Phonon laser action in a tunable, two-level photonic molecule
Grudinin, Ivan S; Vahala, Kerry J
2009-01-01
The phonon analog of an optical laser has long been a subject of interest. We demonstrate a compound microcavity system, coupled to a radio-frequency mechanical mode, that operates in close analogy to a two-level laser system. An inversion produces gain, causing phonon laser action above a pump power threshold of around 50 $\\mu$W. The device features a continuously tunable, gain spectrum to selectively amplify mechanical modes from radio frequency to microwave rates. Viewed as a Brillouin process, the system accesses a regime in which the phonon plays what has traditionally been the role of the Stokes wave. For this reason, it should also be possible to controllably switch between phonon and photon laser regimes. Cooling of the mechanical mode is also possible.
Physical mechanisms of coherent acoustic phonons generation by ultrafast laser action.
Ruello, Pascal; Gusev, Vitalyi E
2015-02-01
In this review we address the microscopic mechanisms that are involved in the photogeneration processes of GHz-THz coherent acoustic phonons (CAP) induced by an ultrafast laser pulse. Understanding and describing the underlying physics is necessary indeed for improving the future sources of coherent acoustic phonons useful for the non-destructive testing optoacoustic techniques. Getting more physical insights on these processes also opens new perspectives for the emerging field of the opto-mechanics where lattice motions (surface and/or interfaces ultrafast displacements, nanostructures resonances) are controlled by light. We will then remind the basics of electron-phonon and photon-phonon couplings by discussing the deformation potential mechanism, the thermoelasticity, the inverse piezoelectric effect and the electrostriction in condensed matter. Metals, semiconductors and oxide materials will be discussed. The contribution of all these mechanisms in the photogeneration process of sound will be illustrated over several examples coming from the rich literature. PMID:25038958
The terahertz phonon laser a full quantum treatment
Camps, I; Pastawski, H M; Foà-Torres, L E F
2001-01-01
The aim of this work is to describe the behavior of a device capable to generate high frequency (~THz) acoustic phonons. This device consists in a GaAs-AlGaAs double barrier heterostructure that, when an external bias is applied, produces a high rate of longitudinal optical LO phonons. These LO phonons are confined and they decay by stimulated emission of a pair of secondary longitudinal optical (LO_2) and transversal acoustic (TA) phonons. The last ones form an intense beam of coherent acoustic phonons. To study this effect, we start from a tight binding Hamiltonian that take into account the electron-phonon (e-ph) and phonon-phonon (ph-ph) interactions. We calculate the electronic current through the double barrier and we obtain a set of five coupled kinetic equations that describes the electron and phonon populations. The results obtained here confirm the behavior of the terahertz phonon laser, estimated by rougher treatments.
Electron-phonon coupling in laser excited metals
Energy Technology Data Exchange (ETDEWEB)
Klett, Isabel; Mueller, Benedikt; Rethfeld, Baerbel [TU Kaiserslautern (Germany)
2011-07-01
Irradiation of metals with an ultrashort laser pulse leads to a hot electron gas while the lattice stays cold. The corresponding electron-phonon coupling has been calculated using a thermalized Fermi distribution function. However, after laser excitation, the electrons cannot be assumed in equilibrium, due to their relaxation time of tens of femtoseconds. In order to allow a nonequilibrium distribution function, the Boltzmann equation is applied. This model is extended by implementing the density of states of real metals into the Boltzmann collision terms. From the solution we extract the electron-phonon coupling in thermal nonequilibrium.
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...
Energy Technology Data Exchange (ETDEWEB)
Khurgin, Jacob B., E-mail: jakek@jhu.edu [Johns Hopkins University, Baltimore, Maryland 21208 (United States)
2014-06-02
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.
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.
Khurgin, Jacob B.
2014-06-01
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.
International Nuclear Information System (INIS)
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.
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 photolu...
Non-thermal processes of coherent acoustic phonons generation in semiconductors by femtosecond laser
Ruello, P.; Gusev, V.; Babilotte, P.; Pezeril, T.; Vaudel, G.; Mounier, D.
2012-03-01
Seeking for the new opportunities to efficiently excite GHz-THz coherent acoustic phonons by femtosecond lasers is an active field of research. Several fundamental objectives have to be addressed in order to achieve this acoustic phonons manipulation by femtosecond laser. Among them, the understanding of femtosecond generation of coherent acoustic phonons remains a key route. Several electron-phonon, photon-phonon and phonon-phonon interaction mechanisms are involved in the processes of generation and remain only partially understood up to now. In this paper, we will present a survey of ultrafast photo-generation of coherent acoustic phonon in semiconductors. We will focus first on the generation of the phonons by fs-laser excitation through the photoinduced modifications of nanoscopic internal electric fields (deformation potential) in non-piezo-active [100] GaAs semiconductor. We will show secondly how it is possible to develop more efficient sources by using piezo-active [111], [-1-1-1] and [411] GaAs semiconductors. In that case, generation of GHz acoustic phonon due to inverse piezoelectrical effect is based on ultrafast light-induced screening of the near surface built-in electric field.
Transient phonon vacuum squeezing due to femtosecond-laser-induced bond hardening
Cheenicode Kabeer, Fairoja; Grigoryan, Naira S.; Zijlstra, Eeuwe S.; Garcia, Martin E.
2014-09-01
Ultrashort optical pulses can be used both to create fundamental quasiparticles in crystals and to change their properties. In noble metals, femtosecond lasers induce bond hardening, but little is known about its origin and consequences. Here we simulate ultrafast laser excitation of silver at high fluences. We compute laser-excited potential-energy surfaces by all-electron ab initio theory and analyze the resulting quantum lattice dynamics. We also consider incoherent lattice heating due to electron-phonon interactions using the generalized two-temperature model. We find phonon hardening, which we attribute to the excitation of s electrons. We demonstrate that this may result in phonon vacuum squeezed states with an optimal squeezing factor of ˜0.001 at the L-point longitudinal mode. This finding implies that ultrafast laser-induced bond hardening may be used as a tool to manipulate the quantum state of opaque materials, where, so far, the squeezing of phonons below the zero-point motion has only been realized in transparent crystals by a different mechanism. On the basis of our finding, we further propose a method for directly measuring bond hardening.
Northrop, Gregory Allen
This thesis describes the development of the phonon imaging method. This technique permits the direct measurement of the angular and temporal distribution of phonons emitted from a point source of heat in insulators at low temperatures. It is a derivative of the ballistic heat pulse method, but one which uses a pulsed laser to allow continuous two dimensional scanning of the phonon source. In this work we have applied this method to the following topics: (1) Phonon Focusing. In pure defect-free crystalline insulators, heat pulses may propagate macroscopic distances without scattering. In contrast to diffusive transport of phonons, which is nearly isotropic, the flux of ballistic phonons coming from a heat pulse will display a large anisotropy directly associated with the elastic anisotropy of the crystal. We use phonon imaging to map this anisotropy in Ge, and analyze the data in terms of directions of theoretically singular flux, or singularity lines. (2) Dispersive Phonon Focusing. The shapes of the geometric phonon focusing patterns observed in a ballistic phonon image are independent of phonon frequency in the long wavelength limit. With the aid of a frequency selective detector, which is sensitive only to high frequencies, we observe dispersive shifts in the phonon focusing singularity pattern. The concept of phonon focusing is extended to allow for dispersion, and the results are applied, along with a lattice dynamics model, to predicting the expected singularity shift vs. phonon frequency in Ge. There is good agreement between the images and theory at 800 GHz. (3) Phonon-Dislocation Scattering in LiF. Phonons are known to be strongly scattered by dislocations in LiF and other alkali-halides. We use the phonon imaging method to probe the anisotropy of this scattering cross section in plastically deformed LiF. We measure a strong dependence upon phonon polarization, with a subset of polarizations propagating the length of the sample without scattering. The results fit the coupling anisotropy predicted by the vibrating string model of phonon-dislocation scattering, confirming it as the primary scattering mechanism in this system.
Random laser action in bovine semen
Smuk, Andrei; Lazaro, Edgar; Olson, Leif P.; Lawandy, N. M.
2011-03-01
Experiments using bovine semen reveal that the addition of a high-gain water soluble dye results in random laser action when excited by a Q-switched, frequency doubled, Nd:Yag laser. The data shows that the linewidth collapse of the emission is correlated to the sperm count of the individual samples, potentially making this a rapid, low sample volume approach to count determination.
Zhou, Jun; Li, Nianbei; Yang, Ronggui
2014-01-01
The electrons and phonons in metal films after ultra-short pulse laser heating are in highly non-equilibrium states not only between the electron sub-system and the phonon sub-system but also within the electron sub-system. An electrohydrodynamics model consisting of the balance equations of electron density, energy density of electrons, and energy density of phonons is derived from the coupled non-equilibrium electron and phonon Boltzmann transport equations to study the no...
Temperature performance of terahertz quantum-cascade lasers with resonant-phonon active-regions
International Nuclear Information System (INIS)
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)
Energy Technology Data Exchange (ETDEWEB)
Shimada, Toru [Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin (Germany); Hirosaki University, 1 Bunkyo-cho, Hirosaki, Aomori 036-8152 (Japan); Kamaraju, N., E-mail: nkamaraju@lanl.gov [Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin (Germany); Los Alamos National Laboratory, Center for Integrated Nanotechnologies, Los Alamos, New Mexico 87545 (United States); Frischkorn, Christian [Department of Physics, Free University of Berlin, Arnimallee 14, 14195 Berlin (Germany); Wolf, Martin; Kampfrath, Tobias [Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin (Germany)
2014-09-15
We irradiate a ZnTe single crystal with 10-fs laser pulses at a repetition rate of 80?MHz and investigate its resulting gradual modification by means of coherent-phonon spectroscopy. We observe the emergence of a phonon mode at about 3.6?THz whose amplitude and lifetime grow monotonously with irradiation time. The speed of this process depends sensitively on the pump-pulse duration. Our observations strongly indicate that the emerging phonon mode arises from a Te phase induced by multiphoton absorption of incident laser pulses. A potential application of our findings is laser-machining of microstructures in the bulk of a ZnTe crystal, a highly relevant electrooptic material.
Spin correlations as a probe of quantum synchronization in trapped-ion phonon lasers
Hush, Michael R.; Li, Weibin; Genway, Sam; Lesanovsky, Igor; Armour, Andrew D.
2015-06-01
We investigate quantum synchronization theoretically in a system consisting of two cold ions in microtraps. The ions' motion is damped by a standing-wave laser while also being driven by a blue-detuned laser which results in self-oscillation. Working in a nonclassical regime, where these oscillations contain only a few phonons and have a sub-Poissonian number variance, we explore how synchronization occurs when the two ions are weakly coupled using a probability distribution for the relative phase. We show that strong correlations arise between the spin and vibrational degrees of freedom within each ion and find that when two ions synchronize their spin degrees of freedom in turn become correlated. This allows one to indirectly infer the presence of synchronization by measuring the ions' internal state.
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.
Fathololoumi, S.; Dupont, E.; Wasilewski, Z. R.; Chan, Chun Wang Ivan; Razavipour, S. G.; Laframboise, S. R.; Huang, Shengxi; Hu, Qing; Ban, D.; Liu, H.C.
2013-01-01
We experimentally investigated the effect of oscillator strength (radiative transition diagonality) on the performance of resonant phonon-based terahertz quantum cascade lasers that have been optimized using a simplified density matrix formalism. Our results show that the maximum lasing temperature (T max) is roughly independent of laser transition diagonality within the lasing frequency range of the devices under test (3.2–3.7?THz) when cavity loss is kept low. Furthermore, the threshold cur...
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...
Makovetskii, D N
2004-01-01
Two qualitatively different kinds of resonant destabilization of phonon stimulated emission (SE) are experimentally revealed for periodically forced multimode ruby phaser (phonon laser) operating at SE frequencies about 9 GHz, i.e. at microwave acoustic wavelengths of 1 micron. The inversion state of Cromium(3+) spin-system in ruby was created by electromagnetic pump at 23 GHz. Under deep modulation of pump power at low frequencies OMEGA_m = 70-200 Hz deterministic chaotic reconfigurations of the acoustic microwave power spectra (AMPS) were observed. This range of SE destabilization corresponds to the relaxational resonance that is well known for optical class-B lasers. Outside the relaxational resonance range, namely at ultra-low (infrasonic) frequencies OMEGA_m about 10 Hz, the other type of resonant destabilization of stationary phonon SE was observed by us for the first time. This new nonlinear resonance (we call it lambda-resonance) manifests itself as very slow and periodically repeated self-reconfigura...
Zhou, Jun; Li, Nianbei; Yang, Ronggui
2015-06-01
The electrons and phonons in metal films after ultra-short pulse laser heating are in highly non-equilibrium states not only between the electrons and the phonons but also within the electrons. An electrohydrodynamics model consisting of the balance equations of electron density, energy density of electrons, and energy density of phonons is derived from the coupled non-equilibrium electron and phonon Boltzmann transport equations to study the nonlinear thermal transport by considering the electron density fluctuation and the transient electric current in metal films, after ultra-short pulse laser heating. The temperature evolution is calculated by the coupled electron and phonon Boltzmann transport equations, the electrohydrodynamics model derived in this work, and the two-temperature model. Different laser pulse durations, film thicknesses, and laser fluences are considered. We find that the two-temperature model overestimates the electron temperature at the front surface of the film and underestimates the damage threshold when the nonlinear thermal transport of electrons is important. The electrohydrodynamics model proposed in this work could be a more accurate prediction tool to study the non-equilibrium electron and phonon transport process than the two-temperature model and it is much easier to be solved than the Boltzmann transport equations.
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...
Laser air-jet engine: the action of shock waves at low laser pulse repetition rates
International Nuclear Information System (INIS)
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)
Eye tissue structure and refraction alterations upon nondestructive laser action
Sobol', E. N.; Baum, O. I.; Bol'Shunov, A. V.; Sipliviy, V. I.; Ignat'eva, N. Yu.; Zakharkina, O. L.; Lunin, V. V.; Omel'Chenko, A. I.; Kamenskiy, V. A.; Myakov, A. V.
2006-05-01
A new approach to alterations in eye refraction upon nondestructive laser action on the sclera and cornea is studied. It is demonstrated in in vivo experiments on rabbit eyes that sequential laser irradiation of the sclera and cornea yields a significant alteration in the eye refraction. The collagen structure of the sclera and cornea is studied after the nondestructive laser action with noninvasive polarization-sensitive optical coherence tomography. It is demonstrated that collagen fibers that provide for the cornea tension and applanation partially survive in the zone of the local denaturation of sclera. An irradiation mode that corresponds to an increase in the cornea’s plasticity and does not cause visible structural changes is chosen. The simplest theoretical model for alterations in the eye refraction upon the nonablative laser action on sclera is analyzed. The alteration in the cornea curvature upon stretching resulting from the local sclera coagulation and the corresponding decrease in its volume is calculated. The model makes it possible to approximately estimate the laser irradiation modes that provide the desired alterations in eye refraction.
Phonon engineering for nanostructures.
Energy Technology Data Exchange (ETDEWEB)
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.
Tang, Jau
2008-04-01
In this study, we examine the ultrafast structural dynamics of metals induced by a femtosecond laser-heating pulse as probed by time-resolved electron diffraction. Using the two-temperature model and the Grüneisen relationship we calculate the electron temperature, phonon temperature, and impulsive force at each atomic site in the slab. Together with the Fermi-Pasta-Ulam anharmonic chain model we calculate changes of bond distance and the peak shift of Bragg spots or Laue rings. A laser-heated thin slab is shown to exhibit "breathing" standing-wave behavior, with a period equal to the round-trip time for sound wave and a wavelength twice the slab thickness. The peak delay time first increases linearly with the thickness (stressed bulk atoms due to impulsive forces as well as the linear thermal expansion due to lattice temperature jump are shown to contribute to the overall structural changes. Differences between these two mechanisms and their dependence on film thickness and other factors are discussed.
Textural Properties of Silicon Materials Produced by Laser Action.
Czech Academy of Sciences Publication Activity Database
D?ínek, 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 ?R(CZ) GA104/04/0963; GA ?R(CZ) GD203/03/H140 Institutional research plan: CEZ:AV0Z40720504 Keywords : textural properties * laser action * experiments Subject RIV: CF - Physical ; Theoretical Chemistry
Metal fusion by laser radiation action in an oxidizing medium
International Nuclear Information System (INIS)
Interaction of concentrated heat fluxes with metals is found in various scientific and technological applications. In previous studies the process of laser heating of a massive copper target in an oxidizing atmosphere was considered. In this situation an oxide film was formed on the irradiated metal surface, which leads to an intense change in the absorption capability of the target. In the models considered the temperatures were limited to values below the fusion point of copper. In the present study the investigation of laser radiation interaction with a two layer oxide-metal system will be extended in temperature through the point of target fusion to the point of commencement of fusion of the zirconium dioxide layer using the example of zirconium. Results are presented from a calculation of fusion of a massive zirconium plate under the action of laser radiation with consideration of simultaneous surface oxidation. 8 refs., 2 figs
Self-Action of Laser Radiation in Cluster Plasma
International Nuclear Information System (INIS)
We have analytically and numerically studied the self-action dynamics of laser radiation in a plasma with ionized gas clusters. Based on the simplified model of a cluster in the form of a superposition of two charged (electron and ion) bunches, we analyze the nonlinearity mechanisms. We refine the electrodynamic cluster model by the molecular dynamics method. The polarization behavior of the plasma bunch in the main part of the laser pulse is shown to be the same as that in the simplified model. We investigate the self-action dynamics of laser radiation under conditions when the nonlinearity of the stratified medium is determined by the anharmonicity of the electron motion in the cluster, while the group velocity dispersion is determined by both the background plasma and the ionized clusters. Since the characteristic field for the electron nonlinearity depends strongly on the cluster size, the peculiarities of the self-action dynamics result from plasma bunch expansion. The spatiotemporal evolution of the wave field is shown to be accompanied by pulse self-compression near the trailing edge
International Nuclear Information System (INIS)
Experimental evidence is presented for the laser excitation of true eigenstates in molecules. The theoretical treatment and the experimental findings on thermal broadening of electronic resonances which result in the loss of ''identity'' of molecular states are discussed, and it is shown that vibrational relaxation and magnetic field induced couplings depend crucially on the preparation of the state
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...
Bévillon, E.; Colombier, J. P.; Recoules, V.; Stoian, R.
2014-03-01
The electronic behavior of various solid metals (Al, Ni, Cu, Au, Ti, and W) under ultrashort laser irradiation is investigated by means of density functional theory. Successive stages of extreme nonequilibrium on picosecond time scale impact the excited material properties in terms of optical coupling and transport characteristics. As these are generally modelled based on the free-electron classical theory, the free-electron number is a key parameter. However, this parameter remains unclearly defined and dependencies on the electronic temperature are not considered. Here, from first-principles calculations, density of states are obtained with respect to electronic temperatures varying from 10-2 to 105 K within a cold lattice. Based on the concept of localized or delocalized electronic states, temperature dependent free-electron numbers are evaluated for a series of metals covering a large range of electronic configurations. With the increase of the electronic temperature we observe strong adjustments of the electronic structures of transition metals. These are related to variations of electronic occupation in localized d bands, via change in electronic screening and electron-ion effective potential. The electronic temperature dependence of nonequilibrium density of states has consequences on electronic chemical potentials, free-electron numbers, electronic heat capacities, and electronic pressures. Thus electronic thermodynamic properties are computed and discussed, serving as a base to derive energetic and transport properties allowing the description of excitation and relaxation phenomena caused by rapid laser action.
Mannarelli, Massimo
2013-01-01
We analyze the effect of restricted geometries on the contribution of Nambu-Goldstone bosons (phonons) to the shear viscosity, $\\eta$, of a superfluid. For illustrative purpose we examine a simplified system consisting of a circular boundary of radius $R$, confining a two-dimensional rarefied gas of phonons. Considering the Maxwell-type conditions, we show that phonons that are not in equilibrium with the boundary and that are not specularly reflected exert a shear stress on the boundary. In this case it is possible to define an effective (ballistic) shear viscosity coefficient $\\eta \\propto \\rho_{\\rm ph} \\chi R$, where $\\rho_{\\rm ph}$ is the density of phonons and $\\chi$ is a parameter which characterizes the type of scattering at the boundary. For an optically trapped superfluid our results corroborate the findings of Refs. \\cite{Mannarelli:2012su, Mannarelli:2012eg}, which imply that at very low temperature the shear viscosity correlates with the size of the optical trap and decreases with decreasing tempe...
Laser device for the protection of biological objects from the damaging action of ionizing radiation
International Nuclear Information System (INIS)
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 ?-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 ?- rays and the combined action of laser radiation and ? -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)
Laser light: its nature and its action on the eye.
Bessette, F M; Nguyen, L C
1989-01-01
Lasers produce a coherent, focused, monochromatic, high-energy form of light. Because laser surgery is more versatile and precise and is freer of complications than conventional surgery it has become widely accepted in ophthalmology over the past 10 years. Applications range from routine procedures in the fundus to recent, more delicate interventions in the cornea. The argon laser is the most widely used to treat extrafoveal chorioretinal diseases such as age-related macular degeneration and ...
Energy Technology Data Exchange (ETDEWEB)
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 ? 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.
Phonon manipulation with phononic crystals.
Energy Technology Data Exchange (ETDEWEB)
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 factor. In addition, the techniques and scientific understanding developed in the research can be applied to a wide range of materials, with the caveat that the thermal conductivity of such a material be dominated by phonon, rather than electron, transport. In particular, this includes several thermoelectric materials with attractive properties at elevated temperatures (i.e., greater than room temperature), such as silicon germanium and silicon carbide. It is reasonable that phononic crystal patterning could be used for high-temperature thermoelectric devices using such materials, with applications in energy scavenging via waste-heat recovery and thermoelectric cooling for high-performance microelectronic circuits. The only part of the ZT picture missing in this work was the experimental measurement of the Seebeck coefficient of our phononic crystal devices. While a first-order approximation indicates that the Seebeck coefficient should not change significantly from that of bulk silicon, we were not able to actually verify this assumption within the timeframe of the project. Additionally, with regards to future high-temperature applications of this technology, we plan to measure the thermal conductivity reduction factor of our phononic crystals as elevated temperatures to confirm that it does not diminish, given that the nominal thermal conductivity of most semiconductors, including silicon, decreases with temperature above room temperature. We hope to have the opportunity to address these concerns and further advance the state-of-the-art of thermoelectric materials in future projects.
Studies of Phonon Anharmonicity in Solids
Lan, Tian
Today our understanding of the vibrational thermodynamics of materials at low temperatures is emerging nicely, based on the harmonic model in which phonons are independent. At high temperatures, however, this understanding must accommodate how phonons interact with other phonons or with other excitations. We shall see that the phonon-phonon interactions give rise to interesting coupling problems, and essentially modify the equilibrium and non-equilibrium properties of materials, e.g., thermodynamic stability, heat capacity, optical properties and thermal transport of materials. Despite its great importance, to date the anharmonic lattice dynamics is poorly understood and most studies on lattice dynamics still rely on the harmonic or quasiharmonic models. There have been very few studies on the pure phonon anharmonicity and phonon-phonon interactions. The work presented in this thesis is devoted to the development of experimental and computational methods on this subject. Modern inelastic scattering techniques with neutrons or photons are ideal for sorting out the anharmonic contribution. Analysis of the experimental data can generate vibrational spectra of the materials, i.e., their phonon densities of states or phonon dispersion relations. We obtained high quality data from laser Raman spectrometer, Fourier transform infrared spectrometer and inelastic neutron spectrometer. With accurate phonon spectra data, we obtained the energy shifts and lifetime broadenings of the interacting phonons, and the vibrational entropies of different materials. The understanding of them then relies on the development of the fundamental theories and the computational methods. We developed an efficient post-processor for analyzing the anharmonic vibrations from the molecular dynamics (MD) calculations. Currently, most first principles methods are not capable of dealing with strong anharmonicity, because the interactions of phonons are ignored at finite temperatures. Our method adopts the Fourier transformed velocity autocorrelation method to handle the big data of time-dependent atomic velocities from MD calculations, and efficiently reconstructs the phonon DOS and phonon dispersion relations. Our calculations can reproduce the phonon frequency shifts and lifetime broadenings very well at various temperatures. To understand non-harmonic interactions in a microscopic way, we have developed a numerical fitting method to analyze the decay channels of phonon-phonon interactions. Based on the quantum perturbation theory of many-body interactions, this method is used to calculate the three-phonon and four-phonon kinematics subject to the conservation of energy and momentum, taking into account the weight of phonon couplings. We can assess the strengths of phonon-phonon interactions of different channels and anharmonic orders with the calculated two-phonon DOS. This method, with high computational efficiency, is a promising direction to advance our understandings of non-harmonic lattice dynamics and thermal transport properties. These experimental techniques and theoretical methods have been successfully performed in the study of anharmonic behaviors of metal oxides, including rutile and cuprite stuctures, and will be discussed in detail in Chapters 4 to 6. For example, for rutile titanium dioxide (TiO2), we found that the anomalous anharmonic behavior of the B1g mode can be explained by the volume effects on quasiharmonic force constants, and by the explicit cubic and quartic anharmonicity. For rutile tin dioxide (SnO2), the broadening of the B2 g mode with temperature showed an unusual concave downwards curvature. This curvature was caused by a change with temperature in the number of down-conversion decay channels, originating with the wide band gap in the phonon dispersions. For silver oxide (Ag2O), strong anharmonic effects were found for both phonons and for the negative thermal expansion.
Biological Effects of Contact Action of 1470 vs. 810 nm Semiconductor Lasers in vitro
Directory of Open Access Journals (Sweden)
N.A. Schumilova
2015-01-01
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.
Laser action from a sugar-threaded polyrotaxane
Mroz, MM; Perissinotto, S; Virgili, T.; Gigli, G; Salerno, M.; Frampton, MJ; Sforazzini, G; Anderson, HL; Lanzani, G
2009-01-01
We present gain and lasing results from a polyrotaxane consisting of a conjugated polymer (polyfluorene-alt-biphenylene) threaded through sugar macrocycles (? -cyclodextrin). Encapsulation suppresses interchain charge separation, leading to lasing emission not observed in the unthreaded polymer, and enlargement of the stimulated emission in threaded polymer is observed. We demonstrate all-optical switching distributed feedback laser. © 2009 American Institute of Physics.
Plasma and shock generation by indirect laser pulse action.
Czech Academy of Sciences Publication Activity Database
Kasperzcuk, A.; Borodziuk, S.; Demchenko, N. N.; Gus´kov, S.Y.; Jungwirth, Karel; Kálal, M.; Králiková, Božena; Krouský, Eduard; Limpouch, Ji?í; Mašek, Karel; Pisarczyk, P.; Pisarczyk, T.; Pfeifer, Miroslav; Rohlena, Karel; Rozanov, V. B.; Skála, Ji?í; Ullschmied, Ji?í
Melville : American Institut of Physics, 2005 - (Sadowski, M.; Dudeck, M.; Hartfus, H.; Pawelec, E.), s. 283-286 ISBN 0-7354-0304-X. ISSN 0094-243X. - (AIP Conference Proceedings. 812). [PLASMA 2005. Opole-Turawa (PL), 06.09.2005-09.09.2005] R&D Projects: GA MŠk(CZ) LC528 Grant ostatní: EC - LASERLAB-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
First principles of phonon squeezing in silicon
Energy Technology Data Exchange (ETDEWEB)
Zier, Tobias; Zijlstra, Eeuwe S.; Garcia, Martin E. [Theoretische Physik, Universitaet Kassel, Heinrich-Plett-Str. 40, 34132 Kassel (Germany)
2011-07-01
When silicon is excited by an intense ultrashort laser pulse, an extreme nonequilibrium state is induced, which consists of hot electrons (several 1000 K) and cold ions (near room temperature). The excited carriers change the potential energy surface seen by the ions, leading to a softening of the phonon modes and phonon squeezing. On the basis of density functional theory we perform a study of these effects, treating the phonons both quantum mechanically and classically, including anharmonic effects in the latter case by means of large-scale molecular dynamics simulations. Our results indicate that the initial ionic temperature before the laser excitation should not exceed approximately 77 K in order to observe quantum effects. At higher temperatures the anharmonicities amplify the classical phonon squeezing and cannot be ignored.
Ashkenazi, J.; Dacorogna, M.
1981-01-01
By using stationarity properties within the finite temperature density functional approach, it is shown that the calculation of phonons and electron-phonon coupling processes can be based on the coupling between renormalized "bare" phonons and the HRS one-electron system, under the condition that the potential remains "frozen". This explains the success of calculations of phonon anomalies and electron-phonon coupling parameters in transition metals which were based on rigidly moving potential...
Study of Phonon Modes in Germanium Nanowires
Wang, Xi; Shakouri, Ali; Yu, Bin; Sun, Xuhui; Meyyappan, Meyya
2007-01-01
The observation of pure phonon confinement effect in germanium nanowires is limited due to the illumination sensitivity of Raman spectra. In this paper we measured Raman spectra for different size germanium nanowires with different excitation laser powers and wavelengths. By eliminating the local heating effect, the phonon confinement effect for small size nanowires was clearly identified. We have also fitted the Raman feature changes to estimate the size distribution of nan...
Study of Phonon Modes in Germanium Nanowires
Wang, X; Shakouri, A; Sun, X; Yu, B; Meyyappan, Meyya; Shakouri, Ali; Sun, Xuhui; Wang, Xi; Yu, Bin
2007-01-01
The observation of pure phonon confinement effect in germanium nanowires is limited due to the illumination sensitivity of Raman spectra. In this paper we measured Raman spectra for different size germanium nanowires with different excitation laser powers and wavelengths. By eliminating the local heating effect, the phonon confinement effect for small size nanowires was clearly identified. We have also fitted the Raman feature changes to estimate the size distribution of nanowires for the first time.
Control of generation regimes of ring chip laser under the action of the stationary magnetic field
International Nuclear Information System (INIS)
We consider realisation of different generation regimes in an autonomous ring chip laser, which is a rather complicated problem. We offer and demonstrate a simple and effective method for controlling the radiation dynamics of a ring Nd:YAG chip laser when it is subjected to a stationary magnetic field producing both frequency and substantial amplitude nonreciprocities. The amplitude and frequency nonreciprocities of a ring cavity, arising under the action of this magnetic field, change when the magnet is moved with respect to the active element of the chip laser. Some self-modulation and stationary generation regimes as well as the regime of beatings and dynamic chaos regime are experimentally realised. Temporal and spectral characteristics of radiation are studied and conditions for the appearance of the generation regime are found. (control of laser radiation parameters)
Manipulation of Phonons with Phononic Crystals
Energy Technology Data Exchange (ETDEWEB)
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.
Frequency stabilization of the zero-phonon line of a quantum dot via phonon-assisted active feedback
Energy Technology Data Exchange (ETDEWEB)
Hansom, Jack; Schulte, Carsten H. H.; Matthiesen, Clemens; Stanley, Megan J.; Atatüre, Mete [Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE (United Kingdom)
2014-10-27
We report on the feedback stabilization of the zero-phonon emission frequency of a single InAs quantum dot. The spectral separation of the phonon-assisted component of the resonance fluorescence provides a probe of the detuning between the zero-phonon transition and the resonant driving laser. Using this probe in combination with active feedback, we stabilize the zero-phonon transition frequency against environmental fluctuations. This protocol reduces the zero-phonon fluorescence intensity noise by a factor of 22 by correcting for environmental noise with a bandwidth of 191?Hz, limited by the experimental collection efficiency. The associated sub-Hz fluctuations in the zero-phonon central frequency are reduced by a factor of 7. This technique provides a means of stabilizing the quantum dot emission frequency without requiring access to the zero-phonon emission.
International Nuclear Information System (INIS)
Structural features of the laser radiation self-focusing dynamics in the electromagnetic induced transparency (EIT) band are studied for an atomic system with a ?-type energy level diagram. Effective nonlinearity of an EIT medium is manifested primarily as nonlinear dispersion (dependence of the group velocity on the wave amplitude). Qualitative analysis of the dynamics of self-action of laser pulses, which is confirmed by numerical simulation, shows that nonlinear evolution of a 3D wave packet follows the scenario of self-focusing, which serves as the background on which the envelope profile turnover and the formation of a shock wave occur at an advanced rate
Zharova, N. A.; Litvak, A. G.; Mironov, V. A.
2007-11-01
Structural features of the laser radiation self-focusing dynamics in the electromagnetic induced transparency (EIT) band are studied for an atomic system with a ?-type energy level diagram. Effective nonlinearity of an EIT medium is manifested primarily as nonlinear dispersion (dependence of the group velocity on the wave amplitude). Qualitative analysis of the dynamics of self-action of laser pulses, which is confirmed by numerical simulation, shows that nonlinear evolution of a 3D wave packet follows the scenario of self-focusing, which serves as the background on which the envelope profile turnover and the formation of a shock wave occur at an advanced rate.
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...
Lanthanide and actinide lasers
International Nuclear Information System (INIS)
Stimulated emission has now been observed from twelve lanthanide ions and one actinide ion. Host media have included crystalline and amorphous solids, metallo-organic and inorganic aprotic liquids, and metal and molecular vapors. Laser action spans a spectral range from approximately 0.3 to 4.0 ?m and involves electronic and phonon-assisted 4f-4f, 5d-4f, and 5f-5f transitions. The lanthanides have enjoyed their greatest utilization in optically-pumped solid-state lasers; sizes range from thin films and small fibers for integrated optics applications to large rods and disks in high-power glass lasers for fusion experiments. The spectroscopic properties which distinguish the operation of lanthanide and actinide lasers in various hosts are reviewed. Recent results and possible future directions to exploit the unique characteristics of lanthanide and actinide elements for lasers are also discussed. 120 references, 7 figures, 4 tables
Phonon counting and intensity interferometry of a nanomechanical resonator
Cohen, Justin D; MacCabe, Gregory S; Groblacher, Simon; Safavi-Naeini, Amir H; Marsili, Francesco; Shaw, Matthew D; Painter, Oskar
2014-01-01
Using an optical probe along with single photon detection we have performed effective phonon counting measurements of the acoustic emission and absorption processes in a nanomechanical resonator. Applying these measurements in a Hanbury Brown and Twiss set-up, phonon correlations of the nanomechanical resonator are explored from below to above threshold of a parametric instability leading to self-oscillation of the resonator. Discussion of the results in terms of a "phonon laser", and analysis of the sensitivity of the phonon counting technique are presented.
DYE LASER SOURCE OF MONOCHROMATIC UV-B AND UV-C RADIATIONS FOR BIOLOGICAL ACTION SPECTROSCOPY
The authors have used a flashlamp driven tunable dye laser as a radiation source for observing UV-C and UV-B action spectra of two eukaryotic microorganisms. The general nature of the irradiation system and various operating parameters are described. The laser produces the high p...
Coherent phonon-induced optical modulation in semiconductors at terahertz frequencies
International Nuclear Information System (INIS)
The coherent modulation of electronic and vibrational nonlinearities in atoms and molecular gases by intense few-cycle pulses has been used for high-harmonic generation in the soft x-ray and attosecond regime, as well as for Raman frequency combs that span multiple octaves from the terahertz to petahertz frequency regions. In principle, similar high-order nonlinear processes can be excited efficiently in solids and liquids on account of their high nonlinear polarizability densities. In this paper, we demonstrate the phononic modulation of the optical index of Si and GaAs for excitation and probing near their direct band gaps, respectively at ?3.4 and ?3.0 eV. The large amplitude coherent longitudinal optical (LO) polarization due to the excitation of LO phonons of Si (001) and LO phonon–plasmon coupled modes in GaAs (001) excited by 10 fs laser pulses induces effective amplitude and phase modulation of the reflected probe light. The combined action of the amplitude and phase modulation in Si and GaAs generates phonon frequency combs with more than 100 and 60 THz bandwidth, respectively. (paper)
Ultrafast optical generation of coherent phonons in CdTe1-xSex quantum dots
Bragas, A V; Costantino, S; Ingale, A; Zhao, J; Merlin, R; Ingale, Alka
2003-01-01
We report on the impulsive generation of coherent optical phonons in CdTe0.68Se0.32 nanocrystallites embedded in a glass matrix. Pump probe experiments using femtosecond laser pulses were performed by tuning the laser central energy to resonate with the absorption edge of the nanocrystals. We identify two longitudinal optical phonons, one longitudinal acoustic phonon and a fourth mode of a mixed longitudinal-transverse nature. The amplitude of the optical phonons as a function of the laser central energy exhibits a resonance that is well described by a model based on impulsive stimulated Raman scattering. The phases of the coherent phonons reveal coupling between different modes. At low power density excitations, the frequency of the optical coherent phonons deviates from values obtained from spontaneous Raman scattering. This behavior is ascribed to the presence of electronic impurity states which modify the nanocrystal dielectric function and, thereby, the frequency of the infrared-active phonons.
Jäger, J. V.; Scherbakov, A. V.; Glavin, B. A.; Salasyuk, A. S.; Campion, R. P.; Rushforth, A. W.; Yakovlev, D. R.; Akimov, A. V.; Bayer, M.
2015-01-01
We realize resonant driving of the magnetization precession by monochromatic phonons in a thin ferromagnetic layer embedded into a phononic Fabry-Perot resonator. A femtosecond laser pulse excites resonant phonon modes of the structure in the 10-40 GHz frequency range. By applying an external magnetic field, we tune the precession frequency relative to the frequency of the phonons localized in the cavity and observe the enormous increase in the amplitude of the magnetization...
Phonon-phonon interactions in transition metals
Chaput, Laurent; Togo, Atsushi; Tanaka, Isao; Hug, Gilles
2011-01-01
In this paper the phonon self energy produced by anharmonicity is calculated using second order many body perturbation theory for all bcc, fcc and hcp transition metals. The symmetry properties of the phonon interactions are used to obtain an expression for the self energy as a sum over irreducible triplets, very similar to integration in the irreducible part of the Brillouin zone for one particle properties. The results obtained for transition metals shows that the lifetime...
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.
International Nuclear Information System (INIS)
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)
Self-action of laser radiation in the conditions of electromagnetic induced transparence
International Nuclear Information System (INIS)
The peculiarities of the laser radiation self-action dynamics in the band of the electromagnetic induced transparence (EIT) in the atoms gas with the energy levels ?-scheme are analytically and numerically studied. The self-consistent equations system, describing the spatial-time evolution of the finite amplitude wave packet in the field of the feed-up uniform wave, is obtained. The peculiarities of the self-action in the considered system, connected with the competition of the radiation diffraction, nonlinear dispersion and absorption in the medium are qualitatively analyzed; in particular, the conditions of the experimental wave beam self-focusing are determined. The results of the accomplished consideration are confirmed by the numerical modeling of the wave packets spatial-time evolution
Phonon-dislocation interaction
International Nuclear Information System (INIS)
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
Action of UV excimer laser radiation and fast neutrons on DNA and chromatin proteins of tumour cells
International Nuclear Information System (INIS)
We studied the action on DNA and chromatin proteins from Walker rat tumours of a laser radiation with ? = 248 nm, from an excimer laser, model 1701 - Physical Institute Moscow (0.5-3 MJ/m2 doses) and of a fast neutron beam, produced at the IAP Cyclotron in Bucharest (d(13 MeV) + Be thick target) (5-100 Gy doses). The DNA modifications were established by thermal transitions and by fluorescence properties of complexes with ethidium bromide. The action on chromatin proteins was evaluated by intrinsic fluorescence and by gel electrophoresis. The modifications produced are dose dependent and characteristic of laser radiation and fast neutrons. The complex action includes: the production of DNA strand breaks, protein destruction and chromatin conformation modifications. (Author)
Osychenko, A. A.; Zalesskii, A. D.; Krivokharchenko, A. S.; Zhakhbazyan, A. K.; Ryabova, A. V.; Nadtochenko, V. A.
2015-05-01
Using the method of femtosecond laser surgery we study the fusion of two-cell mouse embryos under the action of tightly focused femtosecond laser radiation with the fusion efficiency reaching 60%. The detailed statistical analysis of the efficiency of blastomere fusion and development of the embryo up to the blastocyst stage after exposure of the embryos from different mice to a femtosecond pulse is presented. It is shown that the efficiency of blastocyst formation essentially depends on the biological characteristics of the embryo, namely, the strain and age of the donor mouse. The possibility of obtaining hexaploid embryonal cells using the methods of femtosecond laser surgery is demonstrated.
Phonon conduction in superlattices
Saini, Richa; Ashokan, Vinod; Indu, B. D.
2015-06-01
The lattice thermal conductivity of InAs/AlSb superlattices is investigated on the basis of modified Callaway model, which successfully explains the inadequacies of Matthiessen's rule. In the new formulation, the relaxation times of various contributing processes have been observed in terms of line widths. The evaluation of line widths is carried out by double time temperature dependent Green's function theory, using a comprehensive Hamiltonian which includes the contribution due to electrons, phonons, impurities, anharmonicities and interactions thereof. The frequency line widths are observed as an extremely sensitive quantity in the transport phenomena of superlattices, as it depends on large number of scattering events, namely; combined boundary, impurity, phonon-phonon and interference scattering processes. It is observed in the present work that the lattice thermal conductivity of superlattices is much less than that of a bulk sample. This can be attributed due to the reduction of phonon group velocity and strong phonon-phonon interactions, which in turn causes the decrease in relaxation times and phonon conductivity. Also, it is remarkable to note that the present theoretical model is equally application to all quantum well structures.
Characteristics of pulsed laser action due to transitions in barium atoms
Energy Technology Data Exchange (ETDEWEB)
Isaev, A.A.; Lemmerman, G.Yu.; Markova, S.V.; Petrash, G.G.
1979-09-01
Pulsed laser action has been studied at the 1.13- and 1.5-micron lines of the barium atom. A discharge tube 25 mm in diameter and 85 cm in length has been used. The supply power amounted to 2.5 kW at excitation pulse repetition rates of 8 and 13.3 kHz. Average lasing power has been investigated as a function of buffer gas pressure and supply power. Spectral and temporal characteristics have been studied. A maximum average lasing power of 12.5 W has been achieved, the efficiency being 0.5%, whereas the maximum efficiency was as high as 0.72%
International Nuclear Information System (INIS)
We have investigated the processes of excitation and ionisation of monomers and clusters of CF3I, IF2CCOF and Fe(CO)5 molecules under the action of femtosecond laser radiation at the wavelengths of 266, 400 and 800 nm. It is concluded that the nature of the excitation of free molecules and clustered molecules by femtosecond pulses is different. The simulation of the ionisation yield of the objects under study has shown that the multiphoton ionisation is the key mechanism in the case of free molecules, while the field ionisation may play a significant role for clusters, in particular, in the case of ionisation at the wavelength of ? = 800 nm. (interaction of radiation with matter)
Lasing action induced by femtosecond laser filamentation in ethanol flame for combustion diagnosis
Chu, Wei; Li, Helong; Ni, Jielei; Zeng, Bin; Yao, Jinping; Zhang, Haisu; Li, Guihua; Jing, Chenrui; Xie, Hongqiang; Xu, Huailiang; Yamanouchi, Kaoru; Cheng, Ya
2014-03-01
We experimentally demonstrate the generation of lasing action in the laminar ethanol/air flame on an alcohol burner array using femtosecond laser filament excitation. By probing the backward emissions of combustion species, it is found that as the interaction length of the filament in the flame increases, the signal's intensity at the 388 nm band for the B2? -X2? transition of CN increases exponentially, but that at the 474 nm band for A3?g-X'3?u transition of C2 increases linearly. The exponential behavior of the CN emissions is ascribed to amplified spontaneous emission, which opens up a way to overcome the quenching effect of specific species in combustion diagnosis.
Phonon Thermal Conduction in Graphene
Nika, D. L.; Pokatilov, E. P.; Askerov, A. S.; Balandin, A. A.
2008-01-01
We investigated theoretically the phonon thermal conductivity of single layer graphene. The phonon dispersion for all polarizations and crystallographic directions in graphene lattice was obtained using the valence-force field method. The three-phonon Umklapp processes were treated exactly using an accurate phonon dispersion and Brillouin zone, and accouting for all phonon relaxation channels allowed by the momentum and energy conservation laws. The uniqueness of graphene wa...
Coherent acoustic phonons in nanostructures investigated by asynchronous optical sampling
Dekorsy, Thomas; Hudert, Florian; Cerna, Roland; Schaefer, Hanjo; Janke, Christof; Bartels, Albrecht; Köhler, K.; Braun, Stefan; Wiemer, Maik; Mantl, Siegfried
2006-01-01
A new optical pump-probe technique is implemented for the investigation of acoustic phonon dynamics in the GHz to THz frequency range which is based on two asynchronously linked femtosecond lasers. Asynchronous optical sampling (ASOPS) provides the performance of on all-optical oscilloscope and allows us to record optically induced lattice dynamics over nanosecond times with 200 femtoseconds resolution at scan rates of 10 kHz. The generation of coherent acoustic phonons and their propagation ...
Hornreich, R.; Kugler, M.; Shtrikman, S.; Sommers, C.
1997-01-01
We present structures, based on rods, that exhibit phonon band gaps. Structures based on rods made out of segments of different materials have very large gaps or multiple gaps. For homogeneous cylinders smaller gaps exist. Possible applications are discussed.
Perrin, Bernard
2007-06-01
logo.jpg" ALT="Conference logo"/> 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 published in the present proceedings. The traditional topics of this conference series (phonons in superconductors and new materials, lattice dynamics, phonons in glasses and disordered materials, phase transitions, light, neutrons and x-ray inelastic scattering) were still very important in the scientific program but an increasing number of contributions occurred in the fields of coherent phonon generation, phonons in nanoscaled structures and nano/micro thermal phonon transport, expressing the growing involvement of condensed matter physicists in nanosciences. Areas like acoustic solitons and phononic crystals are now well established. Two noteworthy contributions have been brought in the long term quest for an operational SASER : one by Harold De Wijn's group from Utrecht in the classical ruby system and another one by Anthony Kent's group from Nottingham, who used semiconductor nanodevices to realize both an amplifying medium and a cavity. With these semiconductor devices the possibility for engineering, generation and detection of THz acoustic phonons are now imminent. By tradition, a prize is awarded every three years at the International Conference on Phonon Scattering in Condensed Matter to honour a scientist for his outstanding contributions to the field of phonon physics. For this twelfth edition, Humphrey Maris has been honoured for his numerous breakthroughs in the physics of phonons and quantum fluids. According to the words of James Wolfe 'Humphrey Maris has delighted and innovated the members of our phonon community with an entertaining style and challenging wit'. Prizes were also awarded for the best presentations during the poster sessions. The two winners were Peter van Capel from Utrecht, Netherlands, ('Simulations of acoustic soliton-induced chirping of exciton resonances') and Patrick Emery from Lille, France, ('Acoustic attenuation in silica in the 100-250 GHz range using coloured picosecond ultrasonics). Both prizes were o
Phononic and photonic nanostructures
Sotomayor Torres, C. M.
