shedding light: laser physics and mechanism of action.

    De Felice, E

    2010-02-01

    Lasers have affected health care in many ways. Clinical applications have been found in a number of medical and surgical specialities. In particular, applications of laser technology in phlebology has made it essential for vein physicians to obtain a fundamental knowledge of laser physics, laser operation and also to be well versed in laser safety procedures. This article reviews recommended text books and current literature to detail the basics of laser physics and its application to venous disease. Laser safety and laser side effects are also discussed. PMID:20118342

  7. Coherent phonon coupled with exciton in semiconducting single-walled carbon nanotubes using a few-cycle pulse laser

    Kobayashi, Takayoshi, E-mail: kobayashi@ils.uec.ac.jp [Advanced Ultrafast Laser Research Center and Department of Engineering Science, Faculty of Informatics and Engineering, University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585 (Japan); JST, CREST, 5 Sanbancho, Chiyoda-ku, Tokyo 102-0075 (Japan); Department of Electrophysics, National Chiao-Tung University, Hsinchu 30010, Taiwan (China); Institute of Laser Engineering, Osaka University, 2-6 Yamada-oka, Suita, Osaka 565-0871 (Japan); Nie, Zhaogang; Du, Juan; Xue, Bing [Advanced Ultrafast Laser Research Center and Department of Engineering Science, Faculty of Informatics and Engineering, University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585 (Japan); JST, CREST, 5 Sanbancho, Chiyoda-ku, Tokyo 102-0075 (Japan)

    2014-08-01

    The vibrational wavepackets dynamics of single-walled carbon nanotubes (SWCNTs) are studied through the modulation of the transition probability in the visible spectral range of the systems. The modulations corresponding to the radial breathing mode (RBM), observed in the time traces for the four chiral systems (6,4), (6,5), (7,5), and (8,3), have been analyzed. The vibrational modes of the coherent phonon spectra are identified from the two-dimensional distribution of probe photon energy versus Fourier frequency. The present study pointed out that the observed probe photon energy dependence is due to both the imaginary and real parts of the third-order susceptibility, corresponding to derivative type dependence of the absorbed photon energy spectrum due to molecular-phase modulation, Raman (and Raman-like) gain and loss processes, and molecular phase modulation, respectively. - Highlights: • Vibrational dynamics are studied through the modulation of transition probability. • Probe λ dependence of amplitude is due to complex third-order susceptibility. • Coherent phonon dynamics are induced by Raman loss and gain. • Molecular phase modulation by vibration introduces a periodical shift of spectrum.

  8. Phononic crystal devices

    El-Kady, Ihab F.; Olsson, Roy H.

    2012-01-10

    Phononic crystals that have the ability to modify and control the thermal black body phonon distribution and the phonon component of heat transport in a solid. In particular, the thermal conductivity and heat capacity can be modified by altering the phonon density of states in a phononic crystal. The present invention is directed to phononic crystal devices and materials such as radio frequency (RF) tags powered from ambient heat, dielectrics with extremely low thermal conductivity, thermoelectric materials with a higher ratio of electrical-to-thermal conductivity, materials with phononically engineered heat capacity, phononic crystal waveguides that enable accelerated cooling, and a variety of low temperature application devices.

  9. Analgesic action of laser therapy (LLLT) in an animal model

    Daniel Pozza; Patricia Fregapani; João Weber; Marília Gerhardt de Oliveira; Marcos André de Oliveira; Nelson Ribeiro Neto; João Macedo Sobrinho

    2008-01-01

    OBJECTIVES: To evaluate the analgesic effect of laser therapy on healthy tissue of mice.STUDY DESIGN: Forty-five animals were divided in three groups of 15: A--infrared laser irradiation (830 nm, Kondortech, São Carlos, SP, Brazil); B--red laser irradiation (660 nm, Kondortech, São Carlos, SP, Brazil); C-- ham irradiation with laser unit off. After laser application, the mice remained immobilized for the injection of 30 microl of 2% formalin in the plantar pad of the irradiated hind paw. The ...

  10. Polaritons in cuprous oxide perturbed by LA-phonons

    Roslyak, Oleksiy; Birman, Joseph L.

    2007-01-01

    We present a comparative analysis of a 'conventional' phonoriton (coherent superposition of exciton-photon-phonon) and a polariton (coherent exciton-photon superposition) 'weakly' coupled to the LA-phonons bath. Depending on duration of the pumping laser field the phonon-induced decoherence results in two distinct types of excitation. Long ($ms$) laser pumping pulses form an 'equilibrium' polariton. The generic feature here is a pronounced photo-thermal bi-stability. i.e. formation of four di...

  11. Properties of nanocones formed on a surface of semiconductors by laser radiation: quantum confinement effect of electrons, phonons, and excitons.

    Medvid, Artur; Onufrijevs, Pavels; Mychko, Alexander

    2011-01-01

    On the basis of the analysis of experimental results, a two-stage mechanism of nanocones formation on the irradiated surface of semiconductors by Nd:YAG laser is proposed for elementary semiconductors and solid solutions, such as Si, Ge, SiGe, and CdZnTe. Properties observed are explained in the frame of quantum confinement effect. The first stage of the mechanism is characterized by the formation of a thin strained top layer, due to redistribution of point defects in temperature-gradient field induced by laser radiation. The second stage is characterized by mechanical plastic deformation of the stained top layer leading to arising of nanocones, due to selective laser absorption of the top layer. The nanocones formed on the irradiated surface of semiconductors by Nd:YAG laser possessing the properties of 1D graded bandgap have been found for Si, Ge, and SiGe as well, however QD structure in CdTe was observed. The model is confirmed by "blue shift" of bands in photoluminescence spectrum, "red shift" of longitudinal optical line in Raman back scattering spectrum of Ge crystal, appearance of Ge phase in SiGe solid solution after irradiation by the laser at intensity 20 MW/cm2, and non-monotonous dependence of Si crystal micro-hardness as function of the laser intensity. PMID:22060172

  12. Properties of nanocones formed on a surface of semiconductors by laser radiation: quantum confinement effect of electrons, phonons, and excitons

    Medvid Artur

    2011-01-01

    Full Text Available Abstract On the basis of the analysis of experimental results, a two-stage mechanism of nanocones formation on the irradiated surface of semiconductors by Nd:YAG laser is proposed for elementary semiconductors and solid solutions, such as Si, Ge, SiGe, and CdZnTe. Properties observed are explained in the frame of quantum confinement effect. The first stage of the mechanism is characterized by the formation of a thin strained top layer, due to redistribution of point defects in temperature-gradient field induced by laser radiation. The second stage is characterized by mechanical plastic deformation of the stained top layer leading to arising of nanocones, due to selective laser absorption of the top layer. The nanocones formed on the irradiated surface of semiconductors by Nd:YAG laser possessing the properties of 1D graded bandgap have been found for Si, Ge, and SiGe as well, however QD structure in CdTe was observed. The model is confirmed by "blue shift" of bands in photoluminescence spectrum, "red shift" of longitudinal optical line in Raman back scattering spectrum of Ge crystal, appearance of Ge phase in SiGe solid solution after irradiation by the laser at intensity 20 MW/cm2, and non-monotonous dependence of Si crystal micro-hardness as function of the laser intensity.

  13. Laser action in runaway electron pre-ionized diffuse discharges

    Panchenko, Alexei N.; Lomaev, Mikhail I.; Panchenko, Nikolai A.; Tarasenko, Viktor F.; Suslov, Alexei I.

    2015-12-01

    Formation features of run-away electron preionized diffuse discharge (REP DD) and REP DD properties in different experimental conditions are studied. It was shown that sufficient uniformity of REP DD allows its application as an excitation source of lasers on different gas mixtures at elevated pressure. Promising results of REP DD application for development of gas lasers are shown. Stimulated radiation in the IR, visible and UV spectral ranges was obtained in the diffuse discharge. Ultimate efficiency of non-chain HF(DF) chemical and nitrogen lasers on mixtures of SF6 with H2(D2) and N2 was achieved. New operation mode of nitrogen laser is demonstrated under REP DD excitation. Kinetic model of the REP DD in mixtures of nitrogen with SF6 is developed allowing to predict the radiation parameters of nitrogen laser at λ = 337,1 nm. Long-pulse operation of rare gas halide lasers was achieved.

  14. Laser therapy of infectious diseases: results and mechanism of therapeutic action

    Ovsiannikov, Victor; Sologub, T.; Pustashova, N.; Kuznetsov, N.; Masterova, O.; Rakhmanova, A.; Sizova, N.; Karpushina, I. A.

    2001-10-01

    We used laser therapies for viral hepatitis since 1993 and for HIV-patients since 1995. For these purposes we developed the special infrared laser and proposed some schemes of laser action on organism. Our laser works in pulse-periodical regime on the wavelength 890 nm with an average power of laser radiation (10 divided by 60) mW. All laser action was produced transcutaneous only. We did not observe any side effects or negative results from laser therapy with our laser. The treatment of viral hepatitis was produced by means of irradiation a blood in cubital veins, liver and thymus (breast bone area). Laser therapy was produced both on the usual base and disintoxical therapies. More than 300 viral hepatitis patients had received the laser treatment and for the most of them it gave a positive results. The treatment of HIV-patients was produced by means of irradiation six areas of their organism, which are responsible for immune system work. All our HIV-patients (25 men) who received laser treatment live up to now.

  15. Laser device for the protection of biological objects from the damaging action of ionizing radiation

    The search for ideal protective agents for use in radiotherapy or post-exposure treatment of victims of radiation accidents is one of the actual problems of radiation protection. Laser irradiation device for the protection of biological objects from the action of ionizing radiation to be used in practice has been manufactured (invention patent RU 2 428 228 C2). This device is used to study the action of various doses of laser radiation and combined irradiation with laser and gamma-radiation, on peripheral blood parameters and number of bone marrow karyocytes of the experimental mice line C57BL/6. The mice were irradiated with ionizing and laser radiation, separately one by one in a special bench. The time interval between two types of irradiation did not exceed 30 min. First, the mice were exposed to γ-radiation then to laser radiation. It was shown that laser radiation can be applied to improve the recovery of hemato genesis after the action of ionizing radiation on biological objects. Then, experiments were conducted to study the action of γ- rays and the combined action of laser radiation and γ -rays on survival, weight and skin of experimental mice. The authors investigated also the action of gamma-rays and combined effects of 650 nm laser radiation and gamma-rays on general mitotic index of bone marrow cells of mice. The method of the laser radiation-protection of biological objects contributes to an increase in the viability of mice, prevents the damages of skin and also increases the mitotic activity of mice bone marrow cells. (authors)

  16. Phonon-Assisted Anti-Stokes Lasing in ZnTe Nanoribbons.

    Zhang, Qing; Liu, Xinfeng; Utama, M Iqbal Bakti; Xing, Guichuan; Sum, Tze Chien; Xiong, Qihua

    2016-01-13

    Phonon-assisted anti-Stokes emission and its stimulated emission in polar semiconductor ZnTe are demonstrated via the annihilation of phonons as a result of strong exciton-phonon coupling. The findings are not only important for developing high-power radiation-balanced lasers, but are also promising for manufacturing ultraefficient solid-state laser coolers. PMID:26573758

  17. Injectorless quantum cascade laser with two-phonon-resonance design using four alloys for emission wavelengths between 5 and 9 µm

    The wavelength-dependent threshold and power performance of an injectorless quantum cascade laser design using four alloys and the two-phonon-resonance depletion scheme were investigated. A 7 µm design, which reached threshold current densities as low as 0.45 kA cm−2 at 300 K and overall efficiencies above 2%, was taken as a reference. Variations in layer thickness and composition were applied to study the effects of coupling energy and transition time, increasing the output efficiency up to 5.7%. With regard to the transmission windows from 3 to 5 µm and 8 to 12 µm, the design scheme of the reference was also modified to emission wavelengths between 5 and 9 µm. All devices yield threshold current densities below 1.5 kA cm−2 at 300 K, and at least 550 mW of output power. The characteristic temperatures vary indirectly proportional to the emission wavelength from 100 K at 5 µm to 300 K at 9 µm

  18. Manipulation of Phonons with Phononic Crystals

    Leseman, Zayd Chad [Univ. of New Mexico, Albuquerque, NM (United States)

    2015-07-09

    There were three research goals associated with this project. First, was to experimentally demonstrate phonon spectrum control at THz frequencies using Phononic Crystals (PnCs), i.e. demonstrate coherent phonon scattering with PnCs. Second, was to experimentally demonstrate analog PnC circuitry components at GHz frequencies. The final research goal was to gain a fundamental understanding of phonon interaction using computational methods. As a result of this work, 7 journal papers have been published, 1 patent awarded, 14 conference presentations given, 4 conference publications, and 2 poster presentations given.

  19. Plasma and shock generation by indirect laser pulse action

    Kasperzcuk, A.; Borodziuk, S.; Demchenko, N. N.; Gus´kov, S.Y.; Jungwirth, Karel; Kálal, M.; Králiková, Božena; Krouský, Eduard; Limpouch, Jiří; Mašek, Karel; Pisarczyk, P.; Pisarczyk, T.; Pfeifer, Miroslav; Rohlena, Karel; Rozanov, V. B.; Skála, Jiří; Ullschmied, Jiří

    Melville: American Institut of Physics , 2005 - (Sadowski, M.; Dudeck, M.; Hartfus, H.; Pawelec, E.), s. 283-286. (AIP Conference Proceedings. 812). ISBN 0-7354-0304-X. ISSN 0094-243X. [PLASMA 2005. Opole-Turawa (PL), 06.09.2005-09.09.2005] R&D Projects: GA MŠk(CZ) LC528 Grant ostatní: EC - LASER LAB-EUROPE(XE) RII3-CT-2003-506350 Institutional research plan: CEZ:AV0Z10100523; CEZ:AV0Z20430508 Keywords : plasma production by laser * plasma heating by laser * plasma shock waves Subject RIV: BL - Plasma and Gas Discharge Physics http://dx.doi.org/10.1063/1.2168843

  20. Phonon Transport in Graphene

    Denis L. Nika; Balandin, Alexander A.

    2012-01-01

    Properties of phonons - quanta of the crystal lattice vibrations - in graphene have attracted strong attention of the physics and engineering communities. Acoustic phonons are the main heat carriers in graphene near room temperature while optical phonons are used for counting the number of atomic planes in Raman experiments with few-layer graphene. It was shown both theoretically and experimentally that transport properties of phonons, i.e. energy dispersion and scattering rates, are substant...

  1. Biological Effects of Contact Action of 1470 vs. 810 nm Semiconductor Lasers in vitro

    Schumilova N.A.

    2014-12-01

    Full Text Available The aim of the investigation is to identify the character of biological effects of contact action of semiconductor laser with a wavelength of 1470 nm on the tissues with different optical and mechanical properties compared to the exposure to laser radiation with a wavelength of 810 nm. Materials and Methods. The study was performed on a chicken muscle tissue, liver of the cattle, nasal polyp, removed nasal septum cartilage. While making a linear incision of the tissues by the laser with a speed of 2 mm/s assessment of the width of ablation and coagulation zones, and the crater depth with the following measurement under the microscopy conditions were carried on. Weighing of the tissue specimens before and after the spot action was performed. Standardization of the operating speed was achieved by using uniformly moving recorder chart. Results. Radiation power increment of 1470 nm wavelength laser contributes to the increase of the ablation and coagulation zone width to a greater degree compared to 810 nm laser. Exposure to 1470 nm laser with a power of 1 W causes the tissue to stick to the fiber. When power is 2 W, coagulation zone of soft tissues is comparable, and in some cases exceeds it after treatment by 810 nm laser. In relation to the crater depth, 1470 nm radiation is inferior to 810 nm radiation, but is superior in relation to vaporization abilities. Conclusion. For tissue ablation with 1470 nm laser a power of 2 W is optimal, as it provides a sparing superficial effect, and in a number of cases exceeds the action of 810 nm 7 W laser by its coagulation properties. Generation of a crater with a less depth after application of 1470 nm laser allows it to be recommended for superficial coagulation of vascular lesions.

  2. Study on modes of energy action in laser-induction hybrid cladding

    The shape and microstructure in laser-induction hybrid cladding were investigated, in which the cladding material was provided by means of three different methods including the powder feeding, cold pre-placed coating (CPPC) and thermal pre-placed coating (TPPC). Moreover, the modes of energy action in laser-induction hybrid cladding were also studied. The results indicate that the cladding material supplying method has an important influence on the shape and microstructure of coating. The influence is decided by the mode of energy action in laser-induction hybrid cladding. During the TPPC hybrid cladding of Ni-based alloy, the laser and induction heating are mainly performed on coating. During the CPPC hybrid cladding of Ni-based alloy, the laser and induction heating are mainly performed on coating and substrate surface, respectively. In powder feeding hybrid cladding, a part of laser is absorbed by the powder particles directly, while the other part of laser penetrating powder cloud radiates on the molten pool. Meanwhile, the induction heating is entirely performed on the substrate. In addition, the wetting property on the interface is improved and the metallurgical bond between the coating and substrate is much easier to form. Therefore, the powder feeding laser-induction hybrid cladding has the highest cladding efficiency and the best bond property among three hybrid cladding methods.

  3. Random Laser Action in Nd:YAG Crystal Powder

    Jon Azkargorta

    2016-05-01

    Full Text Available This work explores the room temperature random stimulated emission at 1.064 μm of a Nd:YAG crystal powder (Neodymium-doped yttrium aluminum garnet in a very simple pump configuration with no assistance from an internal mirror. The laser threshold energy as a function of pump beam area and pump wavelength has been measured, as well as the temporal dynamics of emission pulses. The absolute energy of stimulated emission and the absolute laser slope efficiency have been measured by using a method proposed by the authors. The results show a surprising high efficiency that takes the low Nd3+ ion concentration of the crystal powder into account.

  4. Experimental aspects concerning the laser action on the living tissue

    Ciuchita, Tavi; Antipa, Ciprian; Stanescu, Constantin S.; Anghel, Sorin; Calugareanu, Mircea

    2001-06-01

    The paper presents some experimental methods of the treatment and investigation aspects and results concerning the interaction of the low energy laser (LEL) with living tissue in the treatment of some skin diseases: lichen ruber planus (LP) and infectious finger pulpits (IFP), scalp alopecia (SA) and crural ulcers (CU). We concluded that LEL therapy is a useful complementary method in the treatments of these skin diseases .

  5. Length-scale dependent phonon interactions

    Srivastava, Gyaneshwar

    2014-01-01

    This book presents  a comprehensive description of phonons and their interactions in systems with different dimensions and length scales. Internationally-recognized leaders describe theories and measurements of phonon interactions  in relation to the design of materials with exotic properties such as metamaterials, nano-mechanical systems, next-generation electronic, photonic, and acoustic devices, energy harvesting, optical information storage, and applications of phonon lasers in a variety of fields. The emergence of techniques for control of semiconductor properties and geometry has enabled engineers to design structures in which functionality is derived from controlling electron behavior. As manufacturing techniques have greatly expanded the list of available materials and the range of attainable length scales, similar opportunities now exist for designing devices whose functionality is derived from controlling phonon behavior. However, progress in this area is hampered by gaps in our knowledge of phono...

  6. Study on laser action from UV-curable chiral nematic liquid crystals

    This paper describes the study on laser action from UV-curable chiral nematic liquid crystals (CLCs) doped with a fluorescent dye before and after photopolymerization of CLC host. When an optically active agent without crosslinkable moiety was doped in a UV-curable nematic liquid crystal, the laser action from the CLC cell was quite different before and after photopolymerization. Before the polymerization, optically pumping of dye-doped CLC cells with a linearly polarized laser beam gave rise to the laser emission with circular polarization at the band edge of CLC reflection as a consequence of the internal distributed feedback effect. Successively, photopolymerization of the CLC with 365 nm light brought about the thorough disappearance of the CLC reflection band probably due to the phase separation leading to the emergence of amplified spontaneous emission of fluorescent dye by optically pumping. In contrast, the dye-doped CLC cell including a crosslinkable agent with a cholesteryl residue enabled the mirrorless laser action after photopolymerization. This is because the selective reflection band of CLC host was retained by the planar structure of cholesteric polymer network

  7. Photon-phonon superradiation

    Andrianov, S.N.; Samartsev, V.V.; Sheibut, Y.E. [Zavoiskii Physicotechnical Institute, Tatarstan (Russian Federation)

    1995-09-01

    The theory of photon-phonon superradiation in extended samples of impurity molecular crystals was developed within the framework of the nonequilibrium statistical operator method. Optical superradiation on indirect transitions of anisotropic impurity molecules involving resonant phonons under conditions of their hermodynamic equilibrium was studied. Two-quantum superradiation on a Stokes indirect transition accompanied by emission of coherent photons and phonons with nonequilibrium initial phonon subsystem was also examined. Prerequisites to the effect were analyzed and its main properties were described. 16 refs., 3 figs.

  8. Vertical cavity surface emitting laser action of an all monolithic ZnO-based microcavity

    Kalusniak, S.; Sadofev, S.; Halm, S.; Henneberger, F.

    2010-01-01

    We report on room temperature laser action of an all monolithic ZnO-based vertical cavity surface emitting laser (VCSEL) under optical pumping. The VCSEL structure consists of a 2{\\lambda} microcavity containing 8 ZnO/Zn(0.92)Mg(0.08)O quantum wells embedded in epitaxially grown Zn(0.92)Mg(0.08)O/Zn(0.65)Mg(0.35)O distributed Bragg reflectors (DBRs). As a prerequisite, design and growth of high reflectivity DBRs based on ZnO and (Zn,Mg)O for optical devices operating in the ultraviolet and bl...

  9. Phonon-dislocation interaction

    Thermal conductivity measurements on LiF crystals in the temperature range 0.04 to 30 K have demonstrated that, throughout this range, thermal phonons interact with dislocations via a dynamic or resonant process which is highly frequency- and phonon-mode dependent. The results of earlier work are consistent with this interpretation

  10. Real time monitoring of drug action on T. cruzi parasites using a biospeckle laser method

    Ansari, M. Z.; Grassi, H. C.; Cabrera, H.; Andrades, E. D. J.

    2016-06-01

    In this paper, we report on a biospeckle laser method used to monitor a specific drug action on T. cruzi parasites. Experimental results from fast biospeckle monitoring of the parasites’ activity under the influence of the drug demonstrate the effectiveness of the proposed method. We measure the speckle parameters such as spatiotemporal correlation and speckle grain size to assess the immediate action of the drug on the parasites during a very short incubation period. From a practical point of view, this aproach allows us to validate biospeckle as a fast, non-invasive and alternative method to test candidate drugs on T. cruzi parasites.

  11. Self-consistent description of spin-phonon dynamics in ferromagnets

    Nieves, P.; Serantes, D.; Chubykalo-Fesenko, O.