2011-01-01
The Phononic and Photonic nanostructures (P2N) group investigates the interaction of photons, phonons and electrons in nanoscale condensed matter underpinn ed by research in nanofabrication and nanometrology. Its long term aim is to develop new information technology concepts where information processing is achieved with multiple state variables. The P2N group research on nanoscale thermal transport impacts thermal management in nanoelectronics. Similarly, the optical studies of acousti...
Influence of confined acoustic phonons on the Radioelectric field in a Quantum well
Long, Do Tuan; Quang Bau, Nguyen
2015-06-01
The influence of confined acoustic phonons on the Radioelectric field in a quantum well has been studied in the presence of a linearly polarized electromagnetic wave and a laser radiation. By using the quantum kinetic equation for electrons with confined electrons - confined acoustic phonons interaction, the analytical expression for the Radio electric field is obtained. The formula of the Radio electric field contains the quantum number m characterizing the phonons confinement and comes back to the case of unconfined phonons when m reaches to zero. The dependence of the Radio electric field on the frequency of the laser radiation, in case of confined acoustic phonons, is also achieved by numerical method for a specific quantum well AlGaAs/GaAs/AlGaAs. Results show that the Radio electric field has a peak and reaches saturation as the frequency of the laser radiation increases.
Strong Acoustic Phonon Localization in Copolymer-Wrapped Carbon Nanotubes.
Sarpkaya, Ibrahim; Ahmadi, Ehsaneh D; Shepard, Gabriella D; Mistry, Kevin S; Blackburn, Jeffrey L; Strauf, Stefan
2015-06-23
Understanding and controlling exciton-phonon interactions in carbon nanotubes has important implications for producing efficient nanophotonic devices. Here we show that laser vaporization-grown carbon nanotubes display ultranarrow luminescence line widths (120 ?eV) and well-resolved acoustic phonon sidebands at low temperatures when dispersed with a polyfluorene copolymer. Remarkably, we do not observe a correlation of the zero-phonon line width with (13)C atomic concentration, as would be expected for pure dephasing of excitons with acoustic phonons. We demonstrate that the ultranarrow and phonon sideband-resolved emission spectra can be fully described by a model assuming extrinsic acoustic phonon localization at the nanoscale, which holds down to 6-fold narrower spectral line width compared to previous work. Interestingly, both exciton and acoustic phonon wave functions are strongly spatially localized within 5 nm, possibly mediated by the copolymer backbone, opening future opportunities to engineer dephasing and optical bandwidth for applications in quantum photonics and cavity optomechanics. PMID:26039893
PHONONS IN INTRINSIC JOSEPHSON SYSTEMS
International Nuclear Information System (INIS)
Subgap structures in the I-V curves of layered superconductors are explained by the excitation of phonons by Josephson oscillations. In the presence of a magnetic field applied parallel to the layers additional structures due to fluxon motion appear. Their coupling with phonons is investigated theoretically and a shift of the phonon resonances in strong magnetic fields is predicted
PHONONS IN INTRINSIC JOSEPHSON SYSTEMS
Energy Technology Data Exchange (ETDEWEB)
C. PREIS; K. SCHMALZL; ET AL
2000-10-01
Subgap structures in the I-V curves of layered superconductors are explained by the excitation of phonons by Josephson oscillations. In the presence of a magnetic field applied parallel to the layers additional structures due to fluxon motion appear. Their coupling with phonons is investigated theoretically and a shift of the phonon resonances in strong magnetic fields is predicted.
Trigo, Mariano; Reis, David
2014-03-01
In a solid, the elementary excitations of the crystalline lattice (phonons) determine the macroscopic properties such as thermal transport and structural stability. The spectrum of these elementary excitations is normally obtained from inelastic neutron and x-ray scattering near equilibrium conditions, which is a Fourier transform of the spatial and temporal correlations of the system. Recent advances in Free Electron Laser sources provide sufficient flux and time-resolution to explore the dynamics of solids at the fundamental time- and length-scales of the atomic motions. In this talk I will show that by probing phonon correlations by femtosecond diffuse scattering in photoexcited germanium, we were able to obtain the phonon dispersion with extreme frequency and momentum resolution without analyzing the energy of the outgoing photon. I will show that time-dependent coherences are generated when an ultrafast laser pulse slightly quenches the phonon frequencies, generating pairs of correlated phonons at equal and opposite momenta. Using this approach we obtain an extremely high-resolution probe of the excited-state phonon dispersion over large sections of momentum space by a simple Fourier transform.
PHONONS IN AMORPHOUS MATERIALS
Hunklinger, S.
1982-01-01
The study of the propagation of phonons is an important tool to investigate the sometimes unexpected and puzzling dynamic properties of amorphous solids. At first, as a typical example, we shall discuss the acoustic properties of vitreous silica. In the second part of the review emphasis will be given to the anomalous low temperature properties of amorphous materials.
On liberation of anomalous large hydrogen volumes from metals under laser action
International Nuclear Information System (INIS)
Experiments on hydrogen isolation from the metal under laser effect are conducted. The experiments have shown that under the assigned parameters of laser pulse and focusing geometry the quantity of hydrogen, isolated from the samples investigated (titanium and aluminium alloys, steel) grows in a direct proportion to the number of flashes of evaporation laser. 12 refs., 2 figs., 1 tab
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.
Highly efficient surface modification of solids by dual action of XUV/Vis-NIR laser pulses.
Czech Academy of Sciences Publication Activity Database
Mocek, Tomáš; Jakubczak, Krzysztof; Polan, Ji?í; Homer, Pavel; Rus, Bed?ich; Kim, I.J.; Kim, C. M.; Park, S.B.; Kim, T.K.; Lee, G.H.; Nam, C. H.; Chalupský, Jaromír; Hájková, V?ra; Juha, Libor
Dordrecht : Springer, 2009 - (Ciaran, L.; Riley, D.), s. 401-406 ISBN 978-1-4020-9923-6. [International Conference on X-Ray Lasers /11th./. Belfast (GB), 17.08.2008-22.08.2008] R&D Projects: GA ?R GC202/07/J008; GA AV ?R KAN300100702 Institutional research plan: CEZ:AV0Z10100523 Keywords : high-order harmonic generation * material processing * nanopatterning * laser induced periodic surface structures Subject RIV: BH - Optics, Masers, Lasers
Increased laser action in commercial dyes from fluorination regardless of their skeleton
International Nuclear Information System (INIS)
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)
Beller Lectureship: Surface Plasmon Laser Action Near the Surface Plasmon Frequency
Oulton, Rupert F.
2013-03-01
Lasers have recently been scaled in size beyond the diffraction limit of light by using electromagnetic surface excitations of metals. In this talk, I will discuss our approach to constructing surface plasmon (SP) lasers using semiconductor materials and outline potential applications that exploit the strong interaction of nanoscale light with matter. I will also present recent results on room temperature SPs lasers operating near the SP frequency by utilizing Zinc Oxide as a gain material combined with a Silver substrate. Surface plasmon lasers could be the most efficient and compact method of delivering optical energy to the nanoscale. There are two benefits: firstly, the efficiently generated (focused) coherent laser field can be extremely intense; and secondly, vacuum fluctuations within the laser cavity are considerably stronger than in free space. Consequently, SP lasers have the unique ability to drastically enhance both coherent and incoherent light-matter interactions bringing fundamentally new capabilities to bio-sensing, data storage, photolithography and optical communications. While there is a great deal of research to do on SP laser systems, this talk highlights the feasibility of nano-scale light sources and the potential of laser science at the nanoscale.
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.
High efficiency laser action of 1% at. Yb3+:Sc2O3 ceramic.
Czech Academy of Sciences Publication Activity Database
Pirri, A.; Toci, G.; Nikl, Martin; Vannini, M.
2012-01-01
Ro?. 20, ?. 20 (2012), s. 22134-22142. ISSN 1094-4087 Grant ostatní: AV?R(CZ) M100100910 Institutional research plan: CEZ:AV0Z10100521 Keywords : laser materials * solid state lasers * Yb-doped * Sc 2 O 3 Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.546, year: 2012
The effect of far infrared generated nonequilibrium phonons on optical dephasing in LaF3:Pr3+
International Nuclear Information System (INIS)
The emissive properties of fluorescent and laser materials demonstrate a marked dependence on the equilibrium phonon population, in the form of a temperature dependence of the optical linewidths (dephasing time). Under conditions of pulsed excitation a nonequilibrium phonon population an be generated which can effect not only the spectral distribution of the optical emission but also the lifetime of the transition. In this work the effect of dephasing of the 3H4-3P4 transition in LaF3:Pr3+ by a non-equilibrium phonon population is investigated. A nonequilibrium phonon population is generated using far infrared (FIR) radiation to pump a low lying electronic state which can then relax by the emission of resonant phonons. The effect of nonequilibrium phonon populations on the dephasing time in this case the nonequilibrium phonon were generated using resonant optical pumping
Makovetskii, D N
2012-01-01
A problem of self-organized motions in solid-state nonequilibrium media has been studied experimentally using methods of quantum acoustics. Generalized Poincare cross-sections of microwave power spectra (MPS) have been obtained in an optical-wavelengths acoustic laser (paramagnetic phaser) based on ruby crystal. Considerable narrowing of MPS and their autowave-like superslow motion have been observed under conditions of periodical pump modulation beyond the region of the phaser relaxation resonance. Some preliminar experimental results of this work were published in: Solid State Communications, Vol.90, No.8, P.501 (1994). An interpretation of the experimental data see arXiv:1101.0482v1 ; arXiv:cond-mat/0410460v1 ; arXiv:cond-mat/0303188v1 .
Optical Investigations of Powerful Laser Actions on Massive and Flyer Targets
International Nuclear Information System (INIS)
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: ?1 = 1.315 ?m and ?3 0.438 ?m. Two types of targets made of Al were used: single massive targets, and double targets consisting of a foil or disk (6 ?m thick for both cases) placed in front of the massive target part at a distance of 200-500 ?m. Experiments with single massive targets were performed at laser intensities in the range of 1013-1015 W/cm2 by varying the laser beam diameters on the target surface from 70 ?m up to 1200 ?m (i.e. moving the target away from the focus). The double targets were illuminated by laser energies EL = 100-500 J focused always on a diameter of 250 ?m. In all experiments performed the laser pulse duration was equal to 400 ps. 3-frame interferometry was employed to investigate the plasma dynamics through measurements of the electron density distribution time development as well as of the disks and foil fragments velocities. The dimensions and shapes of craters were obtained by crater replica technology and microscopy measurement. The experiments were complemented by a 2-D analytical theory and computer simulations, which helped at interpretation of the results. 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 macroparticle impact were obtained from the measured crater parameters for both the wavelengths of laser radiation
Optical investigations of powerful laser actions on massive and flyer targets
International Nuclear Information System (INIS)
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: ?1 = 1.315 ?m and ?3 0.438 ?m. Two types of targets made of Al were used: single massive targets and double targets consisting of a foil or disk (6 ?m and 11 ?m thick for both cases) placed in front of the massive target at the distance of 200-500 ?m. 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 ?m up to 1200 ?m (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 ?m. 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)
Optical investigation of powerful laser actions on massive and flyer targets.
Czech Academy of Sciences Publication Activity Database
Pisarczyk, T.; Borodziuk, S.; Demchenko, N. N.; Gus´kov, S.Y.; Jungwirth, Karel; Kálal, M.; Kasperzcuk, A.; Králiková, Božena; Krouský, Eduard; Limpouch, Ji?í; Mašek, Karel; Pisarczyk, P.; Pfeifer, Miroslav; Rohlena, Karel; Rozanov, V. B.; Skála, Ji?í; Ullschmied, Ji?í
Melville : American Institut of Physics, 2005 - (Sadowski, M.; Dudeck, M.; Hartfus, H.; Pawelec, E.), 64-71 ISBN 0-7354-0304-X. ISSN 0094-243X. - (AIP Conference Proceedings. 812). [PLASMA 2005. Opole-Turawa (PL), 06.09.2005-09.09.2005] R&D Projects: GA MŠk(CZ) LC528 Grant ostatní: EC - LASERLAB-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
Vasil'chenko, Zh V.; Azharonok, V. V.; Filatova, I. I.; Shimanovich, V. D.; Golubev, V. S.; Zabelin, A. M.
1996-09-01
Emission spectroscopy methods were used in an investigation of thermodynamic parameters of a surface plasma formed by the action of cw CO2 laser radiation of (2-5)×106 W cm-2 intensity on stainless steel in a protective He or Ar atmosphere. The spatiotemporal structure and pulsation characteristics of the plasma plume were used to determine the fields of the plasma electron density and temperature.
Electron - phonon interaction in strongly correlated systems. Acoustical phonon case
International Nuclear Information System (INIS)
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)
Fedorov, A. V.; Martyshkin, D. V.; Fedorov, V. V.
2010-09-01
The temperature dependences and mechanisms of broadening of zero-phonon lines of F+3 (488 nm) and N1 (523 nm) colour centres in LiF crystals are investigated. The results obtained make it possible to determine the quadratic electronic—vibrational coupling constant for N1 colour centres. The experimental data on the spectral hole burning in zero-phonon lines of F+3 and N1 colour centres indicate that the latter are positively charged.
Energy Technology Data Exchange (ETDEWEB)
Farber, D; Chiang, T; Krisch, M; Occelli, F; Schwartz, A; Wall, M; Xu, R; Boro, C
2003-12-17
Plutonium (Pu) is well known to have complex and unique physico-chemical properties [1]. Notably, the pure metal exhibits six solid-state phase transformations with large volume expansions and contractions along the way to the liquid state: {alpha} {yields} {beta} {yields} {gamma} {yields} {delta} {yields} {delta}' {yields} {var_epsilon} {yields} liquid. Unalloyed Pu melts at a relatively low temperature {approx}640 C to yield a higher density liquid than that of the solid from which it melts. Detailed understanding of the properties of plutonium and plutonium-based alloys is critical for the safe handling, utilization, and long-term storage of these important, but highly toxic materials. However, both technical and safety issues have made experimental observations extremely difficult. Phonon dispersion curves (PDCs) are key experimental data to the understanding of the basic properties of Pu materials such as: force constants, sound velocities, elastic constants, thermodynamics, phase stability, electron-phonon coupling, structural relaxation, etc. However, phonon dispersion curves (PDCs) in plutonium (Pu) and its alloys have defied measurement for the past few decades since the discovery of this element in 1941. This is due to a combination of the high thermal-neutron absorption cross section of plutonium and the inability to grow the large single crystals (with dimensions of a few millimeters) necessary for inelastic neutron scattering. Theoretical simulations of the Pu PDC continue to be hampered by the lack of suitable inter-atomic potentials. Thus, until recently the PDCs for Pu and its alloys have remained unknown experimentally and theoretically. The experimental limitations have recently been overcome by using a tightly focused undulator x-ray micro-beam scattered from single-grain domains in polycrystalline specimens. This experimental approach has been applied successfully to map the complete PDCs of an fcc {delta}-Pu-Ga alloy using the high resolution inelastic x-ray scattering (HRIXS) capability on ID28 [2].
Ab initio simulation of coherent phonons in BN-nanotubes
Energy Technology Data Exchange (ETDEWEB)
Bauerhenne, Bernd; Zijlstra, Eeuwe S.; Garcia, Martin E. [Theoretische Physik, Universitaet Kassel, Heinrich-Plett-Str. 40, 34132 Kassel (Germany)
2011-07-01
BN nanotubes are isostructural to carbon nanotubes with boron and nitrogen atoms occupying the even and odd sublattices, respectively. An intense ultrashort laser pulse excites the electronic system to very high temperatures, whereas the ions remain close to their initial state. The ensuing laser-induced processes of electronic origin include bond softening, phonon frequency changes (hardening or softening), and the excitation of coherent phonons. We study these processes by means of large-scale molecular dynamics simulations based on density functional theory, including levels of excitation where the nanotube breaks. Our results show a strong radial breathing mode, increasing in amplitude with the laser-induced electronic temperature. We also determine the damage threshold.
Ab initio simulation of coherent phonons in BN-nanotubes
International Nuclear Information System (INIS)
BN nanotubes are isostructural to carbon nanotubes with boron and nitrogen atoms occupying the even and odd sublattices, respectively. An intense ultrashort laser pulse excites the electronic system to very high temperatures, whereas the ions remain close to their initial state. The ensuing laser-induced processes of electronic origin include bond softening, phonon frequency changes (hardening or softening), and the excitation of coherent phonons. We study these processes by means of large-scale molecular dynamics simulations based on density functional theory, including levels of excitation where the nanotube breaks. Our results show a strong radial breathing mode, increasing in amplitude with the laser-induced electronic temperature. We also determine the damage threshold.
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.
Theory of phonon dynamics in an ion trap
Dutta, T; Sengupta, K
2015-01-01
We develop a theory to address the non-equilibrium dynamics of phonons in a one-dimensional trapped ion system. We elaborate our earlier results obtained in Phys. Rev. Lett. {\\bf 111}, 170406 (2013) to chart out the mechanism of dynamics-induced cooling and entanglement generation between phonons in these systems when subjected to a linear ramp protocol inducing site-specific tuning of on-site interactions between the phonons. We further extend these studies to non-linear ramps and periodic drive protocols and identify the optimal ramp protocol for minimal cooling and entanglement generation time. We qualitatively address the effect of noise arising out of fluctuation of the intensity of the laser used to generate entanglement and provide a detailed discussion of a realistic experimental setup which may serve as a test bed for our theory.
Accelerating piston action and plasma heating in high-energy density laser plasma interactions
Levy, M. C.; Wilks, S. C.; Baring, M. G.
2013-03-01
In the field of high-energy density physics (HEDP), lasers in both the nanosecond and picosecond regimes can drive conditions in the laboratory relevant to a broad range of astrophysical phenomena, including gamma-ray burst afterglows and supernova remnants. In the short-pulse regime, the strong light pressure (>Gbar) associated ultraintense lasers of intensity I > 1018 W/cm2 plays a central role in many HEDP applications. Yet, the behavior of this nonlinear pressure mechanism is not well-understood at late time in the laser-plasma interaction. In this paper, a more realistic treatment of the laser pressure 'hole boring' process is developed through analytical modeling and particle-in-cell simulations. A simple Liouville code capturing the phase space evolution of ponderomotively-driven ions is employed to distill effects related to plasma heating and ion bulk acceleration. Taking into account these effects, our results show that the evolution of the laser-target system encompasses ponderomotive expansion, equipartition, and quasi-isothermal expansion epochs. These results have implications for light piston-driven ion acceleration scenarios, and astrophysical applications where the efficiencies of converting incident Poynting flux into bulk plasma flow and plasma heat are key unknown parameters.
Efficient materials processing by dual action of XUV/Vis-NIR ultrashort laser pulses.
Czech Academy of Sciences Publication Activity Database
Jakubczak, Krzysztof; Mocek, Tomáš; Polan, Ji?í; Homer, Pavel; Rus, Bed?ich; Kim, I.J.; Kim, C. M.; Park, S.B.; Kim, T.K.; Lee, G.H.; Nam, C. H.; Chalupský, Jaromír; Hájková, V?ra; Juha, Libor; Sobota, Jaroslav; Fo?t, Tomáš
Bellingham : SPIE, 2009 - (Juha, L.; Bajt, S.; Sobierajski, R.), 73610A/1-73610A/5 ISBN 9780819476357. ISSN 0277-786x. - (Proceedings of SPIE. 7361). [Damage to VUV, EUV, and X-Ray Optics II. Prague (CZ), 21.04.2009-23.04.2009] R&D Projects: GA AV ?R KAN300100702; GA MŠk LC510; GA MŠk(CZ) LC528; GA MŠk LA08024; GA ?R 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
Bacterial action of carbon dioxide laser radiation in experimental dental root canals
International Nuclear Information System (INIS)
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
Low intensity red laser action on Escherichia coli cultures submitted to stress conditions
International Nuclear Information System (INIS)
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)
International Nuclear Information System (INIS)
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.
International Nuclear Information System (INIS)
Formation of a liquid phase with a transition to a homogeneous amorphous state under the surface layer solidification is detected under picosecond laser pulse effect on the microcrystalline graphite. A periodic surface structure is produced in the heating region with the period of the order of the length of the heating pulse wave, its strokes following the direction of this pulse polarization. Study of the probing laser pulse reflection kinetics has shown, that the typical time of liquid phase and solidification life makes up ? 10-10 s
Anomalous effect of phonon wind on lateral migration of excitons in ultrathin quantum CdTe/ZnTe well
Onishchenko, E E; Zajtsev, V V
2001-01-01
The effect of the acoustic phonons nonequilibrium flux on the photoluminescence of the CdTe/ZnTe thin quantum well, excited quasi-resonantly by the He-Ne-laser is studied. It is established that the phonon flux leads to the change in the form of the quantum well luminescence band even by low generation capacities. It is assumed that the nonequilibrium phonons flux stimulates the excitons migration in the quantum well plane, conditioned by the tunnel transitions between the potential local minima, which are accompanied by the phonons induced emission
Berry Curvature and Phonon Hall Effect
Qin, Tao; Shi, Junren
2012-02-01
We establish the general phonon dynamics of magnetic solids by incorporating the Mead-Truhlar correction in the Born-Oppenheimer approximation. The effective magnetic-field acting on the phonons naturally emerges, giving rise to the phonon Hall effect. A general formula of the intrinsic phonon Hall conductivity is obtained by using the corrected Kubo formula with the energy magnetization contribution properly incorporated. The resulting phonon Hall conductivity is fully determined by the phonon Berry curvature and the dispersions. Based on the formula, the topological phonon system could be rigorously defined. In the low temperature regime, we predict that the phonon Hall conductivity is proportional to T^3 for the ordinary phonon systems, while that for the topological phonon systems has the linear T dependence with the quantized temperature coefficient. [4pt] [1] Tao Qin and Junren Shi, arXiv:1111.1322 (2011) [0pt] [2] Tao Qin, Qian Niu and Junren Shi, Phys. Rev. Lett., Accepted, (2011).
2-D modeling of dual-mode acoustic phonon excitation of a triangular nanoplate
International Nuclear Information System (INIS)
Graphical abstract: Modeling the lattice dynamics of a triangular plate with the arrows indicating the direction of impulsive thermal stress. We investigated ultrafast structural dynamics of triangular nanoplates based on 2-D Fermi-Pasta-Ulam model to explain coherent acoustic phonon excitation in nanoprisms. - Abstract: In this theoretical work, we investigated coherent phonon excitation of a triangular nanoplate based on 2-D Fermi-Pasta-Ulam lattice model. Based on the two-temperature model commonly used in description of laser heating of metals, we considered two kinds of forces related to electronic and lattice stresses. Based on extensive simulation and analysis, we identified two major planar phonon modes, namely, a standing wave mode related to the triangle bisector and another mode corresponding to half of the side length. This work elucidates the roles of laser-induced electronic stress and lattice stress in controlling the initial phase and the amplitude ratio between these two phonon modes.
High efficiency laser action of 1% at. Yb3+:2O3 ceramic.
Pirri, Angela; Toci, Guido; Nikl, Martin; Vannini, Matteo
2012-09-24
We report the spectroscopic characteristics and the laser performances of a low-doped 1% at. Yb:Sc(2)O(3) ceramic sample. Under end- pumping at 933 nm and 968 nm in quasi-CW mode, at 1040.5 nm the laser delivers a maximum output power of 4.3 W and 1.77 W, respectively with a corresponding slope efficiency of 74% and 80%, which are, to the best of our knowledge, the highest value reported in literature for ceramics. We explored the tuning range of the sample, which spans from 1005 nm to 1050.5 nm, and finally we characterized the low losses tunable cavity at 1032 nm. PMID:23037362
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.
Energy Technology Data Exchange (ETDEWEB)
Wong, Joe; Krisch, M.; Farber, D.; Occelli, F.; Schwartz, A.; Chiang, T.C.; Wall, M.; Boro, C.; Xu, Ruqing (UIUC); (LLNL); (ESRF); (LANL)
2010-11-16
Plutonium (Pu) is well known to have complex and unique physico-chemical properties. Notably, the pure metal exhibits six solid-state phase transformations with large volume expansions and contractions along the way to the liquid state: {alpha} {yields} {beta} {yields} {gamma} {yields} {delta} {yields} {delta}{prime} {yields} {var_epsilon} {yields} liquid. Unalloyed Pu melts at a relatively low temperature {approx}640 C to yield a higher density liquid than that of the solid from which it melts, (Figure 1). Detailed understanding of the properties of plutonium and plutonium-based alloys is critical for the safe handling, utilization, and long-term storage of these important, but highly toxic materials. However, both technical and and safety issues have made experimental observations extremely difficult. Phonon dispersion curves (PDCs) are key experimenta l data to the understanding of the basic properties of Pu materials such as: force constants, sound velocities, elastic constants, thermodynamics, phase stability, electron-phonon coupling, structural relaxation, etc. However, phonon dispersion curves (PDCs) in plutonium (Pu) and its alloys have defied measurement for the past few decades since the discovery of this element in 1941. This is due to a combination of the high thermal-neutron absorption cross section of plutonium and the inability to grow the large single crystals (with dimensions of a few millimeters) necessary for inelastic neutron scattering. Theoretical simulations of the Pu PDC continue to be hampered by the lack of suitable inter -atomic potentials. Thus, until recently the PDCs for Pu and its alloys have remained unknown experimentally and theoretically. The experimental limitations have recently been overcome by using a tightly focused undulator x-ray micro-beam scattered from single -grain domains in polycrystalline specimens. This experimental approach has been applied successfully to map the complete PDCs of an fcc d-Pu-Ga alloy using the high resolution inelastic x-ray scattering (HRIXS) capability on ID28. The complete PDCs for an fcc Pu-0.6 wt% Ga alloy are plotted in Figure 2, and represent the first full set of phonon dispersions ever determined for any Pu-bearing materials. The solid curves (red) are calculated using a standard Born-von Karman (B-vK) force constant model. An adequate fit to the experimental data is obtained if interactions up to the fourth-nearest neighbours are included. The dashed curves (blue) are recent dynamical mean field theory (DMFT) results by Dai et al. The elastic moduli calculated from the slopes of the experimental phonon dispersion curves near the {Lambda} point are: C{sub 11} = 35.3 {+-} 1.4 GPa, C{sub 12} = 25.5 {+-} 1.5 GPa and C{sub 44} = 30.53 {+-} 1.1 GPa. These values are in excellent agreement with those of the only other measurement on a similar alloy (1 wt % Ga) using ultrasonic techniques as well as with those recently calculated from a combined DMFT and linear response theory for pure {delta}-Pu. Several unusual features, including a large elastic anisotropy, a small shear elastic modulus C{prime}, a Kohn-like anomaly in the T{sub 1}[011] branch, and a pronounced softening of the [111] transverse modes are found. These features can be related to the phase transitions of plutonium and to strong coupling between the lattice structure and the 5f valence instabilities. The HRIXS results also provide a critical test for theoretical treatments of highly correlated 5f electron systems as exemplified by recent dynamical mean field theory (DMFT) calculations for {delta}-plutonium. The experimental-theoretical agreements shown in Figure 2 in terms of a low shear elastic modulus C{prime}, a Kohn-like anomaly in the T{sub 1}[011] branch, and a large softening of the T[111] modes give credence to the DMFT approach for the theoretical treatment of 5f electron systems of which {delta}-Pu is a classic example. However, quantitative differences remain. These are the position of the Kohn anomaly along the T{sub 1}[011] branch, the energy maximum of the T[111] mode s
International Nuclear Information System (INIS)
Plutonium (Pu) is well known to have complex and unique physico-chemical properties. Notably, the pure metal exhibits six solid-state phase transformations with large volume expansions and contractions along the way to the liquid state: ? ? ? ? ? ? (delta) ? (delta)(prime) ? (varepsilon) ? liquid. Unalloyed Pu melts at a relatively low temperature ?640 C to yield a higher density liquid than that of the solid from which it melts, (Figure 1). Detailed understanding of the properties of plutonium and plutonium-based alloys is critical for the safe handling, utilization, and long-term storage of these important, but highly toxic materials. However, both technical and and safety issues have made experimental observations extremely difficult. Phonon dispersion curves (PDCs) are key experimenta l data to the understanding of the basic properties of Pu materials such as: force constants, sound velocities, elastic constants, thermodynamics, phase stability, electron-phonon coupling, structural relaxation, etc. However, phonon dispersion curves (PDCs) in plutonium (Pu) and its alloys have defied measurement for the past few decades since the discovery of this element in 1941. This is due to a combination of the high thermal-neutron absorption cross section of plutonium and the inability to grow the large single crystals (with dimensions of a few millimeters) necessary for inelastic neutron scattering. Theoretical simulations of the Pu PDC continue to be hampered by the lack of suitable inter -atomic potentials. Thus, until recently the PDCs for Pu and its alloys have remained unknown experimentally and theoretically. The experimental limitations have recently been overcome by using a tightly focused undulator x-ray micro-beam scattered from single -grain domains in polycrystalline specimens. This experimental approach has been applied successfully to map the complete PDCs of an fcc d-Pu-Ga alloy using the high resolution inelastic x-ray scattering (HRIXS) capability on ID28. The complete PDCs for an fcc Pu-0.6 wt% Ga alloy are plotted in Figure 2, and represent the first full set of phonon dispersions ever determined for any Pu-bearing materials. The solid curves (red) are calculated using a standard Born-von Karman (B-vK) force constant model. An adequate fit to the experimental data is obtained if interactions up to the fourth-nearest neighbours are included. The dashed curves (blue) are recent dynamical mean field theory (DMFT) results by Dai et al. The elastic moduli calculated from the slopes of the experimental phonon dispersion curves near the ? point are: C11 = 35.3 ± 1.4 GPa, C12 = 25.5 ± 1.5 GPa and C44 = 30.53 ± 1.1 GPa. These values are in excellent agreement with those of the only other measurement on a similar alloy (1 wt % Ga) using ultrasonic techniques as well as with those recently calculated from a combined DMFT and linear response theory for pure (delta)-Pu. Several unusual features, including a large elastic anisotropy, a small shear elastic modulus C(prime), a Kohn-like anomaly in the T1[011] branch, and a pronounced softening of the [111] transverse modes are found. These features can be related to the phase transitions of plutonium and to strong coupling between the lattice structure and the 5f valence instabilities. The HRIXS results also provide a critical test for theoretical treatments of highly correlated 5f electron systems as exemplified by recent dynamical mean field theory (DMFT) calculations for (delta)-plutonium. The experimental-theoretical agreements shown in Figure 2 in terms of a low shear elastic modulus C(prime), a Kohn-like anomaly in the T1[011] branch, and a large softening of the T[111] modes give credence to the DMFT approach for the theoretical treatment of 5f electron systems of which (delta)-Pu is a classic example. However, quantitative differences remain. These are the position of the Kohn anomaly along the T1[011] branch, the energy maximum of the T[111] mode s and the softening of the calculated T[100] branch near the X point, which is not observed experime
Phonon scattering at siliconcrystal surfaces
Marx, Dieter; Eisenmenger, Wolfgang
1982-01-01
Our observations of the reflection or backscattering of high-frequency phonons (v =280 GHz to 1 THz) at silicon-solid interfaces disagree significantly with predictions from the acoustic mismatch model. Interfaces composed of materials theoretically wellmatched, show high scattering experimentally. In contrast, interfaces theoretically poorly matched, show less phonon scattering than expected. Generally, this is best expressed by the fact that the interface scattering ranges from roughly 30?6...
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
International Nuclear Information System (INIS)
A calculation of the electron-LA phonon scattering contribution for an electron gas under the action of strong magnetic field is performed using memory function formalism. We take into account, through vertex corrections in the diffusive pole approximation, the combined effect due to the presence of impurities in the material, which renormalizes the polarization function. The renormalized electron-phonon interaction is discussed and we calculate, in the low temperature regime, the dependence of the phonon channel resistivity in terms of the strength of magnetic field. (author). 7 refs
Photonic and phononic quasicrystals
Energy Technology Data Exchange (ETDEWEB)
Steurer, Walter; Sutter-Widmer, Daniel [Laboratory of Crystallography, Department of Materials, ETH Zurich, Wolfgang-Pauli-Strasse 10, CH-8093 Zurich (Switzerland)
2007-07-07
This review focuses on the peculiarities of quasiperiodic order for the properties of photonic and phononic (sonic) heterostructures. The most beneficial feature of quasiperiodicity is that it can combine perfectly ordered structures with purely point-diffractive spectra of arbitrarily high rotational symmetry. Both are prerequisites for the construction of isotropic band gap composites, in particular from materials with low index contrast, which are required for numerous applications. Another interesting property of quasiperiodic structures is their scaling symmetry, which may be exploited to create spectral gaps in the sub-wavelength regime. This review covers structure/property relationships of heterostructures based on one-dimensional (1D) substitutional sequences such as the Fibonacci, Thue-Morse, period-doubling, Rudin-Shapiro and Cantor sequence as well as on 1D modulated structures, further on 2D tilings with 8-, 10-, 12- and 14-fold symmetry as well as on the pinwheel tiling, the Sierpinski gasket and on curvilinear tilings and, finally, on the 3D icosahedral Penrose tiling. (topical review)
New Mid-IR Lasers Based on Rare-Earth-Doped Sulfide and Chloride Materials
Energy Technology Data Exchange (ETDEWEB)
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 KPb{sub 2}Cl{sub 5}, predictions indicate that laser operation to 9 {micro}m may be possible, a wavelength previously considered unreachable in a room-temperature, solid-state host.
DEFF Research Database (Denmark)
Nysteen, Anders; Nielsen, Per Kær
2012-01-01
It is well-known that decoherence deteriorates the efficiency of cavity QED systems containing quantum dots (QDs), and that a major contribution stems from the coupling between the electrical carriers in the QD and acoustic phonons [1]. Employing a recently published model [2], we demonstrate how a 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 causes the QD lifetime to be unaffected by phonon processes at specific QD-cavity detunings. Furthermore, as shown in Fig. 2b, a proper choice of the QD wavefunction minimizes the phonon-induced pure dephasing rate, both in terms of the short-time magnitude and the long-time constant value. Furthermore we show, that even for realistic QDs, where We and Wg are determined by the QD shape and material composition, a significant suppression of phonon-induced processes is possible. Thus, more efficient quantum systems may be obtained if the QD wavefunctions are properly matched with the phononic properties of the surroundings.
Studies on nonequilibrium phonons by optical techniques
International Nuclear Information System (INIS)
This paper describes optical techniques of phonon generation and detection and the application for the study of phonon scattering processes. Special emphasis is put on the discussion of high-frequency acoustic phonons in the terahertz frequency range. As important phonon scattering processes, spontaneous decay of acoustic phonons by splitting processes, caused by the crystal anharmonicity, and elastic resonance scattering and inelastic scattering at impurity ions are treated. The optical detection techniques discussed are based on the observation of phonon-induced fluorescence from impurity probe ions
Wave front dislocations appearance under the laser beam self-action in liquid crystal
International Nuclear Information System (INIS)
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
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.
Phonon-induced electrical conductance in semiconductors
Lassmann, Kurt; Burger, Wilfried
1986-01-01
The bath of thermal phonons is a well-known source of impedance to electronic conduction in solids. Turning the tables, a change in electronic conductance may be used for phonon detection, as will be discussed in the following.
Phonon scattering at surfaces and interfaces
Eisenmenger, Wolfgang
1986-01-01
The following report on experiments with frequency-dependent phonon backscattering at differently prepared Si and Al203 surfaces demonstrates the variety of phenomena in phonon backscattering of real surfaces to be explained by appropriate models.
Nanoscale phononic interconnects in THz frequencies.
Sgouros, Aris P; Neupane, Mahesh R; Sigalas, M M; Aravantinos-Zafiris, N; Lake, Roger K
2014-11-14
Phononic computing is emerging as an alternative computing paradigm to the conventional electronic and optical computing. In this study, we propose and analyze various phononic interconnects, such as nano-scaled phononic resonators, waveguides and switches, on the ?111? surface of 3C-SiC and 3C-GeSi with substitutional and vacancy defects. This is achieved by simultaneously introducing defects of various types, and by varying their specific locations on the surface. To calculate the intrinsic and the defect-induced vibrational properties, such as the phononic bandgap and the variation in the phonon spectra, the total phonon density of states (TPDOS) and the partial phonon density of states (PPDOS) were calculated using molecular dynamics simulations with semi-empirical potentials. The proposed phononic interconnects, in conjunction with electronic and/or photonic interconnects, can be used in the current and future devices. PMID:25260120
Ultrafast electron-phonon decoupling in graphite
Ishioka, Kunie; Hase, Muneaki; Kitajima, Masahiro; Wirtz, Ludger; Rubio Secades, Ángel; Petek, Hrvoje
2008-01-01
We report the ultrafast dynamics of the 47.4 THz coherent phonons of graphite interacting with a photoinduced non-equilibrium electron-hole plasma. Unlike conventional materials, upon photoexcitation the phonon frequency of graphite upshifts, and within a few picoseconds relaxes to the stationary value. Our first-principles density functional calculations demonstrate that the phonon stiffening stems from the light-induced decoupling of the non-adiabatic electron-phonon inter...
Phononic crystals and acoustic metamaterials
Directory of Open Access Journals (Sweden)
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.
Introduction to phonons and electrons
Lou, Liang-fu
2003-01-01
This book focuses on phonons and electrons, which the student needs to learn first in solid state physics. The required quantum theory and statistical physics are derived from scratch. Systematic in structure and tutorial in style, the treatment is filled with detailed mathematical steps and physical interpretations. This approach ensures a self-sufficient content for easier teaching and learning. The objective is to introduce the concepts of phonons and electrons in a more rigorous and yet clearer way, so that the student does not need to relearn them in more advanced courses. Examples are th
Phonon drag in ballistic quantum wires
Muradov, M. I.
2001-01-01
The acoustic phonon-mediated drag-contribution to the drag current created in the ballistic transport regime in a one-dimensional nanowire by phonons generated by a current-carrying ballistic channel in a nearby nanowire is calculated. The threshold of the phonon-mediated drag current with respect to bias or gate voltage is predicted.
Ab initio calculations of phonon dispersion and lattice dynamics in TlGaTe2
International Nuclear Information System (INIS)
This work reports the results of DFT-based calculations of phonon spectra of TlGaTe2. 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)
Wang, Cih-Su; Liau, Chi-Shung; Sun, Tzu-Ming; Chen, Yu-Chia; Lin, Tai-Yuan; Chen, Yang-Fang
2015-03-01
A new approach is proposed to light up band-edge stimulated emission arising from a semiconductor with dipole-forbidden band-gap transition. To illustrate our working principle, here we demonstrate the feasibility on the composite of SnO2 nanowires (NWs) and chicken albumen. SnO2 NWs, which merely emit visible defect emission, are observed to generate a strong ultraviolet fluorescence centered at 387 nm assisted by chicken albumen at room temperature. In addition, a stunning laser action is further discovered in the albumen/SnO2 NWs composite system. The underlying mechanism is interpreted in terms of the fluorescence resonance energy transfer (FRET) from the chicken albumen protein to SnO2 NWs. More importantly, the giant oscillator strength of shallow defect states, which is served orders of magnitude larger than that of the free exciton, plays a decisive role. Our approach therefore shows that bio-materials exhibit a great potential in applications for novel light emitters, which may open up a new avenue for the development of bio-inspired optoelectronic devices.
Electron and phonon correlations in systems of one-dimensional electrons coupled to phonons
Chen, Leiming
2008-01-01
Electron and phonon correlations in systems of one-dimensional electrons coupled to phonons are studied at low temperatures by emphasizing on the effect of electron-phonon backward scattering. It is found that the $2k_F$-wave components of the electron density and phonon displacement field share the same correlations. Both correlations are quasi-long-ranged for a single conducting chain coupled to one-dimensional or three-dimensional phonons, and they are long-ranged for rep...
Bykovskii, N. E.; Zavedeev, E. V.; Senatskii, Yu. V.
2015-04-01
Craters on the surface of an yttrium-aluminum garnet crystal plate under irradiation by nanosecond laser pulses with an intensity of 109-1010 W/cm2 and a wide (˜500Å) spectrum have been studied. The mechanism of crater formation as a result of plastic deformation of the surface during the laser action has been discussed. The proposed mechanism takes into account specific features of nonlinear effects under the action of a broadband radiation on the medium. In the stimulated Brillouin scattering of pumping radiation, acoustic waves transform into shock waves, on the fronts of which stimulated Raman scattering develops. As a result, crystal lattice defects formed on the shock-wave fronts are dragged in the direction of pumping, which leads to a high-rate deformation of the crystal surface.
Yoctocalorimetry: phonon counting in nanostructures
Roukes, M.L.
1998-01-01
It appears feasible with nanostructures to perform calorimetry at the level of individual thermal phonons. Here I outline an approach employing monocrystalline mesoscopic insulators, which can now be patterned from semiconductor heterostructures into complex geometries with full, three- dimensional relief. Successive application of these techniques also enables definition of integrated nanoscale thermal transducers; coupling these to a dc SQUID readout yields the requisite e...
Sound and heat revolutions in phononics
Maldovan, Martin
2013-11-01
The phonon is the physical particle representing mechanical vibration and is responsible for the transmission of everyday sound and heat. Understanding and controlling the phononic properties of materials provides opportunities to thermally insulate buildings, reduce environmental noise, transform waste heat into electricity and develop earthquake protection. Here I review recent progress and the development of new ideas and devices that make use of phononic properties to control both sound and heat. Advances in sonic and thermal diodes, optomechanical crystals, acoustic and thermal cloaking, hypersonic phononic crystals, thermoelectrics, and thermocrystals herald the next technological revolution in phononics.
Nonlinear phononics using atomically thin membranes
Midtvedt, Daniel; Isacsson, Andreas; Croy, Alexander
2014-09-01
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.
International Nuclear Information System (INIS)
The effects of nanocavities embedded in a narrow constriction on ballistic phonon transport in a semiconductor nanowire are investigated. It is shown that when more than one nanocavity is embedded in a narrow constriction with a fixed length, the nanowire has selective transmission and filter actions for the ballistic phonon. The number of resonant transmission peaks increases with the number n of cavities, while the frequencies of the main peaks are independent of n. The thermal conductance can be enhanced significantly, and the enhancement alters in different temperature ranges with the number n of cavities, depending on the competition between the transmission enhancement and scatter enhancement of the ballistic phonon. This structure may be a promising candidate for selective frequency generator and filter for the ballistic phonon in nanophononics.
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.
The graphene phonon dispersion with C{sup 12} and C{sup 13} isotopes
Energy Technology Data Exchange (ETDEWEB)
Whiteway, Eric; Bernard, Simon; Yu, Victor; Hilke, Michael [Department of Physics, McGill University, Montréal H3A 2T8 (Canada); Austing, D. Guy [National Research Council of Canada, Ottawa, Ontario K1A 0R6 (Canada)
2013-12-04
Using very uniform large scale chemical vapor deposition grown graphene transferred onto silicon, we were able to identify 15 distinct Raman lines associated with graphene monolayers. This was possible thanks to a combination of different carbon isotopes and different Raman laser energies and extensive averaging without increasing the laser power. This allowed us to obtain a detailed experimental phonon dispersion relation for many points in the Brillouin zone. We further identified a D+D' peak corresponding to a double phonon process involving both an inter- and intra-valley phonon. In order to both eliminate substrate effects and to probe large areas, we undertook to study Raman scattering for large scale chemical vapor deposition (CVD) grown graphene using two different isotopes (C12 and C13) so that we can effectively exclude and subtract the substrate contributions, since a heavier mass downshifts only the vibrational properties, while keeping all other properties the same.
Piezoelectric surface acoustical phonon amplification in graphene on a GaAs substrate
Energy Technology Data Exchange (ETDEWEB)
Nunes, O. A. C., E-mail: oacn@unb.br [Institute of Physics, University of Brasilia, Brasilia, 70910-900 DF (Brazil)
2014-06-21
We study the interaction of Dirac Fermions in monolayer graphene on a GaAs substrate in an applied electric field by the combined action of the extrinsic potential of piezoelectric surface acoustical phonons of GaAs (piezoelectric acoustical (PA)) and of the intrinsic deformation potential of acoustical phonons in graphene (deformation acoustical (DA)). We find that provided the dc field exceeds a threshold value, emission of piezoelectric (PA) and deformation (DA) acoustical phonons can be obtained in a wide frequency range up to terahertz at low and high temperatures. We found that the phonon amplification rate R{sup PA,DA} scales with T{sub BG}{sup S?1} (S=PA,DA), T{sub BG}{sup S} being the Block?Gru{sup ¨}neisen temperature. In the high-T Block?Gru{sup ¨}neisen regime, extrinsic PA phonon scattering is suppressed by intrinsic DA phonon scattering, where the ratio R{sup PA}/R{sup DA} scales with ?1/?(n), n being the carrier concentration. We found that only for carrier concentration n?10{sup 10}cm{sup ?2}, R{sup PA}/R{sup DA}>1. In the low-T Block?Gru{sup ¨}neisen regime, and for n=10{sup 10}cm{sup ?2}, the ratio R{sup PA}/R{sup DA} scales with T{sub BG}{sup DA}/T{sub BG}{sup PA}?7.5 and R{sup PA}/R{sup DA}>1. In this regime, PA phonon dominates the electron scattering and R{sup PA}/R{sup DA}<1 otherwise. This study is relevant to the exploration of the acoustic properties of graphene and to the application of graphene as an acoustical phonon amplifier and a frequency-tunable acoustical phonon device.
Phonon-phonon interaction in gadolinium-gallium garnet crystals
International Nuclear Information System (INIS)
Propagation velocity and temperature dependence of the sound wave attenuation coefficient in gadolinium-gallium garnet crystals are measured. The measurements are carried out in the frequency range 0.4 to 2.0 GHz and temperature range 77 to 293 K. On the basis of the measurements Debye temperature, specific heat of crystal as a function of temperature, and the temperature dependence of thermal phonon lifetime are determined. For calculation it is assumed that the examined material is isotropic. (author)
International Nuclear Information System (INIS)
Phonon-induced fluorescence changes have been obtained in the shape of the spectra of selectively laser-excited dye molecules in noncrystalline organic solids, e.g. perylene molecules in Langmuir films of Cd arachidate. The changes in the zero-phonon lines and in the sidebands are observed after heat pulse irradiation (phonon memory), and by realtime phonon detection. The results are explained by electron-phonon interaction and by the model of matrix-shift variations caused by phonon-induced transitions in two-level systems in amorphous solids. (orig.)
Ultrafast coupling of coherent phonons with a nonequilibrium electron-hole plasma in GaAs
Basak, Amlan Kumar; Petek, Hrvoje; Ishioka, Kunie; Thatcher, Evan M.; Stanton, Christopher J.
2015-03-01
We present a joint experimental theoretical study of the coupling of coherent phonons in bulk GaAs with a nonequilibrium electron-hole plasma following photoexcitation at the E1 gap by ultrafast laser pulses. In contrast to prior coherent phonon experiments where photoexcitation across the E0 gap generated electrons in the ? valley, for the E1 gap excitation, the majority of the electrons are generated in the satellite L valleys. This leads to a drastically different situation from the previous studies because the damping of electrons is now faster due to the higher scattering rates in the L valley, and, in addition, the diffusion of carriers has a significant effect on the plasma response due to the shorter optical absorption depth of the pump-probe light. Reflectivity measurements show coherent phonon-plasmon oscillations, whose frequencies lie between the transverse and longitudinal optical phonon frequencies due to the heavy damping and change with time due to the diffusion of the plasma. We analyze the experimental data with a theoretical model that describes the time and density-dependent coupling of the coherent phonon and the electron-hole plasma as the photoexcited carriers diffuse into the sample on a subpicosecond time scale. The calculated phonon-plasmon dynamics qualitatively reproduce the experimentally observed time-dependent frequency.
Refraction Characteristics of Phononic Crystals
Nemat-Nasser, Sia
2014-01-01
The refraction properties of phononic crystals are revealed by examining the anti-plane shear waves in doubly periodic elastic composites with unit cells containing rectangular and/or elliptical inclusions. The band-structure, group velocity, and energy-flux vector are calculated using a powerful variational method which accurately and efficiently yields all the field quantities over multiple frequency pass-bands. Equifrequency contours and energy-flux vectors are calculated...
Phonons from neutron powder diffraction
Dimitrov, D. A.; Louca, D.; Röder, H.
1998-01-01
The spherically averaged structure function $\\soq$ obtained from pulsed neutron powder diffraction contains both elastic and inelastic scattering via an integral over energy. The Fourier transformation of $\\soq$ to real space, as is done in the pair density function (PDF) analysis, regularizes the data, i.e. it accentuates the diffuse scattering. We present a technique which enables the extraction of off-center phonon information from powder diffraction experiments by compar...
Firas J. Al-Maliki
2012-01-01
The synthesis, structural characterization, and amplified spontaneous emission spectroscopy of dye-scattering particles in inorganic medium based on Rhodamine 610-TiO2 nanoparticles confined in silica xerogel matrix have been reported. Optimum concentrations have been determined depending on the normal fluorescence spectra for laser dye, in order to provide amplification, and TiO2 nanoparticals as scatter center. Random Laser has been studied under second harmonic Nd: YAG laser excitation. At...
Thermal conductance boost in phononic crystal nanostructures
Anufriev, Roman; Nomura, Masahiro
2015-06-01
A theoretical study of coherent phonon scattering in thin-film phononic-crystal nanostructures (also called thermocrystals) is presented. It is commonly assumed that phononic crystals may only reduce thermal conductivity of materials. In this theoretical paper, contrary to this assumption, we demonstrate that phononic nanopatterning can enhance the thermal conductance of thin films under certain conditions. That is to say, it is shown that a thin membrane with many holes can have a higher thermal conductance than an unpatterned membrane. This effect originates from the increase in the density of states due to the coherent modifications of phonon dispersion. This counterintuitive phenomenon, called the thermal conductance boost effect, can be used for applications involving phonon management.
Polymer-Based Hypersonic Phononic Crystals
Gorishnyy, Taras; Fytas, George; Thomas, Edwin
2005-03-01
The ability to influence high frequency phonons has great importance for both fundamental science and practical applications. A number of important physical processes, such as thermal energy flow, charge carrier mobility and lifetime, and the superconductivity transition, can be altered by modifying the phononic dispersion relation of a medium. Applications range from thermal management and thermoelectricity, to enhanced microelectronic and opto-electronic devices. In this talk we will discuss the use hypersonic phononic crystals to achieve control over the emission and propagation of high frequency phonons. We fabricate high quality, 2D single crystalline hypersonic crystals using interference lithography and perform direct measurement of their phononic band structure with Brillouin light scattering. Numerical calculations are employed to explain the nature of the observed propagation modes. This work lays the foundation for experimental studies of hypersonic crystals and, more generally, phonon-dependent processes in periodic nanostructures.
Phonon wind on excitons in silicon
International Nuclear Information System (INIS)
We observed experimentally the strong effect of nonequilibrium phonons on the intensity of the luminescence of free and bound excitons, created by optical illumination of a Si surface immersed in liquid helium (T=1.8 K). The polarity of the phonon-induced luminescence signal strongly depends on the perfection of the surface. Two factors were included in the theoretical explanation of this effect: (1) the phonon-induced dissociation of bound excitons, and (2) the drag of free excitons by phonon flux (phonon-wind effect) which shifts the exciton cloud to the surface, where exciton recombination is strong. This effect is used to study spectral features of phonon propagation in Si and a-Si:H films. (orig.)
Temperature dependence of phonons in pyrolitic graphite
International Nuclear Information System (INIS)
Dispersion curves for longitudinal and transverse phonons propagating along and near the c-axis in pyrolitic graphite at temperatures between 40K and 15000C have been measured by neutron spectroscopy. The observed frequencies decrease markedly with increasing temperature (except for the transverse optical ''rippling'' modes in the hexagonal planes). The neutron groups show interesting asymmetrical broadening ascribed to interference between one phonon and many phonon processes
Twisted phonons in Bose–Einstein condensates
International Nuclear Information System (INIS)
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)
Electron-phonon coupling in one dimension
International Nuclear Information System (INIS)
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)
Czech Academy of Sciences Publication Activity Database
Pisarczyk, T.; Gus'kov, S.; Doskach, I. Ya.; Kasperczuk, A.; Borodziuk, S.; Kálal, M.; Krouský, Eduard; Limpouch, J.; Mašek, Karel; Pisarczyk, P.; Rohlena, Karel; Rozanov, V.; Ullschmied, Ji?í
Cairo : Egyptian Atomic Energy Authority(EAEA), 2003. s. 43. [First Cairo Conference on Plasma Physics & Applications. 11.10.2003-15.10.2003, Cairo] R&D Projects: GA MŠk LN00A100 Institutional research plan: CEZ:AV0Z2043910 Keywords : PALS laser system, laser targets, craters, plasma expansion Subject RIV: BL - Plasma and Gas Discharge Physics
Resonant tunneling in a pulsed phonon field
DEFF Research Database (Denmark)
Kral, P.; Jauho, Antti-Pekka
1999-01-01
We theoretically investigate resonant tunneling through a single level assisted by short LO phonon pulses. The analysis is based on the recently developed nonequilibrium linked-cluster expansion [P. Kral, Phys. Rev. B 56, 7293 (1997)], extended in this work to transient situations, The nonequilibrium spectral function for the resonance displays the formation and decay of the phonon sidebands on ultrashort time scales. The time-dependent tunneling current through the individual phonon satellites reflects this quasiparticle formation by oscillations, whose time scale is set by the frequency of the phonon field and its harmonics. These oscillations are washed out at elevated temperatures. [S0163-1829(99)04208-3].
Ballistic phonon transport in holey silicon.
Lee, Jaeho; Lim, Jongwoo; Yang, Peidong
2015-05-13
When the size of semiconductors is smaller than the phonon mean free path, phonons can carry heat with no internal scattering. Ballistic phonon transport has received attention for both theoretical and practical aspects because Fourier's law of heat conduction breaks down and the heat dissipation in nanoscale transistors becomes unpredictable in the ballistic regime. While recent experiments demonstrate room-temperature evidence of ballistic phonon transport in various nanomaterials, the thermal conductivity data for silicon in the length scale of 10-100 nm is still not available due to experimental challenges. Here we show ballistic phonon transport prevails in the cross-plane direction of holey silicon from 35 to 200 nm. The thermal conductivity scales linearly with the length (thickness) even though the lateral dimension (neck) is as narrow as 20 nm. We assess the impact of long-wavelength phonons and predict a transition from ballistic to diffusive regime using scaling models. Our results support strong persistence of long-wavelength phonons in nanostructures and are useful for controlling phonon transport for thermoelectrics and potential phononic applications. PMID:25861026
Phonon-assisted transient electroluminescence in Si
International Nuclear Information System (INIS)
The phonon-replica infrared emission is observed at room temperature from indirect band gap Si light-emitting diode under forward bias. With increasing injection current density, the broadened electroluminescence spectrum and band gap reduction are observed due to joule heating. The spectral-resolved temporal response of electroluminescence reveals the competitiveness between single (TO) and dual (TO?+?TA) phonon-assisted indirect band gap transitions. As compared to infrared emission with TO phonon-replica, the retarder of radiative recombination at long wavelength region (?1.2??m) indicates lower transition probability of dual phonon-replica before thermal equivalent.
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
Effect of magnon-phonon interaction on transverse acoustic phonon excitation at finite temperature
International Nuclear Information System (INIS)
A magnon-phonon interaction model is developed on the basis of two-dimensional square Heisenberg ferromagnetic system. By using Matsubara Green function theory transverse acoustic phonon excitation is studied and transverse acoustic phonon excitation dispersion curves is calculated on the main symmetric point and line in the first Brillouin zone. On line ? it is found that there is hardening for transverse acoustic phonon on small wave vector zone (nearby point ?), there is softening for transverse acoustic phonon on the softening zone and there is hardening for transverse acoustic phonon near point M. On line ? it is found there is no softening and hardening for transverse acoustic phonon. On line Z it is found that there is softening for transverse acoustic phonon on small wave vector zone (nearby point X) and there is hardening for transverse acoustic phonon nearby point M. The influences of various parameters on transverse acoustic phonon excitation are also explored and it is found that the coupling of the magnon-phonon and the spin wave stiffness constant play an important role for the softening of transverse acoustic phonon
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.
Dynamics of internal electric and phonon fields in n-GaAs pumped with ultrashort pulses
Scientific Electronic Library Online (English)
Fabrício M., Souza; J. Carlos, Egues.
1999-12-01
Full Text Available We investigate the ultrafast dynamics of an electron-hole plasma coupled to phonons in bulk GaAs excited with femtosecond laser pulses. Our approach is based on balance equations directly derived from the Boltzmann equation within the relaxation-time approximation. Poisson's equation together with a [...] phenomenological driven-harmonic-oscillator equation supplements our description by accounting for time-dependent electric and vibrational fields. Our calculated internal fields show oscillations at frequencies characteristic of those of coupled plasmon-phonon modes. Our results are consistent with recent experimental data.
Angular Momentum of Phonons and Einstein-de Haas Effect
Zhang, Lifa; Niu, Qian
2013-01-01
We study angular momentum of phonons in a magnetic crystal. In the presence of a spin-phonon interaction, we obtain a nonzero angular momentum of phonons, which is an odd function of magnetization. At zero temperature, phonon has a zero-point angular momentum besides a zero-point energy. With increasing temperature, the total phonon angular momentum diminishes and approaches to zero in the classical limit. The nonzero phonon angular momentum can have a significant impact on ...
Sound-Particles and Phonons with Spin 1
Directory of Open Access Journals (Sweden)
Samoilov V.
2011-01-01
Full Text Available We present a new model for solids which is based on the stimulated vibration of independent neutral Fermi-atoms, representing independent harmonic oscillators with natural frequencies, which are excited by actions of the longitudinal and transverse elastic waves. Due to application of the principle of elastic wave-particle duality, we predict that the lattice of a solid consists of two type Sound Boson-Particles with spin 1 with finite masses. Namely, these lattice Boson-Particles excite the longitudinal and transverse phonons with spin 1. In this letter, we estimate the masses of Sound Boson-Particles which are around 500 times smaller than the atom mass.
Interaction of coherent phonons with defects and elementary excitations.
Hase, Muneaki; Kitajima, Masahiro
2010-02-24
We present an overview of the feasibility of using coherent phonon spectroscopy to study interaction dynamics of excited lattice vibrations with their environments. By exploiting the features of coherent phonons with a pump-probe technique, one can study lattice motions in a sub-picosecond time range. The dephasing properties tell us not only about interaction dynamics with carriers (electrons and holes) or thermal phonons but also about point defects in crystals. Modulations of the coherent phonon amplitude by more than two modes are closely related to phonon-carrier or phonon-phonon interferences. Related to this phenomenon, formation of coherent phonons at higher harmonics gives direct evidence for phonon-phonon couplings. A combined study of coherent phonons and ultrafast carrier response can be useful for understanding phonon-carrier interaction dynamics. For metals like zinc, nonequilibrium electrons may dominate the dynamics of both relaxation and generation of coherent phonons. The frequency chirp of coherent phonons can be a direct measure of how and when phonon-phonon and phonon-carrier couplings occur. Carbon nanotubes show some complicated behavior due to the existence of many modes with different symmetries, resulting in superposition or interference. To illustrate one of the most interesting applications, the selective excitation of specific phonon modes through the use of a pulse train technique is shown. PMID:21386377
Splash, pop, sizzle: Information processing with phononic computing
Sklan, Sophia R.
2015-05-01
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.
Splash, pop, sizzle: Information processing with phononic computing
Directory of Open Access Journals (Sweden)
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.
Sensitivity of the system of cytochrome P-450 of poultry liver to the action of red laser light
International Nuclear Information System (INIS)
It is detected that irradiation of poultry embryos by red laser light (? = 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
Interface phonon modes in strained semiconductor superlattices
Energy Technology Data Exchange (ETDEWEB)
Ren, S.F.; Stanfield, J. (Illinois State Univ. Normal, IL (United States). Dept. of Physics)
1998-12-20
Phonon modes in strained ZnTe/CdSe superlattices are studied. The macroscopic interface modes and two different types of microscopic interface modes are identified. Interface phonon modes in (ZnTe)[sub 8](CdSe)[sub 8] superlattice with interchange of atomic layers across interfaces are calculated and compared with the results of superlattice with ideal interfaces.
Interface Phonon Modes in Strained Semiconductor Superlattices
Ren, Shang-Fen; Stanfield, Jason
Phonon modes in strained ZnTe/CdSe superlattices are studied. The macroscopic interface modes and two different types of microscopic interface modes are identified. Interface phonon modes in (ZnTe)8(CdSe)8 superlattice with interchange of atomic layers across interfaces are calculated and compared with the results of superlattice with ideal interfaces.
Resonant Tunneling with Electron-Phonon Interaction.
Wingreen, Ned Scott
An exactly solvable model for resonant tunneling with electron-phonon interaction is presented and the results are compared with experimentally observed phonon-assisted resonant tunneling. While an electron tunnels through a localized state, it can exchange energy with the phonon system and thereby move closer to or farther from the resonance condition. As a result, the total transmission probability as a function of incident energy will depend on the electron -phonon interaction during tunneling. The transmission probability through a single resonant site coupled to phonons is solved for in the limit of a uniform density of states in the leads. To carry out the solution we employ S-matrix scattering theory and a Green function analysis of a localized state coupled to phonons. The presence of phonons alters the transmission spectrum by generating inelastic sidebands and suppressing the elastic tunneling resonance, but does not change the overall transmissivity of the tunneling structure. Contact is made with experiment by calculating the current transmitted through the resonant site including interaction with an Einstein band of optic phonons. The structure in the current-voltage characteristic for a coupling strength appropriate to GaAs reproduces the experimentally observed structure in the current for a GaAs/AlGaAs double -barrier heterostructure.
Laser phase noise effects on the dynamics of optomechanical resonators
Phelps, Gregory; Meystre, Pierre
2011-05-01
We present a theoretical analysis of the effects of laser phase noise on the sideband cooling of opto-mechanical oscillators, demonstrating how it limits the minimum occupation number of the phonon mode being cooled and how it modifies optical cooling rate and mechanical frequency shift of the mechanical element. We also comment on the effects of laser phase noise on coherent oscillations of the mechanical element in the blue detuned regime and on the back-action evasion detection method where an additional drive is used to prevent heating of one quadrature of motion of the oscillator. This work was supported by the US Office of Naval Research, the US National Science Foundation, the US Army Research Office and the DARPA ORCHID program through a grant from AFOSR.
Li, Chen; Delaire, Olivier; Chen, Xin; Singh, David; May, Andrew; Ma, Jie; McGuire, Michael; Ehlers, Georg; Christianson, Andrew; Huq, Ashfia
2013-03-01
Thermoelectric materials can convert waste heat into electrical energy, and have attracted much attention in recent years for power generation. IV-VI compounds in rock salt structure include some of the most efficient thermoelectric materials and giant phonon anharmonicity is believed to contribute to the low thermal conductivity. In this work, phonon dispersions and linewidths in single-crystalline SnTe were measured at a series of temperatures using time-of-flight and triple-axis neutron spectrometers to study the temperature dependence of the phonon dynamics and phonon anharmonicity. Phonon calculations and molecular dynamics simulations with first-principles methods were used to identify the anomalies in phonon modes and the results were compared to the measurements. Because the phonons involved have an important contribution to the lattice thermal conductivity in this system, the anharmonic coupling is likely to provide a key insight in understanding the surprisingly low thermal conductivity of the rocksalt tellurides in general. Thermoelectric materials can convert waste heat into electrical energy, and have attracted much attention in recent years for power generation. IV-VI compounds in rock salt structure include some of the most efficient thermoelectric materials and giant phonon anharmonicity is believed to contribute to the low thermal conductivity. In this work, phonon dispersions and linewidths in single-crystalline SnTe were measured at a series of temperatures using time-of-flight and triple-axis neutron spectrometers to study the temperature dependence of the phonon dynamics and phonon anharmonicity. Phonon calculations and molecular dynamics simulations with first-principles methods were used to identify the anomalies in phonon modes and the results were compared to the measurements. Because the phonons involved have an important contribution to the lattice thermal conductivity in this system, the anharmonic coupling is likely to provide a key insight in understanding the surprisingly low thermal conductivity of the rocksalt tellurides in general. Funding from the US DOE, Office of Basic Energy Sciences, Materials Science and Engineering Division, and from the S3TEC Energy Frontier Research Center, DOE DE-SC0001299.
Phononic crystals and elastodynamics: Some relevant points
Directory of Open Access Journals (Sweden)
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.
Phonon dynamics of plutonium chalcogenides and pnictides
International Nuclear Information System (INIS)
We have investigated the phonon dynamics of the plutonium compounds (PuX; X = S, Se, Te, As, and Sb) by using rigid ion (RIM) and breathing shell models (BSM), later includes breathing motion of the electrons of the Pu-atoms due to f-d hybridization. We discuss the significance of these two approaches in predicting the phonon dispersion curves of PuX compounds and examine the role of electron-phonon interactions. Dominant ionic nature of bonding has been predicted for PuX compounds from the large LO-TO phonon splitting at zone center. We also report the one phonon density of states and first time calculated the lattice specific heat for these compounds.
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
2015-01-01
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. PMID:26112474
Temperature-dependent nonlinear phonon shifts in a supported MoS2 monolayer.
Taube, Andrzej; Judek, Jaros?aw; Jastrz?bski, Cezariusz; Duzynska, Anna; ?witkowski, Krzysztof; Zdrojek, Mariusz
2014-06-25
We report Raman spectra measurements on a MoS(2) monolayer supported on SiO(2) as a function of temperature. Unlike in previous studies, the positions of the two main Raman modes, E(2g)(1) and A(1g) exhibited nonlinear temperature dependence. Temperature dependence of phonon shifts and widths is explained by optical phonon decay process into two acoustic phonons. On the basis of Raman measurements, local temperature change under laser heating power at different global temperatures is derived. Obtained results contribute to our understanding of the thermal properties of two-dimensional atomic crystals and can help to solve the problem of heat dissipation, which is crucial for use in the next generation of nanoelectronic devices. PMID:24897497
Coherent phonon frequency comb generated by few-cycle femtosecond pulses in Si
Directory of Open Access Journals (Sweden)
Petek Hrvoje
2013-03-01
Full Text Available We explore the coherent phonon induced refractive index modulation of a Si(001 surface upon the excitation in near-resonance with the direct band gap of Si. Through the anisotropic e–h pair generation and coherent Raman scattering, ? 10-fs laser pulses exert a sudden electrostrictive force on Si lattice launching coherent LO phonon oscillations at 15.6 THz frequency. The concomitant oscillatory change in the optical constants modulates the reflected probe light at the fundamental LO phonon frequency, generating a broad comb of frequencies at exact integer multiples of the fundamental frequency extending to beyond 100 THz. On the basis of an analytical model, we show that the simultaneous amplitude and phase modulation of the reflected light by the coherent lattice polarization at 15.6 THz generates the frequency comb.
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
2015-01-01
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. PMID:26112474
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.
Phonon mediated quantum spin simulator made from a two-dimensional Wigner crystal in Penning traps
Wang, Joseph; Keith, Adam; Freericks, J. K.
2013-03-01
Motivated by recent advances in quantum simulations in a Penning trap, we give a theoretical description for the use of two-dimensional cold ions in a rotating trap as a quantum emulator. The collective axial phonon modes and planar modes are studied in detail, including all effects of the rotating frame. We show the character of the phonon modes and spectrum, which is crucial for engineering exotic spin interactions. In the presence of laser-ion coupling with these coherent phonon excitations, we show theoretically how the spin-spin Hamiltonian can be generated. Specifically, we notice certain parameter regimes in which the level of frustration between spins can be engineered by the coupling to the planar modes. This may be relevant to the quantum simulation of spin-glass physics or other disordered problems. Motivated by recent advances in quantum simulations in a Penning trap, we give a theoretical description for the use of two-dimensional cold ions in a rotating trap as a quantum emulator. The collective axial phonon modes and planar modes are studied in detail, including all effects of the rotating frame. We show the character of the phonon modes and spectrum, which is crucial for engineering exotic spin interactions. In the presence of laser-ion coupling with these coherent phonon excitations, we show theoretically how the spin-spin Hamiltonian can be generated. Specifically, we notice certain parameter regimes in which the level of frustration between spins can be engineered by the coupling to the planar modes. This may be relevant to the quantum simulation of spin-glass physics or other disordered problems. This work was supported under ARO grant number W911NF0710576 with funds from the DARPA OLE Program. J. K. F. also acknowledges the McDevitt bequest at Georgetown University. A. C. K. also acknowledges support of the National Science Foundation under grant
Directory of Open Access Journals (Sweden)
Fabrício Borges Oliveira
2012-01-01
Full Text Available OBJETIVO: Avaliar a ação precoce do laser terapêutico e do ultrassom no processo de regeneração de uma lesão experimental em ratos. MÉTODO: Utilizou-se 24 ratos. Dezoito foram submetidos ao procedimento cirúrgico de lesão do nervo ciático por compressão, através de uma pinça hemostática acima da fossa poplítea. Os animais foram divididos em três grupos com seis animais em cada. Grupo controle normal. GI: controle lesado sem intervenção terapêutica. GII: intervenção terapêutica do laser ArGaAl. GIII: intervenção terapêutica do ultrassom Pulsado. Iniciamos as intervenções terapêuticas 24 horas após a lesão, com aplicações diárias, por um período de quatorze dias consecutivos. RESULTADOS: Ao avaliar a perimetria dos músculos da coxa direita obteve-se os seguintes valores médios de diminuição (mm, para cada grupo GI: 0,45; GII: 0,42; GIII: 0,40. Quanto ao tempo de deslocamento tanto o GII e GIII apresentaram diferença significativa, quando comparados ao GI. Na avaliação final do IFC o GII sobressaiu ao GIII. Quanto a cicatrização observou-se grande melhora no GII e GIII. CONCLUSÃO: Os resultados evidenciaram que a recuperação nervosa foi maior com a aplicação do laser. Nível de evidência II, Estudos terapêuticos - Investigação dos resultados do tratamentoOBJECTIVE: To assess the efficacy of early therapeutic laser and ultrasound in the regeneration process of an injury in rats. METHODS: We used 24 rats. Eighteen underwent surgery for sciatic nerve compression by a hemostat above the popliteal fossa. The animals were divided into three groups of six animals each. Normal control group. GI: Injured control without therapeutic intervention. GII: laser ArGaAl therapeutic intervention. GIII: therapeutic intervention of Pulsed Ultrasound. We begin therapeutic interventions 24 hours after injury, with daily applications for a period of fourteen consecutive days. RESULTS: In assessing the girth of the muscles of the right they, the following average decrease (in mm for each GI: 0.45, GII: 0.42, GIII: 0.40 In relation to travel time, both GII and GIII presented significant difference when compared to GI. In the final evaluation of the IFC, GII excelled in the GIII. As for the healing observed, a major great improvement was observed in GII and GIII. CONCLUSION: The results showed that nerve recovery was higher with the laser application. Level of evidence II, Therapeutic Studies - Investigation of the results of treatment.
Scientific Electronic Library Online (English)
Fabrício Borges, Oliveira; Valéria Martins Dias, Pereira; Ana Paula Nassif Tondato da, Trindade; Antônio Carlos, Shimano; Ronaldo Eugênio Calçada Dias, Gabriel; Ana Paula Oliveira, Borges.
Full Text Available OBJETIVO: Avaliar a ação precoce do laser terapêutico e do ultrassom no processo de regeneração de uma lesão experimental em ratos. MÉTODO: Utilizou-se 24 ratos. Dezoito foram submetidos ao procedimento cirúrgico de lesão do nervo ciático por compressão, através de uma pinça hemostática acima da fos [...] sa poplítea. Os animais foram divididos em três grupos com seis animais em cada. Grupo controle normal. GI: controle lesado sem intervenção terapêutica. GII: intervenção terapêutica do laser ArGaAl. GIII: intervenção terapêutica do ultrassom Pulsado. Iniciamos as intervenções terapêuticas 24 horas após a lesão, com aplicações diárias, por um período de quatorze dias consecutivos. RESULTADOS: Ao avaliar a perimetria dos músculos da coxa direita obteve-se os seguintes valores médios de diminuição (mm), para cada grupo GI: 0,45; GII: 0,42; GIII: 0,40. Quanto ao tempo de deslocamento tanto o GII e GIII apresentaram diferença significativa, quando comparados ao GI. Na avaliação final do IFC o GII sobressaiu ao GIII. Quanto a cicatrização observou-se grande melhora no GII e GIII. CONCLUSÃO: Os resultados evidenciaram que a recuperação nervosa foi maior com a aplicação do laser. Nível de evidência II, Estudos terapêuticos - Investigação dos resultados do tratamento Abstract in english OBJECTIVE: To assess the efficacy of early therapeutic laser and ultrasound in the regeneration process of an injury in rats. METHODS: We used 24 rats. Eighteen underwent surgery for sciatic nerve compression by a hemostat above the popliteal fossa. The animals were divided into three groups of six [...] animals each. Normal control group. GI: Injured control without therapeutic intervention. GII: laser ArGaAl therapeutic intervention. GIII: therapeutic intervention of Pulsed Ultrasound. We begin therapeutic interventions 24 hours after injury, with daily applications for a period of fourteen consecutive days. RESULTS: In assessing the girth of the muscles of the right they, the following average decrease (in mm) for each GI: 0.45, GII: 0.42, GIII: 0.40 In relation to travel time, both GII and GIII presented significant difference when compared to GI. In the final evaluation of the IFC, GII excelled in the GIII. As for the healing observed, a major great improvement was observed in GII and GIII. CONCLUSION: The results showed that nerve recovery was higher with the laser application. Level of evidence II, Therapeutic Studies - Investigation of the results of treatment.
Coherent phonon and surface-enhanced Raman scattering dynamics in solids
Energy Technology Data Exchange (ETDEWEB)
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.
Fluctuation properties of phonons generated by ultrafast optical excitation of a quantum dot
Energy Technology Data Exchange (ETDEWEB)
Reiter, D.E.; Wigger, D.; Daniels, J.M.; Papenkort, T.; Kuhn, T. [Institut fuer Festkoerpertheorie, Westfaelische Wilhelms-Universitaet Muenster, Wilhelm-Klemm-Str. 10, 48149 Muenster (Germany); Vagov, A.; Axt, V.M. [Theoretische Physik III, Universitaet Bayreuth, 95440 Bayreuth (Germany)
2011-04-15
In this paper, the fluctuation properties of phonons after the optical excitation of a quantum dot with an ultrashort laser pulse are studied theoretically. When a single pulse with pulse area {pi} creates an exciton in the system, a coherent phonon state builds up. Fluctuations of coherent states are time independent and equal to the vacuum fluctuations. By an excitation with a {pi}/2 pulse a superposition of ground and exciton state is created. In this case the phonon system becomes entangled with the electronic system. In the phonon subsystem this leads to the formation of a statistical mixture of the vacuum and the coherent state. The fluctuations of this mixture oscillate in time with both the single and the double phonon frequency, but never exhibit squeezing. The discrepancies with the predictions made in a Raman tensor model are briefly discussed. All scenarios are illustrated using the Wigner function. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
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.
The Phonon Drag Effect in Single-Walled Carbon Nanotubes
Scarola, V. W.; Mahan, G. D.
2002-01-01
A variational solution of the coupled electron-phonon Boltzmann equations is used to calculate the phonon drag contribution to the thermopower in a 1-D system. A simple formula is derived for the temperature dependence of the phonon drag in metallic, single-walled carbon nanotubes. Scattering between different electronic bands yields nonzero values for the phonon drag as the Fermi level varies.
Laser performance at 1064 nm in Nd3+ doped oxi-tellurite glasses
Bell, Maria Jose; Anjos, Virgílio; Moreira, Lyane; Falci, Rodrigo; Kassab, Luciana; Silva, D.; Doualan, Jean Louis; Camy, Patrice; Moncorge, Richard
2015-03-01
The search for Nd3+ doped new solid-state laser hosts having specific thermo-mechanical and optical properties is very active. Among tellurites, the TeO2-ZnO glass combines good mechanical stability, chemical durability, high linear and nonlinear refractive indices, low phonon energies (~750 cm-1) and a wide transmission window (0.4-6 ?m). Their high nonlinear optical properties can be used for the development of Kerr-lens mode-locked subpicosecond lasers. The present work concentrates on the luminescence properties and the laser performance of a TeO2-ZnO tellurite glasses doped with Nd3+. True continuous-wave laser action is achieved by pumping the sample with a CW Ti:Sapphire laser inside a standard two-mirror laser cavity. A low laser threshold of 8 mW and a laser slope efficiency of 21% could be obtained for an output coupler transmission of 2.7%, which is an encouraging improvement compared to what was reported in the past with other Nd-doped tellurite bulk glasses. Authors acknowledge the support of agencies CAPES, FAPEMIG National Institute of Photonics (INCT Project/CNPQ) and COFECUB.
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 systematic experimental and numerical investigation on gain dynamics and the identification of different stable operating regimes has been carried out.
International Nuclear Information System (INIS)
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
Energy resolved phonon scattering in thin film amorphous solids
International Nuclear Information System (INIS)
Energy resolved phonon scattering measurements were performed using a novel heat pulse technique. Two thin film phonon generators were deposited on one face of a sapphire crystal substrate and two phonon detectors were deposited on the opposite face, under one of which a thin film amorphous material was deposited. The phonon detectors were superconducting tunnel heterojunctions. A comparison of the number of phonons detected at each junction gave information on the fraction of phonons transmitted through the amorphous film as a function of energy from which the phonon mean free path as a function of energy could be deduced. Materials investigated were silicon monoxide and germanium. (author)
Rotational Modes in Phononic Crystals
Wu, Ying; Peng, Pai; Mei, Jun
2014-03-01
We propose a lumped model for the rotational modes in two-dimensional phononic crystals comprised of square arrays of solid cylindrical scatterers in solid hosts. The model not only can reproduce the dispersion relations in a certain range with one fitted parameter, but also gives simple analytical expressions for the frequencies of the eigenmodes at the high symmetry points in the Brillouin zone. These expressions provide physical understandings of the rotational modes as well as certain translational and hybrid mode, and predict the presence of accidental degeneracy of the rotational and dipolar modes, which leads to a Dirac-like cone in the Brillouin zone center. Supported by KAUST Baseline Research Fund, National Natural Science Foundation of China (Grants No. 10804086 and No. 11274120), and the Fundamental Research Funds for the Central Universities (Grant No. 2012ZZ0077).
Phonon excitations in multicomponent amorphous solids
International Nuclear Information System (INIS)
The method of two-time temperature-dependent Green's functions is used to investigate phonon excitations in multicomponent amorphous solids. The equation obtained for the energy spectrum of the phonon excitations takes into account the damping associated with scattering of phonons by structure fluctuations. The quasicrystal approximation is considered, and as an example explicit expressions are obtained for the case of a two-component amorphous solid for the frequencies of the acoustical and optical modes and for the longitudinal and transverse velocities of sound. The damping is investigated
International Nuclear Information System (INIS)
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)
International Nuclear Information System (INIS)
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)
Dynamical stabilization of the bcc phase in lanthanum and thorium by phonon-phonon interaction
Souvatzis, P.; Bjorkman, T.; Eriksson, O.; P. Andersson; Rudin, M. I. Katsnelson S- P
2009-01-01
The recently developed self consistent {\\it ab initio} lattice dynamical method (SCAILD) has been applied to the high temperature bcc phase of La and Th which are dynamically unstable at low temperatures. The bcc phase of these metals is found to be stabilized by phonon-phonon interactions. The calculated high temperature phonon frequencies for La are found to be in good agreement with the corresponding experimental data.
BEDT-TTF organic superconductors: the entangled role of phonons
Girlando, Alberto; Masino, Matteo; Brillante, Aldo; Della Valle, Raffaele G.; Venuti, Elisabetta
2002-01-01
We calculate the lattice phonons and the electron-phonon coupling of the organic superconductor \\kappa-(BEDT-TTF)_2 I_3, reproducing all available experimental data connected to phonon dynamics. Low-frequency intra-molecular vibrations are strongly mixed to lattice phonons. Both acoustic and optical phonons are appreciably coupled to electrons through the modulation of the hopping integrals (e-LP coupling). By comparing the results relevant to superconducting \\kappa- and \\be...
Phonon Properties of CoSb2 Single Crystals
Energy Technology Data Exchange (ETDEWEB)
Petrovic C.; Lazarevic, N.; Radonjic, M.M.; Hu, R.; Tanaskovic, D.; Popovic, Z.V.
2012-04-04
The phonon properties of CoSb{sub 2} have been investigated by Raman scattering spectroscopy and lattice dynamics calculations. Sixteen out of eighteen Raman active modes predicted by factor-group analysis are experimentally observed and assigned. The calculated and measured phonon energies at the {Lambda} point are in very good agreement. The temperature dependence of the A{sub g} symmetry modes is well represented by phonon-phonon interactions without contribution from any other phonon or electron related interactions.
Phonon properties of CoSb2 single crystals.
Lazarevi?, N; Radonji?, M M; Hu, Rongwei; Tanaskovi?, D; Petrovic, C; Popovi?, Z V
2012-04-01
The phonon properties of CoSb(2) have been investigated by Raman scattering spectroscopy and lattice dynamics calculations. Sixteen out of eighteen Raman active modes predicted by factor-group analysis are experimentally observed and assigned. The calculated and measured phonon energies at the ? point are in very good agreement. The temperature dependence of the A(g) symmetry modes is well represented by phonon-phonon interactions without contribution from any other phonon or electron related interactions. PMID:22406874
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
Acoustic response to the action of nanosecond laser pulses on an In/CdTe thin-film heterostructure
Vlasenko, A. I.; Veleshchuk, V. P.; Gnatyuk, V. A.; Levitskii, S. N.; Vlasenko, Z. K.; Ivlev, G. D.; Gatskevich, E. I.
2015-06-01
The photothermoacoustic method has been used for diagnostics of thermobarodynamic processes in the metal In(400 nm)/semiconductor (CdTe) thin-film system under nanosecond laser irradiation (7 ns, ? = 532 nm) in natural conditions (in air) and in a liquid medium (water). From the analysis of the data obtained, the dependence of the pressure induced in the energy-release region on the irradiation energy density has been established and the melting threshold of In film has been determined. Under irradiation of In/CdTe in water, the pressure is higher than in air: 17 times higher at the melting threshold of In film and 30 times higher at twice the temperature. It has been found that the laser pulse treatment of In/CdTe/Au samples in water makes it possible to obtain diode structures with better parameters: smaller leak currents and a steeper current-voltage characteristic under the forward bias of the p- n junction.
Strong Coupling between Nanoscale Metamaterials and Phonons
Energy Technology Data Exchange (ETDEWEB)
Shelton, David J.; Brener, Igal; Ginn, James C.; Sinclair, Michael B.; Peters, David W.; Coffey, Kevin R.; Boreman, Glenn D.
2011-01-01
We use split ring resonators (SRRs) at optical frequencies to study strong coupling between planar metamaterials and phonon vibrations in nanometer-scale dielectric layers. A series of SRR metamaterials were fabricated on a semiconductor wafer with a thin intervening SiO{sub 2} dielectric layer. The dimensions of the SRRs were varied to tune the fundamental metamaterial resonance across the infrared (IR) active phonon band of SiO{sub 2} at 130 meV (31 THz). Strong anticrossing of these resonances was observed, indicative of strong coupling between metamaterial and phonon excitations. This coupling is very general and can occur with any electrically polarizable resonance including phonon vibrations in other thin film materials and semiconductor band-to-band transitions in the near to far IR. These effects may be exploited to reduce loss and to create unique spectral features that are not possible with metamaterials alone.
Non-adiabatic phonon dispersion of graphene
International Nuclear Information System (INIS)
Recently, failure of the adiabatic approximation has been observed in the charge doping dependence of the Raman spectrum of graphene. The theoretical work has been limited to the phonon dispersion modification in the vicinity of the Brillouin zone center. Here, we present estimation of the non-adiabatic effects on the phonons close to the K point of the Brillouin zone obtained by a perturbation scheme within a non-orthogonal tight-binding model. We show that the explicit account of the dynamic effects change the shape of the Kohn anomaly of the TO phonon branch at the K point. The increase of the charge doping level essentially removes the Kohn anomaly. These results are important for modelling phenomena, in which phonons at the K point are involved, e.g., defect- and second-order Raman scattering
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.
Phonon spectra of a Fibonacci chain
International Nuclear Information System (INIS)
Based on more realistic physics we study the phonon spectra of the Fibonacci chain by taking into account a nonlinear resistance. It is found that the nonlinear force should be very weak and consequently, the continuity, range and gaps of the phonon spectra would be still controlled dominantly by the relative strength of spring constants and chain length. It means that even if no additional nonlinear resistance was taken into account, the conventional results of phonon spectra are exactly correct. On the other hand, in the framework of a conventional model we investigated the relationship between the biggest gaps of phonon spectra and defects of Fibonacci-like aperiodic chains. By means of numerical calculations one can obtain quantitatively the maximum of the length of a one-dimensional aperiodic chain sensitive to boundaries. This method would be useful for the calculation of quasiperiodic and aperiodic lattices
Acoustic and optical phonons in metallic diamond
Directory of Open Access Journals (Sweden)
M. Hoesch, T. Fukuda, T. Takenouchi, J.P. Sutter, S. Tsutsui, A.Q.R. Baron, M. Nagao, Y. Takano, H. Kawarada and J. Mizuki
2006-01-01
Full Text Available The dispersion of acoustic and optical phonons in highly boron-doped diamond has been measured by inelastic X-ray scattering at an energy resolution of 6.4 meV. The sample is doped in the metallic regime and shows superconductivity below 4.2 K (midpoint. The data are compared to pure and nitrogen-doped diamond that represent the non-metallic state. No difference is found for the acoustic phonons in the three samples, while the optical phonons show a shift of the dispersion (softening in qualitative agreement with earlier results from Raman spectroscopy. The presence of boron and nitrogen incorporated into the diamond lattice leads to structural disorder. Evidence for this is found both in the observation of otherwise symmetry-forbidded Bragg intensity at (0 0 2 and intensity from acoustic phonon modes in the vicinity of (0 0 2.
Phonon-mediated detection of particles
International Nuclear Information System (INIS)
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
Influence of phonons on semiconductor quantum emission
Energy Technology Data Exchange (ETDEWEB)
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.)
Symmetry-Adapted Phonon Analysis of Nanotubes
Aghaei, Amin; Elliott, Ryan S
2013-01-01
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 Ob...
International Nuclear Information System (INIS)
Recently, it was reported that a plasma-jet could be efficiently applied for the antisepsis of wounds. In this case, the discharge in an argon gas stream was used to produce a so-called ''cold plasma'' on the skin surface. The thermal action of the plasma on the skin was investigated in the present study by means of laser scanning microscopy (LSM) and by histological analysis. Consequently, the plasma beam was moved with a definite velocity at an optimal distance over the skin surface. The structural changes of the tissue were analyzed. It was found by LSM that a thermal damage could be detected only in the upper cell layers of the stratum corneum (SC) at moving velocities of the plasma beam, usually applied in clinical practice. Deeper parts of the SC were not damaged. The structural changes were so superficial that they could be detected only by LSM but not by analysis of the histological sections
Lademann, O.; Richter, H.; Patzelt, A.; Alborova, A.; Humme, D.; Weltmann, K.-D.; Hartmann, B.; Hinz, P.; Kramer, A.; Koch, S.
2010-06-01
Recently, it was reported that a plasma-jet could be efficiently applied for the antisepsis of wounds. In this case, the discharge in an argon gas stream was used to produce a so-called ``cold plasma'' on the skin surface. The thermal action of the plasma on the skin was investigated in the present study by means of laser scanning microscopy (LSM) and by histological analysis. Consequently, the plasma beam was moved with a definite velocity at an optimal distance over the skin surface. The structural changes of the tissue were analyzed. It was found by LSM that a thermal damage could be detected only in the upper cell layers of the stratum corneum (SC) at moving velocities of the plasma beam, usually applied in clinical practice. Deeper parts of the SC were not damaged. The structural changes were so superficial that they could be detected only by LSM but not by analysis of the histological sections.
Phonon coherence in isotopic silicon superlattices
Energy Technology Data Exchange (ETDEWEB)
Frieling, R.; Radek, M.; Eon, S.; Bracht, H., E-mail: bracht@uni-muenster.de [Institute of Materials Physics, Westfälische Wilhelms-Universität Münster, 48149 Münster (Germany); Wolf, D. E. [Faculty of Physics, University Duisburg-Essen, 47048 Duisburg (Germany)
2014-09-29
Recent experimental and theoretical investigations have confirmed that a reduction in thermal conductivity of silicon is achieved by isotopic silicon superlattices. In the present study, non-equilibrium molecular dynamics simulations are performed to identify the isotope doping and isotope layer ordering with minimum thermal conductivity. Furthermore, the impact of isotopic intermixing at the superlattice interfaces on phonon transport is investigated. Our results reveal that the coherence of phonons in isotopic Si superlattices is prevented if interfacial mixing of isotopes is considered.
Frequency dependence of dispersive phonon images
Scientific Electronic Library Online (English)
K., Jakata; A.G., Every.
2008-10-01
Full Text Available In the past, lattice dynamics models have been used in interpreting dispersive phonon focusing patterns of crystals. They have had mixed success in accounting for observed images and, moreover, different models applied to the same crystal tend to differ significantly in their predictions. In this pa [...] per we interpret observed phonon focusing images of two cubic crystals, germanium and silicon, through an extension of continuum elasticity theory that takes into account the first deviation from linearity of the phonon dispersion relation. This is done by incorporating fourth-order spatial derivatives of the displacement field in the wave equation. The coefficients of the higher-order derivatives are determined by fitting to phonon dispersion relations for the acoustic branches measured by neutron scattering in the [100], [111] and [110] symmetry directions. With this model we simulate phonon images of Si and Ge projected onto the (100), (110) and (111) observation planes. These are able to account well for the observed phonon images.
Toward quantitative modeling of silicon phononic thermocrystals
Lacatena, V.; Haras, M.; Robillard, J.-F.; Monfray, S.; Skotnicki, T.; Dubois, E.
2015-03-01
The wealth of technological patterning technologies of deca-nanometer resolution brings opportunities to artificially modulate thermal transport properties. A promising example is given by the recent concepts of "thermocrystals" or "nanophononic crystals" that introduce regular nano-scale inclusions using a pitch scale in between the thermal phonons mean free path and the electron mean free path. In such structures, the lattice thermal conductivity is reduced down to two orders of magnitude with respect to its bulk value. Beyond the promise held by these materials to overcome the well-known "electron crystal-phonon glass" dilemma faced in thermoelectrics, the quantitative prediction of their thermal conductivity poses a challenge. This work paves the way toward understanding and designing silicon nanophononic membranes by means of molecular dynamics simulation. Several systems are studied in order to distinguish the shape contribution from bulk, ultra-thin membranes (8 to 15 nm), 2D phononic crystals, and finally 2D phononic membranes. After having discussed the equilibrium properties of these structures from 300 K to 400 K, the Green-Kubo methodology is used to quantify the thermal conductivity. The results account for several experimental trends and models. It is confirmed that the thin-film geometry as well as the phononic structure act towards a reduction of the thermal conductivity. The further decrease in the phononic engineered membrane clearly demonstrates that both phenomena are cumulative. Finally, limitations of the model and further perspectives are discussed.
Toward quantitative modeling of silicon phononic thermocrystals
International Nuclear Information System (INIS)
The wealth of technological patterning technologies of deca-nanometer resolution brings opportunities to artificially modulate thermal transport properties. A promising example is given by the recent concepts of 'thermocrystals' or 'nanophononic crystals' that introduce regular nano-scale inclusions using a pitch scale in between the thermal phonons mean free path and the electron mean free path. In such structures, the lattice thermal conductivity is reduced down to two orders of magnitude with respect to its bulk value. Beyond the promise held by these materials to overcome the well-known “electron crystal-phonon glass” dilemma faced in thermoelectrics, the quantitative prediction of their thermal conductivity poses a challenge. This work paves the way toward understanding and designing silicon nanophononic membranes by means of molecular dynamics simulation. Several systems are studied in order to distinguish the shape contribution from bulk, ultra-thin membranes (8 to 15?nm), 2D phononic crystals, and finally 2D phononic membranes. After having discussed the equilibrium properties of these structures from 300?K to 400?K, the Green-Kubo methodology is used to quantify the thermal conductivity. The results account for several experimental trends and models. It is confirmed that the thin-film geometry as well as the phononic structure act towards a reduction of the thermal conductivity. The further decrease in the phononic engineered membrane clearly demonstrates that both phenomena are cumulative. Finally, limitations of the model and further perspectives are discussed
Hu, Huayu
2015-01-01
Nonperturbative calculation of QED processes participated by a strong electromagnetic field, especially provided by strong laser facilities at present and in the near future, generally resorts to the Furry picture with the usage of analytical solutions of the particle dynamical equation, such as the Klein-Gordon equation and Dirac equation. However only for limited field configurations such as a plane-wave field could the equations be solved analytically. Studies have shown significant interests in QED processes in a strong field composed of two counter-propagating laser waves, but the exact solutions in such a field is out of reach. In this paper, inspired by the observation of the structure of the solutions in a plane-wave field, we develop a new method and obtain the analytical solution for the Klein-Gordon equation and equivalently the action function of the solution for the Dirac equation in this field, under a largest dynamical parameter condition that there exists an inertial frame in which the particl...