    2016-07-01

    Several recently reported exciting phenomena such as spin caloritronics or ultrafast laser-induced spin dynamics involve the action of temperature on spin dynamics. However, the inverse effect of magnetization dynamics on temperature change is very frequently ignored. Based on the density matrix approach, in this work we derive a self-consistent model for describing the magnetization and phonon temperature dynamics in ferromagnets in the framework of the quantum Landau-Lifshitz-Bloch equation. We explore potential applicability of our approach for two cases, inspired by magnetocaloric effect and magnetic fluid hyperthermia. In the first case, the spin-phonon dynamics is governed by the longitudinal relaxation in bulk systems close to the Curie temperature; while in the second case it is described by the transverse relaxation during the hysteresis cycle of individual nanoparticles well below the Curie temperature.

  12. Development and characterization of the Ion Laser InterAction Setup (ILIAS)

    The Ion Laser InterAction Setup ILIAS at the VERA-facility in Vienna is developed to explore laser photodetachment of negative ions in a gas-filled radio frequency quadrupole (RFQ) cooler. The aim of this project is a novel technique for element-selective negative ion beam purification in accelerator mass spectrometry (AMS). For this purpose, the ion cooler has to be suited to decelerate and cool intense atomic and molecular negative ion beams with keV energies. In this talk I give an update on the current status and performance of the RFQ ion cooler. Recent experimental results will be discussed: This includes the suppression of a Cu¯ test beam by more than 99.999% by laser photodetachment, the suppression of MgO¯ vs. AlO¯ and comprehensive measurements of the ion residence time inside the RFQ ion cooler. (author)

  13. Gas-dynamic explosion of water microparticles under action high-power femtosecond laser pulses

    Zemlyanov, Alexander A.; Geints, Yuri E.; Apeksimov, Dmitrii V.

    2006-02-01

    Among the broad audience of problems of atmospheric nonlinear optics the important place is occupied with a problem about interaction of intensive laser radiation with water microparticles. Drops, being in a field of powerful light radiation, owing to effects of evaporation or explosion change the optical characteristics and influence on the optical properties of an environment. It results to that process and the distribution of intensive laser radiation in a particle is characterized by self-influence and is capable to change the internal power of a drop due to occurrence of areas of optical breakdown. In the report the model of destruction of water microparticles under action of supershort laser radiation is submitted. The physical contents of model is the effect of shock boiling up of a liquid at it gas-dynamic expansion from areas subject to optical breakdown.

  14. Phonon-induced polariton superlattices

    de Lima, Jr., M. M.; Poel, Mike van der; Santos, P. V.;

    2006-01-01

    We show that the coherent interaction between microcavity polaritons and externally stimulated acoustic phonons forms a tunable polariton superlattice with a folded energy dispersion determined by the phonon population and wavelength. Under high phonon concentration, the strong confinement of the...... optical and excitonic polariton components in the phonon potential creates weakly coupled polariton wires with a virtually flat energy dispersion....

  15. Phonon-induced polariton superlattices.

    de Lima, M M; van der Poel, M; Santos, P V; Hvam, J M

    2006-07-28

    We show that the coherent interaction between microcavity polaritons and externally stimulated acoustic phonons forms a tunable polariton superlattice with a folded energy dispersion determined by the phonon population and wavelength. Under high phonon concentration, the strong confinement of the optical and excitonic polariton components in the phonon potential creates weakly coupled polariton wires with a virtually flat energy dispersion. PMID:16907587

  16. Phonon-induced polariton superlattices

    Lima, Jr., Enio; Van Der Poel, Mike; Santos, P.V.; Hvam, Jørn Märcher

    2006-01-01

    We show that the coherent interaction between microcavity polaritons and externally stimulated acoustic phonons forms a tunable polariton superlattice with a folded energy dispersion determined by the phonon population and wavelength. Under high phonon concentration, the strong confinement of the optical and excitonic polariton components in the phonon potential creates weakly coupled polariton wires with a virtually flat energy dispersion.

  17. Birefringent phononic structures

    I. E. Psarobas

    2014-12-01

    Full Text Available Within the framework of elastic anisotropy, caused in a phononic crystal due to low crystallographic symmetry, we adopt a model structure, already introduced in the case of photonic metamaterials, and by analogy, we study the effect of birefringence and acoustical activity in a phononic crystal. In particular, we investigate its low-frequency behavior and comment on the factors which determine chirality by reference to this model.

  18. Squeezed Phonon Wave Packet Generation by Optical Manipulation of a Quantum Dot

    Daniel Wigger

    2015-02-01

    Full Text Available In solid-state physics, the quantized lattice vibrations, i.e., the phonons, play a vital role. Phonons, much like photons, satisfy bosonic commutation relations, and therefore, various concepts well-known in quantum optics can be transferred to the emerging field of phononics. Examples are non-classical states and, in particular, squeezed states. We discuss the generation of phonon squeezing by optically exciting a quantum dot and show that by excitation with detuned continuous wave laser fields, sequences of squeezed phonon wave packets are created, which are emitted from the quantum dot region into the surrounding material.

  19. Deformation of a laser plasma corona under the action of a ponderomotive force and accompanying effects

    The pattern of deformation of the density profile of an inhomogeneous laser plasma flow due to the action of a ponderomotive force is identified. The dynamic pattern of generation of non-linear potential fields in the plasma, including caviton-trapped fields, is demonstrated. By isolating the dissipative mechanisms, it was possible to determine the proportion of the energy dissipated in the plasma as a result of the Cherenkov mechanism of interaction between the potential fields and electrons, and thus, the energy which results in the generation of hot electrons. It was shown that a comparatively low plasma flow rate qualitatively alters the pattern of interaction between laser radiation and a plasma. In particular, the formation of cavitons is impeded, the generation of short-wavelength longitudinal fields is suppressed, and the proportion of electromagnetic radiation energy absorbed as a result of the Cherenkov interaction is reduced, i.e., the energy transferred to the fast electrons is reduced. (author)

  20. Protective action of low-intensity laser radiation relative to the toxic effect of metals (experimental study in vitro)

    Dejneka, S. Y.

    1997-12-01

    The study of a possible cytotoxic effect of different doses of low-insensitive laser radiation and protective action of low-intensive laser radiation relative to the toxic effect of metals was carried out by means of the alternative method of investigation in vitro on cell cultura Hela. It was established that the investigated doses of low-intensive laser radiation had not produced any toxic effect on cell culture Hela, so the mentioned doses were not cytotoxic. It was revealed that laser radiation reduced the level of the cytotoxic effect of the studied metal salts on the cell culture, and possessed the protective action against the toxic effect of metals. This action has a clear-cut dose- related character.

  1. All-optical transistor action by off-resonant activation at laser threshold

    Andrews, David L

    2009-01-01

    The development of viable all-optical data processing systems has immense importance for both the computing and telecommunication industries, but device realization remains elusive. In this Letter, we propose an innovative mechanism deployed as a basis for all optical transistor action. In detail, it is determined that an optically pumped system, operating just below laser threshold, can exhibit a greatly enhanced output on application of an off-resonant beam of sufficient intensity. The electrodynamics of the underlying, nonlinear optical mechanism is analyzed, model calculations are performed, and the results are illustrated graphically.

  2. Phonon wave propagation in ballistic-diffusive regime

    Tang, Dao-Sheng; Hua, Yu-Chao; Nie, Ben-Dian; Cao, Bing-Yang

    2016-03-01

    Wide applications of ultra-short pulse laser technique in micromachining and thermophysical properties' measurements make the study on ultrafast transient thermal transport necessarily essential. When the characteristic time is comparable to the phonon relaxation time, phonons propagate in ballistic-diffusive regime and thermal wave occurs. Here, ultrafast transient phonon transport is systematically investigated based on the Monte Carlo (MC) simulations, the Cattaneo-Vernotte (C-V) model, and the phonon Boltzmann transport equation (BTE). It is found that remarkable differences exist between the C-V model and the MC simulations when describing the evolution of the thermal wave excited by the ultra-short heat pulse. The C-V model predicts a non-dispersive dissipative thermal wave, while the MC simulation with Lambert emission predicts a dispersive dissipative thermal wave. Besides, different phonon emissions can significantly influence the evolution of the thermal wave in the MC simulations. A modified C-V model with a time- and position-dependent effective thermal conductivity is derived based on the phonon BTE to characterize the evolution of the transport regime from ballistic to diffusive. The integrations on moments of the distribution function cause the loss of the information of the phonon distribution in wave vector space, making the macroscopic quantities incomplete when describing the ballistic transport processes and corresponding boundary conditions. Possible boundary conditions for the phonon BTE in practice are also discussed on different heating methods.

  3. Coherent control of acoustic phonons in semiconductor superlattices

    Bartels, Albrecht; Dekorsy, Thomas; Kurz, Heinrich; Köhler, Klaus

    1998-01-01

    Coherent acoustic phonons are generated in GaAs/AlAs superlattices by excitation with femtosecond laser pulses. Several modes of the acoustic phonon spectrum are observed, in agreement with the effect of zone folding in the mini-Brillouin zone of the superlattice. By applying successive pump pulses we are able to silence the first back-folded mode near q=0, while selectively enhancing the coherent amplitude of higher order backfolded modes. This increase in the spectroscopic sensitivity opens...

  4. Phonon dispersion in vanadium

    Complete text of publication follows. Phonon dispersion curves in Vanadium metal are investigated by neutron inelastic scattering using three-axis spectrometers. Due to extremely low coherent scattering amplitude of neutrons in natural isotope mixture of vanadium the phonon frequencies could be determined in the energy range below about 15 meV. Several phonon groups were measured with the polarised neutron scattering set-up. It is demonstrated that the intensity of coherent inelastic scattering observed in the non-spin-flip channel vanishes in the spin-flip channel. The phonon density of states is measured on a single crystal keeping the momentum transfer equal to a vector of reciprocal lattice where the coherent inelastic scattering is suppressed. Phonon dispersion curves in vanadium, as measured by neutron and earlier by X-ray scattering, are described in frames of a charge-fluctuation model involving monopolar and dipolar degrees of freedom. The model parameters are compared for different transition metals with body-centred cubic-structure. (author)

  5. Preface: Phonons 2007

    Perrin, Bernard

    2007-06-01

    The conference PHONONS 2007 was held 15-20 July 2007 in the Conservatoire National des Arts et Métiers (CNAM) Paris, France. CNAM is a college of higher technology for training students in the application of science to industry, founded by Henri Grégoire in 1794. This was the 12th International Conference on Phonon Scattering in Condensed Matter. This international conference series, held every 3 years, started in France at Sainte-Maxime in 1972. It was then followed by meetings at Nottingham (1975), Providence (1979), Stuttgart (1983), Urbana-Champaign (1986), Heidelberg (1989), Ithaca (1992), Sapporo (1995), Lancaster (1998), Dartmouth (2001) and St Petersburg (2004). PHONONS 2007 was attended by 346 delegates from 37 different countries as follows: France 120, Japan 45, Germany 25, USA 25, Russia 21, Italy 13, Poland 9, UK 9, Canada 7, The Netherlands 7, Finland 6, Spain 6, Taiwan 6, Greece 4, India 4, Israel 4, Ukraine 4, Serbia 3, South Africa 3, Argentina 2, Belgium 2, China 2, Iran 2, Korea 2, Romania 2, Switzerland 2, and one each from Belarus, Bosnia-Herzegovina, Brazil, Bulgaria, Egypt, Estonia, Mexico, Moldova, Morocco, Saudi Arabia, Turkey. There were 5 plenary lectures, 14 invited talks and 84 oral contributions; 225 posters were presented during three poster sessions. The first plenary lecture was given by H J Maris who presented fascinating movies featuring the motion of a single electron in liquid helium. Robert Blick gave us a review on the new possibilities afforded by nanotechnology to design nano-electomechanical systems (NEMS) and the way to use them to study elementary and fundamental processes. The growing interest for phonon transport studies in nanostructured materials was demonstrated by Arun Majumdar. Andrey Akimov described how ultrafast acoustic solitons can monitor the optical properties of quantum wells. Finally, Maurice Chapellier told us how phonons can help tracking dark matter. These 328 presentations gave rise to 185 articles

  6. Phonon Localization in Heat Conduction

    Luckyanova, Maria N.; Mendoza, Jonathan; Lu, Hong; Huang, Shengxi; Zhou, Jiawei; Li, Mingda; Kirby, Brian J.; Grutter, Alexander J.; Puretzky, Alexander A.; Dresselhaus, Millie S.; Gossard, Arthur; Chen, Gang

    2016-01-01

    Departures in phonon heat conduction from diffusion have been extensively observed in nanostructures through their thermal conductivity reduction and largely explained with classical size effects neglecting phonon's wave nature. Here, we report localization-behavior in phonon heat conduction due to multiple scattering and interference of phonon waves, observed through measurements of the thermal conductivities of GaAs/AlAs superlattices with ErAs nanodots randomly distributed at the interface...

  7. Theoretical study on ultrafast dynamics of coherent acoustic phonons in semiconductor nanocrystals

    Huang, Tongyun; Han, Peng; Wang, Xinke; Feng, Shengfei; Sun, Wenfeng; Ye, Jiasheng; Zhang, Yan

    2016-05-01

    We present a theoretical study on the ultrafast dynamics of coherent acoustic phonons in semiconductor quantum dots using continuum model calculations. The excitonic states and the coherent acoustic vibrational modes of semiconductor quantum dots are calculated using the effective mass approximation and continuum elastic medium model, respectively. By solving the Liouville–von Neumann equation and the equation of motion, we obtain the oscillation of coherent acoustic phonon amplitude excited by a pump pulse laser. Owing to the ultrafast excitation of coherent phonons, both the amplitude and the phase of the coherent phonon oscillation are constant with time. This coherent phonon oscillation results in conservation of the coherence of the exciton state, which cannot exist in a system interacting with incoherent phonons. We further study the amplitude and the period of coherent acoustic phonon oscillation as a function of pump pulse energy detuning, quantum dot size, and material.

  8. Temperature Dependence of Brillouin Light Scattering Spectra of Acoustic Phonons in Silicon

    Somerville, Kevin; Klimovich, Nikita; An, Kyongmo; Sullivan, Sean; Weathers, Annie; Shi, Li; Li, Xiaoqin

    2015-03-01

    Thermal management represents an outstanding challenge in many areas of technology. Electrons, optical phonons, and acoustic phonons are often driven out of local equilibrium in electronic devices or during laser-material interaction processes. Interest in non-equilibrium transport processes has motivated the development of Raman spectroscopy as a local temperature sensor of optical phonons and intermediate frequency acoustic phonons, whereas Brillouin light scattering (BLS) has recently been explored as a temperature sensor of low-frequency acoustic phonons. Here, we report temperature dependent BLS spectra of silicon, with Raman spectra taken simultaneously for comparison. The origins of the observed temperature dependence of the BLS peak position, linewidth, and intensity are examined in order to evaluate their potential use as temperature sensors for acoustic phonons. We determine that the integrated BLS intensity can be used measure the temperature of specific acoustic phonon modes. This work is supported by National Science Foundation (NSF) Thermal Transport Processes Program under Grant CBET-1336968.

  9. High energy phonons: overview

    Neutron scattering has been important in the measurement and interpretation of phonon dispersion relations. As these measurements are extended to higher energies they may yield new types of information or information about different types of systems. Several examples are discussed including: dispersion in high frequency internal modes, application to molecular crystals and the use of vibrational modes of hydrogen as a structural probe

  10. Transport in phonon systems

    This book gives as systematic application of the methods of physical kinetics to phonon systems. The results presented are of direct relevance to materials whose transport and other properties are dominated by phonons. This class of materials includes most common dielectrics as well as such unusual substances as He-II, glasses and some semiconductors. The theory is presented in its rigorous mathematical formulation, and qualitative physical reasoning is given only to elucidate some of the results thus obtained. An introductory chapter, containing the derivation of phonon spectra in the harmonic approximation and the perturbative treatment of anharmonicity as well as the fundamentals of physical kinetics, makes the text accessible for those who enter this field as beginners. Subsequent chapters deal with heat transport, second sound, dielectric losses, sound attenuation, etc. The basic equations of phonon hydrodynamics and the superdiffusion equation are derived and solved for specific cases. The application of sophisticated field-theoretical methods (Kubo formula, Feynman diagrams) is limited and delegated to an appendix, because they only exceptionally go beyond what ordinary quantum-mechanical perturbation theory or the Boltzmann equation provide for the systems under consideration. Th0191thor's preference for the less formal approach gives the reader a grip of the physical significance of the assumptions involved and thus of the limits of validity of the theory. (Auth.)

  11. Continuous mode cooling and phonon routers for phononic quantum networks

    We study the implementation of quantum state transfer protocols in phonon networks, where, in analogy to optical networks, quantum information is transmitted through propagating phonons in extended mechanical resonator arrays or phonon waveguides. We describe how the problem of a non-vanishing thermal occupation of the phononic quantum channel can be overcome by implementing optomechanical multi- and continuous mode cooling schemes to create a ‘cold’ frequency window for transmitting quantum states. In addition, we discuss the implementation of phonon circulators and switchable phonon routers, which rely only on strong coherent optomechanical interactions and do not require strong magnetic fields or specific materials. Both techniques can be applied and adapted to various physical implementations, where phonons coupled to spin- or charge-based qubits are used for on-chip networking applications. (paper)

  12. Infrared-Phonon Polariton Resonance of the Nonlinear Susceptibility in GaAs

    Dekorsy, Thomas; Yakovlev, Vladislav A.; Seidel, Wolfgang; Helm, Manfred; Keilmann, Fritz

    2003-01-01

    Nonlinear probing of the fundamental lattice vibration of polar crystals is shown to reveal insight into higher-order cohesive lattice forces. With a free-electron laser tunable in the far infrared we experimentally investigate the dispersion of the second-order susceptibility due to the phonon resonance in GaAs. We observe a strong resonance enhancement of second harmonic light generation at half the optical phonon frequency, and in addition a minimum at a higher frequency below the phonon f...

  13. Resonant squeezing and the anharmonic decay of coherent phonons

    Fahy, Stephen; Murray, Éamonn D.; Reis, David A.

    2016-04-01

    We show that the anharmonic decay of large-amplitude coherent phonons in a solid generates strongly enhanced squeezing of the phonon modes near points of the Brillouin zone where energy conservation in the three-phonon decay process is satisfied. The squeezing process leads to temporal oscillations of the mean-square displacement of target modes in resonance with the coherent phonon, which are characteristic of coherent phonon decay and do not occur in the decay of a phonon in a well-defined number state. For realistic material parameters of optically excited group-V semimetals, we predict that this squeezing results in strongly enhanced oscillations of the x-ray diffuse scattering intensity at sharply defined values of the x-ray momentum transfer. Numerical simulations of the phonon dynamics and the x-ray diffuse scattering in optically excited bismuth, using harmonic and anharmonic force parameters calculated with constrained density functional theory, demonstrate oscillations of the diffuse scattering intensity of magnitude 10%-20% of the thermal background at points of the Brillouin zone, where resonance occurs. Such oscillations should be observable using time-resolved optical-pump and x-ray-probe facilities available at current x-ray free-electron laser sources.

  14. Dynamics of nonequilibrium electron-phonon system for semiconductors and metals in a strong electrical field

    Formation of non-stationary nonequilibrium electron and phonon distribution functions (DFs) is investigated at action on metal of a strong pulse electric field. For concreteness parameters are taken for the nickel having reference temperature of 20 K. It is shown: (i) electron distribution function occurs as a result of impacts to imperfections of a lattice; (ii) electron distribution function does not become thermodynamically equilibrium as electron-electron impacts in the given situation give essentially smaller contribution, than electron-phonon collisions, and collisions with a 'another's' subsystem do not result to thermalization; (v) electron and phonon distribution functions have high-energy 'tails' as at electron-phonon impacts the momentum is transferred by enough small transfer of energy, is born much phonons at Debye energy, i.e. phonon distribution function have maximum for Debye phonons.

  15. Phononic crystals fundamentals and applications

    Adibi, Ali

    2016-01-01

    This book provides an in-depth analysis as well as an overview of phononic crystals. This book discusses numerous techniques for the analysis of phononic crystals and covers, among other material, sonic and ultrasonic structures, hypersonic planar structures and their characterization, and novel applications of phononic crystals. This is an ideal book for those working with micro and nanotechnology, MEMS (microelectromechanical systems), and acoustic devices. This book also: Presents an introduction to the fundamentals and properties of phononic crystals Covers simulation techniques for the analysis of phononic crystals Discusses sonic and ultrasonic, hypersonic and planar, and three-dimensional phononic crystal structures Illustrates how phononic crystal structures are being deployed in communication systems and sensing systems.

  16. Phonon operators for deformed nuclei

    The mathematical formalism with the phonon operators independent of the signature of the angular momentum projection turns out to be inadequate for describing excited states of deformed nuclei. New phonon operators are introduced which depend on the signature of the angular momentum projection on the symmetry axis of a deformed nucleus. It is shown that the calculations with the new phonons take correctly into account the Pauli principle in two-phonon components of wave functions. The results obtained differ from those given by the phonons independent of the signature of the angular momentum projection. The new phonons must be used in deformed nuclei at taking systematically the Pauli principle into account and in calculations involving wave functions of excited states having components with more than one-phonon operator

  17. Suppression of nonlinear phonon relaxation in Yb:YAG thin disk via zero phonon line pumping.

    Smrž, Martin; Miura, Taisuke; Chyla, Michal; Nagisetty, Siva; Novák, Ondřej; Endo, Akira; Mocek, Tomáš

    2014-08-15

    A quantitative comparison of conventional absorption line (940 nm) pumping and zero phonon line (ZPL) (969 nm) pumping of a Yb:YAG thin disk laser is reported. Characteristics of an output beam profile, surface temperature, and deformation of a thin disk under the different pump wavelengths are evaluated. We found that a nonlinear phonon relaxation (NPR) of the excited state in Yb:YAG, which induces nonlinear temperature rise and large aspheric deformation, did not appear in the case of a ZPL pumped Yb:YAG thin disk. This means that the advantage of ZPL pumping is not only the reduction of quantum defect but also the suppression of NPR. The latter effect is more important for high power lasers. PMID:25121908

  18. Phonon Gas Model (PGM) workflow in the VLab Science Gateway

    da Silveira, P.; Zhang, D.; Wentzcovitch, R. M.

    2013-12-01

    This contribution describes a scientific workflow for first principles computations of free energy of crystalline solids using the phonon gas model (PGM). This model was recently implemented as a hybrid method combining molecular dynamics and phonon normal mode analysis to extract temperature dependent phonon frequencies and life times beyond perturbation theory. This is a demanding high throughout workflow and is currently being implemented in VLab Cyberinfrastructure [da Silveira et al., 2008], which has recently been integrated to the XSEDE. First we review the underlying PGM, its practical implementation, and calculation requirements. We then describe the workflow management and its general method for handling actions. We illustrate the PGM application with a calculation of MgSiO3-perovskite's anharmonic phonons. We conclude with an outlook of workflows to compute other material's properties that will use the PGM workflow. Research supported by NSF award EAR-1019853.

  19. Absence of phase-dependent noise in time-domain reflectivity studies of impulsively excited phonons

    Hussain, A.

    2010-06-17

    There have been several reports of phase-dependent noise in time-domain reflectivity studies of optical phonons excited by femtosecond laser pulses in semiconductors, semimetals, and superconductors. It was suggested that such behavior is associated with the creation of squeezed phonon states although there is no theoretical model that directly supports such a proposal. We have experimentally re-examined the studies of phonons in bismuth and gallium arsenide, and find no evidence of any phase-dependent noise signature associated with the phonons. We place an upper limit on any such noise at least 40–50 dB lower than previously reported.

  20. Phonon operators in deformed nuclei

    For the description of the excited states in deformed nuclei new phonon operators are introduced, which depend on the sign of the angular momentum projection onto the symmetry axis of a deformed nucleus. In the calculations with new phonons the Pauli principle is correctly taken into account in the two-phonon components of the wave functions. There is a difference in comparison with the calculation with phonons independent of the sign of the angular momentum projection. The new phonons should be used in deformed nuclei if the Pauli principle is consistently taken into account and in the calculations with the excited state wave functions having the components with more than one phonon operator

  1. Phonon sidebands in semiconductor luminescence

    Feldtmann, T.; Kira, M.; Koch, S.W. [Department of Physics and Materials Sciences Center, Philipps University, Marburg (Germany)

    2009-02-15

    A microscopic theory of LO-phonon assisted photoluminescence in semiconductors is presented. In order to systematically describe Coulomb and light-matter interaction, a cluster-expansion scheme is employed. The carrier-phonon coupling is treated non-perturbatively within the polaron picture. Luminescence equations are derived, which produces phonon sidebands to arbitrary order. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  2. Temperature dependence of Brillouin light scattering spectra of acoustic phonons in silicon

    Electrons, optical phonons, and acoustic phonons are often driven out of local equilibrium in electronic devices or during laser-material interaction processes. The need for a better understanding of such non-equilibrium transport processes has motivated the development of Raman spectroscopy as a local temperature sensor of optical phonons and intermediate frequency acoustic phonons, whereas Brillouin light scattering (BLS) has recently been explored as a temperature sensor of low-frequency acoustic phonons. Here, we report the measured BLS spectra of silicon at different temperatures. The origins of the observed temperature dependence of the BLS peak position, linewidth, and intensity are examined in order to evaluate their potential use as temperature sensors for acoustic phonons

  3. Direct acoustic phonon excitation by intense and ultrashort terahertz pulses

    We report on the direct and resonant excitation of acoustic phonons in an AlGaAs intrinsic semiconductor using intense coherent and single cycle terahertz pulses created by two-color femtosecond laser pulse filamentation in air. While the electrons are left unperturbed, we follow the lattice dynamics with time-delayed optical photons tuned to the interband transition.

  4. Electron–phonon coupling in hybrid lead halide perovskites

    Wright, Adam D.; Verdi, Carla; Milot, Rebecca L.; Eperon, Giles E.; Pérez-Osorio, Miguel A.; Snaith, Henry J.; Giustino, Feliciano; Johnston, Michael B.; Herz, Laura M.

    2016-01-01

    Phonon scattering limits charge-carrier mobilities and governs emission line broadening in hybrid metal halide perovskites. Establishing how charge carriers interact with phonons in these materials is therefore essential for the development of high-efficiency perovskite photovoltaics and low-cost lasers. Here we investigate the temperature dependence of emission line broadening in the four commonly studied formamidinium and methylammonium perovskites, HC(NH2)2PbI3, HC(NH2)2PbBr3, CH3NH3PbI3 and CH3NH3PbBr3, and discover that scattering from longitudinal optical phonons via the Fröhlich interaction is the dominant source of electron–phonon coupling near room temperature, with scattering off acoustic phonons negligible. We determine energies for the interacting longitudinal optical phonon modes to be 11.5 and 15.3 meV, and Fröhlich coupling constants of ∼40 and 60 meV for the lead iodide and bromide perovskites, respectively. Our findings correlate well with first-principles calculations based on many-body perturbation theory, which underlines the suitability of an electronic band-structure picture for describing charge carriers in hybrid perovskites. PMID:27225329

  5. Electron-phonon coupling in hybrid lead halide perovskites.

    Wright, Adam D; Verdi, Carla; Milot, Rebecca L; Eperon, Giles E; Pérez-Osorio, Miguel A; Snaith, Henry J; Giustino, Feliciano; Johnston, Michael B; Herz, Laura M

    2016-01-01

    Phonon scattering limits charge-carrier mobilities and governs emission line broadening in hybrid metal halide perovskites. Establishing how charge carriers interact with phonons in these materials is therefore essential for the development of high-efficiency perovskite photovoltaics and low-cost lasers. Here we investigate the temperature dependence of emission line broadening in the four commonly studied formamidinium and methylammonium perovskites, HC(NH2)2PbI3, HC(NH2)2PbBr3, CH3NH3PbI3 and CH3NH3PbBr3, and discover that scattering from longitudinal optical phonons via the Fröhlich interaction is the dominant source of electron-phonon coupling near room temperature, with scattering off acoustic phonons negligible. We determine energies for the interacting longitudinal optical phonon modes to be 11.5 and 15.3 meV, and Fröhlich coupling constants of ∼40 and 60 meV for the lead iodide and bromide perovskites, respectively. Our findings correlate well with first-principles calculations based on many-body perturbation theory, which underlines the suitability of an electronic band-structure picture for describing charge carriers in hybrid perovskites. PMID:27225329

  6. Sub-Poissonian phonon statistics in an acoustical resonator coupled to a pumped two-level emitter

    Ceban, V., E-mail: victor.ceban@phys.asm.md; Macovei, M. A., E-mail: macovei@phys.asm.md [Academy of Sciences of Moldova, Institute of Applied Physics (Moldova, Republic of)

    2015-11-15

    The concept of an acoustical analog of the optical laser has been developed recently in both theoretical and experimental works. We here discuss a model of a coherent phonon generator with a direct signature of the quantum properties of sound vibrations. The considered setup is made of a laser-driven quantum dot embedded in an acoustical nanocavity. The system dynamics is solved for a single phonon mode in the steady-state and in the strong quantum dot—phonon coupling regime beyond the secular approximation. We demonstrate that the phonon statistics exhibits quantum features, i.e., is sub-Poissonian.

  7. Electron - phonon interaction in strongly correlated systems. Acoustical phonon case

    We investigate the interaction of strongly correlated electrons with acoustical phonons in the frame of Hubbard-Holstein model. The electron-phonon interaction and on-site Coulomb repulsion are considered to be strong. By using the Lang-Firsov canonical transformation this problem has been transformed to the problem of mobile polarons. A new diagram technique is used in order to handle the strong Coulomb repulsion of the electrons and the existence of phonon clouds surrounding the electrons. The generalized Wick theorems for chronological products of electron and phonon-clouds operators have been formulated. We have found the collective mode of phonon clouds that surround electrons and discussed the physics of the emission and absorption of this mode by the polarons. We have also discussed the difference in the behaviour of optical and acoustical phonon-clouds surrounding polarons during their movement through the crystal lattice. The aim of the present paper is to gain further insight into the mutual influence of strong on-site Coulomb repulsion and strong electron-phonon interaction using the single band Hubbard-Holstein model and a recently developed diagram approach. We consider now the most interesting case as regards superconductivity of coupling of correlated electrons with dispersion acoustical phonons. (authors)

  8. Acoustic Metamaterials and Phononic Crystals

    2013-01-01

    This comprehensive book presents all aspects of acoustic metamaterials and phononic crystals. The emphasis is on acoustic wave propagation phenomena at interfaces such as refraction, especially unusual refractive properties and negative refraction. A thorough discussion of the mechanisms leading to such refractive phenomena includes local resonances in metamaterials and scattering in phononic crystals.

  9. Tunable Topological Phononic Crystals

    Chen, Ze-Guo

    2016-05-27

    Topological insulators first observed in electronic systems have inspired many analogues in photonic and phononic crystals in which remarkable one-way propagation edge states are supported by topologically nontrivial band gaps. Such band gaps can be achieved by breaking the time-reversal symmetry to lift the degeneracy associated with Dirac cones at the corners of the Brillouin zone. Here, we report on our construction of a phononic crystal exhibiting a Dirac-like cone in the Brillouin zone center. We demonstrate that simultaneously breaking the time-reversal symmetry and altering the geometric size of the unit cell result in a topological transition that we verify by the Chern number calculation and edge-mode analysis. We develop a complete model based on the tight binding to uncover the physical mechanisms of the topological transition. Both the model and numerical simulations show that the topology of the band gap is tunable by varying both the velocity field and the geometric size; such tunability may dramatically enrich the design and use of acoustic topological insulators.

  10. Graviton laser

    Landry, A.; Paranjape, M. B.

    2016-01-01

    We consider the possibility of creating a graviton laser. The lasing medium would be a system of contained, ultra cold neutrons. Ultra cold neutrons are a quantum mechanical system that interacts with gravitational fields and with the phonons of the container walls. It is possible to create a population inversion by pumping the system using the phonons. We compute the rate of spontaneous emission of gravitons and the rate of the subsequent stimulated emission of gravitons. The gain obtainable...

  11. Coherent phonon oscillations in CsPbCl{sub 3} nanocrystals

    Nemec, P.; Maly, P. [Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 3, 121 16 Prague 2 (Czech Republic); Nitsch, K.; Nikl, M. [Institute of Physics, Academy of Sciences of the Czech Republic, Cukrovarnicka 6, 162 53 Prague 6 (Czech Republic)

    2004-11-01

    Coherent optical phonons in CsPbCl{sub 3} nanocrystals are generated by femtosecond laser pulse irradiation and measured in a pump-probe experiment as a transmission modulation in the time domain. The phonon dephasing times ranging from 3 ps to 8 ps (at 10 K) are independent of the laser wavelength. On the contrary, the phase of the coherent phonons depends significantly on the laser wavelength when tuned through the excitonic absorption band. This suggests a change of the coherent phonon generation mechanism from displacive-type to impulsive-type when the material is opaque and transparent, respectively. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  12. Probe And Enhancement Of SBS Based Phonons In Infrared Fibers Using Waveguide Coupled External Radiation

    Yu, Chung; Chong, Yat C.; Fong, Chee K.

    1989-06-01

    Interaction of GHz and MHz radiation with CO2 laser propagation in a silver halide fiber using sBs based phonon coupling is furthet investigated. The external signal serves to both probe and enhance laser generated sBs phonons in the fiber. Efficient coupling of microwave radiation into the fiber is accomplished by placing the fiber in a hollow metallic waveguide, designed and constructed to transmit the dominant mode in the 0.9-2.0 GHz band. MHz radiation is conveniently coupled into the fiber using the guided microwave radiation as carrier. Phonon emissions from the fiber under CO2 laser pumping are first established on a spectrum analyzer; low frequency generators ale then tuned to match these frequencies and their maximum interaction recorded. Such interactions are systematically studied by monitoring the amplitude and waveform of the reflected and transmitted laser pulse at various power levels and frequencies of the externally coupled radiation. A plot of reflected laser power versus incident laser power reveals a distinct sBs generated phonon threshold. Variouslaunch directions of the GHz and MHz radiation with respect to the direction of laser propagation are realized to verify theory governing sBs interactions. The MHz radiation and its associated phonons in the fiber are convenient tools for probing sBs related phenomenon in infrared fibers.

  13. Phonon dispersion relation in zircon

    The silicate mineral zircon is one of the major constituents of the earth's crust. The low thermal expansion, structural and chemical stability of zircon ZrSiO4 (space group I41/amd; Z=2) enable it as a host material for radioactive elements uranium and thorium in the earth's crust. Phonon spectrum is needed to understand the thermodynamic behaviour of this mineral. Lattice dynamical calculations of the phonon dispersion relation have been carried out and some acoustic phonons of zircon have also been measured

  14. Increased laser action in commercial dyes from fluorination regardless of their skeleton

    The direct and simple fluorination of representative organic laser dyes with emission covering the entire visible spectrum, from blue to red, including Coumarin 460, Pyrromethene 546, Rhodamine 6G and Perylene Red, enhances laser efficiencies by a factor up to 1.8 with respect to the corresponding non-fluorinated parent dyes. More importantly, fluorination also significantly enhances the photostability of the dyes, even under drastic laser pumping conditions. (letter)

  15. Backward air lasing actions induced by femtosecond laser filamentation: influence of population inversion lifetime

    Xie, Hongqiang; chu, Wei; Zeng, Bin; Yao, Jinping; Jing, Chenrui; Li, Ziting; Cheng, Ya

    2015-01-01

    We experimentally investigate generation of backward 357 nm N2 laser in a gas mixture of N2/Ar using 800-nm femtosecond laser pulses, and examine the involved gain dynamics based on pump-probe measurements. Our findings show that a minimum lifetime of population inversion in the excited N2 molecules is required for generating intense backward nitrogen lasers, which is ~0.8 ns under our experimental conditions. The results shed new light on the mechanism for generating intense backward lasers from ambient air, which are highly in demand for high sensitivity remote atmospheric sensing application.

  16. Reliability of Raman measurements of thermal conductivity of single-layer graphene due to selective electron-phonon coupling: A first-principles study

    Vallabhaneni, Ajit K.; Singh, Dhruv; Bao, Hua; Murthy, Jayathi; Ruan, Xiulin

    2016-03-01

    Raman spectroscopy has been widely used to measure thermal conductivity (κ ) of two-dimensional (2D) materials such as graphene. This method is based on a well-accepted assumption that different phonon polarizations are in near thermal equilibrium. However, in this paper, we show that, in laser-irradiated single-layer graphene, different phonon polarizations are in strong nonequilibrium, using predictive simulations based on first principles density functional perturbation theory and a multitemperature model. We first calculate the electron cooling rate due to phonon scattering as a function of the electron and phonon temperatures, and the results clearly illustrate that optical phonons dominate the hot electron relaxation process. We then use these results in conjunction with the phonon scattering rates computed using perturbation theory to develop a multitemperature model and resolve the spatial temperature distributions of the energy carriers in graphene under steady-state laser irradiation. Our results show that electrons, optical phonons, and acoustic phonons are in strong nonequilibrium, with the flexural acoustic (ZA) phonons showing the largest nonequilibrium to other phonon modes, mainly due to their weak coupling to other carriers in suspended graphene. Since ZA phonons are the main heat carriers in graphene, we estimate that neglecting this nonequilibrium leads to underestimation of thermal conductivity in experiments at room temperature by a factor of 1.35 to 2.6, depending on experimental conditions and assumptions used. Underestimation is also expected in Raman measurements of other 2D materials when the optical-acoustic phonon coupling is weak.

  17. Q-phonon scheme in the collective nuclear model

    The Q-phonon scheme developed in the framework of the algebraic collective nuclear model is discussed. It is shown that in the framework of this scheme the low-lying collective states of the even-even nuclei can be presented with an accuracy better than 90% of the norm using one or maximum two components of the Q-phonon basis constructed by an action of the fixed number of the quadrupole operators Q on the exact ground state of the system. Different applications of this approximate scheme are discussed. It is shown that using this scheme the relations between several E2-transition probabilities or between the energies of the collective states can be derived. It is shown also that the Q-phonon scheme can be used to extract an information about the equilibrium shapes of nuclei and their fluctuations from the data on the E2-transition probabilities

  18. Optical investigations of powerful laser actions on massive and flyer targets

    In this paper we present experimental, theoretical, and computer simulation studies of craters formation produced by high power lasers in single and double layer targets. The experimental investigation was carried out using the PALS (Prague Asterix Laser System) facility working with two different laser beam wavelengths: λ1 = 1.315 μm and λ3 0.438 μm. Two types of targets made of Al were used: single massive targets and double targets consisting of a foil or disk (6 μm and 11 μm thick for both cases) placed in front of the massive target at the distance of 200-500 μm. Experiments with single massive targets were performed at laser intensities in the range of 1013-1015 W/cm2 by varying the laser beam diameter on the target surface from 70 μm up to 1200 μm (moving the target away from the focus). The double targets were illuminated by laser energies EL = 100-500 J always focused on diameter of 250 μm. In all experiments performed the laser pulse duration was equal to 400 ps. The 3-frame interferometry was employed to investigate the plasma dynamics by means of the electron density distribution time development as well as the disks and foil fragments velocity measurements. Dimensions and shapes of craters were obtained by crater replica technology and microscopy measurement. Experimental results were complemented by two-dimensional analytical theory and computer simulations to help their interpretation. This way the values of laser energy absorption coefficient, ablation loading efficiency and efficiency of energy transfer as well as two-dimensional shock wave generation at the laser-driven macro-particle impact were obtained from measured craters' parameters for both wavelengths of laser radiation. (author)

  19. Phononic crystals and acoustic metamaterials

    Ming-Hui Lu; Liang Feng; Yan-Feng Chen

    2009-01-01

    Phononic crystals have been proposed about two decades ago and some important characteristics such as acoustic band structure and negative refraction have stimulated fundamental and practical studies in acoustic materials and devices since then. To carefully engineer a phononic crystal in an acoustic “atom” scale, acoustic metamaterials with their inherent deep subwavelength nature have triggered more exciting investigations on negative bulk modulus and/or negative mass density. Acoustic surf...

  20. Phonon spectra in quantum wires

    Ilić Dušan; Raković Dejan; Šetrajčić Jovan

    2007-01-01

    Green's function method, adjusted to bound crystalline structures, was applied to obtain the phonon dispersion law in quantum wires. The condition of the existence of small mechanical atom movements defining phonon spectra can be found by solving the secular equation. This problem was presented graphically for different boundary parameters. The presence of boundaries, as well as the change of boundary parameters, leads to the appearance of new properties of the layered structure. The most imp...

  1. On possibility of high-power terahertz emission from target under the action of powerful laser pulses

    Didenko, A. N.; Rashchikov, V. I.; Fortov, V. E.

    2011-03-01

    The possibility of terahertz (THz) emission from a target irradiated by short (˜0.1 ns) high-intensity ( I ˜ 1018-1019 W/cm2) laser pulses has been studied by numerical simulations using a relativistic electromagnetic PIC code. The laser pulse action on the target generates plasma and the runaway electrons form a virtual cathode, which oscillates in the intrinsic field of electrons and the field of plasma ions. These oscillations account for the emission of radiation in a THz range. The generation efficiency is about three times as high as that in the absence of ions (according to the conventional reditron mechanism). Explanation of the observed phenomena is proposed.

  2. Theory of Raman Lasing due to Coupled Intersubband Plasmon-Phonon Modes in Asymmetric Coupled Double Quantum Wells

    Maung, S. M.; Katayama, S.

    2005-06-01

    A theory of Raman laser gain due to coupled intersubband (ISB) plasmon-optical phonon modes in asymmetric coupled double quantum wells (ACDQWs) is presented. Based on the charge-density-excitations (CDE) mechanism, we take into account the electron-electron and electron-phonon (confined LO phonon and interface (IF) phonons) interactions in the scattering cross-section. For Al0.35Ga0.65As/GaAs ACDQWs the calculated coupled mode energies which are responsible for the lasing Stokes emission are well consistent with recent experiments.

  3. Graviton laser

    Landry, A

    2016-01-01

    We consider the possibility of creating a graviton laser. The lasing medium would be a system of contained, ultra cold neutrons. Ultra cold neutrons are a quantum mechanical system that interacts with gravitational fields and with the phonons of the container walls. It is possible to create a population inversion by pumping the system using the phonons. We compute the rate of spontaneous emission of gravitons and the rate of the subsequent stimulated emission of gravitons. The gain obtainable is directly proportional to the density of the lasing medium and the fraction of the population inversion. The applications of a graviton laser would be interesting.

  4. Optical investigation of powerful laser actions on massive and flyer targets

    Pisarczyk, T.; Borodziuk, S.; Demchenko, N. N.; Gus´kov, S.Y.; Jungwirth, Karel; Kálal, M.; Kasperzcuk, A.; Králiková, Božena; Krouský, Eduard; Limpouch, Jiří; Mašek, Karel; Pisarczyk, P.; Pfeifer, Miroslav; Rohlena, Karel; Rozanov, V. B.; Skála, Jiří; Ullschmied, Jiří

    Melville: American Institut of Physics , 2005 - (Sadowski, M.; Dudeck, M.; Hartfus, H.; Pawelec, E.), 64-71. (AIP Conference Proceedings. 812). ISBN 0-7354-0304-X. ISSN 0094-243X. [PLASMA 2005. Opole-Turawa (PL), 06.09.2005-09.09.2005] R&D Projects: GA MŠk(CZ) LC528 Grant ostatní: EC - LASER LAB-EUROPE(XE) RII3-CT-2003-506350 Institutional research plan: CEZ:AV0Z10100523; CEZ:AV0Z20430508 Keywords : plasma heating by laser * plasma diagnostics * laser ablation * laser fusion Subject RIV: BL - Plasma and Gas Discharge Physics http://dx.doi.org/10.1063/1.2168799

  5. Suppressing electron-phonon interactions in semiconductor quantum dot systems by engineering the electronic wavefunctions

    Nysteen, Anders; Nielsen, Per Kær; Mørk, Jesper

    2012-01-01

    proper matching between the electronic wavefuntion and the phonon-induced energy shift of valence and conduction band may be exploited to change the decoherence and decay properties of the QD by suppressing the phonon-induced processes. This effect may be addressed in a photoluminescence experiment......, where a CW laser excites a two-level QD which interacts with a non-Markovian reservoir of acoustical phonons, see Fig. 1a. We assume a simple harmonic confinement of the electronic carriers, resulting in Gaussian wavefunctions, (r) / exp[−r2/(2W2 )], withWe (Wg) being the width of the electron (hole......) wavefunction. In Fig. 1b we plot the stationary QD population vs. the laser frequency. We observe that for non-equal electron and hole wavefunction, the phonon-induced effect on the population surprisingly is fully suppressed at specific detunings. In a coupled QD–cavity system [2, 3], see Fig. 2a, this effect...

  6. Infrared-phonon-polariton resonance of the nonlinear susceptibility in GaAs.

    Dekorsy, T; Yakovlev, V A; Seidel, W; Helm, M; Keilmann, F

    2003-02-01

    Nonlinear probing of the fundamental lattice vibration of polar crystals is shown to reveal insight into higher-order cohesive lattice forces. With a free-electron laser tunable in the far infrared we experimentally investigate the dispersion of the second-order susceptibility due to the phonon resonance in GaAs. We observe a strong resonance enhancement of second harmonic light generation at half the optical phonon frequency, and in addition a minimum at a higher frequency below the phonon frequency. Measuring this frequency and comparison to a theoretical model allows the determination of competing higher-order lattice forces. PMID:12633374

  7. Ultrafast dynamics of carrier LO phonon system in high electric field in polar semiconductors

    Iida, M.; Katayama, S.