High-speed asynchronous optical sampling for high-sensitivity detection of coherent phonons
Dekorsy, Thomas; Taubert, Richard; Hudert, Florian; Schrenk, Gerhard; Bartels, Albrecht; Cerna, Roland; Kotaidis, Vassilios; Plech, Anton; Köhler, Klaus; Schmitz, Johannes; Wagner, Joachim
2007-01-01
A new optical pump-probe technique is implemented for the investigation of coherent acoustic phonon dynamics in the GHz to THz frequency range which is based on two asynchronously linked femtosecond lasers. Asynchronous optical sampling (ASOPS) provides the performance of on all-optical oscilloscope and allows us to record optically induced lattice dynamics over nanosecond times with femtosecond resolution at scan rates of 10 kHz without any moving part in the set-up. Within 1 minute of data ...
International Nuclear Information System (INIS)
As predicted by harmonic theory the coherent inelastic spectrums of neutrons, scattered by a single, non-conducting crystal, for a particular angle of scattering consists of a number of delta-function peaks superposed on a continuous background. The peaks correspond to one-phonon processes in which one phonon is absorbed or emitted by the neutron; the background arises from multi-phonon processes. When anharmonic forces (phonon-phonon interactions) are present, the delta-function peaks are broadened into finite peaks, while their central frequencies are shifted with respect to the harmonic values. In the case of a metal there is in addition to phonon-phonon interactions an interaction between phonons and conduction electrons, which also gives a contribution to the displacement and broadening oftheone-phononpeaks. Continuing earlier work of Van Hove (sho considered the relatively simple case of a non-conductin crystal in its ground state (T = 0oK) ), we have studied the shifts and widths of the scattering peaks as a 'result of the above-mentioned interactions by means of many particle perturbation theory, making extensive use of diagram techniques. Prerequisite to the entire discussion is the assumption that, independent of the strength of the interactions, the width of each peak is small compared to the value of the frequency at its centre; only then the peaks can be considered as being well defined with respect to the background to higher order in the interactions. This condition is expected to be fulfilled for temperatures which are not too high and values of the phonon wave vector which are not too large. Our procedure yields closed formulae for the partial scattering function describing the peaks, which can be evaluated to arbitrarily high accuracy. In particular an expansion for calculating the line shift and line width in powers of u/d and in terms of simple connected diagrams is obtained (u is an average atomic or ionic displacement, d is the smallest interatomic or interionic distance in the crystal). Approximate calculations are performed to give some insight into the orders of magnitude of the effects under study. (author)
Electron and phonon interactions a novel semiclassical approach
Rose, A
1989-01-01
This monograph is a radical departure from the conventional quantum mechanical approach to electron-phonon interactions. It translates the customary quantum mechanical analysis of the electron-phonon interactions carried out in Fourier space into a predominantly classical analysis carried out in real space. Various electron-phonon interactions such as the polar and nonpolar optical phonons, acoustic phonons that interact via deformation potential and via the piezoelectric effect and phonons in metals, are treated in this monograph by a single, relatively simple "classical" model. This model is
Energy Technology Data Exchange (ETDEWEB)
Diakhate, Momar S.; Zijlstra, Eeuwe S.; Garcia, Martin E. [Universitaet Kassel, Theoretische Physik, Kassel (Germany)
2009-07-15
We parameterize the potential energy surface of bismuth after intense laser excitation using accurate full-potential linearized augmented plane wave calculations. Anharmonic contributions up to the fifth power in the A{sub 1g} phonon coordinate are given as a function of the absorbed laser energy. Using a previously described model including effects of electron-phonon coupling and carrier diffusion due to Johnson et al., we obtain the time-dependent potential energy surface for any given laser pulse shape and duration. On the basis of this parameterization we perform quantum dynamical simulations to study the experimentally observed amplitude collapse and revival of coherent A{sub 1g} phonons in bismuth considering work of Misochko et al. Our results strongly indicate that the observed beatings are not related to quantum effects and are most probably of classical origin. (orig.)
Coherent acoustic phonon generation in GaAs{sub 1?x}Bi{sub x}
Energy Technology Data Exchange (ETDEWEB)
Joshya, R. S.; Kini, R. N., E-mail: rajeevkini@iisertvm.ac.in [Indian Institute of Science Education and Research Thiruvananthapuram (IISER-TVM), CET Campus, Thiruvananthapuram, Kerala 695016 (India); Ptak, A. J.; France, R.; Mascarenhas, A. [National Renewable Energy Laboratory (NREL), 1617 Cole Blvd., Golden, Colorado 80401 (United States)
2014-03-03
We have used femtosecond laser pulses to generate coherent acoustic phonons in the dilute Bismide alloy, GaAs{sub 1?x}Bi{sub x}. The observed oscillation periods match well with the oscillation periods calculated using the propagating strain pulse model. We attribute the generation process predominantly to electronic stress due to the absorption of the laser pulse at the surface of the GaAs{sub 1?x}Bi{sub x} layer. Our initial estimates suggest that the incorporation of Bi in GaAs causes an enhancement of the hydrostatic deformation potential because of the resonant state in the valence band due to isolated Bi impurities.
Lubatschowski, H; Kermani, O; Welling, H
1997-02-01
This study was designed to investigate the quality of a scanning and rotating slit delivery system of an ArF-Excimer laser (Nidek EC 5000). The ablation patterns on PMMA samples were examined by REM. The influence of inhomogeneities in the beam profile was simulated on a computer and compared with a conventional large-area ablation system. The impairment of the ablation rate by radiation absorption of the ablation plume was measured as a function of the repetition rate and the application of a fixation ring. The scanning and rotating slit delivery system creates extremely smooth ablation patterns. The delivery system is very tolerant of small-beam inhomogeneities. The ablation rate is very sensitive to the dynamics of the ablation plume. Although the operating procedure takes less time with a large-area ablation system, a scanning and rotating delivery system has the advantage of reliable and homogeneous removal of corneal tissue. PMID:9156635
Phonon Dispersion of Indium along [111
Kaiser, H.; Werner, S. A.; Bakulin, A. S.; Overhauser, A. W.; Fernandez-Baca, J. A.; Smith, H. G.
2001-03-01
The phonon spectrum of indium along [111] has been measured by inelastic neutron scattering^1. The main objective was to test the dynamic pseudopotential theory of phonons with this type of system. The two shear modes at the zone boundary point (1/2,1/2,1/2) are split slightly, caused by the tetragonal distortion (from an otherwise fcc lattice). They have very low frequencies, 0.7 and 1.0 THz for the T1 and T_[2] modes, respectively, compared to the longitudinal mode, 3.4 THz. This confirms the rather unexpected large ratio, 4, of the L mode to the T modes at the zone boundary, as predicted by the model. In general, the measured three phonon branches follow the main features of the predicted phonon dispersion along [111] very well. These measurements verify the theoretical dispersion predicted by the dynamic pseudopotential theory of phonons for free-electron-like metals. ^1A.S. Bakulin et al., Phys. Rev. B (Feb. 1 issue), 2001.
DEFF Research Database (Denmark)
Angelsky, O. V.; Bekshaev, A. Ya.
2014-01-01
Water suspension of light-absorbing nano-sized particles is an example of a medium in which non-linear effects are present at moderate light intensities favorable for optical treatment of organic and biological objects. We study experimentally the phenomena emerging in a thin layer of such a medium under the action of inhomogeneous light field formed due to the Pearcey diffraction pattern near a microlens focus. In this high-gradient field, the light energy absorbed by the particles induces inhomogeneous distribution of the medium refraction index, which results in observable self-diffraction of the incident light, here being strongly sensitive to the medium position with respect to the focus. This technique, based on the complex spatial structure of both the incident and the diffracted fields, can be employed for the detection and measurement of weak non-linearities.
Situation with collective two-phonon states in deformed nuclei
International Nuclear Information System (INIS)
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
Phonons and Lattice Dielectric Properties of Zirconia
Zhao, X; Zhao, Xinyuan; Vanderbilt, David
2001-01-01
We have performed a first-principles study of the structural and vibrational properties of the three low-pressure (cubic, tetragonal, and especially monoclinic) phases of ZrO2, with special attention to the computation of the zone-center phonon modes and related dielectric properties. The calculations have been carried out within the local-density approximation using ultrasoft pseudopotentials and a plane-wave basis. The fully relaxed structural parameters are found to be in excellent agreement with experimental data and with previous theoretical work. The total-energy calculations correctly reproduce the energetics of the ZrO2 phases, and the calculated zone-center phonon frequencies yield good agreement with the infrared and Raman experimental frequencies in the monoclinic phase. The Born effective charge tensors are computed and, together with the mode eigenvectors, used to decompose the lattice dielectric susceptibility tensor into contributions arising from individual infrared-active phonon modes. This w...
Phonon wave interference and thermal bandgap materials
Maldovan, Martin
2015-07-01
Wave interference modifies phonon velocities and density of states, and in doing so creates forbidden energy bandgaps for thermal phonons. Materials that exhibit wave interference effects allow the flow of thermal energy to be manipulated by controlling the material's thermal conductivity or using heat mirrors to reflect thermal vibrations. The technological potential of these materials, such as enhanced thermoelectric energy conversion and improved thermal insulation, has fuelled the search for highly efficient phonon wave interference and thermal bandgap materials. In this Progress Article, we discuss recent developments in the understanding and manipulation of heat transport. We show that the rational design and fabrication of nanostructures provides unprecedented opportunities for creating wave-like behaviour of heat, leading to a fundamentally new approach for manipulating the transfer of thermal energy.
Phonon multiplexing through 1D chains
Scientific Electronic Library Online (English)
A., Avila; D., Reyes.
2008-12-01
Full Text Available Recently, phonon propagation through atomic structures has become a relevant study issue. The most important applications arise in the thermal field, since phonons can carry thermal and acoustic energy. It is expected that technological advances will make possible the engineering of thermal paths ac [...] cording to convenience. A simple phonon multiplexer was analyzed as a spring-mass model. It consists of mono-atomic chains of atoms with a coupling structure between them. Forces between atoms follow Hooke's law and are restricted to be first nearest neighbor interaction. It was possible to establish simple rules on constitutive parameters such as atom masses and bonding forces that enable one to select a wavelength of transmission. The method used enables the study of structures of much greater complexity than the one presented here.
Neutron-Phonon Interaction in Neutron Star Crusts
Sedrakian, Armen
1998-01-01
The phonon spectrum of Coulomb lattice in neutron star crusts above the neutron drip density is affected by the interaction with the ambient neutron Fermi-liquid. For the values of the neutron-phonon coupling constant in the range $0.1 \\le \\lambda \\le 1$ an appreciable renormalization of the phonon spectrum occurs which can lead to a lattice instability manifested in an exponential growth of the density fluctuations. The BCS phonon exchange mechanism of superconductivity lea...
Calculations of the A_1 phonon frequency in photoexcited Tellurium
Tangney, P; Fahy, S.
1998-01-01
Calculations of the A_1 phonon frequency in photoexcited tellurium are presented. The phonon frequency as a function of photoexcited carrier density and phonon amplitude is determined. Recent pump probe experiments are interpreted in the light of these calculatons. It is proposed that, in conjunction with measurements of the phonon period in ultra-fast pump-probe reflectivity experiments, the calculated frequency shifts can be used to infer the evolution of the density of ph...
Temperature dependent resistivity in bilayer graphene due to flexural phonons
H. Ochoa; Castro, Eduardo V.; M. I. Katsnelson; Guinea, F.
2011-01-01
We have studied electron scattering by out-of-plane (flexural) phonons in doped suspended bilayer graphene. We have found the bilayer membrane to follow the qualitative behavior of the monolayer cousin. In the bilayer, different electronic structure combine with different electron-phonon coupling to give the same parametric dependence in resistivity, and in particular the same temperature $T$ behavior. In parallel with the single layer, flexural phonons dominate the phonon c...
The angular spreading of phonon beams in liquid 4He: upward phonon dispersion
International Nuclear Information System (INIS)
Measurements have been made of the angular spreading of initially well defined beams of phonons of energies h/2??/ksub(B) 4He at pressures between SVP and 24 bar. For bath temperatures T 3He. The spreading increases with increasing source temperature and decreases with pressure, becoming undetectable (0) at P >= 17 bar. The decay lengths of the processes giving rise to this spreading are found to be approximately 1 mm. Various scattering mechanisms are considered and it is concluded that the results are consistent with a spontaneous three-phonon decay process allowed when the phonon dispersion curve initially deviates upward from its asymptotic linear form. (author)
Phonon Dispersion of Fe-30%Mn Alloy
U?ur, Gökay; Akgün, ?rfan; U?ur, ?ule
The angular force model of Clark, Gazis and Wallis (CGW) have been applied to calculate the phonon frequencies of antiferromagnetic Fe-30%Mn alloy. Furthermore, the second order elastic constants of the alloy have been computed using a new empirical many body potential (MBP), which has been developed by Akgün and U?ur. The parameters defining the MBP for the alloy have been computed following a procedure given by Akgün and U?ur. The computed elastic constants have been used to calculate the phonon frequencies of the alloy. Finally the theoretical results have been compared with the corresponding experimental values.
Phonon interference effects in molecular junctions
DEFF Research Database (Denmark)
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 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.
Phonon thermal conductivity in single layered manganites
International Nuclear Information System (INIS)
We present measurements of the thermal transport in single crystals of single-layered manganites La1-xSr1+xMnO4 with 0=ph upon hole-doping. The suppression of ?ph originates from scattering of phonons by polaronic holes. The suppression is particularly strong when charge and orbital degrees of freedom are disordered and rather weak in the case of long-range charge and orbital ordering. Moreover, slight anomalies are found in the vicinity of antiferromagnetic phase transitions, probably due to scattering of phonons by magnetic fluctuations
Phonon-Mediated Anomalous Dynamics of Defects
Najafi, A; Najafi, Ali; Golestanian, Ramin
2002-01-01
Dynamics of an array of line defects interacting with a background elastic medium is studied in the linear regime. It is shown that the inertial coupling between the defects and the ambient phonons leads to an anomalous response behavior for the deformation modes of a defect-lattice, in the form of anisotropic and anomalous mass and elastic constants, resonant dissipation through excitation of phonons, and instabilities. The case of a single fluctuating line defect is also studied, and it is shown that it could lead to formation of shock waves in the elastic medium for sufficiently high frequency deformation modes.
Refraction characteristics of phononic crystals
Nemat-Nasser, Sia
2015-08-01
Some of the most interesting refraction properties of phononic crystals are revealed by examining the anti-plane shear waves in doubly periodic elastic composites with unit cells containing rectangular and/or elliptical multi-inclusions. The corresponding band structure, group velocity, and energy-flux vector are calculated using a powerful mixed variational method that accurately and efficiently yields all the field quantities over multiple frequency pass-bands. The background matrix and the inclusions can be anisotropic, each having distinct elastic moduli and mass densities. Equifrequency contours and energy-flux vectors are readily calculated as functions of the wave-vector components. By superimposing the energy-flux vectors on equifrequency contours in the plane of the wave-vector components, and supplementing this with a three-dimensional graph of the corresponding frequency surface, a wealth of information is extracted essentially at a glance. This way it is shown that a composite with even a simple square unit cell containing a central circular inclusion can display negative or positive energy and phase velocity refractions, or simply performs a harmonic vibration (standing wave), depending on the frequency and the wave-vector. Moreover, that the same composite when interfaced with a suitable homogeneous solid can display: (1) negative refraction with negative phase velocity refraction; (2) negative refraction with positive phase velocity refraction; (3) positive refraction with negative phase velocity refraction; (4) positive refraction with positive phase velocity refraction; or even (5) complete reflection with no energy transmission, depending on the frequency, and direction and the wavelength of the plane-wave that is incident from the homogeneous solid to the interface. For elliptical and rectangular inclusion geometries, analytical expressions are given for the key calculation quantities. Expressions for displacement, velocity, linear momentum, strain, and stress components, as well as the energy-flux and group velocity components are given in series form. The general results are illustrated for rectangular unit cells, one with two and the other with four inclusions, although any number of inclusions can be considered. The energy-flux and the accompanying phase velocity refractions at an interface with a homogeneous solid are demonstrated. Finally, by comparing the results of the present solution method with those obtained using the Rayleigh quotient and, for the layered case, with the exact solutions, the remarkable accuracy and the convergence rate of the present solution method are demonstrated.
Optical pumping of hot phonons in GaAs
International Nuclear Information System (INIS)
Optical pumping of hot LO phonons in GaAs has been studied as a function of the excitation photon frequency. The experimental results are in good agreement with a model calculation which includes both inter- and intra-valley electron-phonon scatterings. The GAMMA-L and GAMMA-X intervalley electron-phonon interactions in GaAs have been estimated
Advances in semiconductor lasers and applications to optoelectronics
Dutta, Mitra
2000-01-01
This volume includes highlights of the theories underlying the essential phenomena occurring in novel semiconductor lasers as well as the principles of operation of selected heterostructure lasers. To understand scattering processes in heterostructure lasers and related optoelectronic devices, it is essential to consider the role of dimensional confinement of charge carriers as well as acoustical and optical phonons in quantum structures. Indeed, it is important to consider the confinement of both phonons and carriers in the design and modeling of novel semiconductor lasers such as the tunnel
EMRS Spring Meeting 2014 Symposium D: Phonons and fluctuations in low dimensional structures
2014-11-01
The E-MRS 2014 Spring meeting, held from 26-30th May 2014 in Lille included the Symposium D entitled ''Phonons and Fluctuations in Low Dimensional Structures'', the first edition of its kind. The symposium was organised in response to the increasing interest in the study of phonons in the context of advances in condensed matter physics, electronics, experimental methods and theory and, in particular, the transfer of energy across atomic interfaces and the propagation of energy in the nm-scale. Steering heat by light or vice versa and examining nano-scale energy conversion (as in thermoelectricity and harvesting e.g. in biological systems) are two aspects that share the underlying science of energy processes across atomic interfaces and energy propagation in the nanoscale and or in confined systems. The nanometer scale defies several of the bulk relationships as confinement of electrons and phonons, locality and non-equilibrium become increasingly important. The propagation of phonons as energy carriers impacts not only heat transfer, but also the very concept and handling of temperature in non-equilibrium and highly localised conditions. Much of the needed progress depends on the materials studied and this symposium targeted the interface material aspects as well as the emerging concepts to advance in this field. The symposium had its origins in a series of meetings and seminars including: (1) the first Phonon Engineering Workshop, funded by Catalan Institute for Research and Advanced Studies (ICREA), the then MICINN, the CNRS, VTT, and several EU projects, held in Saint Feliu de Guixols (Girona, Spain) from 24th to 27th of May 2010 with 65 participants from Europe, the USA and Japan; (2) the first Phonons and Fluctuations workshop, held in Paris on 8th and 9th November 2010, supported by French, Spanish and Finnish national projects and EU projects, attended by about 50 researchers; (3) the second Phonon and Fluctuations workshop, held in Paris on 8th and 9th September 2011, attended by 55 researchers and (4) the 3rd Workshop on Phonons & Fluctuations, held in Saint Feliux de Guixols (Girona, Spain) during 21 to 24th May 2012 attended by 65 participants from Europe and the USA. These papers in this proceeding are examples of the work presented at the symposium. They represent the tip of the iceberg, as the symposium attracted over 100 abstracts. The meeting room was usually full with an audience varying between 40 and 100 participants. The plenary presentation was given by Prof. Gang Chen (MIT) on ''Ballistic and Coherent Phonon Heat Conduction in Bulk Materials and Nanostructures'', which was warmly welcome by an eager and highly motivated audience. The invited speakers were: Prof. Thomas Dehoux (U. Bordeaux), Dr S. Chung (U. New South Wales, Australia), Prof. A. Goni (CSIC-ICMAB), Prof. Giuliano Benenti (U. Insubria), Dr. Davide Donadio (Max Planck Institute for Polymer Research, Mainz), Prof. George Fytas (University of Crete), Prof. Dr. Tobias Kippenberg (EPFL, Switzerland), Prof. Bernard Perrin (INSP, Paris), Prof. Gyaneshwar P. Srivastava, U. Exeter) and Prof. Dr. Achim Kittel (U. Oldenburg). The organisers are very grateful to them for supporting the symposium and sharing their latest research results with the symposium participants. The symposium organisers recognised the participation of students and awarded prizes to the two Best Student Presentations, which went to Valeria Lacatena (IEMN, Lille) with an invited presentation entitled ''Efficient reduction of thermal conductivity in silicon using phononic-engineered membranes'' and to Yan Qing Liu (Institute Neel, Grenoble) who presented the talk entitled ''Sensitive 3-omega measurements of epitaxial thermoelectric thin films''. The poster session had about fifty posters and the four best poster prizes went to: Konstanze Hahn et al. (U. Cagliari) poster title ''Determination of Thermal conductivity in (nanostructured) SiGe materials'', Florian Doehring et al. (U. Goettingen) poster title ''Phonon blocking in Multilayers produced by Pulsed Laser Deposition''
Phonon affected transport through molecular quantum.
Czech Academy of Sciences Publication Activity Database
Loos, Jan; Koch, T.; Alvermann, A.; Bishop, A. R.; Fehske, H.
2009-01-01
Ro?. 21, ?. 39 (2009), 395601/1-395601/18. ISSN 0953-8984 Institutional research plan: CEZ:AV0Z10100521 Keywords : quantum dots * electron - phonon interaction * polarons Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.964, year: 2009
Inomogeneous Quantum Groups as Symmetries of Phonons
Bonechi, F; Celeghini, E.(Österreichische Akademie der Wissenschaften, Institut für Hochenergiephysik, A-10560 Wien, Austria 28 28 Funded by the Austrian Ministry for Traffic and Research under the contract GZ 616.360/2-IV GZ 616.363/2-VIII, and by the Fonds für Wissenschaft und Forschung FWF No. P08929-PHY.); Giachetti, R.; Sorace, E.; Tarlini, M.
1992-01-01
The quantum deformed (1+1) Poincare' algebra is shown to be the kinematical symmetry of the harmonic chain, whose spacing is given by the deformation parameter. Phonons with their symmetries as well as multiphonon processes are derived from the quantum group structure. Inhomogeneous quantum groups are thus proposed as kinematical invariance of discrete systems.
Phonon spectral function of the Holstein polaron.
Czech Academy of Sciences Publication Activity Database
Loos, Jan; Hohenadler, M.; Alvermann, A.; Fehske, H.
2006-01-01
Ro?. 18, - (2006), s. 7299-7312. ISSN 0953-8984 Grant ostatní: DFG(DE) SPP1073; DFG and ASCR(DE) 436TSE113/33/0-2 Institutional research plan: CEZ:AV0Z10100521 Keywords : Holstein model * spectral functions * phonons Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.038, year: 2006
PHONONS IN THE DNA DOUBLE HELIX
Prohofsky, E.; Van Zandt, L.; M. Kohli; LU, K; Mei, M.; Putman, B.
1981-01-01
We have calculated a model for the phonon modes of the DNA double helix. We have used these modes in a number of applications to biological problems which use lattice concepts such as soft modes, local modes and quasi-momentum.
``Forbidden'' phonon in the iron chalcogenide series
Fobes, David M.; Zaliznyak, Igor A.; Xu, Zhijun; Gu, Genda; Tranquada, John M.
2015-03-01
Recently, we uncovered evidence for the formation of a bond-order wave (BOW) leading to ferro-orbital order at low temperature, acting to stabilize the bicollinear AFM order, in the iron-rich parent compound, Fe1+yTe. Investigating the inelastic spectra centered near (100) in Fe1+yTe, a signature peak for the BOW formation in the monoclinic phase, we observed an acoustic phonon dispersion in both tetragonal and monoclinic phases. While a structural Bragg peak accompanies the mode in the monoclinic phase, in the tetragonal phase Bragg scattering at this Q is forbidden by symmetry, and we observed no elastic peak. This phonon mode was also observed in superconducting FeTe0.6Se0.4, where structural and magnetic transitions are suppressed. LDA frozen phonon calculations suggested that this mode could result from a spin imbalance between neighboring Fe atoms, but polarized neutron measurements revealed no additional magnetic scattering. We propose that this ``forbidden'' phonon mode may originate from dynamically broken symmetry, perhaps related to the strong dynamic spin correlations in these materials. Work at BNL was supported by BES, US DOE, under Contract No. DE-AC02-98CH10886. Research at ORNL's HFIR and SNS sponsored by Scientific User Facilities Division, BES, US DOE. We acknowledge the support of NIST, in providing neutron research facilities.
Long range optical phonons in liquid water
Elton, Daniel C
2015-01-01
In this work we show that on subpicosecond time scales optical phonon modes can propagate through the H-bond network of water over relatively long distances (2-4 nm). Using molecular dynamics simulation we find propagating optical phonons in the librational and OH stretching bands. The OH stretching phonon only appears when a polarizable model (TTM3-F) is employed. Both of these phonon modes exhibit LO-TO splitting at $k = 0$, indicating long range dipole-dipole interactions in the system. We study the LO-TO splitting as a function of temperature, finding that the splitting increases for the librational mode at higher temperatures but decreases for the stretching mode. Since LO-TO splitting is intimately connected to structure, this analysis opens the door for new insights into how the local structure of water changes with temperature. Our results also explain a previously unnoticed discrepancy one encounters when comparing the librational peaks found in Raman and IR/dielectric spectra. Previously the three R...
Three-dimensional adaptive soft phononic crystals
Babaee, Sahab; Wang, Pai; Bertoldi, Katia
2015-06-01
We report a new class of three-dimensional (3D) adaptive phononic crystals whose dynamic response is controlled by mechanical deformation. Using finite element analysis, we demonstrate that the bandgaps of the proposed 3D structure can be fully tuned by the externally applied deformation. In fact, our numerical results indicate that the system acts as a reversible phononic switch: a moderate level of applied strain (i.e., -0.16) is sufficient to completely suppress the bandgap, and upon the release of applied strain, the deformed structure recovers its original shape, which can operate with a sizable bandgap under dynamic loading. In addition, we investigate how material damping significantly affects the propagation of elastic waves in the proposed 3D soft phononic crystal. We believe that our results pave the way for the design of a new class of soft, adaptive, and re-configurable 3D phononic crystals, whose bandgaps can be easily tuned and switched on/off by controlling the applied deformation.
Kohn anomaly in phonon driven superconductors
International Nuclear Information System (INIS)
Anomalies often occur in the physical world. Sometimes quite unexpectedly anomalies may give rise to new insight to an unrecognized phenomenon. In this paper we shall discuss about Kohn anomaly in a conventional phonon-driven superconductor by using a microscopic approach. Recently Aynajian et al.'s experiment showed a striking feature; the energy of phonon at a particular wave-vector is almost exactly equal to twice the energy of the superconducting gap. Although the phonon mechanism of superconductivity is well known for many conventional superconductors, as has been noted by Scalapino, the new experimental results reveal a genuine puzzle. In our recent work we have presented a detailed theoretical analysis with the help of microscopic calculations to unravel this mystery. We probe this aspect of phonon behaviour from the properties of electronic polarizability function in the superconducting phase of a Fermi liquid metal, leading to the appearance of a Kohn singularity. We show the crossover to the standard Kohn anomaly of the normal phase for temperatures above the transition temperature. Our analysis provides a nearly complete explanation of this new experimentally discovered phenomenon. This report is a shorter version of our recent work in JPCM.
The phonon and thermal properties of a ladder nanostructure
Directory of Open Access Journals (Sweden)
M Mardaani
2011-12-01
Full Text Available In this paper, we study the phonon thermal properties of a ladder nanostructure in harmonic approximation. We present a model consisting of two infinite chains with different masses. Then, we investigate the effect of different masses on the phonon spectrum. Moreover, as a specific case, in the absence of the second neighbor interaction, we calculate the phonon density of states/modes. Finally, we consider the thermal conductivity of the system. The results show that the phonon spectrum shifts down to the lower frequencies by increasing the masses. Furthermore, a frequency gap appears in the phonon spectrum. By increasing the springs constants, the thermal conductance decreases.
Ward, D W; Feurer, T; Nelson, K A; Osgood, R M; Roth, R M; Statz, E R; Stoyanov, N; Beers, Jaime D.; Feurer, Thomas; Nelson, Keith A.; Osgood, Richard M.; Roth, Ryan M.; Statz, Eric; Stoyanov, Nikolay; Ward, David W.
2004-01-01
Using time resolved ultrafast spectroscopy, we have demonstrated that the far infrared (FIR) excitations in ferroelectric crystals may be modified through an arsenal of control techniques from the fields of guided waves, geometrical and Fourier optics, and optical pulse shaping. We show that LiNbO3 and LiTaO3 crystals of 10-250 micron thickness behave as slab waveguides for phonon-polaritons, which are admixtures of electromagnetic waves and lattice vibrations, when the polariton wavelength is on the order of or greater than the crystal thickness. Furthermore, we show that ferroelectric crystals are amenable to processing by ultrafast laser ablation, allowing for milling of user-defined patterns designed for guidance and control of phonon-polariton propagation. We have fabricated several functional structures including THz rectangular waveguides, resonators, splitters/couplers, interferometers, focusing reflectors, and diffractive elements. Electric field enhancement has been obtained with the reflective stru...
The influence of phonon bath on the control of single photon
Zhang, Wei; Lu, Hai-Tao
2015-06-01
The influence of vacuum fluctuation and phonon bath on the probability of single photon emission are both considered in the two-level system model theoretically; by using the master equations and generating function method we get the analytical expression of the second-order fluorescence correlation function, probability of single photon emission, and Mandel’s Q parameter. The results manifest that the coupling between the phonon bath and single photon source destroys the superposition state induced by the square laser pulse, the Rabi oscillation damped rapidly with the increasing of temperature. Theoretically, when the structure parameter of arsenide quantum dots ? scaled to 0.1 times of the sample, the critical coherence-temperature will rise up to hundreds of Kelvin, which means a step forward to the realization of coherent control of single photon source at room temperature. Project supported by the Fundamental Research Funds for the Central Universities of Central South University, China (Grant No. 2014zzts145).
Unified theory of electron–phonon renormalization and phonon-assisted optical absorption
International Nuclear Information System (INIS)
We present a theory of electronic excitation energies and optical absorption spectra which incorporates energy-level renormalization and phonon-assisted optical absorption within a unified framework. Using time-independent perturbation theory we show how the standard approaches for studying vibronic effects in molecules and those for addressing electron–phonon interactions in solids correspond to slightly different choices for the non-interacting Hamiltonian. Our present approach naturally leads to the Allen–Heine theory of temperature-dependent energy levels, the Franck–Condon principle, the Herzberg–Teller effect and to phonon-assisted optical absorption in indirect band gap materials. In addition, our theory predicts sub-gap phonon-assisted optical absorption in direct gap materials, as well as an exponential edge which we tentatively assign to the Urbach tail. We also consider a semiclassical approach to the calculation of optical absorption spectra which simultaneously captures energy-level renormalization and phonon-assisted transitions and is especially suited to first-principles electronic structure calculations. We demonstrate this approach by calculating the phonon-assisted optical absorption spectrum of bulk silicon. (paper)
Wang, Bin; Appavoo, Kannatassen; Brady, Nathaniel; Seo, Minah; Nag, Joyeeta; Prasankumar, Rohit; Hilton, David; Haglund, Richard; Pantelides, Sokrates
2013-03-01
The ultrafast photo-induced phase transition in VO2 is promising for data storage and sensing applications. Our experimental work (the previous talk) shows that in a Au/VO2 hybrid nanostructure, electrons excited in the Au photocathode by an ultrafast laser trigger the insulator-to-metal transition in VO2. Here we report first-principles density-functional calculations showing that the collapse of a 6 THz optical phonon, corresponding to a twisting motion of V atoms, is responsible for the ultrafast phase transition. Above a concentration threshold, we find that injected electrons from Au induce collapse of the VO2phonon, which stimulates the monoclinic-to-rutile structural phase transition. We also show that hole-doping can induce the same effect. The abrupt change of the critical phonon results from the weakening of the V-V bonds induced by the combined flux of injected electrons and holes. Thus, our results explain the experimental finding of plasmonic-electron-driven ultrafast phase transition and represent a step towards manipulating the photo-induced phase transition by surface modification. The ultrafast photo-induced phase transition in VO2 is promising for data storage and sensing applications. Our experimental work (the previous talk) shows that in a Au/VO2 hybrid nanostructure, electrons excited in the Au photocathode by an ultrafast laser trigger the insulator-to-metal transition in VO2. Here we report first-principles density-functional calculations showing that the collapse of a 6 THz optical phonon, corresponding to a twisting motion of V atoms, is responsible for the ultrafast phase transition. Above a concentration threshold, we find that injected electrons from Au induce collapse of the VO2phonon, which stimulates the monoclinic-to-rutile structural phase transition. We also show that hole-doping can induce the same effect. The abrupt change of the critical phonon results from the weakening of the V-V bonds induced by the combined flux of injected electrons and holes. Thus, our results explain the experimental finding of plasmonic-electron-driven ultrafast phase transition and represent a step towards manipulating the photo-induced phase transition by surface modification. Supported by the Office of Science, US DOE (DE-FG02-01ER45916, DE-AC52-06NA25396, DE-AC04-94AL85000) and DTRA (HDTRA1-10-1-0047), NSF (ARI-R2 DMR-0963361, DMR-1207241), GAANN Fellowship (P200A090143), McMinn Endowment (STP), and LDRDP.
On collective two-phonon states in deformed nuclei
International Nuclear Information System (INIS)
The centroid energies of the two-phonon states in doubly even deformed nuclei are calculated within the quasiparticle-phonon nuclear model taking into account the Pauli principle in the two-phonon components of the wave functions. On the example of 154Gd, 160Dy, 168Er, 230Th and 240Pu nuclei it is shown that the collective two-phonon energies are shifted by 1-2 MeV due to the Pauli principle. A strong fragmentation of the two-phonon collective states over many nuclear levels occurs at the excitation energies of 3-4 MeV. It is concluded that the two-phonon states are absent in deformed nuclei. The analysis of the available experimental data on the two-phonon states shows that the experimental data do not contradict the results of these calculations
Single-photon indistinguishability: influence of phonons
DEFF Research Database (Denmark)
Nielsen, Per Kær; Lodahl, Peter
2012-01-01
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 photons emitted from a solid-state cavity QED system. Our model rigorously describes non-Markovian effects to all orders in the phonon coupling constant, being based on an exact diagonalization procedure accounting for the time evoluiton of one-time and two-time photon correlation funcitons. We compare to standard approaches for treating the phonon interaction, namely the Markovian Lindblad formalism and the long-time limit of the non-Markovian timeconvolution-less (TCL) approach, and find large quantitative and qualitative differences [3]. Figures 1(b) and (c) show the calculated indistingusihability as a function of the QD-cavity coupling strength for light emitted from the QD and the cavity, respectively, for all the employed methods. Both the Lindblad and TCL theories deviate significantly from our exact results, where, importantly, the exact results predict a pronounced maximum in the degree of 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, dominating the decoherence for large QD-cavity coupling. Our method captures the physics of the regime of small and as well as large QD-cavity coupling, both corresponding to experimentally relevant situations. Importantly, the commonly used Lindblad formalism fails completely in describing the variations of the indistinguishability predicted by the two other models.
Nanoscale heat transport via electrons and phonons by molecular dynamics simulations
Lin, Keng-Hua
Nanoscale heat transport has become a crucial research topic due to the growing importance of nanotechnology for manufacturing, energy conversion, medicine and electronics. Thermal transport properties at the nanoscale are distinct from the macroscopic ones since the sizes of nanoscale features, such as free surfaces and interfaces, are comparable to the wavelengths and mean free paths of the heat carriers (electrons and phonons), and lead to changes in thermal transport properties. Therefore, understanding how the nanoscale features and energy exchange between the heat carriers affect thermal transport characteristics are the goals of this research. Molecular dynamics (MD) is applied in this research to understand the details of nanoscale heat transport. The advantage of MD is that the size effect, anharmonicity, atomistic structure, and non-equilibrium behavior of the system can all be captured since the dynamics of atoms are described explicitly in MD. However, MD neglects the thermal role of electrons and therefore it is unable to describe heat transport in metal or metal-semiconductor systems accurately. To address this limitation of MD, we develop a method to simulate electronic heat transport by implementing electronic degrees of freedom to MD. In this research, nanoscale heat transport in semiconductor, metal, and metal-semiconductor systems is studied. Size effects on phonon thermal transport in SiGe superlattice thin films and nanowires are studied by MD. We find that, opposite to the macroscopic trend, superlattice thin films can achieve lower thermal conductivity than nanowires at small scales due to the change of phonon nature caused by adjusting the superlattice periodic length and specimen length. Effects of size and electron-phonon coupling rate on thermal conductivity and thermal interface resistivity in Al and model metal-semiconductor systems are studied by MD with electronic degrees of freedom. The results show that increasing the specimen length or the electron-phonon coupling rate increases the electronic contribution in thermal transport and therefore increases the thermal conductivity; moreover, the thermal interface resistivity in metal-semiconductor systems is observed to depend on the heat flux direction due to the direction-dependent energy transfer pathways between electrons and phonons at the interface. MD with electronic degrees of freedom is also applied to simulate heat transport across the metal-semiconductor interface under the non-equilibrium conditions, mimicking the ultrafast laser heating in transient thermoreflectance measurements. The effect of local and non-local electron-phonon coupling across the interface are examined, since the experimental evidence suggests that non-local electron-phonon coupling occurs under the non-equilibrium conditions. Our results show that non-local electron-phonon coupling not only facilitates energy transfer across the interface but also enhances ballistic transport of the high frequency phonon modes in a semiconductor. In summary, our study provides an insight into the details of nanoscale heat transport in various systems by MD and MD with electronic degrees of freedom.
Femtosecond laser-matter interaction theory, experiments and applications
Gamaly, Eugene G
2011-01-01
Basics of Ultra-Short Laser-Solid InteractionsSubtle Atomic Motion Preceding a Phase Transition: Birth, Life and Death of PhononsUltra-Fast Disordering by fs-Lasers: Superheating Prior to Entropy CatastropheAblation of SolidsUltra-Short Laser-Matter Interaction Confined Inside a Bulk of Transparent SolidApplications of Ultra-Short Laser-Matter InteractionsConclusion Remarks
Theory of coherent phonons in carbon nanotubes and graphene nanoribbons
International Nuclear Information System (INIS)
We survey our recent theoretical studies on the generation and detection of coherent radial breathing mode (RBM) phonons in single-walled carbon nanotubes and coherent radial breathing like mode (RBLM) phonons in graphene nanoribbons. We present a microscopic theory for the electronic states, phonon modes, optical matrix elements and electron–phonon interaction matrix elements that allows us to calculate the coherent phonon spectrum. An extended tight-binding (ETB) model has been used for the electronic structure and a valence force field (VFF) model has been used for the phonon modes. The coherent phonon amplitudes satisfy a driven oscillator equation with the driving term depending on the photoexcited carrier density. We discuss the dependence of the coherent phonon spectrum on the nanotube chirality and type, and also on the graphene nanoribbon mod number and class (armchair versus zigzag). We compare these results with a simpler effective mass theory where reasonable agreement with the main features of the coherent phonon spectrum is found. In particular, the effective mass theory helps us to understand the initial phase of the coherent phonon oscillations for a given nanotube chirality and type. We compare these results to two different experiments for nanotubes: (i) micelle suspended tubes and (ii) aligned nanotube films. In the case of graphene nanoribbons, there are no experimental observations to date. We also discuss, based on the evaluation of the electro, based on the evaluation of the electron–phonon interaction matrix elements, the initial phase of the coherent phonon amplitude and its dependence on the chirality and type. Finally, we discuss previously unpublished results for coherent phonon amplitudes in zigzag nanoribbons obtained using an effective mass theory. (topical review)
Phonons as building blocks in nuclear structure
International Nuclear Information System (INIS)
The structure of a nuclear system in terms of eigenmodes (phonons) of subsystems is investigated in three different approaches. In the frame of nuclear field theory the three identical particle system is analysed and the elimination of spurious states due to the violation of the Pauli principle is emphasized. In terms of weak coupling, a new approach of the shell model is proposed which is shown to be rapidly convergent with the number of basis vectors. Applications of three particle systems in the lead region are made. Lastly, a microscopic multiphonon theorie of collective K=0 states in deformed nuclei based on a Tamm Dancoff phonon is developed. The role of the Pauli principle as well as comparisons with boson expansion methods are deeply analysed
Phonon Transport Simulator (PhonTS)
Chernatynskiy, Aleksandr; Phillpot, Simon R.
2015-07-01
Thermal conductivity prediction remains an important subject in many scientific and engineering areas. Only recently has such prediction become possible on the basis of the first principles calculations, thus ensuring high quality results. Implementation of the methodology, however, is technically challenging and requires a lengthy development process. We thus introduce the Phonon Transport Simulator (PhonTS), a Fortran90, fully parallel code to perform such calculations. PhonTS possesses a large array of options and returns the thermal conductivity tensor together with related quantities, such as spectral thermal conductivity, phonon lifetimes, mean free paths and Grüneisen parameters. First principles calculations are implemented via convenient interfaces to widely-used third-party codes, while many classical potentials are included in PhonTS itself. The code is carefully validated against data published in the literature from various thermal conductivity computational techniques and against experimental data.
Structural Properties and Phonon dispertion of NACl
Directory of Open Access Journals (Sweden)
R. Khoda-Bakhsh
2001-06-01
Full Text Available Although many phenomena in condensed matter Physics can be understood on the basis of a model, there are also considerable number of physical properties of solid which can not be explained except in the framework of lattice dynamics. We have calculated the phonon frequencies of Na Cl, using an approach which is a combination of frozen phonon and force constants methods in the framework of density functional pseudopotential theory. The dispersion relation curves, were calculated along symmetry direction ?, ? and Ù. We also calculated Grunesein parameters for all modes at X and L points in Brillion zone. The calcutions are made in the framework of density functional and pseudopotential theory, using super cell method, with the valence orbitals expanded in plane waves.
Electron-phonon superconductivity beyond Migdal's theorem
International Nuclear Information System (INIS)
One of the common elements between the various high Tc superconductors, cuprates and C60 compounds, is the very small value of the Fermi energy, comparable with the Debye phonon frequencies. This situation implies a breakdown of Migdal's theorem for the electron-phonon many body problem and leads to important nonadiabatic effects. We have generalized Eliashberg equations to include vertex corrections and other nonadiabatic effects in a perturbative scheme. This leads to a rather complex situation in which the critical temperature for superconductivity can be strongly enhanced if the el-ph scattering involves mainly small momenta. Recent studies show that this situation can be naturally realized in view of electronic correlations. ((orig.))
Phonon spectroscopy with superconducting tunnel junctions
International Nuclear Information System (INIS)
Superconducting tunnel junctions can be used as generators and detectors of monochromatic phonons of frequency larger than 80 GHz, as was first devised by Eisenmenger and Dayem (1967) and Kinder (1972a, 1973). In this report, we intend to give a general outline of this type of spectroscopy and to present the results obtained so far. The basic physics underlying phonon generation and detection are described in chapter I, a wider approach being given in the references therein. In chapter II, the different types of junctions are considered with respect to their use. Chapter III deals with the evaporation technique for the superconducting junctions. The last part of this report is devoted to the results that we have obtained on ?-irradiated LiF, pure Si and Phosphorous implanted Si. In these chapters, the limitations of the spectrometer are brought out and suggestions for further work are given
Phonon focusing and second sound in solids
International Nuclear Information System (INIS)
This article gives a survey of the elastic wave surfaces for crystals, the phenomenon of phonon focusing, the heat pulse experiments and second sound in solids. Because of the elastic anisotropy of crystals, the group velocity of the acoustic wave is generally not coincident with the wave velocity and consequently, the phonons are focused in certain directions of the crystal. The nature of the constant frequency surfaces for the slow shear (ST), fast shear (FT) and longitudinal (L) modes and their singularities are discussed. Illustrations are given for the sections of these surfaces by the principal planes, as well as the three dimensional view of the inverse velocity and intensity surfaces. (author). 32 refs., 20 figs
Quantum mode phonon forces between chainmolecules
DEFF Research Database (Denmark)
Bohr, Jakob
2001-01-01
A phenomenological description of the contributions of phonons to molecular force is developed. It uses an approximation to consider macromolecules as solid continua. The molecular modes of a molecule can then be characterized by a Debye-like description of the partition function. The resulting bimolecular interaction is a truly many-body force that is temperature dependent and can be of the order of 1 eV. These phonon forces depend on molecular shape, composition, and density. They may therefore also be important for large molecular conformational changes, including the unfolding of chain molecules. For the later case, a significant change in zero-point energy is found. This may be the underlying cause for cold denaturation of proteins. (C) 2001 John Wiley & Sons, Inc.
Mesoscopic Hydro-Thermodynamics of Phonons
Vasconcellos, Aurea R.; Castro, A. R. B.; C. A. B. Silva; Roberto Luzzi
2012-01-01
A generalized Hydrodynamics, referred to as Mesoscopic Hydro-Thermodynamics, of phonons in semiconductors is presented. It involves the descriptions of the motion of the quasi-particle density and of the energy density. The hydrodynamic equations, which couple both types of movement via thermo-elastic processes, are derived starting with a generalized Peierls-Boltzmann kinetic equation obtained in the framework of a Non-Equilibrium Statistical Ensemble Formalism, providing s...
PHONON RAMAN SPECTROSCOPY IN GRAPHITE INTERCALATION COMPOUNDS
Hwang, D.; Solin, S.
1981-01-01
The atoms or molecules intercalated in a graphite intercalation compound are correlated spatially among themselves, resulting in a static structure factor with sharp peaks. Graphite phonons with momenta corresponding to these structure factor peaks have a higher probability of being scattered into the Brillouin zone center and becoming Raman active. With this momentum selection scheme, we can interpret the observed Raman features of graphite intercalation compounds with various in-plane struc...
Electron-phonon interaction in nanodevices.
Czech Academy of Sciences Publication Activity Database
Král, Karel
Warrendale : TMS (The Minerals, Metals & Materials Society), 2008, s. 81-86. ISBN 978-0-87339-716-2. [TMS 2008 Annual Meeting & Exhibition. New Orleans, Louisiana (US), 09.03.2008-13.03.2008] R&D Projects: GA MŠk OC08001 Institutional research plan: CEZ:AV0Z10100520 Keywords : nanomaterials * electron-phonon interaction * quantum dots * nanodevice Subject RIV: BM - Solid Matter Physics ; Magnetism
Pressure-enabled phonon engineering in metals
Nicholas A. Lanzillo; Thomas, Jay B.; Watson, Bruce; Washington, Morris; Nayak, Saroj K.
2014-01-01
Understanding the pressure response of the electrical properties of metals provides a fundamental way of manipulating material properties for potential device applications. In particular, the electrical resistivity of a metal, which is an intrinsic property determined primarily by the interaction strength between electrons and collective lattice vibrations (phonons), can be reduced when the metal is pressurized. In this article, we show that first-principles calculations of the resistivity, a...
Phonon Engineering in Isotopically Disordered Silicon Nanowires.
Mukherjee, S; Givan, U; Senz, S; Bergeron, A; Francoeur, S; de la Mata, M; Arbiol, J; Sekiguchi, T; Itoh, K M; Isheim, D; Seidman, D N; Moutanabbir, O
2015-06-10
The introduction of stable isotopes in the fabrication of semiconductor nanowires provides an additional degree of freedom to manipulate their basic properties, design an entirely new class of devices, and highlight subtle but important nanoscale and quantum phenomena. With this perspective, we report on phonon engineering in metal-catalyzed silicon nanowires with tailor-made isotopic compositions grown using isotopically enriched silane precursors (28)SiH4, (29)SiH4, and (30)SiH4 with purity better than 99.9%. More specifically, isotopically mixed nanowires (28)Si(x)(30)Si(1-x) with a composition close to the highest mass disorder (x ? 0.5) were investigated. The effect of mass disorder on the phonon behavior was elucidated and compared to that in isotopically pure (29)Si nanowires having a similar reduced mass. We found that the disorder-induced enhancement in phonon scattering in isotopically mixed nanowires is unexpectedly much more significant than in bulk crystals of close isotopic compositions. This effect is explained by a nonuniform distribution of (28)Si and (30)Si isotopes in the grown isotopically mixed nanowires with local compositions ranging from x = ?0.25 to 0.70. Moreover, we also observed that upon heating, phonons in (28)Si(x)(30)Si(1-x) nanowires behave remarkably differently from those in (29)Si nanowires suggesting a reduced thermal conductivity induced by mass disorder. Using Raman nanothermometry, we found that the thermal conductivity of isotopically mixed (28)Si(x)(30)Si(1-x) nanowires is ?30% lower than that of isotopically pure (29)Si nanowires in agreement with theoretical predictions. PMID:25993500
Robinson, Richard; Otelaja, Obafemi; Hertzberg, Jared; Aksit, Mahmut; Stewart, Derek
2013-03-01
Phonons are the dominant heat carriers in dielectrics and a clear understanding of their behavior at the nanoscale is important for the development of efficient thermoelectric devices. In this work we show how acoustic phonon transport can be directly probed by the generation and detection of non-equilibrium phonons in microscale and nanoscale structures. Our technique employs a scalable method of fabricating phonon generators and detectors by forming Al-AlxOy-Al superconducting tunnel junctions on the sidewalls of a silicon mesa etched with KOH and an operating temperature of 0.3K. In the line-of-sight path along the width of these mesas, phonons with frequency ~100 GHz can propagate ballistically The phonons radiate into the mesa and are observed by the detector after passing through the mesa. We fabricated silicon nanosheets of width 100 to 300 nm along the ballistic path and observe surface scattering effects on phonon transmission when the characteristic length scale of a material is less than the phonon mean free path. We compare our results to the Casimir-Ziman theory. Our methods can be adapted for studying phonon transport in other nanostructures and will improve the understanding of phonon contribution to thermal transport. The work was supported in part by the National Science Foundation under Agreement No. DMR-1149036.
Phonon-lifetimes in demixing systems
International Nuclear Information System (INIS)
The dynamics of silver-alkali halide mixed single crystals (AgxNa1-xBr, x = 0.23, 0.35, 0.40 and 0.70) were studied by inelastic neutron scattering during the process of spinodal decomposition. Using the thermal three-axes spectrometer PUMA as well as the time-of-flight spectrometer IN5, the time evolution of phonons was observed in time-resolved, stroboscopic measurements. Complementary to the study of long wavelength acoustic phonons, as studied previously, we extended these investigations to Brillouin-zone boundary modes that are particularly sensitive to variations of the local structure. Starting from the homogeneous mixed phase the behaviour of these modes during demixing is observed in real-time. A simple dynamical model based on local structure variants helps to interpret the results. It is shown that the phonon lifetimes vary strongly during the phase separation and increase drastically during the coarsening process. Up to a critical size of precipitates of about 10 nm, zone-boundary modes are found to be strongly damped, while beyond the line widths are reduced to the experimental resolution. This finding leads to the conclusion that the typical mean free path of these modes is of the order of 10 nm, which corresponds to 20 unit cells. (paper)
Correlation-enhanced electron-phonon coupling
Yin, Zhiping
2015-03-01
Electron-phonon coupling (EPC) plays an important role in many material properties such as resistivity and conventional superconductivity. Accurate theoretical calculations of EPC in solids is essential for computational design, discovery and optimization of many functional materials. The widely used density functional theory (DFT) in the local density approximation (LDA) and generalized gradient approximation (GGA) can reasonably compute the EPC in weakly correlated materials but suffers from important shortcomings in strongly correlated materials. The self-energy of the quasiparticles in correlated materials modifies the LDA/GGA electronic structures hence the phonon frequencies and EPC. In this talk, I will discuss two types of underestimation of the EPC by LDA/GGA and propose a simple yet efficient methodology to evaluate the realistic EPC by using advanced electronic structure method beyond LDA/GGA. The extraordinarily high superconducting temperatures that are observed in two distinct classes of compounds-the bismuthates and the transition-metal chloronitrides can be readily accounted for by the correlation-enhanced EPC. Further impact of electronic correlation on the coupling of phonons and electronic degrees of freedom will also be discussed. This work was supported by the AFOSR-MURI Program.
Reduction of Thermal Conductivity by Nanoscale 3D Phononic Crystal
Yang, Lina; Li, Baowen
2013-01-01
The thermal conductivity of nanostructures needs to be as small as possible so that it will have a greater efficiency for solid-state electricity generation/refrigeration by thermoelectrics. We studied how the period length and the mass ratio affect the thermal conductivity of isotopic nanoscale 3D phononic crystal of Si. Simulation results by equilibrium molecular dynamics show isotopic nanoscale 3D phononic crystal can make a significance reduction on the thermal conductivity of bulk Si at high temperature,1000 K. Size and mass effects are obvious in manipulating thermal conductivity. The thermal conductivity decreases as the period length and mass ratio increases. The phonon dispersion curves show the decrease of group velocities in 3D phononic crystals. The phonon's localization and band gap is clearly shown in spectra of normalized inverse participation ratio in nanoscale 3D phononic crystal structure.
NATO Advanced Study Institute on Nonequilibrium Phonon Dynamics
1985-01-01
Phonons are always present in the solid state even at an absolute temperature of 0 K where zero point vibrations still abound. Moreover, phonons interact with all other excitations of the solid state and, thereby, influence most of its properties. Historically experimental information on phonon transport came from measurements of thermal conductivity. Over the past two decades much more, and much more detailed, information on phonon transport and on many of the inherent phonon interaction processes have come to light from experiments which use nonequilibrium phonons to study their dynamics. The resultant research field has most recently blossomed with the development of ever more sophisticated experimental and theoretical methods which can be applied to it. In fact, the field is moving so rapidly that new members of the research community have difficulties in keeping up to date. This NATO Advanced Study Institute (ASI) was organized with the objective of overcoming the information barrier between those expert...
Ding, X.; Salje, E. K. H.
2015-05-01
Thermal conductivity of ferroelastic device materials can be reversibly controlled by strain. The nucleation and growth of twin boundaries reduces thermal conductivity if the heat flow is perpendicular to the twin wall. The twin walls act as phonon barriers whereby the thermal conductivity decreases linearly with the number of such phonon barriers. Ferroelastic materials also show elasto-caloric properties with a high frequency dynamics. The upper frequency limit is determined by heat generation on a time scale, which is some 5 orders of magnitude below the typical bulk phonon times. Some of these nano-structural processes are irreversible under stress release (but remain reversible under temperature cycling), in particular the annihilation of needle domains that are a key indicator for ferroelastic behaviour in multiferroic materials.
Czech Academy of Sciences Publication Activity Database
Mocek, Tomáš; Jakubczak, Krzysztof; Kozlová, Michaela; Polan, Ji?í; Homer, Pavel; H?ebí?ek, J.; Sawicka, Magdalena; Kim, I.J.; Park, S.B.; Kim, C. M.; Lee, G.H.; Kim, T.K.; Nam, C. H.; Chalupský, Jaromír; Hájková, V?ra; Juha, Libor; Sobota, Jaroslav; Fo?t, Tomáš; Rus, Bed?ich
2010-01-01
Ro?. 165, 6-10 (2010), s. 551-558. ISSN 1042-0150 R&D Projects: GA AV ?R KAN300100702; GA MŠk(CZ) LC528; GA MŠk LA08024; GA ?R GC202/07/J008 Institutional research plan: CEZ:AV0Z10100523; CEZ:AV0Z20650511 Keywords : XUV lasers * ablation * microstructuring * laser-induced periodic surface structures Subject RIV: BH - Optics, Masers, Lasers Impact factor: 0.660, year: 2010
Phonon-Assisted Auger Recombination in Medium and Wide Band-Gap Materials from First Principles
Steiauf, Daniel; Kioupakis, Emmanouil; van de Walle, Chris G.
2014-03-01
GaN and GaAs and their alloys are technologically important materials for solid-state optoelectronic devices such as LEDs and lasers. The internal quantum efficiency of these devices, defined as the fraction of electron-hole pairs converted to photons, is limited by nonradiative loss mechanisms. Auger recombination is such a mechanism which limits the efficiency at high carrier densities. The energy and momentum of an electron-hole pair is transferred to a third carrier instead of creating a photon. We present state-of-the-art results of first-principles calculations of the Auger recombination rate coefficients both for the simple direct purely Coulombic process and the indirect phonon-assisted process. We find the absolute values of these recombination rates as well as their relative importance. In GaAs, when energy and momentum of the recombining pair are transferred to an Auger electron, the phonon-assisted process is several orders of magnitude stronger than the direct process, while for recombinations that create an Auger hole, the direct and phonon-assisted processes contribute almost equally. For lower band gaps, the electron processes become equally strong, and also the direct process becomes comparable in magnitude. This work was supported as part of the CEEM, an EFRC funded by the U.S. DoE, Office of Science, BES under Award Number DE-SC0001009.
Interface Phonon Modes in ZnTe/CdSe Strained Superlattices
Ren, Shang-Fen Ren; Stanfield, Jason
1998-03-01
ZnTe/CdSe superlattice is one of the wide-gap semiconductor superlattices with potential applications in blue-green diode lasers grown successfully in recent years. Its two constituent compounds, ZnTe and CdSe, do not share a common atom, and they also have closely matched lattice constants. There are experimental evidances that in ZnTe/CdSe superlattices there exist two to three layers of atomic interdiffusion and interchange of entire atom layers across the interfaces, and first principles calculations of total energy also confirmed the possibility of inetrchanges of entire atomic layers at interfaces. Here we report our theoretical studies of interface phonons in strained ZnTe/CdSe superlattices by using a first principle psudopotental method and a valence force field model. Phonon modes in superlattice with ideal interfaces (IDSL) and with interchanged interfaces (ICSL) of (ZnTe)8(CdSe)8 are calculated and comapred. Several unique features of phonon modes of ICSL different from that of IDSL are identified. These features are related to the interface structures of the superlattices, and they are model independent and experimentally detectable. These results provide more information about interface structures in ZnTe/CdSe superlattices, and we hope that our calculations can stimulate more experimental measurements in such materials.
Fractional Carbon Dioxide Laser Resurfacing
Ramsdell, William M.
2012-01-01
Currently available ablative fractional CO2 lasers provide excellent results and diminish down time with fewer complications than previous generation CO2 lasers. Mechanisms of action, treatment parameters, as well as pre- and postoperative care will be discussed.
Nanophotonic cavity optomechanics with propagating phonons in microwave Ku band
Li, Huan; Liu, Qiyu; Li, Mo
2015-01-01
Sideband-resolved coupling between multiple photonic nanocavities and propagating mechanical waves in microwave Ku-band is demonstrated. Coherent and strong photon-phonon interaction is manifested with optomechanically induced transparency and absorption, and phase-coherent interaction in multiple cavities. Inside an echo chamber it is shown that a phonon pulse can interact with an embedded nanocavity for multiple times. Our device provides a scalable platform to optomechanically couple phonons and photons for microwave photonics and quantum photonics.
Phonon energy in an anharmonic quasi-one-dimensional solid
Grado-Caffaro, M.A.; M. Grado-Caffaro
2011-01-01
For the first time, the phonon energy per unit volume in a large anharmonic quasi-one-dimensional solid is determined by considering all polarizations of the various modes of phonon propagation and by assuming the solid as a lattice of atoms behaving as Morse oscillators. In this context, the equilibrium phonon occupation number, which is given by the Bose distribution, replaces formally the vibrational quantum number into the expression for the Morse-oscillator energy. In addition, the quasi...
Single-mode phonon transmission in symmetry broken carbon nanotubes
WANG Jian; Wang, Jian-Sheng
2008-01-01
Normal mode phonon transmissions are studied in carbon nanotubes with the presence of Stone-Wales (SW) defect, using a mode-matching method and through the analysis of symmetry. The calculation shows that the transmission for low group velocity acoustic phonons is evidently reduced at high frequency range, and that this SW defect induced symmetry breaking strongly inhibits the transmission of long wave optical phonons in carbon nanotubes. The characteristic features of trans...
Strong coupling superconductivity mediated by three-dimensional anharmonic phonons
Hattori, Kazumasa; Tsunetsugu, Hirokazu
2010-01-01
We investigate three dimensional anharmonic phonons in tetrahedral symmetry and superconductivity mediated by these phonons. Three dimensional anharmonic phonon spectra are calculated directly by solving Schr\\"odinger equation and the superconducting transition temperature is determined by using the theory of strong coupling superconductivity assuming an isotropic gap function. With increasing the third order anharmonicity $b$ of the tetrahedral ion potential, we find a cros...
Electron-Phonon Interacation in Quantum Dots: A Solvable Model
Stauber, T.; Zimmermann, R.; de Castella, H.
2005-01-01
The relaxation of electrons in quantum dots via phonon emission is hindered by the discrete nature of the dot levels (phonon bottleneck). In order to clarify the issue theoretically we consider a system of $N$ discrete fermionic states (dot levels) coupled to an unlimited number of bosonic modes with the same energy (dispersionless phonons). In analogy to the Gram-Schmidt orthogonalization procedure, we perform a unitary transformation into new bosonic modes. Since only $N(N...
Donor Spin Qubits in Ge-based Phononic Crystals
Smelyanskiy, V.N.; Hafiychuk, V. V.; Vasko, F. T.; Petukhov, A. G.
2014-01-01
We propose qubits based on shallow donor electron spins in germanium. Spin-orbit interaction for donor spins in germanium is in many orders of magnitude stronger than in silicon. In a uniform bulk material it leads to very short spin lifetimes. However the lifetime increases dramatically when the donor is placed into a quasi-2D phononic crystal and the energy of the Zeeman splitting is tuned to lie within a phonon bandgap. In this situation single phonon processes are suppre...
Spin Conductance in one-dimensional Spin-Phonon systems
Louis, Kim; Zotos, Xenophon
2005-01-01
We present results for the spin conductance of the one dimensional spin-1/2 Heisenberg and XY model coupled to phonons. We apply an approach based on the Stochastic Series Expansion (Quantum Monte Carlo) method to evaluate the conductance for a variety of phonon dispersions and values of spin-phonon coupling. From our numerical simulations and analytical arguments, we derive several scaling laws for the conductance.
Electron-phonon heat transfer in monolayer and bilayer graphene
Viljas, J. K.; Heikkilä, T. T.
2010-01-01
We calculate the heat transfer between electrons to acoustic and optical phonons in monolayer and bilayer graphene (MLG and BLG) within the quasiequilibrium approximation. For acoustic phonons, we show how the temperature-power laws of the electron-phonon heat current for BLG differ from those previously derived for MLG and note that the high-temperature (neutral-regime) power laws for MLG and BLG are also different, with a weaker dependence on the electronic temperature in ...
Phononics: Manipulating heat flow with electronic analogs and beyond
Li, Nianbei; Ren, Jie; WANG, LEI; Zhang, Gang; Hänggi, Peter; Li, Baowen
2011-01-01
The form of energy termed heat that typically derives from lattice vibrations, i.e. the phonons, is usually considered as waste energy and, moreover, deleterious to information processing. However, with this colloquium, we attempt to rebut this common view: By use of tailored models we demonstrate that phonons can be manipulated like electrons and photons can, thus enabling controlled heat transport. Moreover, we explain that phonons can be put to beneficial use to carry and...
Electron-Phonon Interaction and Phonon Softening in Systems with Magnetovolume Instabilities
Herper, H.; Entel, P.; Weber, W.
1995-01-01
The interrelation of Invar and martensitic behaviour in transition metal alloys like Fe65Ni35 is discussed on the basis of ab initio calculations for stoichiometric systems like Fe3Ni. We also examined face centered cubic iron as a model system for Antiinvar which like Invar shows a pronounced phonon softening. Neutron scattering experiments on Invar systems have shown that the TA1 phonon mode softens for small wavevectors (vector q) along the [110] direction in the fcc lattice. To day there ...
Phonons and electron-phonon coupling in graphene-h-BN heterostructures
Energy Technology Data Exchange (ETDEWEB)
Slotman, Guus J.; Wijs, Gilles A. de; Fasolino, Annalisa; Katsnelson, Mikhail I. [Institute for Molecules and Materials, Radboud University Nijmegen (Netherlands)
2014-10-15
First principle calculations of the phonons of graphene-h-BN heterostructures are presented and compared to those of the constituents. It is shown that AA and AB' stacking are not only energetically less favoured than AB but also dynamically unstable. Low energy flat phonon branches of h-BN character with out of plane displacement have been identified and their coupling to electrons in graphene has been evaluated. (copyright 2014 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Calculations of the $A_{1}$ phonon frequency in photoexcited Tellurium
Tangney, P
1999-01-01
Calculations of the A_1 phonon frequency in photoexcited tellurium are presented. The phonon frequency as a function of photoexcited carrier density and phonon amplitude is determined. Recent pump probe experiments are interpreted in the light of these calculatons. It is proposed that, in conjunction with measurements of the phonon period in ultra-fast pump-probe reflectivity experiments, the calculated frequency shifts can be used to infer the evolution of the density of photoexcited carriers on a sub-picosecond time-scale.
Anomalous phonon drag in point contact in magnetic field
International Nuclear Information System (INIS)
It is shown that the phonon drag and heat release asymmetry in metal point contact (PC) placed in the high magnetic field are highly sensitive to the relation of the contact areas for phonons and electrons. A distinctive feature of the adopted model of a PC is that the aperture for the electrons is smaller in diameter (d) than the aperture (of diameter D) for the phonons. In this case the magnetic field changes significantly (by the factor (D/d)2 the phonon-drag thermopower
Acoustic phonon transport through a T-shaped quantum waveguide
International Nuclear Information System (INIS)
We study the transmission coefficient and thermal conductivity for acoustic phonons crossing a T-shaped quantum waveguide at low enough temperatures by use of the scattering-matrix method. Our results show that relatively small changes in the stub length and width can induce strong variations in the phonon transmission and thermal conductivity. Compared with the electron case in such a structure, acoustic phonon transmission and thermal conductivity exhibit some novel and interesting features. The phonon transmission coefficients and thermal conductivity can be artificially controlled by adjusting the parameters of the proposed microstructure
Phonon dynamics and Urbach energy studies of MgZnO alloys
Huso, Jesse; Che, Hui; Thapa, Dinesh; Canul, Amrah; McCluskey, M. D.; Bergman, Leah
2015-03-01
The MgxZn1-xO alloy system is emerging as an environmentally friendly choice in ultraviolet lighting and sensor technologies. Knowledge of defects which impact their optical and material properties is a key issue for utilization of these alloys in various technologies. The impact of phase segregation, structural imperfections, and alloy inhomogeneities on the phonon dynamics and electronic states of MgxZn1-xO thin films were studied via selective resonant Raman scattering (SRRS) and Urbach analyses, respectively. A series of samples with Mg composition from 0-68% were grown using a sputtering technique, and the optical gaps were found to span a wide UV range of 3.2-5.8 eV. The extent of the inherent phase segregation was determined via SRRS using two UV-laser lines to achieve resonance with the differing optical gaps of the embedded cubic and wurtzite structural domains. The occurrence of Raman scattering from cubic structures is discussed in terms of relaxation of the selection rules due to symmetry breaking by atomic substitutions. The Raman linewidth and Urbach energy behavior indicate the phase segregation region occurs in the range of 47-66% Mg. Below the phase segregation, the longitudinal optical phonons are found to follow the model of one-mode behavior. The phonon decay model of Balkanski et al. indicates that the major contributor to Raman linewidth arises from the temperature-independent term attributed to structural defects and alloy inhomogeneity, while the contribution from anharmonic decay is relatively small. Moreover, a good correlation between Urbach energy and Raman linewidth was found, implying that the underlying crystal dynamics affecting the phonons also affect the electronic states. Furthermore, for alloys with low Mg composition structural defects are dominant in determining the alloy properties, while at higher compositions alloy inhomogeneity cannot be neglected.
Laser Refractometry for Biomedical Diagnostics
International Science & Technology Center (ISTC)
Application of a New Method of Laser Refractometry for Determining the Stimulating Action Mechanisms of Optical Therapy, for Disease Diagnostics and Treatment Efficiency Evaluating of Pneumonia and Helminthosis
Lin, Keng-Hua; Strachan, Alejandro
2015-07-01
Motivated by significant interest in metal-semiconductor and metal-insulator interfaces and superlattices for energy conversion applications, we developed a molecular dynamics-based model that captures the thermal transport role of conduction electrons in metals and heat transport across these types of interface. Key features of our model, denoted eleDID (electronic version of dynamics with implicit degrees of freedom), are the natural description of interfaces and free surfaces and the ability to control the spatial extent of electron-phonon (e-ph) coupling. Non-local e-ph coupling enables the energy of conduction electrons to be transferred directly to the semiconductor/insulator phonons (as opposed to having to first couple to the phonons in the metal). We characterize the effect of the spatial e-ph coupling range on interface resistance by simulating heat transport through a metal-semiconductor interface to mimic the conditions of ultrafast laser heating experiments. Direct energy transfer from the conduction electrons to the semiconductor phonons not only decreases interfacial resistance but also increases the ballistic transport behavior in the semiconductor layer. These results provide new insight for experiments designed to characterize e-ph coupling and thermal transport at the metal-semiconductor/insulator interfaces.
Lin, Keng-Hua; Strachan, Alejandro
2015-07-21
Motivated by significant interest in metal-semiconductor and metal-insulator interfaces and superlattices for energy conversion applications, we developed a molecular dynamics-based model that captures the thermal transport role of conduction electrons in metals and heat transport across these types of interface. Key features of our model, denoted eleDID (electronic version of dynamics with implicit degrees of freedom), are the natural description of interfaces and free surfaces and the ability to control the spatial extent of electron-phonon (e-ph) coupling. Non-local e-ph coupling enables the energy of conduction electrons to be transferred directly to the semiconductor/insulator phonons (as opposed to having to first couple to the phonons in the metal). We characterize the effect of the spatial e-ph coupling range on interface resistance by simulating heat transport through a metal-semiconductor interface to mimic the conditions of ultrafast laser heating experiments. Direct energy transfer from the conduction electrons to the semiconductor phonons not only decreases interfacial resistance but also increases the ballistic transport behavior in the semiconductor layer. These results provide new insight for experiments designed to characterize e-ph coupling and thermal transport at the metal-semiconductor/insulator interfaces. PMID:26203038
Phonons in InAs quantum dot structures
International Nuclear Information System (INIS)
We present a Raman study of the phonon spectra of periodical structures with (In,Ga)As QDs in (Al,Ga)As matrix as well as AlAs QDs embedded in InAs grown by molecular beam epitaxy. Raman scattering by optical, interface and acoustic phonons was observed in the QD structures. TO and LO phonons in the QDs are strongly affected by both strain and confinement. The Raman study reveals a two-mode behavior of optical phonons in the whole composition range for both InGaAs QDs and the AlGaAs matrix. Raman scattering by InAs- and GaAs-like LO phonons in InGaAs QDs shows a size-selective resonant behaviour. Interface phonons were investigated in InGaAs QDs and the AlGaAs matrix. Their frequency positions were analyzed as a function of the alloy content within the dielectric continuum model. The positions of IF phonons in the QD structures observed in the experiment agree well with calculated ones assuming that the QDs have the shape of oblate ellipsoids. Multiple phonon Raman scattering involving both pure overtones of the first-order InAs, GaAs and AlAs optical and interface phonons and combination of phonons from the materials is observed in the vicinity with E0 resonance in QDs. Possible mechanisms of these processes are discussed. Low frequency resonant Raman scattering by acoustic phonons was observed in the QD structures. The periodic oscillations seen in the Raman spectra are well described by the elastic continuum model. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Phonon hydrodynamics and its applications in nanoscale heat transport
Guo, Yangyu; Wang, Moran
2015-09-01
Phonon hydrodynamics is an effective macroscopic method to study heat transport in dielectric solid and semiconductor. It has a clear and intuitive physical picture, transforming the abstract and ambiguous heat transport process into a concrete and evident process of phonon gas flow. Furthermore, with the aid of the abundant models and methods developed in classical hydrodynamics, phonon hydrodynamics becomes much easier to implement in comparison to the current popular approaches based on the first-principle method and kinetic theories involving complicated computations. Therefore, it is a promising tool for studying micro- and nanoscale heat transport in rapidly developing micro and nano science and technology. However, there still lacks a comprehensive account of the theoretical foundations, development and implementation of this approach. This work represents such an attempt in providing a full landscape, from physical fundamental and kinetic theory of phonons to phonon hydrodynamics in view of descriptions of phonon systems at microscopic, mesoscopic and macroscopic levels. Thus a systematical kinetic framework, summing up so far scattered theoretical models and methods in phonon hydrodynamics as individual cases, is established through a frame of a Chapman-Enskog solution to phonon Boltzmann equation. Then the basic tenets and procedures in implementing phonon hydrodynamics in nanoscale heat transport are presented through a review of its recent wide applications in modeling thermal transport properties of nanostructures. Finally, we discuss some pending questions and perspectives highlighted by a novel concept of generalized phonon hydrodynamics and possible applications in micro/nano phononics, which will shed more light on more profound understanding and credible applications of this new approach in micro- and nanoscale heat transport science.
International Nuclear Information System (INIS)
This in vitro study compares two different types of tooth bleaching agents stimulated with two different irradiation fonts. These fonts accelerate the action of the bleaching agents upon the enamel surface by heating up the materials. We used the xenon plasma arc lamp and a 960 nm fiber-coupled diode laser to irradiate the two materials containing 35% of hydrogen peroxide (Opus White and Opalescence extra). The color of the teeth was measured with a spectrophotometer using the CIELAB color system that gives the numeric values of L*a*b*. (author)
Large scale phononic metamaterials for seismic isolation
Aravantinos-Zafiris, N.; Sigalas, M. M.
2015-08-01
In this work, we numerically examine structures that could be characterized as large scale phononic metamaterials. These novel structures could have band gaps in the frequency spectrum of seismic waves when their dimensions are chosen appropriately, thus raising the belief that they could be serious candidates for seismic isolation structures. Different and easy to fabricate structures were examined made from construction materials such as concrete and steel. The well-known finite difference time domain method is used in our calculations in order to calculate the band structures of the proposed metamaterials.
Spectroscopy of nonequilibrium electrons and phonons
Shank, CV
1992-01-01
The physics of nonequilibrium electrons and phonons in semiconductors is an important branch of fundamental physics that has many practical applications, especially in the development of ultrafast and ultrasmall semiconductor devices. This volume is devoted to different trends in the field which are presently at the forefront of research. Special attention is paid to the ultrafast relaxation processes in bulk semiconductors and two-dimensional semiconductor structures, and to their study by different spectroscopic methods, both pulsed and steady-state. The evolution of energy and space distrib
Temperature dependent phonon properties of thermoelectric materials
Hellman, Olle; Broido, David; Fultz, Brent
2015-03-01
We present recent developments using the temperature dependent effective potential technique (TDEP) to model thermoelectric materials. We use ab initio molecular dynamics to generate an effective Hamiltonian that reproduce neutron scattering spectra, thermal conductivity, phonon self energies, and heat capacities. Results are presented for (among others) SnSe, Bi2Te3, and Cu2Se proving the necessity of careful modelling of finite temperature properties for strongly anharmonic materials. Supported by the Swedish Research Council (VR) Project Number 637-2013-7296.
Semi-Dirac points in phononic crystals
Zhang, Xiujuan
2014-01-01
A semi-Dirac cone refers to a peculiar type of dispersion relation that is linear along the symmetry line but quadratic in the perpendicular direction. It was originally discovered in electron systems, in which the associated quasi-particles are massless along one direction, like those in graphene, but effective-mass-like along the other. It was reported that a semi-Dirac point is associated with the topological phase transition between a semi-metallic phase and a band insulator. Very recently, the classical analogy of a semi-Dirac cone has been reported in an electromagnetic system. Here, we demonstrate that, by accidental degeneracy, two-dimensional phononic crystals consisting of square arrays of elliptical cylinders embedded in water are also able to produce the particular dispersion relation of a semi-Dirac cone in the center of the Brillouin zone. A perturbation method is used to evaluate the linear slope and to affirm that the dispersion relation is a semi-Dirac type. If the scatterers are made of rubber, in which the acoustic wave velocity is lower than that in water, the semi-Dirac dispersion can be characterized by an effective medium theory. The effective medium parameters link the semi-Dirac point to a topological transition in the iso-frequency surface of the phononic crystal, in which an open hyperbola is changed into a closed ellipse. This topological transition results in drastic change in wave manipulation. On the other hand, the theory also reveals that the phononic crystal is a double-zero-index material along the x-direction and photonic-band-edge material along the perpendicular direction (y-direction). If the scatterers are made of steel, in which the acoustic wave velocity is higher than that in water, the effective medium description fails, even though the semi-Dirac dispersion relation looks similar to that in the previous case. Therefore different wave transport behavior is expected. The semi-Dirac points in phononic crystals described in this work would offer new ways to manipulate acoustic waves with simple periodic structures. Copyright © 2014 by ASME.
Two-phonon excitations in 170Er
International Nuclear Information System (INIS)
Recent experiments at the GEANIE/WNR facility and the University of Kentucky accelerator have yielded strong evidence for a two-gamma excitation in 170Er. This new case can be added to a handful of previously identified examples of two-gamma vibrations, all of them discovered in this decade. In this paper the experimental evidence for a two-phonon excitation 170Er is presented and the current state of understanding of these structures is reviewed in the context of this and other recent findings
Two-phonon excitations in 170Er
International Nuclear Information System (INIS)
Recent experiments at the GEANIE/WNR facility and the University of Kentucky accelerator have yielded strong evidence for a two-gamma excitation in 170Er. This new case can be added to a handful of previously identified examples of two-gamma vibrations, all of them discovered in this decade. In this paper the experimental evidence for a two-phonon excitation 170Er is presented and the current state of understanding of these structures is reviewed in the context of this and other recent findings. (c) 1999 American Institute of Physics
Phonon scattering in graphene over substrate steps
International Nuclear Information System (INIS)
We calculate the effect on phonon transport of substrate-induced bends in graphene. We consider bending induced by an abrupt kink in the substrate, and provide results for different step-heights and substrate interaction strengths. We find that individual substrate steps reduce thermal conductance in the range between 5% and 47%. We also consider the transmission across linear kinks formed by adsorption of atomic hydrogen at the bends and find that individual kinks suppress thermal conduction substantially, especially at high temperatures. Our analysis show that substrate irregularities can be detrimental for thermal conduction even for small step heights.
International Nuclear Information System (INIS)
Nonlinear radiation dynamics of a solid-state ring laser is studied in the region of laser parameters corresponding to the parametric resonance between the self-modulation and relaxation oscillations. Bistable regions are found in which, apart from the self-modulation regime of the first kind, a stable quasi-periodic self-modulation regime exists. Temporal and spectral emission parameters of counterpropagating waves are considered in the bistable self-modulation generation regimes. The effect of noise on the bistable self-modulation oscillations is studied. It is shown that during the interaction of noise, spectral peaks split at relaxation and self-modulation frequencies. (control of laser radiation parameters)
Phonon Mediated Off-Resonant Quantum Dot-Cavity Coupling
Majumdar, Arka; Gong, Yiyang; Kim, Erik D.; vuckovic, Jelena
2010-01-01
A theoretical model for the phonon-mediated off-resonant coupling between a quantum dot and a cavity, under resonant excitation of the quantum dot, is presented. We show that the coupling is caused by electron-phonon interaction in the quantum dot and is enhanced by the cavity. We analyze recently observed resonant quantum dot spectroscopic data by our theoretical model.
Phonon-based scalable quantum computing and sensing (Presentation Video)
El-Kady, Ihab
2015-04-01
Quantum computing fundamentally depends on the ability to concurrently entangle and individually address/control a large number of qubits. In general, the primary inhibitors of large scale entanglement are qubit dependent; for example inhomogeneity in quantum dots, spectral crowding brought about by proximity-based entanglement in ions, weak interactions of neutral atoms, and the fabrication tolerances in the case of Si-vacancies or SQUIDs. We propose an inherently scalable solid-state qubit system with individually addressable qubits based on the coupling of a phonon with an acceptor impurity in a high-Q Phononic Crystal resonant cavity. Due to their unique nonlinear properties, phonons enable new opportunities for quantum devices and physics. We present a phononic crystal-based platform for observing the phonon analogy of cavity quantum electrodynamics, called phonodynamics, in a solid-state system. Practical schemes involve selective placement of a single acceptor atom in the peak of the strain field in a high-Q phononic crystal cavity that enables strong coupling of the phonon modes to the energy levels of the atom. A qubit is then created by entangling a phonon at the resonance frequency of the cavity with the atomic acceptor states. We show theoretical optimization of the cavity design and excitation waveguides, along with estimated performance figures of the phoniton system. Qubits based on this half-sound, half-matter quasi-particle, may outcompete other quantum architectures in terms of combined emission rate, coherence lifetime, and fabrication demands.
Phonon Dispersions of Graphene from Unzipping Carbon Nanotubes
Kandemir, B. S.; Aydin, Emine
2015-06-01
We calculate the phonon spectra of chiral single-walled carbon nanotubes and graphene within a mass and spring model which includes up to third neighbour interactions together with a radial bond-bending interaction. Firstly, the classical Hamiltonian for lattice vibrations of chiral single-walled carbon nanotubes is derived and then it is quantized. The resultant Hamiltonian is diagonalized under a unitary transformation scheme to obtain phonon modes as a function of momentum vector. Using resolvent formalism we analytically obtain phonon dispersions of these structures. We show that our calculated results for chiral SWCNTs reproduce well the results found for achiral SWCNTs. Finally, we introduce an unzipping technique to obtain full analytical phonon dispersion curves of graphene using phonon dispersions of chiral SWCNTs. We compare our analytical results for the phonon dispersions of graphene to the available experimental data and show that they agree well with the experiment. Our analytical results not only provide a basis for understanding phonon dispersions of carbon nanotubes, but also illuminate the bare phonon structure of graphene.
Phonons and charge-transfer excitations in HTS superconductors
International Nuclear Information System (INIS)
Some of the experimental and theoretical evidence implicating phonons and charge-transfer excitations in HTS superconductors is reviewed. It is suggested that superconductivity may be driven by a synergistic interplay of (anharmonic) phonons and electronic degrees of freedom (e.g., charge fluctuations, excitons). 47 refs., 5 figs
Phonon thermal transport through tilt grain boundaries in strontium titanate
Energy Technology Data Exchange (ETDEWEB)
Zheng, Zexi; Chen, Xiang; Yang, Shengfeng; Xiong, Liming; Chen, Youping [Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, Florida 32611 (United States); Deng, Bowen; Chernatynskiy, Aleksandr [Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611 (United States)
2014-08-21
In this work, we perform nonequilibrium molecular dynamics simulations to study phonon scattering at two tilt grain boundaries (GBs) in SrTiO{sub 3}. Mode-wise energy transmission coefficients are obtained based on phonon wave-packet dynamics simulations. The Kapitza conductance is then quantified using a lattice dynamics approach. The obtained results of the Kapitza conductance of both GBs compare well with those obtained by the direct method, except for the temperature dependence. Contrary to common belief, the results of this work show that the optical modes in SrTiO{sub 3} contribute significantly to phonon thermal transport, accounting for over 50% of the Kapitza conductance. To understand the effect of the GB structural disorder on phonon transport, we compare the local phonon density of states of the atoms in the GB region with that in the single crystalline grain region. Our results show that the excess vibrational modes introduced by the structural disorder do not have a significant effect on phonon scattering at the GBs, but the absence of certain modes in the GB region appears to be responsible for phonon reflections at GBs. This work has also demonstrated phonon mode conversion and simultaneous generation of new modes. Some of the new modes have the same frequency as the initial wave packet, while some have the same wave vector but lower frequencies.
RENORMALIZED RESPONSE THEORY WITH APPLICATIONS TO PHONON ANOMALIES
Falter, C.; Ludwig, W.; Selmke, M.
1981-01-01
A recently developed renormalization method for the electron response problem in effective ion-interactions is applied to phonon anomalies. A microscopic mechanism for the anomalies is proposed and its relation to the electron-phonon-coupling parameter ? and thus to Tc is discussed.
Quasiparticle-phonon coupling in inelastic proton scattering
International Nuclear Information System (INIS)
Multistep-processes in inelastic proton scattering from 89Y are analyzed by using CCBA and DWBA on a quasiparticle phonon nuclear structure model. Indirect excitations caused by quasiparticle phonon coupling effects are found to be very important for the transition strengths and the shape of angular distributions. Core excitations are dominant for the higher order steps of the reaction. (author)
Phonon density of states in V3Si
International Nuclear Information System (INIS)
The observation by inelastic neutron scattering techniques of a high energy peak in the phonon spectrum (14 THz) of V3Si is reported, and is attributed to a peak in the phonon density of states due to vanadium motions by the incoherent inelastic neutron scattering process
Angular resolved phonon emission from excited quantum dots
International Nuclear Information System (INIS)
We calculate the angular emission characteristics of phonons from parabolic confined quantum dots containing a single or two interacting electrons. The emission spectra are shown to be generally characterized by a narrow polar angle giving a phonon propagation direction explicitly characterized by the energy difference of the transition. In addition, the phonon emission spectra contain a given number of azimuthally oriented lobes which reflect the quantum structure of the initial excited state. This implies that measurements of angular resolved phonon emission spectra can give detailed information on the electronic charge distribution and energy spectra of excited quantum states. When such a structure is known, a large-scale ordering of identical quantum dots with respect to the emission angles may realize phonon amplification by stimulated emission. (paper)
Controlling elastic waves with small phononic crystals containing rigid inclusions
Peng, Pai
2014-05-01
We show that a two-dimensional elastic phononic crystal comprising rigid cylinders in a solid matrix possesses a large complete band gap below a cut-off frequency. A mechanical model reveals that the band gap is induced by negative effective mass density, which is affirmed by an effective medium theory based on field averaging. We demonstrate, by two examples, that such elastic phononic crystals can be utilized to design small devices to control low-frequency elastic waves. One example is a waveguide made of a two-layer anisotropic elastic phononic crystal, which can guide and bend elastic waves with wavelengths much larger than the size of the waveguide. The other example is the enhanced elastic transmission of a single-layer elastic phononic crystal loaded with solid inclusions. The effective mass density and reciprocal of the modulus of the single-layer elastic phononic crystal are simultaneously near zero. © CopyrightEPLA, 2014.
Low Frequency Thermal Conductivity in Micro Phononic Crystals
Anjos, Virgilio; Arantes, Alison
2015-03-01
We study theoretically the cumulative thermal conductivity of a micro phononic crystal at low temperature regime. The phononic crystal considered presents carbon microtubes inclusions arranged periodically in a two-dimensional square lattice embebed in soft elastic matrix. Moderate and high impedance mismatch are considered concerning the material composition. The low frequency phonon spectra (up to tens of GHz) are obtained solving the generalized wave equation for inhomogeneous media within the Plane Wave Expansion method. We consider low temperatures in order to increase the participation of GHz thermal phonons. We observed suppression in the cumulative thermal conductivity at the band gap region and thus a reduction of thermal conductivity of the phononic crystal when compared with the bulk matrix. The authors would like to thank the Brazilian agencies, National Council of Technological and Scientific Development (CNPq), Foundation for Research Support of Minas Gerais (FAPEMIG) and CAPES for their support.
Phase seeding of a terahertz quantum cascade laser
Oustinov, Dimitri; Jukam, Nathan; Rungsawang, Rakchanok; Madéo, Julien; Barbieri, Stefano; Filloux, Pascal; Sirtori, Carlo; Marcadet, Xavier; Tignon, Jérôme; Dhillon, Sukhdeep
2010-01-01
The amplification of spontaneous emission is used to initiate laser action. Since the phase of spontaneous emission is random, the phase of the coherent laser emission (the carrier phase) will also be random each time laser action begins. This prevents phase resolved detection of the laser field. Here, we demonstrate how the carrierphase can be fixed in a semiconductor laser: a quantum cascade laser. This is performed by injection seeding a quantum cascade laser with coherent terahertz pulses...
Influence of laser heating on the X-ray diffraction intensity of InSb
Energy Technology Data Exchange (ETDEWEB)
Walkenhorst, Jessica; Zijlstra, Eeuwe S.; Garcia, Martin E. [Theoretische Physik, Fachbereich Naturwissenschaften, Universitaet Kassel, Heinrich-Plett-Str. 40, 34132 Kassel (Germany)
2008-07-01
Hillyard et al. have measured the X-ray diffraction intensity of the (111) peak of InSb after intense laser excitation, which provides insight in the first stages of laser-induced ultrafast melting. They found that the diffraction peak follows a Gaussian decay. This time-dependence has been analyzed using the Debye model for the atomic vibrations, assuming the laser heating to produce a uniform softening of all phonon frequencies. We performed (i) first principle electronic structure calculations, (ii) molecular dynamic simulations to calculate the phonon frequencies at the {gamma}-, X- and L-point and the resulting X-ray intensity. We found, that dramatic phonon softening does not occur at all the investigated k-points but instead the softening of the transverse acoustic phonons at the X-point suffices to explain the measured Gaussian X-ray intensity decay and perfectly reproduces the decay's measured time constant.
Doppleron-phonon resonance in cadmium
International Nuclear Information System (INIS)
The resonance interaction between a doppleron wave and a sound wave in cadmium located in a magnetic field parallel to the hexagonal axis is investigated. A theory of the doppleron-phonon resonance is constructed which takes into account the induction, as well as the deformation interaction of the electrons with the lattice vibrations. The effect of the resonance on the properties of the doppleron and the sound wave is studied. It is shown that the attenuation of both waves is maximal in the resonance region. The oscillations of the surface resistance of a cadmium plate located in a magnetic field H [0001] is experimentally studied in the 25-100 MHz frequency range. It is found that in the region of field intensities corresponding to the doppleron-phonon resonance the amplitude of the doppleron oscillations decreases significantly, and an additional series of oscillations appears. The theoretical and experimental results are in qualitative agreement. Comparison of the theoretical results with the experimental data leads to the conclusion that the electron-lattice deformation interaction in cadmium predominates over the induction interaction and allows the deformation-interaction constant to be estimated
Electron--phonon interaction in superconducting vanadium
International Nuclear Information System (INIS)
Electron-phonon interaction in superconducting vanadium is measured through the mechanism of the ultrasonic attenuation coefficient. Measurements were made as a function of temperature and magnetic field in three single crystal vanadium samples with resistivity ratios of 7.8, 245, and 450, to be referred to as samples I, II, and III, respectively. Emphasis has been placed on the mixed state region near H/sub c2/ where the data have been compared with the theoretical predictions of Houghton and Maki (HM). To facilitate comparison of the results, transverse waves were used in all three samples with phonon wave vector, q, parallel to the applied magnetic field, H. The direction of propagation was [110], [110], and [100], for a frequency of 255 MHz, 15 MHz, and 45 MHz, in sample I, II, and III respectively. Longitudinal waves of 135 MHz and q parallel H were also used in sample I. The predicted temperature and field dependence, in all cases, agree with the experimental results. The values obtained for the electron mean free path, used as a fitting parameter for the HM theory to the experimental results, are compared with the values obtained from dc conductivity measurements and from free-electron model predictions for attenuation versus frequency. The zero temperature BCS energy gap is also found for each sample and the resulting good agreement between the BCS prediction, and the experimentally found dependence, of the ultrasonic attenuation on temperature is graphically illustrated
One-phonon excitations in hot nuclei
International Nuclear Information System (INIS)
The RPA equations in a hot nucleus are derived within the formalism of the thermodynamics. Following the main prescriptions of the TFD we express the Hamiltonian of the quasiparticle-phonon nuclear model with a separable effective interaction in both particle-particle and particle-hole channels in terms of the so-called thermal quasiparticle operators. This has been done by two successive canonical transformations - the usual Bogoliubov transformation and the thermal Bogoliubov transformation. The coefficients of the transformations are determined by minimizing the free energy potential of a hot nucleus in the thermal vacuum state. Then the RPA part of the thermal Hamiltonian is extracted and the variational principle is used to derive the equations for thermal one-phonon states. For the case when only particle -hole interaction is taken into account, our results coincide with the results of the Green function method and the equation-of-motion method. This approach can be extended beyond the RPA as well. 15 refs. (author)
Search for the 3-phonon state of 40Ca
International Nuclear Information System (INIS)
We study collective vibrational states of the nucleus: giant resonances and multiphonon states. It has been shown that multiphonon states, which are built with several superimposed giant resonances, can be excited in inelastic heavy ion scattering near the grazing angle. No three photon states have been observed until now. An experiment has been performed at GANIL, aiming at the observation of the 3-phonon state built with the giant quadrupole resonance (GQR) in 40Ca, with the reaction 40Ca + 40Ca at 50 A.Me.V. The ejectile was identified in the SPEG spectrometer. Light charged particles were detected in 240 CsI scintillators of the INDRA 4? array. The analysis confirms the previous results about the GQR and the 2-phonon state in 40Ca. For the first time, we have measured an important direct decay branch of the GQR by alpha particles. Applying the so-called 'missing energy method' to events containing three protons measured in coincidence with the ejectile, we observe a direct decay branch revealing the presence of a 3-phonon state in the excitation energy region expected for the triple GQR. Dynamical processes are also studied in the inelastic channel, emphasizing a recently discovered mechanism named towing-mode. We observe for the first time the towing-mode of alpha particles. The energies of multiphonon states in 40Ca and 208Pb have been computed microscopically including some anharmonicities via boson mapping methods. The basis of the calculation has been extended to the 3-phonon states. Our results show large anharmonicities (several MeV), due to the coupling of 3-phonon states to 2-phonon states. The extension of the basis to 4-phonon states has been performed for the first time. The inclusion of the 4 phonon states in the calculation did not affect the previous observations concerning the 2-phonon states. Preliminary results on the anharmonicities of the 3-phonon states are presented. (author)
Phong, Tran Cong; Phuong, Le Thi Thu; Hien, Nguyen Dinh; Lam, Vo Thanh
2015-07-01
We investigate the influence of phonon confinement on the optically detected magneto-phonon resonance (ODMPR) effect and ODMPR line-width in quantum wells. The ODMPR conditions as functions of the well's width and the photon energy are also obtained. The shifts of ODMPR peaks caused by the confined phonon are discussed. The numerical result for the GaAs/AlAs quantum well shows that in the two cases of confined and bulk phonons, the line-width (LW) decreases with increasing well's width and increases with increasing temperature. Furthermore, in the small range of the well's width, the influence of phonon confinement plays an important role and cannot be neglected in reaching the ODMPR line-width.