    2001-03-01

    The dynamics of carriers excited by an ultrashort laser pulse is simulated numerically in the presence of a strong electric field. The carrier density matrices (DMs) are treated within the equation of motion method by taking interaction with longitudinal optical (LO) phonons into account. It is shown that the temporal evolution of an electron DM exhibits a strong modification owing to LO phonon emissions in addition to interferences between the interband polarization and the optical pulse field in the external strong electric field.

  8. Analysis of the stress raising action of flaws in laser clad deposits

    Highlights: ► Laser clad defects are 0D-pores/inclusions, 1D-clad waviness or 2D-planar defects. ► Surface pore of laser clad bar initiates fatigue cracks. ► Side edge surface pores are more critical than in-clad surface pores. ► Smaller notch radius and angle of as-laser clad surface raises stress significantly. ► Planar inner defects grow faster towards surface. - Abstract: Fatigue cracking of laser clad cylindrical and square section bars depends upon a variety of factors. This paper presents Finite Element Analysis (FEA) of the different macro stress fields generated as well as stress raisers created by laser cladding defects for four different fatigue load conditions. As important as the defect types are their locations and orientations, categorized into zero-, one- and two-dimensional defects. Pores and inclusions become critical close to surfaces. The performance of as-clad surfaces can be governed by the sharpness of surface notches and planar defects like hot cracks or lack-of-fusion (LOF) are most critical if oriented vertically, transverse to the bar axis. The combination of the macro stress field with the defect type and its position and orientation determines whether it is the most critical stress raiser. Based on calculated cases, quantitative and qualitative charts were developed as guidelines to visualize the trends of different combinations

  9. Scattering of phonons by dislocations

    By 1950, an explicit effort had been launched to use lattice thermal conductivity measurements in the investigation of defect structures in solids. This technique has been highly successful, especially when combined with the measurements of other properties such as optical absorption. One exception has been the study of dislocations. Although dislocations have a profound effect on the phonon thermal conductivity, the mechanisms of the phonon-dislocation interaction are poorly understood. The most basic questions are still debated in the literature. It therefore is pointless to attempt a quantitative comparison between an extensive accumulation of experimental data on the one hand, and the numerous theoretical models on the other. Instead, this chapter will attempt to glean a few qualitative conclusions from the existing experimental data. These results will then be compared with two general models which incorporate, in a qualitative manner, most of the proposed theories of the phonon-dislocation interaction. Until very recently, measurement of thermal conductivity was the only means available to probe the interaction between phonons and defects at phonon frequencies above the standard ultrasonic range of approx. = 109 Hz. The introductory paragraphs provide a brief review of the thermal-conductivity technique and the problems which are encountered in practice. There is also a brief presentation of the theoretical models and the complications that may occur in more realistic situations

  10. Bacterial action of carbon dioxide laser radiation in experimental dental root canals

    The ability of a carbon dioxide laser to sterilize the root canal of human teeth has been investigated. Three oral bacteria, Streptococcus sanguis, Streptococcus mutans, and Actinomyces viscosus, and three other bacteria, Bacillus cereus, Staphyloccus aureus, and Pseudomonoas aeruginosa were used as experimental organisms. Exposure of cells on glass slides to laser radiation showed there was little difference in the exposure required to kill these six organisms. Complete recovery of bacteria from the root canal was initially a problem and was only achieved when bacterial manipulations and removal were carried out in rapid succession, within 5 min of inoculation. However, the geometry of the instrumented canal and the laser alignment were major factors in achieving consistent cell death of oral bacteria in the root canals. Using sets of 10 teeth, four repeated exposures of 10 W for 1 s was found to sterilize 4 or more of the teeth

  11. Efficient materials processing by dual action of XUV/Vis-NIR ultrashort laser pulses

    Jakubczak, Krzysztof; Mocek, Tomáš; Polan, Jiří; Homer, Pavel; Rus, Bedřich; Kim, I.J.; Kim, C. M.; Park, S.B.; Kim, T.K.; Lee, G.H.; Nam, C. H.; Chalupský, Jaromír; Hájková, Věra; Juha, Libor; Sobota, Jaroslav; Fořt, Tomáš

    Bellingham: SPIE, 2009 - (Juha, L.; Bajt, S.; Sobierajski, R.), 73610A/1-73610A/5. (Proceedings of SPIE. 7361). ISBN 9780819476357. ISSN 0277-786x. [Damage to VUV, EUV, and X-Ray Optics II. Prague (CZ), 21.04.2009-23.04.2009] R&D Projects: GA AV ČR KAN300100702; GA MŠk LC510; GA MŠk(CZ) LC528; GA MŠk LA08024; GA ČR GC202/07/J008 Institutional research plan: CEZ:AV0Z10100523; CEZ:AV0Z20650511 Keywords : High-order Harmonic Generation (HHG) * materials machining * nanopatterning * femtosecond laser pulses * Laser Induced Periodic Surface Structures (LIPSS) Subject RIV: BH - Optics, Masers, Lasers http://dx.doi.org/10.1117/12.822433

  12. Low intensity red laser action on Escherichia coli cultures submitted to stress conditions

    Clinical applications of low intensity lasers are based on the biostimulation effect and considered to occur mainly at cells under stressful conditions. Also, although the cytochrome is a chromophore to red and near infrared radiations, there are doubts whether indirect effects of these radiations could occur on the DNA molecule by oxidative mechanisms. Thus, this work evaluated the survival, filamentation and morphology of Escherichia coli cultures proficient and deficient in oxidative DNA damage repair exposed to low intensity red laser under stress conditions. Wild type and endonuclease III deficient E. coli cells were exposed to laser (658 nm, 1 and 8 J cm−2) under hyposmotic stress and bacterial survival, filamentation and cell morphology were evaluated. Laser exposure: (i) does not alter the bacterial survival in 0.9% NaCl, but increases the survival of wild type and decreases the survival of endonuclease III deficient cells under hyposmotic stress; (ii) increases filamentation in 0.9% NaCl but decreases in wild type and increases in endonuclease III deficient cells under hyposmotic stress; (iii) decreases the area and perimeter of wild type, does not alter these parameters in endonuclease III deficient cells under hyposmotic stress but increases the area of these in 0.9% NaCl. Low intensity red laser exposure has different effects on survival, filamentation phenotype and morphology of wild type and endonuclease III deficient cells under hyposmotic stress. Thus, our results suggest that therapies based on low intensity red lasers could take into account physiologic conditions and genetic characteristics of cells. (paper)

  13. Influence of ionizing radiation on optical hardness of transparent dielectrics to action of huge intensity laser light

    . Significant growth of total number of ions of all frequency rates of charge NΣ reduction of maximal energy Emax and frequency rates of a charge Zmax ions are observed. Correlation between parameters of superficial damage - threshold qs and the size of damage d and characteristics of ion plasma - NΣ, Zmax and Emax are also observed. Damages, as microscopic researches have shown, looked like the micro crater representing the fused layer with a flat bottom and melted edges. Such structure of craters is consequences of the thermal action accompanying damages by plasma. With growth of a doze γ -irradiations of investigated glasses the sizes of damage grow considerably with the increase in diameter d of formed the craters received at the same values q. It is shown that the increase in intensity of a laser radiation up to 1000 GWt/cm2 leads to the catastrophic damage of the surface leading to breaking of glass. Results of microscopic researches show that the damage of surface and volume of the investigated non- irradiated glasses begins locally in the separate from each other small size parts where the congestion of the absorbing defects breaking the structure of glass was formed. Those are initially present in structure of glass alien impurity inclusions, dislocations and vacancies, bubbles and pores and others of heterogeneity. Concentration of absorbing defects in glass considerably increases due to formation of the radiating defects caused by γ - irradiation. This leads to an additional power consumption of a laser radiation on heating and evaporation of substance of a target, and consequently to reduction of a part of laser radiation, too, which is spent for heating and ionization of plasma. This seems to be a reason for reduction Z max and Emax of emitted ion by plasma and strong growth of output of ions from plasma of γ - irradiated glass connected with recombined processes taking place in plasma. (author)

  14. Correction of eye refraction by nonablative laser action on thermomechanical properties of cornea and sclera

    A new approach is proposed for correcting the eye refraction by controlled variation of the mechanical properties of the sclera and cornea upon nondestructive laser heating. Experimental ex vivo studies of rabbit and pig eyes show that laser-induced local denaturation of the sclera changes the refraction of the cornea by 3 diopters on the average, and the subsequent nondestructive irradiation of the cornea increases its plasticity, which leads to a further increase in its radius of curvature and a decrease in refraction down to 7 diopters.

  15. Laser-assisted drug delivery: mode of action and use in daily clinical practice.

    Braun, Stephan Alexander; Schrumpf, Holger; Buhren, Bettina Alexandra; Homey, Bernhard; Gerber, Peter Arne

    2016-05-01

    Topical application of pharmaceutical agents is a basic principle of dermatological therapy. However, the effective barrier function of the skin significantly impairs the bioavailability of most topical drugs. Fractional ablative lasers represent an innovative strategy to overcome the epidermal barrier in a standardized, contact-free manner. The bioavailability of topical agents can be significantly enhanced using laser-assisted drug delivery (LADD). In recent years, the principle of LADD has become well established for various dermatological indications. Herein, we review the current literature on LADD and present potential future applications. PMID:27119468

  16. Random laser action in stoichiometric Nd3Ga5O12 garnet crystal powder

    Iparraguirre, I.; Azkargorta, J.; Kamada, K.; Yoshikawa, A.; Rodríguez-Mendoza, U. R.; Lavín, V.; Barredo-Zuriarrain, M.; Balda, R.; Fernández, J.

    2016-03-01

    This work explores the room temperature infrared random laser (RL) performance of Nd3+ ions in a new stoichiometric Nd3Ga5O12 crystal powder. The time-resolved measurements show that the RL pulse is able to follow the subnanosecond oscillations of the pump pulse profile. The pump threshold energy and the absolute stimulated emission energy have been measured using a method developed by the authors. The laser slope efficiency is the highest compared to other Nd3+ stoichiometric RL crystals.

  17. Action of a 904-nm diode laser in orthopedics and traumatology: a clinical study on 447 cases

    Tam, Giuseppe

    2001-10-01

    Objective: The evidence in medical literature is that a beneficial analgesic effect can only be obtained by employing laser radiation of relatively low power density and wavelengths which are able to penetrate tissue. For this reason the semiconductor, or laser diode (GaAs, 904 nm), is the most appropriate choice in pain-reduction therapy. Summary Background Data: Low power laser (or LLL) acts on the Prostaglandins synthesis, increases the endorphins synthesis in the Rolando gelatinous substance and in the dorsal horn of the spinal cord. The L-Arginine, which is the classic substrate of nitric oxide, carries on vasodilatory and anti- inflammatory action. Methods: Treatment was carried out on 447 cases and 435 patients (250 women and 185 men) between 20th May 1987 and 31st December 1999. The patients, whose age ranged from 25 to 70, were suffering from rheumatic, degenerative and traumatic pathologies as well as cutaneous ulcers. The majority of patients had been seen by orthopaedists and rheumatologists and had undergone x-ray, ultrasound scan, etc. All patients had previously received drug-based treatment and/or physiotherapy, with poor results. Two thirds were experiencing acute symptomatic pain, while the others presented a chronic pathology with recurrent crises. We used a pulsed IR diode laser, GaAs emitting at 904 nm. Frequency of treatment: 1 application per day for 5 consecutive days, followed by a 2-day interval. The percentage reduction in symptoms or improvement in functional status were determined on the basis of objective analysis as it happens in the Legal and Insurance Medicine field. Results: Very good results were achieved especially with cases of symptomatic osteoarthritis of the cervical vertebrae, with sport-related injuries, epicondylitis, osteoarthritis of the knee, periarthritis and with cutaneous ulcers. The beneficial action of the LLLT in the latter pathology is linked to the increase in collagen and to fibroblast proliferation. The total

  18. Phonon spectra in quantum wires

    Ilić Dušan

    2007-01-01

    Full Text Available Green's function method, adjusted to bound crystalline structures, was applied to obtain the phonon dispersion law in quantum wires. The condition of the existence of small mechanical atom movements defining phonon spectra can be found by solving the secular equation. This problem was presented graphically for different boundary parameters. The presence of boundaries, as well as the change of boundary parameters, leads to the appearance of new properties of the layered structure. The most important feature is that, beside the allowed energy zones (which are continuous as in the bulk structure, zones of forbidden states appear. Different values of the boundary parameters lead to the appearance of lower and upper energy gaps, or dispersion branches spreading out of the bulk energy zone. The spectra of phonons in corresponding unbound structures were correlated to those in bound structures.

  19. Electron-Phonon Coupling and Energy Flow in a Simple Metal beyond the Two-Temperature Approximation

    Waldecker, Lutz; Bertoni, Roman; Ernstorfer, Ralph; Vorberger, Jan

    2016-04-01

    The electron-phonon coupling and the corresponding energy exchange are investigated experimentally and by ab initio theory in nonequilibrium states of the free-electron metal aluminium. The temporal evolution of the atomic mean-squared displacement in laser-excited thin freestanding films is monitored by femtosecond electron diffraction. The electron-phonon coupling strength is obtained for a range of electronic and lattice temperatures from density functional theory molecular dynamics simulations. The electron-phonon coupling parameter extracted from the experimental data in the framework of a two-temperature model (TTM) deviates significantly from the ab initio values. We introduce a nonthermal lattice model (NLM) for describing nonthermal phonon distributions as a sum of thermal distributions of the three phonon branches. The contributions of individual phonon branches to the electron-phonon coupling are considered independently and found to be dominated by longitudinal acoustic phonons. Using all material parameters from first-principles calculations except the phonon-phonon coupling strength, the prediction of the energy transfer from electrons to phonons by the NLM is in excellent agreement with time-resolved diffraction data. Our results suggest that the TTM is insufficient for describing the microscopic energy flow even for simple metals like aluminium and that the determination of the electron-phonon coupling constant from time-resolved experiments by means of the TTM leads to incorrect values. In contrast, the NLM describing transient phonon populations by three parameters appears to be a sufficient model for quantitatively describing electron-lattice equilibration in aluminium. We discuss the general applicability of the NLM and provide a criterion for the suitability of the two-temperature approximation for other metals.

  20. Molecular mechanism of therapeutic action of low-intensity visible laser radiation

    The presented data testify to possibility of reversible modification of a spatial structure and biocatalytic activity of enzyme (lactate dehydrogenase) under visible laser radiation effect on buffer solutions of enzyme and enzyme-substrate with long-wave maxima of absorption spectrum, located in UV-region

  1. Damping of coupled phonon--plasmon modes

    Falkovsky, L. A.

    2002-01-01

    The effect of free carriers on dispersion and damping of coupled phonon-plasmon modes is considered in the long-wave approximation. The electron and phonon scattering rate as well as Landau damping are taken into account.

  2. Phonon creation by gravitational waves

    We show that gravitational waves create phonons in a Bose-Einstein condensate (BEC). A traveling spacetime distortion produces particle creation resonances that correspond to the dynamical Casimir effect in a BEC phononic field contained in a cavity-type trap. We propose to use this effect to detect gravitational waves. The amplitude of the wave can be estimated applying recently developed relativistic quantum metrology techniques. We provide the optimal precision bound on the estimation of the wave's amplitude. Finally, we show that the parameter regime required to detect gravitational waves with this technique could be, in principle, within experimental reach in a medium-term timescale. (paper)

  3. Phonon creation by gravitational waves

    Sabín, Carlos; Ahmadi, Mehdi; Fuentes, Ivette

    2014-01-01

    We show that gravitational waves create phonons in a Bose-Einstein condensate (BEC). A traveling spacetime distortion produces particle creation resonances that correspond to the dynamical Casimir effect in a BEC phononic field contained in a cavity-type trap. We propose to use this effect to detect gravitational waves. The amplitude of the wave can be estimated applying recently developed relativistic quantum metrology techniques. We provide the optimal precision bound on the estimation of the wave's amplitude. Finally, we show that the parameter regime required to detect gravitational waves with this technique is within experimental reach.

  4. Phononic crystals and acoustic metamaterials

    Ming-Hui Lu

    2009-12-01

    Full Text Available Phononic crystals have been proposed about two decades ago and some important characteristics such as acoustic band structure and negative refraction have stimulated fundamental and practical studies in acoustic materials and devices since then. To carefully engineer a phononic crystal in an acoustic “atom” scale, acoustic metamaterials with their inherent deep subwavelength nature have triggered more exciting investigations on negative bulk modulus and/or negative mass density. Acoustic surface evanescent waves have also been recognized to play key roles to reach acoustic subwavelength imaging and enhanced transmission.

  5. Topological Nature of the Phonon Hall Effect

    Zhang, Lifa; Ren, Jie; Wang, Jian-Sheng; Li, Baowen

    2010-01-01

    We provide a topological understanding on phonon Hall effect in dielectrics with Raman spinphonon coupling. A general expression for phonon Hall conductivity is obtained in terms of the Berry curvature of band structures. We find a nonmonotonic behavior of phonon Hall conductivity as a function of magnetic field. Moreover, we observe a phase transition in phonon Hall effect, which corresponds to the sudden change of band topology, characterized by the altering of integer Chern numbers. This c...

  6. Phonon Theory of Martensitic Transformation Precursors

    Jin, Yongmei M.; Wang, Yu. U.

    2014-01-01

    A phonon theory of precursor phenomena in martensitic phase transformations is developed. Extending Gr\\"uneisen theory of thermal expansion, this theory addresses the effects of deformation-dependent low-energy phonons on the structural, thermal, and elastic behaviors of pre-martensitic cubic crystals that undergo incomplete phonon softening. It reveals spontaneous symmetry breaking, pre-martensitic transformation, phonon domains, and tweed structure. The theory naturally explains the ubiquit...

  7. First principles phonon calculations in materials science

    Togo, Atsushi; Tanaka, Isao

    2015-01-01

    Phonon plays essential roles in dynamical behaviors and thermal properties, which are central topics in fundamental issues of materials science. The importance of first principles phonon calculations cannot be overly emphasized. Phonopy is an open source code for such calculations launched by the present authors, which has been world-widely used. Here we demonstrate phonon properties with fundamental equations and show examples how the phonon calculations are applied in materials science.

  8. Selective coherent phonon mode generation in single wall carbon nanotubes

    Nugraha, Ahmad R T; Saito, Riichiro

    2016-01-01

    The ultrafast pulse-train technique is theoretically investigated to enhance a specific coherent phonon mode while suppressing the other phonon modes generated in single wall carbon nanotubes (SWNTs). In particular, we focus on the selectivity of the radial breathing mode (RBM) and the G-band for a given SWNT. We find that if the repetition period matches with integer multiple of the RBM phonon period, the RBM amplitude could be enhanced while the amplitudes of the other modes are suppressed. As for the G-band, when we apply a repetition rate of half-integer multiple of the RBM period, the RBM could be suppressed because of destructive interference, while the G-band still survives. It is also possible to keep the G-band and suppress the RBM by applying a repetition rate that matches with integer multiple of the G-band phonon period. However, in this case we have to use a large number of laser pulses.

  9. Structure of the phonon vacuum state

    Mishev, S

    2012-01-01

    The action of the long-range residual force on the the expectation value of observables in the nuclear ground-states is evaluated by finding optimal values for the coefficients of the canonical transformation which connects the phonon vacuum state with the (quasi-)particle ground-state. After estimating the improvements over the predictions of the independent particle approximation we compare the ground-state wave functions obtained using the presented approach with those obtained using the conventional random phase approximation (RPA) and its extended version. The problem with overbinding of the nuclear ground state calculated using the RPA is shown to be removed if one sticks to the prescriptions of the present approach. The reason being that the latter conforms to the original variational formulation. Calculations are performed within the two-level Lipkin model in which we present results for the binding energies.

  10. Cluster formation through the action of a single picosecond laser pulse

    We demonstrate experimentally and describe theoretically the formation of carbon nanoclusters created by single picosecond laser pulses. We show that the average size of a nanocluster is determined exclusively by single laser pulse parameters and is independent of the gas fill (He, Ar, Kr, Xe) and pressure in a range from 20mTorr to 200 Torr. Simple kinetic theory allows estimates to be made of the cluster size, which are in qualitative agreement with the experimental data. We conclude that the role of the buffer gas is to induce a transition between thin solid film formation on the substrate and foam formation by diffusing the clusters through the gas, with no significant effect upon the average cluster size

  11. Spectral Singularities and CPA-Laser Action in a Weakly Nonlinear PT-Symmetric Bilayer Slab

    Mostafazadeh, Ali

    2014-01-01

    We study optical spectral singularities of a weakly nonlinear PT-symmetric bilinear planar slab of optically active material. In particular, we derive the lasing threshold condition and calculate the laser output intensity. These reveal the following unexpected features of the system: 1. For the case that the real part of the refractive index $\\eta$ of the layers are equal to unity, the presence of the lossy layer decreases the threshold gain; 2. For the more commonly encountered situations when $\\eta-1$ is much larger than the magnitude of the imaginary part of the refractive index, the threshold gain coefficient is a function of $\\eta$ that has a local minimum. The latter is in sharp contrast to the threshold gain coefficient of a homogeneous slab of gain material which is a decreasing function of $\\eta$. We use these results to comment on the effect of nonlinearity on the prospects of using this system as a CPA-laser.

  12. VIBRATIONAL FREQUENCIES VIA FROZEN PHONONS

    Harmon, B.; Weber, W.; Hamann, D

    1981-01-01

    We have used a first principles linear combination of atomic orbitals (LCAO) method to calculate the total ground state energy for crystals of Si, Nb and Mo involving lattice distortions. From these calculations the equilibriunm lattice constant, cohesive energy, and bulk modulus as well as the vibrational frequencies for selected phonons were determined.

  13. EMRS Spring Meeting 2014 Symposium D: Phonons and fluctuations in low dimensional structures

    2014-11-01

    . Goettingen) poster title ''Phonon blocking in Multilayers produced by Pulsed Laser Deposition'', Jordi Gomis-Bresco et al. (ICN2) poster '' A 1D PhoXonic Crystal'', Barcelona and Benjamin J Robinson et al. (U. Lancaster) poster ''Scanning Thermal microscopy studies of 2D materials''. The symposium organisers are grateful to the Scientific Committee members, Prof. Bahram Djafari-Rouhani (France), Prof. Dr. Thomas Dekorsy (Germany), Prof. Anthony Kent (UK), Prof. Fabio Marchesoni (Italy), Dr. Natalio Mingo (France), Prof. Pascal Ruello, (France) and Prof. Javier Viejo-Rodriguez (Spain), for their help with all aspects of evaluation of the scientific level of the presentations in the symposium. The symposium was sponsored by the FP7 ICT FET Open Coordination Action EUPHONON (GA. 612086) and by the CNRS GDR ''Thermal Nanosciences and NanoEngineering''. The symposium organisers express their sincere thanks to the staff of the E-MRS for continuous support and timely advice in all organisational aspects. We are indebted to Dr. Erwan Guillotel (ICN2) for his assistance with the organisation of the symposium.

  14. Magnon-phonon interconversion in a dynamically reconfigurable magnetic material

    Guerreiro, Sergio C.; Rezende, Sergio M.

    2015-12-01

    The ferrimagnetic insulator yttrium iron garnet (YIG) is an important material in the field of magnon spintronics, mainly because of its low magnetic losses. YIG also has very low acoustic losses, and for this reason the conversion of a state of magnetic excitation (magnons) into a state of lattice vibration (phonons), or vice versa, broadens its possible applications in spintronics. Since the magnetic parameters can be varied by some external action, the magnon-phonon interconversion can be tuned to perform a desired function. We present a quantum theory of the interaction between magnons and phonons in a ferromagnetic material subject to a dynamic variation of the applied magnetic field. It is shown that when the field gradient at the magnetoelastic crossover region is much smaller than a critical value, an initial elastic excitation can be completely converted into a magnetic excitation, or vice versa. This occurs with conservation of linear momentum and spin angular momentum, implying that phonons created by the conversion of magnons have spin angular momentum and carry spin current. It is shown further that if the system is initially in a quantum coherent state, its coherence properties are maintained regardless of the time dependence of the field.

  15. Jet formation in spallation of metal film from substrate under action of femtosecond laser pulse

    Inogamov, N. A., E-mail: nailinogamov@googlemail.com [Russian Academy of Sciences, Landau Institute for Theoretical Physics (Russian Federation); Zhakhovskii, V. V. [Dukhov All-Russia Research Institute of Automatics (Russian Federation); Khokhlov, V. A. [Russian Academy of Sciences, Landau Institute for Theoretical Physics (Russian Federation)

    2015-01-15

    It is well known that during ablation by an ultrashort laser pulse, the main contribution to ablation of the substance is determined not by evaporation, but by the thermomechanical spallation of the substance. For identical metals and pulse parameters, the type of spallation is determined by film thickness d{sub f}. An important gauge is metal heating depth d{sub T} at the two-temperature stage, at which electron temperature is higher than ion temperature. We compare cases with d{sub f} < d{sub T} (thin film) and d{sub f} ≫ d{sub T} (bulk target). Radius R{sub L} of the spot of heating by an optical laser is the next (after d{sub f}) important geometrical parameter. The morphology of film bulging in cases where d{sub f} < d{sub T} on the substrate (blistering) changes upon a change in radius R{sub L} in the range from diffraction limit R{sub L} ∼ λ to high values of R{sub L} ≫ λ, where λ ∼ 1 μm is the wavelength of optical laser radiation. When d{sub f} < d{sub T}, R{sub L} ∼ λ, and F{sub abs} > F{sub m}, gold film deposited on the glass target acquires a cupola-shaped blister with a miniature frozen nanojet in the form of a tip on the circular top of the cupola (F{sub abs} and F{sub m} are the absorbed energy and the melting threshold of the film per unit surface area of the film). A new physical mechanism leading to the formation of the nanojet is proposed.

  16. Ab initio calculations of phonon dispersion and lattice dynamics in TlGaTe{sub 2}

    Jafarova, Vusala; Orudzhev, Guseyn; Alekperov, Oktay; Mamedov, Nazim; Abdullayev, Nadir; Najafov, Arzu [Institute of Physics (Innovation Sector), 33 H. Javid ave, Baku 1143 (Azerbaijan); Paucar, Raul [Institute of Physics (Innovation Sector), 33 H. Javid ave, Baku 1143 (Azerbaijan); Chiba Institute of Technology, 2-17-1 Tsudanuma, Narashino, Chiba 275-0016 (Japan); Shim, YongGu [Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531 (Japan); Wakita, Kazuki [Chiba Institute of Technology, 2-17-1 Tsudanuma, Narashino, Chiba 275-0016 (Japan)

    2015-06-15

    This work reports the results of DFT-based calculations of phonon spectra of TlGaTe{sub 2}. The dispersion of phonon bands was calculated along the directions of Brillouin zone (BZ) that include symmetry points. The calculated phonon frequencies at the centre of BZ were compared with those obtained by Raman spectroscopy with the aid of a confocal laser microscopy system. A fairly good agreement between the calculated and experimental data was found. Complimentary, molar heat capacity at constant volume and Debye temperature were calculated in the range 5/500 K on the base of the obtained phonon density of states. The obtained temperature dependencies were compared with available experimental data.The results of comparison were satisfactory. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  17. Percutaneous laser lumbar disc decompression - mechanism of action, indications and contraindications.

    Maksymowicz, Wojciech; Barczewska, Monika; Sobieraj, Andrzej

    2004-06-30

    This article describes the development of minimally invasive methods in the treatment of lumbar discopathy, with particular attention to percutaneous laser disc decompression (PLDD). The authors discus the therapeutic operating mechanism of PLDD, emphasizing the importance of the thermal characteristics of laser light, which is responsible for the vaporization and ablation of a small amount of tissue from the nucleus pulposus. This causes a significant reduction in pressure in the closed structure of the disc, and consequently reduced compression exerted by the disk on the dural sac and the nerve roots. Improvement in the flow of cerebro-spinal fluid has also been observed on the level at which the operation is performed. On the basis of our own experience and the reports of other authors, we have specified indications and contra-indications for PLDD. Our conclusion is that PLDD is an effective treatment method for low back pain and ischialgia caused by protrusion or herniation of the nucleus pulposus, with elimination or significant reduction in symptoms in over 75% of those treated; reduction or resolution of neurological deficits that arise in the course of lumbar discopathy has also been observed. This method enables one-stage treatment of multi-level degenerative changes in the intervertebral disc. The only absolute contraindications for PLDD are the presence of sequestration, disturbances in blood coagulation, and bacterial infection. PMID:17675991

  18. Phonon-polariton in two-dimensional piezoelectric phononic crystals

    Yang Mingyi; Wu Liangchieh [Department of Mechanical Engineering, National Taiwan University, Taipei, Taiwan 10617 (China); Tseng Jiunyi [Materials and Chemical Research Laboratories, Industrial Technology Research Institute, Hsinchu, Taiwan 31040 (China)], E-mail: jytseng@itri.org.tw

    2008-06-23

    The phonon-polariton behaviors of two-dimensional piezoelectric phononic crystals (PPCs) were studied using the plane wave expansion method. The governing equations combine Maxwell's equations and Newton's equations of motion. A mode-repulsion can be formed by strong coupling between electromagnetic (EM) waves and elastic waves in the vicinity of the center of the first Brillouin zone for PPC that comprises piezoelectric material and with opposite polarization in different periodically organized areas. Take a 2D ZnO PPC as a numerical example, it was decoupled into two independent groups. One refers to the mixed mode of the in-plane elastic waves and the transverse-magnetic (TM) mode EM waves. The other group refers to the mixed mode of the out-of-plane elastic waves and the transverse-electric (TE) mode EM waves. Coupling repulsion is also observed in these two groups.

  19. Edge phonons in black phosphorus.

    Ribeiro, H B; Villegas, C E P; Bahamon, D A; Muraca, D; Castro Neto, A H; de Souza, E A T; Rocha, A R; Pimenta, M A; de Matos, C J S

    2016-01-01

    Black phosphorus has recently emerged as a new layered crystal that, due to its peculiar and anisotropic crystalline and electronic band structures, may have important applications in electronics, optoelectronics and photonics. Despite the fact that the edges of layered crystals host a range of singular properties whose characterization and exploitation are of utmost importance for device development, the edges of black phosphorus remain poorly characterized. In this work, the atomic structure and behaviour of phonons near different black phosphorus edges are experimentally and theoretically studied using Raman spectroscopy and density functional theory calculations. Polarized Raman results show the appearance of new modes at the edges of the sample, and their spectra depend on the atomic structure of the edges (zigzag or armchair). Theoretical simulations confirm that the new modes are due to edge phonon states that are forbidden in the bulk, and originated from the lattice termination rearrangements. PMID:27412813

  20. Phonon engineering through crystal chemistry

    Toberer, Eric S.; Zevalkink, Alex; Snyder, G. Jeffrey

    2011-01-01

    Mitigation of the global energy crisis requires tailoring the thermal conductivity of materials. Low thermal conductivity is critical in a broad range of energy conversion technologies, including thermoelectrics and thermal barrier coatings. Here, we review the chemical trends and explore the origins of low thermal conductivity in crystalline materials. A unifying feature in the latest materials is the incorporation of structural complexity to decrease the phonon velocity and increase scatter...

  1. Wave front dislocations appearance under the laser beam self-action in liquid crystal

    Subota, Svitlana

    2005-07-01

    We present theoretical study of optical singularity birth and behaviour in an initially smooth wave front of the incident astigmatic Gaussian light beam. Linearly polarised light beam illuminates a homeotropically aligned nematic liquid crystal cell. Strong director anchoring at the cell walls is assumed. Director reorientation profile is found numerically solving Euler-Lagrange equations. We found the threshold intensity for light induced Fredeericksz-type transition. The threshold intensity of light beam is appeared to increase with increasing of beam asymmetry under the constant value of laser beam area and cell thickness. The results are compared with those calculated using Gaussian-like trial function. Utilizing the Huygens-Fresno principle we calculate the propagation of the distorted light beam after the liquid crystal cell. It is found that with distance increasing we can observe at first the dipole, then the quadrupole and then again the dipole of optical vortices whis unit charge. Thus, the trajectory of zero amplitude resembles a deformed rubber ring symmetrical in the xz-, yz-planes and stretched along z-axis.

  2. Wave front dislocations appearance under the laser beam self-action in liquid crystal

    We present theoretical study of optical singularity birth and behaviour in an initially smooth wave front of the incident astigmatic Gaussian light beam. Linearly polarised light beam illuminates a homeotropically aligned nematic liquid crystal cell. Strong director anchoring at the cell walls is assumed. Director reorientation profile is found numerically solving Euler-Lagrange equations. We found the threshold intensity for light induced Fredeericksz-type transition. The threshold intensity of light beam is appeared to increase with increasing of beam asymmetry under the constant value of laser beam area and cell thickness. The results are compared with those calculated using Gaussian-like trial function. Utilizing the Huygens-Fresno principle we calculate the propagation of the distorted light beam after the liquid crystal cell. It is found that with distance increasing we can observe at first the dipole, then the quadrupole and then again the dipole of optical vortices whis unit charge. Thus, the trajectory of zero amplitude resembles a deformed rubber ring symmetrical in the xz-, yz-planes and stretched along z-axis

  3. New Mid-IR Lasers Based on Rare-Earth-Doped Sulfide and Chloride Materials

    Nostrand, M

    2000-09-01

    Applications in remote-sensing and military countermeasures have driven a need for compact, solid-state mid-IR lasers. Due to multi-phonon quenching, non-traditional hosts are needed to extend current solid-state, room-temperature lasing capabilities beyond {approx} 4 {micro}m. Traditional oxide and fluoride hosts have effective phonon energies in the neighborhood of 1000 cm{sup -1} and 500 cm{sup -1}, respectively. These phonons can effectively quench radiation above 2 and 4 {micro}m, respectively. Materials with lower effective phonon energies such as sulfides and chlorides are the logical candidates for mid-IR (4-10 {micro}m) operation. In this report, laser action is demonstrated in two such hosts, CaGa{sub 2}S{sub 4} and KPb{sub 2}Cl{sub 5}. The CaGa{sub 2}S{sub 4}:Dy{sup 3+} laser operating at 4.3 {micro}m represents the first sulfide laser operating beyond 2 {micro}m. The KPb{sub 2}Cl{sub 5}:Dy{sup 3+} laser operating at 2.4 {micro}m represents the first operation of a chloride-host laser in ambient conditions. Laser action is also reported for CaGa{sub 2}S{sub 4}:Dy{sup 3+} at 2.4 {micro}m, CaGa{sub 2}S{sub 4}:Dy{sup 3+} at 1.4 {micro}m, and KPb{sub 2}Cl{sub 5}:Nd{sup 3+} at 1.06 {micro}m. Both host materials have been fully characterized, including lifetimes, absorption and emission cross sections, radiative branching ratios, and radiative quantum efficiencies. Radiative branching ratios and radiative quantum efficiencies have been determined both by the Judd-Ofelt method (which is based on absorption measurements), and by a novel method described herein which is based on emission measurements. Modeling has been performed to predict laser performance, and a new method to determine emission cross section from slope efficiency and threshold data is developed. With the introduction and laser demonstration of rare-earth-doped CaGa{sub 2}S{sub 4} and KPb{sub 2}Cl{sub 5}, direct generation of mid-IR laser radiation in a solid-state host has been demonstrated. In

  4. Wide-stopband aperiodic phononic filters

    Rostem, K.; Chuss, D. T.; Denis, K. L.; Wollack, E. J.

    2016-06-01

    We demonstrate that a phonon stopband can be synthesized from an aperiodic structure comprising a discrete set of phononic filter stages. Each element of the set has a dispersion relation that defines a complete bandgap when calculated under a Bloch boundary condition. Hence, the effective stopband width in an aperiodic phononic filter (PnF) may readily exceed that of a phononic crystal with a single lattice constant or a coherence scale. With simulations of multi-moded phononic waveguides, we discuss the effects of finite geometry and mode-converting junctions on the phonon transmission in PnFs. The principles described may be utilized to form a wide stopband in acoustic and surface wave media. Relative to the quantum of thermal conductance for a uniform mesoscopic beam, a PnF with a stopband covering 1.6–10.4 GHz is estimated to reduce the thermal conductance by an order of magnitude at 75 mK.

  5. Nonlinear phononics using atomically thin membranes

    Midtvedt, Daniel; Isacsson, Andreas; Croy, Alexander

    2014-01-01

    Phononic crystals and acoustic meta-materials are used to tailor phonon and sound propagation properties by facilitating artificial, periodic structures. Analogous to photonic crystals, phononic band gaps can be created, which influence wave propagation and, more generally, allow engineering of the acoustic properties of a system. Beyond that, nonlinear phenomena in periodic structures have been extensively studied in photonic crystals and atomic Bose-Einstein Condensates in optical lattices....

  6. Twisted phonons in Bose–Einstein condensates

    We consider elementary excitations in a Bose–Einstein condensate, carrying a finite amount of angular momentum. We show that these elementary excitations are modified Bogoliubov oscillations or phonons with a helical wave structure. These twisted phonon modes can contribute to the total vorticity in a quantum fluid, thus complementing the contribution of the traditional quantum vortices. Linear and nonlinear versions of twisted phonon modes will be discussed. New envelope soliton solutions are shown to exist in a condensate. (paper)

  7. Electron-phonon coupling in one dimension

    The Ward identity is derived for the electron-phonon coupling in one dimension and the spectrum of elementary excitations is calculated by assuming that the Fermi distribution is not strongly distorted by interaction. The electron-phonon vertex is renormalized in the case of the forward scattering and Migdal's theorem is discussed. A model is proposed for the giant Kohn anomaly. The dip in the phonon spectrum is obtained and found to be in agreement with the experimental data for KCP. (author)

  8. Phonon-phonon interaction in CdGa{sub 2}Se{sub 2} single crystals

    Kerimova, T.G.; Abdullayev, N.A.; Kengerlinski, L.Y.; Mamedova, I.A.; Ibragimov, N.I. [Institute of Physics, Azerbaijan National Academy of Sciences, H. Javid ave. 131, Baku-1143 (Azerbaijan)

    2015-06-15

    Raman scattering spectra of CdGa{sub 2}Se{sub 4} single crystals were measured in temperature range 8-300 K. From the temperature dependence of optical phonons of B (196 cm{sup -1}) and E (246 cm{sup -1}) symmetry type, the lattice deformation and phonon-phonon interaction contributions to the temperature coefficient of phonon shift were calculated. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  9. Watching surface waves in phononic crystals.

    Wright, Oliver B; Matsuda, Osamu

    2015-08-28

    In this paper, we review results obtained by ultrafast imaging of gigahertz surface acoustic waves in surface phononic crystals with one- and two-dimensional periodicities. By use of quasi-point-source optical excitation, we show how, from a series of images that form a movie of the travelling waves, the dispersion relation of the acoustic modes, their corresponding mode patterns and the position and widths of phonon stop bands can be obtained by temporal and spatio-temporal Fourier analysis. We further demonstrate how one can follow the temporal evolution of phononic eigenstates in k-space using data from phononic-crystal waveguides as an example. PMID:26217053

  10. Coherent phonon dynamics of normal metal in ultrafast spectroscopy: Non-equilibrium gauge invariant Green's function approach

    Lee, Hyun C.

    2016-07-01

    The phonon dynamics of normal metal in the coherent regime of ultrafast spectroscopy is studied based on the non-equilibrium gauge invariant Green's function method. The non-equilibrium phonon self-energy is computed explicitly as a function of time in a gauge invariant way up to the second order of electric field of applied laser pulse. The extension beyond the coherent regime and the incorporation of correlation effects are discussed.

  11. Resonant Enhancement of Coherent Phonons in Carbon Nanotubes Observed with Sub-10fs Time Resolution

    Yanagi K.

    2013-03-01

    Full Text Available Using wavelength-resolved pump-probe spectroscopy with a sub-10-fs laser, we investigated resonant enhancement of radial breathing mode and G-mode coherent phonons in carbon nanotubes (CNTs, and successfully distinguished the electronic states of CNTs with different chiralities.

  12. Synchronisation and desynchronisation of self-modulation oscillations in a ring chip laser under the action of a periodic signal and noise

    The effect of pump noise on the synchronisation of selfmodulation oscillations in a solid-state ring laser with periodic pump modulation is studied numerically and experimentally. It is found that, in contrast to desynchronisation that usually occurs under action of noise in the case of 1/1 synchronisation of self-oscillations by a periodic signal, the effect of noise on 1/2 synchronisation may be positive, namely, at a sufficiently low intensity, pump noise is favourable for synchronisation of self-oscillations, for narrowing of their spectrum, and for increasing the signal-to-noise ratio. (lasers)

  13. Phonon counting and intensity interferometry of a nanomechanical resonator

    Cohen, Justin D.; Meenehan, Seán M.; Maccabe, Gregory S.; Gröblacher, Simon; Safavi-Naeini, Amir H.; Marsili, Francesco; Shaw, Matthew D.; Painter, Oskar

    2015-04-01

    In optics, the ability to measure individual quanta of light (photons) enables a great many applications, ranging from dynamic imaging within living organisms to secure quantum communication. Pioneering photon counting experiments, such as the intensity interferometry performed by Hanbury Brown and Twiss to measure the angular width of visible stars, have played a critical role in our understanding of the full quantum nature of light. As with matter at the atomic scale, the laws of quantum mechanics also govern the properties of macroscopic mechanical objects, providing fundamental quantum limits to the sensitivity of mechanical sensors and transducers. Current research in cavity optomechanics seeks to use light to explore the quantum properties of mechanical systems ranging in size from kilogram-mass mirrors to nanoscale membranes, as well as to develop technologies for precision sensing and quantum information processing. Here we use an optical probe and single-photon detection to study the acoustic emission and absorption processes in a silicon nanomechanical resonator, and perform a measurement similar to that used by Hanbury Brown and Twiss to measure correlations in the emitted phonons as the resonator undergoes a parametric instability formally equivalent to that of a laser. Owing to the cavity-enhanced coupling of light with mechanical motion, this effective phonon counting technique has a noise equivalent phonon sensitivity of 0.89 +/- 0.05. With straightforward improvements to this method, a variety of quantum state engineering tasks using mesoscopic mechanical resonators would be enabled, including the generation and heralding of single-phonon Fock states and the quantum entanglement of remote mechanical elements.

  14. Phonon counting and intensity interferometry of a nanomechanical resonator.

    Cohen, Justin D; Meenehan, Seán M; MacCabe, Gregory S; Gröblacher, Simon; Safavi-Naeini, Amir H; Marsili, Francesco; Shaw, Matthew D; Painter, Oskar

    2015-04-23

    In optics, the ability to measure individual quanta of light (photons) enables a great many applications, ranging from dynamic imaging within living organisms to secure quantum communication. Pioneering photon counting experiments, such as the intensity interferometry performed by Hanbury Brown and Twiss to measure the angular width of visible stars, have played a critical role in our understanding of the full quantum nature of light. As with matter at the atomic scale, the laws of quantum mechanics also govern the properties of macroscopic mechanical objects, providing fundamental quantum limits to the sensitivity of mechanical sensors and transducers. Current research in cavity optomechanics seeks to use light to explore the quantum properties of mechanical systems ranging in size from kilogram-mass mirrors to nanoscale membranes, as well as to develop technologies for precision sensing and quantum information processing. Here we use an optical probe and single-photon detection to study the acoustic emission and absorption processes in a silicon nanomechanical resonator, and perform a measurement similar to that used by Hanbury Brown and Twiss to measure correlations in the emitted phonons as the resonator undergoes a parametric instability formally equivalent to that of a laser. Owing to the cavity-enhanced coupling of light with mechanical motion, this effective phonon counting technique has a noise equivalent phonon sensitivity of 0.89 ± 0.05. With straightforward improvements to this method, a variety of quantum state engineering tasks using mesoscopic mechanical resonators would be enabled, including the generation and heralding of single-phonon Fock states and the quantum entanglement of remote mechanical elements. PMID:25903632

  15. Phonon Bandgap Engineering of Strained Monolayer MoS2

    Jiang, Jin-Wu

    2014-01-01

    The phonon band structure of monolayer MoS2 is characteristic for a large energy gap between acoustic and optical branches, which protects the vibration of acoustic modes from being scattered by optical phonon modes. Therefore, the phonon bandgap engineering is of practical significance for the manipulation of phonon-related mechanical or thermal properties in monolayer MoS2. We perform both phonon analysis and molecular dynamics simulations to investigate the tension effect on the phonon ban...

  16. Time-resolved lasing action from single and coupled photonic crystal nanocavity array lasers emitting in the telecom-band

    Englund, Dirk; Vuckovic, Jelena

    2008-01-01

    We measure the lasing dynamics of single and coupled photonic crystal nanocavity array lasers fabricated in the indium gallium arsenide phosphide material system. Under short optical excitation, single cavity lasers produce pulses as fast as 11 ps (FWHM), while coupled cavity lasers show significantly longer lasing duration which is not explained by a simple rate equations model. A Finite Difference Time Domain simulation including carrier gain and diffusion suggests that asynchronous lasing across the nanocavity array extends the laser's pulse duration.

  17. Splash, pop, sizzle: Information processing with phononic computing

    Phonons, the quanta of mechanical vibration, are important to the transport of heat and sound in solid materials. Recent advances in the fundamental control of phonons (phononics) have brought into prominence the potential role of phonons in information processing. In this review, the many directions of realizing phononic computing and information processing are examined. Given the relative similarity of vibrational transport at different length scales, the related fields of acoustic, phononic, and thermal information processing are all included, as are quantum and classical computer implementations. Connections are made between the fundamental questions in phonon transport and phononic control and the device level approach to diodes, transistors, memory, and logic. 