International Nuclear Information System (INIS)
A full quantum microscopic theory is developed to analyze a biexciton radiative cascade coupled to bulk acoustic phonons in a quantum dot. By considering the phonon sub-system in coherent state representation a new approach is proposed for investigating the phonon effects. Via this approach it is possible to obtain an exact analytical result for the phonon kernel in this system. This approach is introduced in the context of an example: the process of generating polarization-entangled photon pairs from the biexciton cascade in a quantum dot. We calculate the exact density matrix (using quantum state tomography) of photons and their concurrence. We show that the exchange interaction and temperature have remarkable effects on the degree of entanglement of the emitted photons. The approach introduced provides an exact analytical result for finite discrete electron states interacting with phonons. (paper)
Makovetskii, D N
2001-01-01
The microwave phonon stimulated emission (SE) has been experimentally and numerically investigated in a nonautonomous microwave acoustic quantum generator, called also microwave phonon laser or phaser (see previous works arXiv:cond-mat/0303188 ; arXiv:cond-mat/0402640 ; arXiv:nlin.CG/0703050) Phenomena of branching and long-time refractority (absence of the reaction on the external pulses) for deterministic chaotic and regular processes of SE were observed in experiments with various levels of electromagnetic pumping. At the pumping level growth, the clearly depined increasing of the number of coexisting SE states has been observed both in real physical experiments and in computer simulations. This confirms the analytical estimations of the branching density in the phase space. The nature of the refractority of SE pulses is closely connected with the pointed branching and reflects the crises of strange attractors, i.e. their collisions with unstable periodic components of the higher branches of SE states in t...
Czech Academy of Sciences Publication Activity Database
Jakubczak, Krzysztof; Mocek, Tomáš; Rus, Bed?ich; H?ebí?ek, J.; Sawicka, Magdalena; Kim, I.J.; Park, S.B.; Kim, T.K.; Lee, G.H.; Nam, C. H.; Chalupský, Jaromír; Hájková, V?ra; Juha, Libor; Sobota, Jaroslav; Fo?t, Tomáš
Bellingham : SPIE, 2009 - (Khounsary, A.; Morawe, C.; Goto, S.), 736010/1-736010/11 ISBN 978-0-8194-7738-5. ISSN 0277-786X. - (Proceedings of SPIE. 7448). [Advances in X-Ray/EUV Optics and Components IV. San Diego (US), 03.08.2009-05.08.2009] R&D Projects: GA AV ?R KAN300100702; GA MŠk LC510; GA MŠk(CZ) LC528; GA MŠk LA08024; GA ?R 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/10.1117/12.826404
International Nuclear Information System (INIS)
Measurements are reported, for the first time, for detection of nonequilibrium phonons emitted from the inhomogeneous gap states of a nonequilibrium superconductor by means of a phonon transmission technique. The observed phonon signal exhibits a clear spatial structure with a certain periodicity. The connection between the I-V characteristic and the phonon signal is discussed
Laser Processing and Chemistry
Bäuerle, Dieter
2011-01-01
This book gives an overview of the fundamentals and applications of laser-matter interactions, in particular with regard to laser material processing. Special attention is given to laser-induced physical and chemical processes at gas-solid, liquid-solid, and solid-solid interfaces. Starting with the background physics, the book proceeds to examine applications of lasers in “standard” laser machining and laser chemical processing (LCP), including the patterning, coating, and modification of material surfaces. This fourth edition has been enlarged to cover the rapid advances in the understanding of the dynamics of materials under the action of ultrashort laser pulses, and to include a number of new topics, in particular the increasing importance of lasers in various different fields of surface functionalizations and nanotechnology. In two additional chapters, recent developments in biotechnology, medicine, art conservation and restoration are summarized. Graduate students, physicists, chemists, engineers, a...
Developments of new laser crystals doped with Yb ions
International Nuclear Information System (INIS)
In the development of laser crystals suitable for the ultra high peak power CPA (Chirped Pulse Amplification) laser system with compact size, four fluoride host crystals were selected and their crystals doped with Yb3+ ions have been grown by a vertical Bridgmann method. Only Yb:LaF3 showed yellowish, the others were transparent. The samples extracted from the boules were evaluated in the measurements of absorption and emission spectrums at room temperature using spectrophotometer. From the comparison of zero phonon levels in three host crystals having the same fluorite structure, it shows that the larger lattice constant, the higher zero phonon level. (author)
Phonon spectral function of the Holstein polaron
International Nuclear Information System (INIS)
The phonon spectral function of the one-dimensional Holstein model is obtained within weak-coupling and strong-coupling approximations based on analytical self-energy calculations. The characteristic excitations found in the limit of small charge-carrier density are related to the known (electronic) spectral properties of Holstein polarons such as the polaron band dispersion. Particular emphasis is laid on the different physics occurring in the adiabatic and anti-adiabatic regimes, respectively. Comparison is made with a cluster approach exploiting exact numerical results on small systems to yield an approximation for the thermodynamic limit. This method, similar to cluster perturbation theory, confirms the analytical findings, and also yields accurate results in the intermediate-coupling regime
Phonon heat conduction in layered anisotropic crystals
Minnich, A. J.
2015-02-01
The thermal properties of anisotropic crystals are of both fundamental and practical interest, but transport phenomena in anisotropic materials such as graphite remain poorly understood because solutions of the Boltzmann equation often assume isotropy. Here, we extend an analytic solution of the transient, frequency-dependent Boltzmann equation to highly anisotropic solids and examine its predictions for graphite. We show that this simple model predicts key results, such as long c -axis phonon mean free paths and a negative correlation of cross-plane thermal conductivity with in-plane group velocity, that were previously observed with computationally expensive molecular-dynamics simulations. Further, using our analytic solution, we demonstrate a method to reconstruct the anisotropic mean free path spectrum of crystals with arbitrary dispersion relations without any prior knowledge of their harmonic or anharmonic properties using observations of quasiballistic heat conduction. These results provide a useful analytic framework to understand thermal transport in anisotropic crystals.
Zero m phonons in metal chalcogenide nanotubes
International Nuclear Information System (INIS)
Phonon dispersions of single-wall MoS2 and WS2 nanotubes are calculated within a full symmetry implemented valence force-field model. Tubular structure is found to be characterized by two Raman active modes: by the in-phase breathing modes (in full analogy to carbon nanotubes) with frequency approaching Brillouin scattering domain (as diameter approaches nm), and by the high-energy breathing mode with sulfur shells breathing in phase, but out of phase relative to the Mo/W atoms. Likewise, the longitudinal rigid-shell mode, where sulfur shells vibrate out of phase whilst Mo/W atoms barely move, is predicted to be a fingerprint of the cylindrical configuration in infrared spectra. It is also found that twisting rigid-layer modes characterize chirality of the tubes. Finally, the large diameter limit is discussed and related to the measured Raman and infrared spectra of the layered structures
Engineering surface waves in flat phononic plates
Estrada, Héctor; Candelas, Pilar; Belmar, Francisco; Uris, Antonio; García de Abajo, F. Javier; Meseguer, Francisco
2012-05-01
Surface acoustic-wave phenomena span a wide range of length scales going from the devastation of earthquakes down to image reconstruction of buried nanostructures. In solid-fluid systems, the so-called Scholte-Stoneley waves (SSWs) dominate the scene at the interface with their evanescent fields decaying away into both media. Understanding and manipulating these waves in patterned surfaces would enable new applications of sound to be devised for imaging and acoustic signal processing, although this task has so far remained elusive. Here, we report SSW modes displaying directional gaps and band folding in fluid-loaded solid phononic plates. The plates are inhomogeneously patterned with in-plane periodic modulations of the elastic constants, but present flat surfaces free of corrugations. We experimentally demonstrate control of SSWs, which opens a promising route toward acoustic fluid sensing, microscopy, and signal processing.
The phonon theory of liquid thermodynamics
Bolmatov, Dima; Trachenko, Kostya
2012-01-01
Heat capacity of matter is considered to be its most important property because it holds information about system's degrees of freedom as well as the regime in which the system operates, classical or quantum. Heat capacity is well understood in gases and solids but not in the third state of matter, liquids, and is not discussed in physics textbooks as a result. The perceived difficulty is that interactions in a liquid are both strong and system-specific, implying that the energy strongly depends on the liquid type and that, therefore, liquid energy can not be calculated in general form [1]. Here, we develop a phonon theory of liquids where this problem is avoided. We demonstrate good agreement of calculated heat capacity of important monatomic, molecular and hydrogen-bonded network liquids such as H2O in a wide range of pressure and temperature.
Controlling Mechanical Dissipation through Phononic Bandgap Substrates
Chang, Laura; Chakram, Srivatsan; Patil, Yogesh Sharad; Vengalattore, Mukund
2015-05-01
One of the fundamental challenges for the quantum control of mechanical systems is the realization of resonators with exceptionally low dissipation, through appropriate material choice and resonator and substrate design. Stoichiometric silicon nitride membrane resonators have in recent years emerged as an ultralow loss mechanical platform. In such resonators, we have demonstrated mechanical quality factors as high as 50 ×106 and f × Q products of 1 ×1014 Hz, with radiation loss to the the supporting substrate being the dominant loss process. We demonstrate the suppression of radiation loss by creating resonators on substrates with a phononic bandgap. We characterize the mechanical properties of these resonators for various substrate parameters and discuss prospects for the observation of quantum optomechanical effects at room temperature. This work was supported by the DARPA QuASAR program through a grant from the ARO and an NSF INSPIRE award.
Cavity-type hypersonic phononic crystals
International Nuclear Information System (INIS)
We report on the engineering of the phonon dispersion diagram in monodomain anodic porous alumina (APA) films through the porosity and physical state of the material residing in the nanopores. Lattice symmetry and inclusion materials are theoretically identified to be the main factors which control the hypersonic acoustic wave propagation. This involves the interaction between the longitudinal and the transverse modes in the effective medium and a flat band characteristic of the material residing in the cavities. Air and filled nanopores, therefore, display markedly different dispersion relations and the inclusion materials lead to a locally resonant structural behavior uniquely determining their properties under confinement. APA films emerge as a new platform to investigate the rich acoustic phenomena of structured composite matter. (paper)
Theory of anharmonic phonons in graphene
Costamagna, Sebastian; Peeters, Francois M.; Michel, Karl H.
2015-03-01
Anharmonic effects in an atomic monolayer thin crystal with honeycomb lattice structure are studied by analytical and numerical lattice dynamical methods. Starting from a semi-empirical model for anharmonic couplings of third and fourth order, we study the in-plane and out-of-plane (flexural) mode components of the generalized wave vector dependent Grüneisen parameters, the thermal tension and the thermal expansion coefficients as function of temperarure and crystal size. From the resonances of the displacement-displacement correlation functions we study the renormalization and decay rate of in-plane and flexural phonons as function of temperature, wave vector and crystal size. Numerical evaluations are made with graphene as a specific model, The work is complementary to crystalline membrane theory and computational studies of anharmonic effects in two-dimensional crystals.
Double Dirac cones in phononic crystals
Li, Yan
2014-07-07
A double Dirac cone is realized at the center of the Brillouin zone of a two-dimensional phononic crystal (PC) consisting of a triangular array of core-shell-structure cylinders in water. The double Dirac cone is induced by the accidental degeneracy of two double-degenerate Bloch states. Using a perturbation method, we demonstrate that the double Dirac cone is composed of two identical and overlapping Dirac cones whose linear slopes can also be accurately predicted from the method. Because the double Dirac cone occurs at a relatively low frequency, a slab of the PC can be mapped onto a slab of zero refractive index material by using a standard retrieval method. Total transmission without phase change and energy tunneling at the double Dirac point frequency are unambiguously demonstrated by two examples. Potential applications can be expected in diverse fields such as acoustic wave manipulations and energy flow control.
Phonon softening and superconductivity in tellurium under pressure
Mauri, F; De Gironcoli, S; Louie, S G; Cohen, M L; Mauri, Francesco; Zakharov, Oleg; Gironcoli, Stefano de; Louie, Steven G.; Cohen, Marvin L.
1996-01-01
The phonon dispersion and the electron-phonon interaction for the $\\beta$-Po and the bcc high pressure phases of tellurium are computed with density-functional perturbation theory. Our calculations reproduce and explain the experimentally observed pressure dependence of the superconducting critical temperature (T$_{\\rm c}$) and confirm the connection between the jump in T$_{\\rm c}$ and the structural phase transition. The phonon contribution to the free energy is shown to be responsible for the difference in the structural transition pressure observed in low and room temperature experiments.
Electron-phonon interaction in Chevrel-phase compounds
International Nuclear Information System (INIS)
Experiments on the electron-phonon interaction in Chevrel-phase compounds (CPC) and a theoretical discussion of their results are presented. The authors particularly discuss measurements of the isotope effect of the transition temperature in Mo6Se8 and SnMo6S8 and tunneling spectroscopy experiments on Cu1.8Mo6S8 and PbMo6S8. These investigations have been performed to get information about the strength of the electron-phonon interaction in CPC, and about the question whether there are phonon modes which couple particularly strongly to the electrons in these compounds. (orig./GSCH)
Phonon Quasidiffusion in Cryogenic Dark Matter Search Large Germanium Detectors
Energy Technology Data Exchange (ETDEWEB)
Leman, S.W.; /MIT, MKI; Cabrera, B.; /Stanford U., Phys. Dept.; McCarthy, K.A.; /MIT, MKI; Pyle, M.; /Stanford U., Phys. Dept.; Resch, R.; /SLAC; Sadoulet, B.; Sundqvist, K.M.; /LBL, Berkeley; Brink, P.L.; Cherry, M.; /Stanford U., Phys. Dept.; Do Couto E Silva, E.; /SLAC; Figueroa-Feliciano, E.; /MIT, MKI; Mirabolfathi, N.; Serfass, B.; /UC, Berkeley; Tomada, A.; /Stanford U., Phys. Dept.
2012-06-04
We present results on quasidiffusion studies in large, 3 inch diameter, 1 inch thick [100] high purity germanium crystals, cooled to 50 mK in the vacuum of a dilution refrigerator, and exposed with 59.5 keV gamma-rays from an Am-241 calibration source. We compare data obtained in two different detector types, with different phonon sensor area coverage, with results from a Monte Carlo. The Monte Carlo includes phonon quasidiffusion and the generation of phonons created by charge carriers as they are drifted across the detector by ionization readout channels.
Surface Event Rejection Using Phonon Information in CDMS
Akerib, D. S.; Attisha, M. J.; Bailey, C. N.; Baudis, L.; Bauer, D. A.; Brink, P. L.; Brusov, P. P.; Bunker, R.; Cabrera, B.; Caldwell, D. O.; Chang, C. L.; Cooley, J.; Crisler, M. B.; Cushman, P.; Daal, M.; Dixon, R.; Dragowsky, M. R.; Driscoll, D. D.; Duong, L.; Ferril, R.; Filippini, J.; Gaitskell, R. J.; Golwala, S. R.; Grant, D. R.; Hennings-Yeomans, R.; Holmgren, D.; Huber, M. E.; Kamat, S.; Leclercq, S.; Lu, A.; Mahapatra, R.; Mandic, V.; Meunier, P.; Mirabolfathi, N.; Nelson, H.; Nelson, R.; Ogburn, R. W.; Perera, T. A.; Pyle, M.; Ramberg, E.; Rau, W.; Reisetter, A.; Ross, R. R.; Sadoulet, B.; Sander, J.; Savage, C.; Schnee, R. W.; Seitz, D. N.; Serfass, B.; Sundqvist, K. M.; Thompson, J.-P. F.; Wang, G.; Yellin, S.; Yoo, J.; Young, B. A.
2007-11-01
The published CDMS analyses have used the shape of the phonon signal rising edge to reject low-ionization-yield surface events which produce acoustic phonons more quickly than bulk events do. To achieve better WIMP sensitivity with future larger exposures, we are using a simplified model of phonon production and propagation to construct event position estimators that help us to find more efficient surface event rejection cuts. We describe this model and the resulting new cuts, and summarize the surface event leakage rates and the sensitivity figures of merit of the five surface event rejection methods developed in the second CDMS II Soudan run data analysis.
Phonon Quasidiffusion in Cryogenic Dark Matter Search Large Germanium Detectors
International Nuclear Information System (INIS)
We present results on quasidiffusion studies in large, 3 inch diameter, 1 inch thick [100] high purity germanium crystals, cooled to 50 mK in the vacuum of a dilution refrigerator, and exposed with 59.5 keV gamma-rays from an Am-241 calibration source. We compare data obtained in two different detector types, with different phonon sensor area coverage, with results from a Monte Carlo. The Monte Carlo includes phonon quasidiffusion and the generation of phonons created by charge carriers as they are drifted across the detector by ionization readout channels.
Phonon Quasidiffusion in Cryogenic Dark Matter Search Large Germanium Detectors
Leman, S W; McCarthy, K A; Pyle, M; Resch, R; Sadoulet, B; Sundqvist, K M; Brink, P L; Cherry, M; Silva, E Do Couto E; Figueroa-Feliciano, E; Mirabolfathi, N; Serfass, B; Tomada, A
2011-01-01
We present results on quasidiffusion studies in large, 3 inch diameter, 1 inch thick [100] high purity germanium crystals, cooled to 50 mK in the vacuum of a dilution refrigerator, and exposed with 59.5 keV gamma-rays from an Am-241 calibration source. We compare data obtained in two different detector types, with different phonon sensor area coverage, with results from a Monte Carlo. The Monte Carlo includes phonon quasidiffusion and the generation of phonons created by charge carriers as they are drifted across the detector by ionization readout channels.
Interface Phonons and Polaron Effect in Quantum Wires
Directory of Open Access Journals (Sweden)
Maslov A
2010-01-01
Full Text Available Abstract The theory of large radius polaron in the quantum wire is developed. The interaction of charge particles with interface optical phonons as well as with optical phonons localized in the quantum wire is taken into account. The interface phonon contribution is shown to be dominant for narrow quantum wires. The wave functions and polaron binding energy are found. It is determined that polaron binding energy depends on the electron mass inside the wire and on the polarization properties of the barrier material.
Confined and interface phonons in combined cylindrical nanoheterosystem
Directory of Open Access Journals (Sweden)
O.M.Makhanets
2006-01-01
Full Text Available The spectra of all types of phonons existing in a complicated combined nanoheterosystem consisting of three cylindrical quantum dots embedded into the cylindrical quantum wire placed into vacuum are studied within the dielectric continuum model. It is shown that there are confined optical (LO and interface phonons of two types: top surface optical (TSO and side surface optical (SSO modes of vibration in such a nanosystem. The dependences of phonon energies on the quasiwave numbers and geometrical parameters of quantum dots are investigated and analysed.
Electron spin-phonon relaxation in quantum dots
Scientific Electronic Library Online (English)
A. M., Alcalde; G. E., Marques.
2004-06-01
Full Text Available We calculate the spin relaxation rates in parabolic quantum dots due to the phonon modulation of the spin-orbit interaction in presence of an external magnetic field. Both, deformation potential (DP) and piezoelectric (PE) electron-phonon couplings are included in the Pavlov-Firsov spin-phonon Hamil [...] tonian. We demonstrate that the spin relaxation rates are particularly sensitive with the Landé g-factor, and that for InAs dots the DP can be necessarily considered in the spin relaxation analysis. Low-temperature (T ~ 0) relaxation rates are found to be small and to depend strongly on size, g-factor, and on magnetic field.
Phonon hardening due to the small-polaron effect
Energy Technology Data Exchange (ETDEWEB)
Ivic, Zoran [Theoretical Physics Department - 020, ' Vinca' Institute of Nuclear Sciences, 11001 Belgrade, P.O. Box 522 (Serbia and Montenegro)]. E-mail: zivic@rt270.vin.bg.ac.yu; Zekovic, Slobodan [Theoretical Physics Department - 020, ' Vinca' Institute of Nuclear Sciences, 11001 Belgrade, P.O. Box 522 (Serbia and Montenegro); Cevizovic, Dalibor [Theoretical Physics Department - 020, ' Vinca' Institute of Nuclear Sciences, 11001 Belgrade, P.O. Box 522 (Serbia and Montenegro); Kostic, Dragan [Theoretical Physics Department - 020, ' Vinca' Institute of Nuclear Sciences, 11001 Belgrade, P.O. Box 522 (Serbia and Montenegro)
2005-01-31
The influence of the small-polaron effect on the vibrational properties of the strongly coupled electron-phonon system is investigated. It was found that polaron-phonon interaction may cause a noticeable renormalization of the phonon spectra. These changes may be observed by the measurements of the speed of sound for which a very specific dependence on temperature, values of coupling constant and adiabatic parameter is expected. We also found that the rise of the small-polaron effective mass as a function of the coupling constant should be considerably moderated than that anticipated without taking into account the modification of the vibrational spectra.
The effects of electron-phonon interactions on bandgaps
Energy Technology Data Exchange (ETDEWEB)
Hague, J P, E-mail: J.P.Hague@open.ac.uk [Department of Physics and Astronomy, Open University, Walton Hall, Milton Keynes MK7 6AA (United Kingdom)
2011-03-01
I compute the spectral functions of a 1D Holstein polaron moving in a modulated potential, to examine the effects of electron-phonon interactions on band gaps. The imaginary time Green function is computed using diagrammatic quantum Monte Carlo, which exactly sums the diagrammatic series. From the imaginary time Green function, spectral functions are computed. The electron-phonon interaction flattens the electronic dispersion and leads to an increase in the gap at momentum k = {pi}/2. At strong coupling, polaron sidebands form in the gap. These results demonstrate the strong effect that electron-phonon interactions can have on band gaps.
Phonon propagation with isotope scattering and spontaneous anharmonic decay
International Nuclear Information System (INIS)
Calculations of the propagation of high-energy phonons introduced into a crystal at T=0 K are presented. The phonons are assumed to undergo elastic scattering and anharmonic decay processes. We show that in addition to the ''quasidiffusion'' component to the phonon propagation (discussed previously by Levinson and co-workers) there is also a contribution that arrives at close to the time expected for ballistic propagation. This latter mode of propagation continues to be of substantial importance even when the elastic scattering is much stronger than the anharmonic processes
Influence of pulse width and detuning on coherent phonon generation
Nakamura, Kazutaka G; Kayanuma, Yosuke
2015-01-01
We investigated the coherent phonon generation mechanism by irradiation of an ultrashort pulse with a simple two-level model. Our derived formulation shows that both impulsive stimulated Raman scattering (ISRS) and impulsive absorption (IA) simultaneously occur, and phonon wave packets are generated in the electronic ground and excited states by ISRS and IA, respectively. We identify the dominant process from the amplitude of the phonon oscillation. For short pulse widths, ISRS is very small and becomes larger as the pulse width increases. We also show that the initial phase is dependent on the pulse width and the detuning.
Heat Transfer by Phonons in Landauer-Datta-Lundstrom Approach
Directory of Open Access Journals (Sweden)
Kruglyak Yu.A.
2014-08-01
Full Text Available The Landauer-Datta-Lundstrom generalized transport model is applied to heat transfer by phonons. In both cases of electrons and phonons the Landauer approach generalized and extended by Datta and Lundstom gives correct quantitative description of transport processes for resistors of any dimension and size in ballistic, quasi-ballistic, and diffusive linear response regimes when there are differences in both voltage and temperature across the device. It is shown that the lattice thermal conductivity can be written in a form that is very similar to the electrical conductivity. Important differences between electrons and phonons are discussed.
Universal features of electron-phonon interactions in atomic wires
De la Vega, L; Agrait, N; Yeyati, A L
2005-01-01
The effect of electron-phonon interactions in the conductance through metallic atomic wires is theoretically analyzed. The proposed model allows to consider an atomic size region electrically and mechanically coupled to bulk electrodes. We show that under rather general conditions the features due to electron-phonon coupling are described by universal functions of the system transmission coefficients. It is predicted that the reduction of the conductance due to electron-phonon coupling which is observed close to perfect transmission should evolve into an enhancement at low transmission. This crossover can be understood in a transparent way as arising from the competition between elastic and inelastic processes.
Update on Laser Trabeculoplasty
El Sayyad Fathi; Helal Magdi
2009-01-01
Newer techniques of Laser Trabeculoplasty have revived the procedure and gained widespread acceptance by the ophthalmic community. This review was undertaken to address the evolution of different laser trabeculoplaty techniques, proposed mechanisms of action as well as review current studies of the therapeutic effects of these interventions.
Update on laser trabeculoplasty
Directory of Open Access Journals (Sweden)
El Sayyad Fathi
2009-01-01
Full Text Available Newer techniques of Laser Trabeculoplasty have revived the procedure and gained widespread acceptance by the ophthalmic community. This review was undertaken to address the evolution of different laser trabeculoplaty techniques, proposed mechanisms of action as well as review current studies of the therapeutic effects of these interventions.
Palmer, A. J.; Hess, L. D.; Stephens, R. R.; Pepper, D. M.
1977-01-01
The results of a two-year investigation into the possibility of developing continuous wave excimer lasers are reported. The program included the evaluation and selection of candidate molecular systems and discharge pumping techniques. The K Ar/K2 excimer dimer molecules and the xenon fluoride excimer molecule were selected for study; each used a transverse and capillary discharges pumping technique. Experimental and theoretical studies of each of the two discharge techniques applied to each of the two molecular systems are reported. Discharge stability and fluorine consumption were found to be the principle impediments to extending the XeF excimer laser into the continuous wave regime. Potassium vapor handling problems were the principal difficulty in achieving laser action on the K Ar/K2 system. Of the four molecular systems and pumping techniques explored, the capillary discharge pumped K Ar/K2 system appears to be the most likely candidate for demonstrating continuous wave excimer laser action primarily because of its predicted lower pumping threshold and a demonstrated discharge stability advantage.
Directory of Open Access Journals (Sweden)
O.Yu. Guseva
2009-09-01
Full Text Available Biochemical changes in oral fluid of patients with chronic generalized parodontitis were investigated; the most informative indices were found out, they were used for estimating complex therapy effectiveness by means of low intensive helium — neon laser radiation and alternating running magnetic field
TWO-MAGNON-ONE-PHONON SCATTERING IN THE LATTICE THERMAL CONDUCTIVITY OF MAGNETIC INSULATORS
Dixon, G
1981-01-01
A simple, but general model of magnon-phonon scattering as an extension of linear spin-wave theory is presented. Both resonant one-magnon-one-phonon and two-magnon-one-phonon scattering processes are considered. The former are included in the thermal conductivity by diagonalizing the magnon-phonon Hamiltonian to obtain coupled magneto elastic modes. The two-magnon-one-phonon processes are treated in the relaxation time approximation. This model has been used to analyze the experimental depend...
Krahne, R; Schueller, C; Carbone, L; Kudera, S; Mannarini, G; Manna, L; Heitmannb, D; Cingolani, R; 10.1021/0524492
2006-01-01
We investigated CdTe nanocrystal tetrapods of different sizes by resonant inelastic light scattering at room temperature and under cryogenic conditions. We observe a strongly resonant behavior of the phonon scattering with the excitonic structure of the tetrapods. Under resonant conditions we detect a set of phonon modes that can be understood as confined longitudinal-optical phonons, surface-optical phonons, and transverse-optical phonons in a nanowire picture.
Coherent phonon optics in a chip with an electrically controlled active device
Poyser, Caroline L.; Akimov, Andrey V.; Campion, Richard P.; Kent, Anthony J.
2015-01-01
Phonon optics concerns operations with high-frequency acoustic waves in solid media in a similar way to how traditional optics operates with the light beams (i.e. photons). Phonon optics experiments with coherent terahertz and sub-terahertz phonons promise a revolution in various technical applications related to high-frequency acoustics, imaging, and heat transport. Previously, phonon optics used passive methods for manipulations with propagating phonon beams that did not enable their extern...
Sartori, Luisa; Betti, Sonia
2015-01-01
Complementary colors are color pairs which, when combined in the right proportions, produce white or black. Complementary actions refer here to forms of social interaction wherein individuals adapt their joint actions according to a common aim. Notably, complementary actions are incongruent actions. But being incongruent is not sufficient to be complementary (i.e., to complete the action of another person). Successful complementary interactions are founded on the abilities: (i) to simulate an...
Khan, Mohammed Zahed Mustafa
2013-03-04
We report on the atypical emission dynamics of InAs/AlGaInAs/InP quantum dash (Qdash) lasers employing varying AlGaInAs barrier thickness (multilayer-chirped structure). The analysis is carried out via fabry-perot (FP) ridge (RW) and stripe waveguide (SW) laser characterization corresponding to the index and gain guided waveguiding mechanisms, respectively, and at different current pulse width operations. The laser emissions are found to emerge from the size dispersion of the Qdash ensembles across the four Qdash-barrier stacks, and governed by their overlapping quasi-zero dimensional density of states (DOS). The spectral characteristics demonstrated prominent dependence on the waveguiding mechanism at quasi-continuous wave (QCW) operation (long pulse width). The RW geometry showed unusual spectral split in the emission spectra on increasing current injection while the SW geometry showed typical broadening of lasing spectra. These effects were attributed to the highly inhomogeneous active region, the nonequilibrium carrier distribution and the energy exchange between Qdash groups across the Qdash-barrier stacks. Furthermore, QCW operation showed a progressive red shift of emission spectra with injection current, resulted from active region heating and carrier depopulation, which was observed to be minimal in the short pulse width (SPW) operation. Our investigation sheds light on the device physics of chirped Qdash laser structure and provides guidelines for further optimization in obtaining broad-gain laser diodes. © (2013) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Correlated electron systems: Emitting electrons through phonons
Scagnoli, Valerio; Staub, Urs
2015-09-01
Ultrashort laser pulses create strain waves that generate highly mobile charges at an oxide interface. These charges propagate into the oxide layer destroying its antiferromagnetic ordering and insulating properties, providing insight into the physics of metal-insulator transitions.
Energy Technology Data Exchange (ETDEWEB)
Walverde, Debora Ayala
2001-07-01
This in vitro study compares two different types of tooth bleaching agents stimulated with two different irradiation fonts. These fonts accelerate the action of the bleaching agents upon the enamel surface by heating up the materials. We used the xenon plasma arc lamp and a 960 nm fiber-coupled diode laser to irradiate the two materials containing 35% of hydrogen peroxide (Opus White and Opalescence extra). The color of the teeth was measured with a spectrophotometer using the CIELAB color system that gives the numeric values of L{sup *}a{sup *}b{sup *}. (author)
Electron-phonon interaction in the Hubbard model
International Nuclear Information System (INIS)
Superconductivity existence in the Hubbard model is studied, taking into account both electron-phonon and electron-electron interactions. Using Sarker's functional integral formalism a system of equations for the dynamical order parameters is derived. (author). 7 refs
Phonon-assisted decoherence and tunneling in quantum dot molecules
DEFF Research Database (Denmark)
Grodecka-Grad, Anna; Foerstner, Jens
2011-01-01
We study the influence of the phonon environment on the electron dynamics in a doped quantum dot molecule. A non-perturbative quantum kinetic theory based on correlation expansion is used in order to describe both diagonal and off-diagonal electron-phonon couplings representing real and virtual processes with relevant acoustic phonons. We show that the relaxation is dominated by phonon-assisted electron tunneling between constituent quantum dots and occurs on a picosecond time scale. The dependence of the time evolution of the quantum dot occupation probabilities on the energy mismatch between the quantum dots is studied in detail. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Electron-phonon coupling as an order-one problem
Powell, B J; Baruah, T; Pederson, Mark R.; Baruah, Tunna
2005-01-01
The coupling between electrons and phonons plays important roles in physics, chemistry and biology. However, the accurate calculation of the electron-phonon coupling constants is computationally expensive as it involves solving the Schrodinger equation for O(N) nuclear configurations, where N is the number of nuclei. Herein we show that by considering the forces on the nuclei caused by the addition or subtraction of an arbitrarily small electronic charge one may calculate the electron-phonon coupling constants from O(1) solutions of the Schrodinger equation. We show that Janak's theorem means that this procedure is exact within the density functional formalism. We demonstrate that the O(1) approach produces numerically accurate results by calculating the electron-phonon coupling constants for a series of molecules ranging in size from H_2 to C_60. We use our approach to introduce a computationally fast approximation for the adiabatic ionisation potentials and electron affinities which is shown to be accurate ...
The Electron-Phonon Interaction as Studied by Photoelectron Spectroscopy
International Nuclear Information System (INIS)
With recent advances in energy and angle resolution, the effects of electron-phonon interactions are manifest in many valence-band photoelectron spectra (PES) for states near the Fermi level in metals
Sum rules and vertex corrections for electron-phonon interactions
R"osch, O; Gunnarsson, O
2006-01-01
We derive sum rules for the phonon self-energy and the electron-phonon contribution to the electron self-energy of the Holstein-Hubbard model in the limit of large Coulomb interaction U. Their relevance for finite U is investigated using exact diagonalization and dynamical mean-field theory. Based on these sum rules, we study the importance of vertex corrections to the electron-phonon interactionin a diagrammatic approach. We show that they are crucial for a sum rule for the electron self-energy in the undoped system while a sum rule related to the phonon self-energy of doped systems is satisfied even if vertex corrections are neglected. We provide explicit results for the vertex function of a two-site model.
Phonon Dynamics and Inelastic Neutron Scattering of Sodium Niobate
Mishra, S K; Mittal, R; Zbiri, M; Rols, S; Schober, H; Chaplot, S L
2013-01-01
Sodium niobate (NaNbO3) exhibits most complex sequence of structural phase transitions in perovskite family and therefore provides as excellent model system for understanding the mechanism of structural phase transitions. We report temperature dependence of inelastic neutron scattering measurements of phonon densities of states in sodium niobate. The measurements are carried out in various crystallographic phases of this material at various temperatures from 300 K to 1048 K. The phonon spectra exhibit peaks centered around 19, 37, 51, 70 and 105 meV. Interestingly, the peak around 70 meV shifts significantly towards lower energy with increasing temperature, while the other peaks do not exhibit an appreciable change. The phonon spectra at 783 K show prominent change and become more diffusive as compared to those at 303 K. In order to better analyze these features, we have performed first principles lattice dynamics calculations based on the density functional theory. The computed phonon density of states is fo...
Phonon excitation and instabilities in biased graphene nanoconstrictions
DEFF Research Database (Denmark)
Gunst, Tue; Lu, Jing Tao
2013-01-01
We investigate how a high current density perturbs the phonons in a biased graphene nanoconstriction coupled to semi-infinite electrodes. The coupling to electrode phonons, electrode electrons under bias, Joule heating, and current-induced forces is evaluated using first principles density functional theory and nonequilibrium Green's function calculations. We observe a strongly nonlinear heating of the phonons with bias and breakdown of the harmonic approximation when the Fermi level is tuned close to a resonance in the electronic structure of the constriction. This behavior is traced back to the presence of negatively damped phonons driven by the current. The effects may limit the stability and capacity of graphene nanoconstrictions to carry high currents.
Non-equilibrium ballistic phonon transport in microstructures
Hertzberg, Jared; Otelaja, Obafemi; Robinson, Richard
2011-03-01
We demonstrate a method to locally excite and detect phonon modes in silicon microstructures. Decay of quasiparticles injected into an adjacent superconducting film excites phonons in a non-thermal spectral distribution. Phonons of frequency of order 100 GHz are detected by the excitations they cause in a second superconducting film, after ballistically traversing microstructures of 10 to 50 micron dimension. Measurements are made at temperatures of 0.3 to 1.2 K. Such a device advances the goal of building a nanoscale phonon spectrometer to study acoustic confinement and surface scattering effects. This work is supported by KAUST (KUS-C1-018-02), NSF (DMR 0520404), and DOE (DE-SC0001086).
Influence of mass contrast in alloy phonon scattering
Shiga, Takuma; Shiomi, Junichiro
2015-01-01
We have investigated the effect of mass contrast on alloy phonon scattering in mass-substituted Lennard-Jones crystals. By calculating the mass-difference phonon scattering rate using a modal analysis method based on molecular dynamics, we have identified the applicability and limits of the widely-used mass-difference perturbation model in terms of magnitude and sign of the mass difference. The result of a phonon -mode-dependent analysis reveals that the critical phonon frequency, above which the mass-difference perturbation theory fails, decreases with the magnitude of the mass difference independently of its sign. This gives rise to a critical mass contrast, above which the mass-difference perturbation model noticeably underestimates the lattice thermal conductivity.
Electron-Phonon Interacation in Quantum Dots: A Solvable Model
Stauber, T; Castella, H
2000-01-01
The relaxation of electrons in quantum dots via phonon emission is hindered by the discrete nature of the dot levels (phonon bottleneck). In order to clarify the issue theoretically we consider a system of $N$ discrete fermionic states (dot levels) coupled to an unlimited number of bosonic modes with the same energy (dispersionless phonons). In analogy to the Gram-Schmidt orthogonalization procedure, we perform a unitary transformation into new bosonic modes. Since only $N(N+1)/2$ of them couple to the fermions, a numerically exact treatment is possible. The formalism is applied to a GaAs quantum dot with only two electronic levels. If close to resonance with the phonon energy, the electronic transition shows a splitting due to quantum mechanical level repulsion. This is driven mainly by one bosonic mode, whereas the other two provide further polaronic renormalizations. The numerically exact results for the electron spectral function compare favourably with an analytic solution based on degenerate perturbatio...
Phonon effect on two coupled quantum dots at finite temperature
Du, Cheng-Ran; Zhu, Ka-di
2007-01-01
The quantum oscillations of population in an asymmetric double quantum dots system coupled to a phonon bath are investigated theoretically. It is shown how the environmental temperature has effect on the system.
International Nuclear Information System (INIS)
In a high powered laser system it is proposed that combustion gases be bled off from a gas turbine engine and their composition adjusted by burning extra fuel in the bleed gases or adding extra substances. Suitable aerodynamic expansion produces a population inversion resulting in laser action in the CO2 species. Alternatively, bleed gases may be taken from the high pressure compressor of the gas turbine engine and an appropriate fuel burned therein. If required, other adjustments may also be made to the composition and the resulting gaseous mixture subjected to aerodynamic expansion to induce laser action as before. (auth)
Band Gaps and Single Scattering of Phononic Crystal
Xiaoyi Huang; Jingcui Peng; Huanyou Wang; Gui Jin
2011-01-01
A method is introduced to study the transmission and scattering properties of acoustic waves in two–dimen- sional phononic band gap (PBG) materials. First, it is used to calculate the transmission coefficients of PBG samples. Second, the transmitted power is calculated based on the far field approach. We have also calcu- lated the scattering cross section, the results indicate that phononic band gap appear in frequency regions between two well separated resonance states.
Moments of the phonon spectra in alkali halides
International Nuclear Information System (INIS)
The results of a systematic calculation of the moments of the phonon spectra for 20 alkali halides are reported. The relevant phonon spectra needed are taken from the Green's function compilations by Haridasan et al. The calculated moments show good agreement with the available experimental data for sodium, potasium and caesium halides. The moments deduced from Debye-Waller factor data and from specific heat data are mutually consistent. A critical inter-comparison of these moments in these crystals is made. (author)
Exciton-Phonon Interaction in Semiconductors with Intermediate Polaron Coupling
Gartner, P.; Jahnke, F.; Schäfer, W.
2003-04-01
The linear absorption of a two-band semiconductor with Coulomb interaction and intermediate electron-LO-phonon coupling is considered. Special attention is payed to the polaron renormalization of the carrier spectrum. It is shown that this may play an important role in the appearance of phonon sidebands in vertexless calculations. To this end the generalized Kadanoff-Baym ansatz (GKBA) is compared with an alternative ansatz which does not rely on the factorization of the spectral Green's function.
Electron-phonon coupling as an order-one problem
Powell, B. J.; Mark R. Pederson; Baruah, Tunna
2005-01-01
The coupling between electrons and phonons plays important roles in physics, chemistry and biology. However, the accurate calculation of the electron-phonon coupling constants is computationally expensive as it involves solving the Schrodinger equation for O(N) nuclear configurations, where N is the number of nuclei. Herein we show that by considering the forces on the nuclei caused by the addition or subtraction of an arbitrarily small electronic charge one may calculate th...
A quantum simulator for electron-phonon interactions
Hague, J P
2011-01-01
We propose an approach for quantum simulation of electron-phonon interactions using Rydberg states of cold atoms and ions. We will show how systems of cold atoms and ions can be mapped onto electron-phonon systems of the Su-Schrieffer-Heeger and extended Holstein type. We discuss how properties of the simulated Hamiltonian can be tuned and how to read physically relevant properties from the simulator.
Ultrafast Relaxation Dynamics of Hot Optical Phonons in Graphene
Wang, Haining; Strait, Jared H.; George, Paul A.; Shivaraman, Shriram; Shields, Virgil B; Chandrashekhar, Mvs; Hwang, Jeonghyun; Ruiz-Vargas, Carlos S.; Rana, Farhan; Spencer, Michael G.; Park, Jiwoong
2009-01-01
Using ultrafast optical pump-probe spectroscopy, we study the relaxation dynamics of hot optical phonons in few-layer and multi-layer graphene films grown by epitaxy on silicon carbide substrates and by chemical vapor deposition on nickel substrates. In the first few hundred femtoseconds after photoexcitation, the hot carriers lose most of their energy to the generation of hot optical phonons which then present the main bottleneck to subsequent carrier cooling. Optical phono...
Reduction of Thermal Conductivity by Nanoscale 3D Phononic Crystal
Yang, Lina; Yang, Nuo; Li, Baowen
2013-01-01
The thermal conductivity of nanostructures needs to be as small as possible so that it will have a greater efficiency for solid-state electricity generation/refrigeration by thermoelectrics. We studied how the period length and the mass ratio affect the thermal conductivity of isotopic nanoscale 3D phononic crystal of Si. Simulation results by equilibrium molecular dynamics show isotopic nanoscale 3D phononic crystal can make a significance reduction on the thermal conductiv...
Superconductivity in molecular solids with Jahn-Teller phonons
Han, J. E.; Gunnarsson, O.; Crespi, V. H.
2002-01-01
We analyze fulleride superconductivity at experimental doping levels, treating the electron-electron and electron-phonon interactions on an equal footing, and establish the existence of novel physics which helps explain the unusually high superconducting transition temperatures in these systems. The Jahn-Teller phonons create a local (intramolecular) pairing that is surprisingly resistant to the Coulomb repulsion, despite the weakness of retardation in these low-bandwidth sy...
Nanophotonic cavity optomechanics with propagating phonons in microwave Ku band
LI Huan; Tadesse, Semere A.; Liu, Qiyu; Li, Mo
2015-01-01
Sideband-resolved coupling between multiple photonic nanocavities and propagating mechanical waves in microwave Ku-band is demonstrated. Coherent and strong photon-phonon interaction is manifested with optomechanically induced transparency and absorption, and phase-coherent interaction in multiple cavities. Inside an echo chamber it is shown that a phonon pulse can interact with an embedded nanocavity for multiple times. Our device provides a scalable platform to optomechani...
Tuning the polarized quantum phonon transmission in graphene nanoribbons
Scuracchio, P.; Dobry, A.; Peeters, F.; Costamagna, S.
2014-01-01
We propose systems that allow a tuning of the phonon transmission function T($\\omega$) in graphene nanoribbons by using C$^{13}$ isotope barriers, antidot structures, and distinct boundary conditions. Phonon modes are obtained by an interatomic fifth-nearest neighbor force-constant model (5NNFCM) and T($\\omega$) is calculated using the non-equilibrium Green's function formalism. We show that by imposing partial fixed boundary conditions it is possible to restrict contributio...
The inverted pendulum, interface phonons and optic Tamm states
Combe, Nicolas
2011-01-01
The propagation of waves in periodic media is related to the parametric oscillators. We transpose the possibility that a parametric pendulum oscillates in the vicinity of its unstable equilibrium positions to the case of waves in lossless unidimensional periodic media. This concept formally applies to any kind of wave. We apply and develop it to the case of phonons in realizable structures and evidence new classes of phonons. Discussing the case of electromagnetic waves, we ...
Optical Phonon Limited High Field Transport in Layered Materials
Chandrasekar, Hareesh; Ganapathi, Kolla L.; Bhattacharjee, Shubhadeep; Bhat, Navakanta; Nath, Digbijoy N.
2015-01-01
An optical phonon limited velocity model has been employed to investigate high-field transport in a selection of layered 2D materials for both, low-power logic switches with scaled supply voltages, and high-power, high-frequency transistors. Drain currents, effective electron velocities and intrinsic cut-off frequencies as a function of carrier density have been predicted thus providing a benchmark for the optical phonon limited high-field performance limits of these materia...
Theory of Phonon Hall Effect in Paramagnetic Dielectrics
Sheng, L; Ting, C S
2006-01-01
Based upon spin-lattice interaction, we propose a theoretical model for the phonon Hall effect in paramagnetic dielectrics. The thermal Hall conductivity is calculated by using the Kubo formula. Our theory reproduces the essential experimental features of the phonon Hall effect discovered recently in ionic dielectric Tb$_3$Ga$_5$O$_{12}$, including the sign, magnitude and linear magnetic field dependence of the thermal Hall conductivity.
Phonon softening: "keyhole" into dynamic stripe-phase
Mukhin, Sergei I.