  18. Splash, pop, sizzle: Information processing with phononic computing

    Sophia R. Sklan

    2015-05-01

    Full Text Available Phonons, the quanta of mechanical vibration, are important to the transport of heat and sound in solid materials. Recent advances in the fundamental control of phonons (phononics have brought into prominence the potential role of phonons in information processing. In this review, the many directions of realizing phononic computing and information processing are examined. Given the relative similarity of vibrational transport at different length scales, the related fields of acoustic, phononic, and thermal information processing are all included, as are quantum and classical computer implementations. Connections are made between the fundamental questions in phonon transport and phononic control and the device level approach to diodes, transistors, memory, and logic.

  19. Phonon dispersion relation of liquid metals

    P B Thakor; P N Gajjar; A R Jani

    2009-06-01

    The phonon dispersion curves of some liquid metals, viz. Na ( = 1), Mg ( = 2), Al ( = 3) and Pb ( = 4), have been computed using our model potential. The charged hard sphere (CHS) reference system is applied to describe the structural information. Our model potential along with CHS reference system is capable of explaining the phonon dispersion relation for monovalent, divalent, trivalent and tetravalent liquid metals.

  20. Microfabricated phononic crystal devices and applications

    Phononic crystals are the acoustic wave analogue of photonic crystals. Here a periodic array of scattering inclusions located in a homogeneous host material forbids certain ranges of acoustic frequencies from existence within the crystal, thus creating what are known as acoustic bandgaps. The majority of previously reported phononic crystal devices have been constructed by hand, assembling scattering inclusions in a viscoelastic medium, predominantly air, water or epoxy, resulting in large structures limited to frequencies below 1 MHz. Recently, phononic crystals and devices have been scaled to VHF (30–300 MHz) frequencies and beyond by utilizing microfabrication and micromachining technologies. This paper reviews recent developments in the area of micro-phononic crystals including design techniques, material considerations, microfabrication processes, characterization methods and reported device structures. Micro-phononic crystal devices realized in low-loss solid materials are emphasized along with their potential application in radio frequency communications and acoustic imaging for medical ultrasound and nondestructive testing. The reported advances in batch micro-phononic crystal fabrication and simplified testing promise not only the deployment of phononic crystals in a number of commercial applications but also greater experimentation on a wide variety of phononic crystal structures. (topical review)

  1. Phonon interference effects in molecular junctions

    Markussen, Troels

    2013-01-01

    We study coherent phonon transport through organic, p-conjugated molecules. Using first principles calculations and Green's function methods, we find that the phonon transmission function in cross-conjugated molecules, like meta-connected benzene, exhibits destructive quantum interference features...

  2. Characterization of phononic heterostructures by infrared thermography

    Exarchos, D. A.; Tragazikis, I.; Psarobas, I.; Matikas, T. E.

    2015-06-01

    This work deals with the development of a new class of metamaterials based on phononic composite structures that can offer vibration protection in a wide range of applications. Such phononic heterostructures is a class of phononic crystals that exhibit spectral gaps with lattice constants of a few orders of magnitude smaller than the relevant acoustic wavelength. The design of a phononic composite metamaterial is based on the formation of omnidirectional frequency gaps. This is very much relevant to the dimensionality of a finite slab of the crystal. In this respect, two dimensional structures are used to cut off acoustic waves. In this study, different infrared thermography techniques were used in order to assess the phononic structure's geometry, as well as to determine the thermal properties of the metamaterial.

  3. Nonlinear phononics using atomically thin membranes.

    Midtvedt, Daniel; Isacsson, Andreas; Croy, Alexander

    2014-01-01

    Phononic crystals and acoustic metamaterials are used to tailor phonon and sound propagation properties by utilizing artificial, periodic structures. Analogous to photonic crystals, phononic band gaps can be created, which influence wave propagation and, more generally, allow engineering of the acoustic properties of a system. Beyond that, nonlinear phenomena in periodic structures have been extensively studied in photonic crystals and atomic Bose-Einstein condensates in optical lattices. However, creating nonlinear phononic crystals or nonlinear acoustic metamaterials remains challenging and only few examples have been demonstrated. Here, we show that atomically thin and periodically pinned membranes support coupled localized modes with nonlinear dynamics. The proposed system provides a platform for investigating nonlinear phononics. PMID:25204322

  4. Phononic crystals and elastodynamics: Some relevant points

    Aravantinos-Zafiris, N. [Dept. of Materials Science, University of Patras, Patras 26504 (Greece); Department of Sound and Musical Instruments Technology, Ionian Islands Technological Educational Institute, Lixouri, 28200 (Greece); Sigalas, M. M. [Dept. of Materials Science, University of Patras, Patras 26504 (Greece); Kafesaki, M. [Institute of Electronic Structure and Laser (IESL), Foundation for Research and Technology, Hellas (FORTH), P.O. Box 1387, 70013 Heraklion, Crete (Greece); Dept. of Materials Science and Technology, Univ. of Crete (Greece); Economou, E. N. [Institute of Electronic Structure and Laser (IESL), Foundation for Research and Technology, Hellas (FORTH), P.O. Box 1387, 70013 Heraklion, Crete (Greece); Dept. of Physics, Univ. of Crete (Greece)

    2014-12-15

    In the present paper we review briefly some of the first works on wave propagation in phononic crystals emphasizing the conditions for the creation of acoustic band-gaps and the role of resonances to the band-gap creation. We show that useful conclusions in the analysis of phononic band gap structures can be drawn by considering the mathematical similarities of the basic classical wave equation (Helmholtz equation) with Schrödinger equation and by employing basic solid state physics concepts and conclusions regarding electronic waves. In the second part of the paper we demonstrate the potential of phononic systems to be used as elastic metamaterials. This is done by demonstrating negative refraction in phononic crystals and subwavelength waveguiding in a linear chain of elastic inclusions, and by proposing a novel structure with close to pentamode behavior. Finally the potential of phononic structures to be used in liquid sensor applications is discussed and demonstrated.

  5. Phononic crystals and elastodynamics: Some relevant points

    In the present paper we review briefly some of the first works on wave propagation in phononic crystals emphasizing the conditions for the creation of acoustic band-gaps and the role of resonances to the band-gap creation. We show that useful conclusions in the analysis of phononic band gap structures can be drawn by considering the mathematical similarities of the basic classical wave equation (Helmholtz equation) with Schrödinger equation and by employing basic solid state physics concepts and conclusions regarding electronic waves. In the second part of the paper we demonstrate the potential of phononic systems to be used as elastic metamaterials. This is done by demonstrating negative refraction in phononic crystals and subwavelength waveguiding in a linear chain of elastic inclusions, and by proposing a novel structure with close to pentamode behavior. Finally the potential of phononic structures to be used in liquid sensor applications is discussed and demonstrated

  6. Phononic crystals and elastodynamics: Some relevant points

    N. Aravantinos-Zafiris

    2014-12-01

    Full Text Available In the present paper we review briefly some of the first works on wave propagation in phononic crystals emphasizing the conditions for the creation of acoustic band-gaps and the role of resonances to the band-gap creation. We show that useful conclusions in the analysis of phononic band gap structures can be drawn by considering the mathematical similarities of the basic classical wave equation (Helmholtz equation with Schrödinger equation and by employing basic solid state physics concepts and conclusions regarding electronic waves. In the second part of the paper we demonstrate the potential of phononic systems to be used as elastic metamaterials. This is done by demonstrating negative refraction in phononic crystals and subwavelength waveguiding in a linear chain of elastic inclusions, and by proposing a novel structure with close to pentamode behavior. Finally the potential of phononic structures to be used in liquid sensor applications is discussed and demonstrated.

  7. Electron-phonon interaction and the generalized kinetic equation for systems interacting with high-intensity electromagnetic wave fields

    The generalized kinetic equation for an electron-phonon system subjected to the action of an intense electromagnetic wave field is derived on the basis of the Bogolubov method of elimination of boson operators, taking into account the electron-phonon collision effects. The conditions are considered under which the collision integral allows the introduction of the relaxation time, and the latter is calculated as a function of the frequency and intensity of the pumping field

  8. Lasers

    Passeron, Thierry

    2012-01-01

    Lasers are a very effective approach for treating many hyperpigmented lesions. They are the gold standard treatment for actinic lentigos and dermal hypermelanocytosis, such as Ota nevus. Becker nevus, hyperpigmented mosaicisms, and lentigines can also be succesfully treated with lasers, but they could be less effective and relapses can be observed. However, lasers cannot be proposed for all types of hyperpigmentation. Thus, freckles and café-aulait macules should not be treated as the relapse...

  9. Phonons dispersions in auxetic lattices

    Sparavigna, A [Dipartimento di Fisica, Politecnico di Torino, C.so Duca degli Abruzzi 24, Turin (Italy)

    2007-12-15

    The modes of vibrations in auxetic structures are studied, with models where the two-dimensional lattice is represented by a planar mesh with rod-like particles connected by strings. An auxetic membrane can be obtained modifying a honeycomb one, according to a model proposed by Evans et al. in 1991 and used to explain a negative elastic Poisson's ratio. This property means that auxetic materials have a lateral extension, instead to shrink, when they are stretched. The models here proposed with rod-like particles inserted in the structure have interesting behaviour of acoustic and rotational branches of phonon dispersions. Complete bandgaps of vibrations can be obtained for a proper choice of lattice coupling parameters and distribution of masses in the unit cell of the lattice.

  10. Hyperbolic phonon-polaritons in boron nitride for near-field optical imaging and focusing

    Li, Peining; Lewin, Martin; Kretinin, Andrey V.; Caldwell, Joshua D.; Novoselov, Kostya S.; Taniguchi, Takashi; Watanabe, Kenji; Gaussmann, Fabian; Taubner, Thomas

    2015-06-01

    Hyperbolic materials exhibit sub-diffractional, highly directional, volume-confined polariton modes. Here we report that hyperbolic phonon polaritons allow for a flat slab of hexagonal boron nitride to enable exciting near-field optical applications, including unusual imaging phenomenon (such as an enlarged reconstruction of investigated objects) and sub-diffractional focusing. Both the enlarged imaging and the super-resolution focusing are explained based on the volume-confined, wavelength dependent propagation angle of hyperbolic phonon polaritons. With advanced infrared nanoimaging techniques and state-of-art mid-infrared laser sources, we have succeeded in demonstrating and visualizing these unexpected phenomena in both Type I and Type II hyperbolic conditions, with both occurring naturally within hexagonal boron nitride. These efforts have provided a full and intuitive physical picture for the understanding of the role of hyperbolic phonon polaritons in near-field optical imaging, guiding, and focusing applications.

  11. Ab initio phonon coupling and optical response of hot electrons in plasmonic metals

    Brown, Ana M; Narang, Prineha; Goddard, William A; Atwater, Harry A

    2016-01-01

    Ultrafast laser measurements probe the non-equilibrium dynamics of excited electrons in metals with increasing temporal resolution. Electronic structure calculations can provide a detailed microscopic understanding of hot electron dynamics, but a parameter-free description of pump-probe measurements has not yet been possible, despite intensive research, because of the phenomenological treatment of electron-phonon interactions. We present ab initio predictions of the electron-temperature dependent heat capacities and electron-phonon coupling coefficients of plasmonic metals. We find substantial differences from free-electron and semi-empirical estimates, especially in noble metals above transient electron temperatures of 2000 K, because of the previously-neglected strong dependence of electron-phonon matrix elements on electron energy. We also present first-principles calculations of the electron-temperature dependent dielectric response of hot electrons in plasmonic metals, including direct interband and phon...

  12. Electrons and Phonons in Semiconductor Multilayers

    Ridley, B. K.

    2014-08-01

    Introduction; 1. Simple models of the electron-phonon interaction; 2. Quantum confinement of carriers; 3. Quasicontinuum theory of lattice vibrations; 4. Bulk vibratory modes in an isotropic continuum; 5. Optical modes in a quantum well; 6. Superlattice modes; 7. Optical modes in various structures; 8. Electron-phonon interaction in a quantum well; 9. Other scattering mechanisms; 10. Quantum screening; 11. The electron distribution function; 12. Spin relaxation; 13. Electrons and phonons in the Wurtzite lattice; 14. Nitride heterostructures; 15. Terahertz sources; References; Index.

  13. Harvesting vibrations via 3D phononic isolators

    Psarobas, Ioannis E.; Yannopapas, Vassilios; Matikas, Theodore E.

    2016-05-01

    We report on the existence of unidirectional phononic band gaps that may span over extended regions of the Brillouin zone and can find application in trapping elastic (acoustic) waves in properly designed multilayered 3D structures. Phononic isolators operate as a result of asymmetrical wave transmission through a slab of a crystallographic phononic structure with broken mirror symmetry. Due to the use of lossless materials in the crystal, the absorption rate is dramatically enhanced when the proposed isolator is placed next to a vibrational harvesting cell. xml:lang="fr"

  14. Longitudinal polar optical phonons in InN/GaN single and double het- erostructures

    Ardali, Sukru; Tiras, Engin [Department of Physics, Faculty of Science, Anadolu University, Yunus Emre Campus, Eskisehir 26470 (Turkey); Gunes, Mustafa; Balkan, Naci [School of Computer Science and Electronic Engineering, University of Essex, Wivenhoe Park, Colchester CO4 3SQ (United Kingdom); Ajagunna, Adebowale Olufunso; Iliopoulos, Eleftherios; Georgakilas, Alexandros [Microelectronics Research Group, IESL, FORTH and Physics Department, University of Crete, P.O. Box 1385, 71110 Heraklion-Crete (Greece)

    2011-05-15

    Longitudinal optical phonon energy in InN epi-layers has been determined independently from the Raman spectroscopy and temperature dependent Hall mobility measurements. Raman spectroscopy technique can be used to obtain directly the LO energy where LO phonon scattering dominates transport at high temperature. Moreover, the Hall mobility is determined by the scattering of electrons with LO phonons so the data for the temperature dependence of Hall mobility have been used to calculate the effective energy of longitudinal optical phonons.The samples investigated were (i) single heterojunction InN with thicknesses of 1.08, 2.07 and 4.7 {mu}m grown onto a 40 nm GaN buffer and (ii) GaN/InN/AlN double heterojunction samples with InN thicknesses of 0.4, 0.6 and 0.8 {mu}m. Hall Effect measurements were carried out as a function of temperature in the range between T = 1.7 and 275 K at fixed magnetic and electric fields. The Raman spectra were obtained at room temperature. In the experiments, the 532 nm line of a nitrogen laser was used as the excitation source and the light was incident onto the samples along of the growth direction (c-axis). The results, obtained from the two independent techniques suggest the following: (1) LO phonon energies obtained from momentum relaxation experiments are generally slightly higher than those obtained from the Raman spectra. (2) LO phonon energy for the single heterojunctions does not depend on the InN thickness. (3) In double heterostructures, with smaller InN thicknesses and hence with increased strain, LO phonon energy increases by 3% (experimental accuracy is < 1%) when the InN layer thickness increases from 400 to 800 nm (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  15. Effects of phonon-phonon coupling on properties of pygmy resonance in 124-132Sn

    Voronov V. V.

    2012-12-01

    Full Text Available Starting from an effective Skyrme interaction we study effects of phonon-phonon coupling on the low-energy electric dipole response in 124-132Sn. The QRPA calculations are performed within a finite rank separable approximation. The inclusion of two-phonon configurations gives a considerable contribution to low-lying strength. Comparison with available experimental data shows a reasonable agreement for the low-energy E1 strength distribution.

  16. Coherent phonon and surface-enhanced Raman scattering dynamics in solids

    Takeda, Jun, E-mail: jun@ynu.ac.jp [Department of Physics, Graduate School of Engineering, Yokohama National University, Yokohama 240-8501 (Japan); Katayama, Ikufumi; Shudo, Ken-ichi [Department of Physics, Graduate School of Engineering, Yokohama National University, Yokohama 240-8501 (Japan); Kitajima, Masahiro [Department of Physics, Graduate School of Engineering, Yokohama National University, Yokohama 240-8501 (Japan); Department of Applied Physics, National Defense Academy, Yokosuka, Kanagawa 239-8686 (Japan); LxRay, Nishinomiya, Hyogo 663-8172 (Japan)

    2014-08-01

    We have demonstrated coherent phonon and surface-enhanced Raman scattering (SERS) dynamics of carbon-related materials: gold (Au) deposited graphite and benzenethiol (BT) self-assembled monolayer (SAM) adsorbed on Au film with roughness. Using ultrafast pump-probe spectroscopy with the enhanced electric field via Au hemispheres or Au film with nanoscale roughness, transient behaviors of high frequency phonons located at surface/interface were sensitively detected. In Au deposited graphite, the electric field near graphite surface around Au nanoparticles, whose typical diameter is ∼10 nm, is strongly enhanced. As a result, the disorder-induced mode (D-mode) near the surface was clearly observed. In BT-SAM, the nanoscale roughness of the Au film might contribute to the amplitude enhancement of coherent vibrations up to the detected level. From these results, we believe that coherent SERS spectroscopy will open the door to observe coherent phonon dynamics even at the level of monolayer and single molecules for future. - Highlights: • Coherent phonon spectroscopy with 7.5 fs laser pulse is utilized to measure SERS dynamics. • Au nanostructures were used to enhance coherent vibrations in graphite/self-assembled monolayer. • D-mode coherent phonon in graphite was sensitively detected due to SERS via Au nanostructures. • High frequency vibrations in benzenethiol self-assembled monolayer were detected due to SERS.

  17. Coherent gigahertz phonons in Ge2Sb2Te5 phase-change materials

    Hase, Muneaki; Fons, Paul; Kolobov, Alexander V.; Tominaga, Junji

    2015-12-01

    Using ≈ 40 fs ultrashort laser pulses, we investigate the picosecond acoustic response from a prototypical phase change material, thin Ge2Sb2Te5 (GST) films with various thicknesses. After excitation with a 1.53 eV-energy pulse with a fluence of ≈ 5 mJ cm-2, the time-resolved reflectivity change exhibits transient electronic response, followed by a combination of exponential-like strain and coherent acoustic phonons in the gigahertz (GHz) frequency range. The time-domain shape of the coherent acoustic pulse is well reproduced by the use of the strain model by Thomsen et al 1986 (Phys. Rev. B 34 4129). We found that the decay rate (the inverse of the relaxation time) of the acoustic phonon both in the amorphous and in the crystalline phases decreases as the film thickness increases. The thickness dependence of the acoustic phonon decay is well modeled based on both phonon-defect scattering and acoustic phonon attenuation at the GST/Si interface, and it is revealed that those scattering and attenuation are larger in crystalline GST films than those in amorphous GST films.

  18. SURFACE PHONON AND CONFINED PHONON POLARITONS IN WURTIZTE NITRIDE THIN-FILM STRUCTURES

    L. ZHANG

    2008-01-01

    The polar phonon polariton modes in a wurtzite thin-film structure have been theoretically investigated in the present paper. It has been confirmed that there are two types of phonon polariton modes, i.e., the surface phonon polariton (SPP) modes and the confined phonon polariton (CPP) modes in wurtzite thin-film systems. The frequency ranges of the SPP and CPP modes have been discussed in detail. The dispersive equations for the two types of polarition modes are also deduced. Numerical calcu...

  19. Monolithic phononic crystals with a surface acoustic band gap from surface phonon-polariton coupling.

    Yudistira, D; Boes, A; Djafari-Rouhani, B; Pennec, Y; Yeo, L Y; Mitchell, A; Friend, J R

    2014-11-21

    We theoretically and experimentally demonstrate the existence of complete surface acoustic wave band gaps in surface phonon-polariton phononic crystals, in a completely monolithic structure formed from a two-dimensional honeycomb array of hexagonal shape domain-inverted inclusions in single crystal piezoelectric Z-cut lithium niobate. The band gaps appear at a frequency of about twice the Bragg band gap at the center of the Brillouin zone, formed through phonon-polariton coupling. The structure is mechanically, electromagnetically, and topographically homogeneous, without any physical alteration of the surface, offering an ideal platform for many acoustic wave applications for photonics, phononics, and microfluidics. PMID:25479504

  20. Phononic crystals: Entering an acoustic phase

    Barreiro, Julio T.

    2015-03-01

    Electrons moving in a one-dimensional crystal can acquire a geometrical phase. Sound waves in phononic crystals are now shown to display the same effect -- underlining the similarity between conventional solids and acoustic metamaterials.

  1. Single-photon indistinguishability: influence of phonons

    Nielsen, Per Kær; Lodahl, Peter; Jauho, Antti-Pekka;

    2012-01-01

    indistinguishability, absent in the approximate theories. The maximum arises due to virtual processes in the highly non-Markovian short-time regime, which dominate the decoherence for small QD-cavity coupling, and phonon-mediated real transitions between the upper and lower polariton branches in the long-time regime......Recent years have demonstrated that the interaction with phonons plays an important role in semiconductor based cavity QED systems [2], consisting of a quantum dot (QD) coupled to a single cavity mode [Fig. 1(a)], where the phonon interaction is the main decoherence mechanism. Avoiding decoherence...... effects is important in linear optical quantum computing [1], where a device emitting fully coherent indistinguishable single photons on demand, is the essential ingredient. In this contribution we present a numerically exact simulation of the effect of phonons on the degree of indistinguishability of...

  2. Toward stimulated interaction of surface phonon polaritons

    Kong, B. D.; Trew, R. J.; Kim, K. W., E-mail: kwk@ncsu.edu [Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, North Carolina 27695-7911 (United States)

    2013-12-21

    Thermal emission spectra mediated by surface phonon polariton are examined by using a theoretical model that accounts for generation processes. Specifically, the acoustic phonon fusion mechanism is introduced to remedy theoretical deficiencies of the near thermal equilibrium treatments. The model clarifies the thermal excitation mechanism of surface phonon polaritons and the energy transfer path under non-zero energy flow. When applied to GaAs and SiC semi-infinite surfaces, the nonequilibrium model predicts that the temperature dependence of the quasi-monochromatic peak can exhibit distinctly different characteristics of either sharp increase or slow saturation depending on the materials, which is in direct contrast with the estimate made by the near-equilibrium model. The proposed theoretical tool can accurately analyze the nonequilibrium steady states, potentially paving a pathway to demonstrate stimulated interaction/emission of thermally excited surface phonon polaritons.

  3. Phonon-mediated detection of particles

    Over the past five years particle physicists, nuclear physicists and astrophysicists have been increasingly interested in using phonons to detect particle interactions. In these detection attempts it is obviously critical to integrate the understanding that the phonon physicists have accumulated on the mechanisms governing the production, propagation and detection of those phonons. Vice versa, some of the issues raised by the particle detection problem may be of significant interest and the high sensitivity methods being developed may become important for phonon physics investigations. These were the motivations for a round table discussion between members of the two communities. This report attempts to summarize the themes of a very interesting discussion. 24 refs., 2 figs., 1 tab

  4. Influence of phonons on semiconductor quantum emission

    Feldtmann, Thomas

    2009-07-06

    A microscopic theory of interacting charge carriers, lattice vibrations, and light modes in semiconductor systems is presented. The theory is applied to study quantum dots and phonon-assisted luminescence in bulk semiconductors and heterostructures. (orig.)

  5. Acoustic Phonon Thermal Transport through a Nanostructure

    LI Wen-Xia; LIU Tian-Yu; LIU Chang-Long

    2006-01-01

    @@ Using the scattering matrix method, we investigate the thermal transport in a nanostructure at low temperatures.It is found that phonon transport exhibits some novel and interesting features: resonant transmission, resonant reflection, and small thermal conductance.

  6. Toward engineered quantum many-body phonon systems

    Soykal, Ö. O.; Tahan, Charles

    2013-01-01

    Arrays of coupled phonon cavities each including an impurity qubit in silicon are considered. We study experimentally feasible architectures that can exhibit quantum many-body phase transitions of phonons, e.g. Mott insulator and superfluid states, due to a strong phonon-phonon interaction (which is mediated by the impurity qubit-cavity phonon coupling). We investigate closed equilibrium systems as well as driven dissipative non-equilibrium systems at zero and non-zero temperatures. Our resul...

  7. Anharmonic effects on a phonon number measurement of a quantum mesoscopic mechanical oscillator

    Santamore, D H; Milburn, G J; Roukes, M L; Goan, Hsi-Sheng

    2004-01-01

    We generalize a proposal for detecting single phonon transitions in a single nanoelectromechanical system (NEMS) to include the intrinsic anharmonicity of each mechanical oscillator. In this scheme two NEMS oscillators are coupled via a term quadratic in the amplitude of oscillation for each oscillator. One NEMS oscillator is driven and strongly damped and becomes a transducer for phonon number in the other measured oscillator. We derive the conditions for this measurement scheme to be quantum limited and find a condition on the size of the anharmonicity. We also derive the relation between the phase diffusion back-action noise due to number measurement and the localization time for the measured system to enter a phonon number eigenstate. We relate both these time scales to the strength of the measured signal, which is an induced current proportional to the position of the readout oscillator.

  8. Phonon cooling by an optomechanical heat pump

    Dong, Ying; Bariani, F.; Meystre, P.

    2015-01-01

    We propose and analyze theoretically a cavity optomechanical analog of a heat pump that uses a polariton fluid to cool mechanical modes coupled to a single pre-cooled phonon mode via external modulation of the substrate of the mechanical resonator. This approach permits to cool phonon modes of arbitrary frequencies not limited by the cavity-optical field detuning deep into the quantum regime from room temperature.

  9. Phonon Cooling by an Optomechanical Heat Pump

    Dong, Ying; Bariani, F.; Meystre, P.

    2015-11-01

    We propose and analyze theoretically a cavity optomechanical analog of a heat pump that uses a polariton fluid to cool mechanical modes coupled to a single precooled phonon mode via external modulation of the substrate of the mechanical resonator. This approach permits us to cool phonon modes of arbitrary frequencies not limited by the cavity-optical field detuning deep into the quantum regime from room temperature.

  10. PHONON ECHOES IN BULK AND POWDERED MATERIALS

    Kajimura, K.

    1981-01-01

    Experimental and theoretical studies of phonon echoes in bulk and powdered materials are reviewed. Phonon echoes have been observed in many materials such as bulk piezoelectric crystals, paramagnets, glasses, doped semiconductors, and piezoelectric, magnetic, and metallic powders, etc. The echoes arise from a time reversal of the phase, like spin echoes, of a primary pulsed acoustic excitation due to a second acoustic or rf pulse. The phase reversal occurs through the nonlinear interactions o...

  11. Photon-phonon anti-stokes upconversion of a photonically, electronically, and thermally isolated opal

    Stem, Michelle R.

    2016-05-01

    The purpose of the present research was to investigate an intense violet shift displayed by a non-toxic, natural silicate material with a highly ordered nanostructure. The material displayed an unexpected, nonlinear 2:3 photon-phonon anti-Stokes upconversion while photonically, electronically, and thermally isolated. Conducted aphotonically and at ambient temperatures, the specimen upconverted a low-power, 650 nm constant wave red laser to an internally highly dispersed 433 nm violet wavelength. The strong dispersion was largely due to nearly total internal reflection of the laser. The upconversion had an efficiency of about 78 %, based on specimen volume, with no detectable thermal variance. The 2:3 anti-Stokes upconversion displayed by this material is likely the result of a previously unknown photon-phonon evanescence response that amplified the energy of a portion of the incident laser photons. Thus, a portion of the incident laser photons were upconverted, and the material converted another portion into an amplified energy that caused the upconversion. Internal micro-lasing appeared to be a means of photon-phonon evanescent energy redistribution, enabling dispersed photonic upconversion. Additional analyses also found an unexpectedly rhythmic photonic structure in spectrophotometric scans, polariscopic color changing, and previously undocumented ultraviolet responses.

  12. Investigation of the degradation of the antireflection coatings of the nonlinear crystal under the action of the high average power laser radiation

    The analysis of the local heating role in the processes of the degradation of the antireflection coatings of the nonlinear crystals when they have been used in the CW and quasi-CW YAG lasers was carried out. The broad sample range of the oxide, nitride and fluoride films deposited on the LiNbO3, BaNaNbO5, LiIO3 KTP and BBO crystals was considered. Investigation of these samples was carried out under the intense heating of their surfaces by the action of the CO2 laser pulses. The analysis of the obtained results with account for the chemical reaction thermodynamics, thermotension and other factors is presented

  13. Physical and technological foundations of graphical treatment processes based on inner defects under the action of powerful pulses of laser radiation

    Davidov, Nicolay N.; Kudaev, Serge V.

    1999-01-01

    Researchers of damage formation in processes in glass are directed on studying the interaction mechanisms of powerful impulses of penetrating laser radiation with materials for the purpose of improvement of optical components resistance. However, the processes of glass structure defects formation as local areas with low factor of visible light admittance can find application in a final glassware processing. Application of treatment modes, using these effects, allows: to increase art expression of decorative glassware for furnish of buildings interior; to solve some problems of manufacturing counter devices, and also indication devices of electronic instruments. Mathematical models of defect formation processes in optically transparent materials under an action of powerful pulses of laser radiation are necessary for development of control principles of glass treatment.

  14. Sensitivity of the system of cytochrome P-450 of poultry liver to the action of red laser light

    It is detected that irradiation of poultry embryos by red laser light (λ = 633 nm) at a doze of 1 - 6 mJ can influence a level of the cytochrome P-450 oxidized form in poultry liver. It is supposed that this level is changed due to variations in the content of lipid peroxide compounds in tissue under low-level red laser radiation and is one of the factors of regulation of the intensity of peroxide processes in tissues

  15. Resonant interactions between discrete phonons in quinhydrone driven by nonlinear electron-phonon coupling

    Rury, Aaron S.

    2016-06-01

    This study reports experimental, computational, and theoretical evidence for a previously unobserved coherent phonon-phonon interaction in an organic solid that can be described by the application of Fano's analysis to a case without the presence of a continuum. Using Raman spectroscopy of the hydrogen-bonded charge-transfer material quinhydrone, two peaks appear near 700 cm-1 we assign as phonons whose position and line-shape asymmetry depend on the sample temperature and light scattering excitation energy. Density functional theory calculations find two nearly degenerate phonons possessing frequencies near the values found in experiment that share similar atomic motion out of the aromatic plane of electron donor and acceptor molecules of quinhydrone. Further analytical modeling of the steady-state light scattering process using the Peierls-Hubbard Hamiltonian and time-dependent perturbation theory motivates assignment of the physical origin of the asymmetric features of each peak's line shape to an interaction between two discrete phonons via nonlinear electron-phonon coupling. In the context of analytical model results, characteristics of the experimental spectra upon 2.33 eV excitation of the Raman scattering process are used to qualify the temperature dependence of the magnitude of this coupling in the valence band of quinhydrone. These results broaden the range of phonon-phonon interactions in materials in general while also highlighting the rich physics and fundamental attributes specific to organic solids that may determine their applicability in next generation electronics and photonics technologies.

  16. Spectral signatures of spin–phonon and electron–phonon interactions in multiferroic iron borates

    Popova, M.N., E-mail: popova@isan.troitsk.ru [Institute of Spectroscopy, RAS, Moscow, Troitsk 142190 (Russian Federation); Boldyrev, K.N.; Klimin, S.A. [Institute of Spectroscopy, RAS, Moscow, Troitsk 142190 (Russian Federation); Stanislavchuk, T.N.; Sirenko, A.A. [Department of Physics, New Jersey Institute of Technology, Newark, NJ 07102 (United States); Bezmaternykh, L.N. [Kirenskiy Institute of Physics, Siberian Branch of RAS, Krasnoyarsk 660036 (Russian Federation)

    2015-06-01

    High-resolution far-infrared reflection and polarized ellipsometry, as well as Raman scattering temperature-dependent measurements are used to study spin-phonon and electron-phonon interactions in rare-earth (RE) iron borates with the R32 structure of a natural mineral huntite, namely, in RFe{sub 3}(BO{sub 3}){sub 4} with R=Pr, Nd, and Sm. Pronounced peculiarities in the ω(T) dependences at the Néel temperature T{sub N}≈32 K are observed for all the compounds studied and the origin of these peculiarities is discussed. A coupling between lattice phonons and crystal-field excitations of a RE ion manifests itself by a renormalization of frequencies and intensities of coupled modes. Modeling of the spectra has revealed the value of about 15 cm{sup −1} for the electron–phonon coupling constant in PrFe{sub 3}(BO{sub 3}){sub 4}. - Highlights: • Rare-earth iron borates exhibit peculiarities in the phonon frequencies at T{sub N}. • We propose mechanisms of the spin-phonon coupling in RFe{sub 3}(BO{sub 3}){sub 4}. • A coupling of phonons and crystal-field excitations manifests itself in the spectra. • The electron-phonon coupling constant for PrFe{sub 3}(BO{sub 3}){sub 4} amounts to 14.6 cm{sup −1}.

  17. Spectral signatures of spin–phonon and electron–phonon interactions in multiferroic iron borates

    High-resolution far-infrared reflection and polarized ellipsometry, as well as Raman scattering temperature-dependent measurements are used to study spin-phonon and electron-phonon interactions in rare-earth (RE) iron borates with the R32 structure of a natural mineral huntite, namely, in RFe3(BO3)4 with R=Pr, Nd, and Sm. Pronounced peculiarities in the ω(T) dependences at the Néel temperature TN≈32 K are observed for all the compounds studied and the origin of these peculiarities is discussed. A coupling between lattice phonons and crystal-field excitations of a RE ion manifests itself by a renormalization of frequencies and intensities of coupled modes. Modeling of the spectra has revealed the value of about 15 cm−1 for the electron–phonon coupling constant in PrFe3(BO3)4. - Highlights: • Rare-earth iron borates exhibit peculiarities in the phonon frequencies at TN. • We propose mechanisms of the spin-phonon coupling in RFe3(BO3)4. • A coupling of phonons and crystal-field excitations manifests itself in the spectra. • The electron-phonon coupling constant for PrFe3(BO3)4 amounts to 14.6 cm−1

  18. 50W CW output power and 12mJ pulses from a quasi-2-level Yb:YAG ceramic rod laser end-pumped at the 969nm zero-phonon line

    Fries, Christian; Weitz, Marco; Theobald, Christian; v. Löwis of Menar, Patric; Bartschke, Jürgen; L'huillier, Johannes A.

    2015-02-01

    With the advent of high power and narrow bandwidth 969 nm pump diodes, direct pumping into the upper laser level of Yb:YAG and hence quasi-2-level lasers became possible. Pumping directly into the emitting level leads to higher quantum efficiency and reduction of non-radiative decay. Consequently, thermal load, thermal lensing and risk of fracture are reduced significantly. Moreover pump saturation and thermal population of uninvolved energy-levels in ground and excited states are benefical for a homogenous distribution of the pump beam as well as the reduction of reabsorption loss compared to 3-level systems, which allows for high-power DPSS lasers. Beside continuous-wave (cw) operation, nanosecond pulses with a repetition rate between 1 and 5 kHz are an attractive alternative to flashlamp-pumped systems (10-100 Hz) in various measurement applications that require higher data acquisition rates because of new faster detectors. Based on measurements of the absorption and a detailed numerical model for pump beam distribution, including beam propagation and saturation factors, power-scaling of a ceramic rod Yb:YAG oscillator was possible. Finally a cw output power of 50 W with 33 % pump efficiency at 1030 nm has been demonstrated (M2 < 1.2). Nanosecond pulses have been produced by cavity-dumping of this system. The cavity-dumped setup allowed for 3-10 ns pulses with a pulse energy of 12.5 mJ at 1 kHz (M2 < 1.1). In order to achieve these results a systematic experimental and numerical investigation on gain dynamics and the identification of different stable operating regimes has been carried out.

  19. Thermal conductivities of one-dimensional anharmonic/nonlinear lattices: renormalized phonons and effective phonon theory

    Nianbei Li

    2012-12-01

    Full Text Available Heat transport in low-dimensional systems has attracted enormous attention from both theoretical and experimental aspects due to its significance to the perception of fundamental energy transport theory and its potential applications in the emerging field of phononics: manipulating heat flow with electronic anologs. We consider the heat conduction of one-dimensional nonlinear lattice models. The energy carriers responsible for the heat transport have been identified as the renormalized phonons. Within the framework of renormalized phonons, a phenomenological theory, effective phonon theory, has been developed to explain the heat transport in general one-dimensional nonlinear lattices. With the help of numerical simulations, it has been verified that this effective phonon theory is able to predict the scaling exponents of temperature-dependent thermal conductivities quantitatively and consistently.

  20. Phonon Recycling for Ultrasensitive Kinetic Inductance Detectors

    Zmuidzinas, Jonas

    Initially proposed (Day et al. 2003; Zmuidzinas 2012) in 1999 by our Caltech/JPL group, and thanks to strong support from NASA, the superconducting (microwave) kinetic inductance detector (MKID or KID) technology continues to develop rapidly as it transitions into applications. The development effort worldwide is intensifying and NASA's continued support of KID development is essential in order to keep pace. Here we propose to investigate and demonstrate a new, low-TRL concept, which we call phonon recycling, that promises to open broad new avenues in KID design and performance. Briefly, phonon recycling allows the detector designer to tailor the responsivity and sensitivity of a KID to match the needs of the application by using geometry to restrict the rate at which recombination phonons are allowed to escape from the detector. In particular, phonon recycling should allow very low noise-equivalent power (NEP) to be achieved without requiring very low operating tem- peratures. Phonon recycling is analogous to the use of micromachined suspension legs to control the flow of heat in a bolometer, as measured by the thermal conductivity G. However, phonon recycling exploits the non-thermal distribution of recombination phonons as well as their very slow decay in crystals at low temperatures. These properties translate to geometrical and mechanical requirements for a phonon-recycled KID that are considerably more relaxed than for a bolometer operating at the same temperature and NEP. Our ultimate goal is to develop detector arrays suitable for a far-infrared (FIR) space mission, which will impose strict requirements on the array sensitivity, yield, uniformity, multiplexing density, etc. Through previous NASA support under the Strategic Astrophysics Technology (SAT) program, we have successfully demonstrated the MAKO submillimeter camera at the Caltech Submillimeter Observatory and have become familiar with these practical issues. If our demonstration of phonon recycling

  1. Symmetry-adapted phonon analysis of nanotubes

    Aghaei, Amin; Dayal, Kaushik; Elliott, Ryan S.

    2013-02-01

    The characteristics of phonons, i.e. linearized normal modes of vibration, provide important insights into many aspects of crystals, e.g. stability and thermodynamics. In this paper, we use the Objective Structures framework to make concrete analogies between crystalline phonons and normal modes of vibration in non-crystalline but highly symmetric nanostructures. Our strategy is to use an intermediate linear transformation from real-space to an intermediate space in which the Hessian matrix of second derivatives is block-circulant. The block-circulant nature of the Hessian enables us to then follow the procedure to obtain phonons in crystals: namely, we use the Discrete Fourier Transform from this intermediate space to obtain a block-diagonal matrix that is readily diagonalizable. We formulate this for general Objective Structures and then apply it to study carbon nanotubes of various chiralities that are subjected to axial elongation and torsional deformation. We compare the phonon spectra computed in the Objective Framework with spectra computed for armchair and zigzag nanotubes. We also demonstrate the approach by computing the Density of States. In addition to the computational efficiency afforded by Objective Structures in providing the transformations to almost-diagonalize the Hessian, the framework provides an important conceptual simplification to interpret the phonon curves. Our findings include that, first, not all non-optic long-wavelength modes are zero energy and conversely not all zero energy modes are long-wavelength; second, the phonon curves accurately predict both the onset as well as the soft modes for instabilities such as torsional buckling; and third, unlike crystals where phonon stability does not provide information on stability with respect to non-rank-one deformation modes, phonon stability in nanotubes is sufficient to guarantee stability with respect to all perturbations that do not involve structural modes. Our finding of characteristic

  2. LO-phonon-assisted polariton lasing in a ZnO-based microcavity

    Orosz, Laurent; Réveret, François; Médard, François; Disseix, Pierre; Leymarie, Joël; Leymarie, Joel; Mihailovic, Martine; Solnyshkov, Dimitri; Malpuech, Guillaume; Zúñiga-Pérez, Jesús; Semond, Fabrice; Leroux, Mathieu; Bouchoule, Sophie; Lafosse, Xavier; Mexis, Meletios

    2012-01-01

    International audience Polariton relaxation mechanisms are analyzed experimentally and theoretically in a ZnO-based polariton laser. A minimum lasing threshold is obtained when the energy difference between the exciton reservoir and the bottom of the lower polariton branch is resonant with the LO phonon energy. Tuning off this resonance increases the threshold, and exciton-exciton scattering processes become involved in the polariton relaxation. These observations are qualitatively reprodu...

  3. Ionizing particle detection based on phononic crystals

    Aly, Arafa H., E-mail: arafa16@yahoo.com, E-mail: arafa.hussien@science.bsu.edu.eg; Mehaney, Ahmed; Eissa, Mostafa F. [Physics Department, Faculty of Science, Beni-Suef University, Beni-Suef (Egypt)

    2015-08-14

    Most conventional radiation detectors are based on electronic or photon collections. In this work, we introduce a new and novel type of ionizing particle detector based on phonon collection. Helium ion radiation treats tumors with better precision. There are nine known isotopes of helium, but only helium-3 and helium-4 are stable. Helium-4 is formed in fusion reactor technology and in enormous quantities during Big Bang nucleo-synthesis. In this study, we introduce a technique for helium-4 ion detection (sensing) based on the innovative properties of the new composite materials known as phononic crystals (PnCs). PnCs can provide an easy and cheap technique for ion detection compared with conventional methods. PnC structures commonly consist of a periodic array of two or more materials with different elastic properties. The two materials are polymethyl-methacrylate and polyethylene polymers. The calculations showed that the energies lost to target phonons are maximized at 1 keV helium-4 ion energy. There is a correlation between the total phonon energies and the transmittance of PnC structures. The maximum transmission for phonons due to the passage of helium-4 ions was found in the case of making polyethylene as a first layer in the PnC structure. Therefore, the concept of ion detection based on PnC structure is achievable.

  4. Ionizing particle detection based on phononic crystals

    Aly, Arafa H.; Mehaney, Ahmed; Eissa, Mostafa F.

    2015-08-01

    Most conventional radiation detectors are based on electronic or photon collections. In this work, we introduce a new and novel type of ionizing particle detector based on phonon collection. Helium ion radiation treats tumors with better precision. There are nine known isotopes of helium, but only helium-3 and helium-4 are stable. Helium-4 is formed in fusion reactor technology and in enormous quantities during Big Bang nucleo-synthesis. In this study, we introduce a technique for helium-4 ion detection (sensing) based on the innovative properties of the new composite materials known as phononic crystals (PnCs). PnCs can provide an easy and cheap technique for ion detection compared with conventional methods. PnC structures commonly consist of a periodic array of two or more materials with different elastic properties. The two materials are polymethyl-methacrylate and polyethylene polymers. The calculations showed that the energies lost to target phonons are maximized at 1 keV helium-4 ion energy. There is a correlation between the total phonon energies and the transmittance of PnC structures. The maximum transmission for phonons due to the passage of helium-4 ions was found in the case of making polyethylene as a first layer in the PnC structure. Therefore, the concept of ion detection based on PnC structure is achievable.

  5. Phonon dynamics of graphene on metals

    Taleb, Amjad Al; Farías, Daniel

    2016-03-01

    The study of surface phonon dispersion curves is motivated by the quest for a detailed understanding of the forces between the atoms at the surface and in the bulk. In the case of graphene, additional motivation comes from the fact that thermal conductivity is dominated by contributions from acoustic phonons, while optical phonon properties are essential to understand Raman spectra. In this article, we review recent progress made in the experimental determination of phonon dispersion curves of graphene grown on several single-crystal metal surfaces. The two main experimental techniques usually employed are high-resolution electron energy loss spectroscopy (HREELS) and inelastic helium atom scattering (HAS). The different dispersion branches provide a detailed insight into the graphene-substrate interaction. Softening of optical modes and signatures of the substrate‧s Rayleigh wave are observed for strong graphene-substrate interactions, while acoustic phonon modes resemble those of free-standing graphene for weakly interacting systems. The latter allows determining the bending rigidity and the graphene-substrate coupling strength. A comparison between theory and experiment is discussed for several illustrative examples. Perspectives for future experiments are discussed.