2005-01-01
The highly distinctive phonon self-energy dependences on the wave vector, calculated respectively for the static and dynamic stripe phase models of the underdoped cuprates are presented. The negative values of the real part of the on-stripe holes polarization loop lead to appearance of localized vibration states in the presence of well-separated stripes, relevant for underdoped cuprates. The localized modes split below the bare optical phonon frequencies exhibiting strong ``...
Decoherence in semiconductor cavity QED systems due to phonon scattering
Kaer, P.; Mork, J.
2014-01-01
We investigate the effect of electron-phonon interactions on the coherence properties of single photons emitted from a semiconductor cavity QED system, i.e. a quantum dot embedded in an optical cavity. The degree of indistinguishability, governing the quantum mechanical interference between two single photons, is calculated as a function of important parameters describing the cavity QED system and the phonon reservoir, e.g. cavity quality factor, light-matter coupling streng...
Spectral hole burning and zero phonon linewidth in semiconductor nanocrystals
Palinginis, Phedon; Tavenner, Sasha; Lonergan, Mark; Wang, Hailin
2003-05-01
Spectral hole burning reveals a sharp zero-phonon line (ZPL) as well as discrete acoustic phonon sidebands in CdSe nanocrystals. The ZPL linewidth obtained from the spectral hole burning depends strongly on the measurement time scale, reflecting effects of spectral diffusion. The nonlinear optical measurement allows us to suppress effects of spectral diffusion leading to a ZPL linewidth as narrow as 6 ?eV.
Exciton-LO-phonon quantum kinetics in InAs/GaAs quantum dots: effects of zone-edge phonon damping
Machnikowski, P; Machnikowski, Pawel; Jacak, Lucjan
2003-01-01
The kinetics of exciton-LO-phonon system after an ultrafast optical excitation in an InAs/GaAs quantum dot is studied theoretically. Influence of anharmonic phonon damping and its interplay with the phonon dispersion is analyzed. The signatures of zone-edge decay process in the absorption spectrum and time evolution are highlighted, providing a possible way of experimental investigation on phonon anharmonicity effects.
International Nuclear Information System (INIS)
The problem of appearance of a plasma in air above an aluminum target irradiated with neodymium or CO2 laser pulses is solved numerically. The published experimental data are shown to agree with the results of calculations carried out assuming evaporation of the target, reduction in the thermal conductivity of the surface layer, and ''flash'' absorption in the vapor. A rectangular pulse and thermally insulated layers 1 ? thick are assumed in the derivation of the dependence of the time of the onset of evaporation and of the time of appearance of a flash on the density of the radiation flux in the range of 0.5--100 MW/cm2. It follows from these calculations that the threshold of plasma formation is not greatly affected by variation of the laser radiation wavelength from 1.06 to 10.6 ?
Energy Technology Data Exchange (ETDEWEB)
Rezende, Sandra Bastos
2001-07-01
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/cm{sup 2} , and for groups G3 and G4 it was 53 mW/cm{sup 2}. The total doses were D = 3 J/cm{sup 2} for groups G2 and G4, and D = 1,3 J/cm{sup 2} 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/cm{sup 2} and the dose of 1,3 J/cm{sup 2} 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)
Energy Technology Data Exchange (ETDEWEB)
Rocha, Dalva Maria
2001-07-01
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)
Czech Academy of Sciences Publication Activity Database
Cihelka, Jaroslav; Matulková, Irena; Sovová, Kristýna; Kamas, Michal; Kubelík, Petr; Ferus, Martin; Juha, Libor; Civiš, Svatopluk
2009-01-01
Ro?. 39, 3-4 (2009), s. 227-227. ISSN 0169-6149 R&D Projects: GA MŠk LC510; GA MŠk(CZ) LC528; GA ?R GA203/06/1278; GA MŠk LA08024 Institutional research plan: CEZ:AV0Z40400503; CEZ:AV0Z10100523 Keywords : planetary atmosphere * lasers * spectroscopy Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.053, year: 2009
International Nuclear Information System (INIS)
The therapy with laser emitting low intensity has been currently used in the most diverse fields of medicine as therapeutic conduct for pain. It is a non invasive, painless, non-thermal and aseptic type therapy, without any collateral effects, having a good cost/benefit relationship. However, for the therapy with low-intensity laser to result in positive effects, a correct diagnosis is fundamental, as well as a protocol of adequate application. n odontology, the majority of patients diagnosed with temporomandibular disorders (TMD), present pain and limitations in the movements of the jaw. In this work, a GaAlAs laser emitting low intensity, was used, ?=785 nm, in patients having a dysfunction of the temporomandibular joint with a complaint of pain. Twenty patients were divided into two groups. The group treated received laser therapy in the temporomandibular articulations and in the muscles affected. The dose applied was 45 J/cm2, while the ten patients in the control group received 0 J/cm2, in a total of nine applications, carried out three times a week, during three weeks. he evaluation of the patients was made through clinical examinations of manual palpation of the masseter, temporal, cervical, posterior neck and sternocleidomastoid muscles, and measurements of opening and laterality of the mouth. The results obtained showed a diminishing of the pain and an increase of the mandibular mobility in the patients treated, when compared to the control group. These results point to this therapy as being an important tool in the treatment of pain in patients with a dysfunction in the TMJ, indicating this therapeutic modality as a co-adjuvant in these treatments. (author)
Frictional drag between quantum wells mediated by phonon exchange
DEFF Research Database (Denmark)
BØnsager, M.C.; Flensberg, Karsten
1998-01-01
We use the Kubo formalism to evaluate the contribution of acoustic-phonon exchange to the frictional drag between nearby two-dimensional electron systems. In the case of free phonons, we find a divergent drag rate (tau(D)(-l)). However, tau(D)(-l) becomes finite when phonon scattering from either lattice imperfections or electronic excitations is accounted for. In the case of GaAs quantum wells, we find that for a phonon mean free path l(ph) smaller than a critical value, imperfection scattering dominates and the drag rate varies as ln(l(ph)/d) over many orders of magnitude of the layer separation d. When l(ph) exceeds the critical value, the drag rate is dominated by coupling through an electron-phonon collective mode localized in the vicinity of the electron layers. We argue that the coupled electron-phonon mode may be observable for realistic parameters. Our theory is in good agreement with experimental results for the temperature, density, and d dependence of the drag rate.
Plasmon-polar-phonon coupling at semiconductor surfaces
Takeshi, Inaoka
1991-11-01
We investigate the plasmon-polar-phonon coupling at semiconductor surfaces by means of decomposing the induced charge density distribution into three components, namely, the component due to carrier density fluctuation, that originating from longitudinal optical phonon polarisation and that which arises right on the surface owing to termination of the phonon and background polarisation at the surface. We are concerned with n-type degenerate polar semiconductors. Carrier electrons are described as a semi-infinite degenerate electron gas, which is treated within the infinite barrier model and the random-phase approximation. The optical phonon polarisation is described by the Lorentzian oscillator model. Analysing the phase relation and the amplitude ratio of the above three components of the induced charge density distribution and evaluating each contribution of these three components to the energy loss intensity elucidate the character in plasmon-polar-phonon coupling at the surface. Each of the three distinct coupled surface modes has its own characteristic mode structure. In parallel with this analysis of coupling at the surface, we also explore the plasmon-polar-phonon coupling in the bulk on the basis of the same decomposing scheme for the induced charge density distribution. Each of the three distinct surface modes has the same character as the bulk modes on the corresponding one of the three bulk dispersion branches. This confirms the result of our previous work, namely, that each of the three distinct surface modes originates from one of the three bulk dispersion branches.
Electron-phonon coupling in the rare-earth metals
DEFF Research Database (Denmark)
Skriver, Hans Lomholt; Mertig, I.
1990-01-01
We have estimated the strength of the mass enhancement of the conduction electrons due to electron-phonon interaction in the rare metals Sc, Y, and La–Lu. The underlying self-consistent energy bands were obtained by means of the scalar relativistic linear-muffin-tin-orbital method, and the electron-phonon parameters were calculated within the Gaspari-Gyorffy formulation. For the heavier rare earths Gd–Tm spin polarization was included both in the band-structure calculations and in the treatment of the electron-phonon coupling to take into account the spin splitting of the conduction electrons induced by the 4f states. The calculated electron-phonon mass enhancement ? exhibits a pronounced variation through the series with a maximum value of 1.07 in Pr and a minimum of 0.3 in Ho. We analyze the experimental data from specific heat and de Haas–van Alphen measurements in light of the calculated electron-phonon contribution to the mass enhancement. Finally, we present for the superconducting elements Sc, Y, La, and Lu a comparison with the empirical electron-phonon coupling constants derived from the transition temperatures.
Phonon effects on analog quantum simulators with ultracold trapped ions
Wang, C -C Joseph
2011-01-01
Linear Paul traps have been used to simulate the transverse field Ising model with long-range spin-spin couplings. We study the effects of phonon creation on the spin-state probability and spin entanglement for such quantum spin simulators. We use a many-body factorization of the quantum time-evolution operator of the system to determine the different roles spins and phonons have in affecting how well the coupled spin-phonon system can be approximated by a simple static Ising model in a time-varying transverse magnetic field. We also examine the problem using adiabatic perturbation theory and exact numerical integration of the Schr\\"odinger equation in a truncated spin-phonon Hilbert space. One of our main results is that generically, small amounts of phonon creation help the probabilities of different spin states look more like that of the pure spin model, but at the cost of reducing the spin entanglement in the spin eigenfunction (determined by tracing out the phonons). We also evaluate the feasibility of g...
Effects of phonon-induced dephasing on Rabi oscillations in GaAs quantum dots
Energy Technology Data Exchange (ETDEWEB)
Lueker, Sebastian; Reiter, Doris; Kuhn, Tilmann [Institut fuer Festkoerpertheorie, Westfaelische Wilhelms-Universitaet Muenster, Wilhelm-Klemm-Str. 10, 48149 Muenster (Germany); Axt, Vollrath Martin [Theoretische Physik III, Universitaet Bayreuth, 95440 Bayreuth (Germany)
2011-07-01
We discuss the laser-induced Rabi oscillation of the exciton occupation in a GaAs quantum dot (QD). Considering the strong confinement limit we model the QD as a two level system. In principle arbitrary superpositions of these two states can be prepared by using light-induced Rabi oscillations. However, the control of the quantum state is limited by dephasing caused by electron-phonon interaction which reduces the coherence of the system and leads to a damping of the Rabi oscillations. Due to the energy structure only phonon-induced pure dephasing is taken into account. We study the impact of the dephasing on the coherence in the density matrix formalism. The many body nature of the problem leads to an infinite hierarchy of equations of motion which we truncate by a correlation expansion. The resulting closed set of equations is solved numerically. The influence of the different orders of this hierarchy is discussed. Recent experiments on Rabi oscillations in semiconductor QDs have been performed showing damped Rabi oscillations in the occupation of the QD exciton state. We compare our model with the experimental data and find a very good qualitative and quantitative agreement.
Theoretical description of the lattice dynamics in laser-excited InSb
Energy Technology Data Exchange (ETDEWEB)
Walkenhorst, Jessica; Gilfert, Christian; Sippel, Christian; Toews, Waldemar; Zijlstra, Eeuwe S.; Garcia, Martin [Theoretische Physik, Fachbereich Naturwissenschaften, Universitaet Kassel, Heinrich-Plett-Str. 40, 34132 Kassel (Germany)
2007-07-01
We performed an ab initio study of the softening of optical transverse and longitudinal phonons in InSb due to femtosecond laser excitation. We calculated the frequencies of the optical phonons at the point and at the zone boundary as a function of the number of excited carriers. Our study was based on all-electron density functional calculations. We found an increasing softening of the phonon modes for increasing laser fluence. However, the drop of the studied phonon frequencies did not exceed 30% of the initial value, even for very high excitation energies (electronic temperatures). We concluded that no dramatic flattening of the potential surface occurs, as was suggested by recent experiments.
Polarization dependent behavior of CdS around the first and second LO-phonon modes
International Nuclear Information System (INIS)
The present work report studies on resonant Raman experimental line shape for CdS around the first and second LO-phonon modes. The application of our method to the study of LO-phonon modes of CdS suggests that the scattered intensity is dominated by the surface and dependent on polarization. Results showed that the Raman spectra for CdS, roughly fall into three groups: a broad line-wing with apparent maxima around 194 cm-1 in the range of 140 and 240 cm-1 which can be ascribed to overtone scattering from acoustic phonons; a band near the 1LO phonon mode which can be attributed to a combination of one-phonon scattering and peak acoustic phonon and finally, a band near the 2LO phonon mode which can be attributed to a combination of two-phonon scattering and peak acoustic phonon.
Polarization dependent behavior of CdS around the first and second LO-phonon modes
Energy Technology Data Exchange (ETDEWEB)
Frausto-Reyes, C., E-mail: cfraus@cio.mx [Centro de Investigaciones en Optica AC, Unidad Aguascalientes, Prolong., Constitucion 607, Fracc. Reserva Loma Bonita, CP 20200, Apartado Postal 507, Ags. (Mexico); Molina-Contreras, J.R., E-mail: rmolina@correo.ita.mx [Departamento de Ingenieria Electrica y Electronica, Instituto Tecnologico de Aguascalientes, Av. Lopez Mateos 1081 Oriente, Fracc. Bonna Gens, CP 20256, Aguascalientes, Ags. (Mexico); Lopez-Alvarez, Y.F. [Departamento de Ingenieria Electrica y Electronica, Instituto Tecnologico de Aguascalientes, Av. Lopez Mateos 1081 Oriente, Fracc. Bonna Gens, CP 20256, Aguascalientes, Ags. (Mexico); Medel-Ruiz, C.I.; Perez Ladron de Guevara, H. [Universidad de Guadalajara, Centro Universitario de los Lagos, Av. Enrique Diaz de Leon s/n, Fracc. Paseos de la Montana, CP 47460, Lagos de Moreno, Jal. (Mexico); Ortiz-Morales, M. [Centro de Investigaciones en Optica AC, Unidad Aguascalientes, Prolong., Constitucion 607, Fracc. Reserva Loma Bonita, CP 20200, Apartado Postal 507, Ags. (Mexico)
2010-10-25
The present work report studies on resonant Raman experimental line shape for CdS around the first and second LO-phonon modes. The application of our method to the study of LO-phonon modes of CdS suggests that the scattered intensity is dominated by the surface and dependent on polarization. Results showed that the Raman spectra for CdS, roughly fall into three groups: a broad line-wing with apparent maxima around 194 cm{sup -1} in the range of 140 and 240 cm{sup -1} which can be ascribed to overtone scattering from acoustic phonons; a band near the 1LO phonon mode which can be attributed to a combination of one-phonon scattering and peak acoustic phonon and finally, a band near the 2LO phonon mode which can be attributed to a combination of two-phonon scattering and peak acoustic phonon.
Theory of phonon properties in doped and undoped CuO nanoparticles
Energy Technology Data Exchange (ETDEWEB)
Bahoosh, S.G. [Institute of Physics, Martin-Luther-University, D-06099 Halle (Germany); Apostolov, A.T. [University of Architecture, Civil Engineering and Geodesy Faculty of Hydrotechnics, Department of Physics, 1, Hristo Smirnenski Blvd., 1046 Sofia (Bulgaria); Apostolova, I.N. [University of Forestry, Faculty of Forest Industry, 10, Kl. Ohridsky Blvd., 1756 Sofia (Bulgaria); Wesselinowa, J.M., E-mail: julia@phys.uni-sofia.bg [University of Sofia, Department of Physics, 5 J. Bouchier Blvd., 1164 Sofia (Bulgaria)
2012-07-02
We have studied the phonon properties of CuO nanoparticles and have shown the importance of the anharmonic spin–phonon interaction. The Raman peaks of CuO nanoparticles shift to lower frequency and become broader as the particle size decreases in comparison with those of bulk CuO crystals owing to size effects. By doping with different ions, in dependence of their radius compared to the host ionic radius the phonon energies ? could be reduced or enhanced. The phonon damping is always enhanced through the ion doping effects. -- Highlights: ? The phonon properties of CuO nanoparticles are studied using a miscroscopic model. ? The phonon energy decreases whereas the damping increases with decreasing of particle size. ? It is shown the importance of the anharmonic spin–phonon interaction. ? By doping with RE-ions the phonon energy is reduced, whereas with TM-ions it is enhanced. ? The phonon damping is always enhanced through the ion doping effects.
Effect of defect configuration on the localization of phonons in two-dimensional phononic crystals
International Nuclear Information System (INIS)
Effects of defect location on the defect frequency and the localization of phonons are investigated in two novel kinds of model, created by moving the location of the native cylinder and inserting an ad-cylinder in the central cellular respectively. The results show that the defect frequency in Model 1 is only related to the distance, while in Model 2, is related not only to the distance, but also to the moving direction. From the pressure distribution, obvious localization phenomenon is found. The position and shape of the localized energy are varied with the position of the defect.
Rabi oscillations in a quantum dot-cavity system coupled to a non-zero temperature phonon bath
Larson, J; Larson, Jonas; Moya-Cessa, Hector
2007-01-01
We study a quantum dot strongly coupled to a single high-finesse optical microcavity mode. We use a rotating wave approximation method, commonly used in ion-laser interactions, to obtain an analytic solution of this problem beyond the Born-Markov approximation. The decay of Rabi oscillations because of the electron-phonon coupling are studied at arbitrary temperature and analytical expressions for the collapse and revival times are presented. Analysis without the rotating wave approximation are presented and new structures and phenomena of the Rabi oscillations occur in this regime either due to level crossings of the energy eigenvalues or because of equidistant eigenenergies.
International Nuclear Information System (INIS)
The Raman spectra of single-walled carbon nanotubes at temperatures up to 730 K and pressures up to 7 GPa have been measured. The behavior of phonon modes and the interaction between nanotubes in bundles have been studied. It has been found that the temperature shift of the vibrational G mode is completely reversible, whereas the temperature shift of radial breathing modes is partially irreversible and the softening of the modes and narrowing of phonon bands are observed. The temperature shift and softening of radial breathing modes are also observed when samples are irradiated by laser radiation with a power density of 6.5 kW/mm2. The dependence of the relative frequency ?/?0 for G+ and G? phonon modes on the relative change A0/A in the triangular lattice constant of bundles of nanotubes calculated using the thermal expansion coefficient and compressibility coefficient of nanotube bundles shows that the temperature shift of the G mode is determined by the softening of the C-C bond in nanotubes. An increase in the equilibrium distances between nanotubes at the breaking of random covalent C-C bonds between nanotubes in bundles of nanotubes is in my opinion the main reason for the softening of the radial breathing modes.
Energy Technology Data Exchange (ETDEWEB)
Meletov, K. P., E-mail: mele@issp.ac.ru [Russian Academy of Sciences, Institute of Solid State Physics (Russian Federation)
2012-12-15
The Raman spectra of single-walled carbon nanotubes at temperatures up to 730 K and pressures up to 7 GPa have been measured. The behavior of phonon modes and the interaction between nanotubes in bundles have been studied. It has been found that the temperature shift of the vibrational G mode is completely reversible, whereas the temperature shift of radial breathing modes is partially irreversible and the softening of the modes and narrowing of phonon bands are observed. The temperature shift and softening of radial breathing modes are also observed when samples are irradiated by laser radiation with a power density of 6.5 kW/mm{sup 2}. The dependence of the relative frequency {Omega}/{Omega}{sub 0} for G{sup +} and G{sup -} phonon modes on the relative change A{sub 0}/A in the triangular lattice constant of bundles of nanotubes calculated using the thermal expansion coefficient and compressibility coefficient of nanotube bundles shows that the temperature shift of the G mode is determined by the softening of the C-C bond in nanotubes. An increase in the equilibrium distances between nanotubes at the breaking of random covalent C-C bonds between nanotubes in bundles of nanotubes is in my opinion the main reason for the softening of the radial breathing modes.
Meletov, K. P.
2012-12-01
The Raman spectra of single-walled carbon nanotubes at temperatures up to 730 K and pressures up to 7 GPa have been measured. The behavior of phonon modes and the interaction between nanotubes in bundles have been studied. It has been found that the temperature shift of the vibrational G mode is completely reversible, whereas the temperature shift of radial breathing modes is partially irreversible and the softening of the modes and narrowing of phonon bands are observed. The temperature shift and softening of radial breathing modes are also observed when samples are irradiated by laser radiation with a power density of 6.5 kW/mm2. The dependence of the relative frequency ?/?0 for G + and G - phonon modes on the relative change A 0/ A in the triangular lattice constant of bundles of nanotubes calculated using the thermal expansion coefficient and compressibility coefficient of nanotube bundles shows that the temperature shift of the G mode is determined by the softening of the C-C bond in nanotubes. An increase in the equilibrium distances between nanotubes at the breaking of random covalent C-C bonds between nanotubes in bundles of nanotubes is in my opinion the main reason for the softening of the radial breathing modes.
Ordonez-Miranda, Jose; Yang, Ronggui; Volz, Sebastian; Alvarado-Gil, J. J.
2015-08-01
Based on the phonon Boltzmann transport equation under the relaxation time approximation, analytical expressions for the temperature profiles of both the steady state and modulated heat conduction inside a thin film deposited on a substrate are derived and analyzed. It is shown that these components of the temperature depend strongly on the ratio between the film thickness and the average phonon mean free path (MFP), and they exhibit the diffusive behavior as predicted by the Fourier's law of heat conduction when this ratio is much larger than unity. In contrast, in the ballistic regime when this ratio is comparable to or smaller than unity, the steady-state temperature tends to be independent of position, while the amplitude and the phase of the modulated temperature appear to be lower than those determined by the Fourier's law. Furthermore, we derive an invariant of heat conduction and a simple formula for the cross-plane thermal conductivity of dielectric thin films, which could be a useful guide for understanding and optimizing the thermal performance of the layered systems. This work represents the Boltzmann transport equation-based extension of the Rosencwaig and Gersho work [J. Appl. Phys. 47, 64 (1976)], which is based on the Fourier's law and has widely been used as the theoretical framework for the development of photoacoustic and photothermal techniques. This work might shed some light on developing a theoretical basis for the determination of the phonon MFP and relaxation time using ultrafast laser-based transient heating techniques.
Mesoscopic hydro-thermodynamics of phonons
Directory of Open Access Journals (Sweden)
Aurea R. Vasconcellos
2013-07-01
Full Text Available A generalized Hydrodynamics, referred to as Mesoscopic Hydro-Thermodynamics, of phonons in semiconductors is presented. It involves the descriptions of the motion of the quasi-particle density and of the energy density. The hydrodynamic equations, which couple both types of movement via thermo-elastic processes, are derived starting with a generalized Peierls-Boltzmann kinetic equation obtained in the framework of a Non-Equilibrium Statistical Ensemble Formalism, providing such Mesoscopic Hydro-Thermodynamics. The case of a contraction in first order is worked out in detail. The associated Maxwell times are derived and discussed. The densities of quasi-particles and of energy are found to satisfy coupled Maxwell-Cattaneo-like (hyperbolic equations. The analysis of thermo-elastic effects is done and applied to investigate thermal distortion in silicon mirrors under incidence of high intensity X-ray pulses in FEL facilities. The derivation of a generalized Guyer-Krumhansl equation governing the flux of heat and the associated thermal conductivity coefficient is also presented.
International Nuclear Information System (INIS)
Dephasing processes for low-lying phonons of Ag+ and Tl+ ?-alumina were observed in the time domain using the femtosecond pulse laser in the temperature range of 15-350 K. The dephasing dynamics associated with the time evolution of the vibrational coherence state can be directly identified with the phonon decay in the femtosecond transient. In this study, the temperature dependence of the dephasing property was decomposed into three terms in order to understand the correlation between vibration and diffusion: (i) a static structural disorder (ii) an anharmonic coupling and (iii) an ionic diffusion. The dephasing property of the low-lying phonon in Ag ?-alumina as a superionic conductor was compared with that of the isomorphous Tl ?-alumina, whose ionic conductivity was about 103 times less than Ag ?-alumina. The magnitude of static disorder shows a large value (??0 = 0. 49 meV) in Ag ?-alumina, which is twice that of Tl ?-alumina (??0 = 0.22 meV) with the same structure and the same number of excess cations by nonstoichiometry. The coefficient of phonon lifetimes originating from the cubic anharmonicity of a potential well is about five times larger in Ag ?-alumina than Tl ?-alumina. A strongly temperature dependent decay component is only seen in the superionic conductor Ag ?-alumina above 200 K, and is not observed in Tl ?-alumina. This is attributed to the phonon dephasing caused by the jump mosing caused by the jump motion of the Ag+ ions. The estimated activation energy and pre-exponential factor are Ea = 71 meV and ?/?0 = 2.86 meV in Ag ?-alumina, respectively, for the correlation time ?c = ?0exp(Ea/kBT). The value of ?/?0 = 2.86 meV, which can be regarded as an attempt frequency for the jump, coincides with the low-lying phonon frequency ??0 = 2.7 meV, but the Ea = 71 meV is different from that of the dc conductivity (Ea = 173 meV). These results, which are strongly coupled with the elementary excitation from oscillation to ionic diffusion in the picosecond time domain, would be of prime importance for the superionic conduction mechanism
Heat transport by phonons in crystalline materials and nanostructures
Koh, Yee Kan
This dissertation presents experimental studies of heat transport by phonons in crystalline materials and nanostructures, and across solid-solid interfaces. Particularly, this dissertation emphasizes advancing understanding of the mean-free-paths (i.e., the distance phonons propagate without being scattered) of acoustic phonons, which are the dominant heat carriers in most crystalline semiconductor nanostructures. Two primary tools for the studies presented in this dissertation are time-domain thermoreflectance (TDTR) for measurements of thermal conductivity of nanostructures and thermal conductance of interfaces; and frequency-domain thermoreflectance (FDTR), which I developed as a direct probe of the mean-free-paths of dominant heat-carrying phonons in crystalline solids. The foundation of FDTR is the dependence of the apparent thermal conductivity on the frequency of periodic heat sources. I find that the thermal conductivity of semiconductor alloys (InGaP, InGaAs, and SiGe) measured by TDTR depends on the modulation frequency, 0.1 ? f ? 10 MHz, used in TDTR measurements. Reduction in the thermal conductivity of the semiconductor alloys at high f compares well to the reduction in the thermal conductivity of epitaxial thin films, indicating that frequency dependence and thickness dependence of thermal conductivity are fundamentally equivalent. I developed the frequency dependence of thermal conductivity into a convenient probe of phonon mean-free-paths, a technique which I call frequency-domain thermoreflectance (FDTR). In FDTR, I monitor the changes in the intensity of the reflected probe beam as a function of the modulation frequency. To facilitate the analysis of FDTR measurements, I developed a nonlocal theory for heat conduction by phonons at high heating frequencies. Calculations of the nonlocal theory confirm my experimental findings that phonons with mean-free-paths longer than two times the penetration depth do not contribute to the apparent thermal conductivity. I employed FDTR to study the mean-free-paths of acoustic phonons in Si1-xGex. I experimentally demonstrate that 40% of heat is carried in Si1-xGe x alloys by phonons with mean-free-path 0.5 ? ? ? 5 mum, and phonons with > 2 mum do not contribute to the thermal conductivity of Si. I employed TDTR and frequency-dependent TDTR to study scattering of long- and medium-wavelength phonons in two important thermoelectric materials embedded with nanoscale precipitates. I find that the through-thickness lattice thermal conductivity of (PbTe)1-x/(PbSe)x nanodot superlattices (NDSLs) approaches the thermal conductivity of bulk homogenous PbTe1-x Sex alloys with the same average composition. On the other hand, I find that 3% of ErAs nanoparticles embedded in InGaAs is sufficient to scatter most of the phonons in InGaAs that have intermediate mean-free-paths, and thus reduces the thermal conductivity of InGaAs below the alloy limit. I find that scattering by nanoparticles approach the geometrical limit and can be readily accounted for by an additional boundary scattering which depends on the concentration of nanoparticles. Finally, I studied the thermal conductance of Au/Ti/Graphene/SiO 2 interfaces by TDTR. I find that heat transport across the interface is dominated by phonons. Even though graphene is only one atomic layer thick, graphene interfaces should be treated as two discrete interfaces instead of one diffuse interface in thermal analysis, suggesting that direct transmission of phonons from Au to SiO2 is negligible. My study is important for thermal management of graphene devices.
Phonon transport in perovskite SrTiO3 from first principles
Feng, Lei; Shiomi, Junichiro
2015-01-01
We investigate phonon transport in perovskite strontium titanate (SrTiO3) which is stable above its phase transition temperature (~105 K) by using first-principles molecular dynamics and anharmonic lattice dynamics. Unlike conventional ground-state-based perturbation methods that give imaginary phonon frequencies, the current calculation reproduces stable phonon dispersion relations observed in experiments. We find the contribution of optical phonons to overall lattice thermal conductivity is larger than 60%, markedly different from the usual picture with dominant contribution from acoustic phonons. The mode- and pseudopotential-dependence analysis suggests the strong attenuation of acoustic phonons transport originated from strong anharmonic coupling with the transversely-polarized ferroelectric modes.
Phonon deficit effect and solid state refrigerators based on superconducting tunnel junctions
Melkonian, G G; Gulian, A M
2003-01-01
Thin film devices have the advantage of being extremely compact, operate in a continuous mode, dissipate little power, and can easily be integrated in cryogenic detectors. Motivated by such possibilities, we investigate the phonon deficit effect in thin film $SIS$ (superconductor--insulator--superconductor) and $SIN$ tunnel junctions. Under certain circumstances, the phonon absorption spectra of such tunnel junctions have spectral windows of phonon absorption/emission. We propose to use phonon filters to select the phonon absorbtion windows and thus to enhance the cooling effect. Membranes attached to such tunnel junctions can be cooled in this way more effectively. We discuss a particular superlattice design of corresponding phonon filters.
Bolometric effect and phonon cooling in graphene-superconductor junctions
Vora, Heli
Graphene, a two-dimensional allotrope of graphite, possesses remarkable electronic properties which stem from the fact that the electrons in graphene are described by the Dirac-Weyl Hamiltonian. As a result, graphene exhibits a linear energy dispersion relation with zero effective mass. With its single-atomic-layer thickness, not only electrons but also phonons are of a two dimensional nature, differentiating graphene from the conventional semiconductor based two-dimensional electron gas systems. The combination of two-dimensional phonons, ultra small volume, low density of states and linear energy spectrum allows graphene to have weak electron-phonon coupling and extremely small electronic heat capacity. These properties make it a desirable material for use in a bolometer device, which is a sensitive electromagnetic radiation detector. We present a novel device design, which combines graphene with superconducting contacts and investigate its bolometric response. Two configurations of superconductor (S)- graphene(G)- superconductor(S) Josephson junction (SGS) and superconductor(S)- insulator(I)- graphene(G) (SIGIS) tunnel junction are studied. Devices with aluminum, niobium and niobium nitride as superconducting contacts are studied. In SIGIS tunnel junctions, titanium oxide is used as the barrier oxide to achieve high efficiency impedance matched bolometers. In these devices, hot electrons are created via application of microwave radiation and their relaxation to the bath temperature is studied. With the hot electrons effectively confined by the superconducting contacts, we demonstrate electron cooling via phonon interactions. This device geometry allows us to study electron-phonon coupling in single and bilayer graphene at low temperatures. In single layer graphene, a disorder-modified temperature dependence of electron-phonon cooling power is observed. And in bilayer graphene, it is shown that the electron-phonon coupling parameter has an inverse dependence on the chemical potential, opposite to that found in single layer graphene.
Thermal characterization of nanoscale phononic crystals using supercell lattice dynamics
Directory of Open Access Journals (Sweden)
Bruce L. Davis
2011-12-01
Full Text Available The concept of a phononic crystal can in principle be realized at the nanoscale whenever the conditions for coherent phonon transport exist. Under such conditions, the dispersion characteristics of both the constitutive material lattice (defined by a primitive cell and the phononic crystal lattice (defined by a supercell contribute to the value of the thermal conductivity. It is therefore necessary in this emerging class of phononic materials to treat the lattice dynamics at both periodicity levels. Here we demonstrate the utility of using supercell lattice dynamics to investigate the thermal transport behavior of three-dimensional nanoscale phononic crystals formed from silicon and cubic voids of vacuum. The periodicity of the voids follows a simple cubic arrangement with a lattice constant that is around an order of magnitude larger than that of the bulk crystalline silicon primitive cell. We consider an atomic-scale supercell which incorporates all the details of the silicon atomic locations and the void geometry. For this supercell, we compute the phonon band structure and subsequently predict the thermal conductivity following the Callaway-Holland model. Our findings dictate that for an analysis based on supercell lattice dynamics to be representative of the properties of the underlying lattice model, a minimum supercell size is needed along with a minimum wave vector sampling resolution. Below these minimum values, a thermal conductivity prediction of a bulk material based on a supercell will not adequately recover the value obtained based on a primitive cell. Furthermore, our results show that for the relatively small voids and void spacings we consider (where boundary scattering is dominant, dispersion at the phononic crystal unit cell level plays a noticeable role in determining the thermal conductivity.
Local modes and phonons around paramagnetic defects in solids
International Nuclear Information System (INIS)
Full text: Defects introduced into crystalline materials can modify their static and dynamical properties and can be used as probes for studying local crystal properties. Question is if a defect participates in phonon motions of a host lattice or it has its own dynamics. If so, what is a coupling between defect motions and collective motions of the crystal lattice? These questions are important in doped semiconductors, and in solids where defects are generated for modification of physical properties. Phonon spectra are available for rather simple inorganic solids where they can be theoretically calculated or measured by neutron scattering technique. The phonon spectra usually deviate significantly from Debye-type phonon spectra presented in most of textbooks of solid-state physics. Vibrations of a simple defect appear in a narrow frequency range are called local mode. Because of a low defect concentration the local modes cannot be detected by neutron scattering, but can be detected by classical spectroscopy methods. Local modes can be identified by Raman and IR spectroscopy when appear in the optical phonon branch region. Local modes appearing in acoustic phonon region are difficult to observe. They can be detected in studies of electron spin relaxation measured by pulsed electron paramagnetic resonance methods. An electron spin system of paramagnetic defects relaxes, after a pulse excitation (in time order of micro- to milliseconds), to initial equilibrium transferring the excitation energy to phonons and/or to local mode of the defect. These two ways can be distinguished in pulsed EPR measurements in a broad temperature range. In the lecture a method of local mode detection with electron-spin echo will be described and results will be presented for paramagnetic ions doped into inorganic and organic solids and for free radicals generated by ionizing radiation in crystals. (author)
Sartori, Luisa; Betti, Sonia
2015-01-01
Complementary colors are color pairs which, when combined in the right proportions, produce white or black. Complementary actions refer here to forms of social interaction wherein individuals adapt their joint actions according to a common aim. Notably, complementary actions are incongruent actions. But being incongruent is not sufficient to be complementary (i.e., to complete the action of another person). Successful complementary interactions are founded on the abilities: (i) to simulate another person's movements, (ii) to predict another person's future action/s, (iii) to produce an appropriate incongruent response which differ, while interacting, with observed ones, and (iv) to complete the social interaction by integrating the predicted effects of one's own action with those of another person. This definition clearly alludes to the functional importance of complementary actions in the perception-action cycle and prompts us to scrutinize what is taking place behind the scenes. Preliminary data on this topic have been provided by recent cutting-edge studies utilizing different research methods. This mini-review aims to provide an up-to-date overview of the processes and the specific activations underlying complementary actions. PMID:25983717
Yoneda, H.; Zhang, J.; Tang, D. Y.; Kaminskii, A. A.
2015-08-01
For the first time we excited four-phonon impulsive stimulated Raman scattering (SRS) in tetragonal GdVO4 single crystal under near-IR femtosecond pumping. All of its recorded ? (3)-nonlinear Stokes cascaded and cross-cascaded fully coherent lasing emissions were identified at internal vibrations of the [VO4]3? units of the studied vanadate. The obtained new fundamental knowledge could significantly enrich the functional potential of this crystal, which is a host crystal for trivalent lanthanide lasants and attractive gain media for Raman laser converters and self-SRS lasers.
Xu, Zhi-Jie
2015-01-01
We first propose fundamental solutions of wave propagation in dispersive chain subject to a localized initial perturbation in the displacement. Analytical solutions are obtained for both second order nonlinear dispersive chain and homogenous harmonic chain using stationary phase approximation. Solution is also compared with numerical results from molecular dynamics (MD) simulations. Locally dominant phonon modes (k-space) are introduced based on these solutions. These locally defined spatially and temporally varying phonon modes k(x, t) are critical to the concept of the local thermodynamic equilibrium (LTE). Wave propagation accompanying with the nonequilibrium dynamics leads to the excitation of these locally defined phonon modes. It is found that the system energy is gradually redistributed among these excited phonons modes (k-space). This redistribution process is only possible with nonlinear dispersion and requires a finite amount of time to achieve a steady state distribution. This time scale is dependent on the spatial distribution (or frequency content) of the initial perturbation and the dispersion relation. Sharper and more concentrated perturbation leads to a faster energy redistribution and dissipation. This energy redistribution generates localized phonons with various frequencies that can be important for phonon-phonon interaction and energy dissipation in nonlinear systems. Depending on the initial perturbation and temperature, the time scale associated with this energy distribution can be critical for energy dissipation compared to the Umklapp scattering process. Ballistic type of heat transport along the harmonic chain reveals that at any given position, the lowest mode (k = 0) is excited first and gradually expanding to the highest mode (kmax(x,t)), where kmax(x,t) can only asymptotically approach the maximum mode kB of the first Brillouin zone (kmax(x,t) ? kB). No energy distributed into modes with kmax(x,t) thermal conductivity that diverges with time.
Phonon Pulse Shape Discrimination in SuperCDMS Soudan
Hertel, S A
2011-01-01
SuperCDMS is the next phase of the Cryogenic Dark Matter Search experiment, which measures both phonon and charge signals generated by particle recoils within a germanium target mass. Charge signals are employed both in the definition of a fiducial volume and in the rejection of electron recoil background events. Alternatively, phonons generated by the charge carriers can also be used for the same two goals. This paper describes preliminary efforts to observe and quantify these contributions to the phonon signal and then use them to reject background events. A simple analysis using only one pulse shape parameter shows bulk electron recoil vs. bulk nuclear recoil discrimination to the level of 1:10^3 (limited by the statistics of the data), with little degradation in discrimination ability down to at least 7 keV recoil energy. Such phonon-only discrimination can provide a useful cross-check to the standard discrimination methods, and it also points towards the potential of a device optimized for a phonon-only ...
Acoustic wave transmission in time-varying phononic crystals
International Nuclear Information System (INIS)
Phononic crystal effects are typically narrowband and highly dependent on the size and spacing of the scatterers within the crystal—properties that are fixed and unchangeable. We propose that it may be possible to dynamically alter the behaviour of phononic crystals by varying the material properties in time. In this paper we seek to extend the existing static phononic crystal theory so as to handle time-varying material parameters and also to provide insight into the factors that govern their behaviour. Beginning with the transmission matrix method, we develop a new method to determine the acoustic wave transmission through a time-varying corrugated tube waveguide, which is analogous to a one-dimensional (1D) phononic crystal. These expressions are further developed for periodic material parameter variation signals. Our method permits the development of a closed-form solution to the acoustic wave transmission through a 1D time-varying phononic crystal. It shows excellent agreement with finite-difference time-domain simulations and with execution times several orders of magnitude faster. Preliminary results show that the band-gap properties can be significantly altered using material parameter time variation as the driving mechanism
Puzzling phonon dispersion curves and vibrational mode instability in superconducting MgCNi3
Directory of Open Access Journals (Sweden)
Prafulla K. Jha
2012-06-01
Full Text Available A first principles calculation of the lattice dynamical properties of superconducting MgCNi3 has been performed using density functional perturbation theory (DFPT. The calculated phonon dispersion curves and phonon density of states have been compared with inelastic x-ray scattering (IXS and inelastic neutron scattering (INS measurements. We show for the first time that phonon dispersion curves for MgCNi3 in whole Brillouin zone are positive (stable phonon modes and in good agreement with the experimental data. The phonon DOS shows absence of phonon density of states at zero energy unlike earlier calculations. There is a good agreement between calculated and experimental electron-phonon parameter and superconducting transition temperature. The Eliasberg function is quantitatively as well as qualitatively different from the phonon density of states. The lattice specific heat and Debye temperature do not show any anomalous behaviour.
SELF-ENERGY OF PHONONS INTERACTING WITH FREE CARRIERS IN SILICON
Pintschovius, L.; J. Vergés; M Cardona
1981-01-01
The dispersion in the self energy of acoustic phonons produced by free electrons and holes in silicon has been measured with neutron scattering. The corresponding electron-phonon interaction mechanisms are discussed.
Optical control of coherent and squeezed phonons: major differences and similarities
Misochko, O V
2013-01-01
Coherent and squeezed phonon oscillations can be excited in solids impulsively by a single femtosecond pulse whose duration is shorter that a phonon period. By applying the second ultrafast pump pulse these oscillations can be significantly, but differently modified.
Impact of phonon coupling on the photon strength function
Achakovskiy, O.; Avdeenkov, A.; Goriely, S.; Kamerdzhiev, S.; Krewald, S.
2015-03-01
The pygmy dipole resonance and photon strength function in stable and unstable Ni and Sn isotopes are calculated within the microscopic self-consistent version of the extended theory of finite Fermi systems, which, in addition to the standard quasiparticle random-phase approximation approach, includes phonon coupling effects. The Skyrme force SLy4 is used. A pygmy dipole resonance in 72Ni is predicted at the mean energy of 12.4 MeV exhausting 25.7% of the total energy-weighted sum rule. The microscopically obtained photon E 1 strength functions are compared with available experimental data and used to calculate nuclear reaction properties. Average radiative widths and radiative neutron capture cross sections have been calculated taking phonon coupling into account as well as uncertainties caused by various microscopic level density models. In all three quantities considered, the contribution of phonon coupling turned out to be significant and is found necessary to explain available experimental data.
Anharmonic phonons and magnons in BiFeO3
Energy Technology Data Exchange (ETDEWEB)
Delaire, Olivier A [ORNL; Ma, Jie [ORNL; Stone, Matthew B [ORNL; Huq, Ashfia [ORNL; Gout, Delphine J [ORNL; Brown, Craig [National Institute of Standards and Technology (NIST); Wang, Kefeng [Nanjing National Laboratory of Microstructures, Nanjing University, Nanjing; Ren, Zhifeng [Boston College, Chestnut Hill
2012-01-01
The phonon density of states (DOS) and magnetic excitation spectrum of polycrystalline BiFeO3 were measured for temperatures 200 < T < 750K , using inelastic neutron scattering (INS). Our results indicate that the magnetic spectrum of BiFeO3 closely resembles that of similar Fe perovskites, such as LaFeO3, despite the cycloid modulation in BiFeO3. We do not find any evidence for a spin gap. A strong T-dependence of the phonon DOS was found, with a marked broadening of the whole spectrum, providing evidence of strong anharmonicity. This anharmonicity is corroborated by large amplitude motions of Bi and O ions observed with neutron diffraction. These results highlight the importance of spin-phonon coupling in this material.
Model potential calculation of phonon dispersion in Tb and Ho
International Nuclear Information System (INIS)
The nonlocality of the rare earth metal model potential (REMMP) of Upadhyaya and Animalu is considered in the full modified scheme of Eschrig and Wonn to study the lattice dynamics of Tb and Ho. The computed phonon dispersion curves are raised by 10 to 15 % when compared to those of the former authors. Next a parameter is suitably adjusted in order to have a reasonable fit with the experimental data. The scheme of Eschrig and Wonn considers only the first order E- and (kq)-dependent terms in the Taylor expansion of the form factor. In the present work the expansion is truncated at the second order and an expression for the energy wave number characteristic, containing additional terms corresponding to E-, (kq)- and mixed dependence, is deduced. When the phonon frequencies of Tb are calculated by including the second order terms, a substantial effect is found. The calculation of phonon frequencies, using nonlocal parameters evaluated from the basic data, is suggested. (author)
Electron-phonon interaction in Graphite Intercalation Compounds
Boeri, L; Giantomassi, M; Andersen, O K; Boeri, Lilia; Bachelet, Giovanni B.; Giantomassi, Matteo; Andersen, Ole K.
2007-01-01
Motivated by the recent discovery of superconductivity in Ca- and Yb-intercalated graphite (CaC$_{6}$ and YbC$_{6}$) and from the ongoing debate on the nature and role of the interlayer state in this class of compounds, in this work we critically study the electron-phonon properties of a simple model based on primitive graphite. We show that this model captures an essential feature of the electron-phonon properties of the Graphite Intercalation Compounds (GICs), namely, the existence of a strong dormant electron-phonon interaction between interlayer and $\\pi ^{\\ast}$ electrons, for which we provide a simple geometrical explanation in terms of NMTO Wannier-like functions. Our findings correct the oversimplified view that nearly-free-electron states cannot interact with the surrounding lattice, and explain the empirical correlation between the filling of the interlayer band and the occurrence of superconductivity in Graphite-Intercalation Compounds.
Probing confined acoustic phonons in free standing small gold nanoparticles
Energy Technology Data Exchange (ETDEWEB)
Mankad, Venu; Jha, Prafulla K. [Department of Physics, M. K. Bhavnagar University, Bhavnagar 364 001 (India); Ravindran, T. R. [Material Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102 (India)
2013-02-21
Polarized and depolarized spectra from gold (Au) nanoparticles of different sizes are investigated in the small size range, between 3 and 7 nm, using low frequency Raman spectroscopy. Acoustic vibrations of the free-standing Au nanoparticles are demonstrated with frequencies ranging from 5 to 35 cm{sup -1}, opening the way to the development of the acoustic resonators. A blue shift in the phonon peaks along with the broadening is observed with a decrease in particle size. Comparison of the measured frequencies with vibrational dynamics calculation and an examination as from the transmission electron microscopy results ascertain that the low frequency phonon modes are due to acoustic phonon quantization. Our results show that the observed low frequency Raman scattering originates from the spherical (l = 0) and quadrupolar (l = 2) vibrations of the spheroidal mode due to plasmon mediated acoustic vibrations in Au nanoparticles.
Phonon-mediated negative differential conductance in molecular quantum dots
Zazunov, A; Martin, T; Zazunov, Alex; Feinberg, Denis; Martin, Thierry
2006-01-01
Transport through a single molecular conductor is considered, showing negative differential conductance behavior associated with phonon-mediated electron tunneling processes. This theoretical work is motivated by a recent experiment by Leroy et al. using a carbon nanotube contacted by an STM tip [Nature {\\bf 432}, 371 (2004)], where negative differential conductance of the breathing mode phonon side peaks could be observed. A peculiarity of this system is that the tunneling couplings which inject electrons and those which collect them on the substrate are highly asymmetrical. A quantum dot model is used, coupling a single electronic level to a local phonon, forming polaron levels. A ``half-shuttle'' mechanism is also introduced. A quantum kinetic formulation allows to derive rate equations. Assuming asymmetric tunneling rates, and in the absence of the half-shuttle coupling, negative differential conductance is obtained for a wide range of parameters. A detailed explanation of this phenomenon is provided, sho...