  6. Phonon dynamics of graphene on metals.

    Al Taleb, Amjad; Farías, Daniel

    2016-03-16

    The study of surface phonon dispersion curves is motivated by the quest for a detailed understanding of the forces between the atoms at the surface and in the bulk. In the case of graphene, additional motivation comes from the fact that thermal conductivity is dominated by contributions from acoustic phonons, while optical phonon properties are essential to understand Raman spectra. In this article, we review recent progress made in the experimental determination of phonon dispersion curves of graphene grown on several single-crystal metal surfaces. The two main experimental techniques usually employed are high-resolution electron energy loss spectroscopy (HREELS) and inelastic helium atom scattering (HAS). The different dispersion branches provide a detailed insight into the graphene-substrate interaction. Softening of optical modes and signatures of the substrate's Rayleigh wave are observed for strong graphene-substrate interactions, while acoustic phonon modes resemble those of free-standing graphene for weakly interacting systems. The latter allows determining the bending rigidity and the graphene-substrate coupling strength. A comparison between theory and experiment is discussed for several illustrative examples. Perspectives for future experiments are discussed. PMID:26886508

  7. A step closer to visualizing the electron___phonon interplay

    Chen, Y.L.; Lee, W.S.; Shen, Z.X.; /Stanford U., Appl. Phys. Dept. /Stanford U., Phys. Dept. /SLAC, PULSE

    2011-01-04

    dynamic information. This pump-probe experiment is reminiscent of the standard method used by bell makers for hundreds of years to judge the quality of their products (hitting a bell then listening to how the sound would fade away), albeit the relevant time scale here is way beyond tens of femtoseconds. Traditionally, ultrafast spectroscopy was carried out to study gas-phase reactions, but it has also been applied to study condensed phase systems since the development of reliable solid-state ultrafast lasers approximately a decade ago. In addition, the ability to control pulse width, wavelength, and amplification of the output of Ti:Sapphire lasers has further increased the capability of this experimental method. During the past decade, many ultrafast pump-probe experiments have been carried out in various fields by using different probing methods, such as photo-resistivity, fluorescence yield, and photoemission, and they have revealed much new information complementary to the equilibrium spectroscopy methods used before. Carbone et al. used the photon-pump, electron (diffraction)-probe method. The pumping photon pulse first drives the electrons in the sample into an oscillating mode along its polarization direction. Then during the delay time, these excited electrons can transfer excess energy to the adjacent nuclei and cause crystal lattice vibration on their way back to the equilibrium state. An ultrashort electron pulse is shot at the sample at various time delays {Delta}t and the diffraction pattern is collected. Because the electron diffraction pattern is directly related to the crystal lattice structure and its motion, this technique provides a natural way to study the electron-phonon coupling problem. Furthermore, by adjusting the pump pulse's relative polarization with respect to the Cu-O bond direction, Carbone et al. were able to acquire the electron-phonon coupling strength along different directions. Focusing on the lattice dynamic along the c axis

  8. Using gold nanorods labelled with antibodies under the photothermal action of NIR laser radiation on Staphylococcus aureus

    Tuchina, E S; Petrov, P O; Kozina, K V; Tuchin, V V [N.G. Chernyshevsky Saratov State University, Saratov (Russian Federation); Ratto, F; Pini, R [Institute of Applied Physics ' Nello Carrara' , National Research Council, via Madonna del Piano 10 50019 Sesto Fiorentino (Italy); Centi, S [University of Florence, Dept. Experimental and Clinical Biomedical Sciences, viale Morgagni 50, 50134 Firenze (Italy)

    2014-07-31

    The effect of NIR laser radiation (808 nm) and gold nanorods on the cells of two strains of Staphylococcus aureus, one of them being methicillin-sensitive and the other being methicillinresistant, is studied. Nanorods having the dimensions 10 × 44 nm with the absorption maximum in the NIR spectral region, functionalised with human immunoglobulins IgA and IgG, are synthesised. It is shown that the use of nanoparticles in combination with NIR irradiation leads to killing up to 97% of the population of microorganisms. (laser biophotonics)

  9. Evolution of Electrical Resistivity, Thermal Conductivity, and Temperature of a solid under the action of Intense Ultrashort Laser pulse

    Singh-Sandhu, A; Kumar, G R; Sandhu, Arvinder S.

    2002-01-01

    The dynamical properties of Cu in a regime relevant to femtosecond micro machining are obtained on picosecond time scales using pump-probe reflectivity study for 100fs, 1015 W cm-2 laser pulses. The electrical resistivity is obtained by solving Helmoltz equations. The dissipation mechanisms and scaling laws are obtained in high and low temperature limits. The 'resistivity saturation' effect in an unexplored regime intermediate to hot plasma and cold solid is studied in detail. The temperature evolution and thermal conductivity is obtained in the temporal range 0 to 30ps after the interaction of laser pulse with solid Cu.

  10. Phonon heat transport in gallium arsenide

    Richa Saini; Vinod Ashokan; B D Indu; R Kumar

    2012-03-01

    The lifetimes of quantum excitations are directly related to the electron and phonon energy linewidths of a particular scattering event. Using the versatile double time thermodynamic Green’s function approach based on many-body theory, an ab-initio formulation of relaxation times of various contributing processes has been investigated with newer understanding in terms of the linewidths of electrons and phonons. The energy linewidth is found to be an extremely sensitive quantity in the transport phenomena of crystalline solids as a collection of large number of scattering processes, namely, boundary scattering, impurity scattering, multiphonon scattering, interference scattering, electron–phonon processes and resonance scattering. The lattice thermal conductivities of three samples of GaAs have been analysed on the basis of modified Callaway model and a fairly good agreement between theory and experimental observations has been reported.

  11. Phonon tunneling through a double barrier system

    Villegas, Diosdado [Departamento de Física, Universidad Central “Marta Abreu” de Las Villas, CP 54830, Santa Clara, Villa Clara (Cuba); Instituto de Física, Universidad Autónoma de Puebla, 18 Sur y San Claudio, Edif. 110A, Ciudad Universitaria, 72570 Puebla (Mexico); León-Pérez, Fernando de [Centro Universitario de la Defensa de Zaragoza, Ctra. de Huesca s/n, E-50090 Zaragoza (Spain); Pérez-Álvarez, R. [Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, CP 62209 Cuernavaca (Mexico); Arriaga, J., E-mail: arriaga@ifuap.buap.mx [Instituto de Física, Universidad Autónoma de Puebla, 18 Sur y San Claudio, Edif. 110A, Ciudad Universitaria, 72570 Puebla (Mexico)

    2015-04-15

    The tunneling of optical and acoustic phonons at normal incidence on a double-barrier is studied in this paper. Transmission coefficients and resonance conditions are derived theoretically under the assumption that the long-wavelength approximation is valid. It is shown that the behavior of the transmission coefficients for the symmetric double barrier has a Lorentzian form close to resonant frequencies and that Breit–Wigner's formula have a general validity in one-dimensional phonon tunneling. Authors also study the so-called generalized Hartman effect in the tunneling of long-wavelength phonons and show that this effect is a numerical artifact resulting from taking the opaque limit before exploring the variation with a finite barrier width. This study could be useful for the design of acoustic devices.

  12. A Correlation Function for Phonon Eigenvectors

    It was shown by van Hove that the Fourier transform of the neutron scattering intensity is a space-time correlation function of the scattering density. In the special case of a single crystal as the scattering system, the coefficients of a Fourier series can be derived from the one-phonon scattering cross-sections corresponding to a phonon of a particular frequency. Evaluation of the Fourier series gives a space correlation function involving the eigenvectors of the mode of vibration being considered. The function is a special case of the van Hove function, closely related to the Patterson function which is used in X-ray crystallography. In the special case of a phonon of wave vector zero (q = 0) the function has a sufficiently simple interpretation that it may be of practical value. (author)

  13. Electron and Phonon Transport in Molecular Junctions

    Li, Qian

    transmission at the Fermi energy. We propose and analyze a way of using π   stacking to design molecular junctions to control heat transport. We develop a simple model system to identify optimal parameter regimes and then use density functional theory (DFT) to extract model parameters for a number of specific......Molecular electronics provide the possibility to investigate electron and phonon transport at the smallest imaginable scale, where quantum effects can be investigated and exploited directly in the design. In this thesis, we study both electron transport and phonon transport in molecular junctions...... DFT method. It is found that the thermal conductance of π-stacked systems can be reduced by 95%, compared with that in a single-molecule junction. Phonon transmission of π-stacked systems is reduced dramatically in the whole frequency range and the left transmission mainly remains below 5 THz....

  14. Photoemission and photo-field-emission from photocathodes with arrays of silicon tips under continuous and pulsed lasers action

    The electron machines's development and improvement go through the discovery of new electron sources of high brightness. After reminding the interests in studying silicon cathodes with array of tips as electron sources, I describe, in the three steps model, the main phenomenological features related to photoemission and photoemission and photo-field-emission from a semi-conductor. the experimental set-ups used for the measurements reported in chapter four, five and six are described in chapter three. In chapter three. In chapter four several aspects of photo-field-emission in continuous and nanosecond regimes, studied on the Clermont-Ferrand's test bench are tackled. We have measured quantum efficacies of 0.4 percent in the red (1.96 eV). Temporal responses in the nanoseconds range (10 ns) were observed with the Nd: YLF laser. With the laser impinging at an oblique angle we obtained ratios of photocurrent to dark current of the order of twenty. The issue of the high energy extracted photocurrent saturation is addressed and I give a preliminary explanation. In collaboration with the L.A.L. (Laboratoire de l'Accelerateur Lineaire) some tests with shortened pulsed laser beam (Nd: YAG laser 35 ps) were performed. Satisfactory response times have been obtained within the limitation of the scope (400 ps). (authors). 101 refs. 93 figs., 27 tabs., 3 photos., 1 append

  15. Cryogenic phonon-mediated particle detectors for dark matter searches and neutrino physics

    This work describes the development of cryogenic phonon-mediated particle detectors for dark matter searches and neutrino detection. The detectors described in this work employ transition-edge sensors, which consist of a meander pattern of thin-film superconductor on a silicon substrate. When phonons from a particle interaction in the crystal impinge on the sensor in sufficient density, sections of the line are driven normal and provide a measurable resistance. A large fraction of the thesis describes work to fully characterize the phonon flux from particle interactions. In one set of experiments, ∼25% of the phonon energy from 59.54 keV gamma-ray events was found to propagate open-quotes ballisticallyclose quotes (i.e., with little or no scattering) across a 300 μm thick crystal of silicon. Gamma-rays produce electron recoils in silicon whereas with dark matter and neutrino experiments nuclear recoils are also of interest. Two experiments were done to measure the ballistic component that arises from neutron events, which interact via nuclear recoil. Measurements indicate that the fraction of energy that is ballistic is ∼50% greater for nuclear recoils than for electron recoils. Two novel detectors were fabricated and tested in an attempt to improve the sensitivity of the detectors. In the first detector, relatively large Al pads were linked by 2 μm wide Ti lines in a meander pattern. Phonons impinging on the Al pads create quasiparticles which diffuse in the Al pad until they are trapped in the lower gap Tl links. The sensitivity of the detector was found to be increased by this open-quotes funnelingclose quotes action. A second detector was built that incorporates 0.25 μm wide lines defined by direct electron-beam exposure of the photoresist. If the superconducting line is sufficiently narrow, single phonons are capable of driving sections normal which should improve the sensitivity and linearity of the detector

  16. Action of diode laser (830 nm) on cutaneous wound healing process: biometrical and histological study in rats

    In this research, it was analyzed the acceleration of the healing process of cutaneous lesions in mice, using a diode laser emitting in 830 nm. The 64 selected animals in this study were randomically divided into four groups of 16 animals each (G1, G2, G3 and G4). Biometric and histological comparisons were accomplished in the following periods: 3, 7 and 14 days after the surgery and laser application. Three laser irradiation configurations were used: a punctual contact (G2) and two non-contact and uniform (G3 and G4). For group G2, the laser intensity was 428 mW/cm2 , and for groups G3 and G4 it was 53 mW/cm2. The total doses were D = 3 J/cm2 for groups G2 and G4, and D = 1,3 J/cm2 for G3. The first group, G1, was considered control and thus not submitted to any treatment after the surgery. All irradiated lesions presented acceleration of the healing process with regard to the control group. However, our results clearly indicate that the smaller laser intensity (uniform irradiation) leaded to the best results. On the other hand, the smaller used dose also leaded to the more significant and expressive results. The combination of the intensity value of 53 mW/cm2 and the dose of 1,3 J/cm2 leaded to optimal results, regarding the Biometric and histological analysis, presenting faster lesion contraction, quicker neoformation of epithelial and conjunctive tissue (with more collagen fibers ). (author)

  17. Clinical and morphologic evaluation of Er:YAG laser action at the front of cervical dentinal hypersensitivity

    This work was achieved in vivo and in vitro to evaluate the efficiency of Er:YAG laser in the cervical dentinal hypersensitivity treatment (HSDC). The Clinical study was achieved in patients with HSDC. The treatment was realized in five sessions: the first for selection, the second for exams (clinic and X-Ray) and trying to remove the etiologic factors that could cause the HSDC. The third and fourth sessions were subjected to the radiation with that protocol: 60 mJ energy ,2 Hz frequency, 6 mm out of focus, under air cooling, 20 seconds each application which the same was repeated four times with one minute breaks, which scanning movements and without using anaesthetics. The fifth was evaluation. The patients were evaluated and registered in a subject scale of pain 0 to 3, in the beginning and end of each session of irradiation, and one month after the last session. The results showed that for the irradiated group occurs significant differences in the beginning of each session and between. For the control group did not occur significant differences in the beginning and after each session, but did show a difference between the sessions. As the control group as the irradiated group, had reduction of sensibility between the session. For the morphologic study nine teeth were selected, 7 molars and 2 pre-molars from operative dentistry discipline. Half of the surface was irradiated with Er:YAG laser, the same protocol used in vivo, and the other half was used as a control without receiving any laser irradiation. Subsequently, specimens were prepared for SEM examinations. The results showed that laser treated surfaces showed a reduction of dentine tubular diameter with partial or total closure of the dentine tubules. For the control group, it was observed bigger amounts smear layer and open dentine tubular. The results obtained indicated that the Er:YAG laser can contribute to the HSDC treatment. (author)

  18. A chip-integrated coherent photonic-phononic memory

    Merklein, Moritz; Vu, Khu; Madden, Stephen J; Eggleton, Benjamin J

    2016-01-01

    Controlling and manipulating quanta of coherent acoustic vibrations - phonons - in integrated circuits has recently drawn a lot of attention, as phonons can function as unique links between radiofrequency and optical signals and access quantum regimes. It has been shown that radiofrequency signals can be controlled and stored via piezo-electrically actuated coherent phonons. Coherent phonons, however, can also be directly excited by optical photons through strong acousto-optic coupling in integrated circuits that guide photons as well as phonons. These hypersound phonons have similar wavelength as the exciting optical field but travel at a 5-orders of magnitude lower velocity. This allows the realization of a coherent optical buffer, a long time desired yet elusive device for on-chip optical signal processing. In this letter we demonstrate a coherent on-chip memory storing the entire coherent information carried by light, phase and amplitude, as acoustic phonons. The photonic-phononic memory provides GHz-band...

  19. Situation with collective two-phonon states in deformed nuclei

    Within the quasiparticle-phonon nuclear model with the operators of phonons depending on the sign of the angular momentum projection, the Pauli principle is taken into account in the two-phonon components of the wave functions. The centroid energies of the collective two-phonon states in even-even deformed nuclei are calculated. It is shown that the inclusion of the Pauli principle leads to their shift by 1-3 MeV towards high energies. The shifts of three-phonon poles due to the Pauli principle are calculated in the three-phonon components of the wave functions. The collective two-phonon states, the centroid energies of which are 3-5 MeV, are expected to be strongly fragmented. The conclusion is confirmed that the collective two-phonon states should not exist in deformed nuclei. The situation in 168Er and in the 228Th isotopes is analysed

  20. Phonon interference effects in molecular junctions

    We study coherent phonon transport through organic, π-conjugated molecules. Using first principles calculations and Green's function methods, we find that the phonon transmission function in cross-conjugated molecules, like meta-connected benzene, exhibits destructive quantum interference features very analogous to those observed theoretically and experimentally for electron transport in similar molecules. The destructive interference features observed in four different cross-conjugated molecules significantly reduce the thermal conductance with respect to linear conjugated analogues. Such control of the thermal conductance by chemical modifications could be important for thermoelectric applications of molecular junctions

  1. Phonon interference effects in molecular junctions

    Markussen, Troels, E-mail: troels.markussen@gmail.com [Center for Atomic-scale Materials Design (CAMD), Department of Physics, Technical University of Denmark, DK-2800 Kgs. Lyngby (Denmark)

    2013-12-28

    We study coherent phonon transport through organic, π-conjugated molecules. Using first principles calculations and Green's function methods, we find that the phonon transmission function in cross-conjugated molecules, like meta-connected benzene, exhibits destructive quantum interference features very analogous to those observed theoretically and experimentally for electron transport in similar molecules. The destructive interference features observed in four different cross-conjugated molecules significantly reduce the thermal conductance with respect to linear conjugated analogues. Such control of the thermal conductance by chemical modifications could be important for thermoelectric applications of molecular junctions.

  2. Quantized phonon-enhanced spin fluctuations

    Koo, Je Huan, E-mail: koo@kw.ac.kr

    2015-01-15

    We investigate the phonon-enhanced spin flipping of f-electrons via s–f exchange interactions, as previously discussed by ourselves [Phys. Rev. B 61, 4289]. The electron–electron interaction U{sub sf} is an order of magnitude stronger than that of Kondo-type bare spin-flipping. Using the similar configuration of Hydrogen, we calculate the quantized energy eigenvalues of this spin fluctuation. We also compare our energy levels with experimental data obtained from inelastic neutron scatterings in which the data below 40 meV may be attributed to phonon modes.

  3. Phonon analogue of topological nodal semimetals

    Po, Hoi Chun; Bahri, Yasaman; Vishwanath, Ashvin

    2015-03-01

    Recently, Kane and Lubensky proposed a mapping between bosonic phonon problems on isostatic lattices to chiral fermion systems based on factorization of the dynamical matrix [Nat. Phys. 10, 39 (2014)]. The existence of topologically protected zero modes in such mechanical problems is related to their presence in the fermionic system and is dictated by a local index theorem. Here we adopt the proposed mapping to construct a two-dimensional mechanical analogue of a fermionic topological nodal semimetal that hosts a robust bulk node in its linearized phonon spectrum. Such topologically protected soft modes with tunable wavevector may be useful in designing mechanical structures with fault-tolerant properties.

  4. Phonon dispersion curves of CsCN

    N K Gaur; Preeti Singh; E G Rini; Jyotsna Galgale; R K Singh

    2004-08-01

    The motivation for the present work was gained from the recent publication on phonon dispersion curves (PDCs) of CsCN from the neutron scattering technique. We have applied the extended three-body force shell model (ETSM) by incorporating the effect of coupling between the translation modes and the orientation of cyanide molecules for the description of phonon dispersion curves of CsCN between the temperatures 195 and 295 K. Our results on PDCs in symmetric direction are in good agreement with the experimental data measured with inelastic neutron scattering technique.

  5. Electronic structure, phonon spectra, and anisotropy of electron-phonon interaction in scandium

    Sichkar, S.M. [Institute of Metal Physics of the National Academy of Sciences of Ukraine, 36 Vernadsky Str., 03142 Kiev (Ukraine); Antonov, V.N. [Institute of Metal Physics of the National Academy of Sciences of Ukraine, 36 Vernadsky Str., 03142 Kiev (Ukraine); Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstrasse 1, 70569 Stuttgart (Germany)

    2012-11-15

    The anisotropy of transport function, electronic structure, Fermi surface, phonon spectra, electron-phonon spectral function, orbital dependence of the cyclotron masses, and extremal cross sections of the Fermi surface of Sc were investigated from first principles using the full potential linear muffin-tin orbital method. The calculations of the dynamic matrix were carried out within the framework of the linear response theory. A good agreement with experimental data of phonon spectra, electrical resistivity, cyclotron masses, and extremal cross sections of the Fermi surface in high symmetry directions was achieved. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  6. Phononic Thermal Conduction Engineering for Bolometers: From Phononic Crystals to Radial Casimir Limit

    Maasilta, I. J.; Puurtinen, T. A.; Tian, Y.; Geng, Z.

    2016-07-01

    We discuss two alternative and complementary means of controlling radial phonon conduction for bolometers in two dimensions: by using phononic crystals or by roughening the surface of the membranes (Casimir limit). For phononic crystals, we present new experiments with a modified geometry and a larger hole periodicity than before, achieving a low thermal conductance {˜ }2 pW/K at 150 mK. Calculations in the Casimir limit, on the other hand, show that for small detector dimensions thermal conductance below 1 fW/K seems achievable.

  7. Optical properties of costal cartilage and their variation in the process of non-destructive action of laser radiation with the wavelength 1.56 μm

    The optical properties of costal cartilage and their variation under the action of laser radiation with the wavelength 1.56 μm are studied. The laser action regime corresponds to that used for changing the cartilage shape. The dynamics of the passed scattered laser radiation was studied by means of the optical fibre system, and the optical properties of the cartilage tissue (on the basis of Monte Carlo modelling of light propagation) – using the setup with two integrating spheres. Under the influence of radiation, the characteristics of which corresponded to those used for the cartilage shape correction, no essential changes in the optical parameters were found. The results obtained in the course of studying the dynamics of optical signals in the process of costal cartilage irradiation can be used for developing control systems, providing the safety and efficiency of laser medical technologies. (biophotonics)

  8. Soft surfaces of nanomaterials enable strong phonon interactions

    Bozyigit, Deniz; Yazdani, Nuri; Yarema, Maksym; Yarema, Olesya; Lin, Weyde Matteo Mario; Volk, Sebastian; Vuttivorakulchai, Kantawong; Luisier, Mathieu; Juranyi, Fanni; Wood, Vanessa

    2016-03-01

    Phonons and their interactions with other phonons, electrons or photons drive energy gain, loss and transport in materials. Although the phonon density of states has been measured and calculated in bulk crystalline semiconductors, phonons remain poorly understood in nanomaterials, despite the increasing prevalence of bottom-up fabrication of semiconductors from nanomaterials and the integration of nanometre-sized components into devices. Here we quantify the phononic properties of bottom-up fabricated semiconductors as a function of crystallite size using inelastic neutron scattering measurements and ab initio molecular dynamics simulations. We show that, unlike in microcrystalline semiconductors, the phonon modes of semiconductors with nanocrystalline domains exhibit both reduced symmetry and low energy owing to mechanical softness at the surface of those domains. These properties become important when phonons couple to electrons in semiconductor devices. Although it was initially believed that the coupling between electrons and phonons is suppressed in nanocrystalline materials owing to the scarcity of electronic states and their large energy separation, it has since been shown that the electron–phonon coupling is large and allows high energy-dissipation rates exceeding one electronvolt per picosecond (refs 10, 11, 12, 13). Despite detailed investigations into the role of phonons in exciton dynamics, leading to a variety of suggestions as to the origins of these fast transition rates and including attempts to numerically calculate them, fundamental questions surrounding electron–phonon interactions in nanomaterials remain unresolved. By combining the microscopic and thermodynamic theories of phonons and our findings on the phononic properties of nanomaterials, we are able to explain and then experimentally confirm the strong electron–phonon coupling and fast multi-phonon transition rates of charge carriers to trap states. This improved understanding of

  9. Experimental studies of electron-phonon interactions in gallium nitride

    Stanton, Nicola Marie

    2001-01-01

    This thesis presents an experimental investigation of the electron-phonon interaction in GaN. Bulk epilayers, grown by MBE, and AIGaN/GaN heterostructures, grown by MOCVD, have been studied. The energy relaxation rate for hot electrons has been measured over a wide range of temperatures, allowing both acoustic and optic phonon emission to be studied in GaN epilayers. Direct phonon measurements, both studying the emission and absorption processes, have been performed. Detection of phonons e...

  10. Sub-Poissonian phononic population in a nanoelectromechanical system

    Merlo, Matteo; Haupt, Federica; Cavaliere, Fabio; Sassetti, Maura

    2007-01-01

    Population of a phononic mode coupled to a single-electron transistor in the sequential tunneling regime is discussed for the experimentally realistic case of intermediate electron-phonon coupling. Features like a sub-Poissonian bosonic distribution are found in regimes where electron transport drives the oscillator strongly out of equilibrium with only few phonon states selectively populated. The electron Fano factor is compared to fluctuations in the phonon distribution, showing that all po...