Structural and phononic characteristics of nitrogenated holey graphene
Sahin, H.
2015-08-01
Recent experimental studies showed that formation of a two-dimensional crystal structure of nitrogenated holey graphene (NHG) is possible. Similar to graphene, NHGs have an atomically thin and strong crystal structure. Using first-principles calculations, we investigate the structural, phononic, and thermal properties of monolayer NHG crystal. Our charge analysis reveals that the charged holey sites of NHG provide a reactive ground for further functionalization by adatoms or molecules. We also found that similar to graphene, the NHG structure has quite high-frequency phonon modes and the presence of nitrogen atoms leads to the emergence of additional vibrational modes. Our phonon analysis reveals the presence of three characteristic Raman-active modes of NHG. Furthermore, the analysis of constant-volume heat capacity showed that the NHG structure has a linear temperature dependence in the low-temperature region. The strong lattice structure and unique thermal properties of the NHG crystal structure are desirable in nanoscale device applications.
Decoherence in semiconductor cavity QED systems due to phonon couplings
DEFF Research Database (Denmark)
Nielsen, Per Kær; MØrk, Jesper
2014-01-01
We investigate the effect of electron-phonon interactions on the coherence properties of single photons emitted from a semiconductor cavity QED (quantum electrodynamics) system, i.e., a quantum dot embedded in an optical cavity. The degree of indistinguishability, governing the quantum mechanical interference between two single photons, is calculated as a function of important parameters describing the cavity QED system and the phonon reservoir, e.g., cavity quality factor, light-matter coupling strength, temperature, and phonon lifetime. We show that non-Markovian effects play an important role in determining the coherence properties for typical parameter values and establish the conditions under which a Markovian approximation may be applied. The calculations are performed using a recently developed second-order perturbation theory, and the limits of validity are established by comparing to an exact diagonalization approach. We find that for large cavity decay rates the perturbation theory may break down.
High temperature superconductivity and electron-phonon coupling
International Nuclear Information System (INIS)
The electron-phonon coupling in a copper oxide based high temperature superconductor has been estimated by taking the anisotropic crystal structure into account. From the Debye temperature of a superconducting material, information about the role of phonons in its superconducting mechanism can be investigated. The void-free acoustic Debye temperature, ?D, of various cuprate high temperature superconductors estimated using the acoustic technique was found to be between 250 and 500 K. The electron-phonon coupling constant was estimated from the transition temperature Tc using the standard BCS theory and also the 2D van Hove scenario with related characteristic temperature. The van Hove scenario seems to explain high temperature superconductivity in the cuprates better than the standard three-dimensional BCS model
High temperature superconductivity and electron-phonon coupling
Energy Technology Data Exchange (ETDEWEB)
Yusoff, A R M [Material Science Laboratory, Physics Department, University of Malaya, 50603 Kuala Lumpur (Malaysia); Abd Majid, W H [Material Science Laboratory, Physics Department, University of Malaya, 50603 Kuala Lumpur (Malaysia); Abd-Shukor, R [School of Applied Physics, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor Darul Ehsan (Malaysia)
2005-06-01
The electron-phonon coupling in a copper oxide based high temperature superconductor has been estimated by taking the anisotropic crystal structure into account. From the Debye temperature of a superconducting material, information about the role of phonons in its superconducting mechanism can be investigated. The void-free acoustic Debye temperature, {theta}{sub D}, of various cuprate high temperature superconductors estimated using the acoustic technique was found to be between 250 and 500 K. The electron-phonon coupling constant was estimated from the transition temperature T{sub c} using the standard BCS theory and also the 2D van Hove scenario with related characteristic temperature. The van Hove scenario seems to explain high temperature superconductivity in the cuprates better than the standard three-dimensional BCS model.
Anomalous phonon behaviour in V sub 3 Si
Yethiraj, M
2002-01-01
In earlier studies of phonons in V sub 3 Si, a gradual softening of the (hh0) branch was observed and attributed to the martensitic transition in this compound, which precedes the onset of superconductivity by a few degrees K. In this work, the temperature dependence of the transverse acoustic (TA) branch along the hh0 direction was studied in greater detail and it is shown that while the TA hh0 mode starts to soften at relatively high temperatures (>200 K), an anomalous softening, which is rather localized in q, occurs just below T sub c. The intensity of this soft-phonon peak correlates extremely well with the onset of the superconducting phase and appears to vary as the order parameter with temperature and applied field. The similarities in the phonon softening and Fermi-surface anisotropy between this compound and the rare-earth nickel borocarbides suggest the existence of a common mechanism for the superconducting transition. (orig.)
Phonon routing in integrated optomechanical cavity-waveguide systems
Fang, Kejie; Luan, Xingsheng; Painter, Oskar
2015-01-01
The mechanical properties of light have found widespread use in the manipulation of gas-phase atoms and ions, helping create new states of matter and realize complex quantum interactions. The field of cavity-optomechanics strives to scale this interaction to much larger, even human-sized mechanical objects. Going beyond the canonical Fabry-Perot cavity with a movable mirror, here we explore a new paradigm in which multiple cavity-optomechanical elements are wired together to form optomechanical circuits. Using a pair of optomechanical cavities coupled together via a phonon waveguide we demonstrate a tunable delay and filter for microwave-over-optical signal processing. In addition, we realize a tight-binding form of mechanical coupling between distant optomechanical cavities, leading to direct phonon exchange without dissipation in the waveguide. These measurements indicate the feasibility of phonon-routing based information processing in optomechanical crystal circuitry, and further, to the possibility of re...
Phonon induced phase grating in quantum dot system.
Cheng, Guang-Ling; Zhong, Wen-Xue; Chen, Ai-Xi
2015-04-20
Electromagnetically induced phase grating is theoretically investigated in the driven two-level quantum dot exciton system at the presence of the exciton-phonon interactions. Due to the phonon-induced coherent population oscillation, the dispersion and absorption spectra are sharply changed and the phase modulation is enhanced via the high refractive index with nearly-vanishing absorption, which could effectively diffract a weak probe light into the first-order direction with the help of a standing-wave control field. Moreover, the diffraction efficiency of the grating can be easily manipulated by controlling the Huang-Rhys factor representing the exciton-phonon coupling, the intensity and detuning of the control field, and the detuning of the probe field. The scheme we present has potential applications in the photon devices for optical-switching and optical-imaging in the micro-nano solid-state system. PMID:25969028
Phonon dispersion of quasi-freestanding graphene on Pt(111)
International Nuclear Information System (INIS)
High-resolution electron energy loss spectroscopy has been used to probe phonon dispersion in quasi-freestanding graphene epitaxially grown on Pt(111). Loss spectra clearly show different dispersing features related to both acoustic and optical phonons. The present results have been compared with graphene systems which strongly interact with the substrate, i.e. the nearly-flat monolayer graphene (MLG)/Ni(111) and the corrugated MLG/Ru(0001). We found that the phonon dispersion of graphene/Pt(111) reproduces well the behavior of pristine graphite. This could be taken as an indication of the negligible interaction between the graphene sheet and the underlying Pt substrate. The softening of out-of-plane modes observed for interacting graphene/metal interfaces does not occur for the nearly-free-standing graphene/Pt(111). (paper)
Photonic-phononic orbital angular momentum in Brillouin parametric conversion
Zhu, Zhihan; Mu, Chunyuan; Li, Hongwei
2014-01-01
Orbital angular momentum (OAM) is a fundamental photonic degree of freedom, showed by Allen and co-workers. Its most attractive feature is an inherently infinite dimensionality, which in recent years has obtained several ground-breaking demonstrations for high information-density communication and processing, both in classical and quantum. Here, by seeking the reason for photonic OAM non-conservation in stimulated Brillouin amplification, we report the first demonstration of the evolution law for OAM in Brillouin process. The parameter of OAM can conveniently transfer between the phonons and different polarized photons due to the photonic spin angular momentum conservation. Our results have revealed a parametric conversion mechanism of Brillouin process for Photonic-phononic OAM, demonstrated the role of phononic OAM and the vortex acoustic wave in this process, and suggested this mechanism may find important applications in OAM-based information communication and processing.
... How to Choose the Best Skin Care Products Laser Resurfacing Uses for Laser Resurfacing Learn more about specific conditions where laser ... skin Scars Sun-damaged skin Wrinkles What is laser resurfacing? Laser resurfacing is a procedure that uses ...
Generation of phonons from electrostriction in small-core optical waveguides
Vincent Laude; Jean-Charles Beugnot
2013-01-01
We investigate the generation of acoustic phonons from electrostriction of optical waves in small core waveguides. We speci?cally consider simple step-index strip waveguides composed of silica or silicon in air, with sub-micron lateral dimen-sions. Such waveguides support one or a few optical modes, but a rich spectrum of acoustic phonons that becomes densely populated as the phonon frequency in-creases. We evaluate rigorously the phonon energy density that results from the electrostriction o...
Phonon-enhanced relaxation and excitation in the Holstein-Hubbard model
Philipp Werner; Martin Eckstein
2013-01-01
We study quenches of the interaction and electron-phonon coupling parameter in the Hubbard-Holstein model, using nonequilibrium dynamical mean field theory. The calculations are based on a generalized Lang-Firsov scheme for time-dependent interactions or externally driven phonons, and an approximate strong-coupling impurity solver. The interaction quench calculations reveal the phonon-assisted decay of excess doublons, while the quenches of the electron-phonon coupling lead ...
Stokes suppression and supercontinuum generation by differential two-phonon excitation.
Nishioka, Hajime
2014-11-01
Stimulated Raman scattering driven by differential coupling of two phonon modes has been demonstrated. These phonon modes are coherently and strongly coupled by external fields via two-phonon excitation at the first Brillouin zone boundary. Up to 11th order of sidebands and a supercontinuum covering entire visible region have been observed. The original Stokes and anti-Stokes lines by the single-phonon stimulated Raman scattering were significantly suppressed. PMID:25401797
Effect of phonon interaction on the ground state of even-even spherical nuclei
International Nuclear Information System (INIS)
The equations for calculating the energy and the structure of the excited states with the wave function containing one- and two-phonon components are obtained. The phonon correlations in the ground state of the nucleus due to the interaction of the phonon modes excitation are taken into account. The numerical estimations of the phonon correlations influence on the energy of the lowest excited states are given
Tai, Po-Tse; Yu, Pyng; Tang, Jau
2011-05-01
In this work we reported experimental measurements of ultrafast structural dynamics in metallic nanoprisms induced by a femtosecond laser pulse. The main focus of this study of anisotropic heating in nanoprisms is about laser fluence effects on photoexcitation of two planar coherent acoustic phonon modes, namely, the breathing mode and the totally symmetric mode. We presented a combined two-temperature model and 2-D Fermi-Pasta-Ulam model to explain both the dependence of the initial phases and the mode weight on the excitation power. Our transient optical absorption data for both the initial fast monotonic decay and the subsequent coherent acoustic oscillations clearly indicate the presence of anisotropic thermal expansion in nanoprisms.
Phonon Scattering by Breathers in the Discrete Nonlinear Schrödinger Equation
Lee, S; Kim, S; Ting, Julian Juhi-Lian
1998-01-01
Linear theory for phonon scattering by discrete breathers in the discrete nonlinear Schroedinger equation using the transfer matrix approach is presented. Transmission and reflection coefficients are obtained as a function of the wave vector of the input phonon. The occurrence of a nonzero transmission, which in fact becomes perfect for a symmetric breather, is shown to be connected with localized eigenmodes thresholds. In the weak-coupling limit, perfect reflection are shown to exist, which requires two scattering channels. A necessary condition for a system to have a perfect reflection is also considered in a general context.
Sub-Poissonian Phonon Lasing in Three-Mode Optomechanics
Lörch, Niels
2015-01-01
We propose to use the resonant enhancement of the parametric instability in an optomechanical system of two optical modes coupled to a mechanical oscillator to prepare mechanical states with sub-Poissonian phonon statistics. Strong single photon coupling is not required. The requirements regarding sideband resolution, circulating cavity power and environmental temperature are in reach with state of the art parameters of optomechanical crystals. Phonon antibunching can be verfied in a Hanburry-Brown-Twiss measurement on the output field of the optomechanical cavity.
Electronic Contributions to the Phonon Damping in Metals
International Nuclear Information System (INIS)
An imaginary part of the dielectric matrix is derived based on a first order perturbation expansion of the valence electron states in a local potential model of the crystal. The results are used to estimate the electronic contributions to the phonon damping in aluminum and lead. The corrections which have been obtained are of the same order of magnitude at small phonon momenta as the damping earlier calculated for the free electrons. However, the discrepancies between the theoretical and experimental results still remain. The major contribution to damping seems to originate in anharmonic effects, even at 80 deg K
Effect of Holstein phonons on the electronic properties of graphene
International Nuclear Information System (INIS)
We obtain the self-energy of the electronic propagator due to the presence of Holstein polarons within the first Born approximation. This leads to a renormalization of the Fermi velocity of 1%. We further compute the optical conductivity of the system at the Dirac point and at finite doping within the Kubo formula. We argue that the effects due to Holstein phonons are negligible and that the Boltzmann approach, which does not include inter-band transitions and can thus not treat optical phonons due to their high energy of ??0 ? 0.1-0.2 eV, remains valid
Hydrogen transport within graphene multilayers by means of flexural phonons
Dario Camiola, Vito; Farchioni, Riccardo; Pellegrini, Vittorio; Tozzini, Valentina
2015-03-01
Graphene sustains transverse out-of-plane mechanical vibrations (flexural phonons). At the nanometer scale, these appear as traveling ripples, or cavities, if excited in counter-phase in alternate multilayers. In this work we explore by means of classical molecular dynamics simulations the possibility of using these moving nano-cavities to actively transport hydrogen. We find that the gas can be efficiently transported for hundreds of nanometers in the wave propagation direction, before the phonons damp down. Therefore, this effect could be used to move and pump gases through multilayers graphene based frameworks.
DYNAMICAL STUDY OF PHONONS IN FERROELECTRIC LEAD TITANATE
Katiyar, R.; Freire, J.
1981-01-01
Lattice dynamical formalism using rigid ion model with long range coulomb forces and short range axially symmetric forces has been applied to the crystal of lead titanate in tetragonal phase. All zone center phonons and a few zone boundary phonons were used in determining the force constant parameters both at room temperature and close to Tc by nonlinear least squares analysis. The results indicate that the Ti-O short range forces are at least one order of magnitude larger than the Pb-O force...
Generalized Kinetic Theory of Electrons and Phonons Models, Equilibrium, Stability
Rossani, A
2003-01-01
In the present paper our aim is to introduce some models for the generalization of the kinetic theory of electrons and phonons (KTEP), as well as to study equilibrium solutions and their stability for the generalized KTEP (GKTEP) equations. We consider a couple of models, relevant to non standard quantum statistics, which give rise to inverse power law decays of the distribution function with respect to energy. In the case of electrons in a phonon background, equilibrium and stability are investigated by means of Lyapounov theory. Connections with thermodynamics are pointed out.
Band gap in hypersonic surface phononic lattice of nickel pillars
Trzaskowska, A.; Mielcarek, S.; Sarkar, J.
2013-10-01
Brillouin light scattering was applied for investigation of surface wave propagation in phononic materials made of a silicon surface loaded with a nanostructure of nickel pillars. The results revealed the presence of phononic energy gap in the GHz range. The presence of such an energy gap was theoretically confirmed by the finite element method. The width of the energy gap was found to be related to the height of the pillars and was shown to be limited by the frequencies of the modes localized in the pillars. The modes were thoroughly analysed.
Optical Conductivity of Graphene Sheet Including Electron-Phonon Interaction
International Nuclear Information System (INIS)
Using an expression of optical conductivity, based on the linear response theory, the Green's function technique and within the Holstein Hamiltonian model, the effect of electron-phonon interaction on the optical conductivity of graphene plane is studied. It is found that the electron-phonon coupling increases the optical conductivity of graphene sheet in the low frequency region due to decreasing quasiparticle weight of electron excitation while the optical conductivity reduces in the high frequency region. The latter is due to role of electrical field's frequency. (condensed matter: electronic structure, electrical, magnetic, and optical properties)
Control of Coherent Acoustic Phonons in Semiconductor Quantum Wells
International Nuclear Information System (INIS)
Using subpicosecond optical pump-probe techniques, coherent zone-folded longitudinal acoustic phonons (ZFLAPs) were investigated in an InGaN multiple quantum well structure. A two-pump differential transmission technique was used to generate and control coherent ZFLAP oscillations through the relative timing and amplitude of the two pump pulses. Enhancement and suppression of ZFLAP oscillations were demonstrated, including complete cancellation of generated acoustic phonons for the first time in any material system. Coherent control was used to demonstrate that ZFLAPs are generated differently in InGaN multiple quantum wells than in GaAs/AlAs superlattices
Contact-Free Germanium Ionization and Phonon Detectors
International Nuclear Information System (INIS)
A new method to study the origin of the dead-layer in ionization-phonon detectors was developed wherein the ionization is measured via a 25 micron gap between the collection electrodes and germanium absorber. Phonon signals are measured with small tungsten thermometers (Tc?90 mK) varnished to the Ge substrates. The Ge samples were studied using collimated 241Am sources. With this geometry, different contributions to the 'dead-layer' effect can be studied independently: Carrier back diffusion, trapping on surface states, Schottky barrier lowering, etc.
Contact-Free Germanium Ionization and Phonon Detectors
Mirabolfathi, N.; Yen, J. J.; Brink, P. L.; Cabrera, B.; Daal, M.; Serfass, B.; Sadoulet, B.; Seitz, D. N.; Sundqvist, K. M.; Tomada, A.
2009-12-01
A new method to study the origin of the dead-layer in ionization-phonon detectors was developed wherein the ionization is measured via a 25 micron gap between the collection electrodes and germanium absorber. Phonon signals are measured with small tungsten thermometers (Tc˜90 mK) varnished to the Ge substrates. The Ge samples were studied using collimated 241Am sources. With this geometry, different contributions to the "dead-layer" effect can be studied independently: Carrier back diffusion, trapping on surface states, Schottky barrier lowering, etc.
Spin Hall Effects Due to Phonon Skew Scattering
Gorini, Cosimo; Eckern, Ulrich; Raimondi, Roberto
2015-08-01
A diversity of spin Hall effects in metallic systems is known to rely on Mott skew scattering. In this work its high-temperature counterpart, phonon skew scattering, which is expected to be of foremost experimental relevance, is investigated. In particular, the phonon skew scattering spin Hall conductivity is found to be practically T independent for temperatures above the Debye temperature TD. As a consequence, in Rashba-like systems a high-T linear behavior of the spin Hall angle demonstrates the dominance of extrinsic spin-orbit scattering only if the intrinsic spin splitting is smaller than the temperature.
Band gap engineering in simultaneous phononic and photonic crystal slabs
Energy Technology Data Exchange (ETDEWEB)
Djafari Rouhani, B.; Pennec, Y.; Vasseur, J.O.; Hassouani, Y.El; Li, C.; Akjouj, A. [Universite de Lille1 Sciences et Technologies, Cite Scientifique, Institut d' Electronique, de Microelectronique et de Nanotechnologie, UMR CNRS 8520, Villeneuve d' Ascq (France); Boudouti, E.H.El; Bria, D. [Universite de Lille1 Sciences et Technologies, Cite Scientifique, Institut d' Electronique, de Microelectronique et de Nanotechnologie, UMR CNRS 8520, Villeneuve d' Ascq (France); Universite d' Oujda, Laboratoire de Dynamique et d' Optique des Materiaux, Faculte des Sciences, Oujda (Morocco)
2011-06-15
We discuss the simultaneous existence of phononic and photonic band gaps in two types of phononic crystals slabs, namely periodic arrays of nanoholes in a Si membrane and of Si nanodots on a SiO{sub 2} membrane. In the former geometry, we investigate in detail both the boron nitride lattice and the square lattice with two atoms per unit cell (these include the square, triangular and honeycomb lattices as particular cases). In the latter geometry, some preliminary results are reported for a square lattice. (orig.)
The inverted pendulum, interface phonons and optic Tamm states
Combe, Nicolas
2011-01-01
The propagation of waves in periodic media is related to the parametric oscillators. We transpose the possibility that a parametric pendulum oscillates in the vicinity of its unstable equilibrium positions to the case of waves in lossless unidimensional periodic media. This concept formally applies to any kind of wave. We apply and develop it to the case of phonons in realizable structures and evidence new classes of phonons. Discussing the case of electromagnetic waves, we show that our concept is related to optic Tamm states one but extends it to periodic Optic Tamm state.
Surface phonon polaritons in semi-infinite semiconductor superlattices
International Nuclear Information System (INIS)
Surface phonon polaritons in a semi-infinite semiconductor superlattice bounded by vacuum are studied. The modes associated with the polaritons are obtained and used to obtain the dispersion relation. Numerical results show that polariton bands exist between the TO and LO phonon frequencies, and are found to approach two surface mode frequencies in the limit of large tangential wave vector. Dependency of frequencies on the ratio of layer thicknesses is shown. Results are illustrated by a GaAs-GaP superlattice bounded by vacuum. (author)
YPHON: A package for calculating phonons of polar materials
Wang, Yi; Chen, Long-Qing; Liu, Zi-Kui
2014-11-01
In our recent works, we have developed a mixed-space approach within the framework of direct method for the first-principle calculation of phonon properties. It makes full use of the accuracy of the force constants calculated in the real space and the dipole-dipole interactions in the reciprocal space, making the accurate phonon calculation possible with the direct method for polar materials. In this paper, an efficient C++ implementation of the mixed-space approach, YPHON, is provided as open source, including demos and Linux scripts for extracting input data to YPHON from the output of VASP.5. The functions of the current package include the calculations of: (1) the phonon dispersions; (2) the phonon density of states; (3) the neutron scattering section weighted phonon density of state; (4) the phonons of the high symmetry structure using the force constants from low symmetry structure; (5) the phonon dispersions of random alloys; and (6) the analysis of the vibrational modes using the point group theory. Catalogue identifier: AETS_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AETS_v1_0.html Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 567815 No. of bytes in distributed program, including test data, etc.: 9763594 Distribution format: tar.gz Programming language: C++, Linux scripts. Computer: Linux systems with a g++ or C++ compiler. Operating system: Linux. RAM: Ranges from a few Mbytes to a few Gbytes, dynamically depending on the system size. Classification: 7.8. External routines: GSL-the GNU Scientific Library (GSL) is a numerical library for C and C++ programmers. VASP.5 or later for the calculations of force constants and dielectric constants and Born effective charge for polar materials. Nature of problem: This package has the purpose of computing accurately phonon properties of polar materials within the small displacement approach. Solution method: Mixed-space approach to the vibration-induced dipole-dipole interaction. Running time: In the scale of a common Linux command.
Phonon Rabi-Assisted Tunneling in Diatomic Molecules
Vernek, E; Ulloa, S E; Sandler, N
2005-01-01
We study electronic transport in diatomic molecules connected to metallic contacts in the regime where both electron-electron and electron-phonon interactions take place. We find that the competition between these interactions results in new resonant conditions for interlevel transitions and polaron formation. The Coulomb repulsion between electrons requires additional energy when electrons attempt phonon-assisted interlevel jumps between fully or partially occupied levels. We apply the equations of motion approach to calculate the electronic Green's functions. The density of states and conductance through the system are shown to exhibit interesting Rabi-like splitting of Coulomb blockade peaks, and strong temperature dependence under the interacting resonant conditions.
Topology optimization of two-dimensional asymmetrical phononic crystals
Energy Technology Data Exchange (ETDEWEB)
Dong, Hao-Wen [Institute of Engineering Mechanics, Beijing Jiaotong University, Beijing 100044 (China); Su, Xiao-Xing [School of Electronic and Information Engineering, Beijing Jiaotong University, Beijing 100044 (China); Wang, Yue-Sheng, E-mail: yswang@bjtu.edu.cn [Institute of Engineering Mechanics, Beijing Jiaotong University, Beijing 100044 (China); Zhang, Chuanzeng [Department of Civil Engineering, University of Siegen, D-57068 Siegen (Germany)
2014-01-17
The multiple elitist genetic algorithm with the adaptive fuzzy fitness granulation (AFFG) is used to design the phononic crystals with large relative bandgap width (BGW) for combined out-of-plane and in-plane wave modes. Without assumption on the symmetry of the unit-cell, we obtain an asymmetrical phononic crystal with the relative BGW which is quite larger than that of the optimized symmetrical structure. With the help of AFFG, the number of the fitness function evaluations is reduced by over 50% and the procedure converges 5 times faster than the conventional evolutionary algorithm to reach the same final fitness values.
Far infrared absorption by acoustic phonons in titanium dioxide nanopowders
Murray, D B; Saviot, L; Pighini, C; Millot, N; Aymes, D; Liu, H L; Murray, Daniel B.; Netting, Caleb H.; Saviot, Lucien; Pighini, Catherine; Millot, Nadine; Aymes, Daniel; Liu, Hsiang-Lin
2006-01-01
We report spectral features of far infrared electromagnetic radiation absorption in anatase TiO2 nanopowders which we attribute to absorption by acoustic phonon modes of nanoparticles. The frequency of peak excess absorption above the background level corresponds to the predicted frequency of the dipolar acoustic phonon from continuum elastic theory. The intensity of the absorption cannot be accounted for in a continuum elastic dielectric description of the nanoparticle material. Quantum mechanical scale dependent effects must be considered. The absorption cross section is estimated from a simple mechanical phenomenological model. The results are in plausible agreement with the absorption being due to a sparse layer of charge on the nanoparticle surface.
Electron-phonon coupling in the rare-earth metals
Skriver, Hans Lomholt; Mertig, I.
2009-01-01
We have estimated the strength of the mass enhancement of the conduction electrons due to electron-phonon interaction in the rare metals Sc, Y, and La–Lu. The underlying self-consistent energy bands were obtained by means of the scalar relativistic linear-muffin-tin-orbital method, and the electron-phonon parameters were calculated within the Gaspari-Gyorffy formulation. For the heavier rare earths Gd–Tm spin polarization was included both in the band-structure calculations and in the treatme...
Topologically Protected Edge States in Gyroscopic Phononic Crystals
Wang, Pai; Bertodi, Katia
2015-03-01
We report some design considerations in realization and observation of topologically non-trivial phononic bandgaps in metamaterials. Symmetry breaking mechanisms can potentially lead to the phononic analogue of electronic quantum hall effect. The goal is to achieve topologically protected one-way propagation of surface elastic waves that are robust against back-scattering/localization. Both theoretical and practical challenges in creating elastic media with broken time-reversal symmetry will be discussed. The candidate design of gyroscopic lattices will be highlighted. The robustness of reflection-immune unidirectional elastic wave has promising applications in surface acoustic wave (SAW) devices that are widely used in modern technologies.
Two-Temperature Pair Potentials and Phonon Spectra for Simple Metals in the Warm Dense Matter Regime
Harbour, L.; Dharma-wardana, M. W. C.; Klug, D. D.; Lewis, L. J.
2015-02-01
We develop ion-ion pair potentials for Al, Na and K for densities and temperatures relevant to the warm-dense-matter (WDM) regime. Furthermore, we emphasize non-equilibrium states where the ion temperature $T_i$ differs from the electron temperature $T_e$. This work focuses mainly on ultra-fast laser-metal interactions where the energy of the laser is almost exclusively transferred to the electron sub-system over femtosecond time scales. This results in a two-temperature system with $T_e>T_i$ and with the ions still at the initial room temperature $T_i=T_r$. First-principles calculations, such as density functional theory (DFT) or quantum Monte Carlo, are as yet not fully feasible for WDM conditions due to lack of finite-$T$ features, e.g. pseudopotentials, and extensive CPU time requirements. Simpler methods are needed to study these highly complex systems. We propose to use two-temperature pair potentials $U_{ii}(r, T_i,T_e)$ constructed from linear-response theory using the non-linear electron density $n(\\mathbf{r})$ obtained from finite-$T$ DFT with a single ion immersed in the appropriate electron fluid. We compute equilibrium phonon spectra at $T_r$ which are found to be in very good agreement with experiments. This gives credibility to our non-equilibrium phonon dispersion relations which are important in determining thermophysical properties, stability, energy-relaxation mechanisms and transport coefficients.
Enforcement actions: Significant actions resolved
International Nuclear Information System (INIS)
This compilation summarizes significant enforcement actions that have been resolved during one quarterly period (October - December 1993) and includes copies of letters, Notices, and Orders sent by the Nuclear Regulatory Commission to licensees with respect to these enforcement actions. It is anticipated that the information in this publication will be widely disseminated to managers and employees engaged in activities licensed by the NRC, so that actions can be taken to improve safety by avoiding future violations similar to those described in this publication
Enforcement actions: Significant actions resolved
International Nuclear Information System (INIS)
This compilation summarizes significant enforcement actions that have been resolved during one quarterly period (July - September 1992) and includes copies of letters, Notices, and Orders sent by the Nuclear Regulatory Commission to licensees with respect to these enforcement actions. It is anticipated that the information in this publication will be widely disseminated to managers and employees engaged in activities licensed by the NRC, so that actions can be taken to improve safety by avoiding future violations similar to those described in this publication
Electronic origin of bond softening and hardening in femtosecond-laser-excited magnesium
International Nuclear Information System (INIS)
Many ultrafast structural phenomena in solids at high fluences are related to the hardening or softening of particular lattice vibrations at lower fluences. In this paper we relate femtosecond-laser-induced phonon frequency changes to changes in the electronic density of states, which need to be evaluated only in the electronic ground state, following phonon displacement patterns. We illustrate this relationship for a particular lattice vibration of magnesium, for which we—surprisingly—find that there is both softening and hardening as a function of the femtosecond-laser fluence. Using our theory, we explain these behaviours as arising from Van Hove singularities: We show that at low excitation densities Van Hove singularities near the Fermi level dominate the change of the phonon frequency while at higher excitations Van Hove singularities that are further away in energy also become important. We expect that our theory can as well shed light on the effects of laser excitation of other materials. (paper)
Jane Crumlish
2009-01-01
In this activity that can be used as a lab or demonstration, learners use Lactaid® and lactose to demonstrate the concept of enzyme action. Learners test a drop of milk and Lactaid® for the presence of glucose using glucose test paper. Learners also discover the color range of glucose test paper readings. In addition, learners construct paper models to help visualize enzyme action.
International Nuclear Information System (INIS)
We report on the femtosecond time-resolved detection of coherent phonons in single-crystal tellurium. For different crystallographic faces a detection scheme is employed which is sensitive to the anisotropic part of the Raman tensor. In this scheme we observe all three Raman allowed phonons, i.e. one of A1 and two of E symmetry. Furthermore, for both doubly degenerate E-symmetry modes obtained from different crystallographic faces, longitudinal optical-transverse optical splitting is observed. In addition, we show that even in the low fluence regime the frequency of the fully symmetric phonon in Te is chirped and that it demonstrates an anomalous dependence on the pump fluence
Enforcement actions: Significant actions resolved
International Nuclear Information System (INIS)
This compilation summarizes significant enforcement actions that have been resolved during one quarterly period (January--March 1990) and includes copies of letters, Notices, and Orders sent by the Nuclear Regulatory Commission to licensees with respect to these enforcement actions. Also included are a number of enforcement actions that had been previously resolved but not published in this NUREG. It is anticipated that the information in this publication will be widely disseminated to managers and employees engaged in activities licensed by the NRC, so that actions can be taken to improve safety by avoiding future violations similar to those described in this publication
Enforcement actions: Significant actions resolved
International Nuclear Information System (INIS)
This compilation summarizes significant enforcement actions that have been resolved during one quarterly period (January--March 1989) and includes copies of letters, Notices, and Orders sent by the Nuclear Regulatory Commission to licensees with respect to these enforcement actions. Also included are a number of enforcement actions that had been previously resolved but not published in this NUREG. It is anticipated that the information in this publication will be widely disseminated to managers and employees engaged in activities licensed by the NRC, so that actions can be taken to improve safety by avoiding future violations similar to those described in this publication
Energy Technology Data Exchange (ETDEWEB)
Laguna, M.
1995-11-01
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.
International Nuclear Information System (INIS)
We first propose fundamental solutions of wave propagation in dispersive chain subject to a localized initial perturbation in the displacement. Analytical solutions are obtained for both second order nonlinear dispersive chain and homogenous harmonic chain using stationary phase approximation. Solution is also compared with numerical results from molecular dynamics (MD) simulations. Locally dominant phonon modes (k-space) are introduced based on these solutions. These locally defined spatially and temporally varying phonon modes k(x, t) are critical to the concept of the local thermodynamic equilibrium (LTE). Wave propagation accompanying with the nonequilibrium dynamics leads to the excitation of these locally defined phonon modes. It is found that the system energy is gradually redistributed among these excited phonons modes (k-space). This redistribution process is only possible with nonlinear dispersion and requires a finite amount of time to achieve a steady state distribution. This time scale is dependent on the spatial distribution (or frequency content) of the initial perturbation and the dispersion relation. Sharper and more concentrated perturbation leads to a faster energy redistribution and dissipation. This energy redistribution generates localized phonons with various frequencies that can be important for phonon-phonon interaction and energy dissipation in nonlinear systems. Depending on the initial perturbation and temperature, the time scale associated with this energy distribution can be critical for energy dissipation compared to the Umklapp scattering process. Ballistic type of heat transport along the harmonic chain reveals that at any given position, the lowest mode (k = 0) is excited first and gradually expanding to the highest mode (kmax(x,t)), where kmax(x,t) can only asymptotically approach the maximum mode kB of the first Brillouin zone (kmax(x,t) ? kB). No energy distributed into modes with kmax(x,t) < k < kB demonstrates that the local thermodynamic equilibrium cannot be established in harmonic chain. Energy is shown to be uniformly distributed in all available phonon modes k ? kmax(x,t) at any position with heat transfer along the harmonic chain. The energy flux along the chain is shown to be a constant with time and proportional to the sound speed (ballistic transport). Comparison with the Fourier' law leads to a time-dependent thermal conductivity that diverges with time. (condensed matter: structural, mechanical, and thermal properties)
Phonon-mediated negative differential conductance in molecular quantum dots
Zazunov, Alex; Feinberg, Denis; Martin, Thierry
2006-03-01
Transport through a single-molecular conductor is considered, showing negative differential conductance behavior associated with phonon-mediated electron tunneling processes. This theoretical work is motivated by a recent experiment by Leroy using a carbon nanotube contacted by a scanning tunneling microscope tip [Nature 432, 371 (2004)], where negative differential conductance of the breathing-mode phonon side peaks could be observed. A peculiarity of this system is that the tunneling couplings which inject electrons and those which collect them on the substrate are highly asymmetrical. A quantum dot model is used, coupling a single electronic level to a local phonon, forming polaron levels. A “half-shuttle” mechanism is also introduced. A quantum kinetic formulation allows us to derive rate equations. Assuming asymmetric tunneling rates and in the absence of the half-shuttle coupling, negative differential conductance (NDC) is obtained for a wide range of parameters. A detailed explanation of this phenomenon is provided, showing that NDC is maximal for intermediate electron-phonon coupling. In addition, in the absence of a gate, the “floating” level results in two distinct lengths for the current plateaus, related to the capacitive couplings at the two junctions. It is shown that the half-shuttle mechanism tends to reinforce the negative differential regions, but it cannot trigger this behavior on its own.
Tuning the polarized quantum phonon transmission in graphene nanoribbons
Scuracchio, P.; Dobry, A.; Costamagna, S.; Peeters, F. M.
2015-07-01
We propose systems that allow a tuning of the phonon transmission function T(?) in graphene nanoribbons by using C13 isotope barriers, antidot structures, and distinct boundary conditions. Phonon modes are obtained by an interatomic fifth-nearest neighbor force-constant model (5NNFCM) and T(?) is calculated using the non-equilibrium Green’s function formalism. We show that by imposing partial fixed boundary conditions it is possible to restrict contributions of the in-plane phonon modes to T(?) at low energy. On the contrary, the transmission functions of out-of-plane phonon modes can be diminished by proper antidot or isotope arrangements. In particular, we show that a periodic array of them leads to sharp dips in the transmission function at certain frequencies {? }? which can be pre-defined as desired by controlling their relative distance and size. With this, we demonstrated that by adequate engineering it is possible to govern the magnitude of the ballistic transmission functions T(? ) in graphene nanoribbons. We discuss the implications of these results in the design of controlled thermal transport at the nanoscale as well as in the enhancement of thermo-electric features of graphene-based materials.
Phonon-enhanced crystal growth and lattice healing
Buonassisi, Anthony; Bertoni, Mariana; Newman, Bonna
2013-05-28
A system for modifying dislocation distributions in semiconductor materials is provided. The system includes one or more vibrational sources for producing at least one excitation of vibrational mode having phonon frequencies so as to enhance dislocation motion through a crystal lattice.
Enhanced Electron-Phonon Coupling at Metal Surfaces
Energy Technology Data Exchange (ETDEWEB)
Plummer, Ward E.
2010-08-04
The Born-Oppenheimer approximation (BOA) decouples electronic from nuclear motion, providing a focal point for most quantum mechanics textbooks. However, a multitude of important chemical, physical and biological phenomena are driven by violations of this approximation. Vibronic interactions are a necessary ingredient in any process that makes or breaks a covalent bond, for example, conventional catalysis or enzymatically delivered biological reactions. Metastable phenomena associated with defects and dopants in semiconductors, oxides, and glasses entail violation of the BOA. Charge exchange in inorganic polymers, organic slats and biological systems involves charge- induced distortions of the local structure. A classic example is conventional superconductivity, which is driven by the electron-lattice interaction. High-resolution angle-resolved photoemission experiments are yielding new insight into the microscopic origin of electron-phonon coupling (EPC) in anisotropic two-dimensional systems. Our recent surface phonon measurement on the surface of a high-Tc material clearly indicates an important momentum dependent EPC in these materials. In the last few years we have shifted our research focus from solely looking at electron phonon coupling to examining the structure/functionality relationship at the surface of complex transition metal compounds. The investigation on electron phonon coupling has allowed us to move to systems where there is coupling between the lattice, the electrons and the spin.
Quantum dot nanodevice with electron-phonon interaction.
Czech Academy of Sciences Publication Activity Database
Král, Karel
Vladivostok : Ioffe Physico-Technical Institute, 2008, s. 128-128. ISBN N. [Nanostructures: Physics and Technology, International Symposium /16./. Vladivostok (RU), 14.07.2008-19.07.2008] R&D Projects: GA MŠk ME 866 Institutional research plan: CEZ:AV0Z10100520 Keywords : nanodevice * electron-phonon interaction Subject RIV: BE - Theoretical Physics
Neutron scattering study of phonon dynamics on cage compounds
Lee, C. H.; Yoshizawa, H.; Hase, I.; Sugawara, H.; Avila, M. A.; Takabatake, T.; Sato, H.
2007-03-01
Filled skutterudite compounds have attracted great attention due to their potential as thermoelectric devices. In particular, their low lattice thermal conductivity is advantageous to achieve high thermoelectric performance. To improve the performance further, it is important to clarify the origin of their low lattice thermal conductivity. Previous studies suggest that the low thermal conductivity is a consequence of free vibration of rare-earth atoms in large lattice cages, which is so called rattling effect. To confirm the hypothesis, we have studied phonon dynamics of CeRu4Sb12 by neutron scattering using single crystal samples at JRR-3M reactor of JAERI in Tokai. As results, we have found optical phonons associated with large vibration of Ce atoms at relatively low energy of E=6meV, which show an anticrossing with acoustic phonons. According to the analysis based on a Born-von K'arm'an force model, the longitudinal force constants of the nearest Ce-Sb and Ce-Ru are both estimated to be 0.025 mdyn/A, while that of the nearest Ru-Sb shows a large value of 1.4 mdyn/A, indicating that the Ce atoms are bound very weakly with surrounding rigid RuSb6-octahedron cages. We will discuss that the origin of the low lattice thermal conductivity can be intensive Umklapp scattering originating from low-lying optical phonons.
Ab initio study of electron-phonon interaction in phosphorene
Liao, Bolin; Zhou, Jiawei; Qiu, Bo; Dresselhaus, Mildred S.; Chen, Gang
2015-06-01
The monolayer of black phosphorus, or "phosphorene," has recently emerged as a two-dimensional semiconductor with intriguing highly anisotropic transport properties. Existing calculations of its intrinsic phonon-limited electronic transport properties so far rely on the deformation potential approximation, which is in general not directly applicable to anisotropic materials since the deformation along one specific direction can scatter electrons traveling in all directions. We perform a first-principles calculation of the electron-phonon interaction in phosphorene based on density functional perturbation theory and Wannier interpolation. Our calculation reveals that (1) the high anisotropy provides extra phase space for electron-phonon scattering, and (2) optical phonons have appreciable contributions. Both effects cannot be captured by the deformation potential calculations. Our simulation predicts carrier mobilities ˜170 c m2/V s for both electrons and holes at 300 K , and a thermoelectric figure of merit z T of up to 0.14 in p -type impurity-free phosphorene at 500 K .
Electron-phonon coupling of the actinide metals
DEFF Research Database (Denmark)
Skriver, H. L.; Mertig, I.
1985-01-01
The authors have estimated the strength of the electron-phonon coupling in Fr and Ra plus the light actinides Ac through Pu. The underlying self-consistent band-structure calculations were performed by the scalar relativistic linear-muffin-tin-orbital method including l quantum numbers s through g, and the electron-phonon parameters were obtained within the rigid-atomic-sphere approximation. The electron-phonon coupling in Fr through Th is found to be dominated by pd and df scattering and in Pa through Pu by pd and fg scattering. At the equilibrium volumes and as a function of atomic number, the electron-phonon parameter ? is found to attain its maximum value in Ac, and they predict a transition temperature of 9K for this metal. In the light actinides Th through Pu, ? is found to be of order 0.4 and within a factor of 2 of experiments which is also the accuracy found in studies of the transition metals. The Hopfield parameter ? is found to increase under compression in Th and U, as are the individual l,l+1 contributions to ?, except the df contribution which is approximately pressure independent in Th and negligible in U. The calculations suggest that the unusual pressure dependence of T c in Th may be related to the changeover from an s-to- d to an s-to-f electronic transition and a related change in the topology of the Fermi surface
Phonon number quantum jumps in an optomechanical system
Gangat, A A; Milburn, G J
2011-01-01
We describe an optomechanical system in which the mean phonon number of a single mechanical mode conditionally displaces the amplitude of the optical field. On average the displacement is given by $\\chi\\bar{n}_b/\\kappa$, where $\\bar{n}_b$ is the mean phonon number operator for the mechanical oscillator, $\\kappa$ is the cavity linewidth and $\\chi$ characterises the strength of the interaction. Using homodyne detection of the output field we establish the conditions under which phonon number quantum jumps near the mechanical ground state can be inferred from the measurement record as $\\kappa\\gg\\gamma\\bar{N}$ and $\\frac{\\chi^2}{\\kappa}\\gg\\gamma\\bar{N}$, where $\\gamma$ is the linewidth of the mechanical resonator and $\\bar{N}$ characterises the mean thermal phonon number in the mechanical resonator bath at its resonant frequency. We present simulations of the conditional dynamics of the measured system using the stochastic master equation. In the good-measurement limit, the conditional evolution of the mean phono...
THE PHONON SPECTRUM EMITTED BY SUPERCONDUCTING Sn TUNNEL JUNCTIONS
Berberich, P.; Kinder, H.
1981-01-01
The phonon spectra emitted by superconducting tunnel junctions were directly analyzed with high resolution using tunable acceptor states of B in Si as a spectrometer. A consistent and detailed experimental picture of the different parts of the spectra under various injection conditions was obtained for the first time.
Tuning the polarized quantum phonon transmission in graphene nanoribbons.
Scuracchio, P; Dobry, A; Costamagna, S; Peeters, F M
2015-07-31
We propose systems that allow a tuning of the phonon transmission function T(?) in graphene nanoribbons by using C(13) isotope barriers, antidot structures, and distinct boundary conditions. Phonon modes are obtained by an interatomic fifth-nearest neighbor force-constant model (5NNFCM) and T(?) is calculated using the non-equilibrium Green's function formalism. We show that by imposing partial fixed boundary conditions it is possible to restrict contributions of the in-plane phonon modes to T(?) at low energy. On the contrary, the transmission functions of out-of-plane phonon modes can be diminished by proper antidot or isotope arrangements. In particular, we show that a periodic array of them leads to sharp dips in the transmission function at certain frequencies [Formula: see text] which can be pre-defined as desired by controlling their relative distance and size. With this, we demonstrated that by adequate engineering it is possible to govern the magnitude of the ballistic transmission functions [Formula: see text] in graphene nanoribbons. We discuss the implications of these results in the design of controlled thermal transport at the nanoscale as well as in the enhancement of thermo-electric features of graphene-based materials. PMID:26150409
Neutron scattering studies of electron--phonon interactions
International Nuclear Information System (INIS)
This review is an attempt to summarize the areas in which neutron scattering has been used in studying electron-phonon interactions, and to display some of the key results. The examples chosen reflect the interests of the author and represent in no way a complete survey of the subject. 48 references
Phonon Diodes and Transistors from Magneto-acoustics
Sklan, Sophia R.; Jeffrey C. Grossman
2014-01-01
By sculpting the magnetic field applied to magneto-acoustic materials, phonons can be used for information processing. Using a combination of analytic and numerical techniques, we demonstrate designs for diodes (isolators) and transistors that are independent of their conventional, electronic formulation. We analyze the experimental feasibility of these systems, including the sensitivity of the circuits to likely systematic and random errors.
(Sd)-f hybridization in the phonon spectrum of thorium
International Nuclear Information System (INIS)
It is observed that contribution from (Sd)-f hybridization associated with the local field correction can be approximated by a short-range (Born-Mayer) potential in the phonon spectrum of thorium in the framework of a rare-earth metal model potential (REMMP) method. Calculated results agree reasonably well with experiment. (author)
Polar phonon mixing in magnetoelectric EuTiO3.
Czech Academy of Sciences Publication Activity Database
Goian, Veronica; Kamba, Stanislav; Hlinka, Ji?í; Van?k, P?emysl; Belik, A.A.; Kolodiazhnyi, T.; Petzelt, Jan
2009-01-01
Ro?. 71, ?. 3 (2009), 429-433. ISSN 1434-6028 R&D Projects: GA ?R(CZ) GA202/09/0682 Institutional research plan: CEZ:AV0Z10100520 Keywords : multiferroics * infrared spectroscopy * phonons Subject RIV: BM - Solid Matter Phys ics ; Magnetism Impact factor: 1.466, year: 2009