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
A phonon laser in ultra-cold matter
J. T MENDONÇA; Brodin, G.; M.Marklund; Terças, H
2009-01-01
We show the possible excitation of a phonon laser instability in an ultra-cold atomic gas confined in a magneto-optical trap. Such an effect results from a negative Landau damping of the collective density perturbations in the gas, leading to the coherent emission of phonons. This laser instability can be driven by a blue-detuned laser superimposed to the usual red-detuning laser beams which usually provide the cooling mechanism. Threshold conditions, instability growth rate...
Laser demonstrations of rare-earth ions in low-phonon chloride and sulfide crystals
Energy Technology Data Exchange (ETDEWEB)
Nostrand, M; Page, R; Payne, S; Schunemann, P; Isaenko, L
2000-04-01
Laser results are summarized for the low-phonon hosts KPb{sub 2}Cl{sub 5} and CaGa{sub 2}S{sub 4}. Radiative quantum efficiencies were determined in KPb{sub 2}Cl{sub 5}:Dy{sup 3+} directly from emission spectra in order to accurately determine its long-wavelength potential. The results indicate that room-temperature laser action should be possible to near 9 {micro}m in this host.
Benjamin, Seldon David
Unique lasing processes in III-V semiconductor lasers are examined. The dynamics of stimulated photon emission in thin AlGaAs/GaAs single quantum well lasers are observed experimentally and modeled by rate equations describing the electron and photon densities. Agreement between experiment and theory are achieved when the transition probability matrix, calculated with the spreading out of electron and hole wave functions taken into account, is used. The phonon assisted stimulated photon emission observed in this work is delayed with respect to the unassisted emission. This observation is modeled by using a weaker matrix element for the unassisted process which is expected from theory and thus supports our claim that this emission is phonon assisted. Rate equations developed to simulate doubly stimulated emission of photons and phonons do not describe the experimental data so the possibility of stimulated phonon emission is ruled out for the samples studied in this work. Vertical Cavity Surface Emitting Lasers are also studied since they can be designed to support unique lasing processes. The design and growth of vertical cavity surface emitting lasers are discussed and these concepts are applied to the realization of a vertical cavity surface emitting laser with the thinnest active layer of any laser yet reported. Stimulated emission supported across the sub-monolayer thick InAs single quantum well active region can be understood by considering the spreading of the electron and hole wavefunctions beyond the confines of the quantum well to increase the length of the effective gain region. The dynamics of laser action in vertical cavity surface emitting lasers are also studied and reveal that low threshold lasers may not be suitable for high speed operation due to their relatively long photon lifetimes. Finally a structure is proposed to implement a multi-wavelength vertical cavity surface emitting laser using an active region that encourages phonon assisted stimulated emission.
Coherent control of LO-phonon dynamics in opaque semiconductors by femtosecond laser pulses
Dekorsy, Thomas; Kütt, Waldemar; Pfeifer, Torsten; Kurz, Heinrich
1993-01-01
Coherent longitudinal optical phonons are generated via ultrafast screening of GaAs surface-space-charge fields by free carriers excited with femtosecond laser pulses. The coherent phonons are observed in a pump probe experiment through anisotropic changes in the refractive index. Since the electro-optic observation of phonons in the time domain allows the determination of both the amplitude and the phase of coherent lattice vibrations, we are able to superpose two coherently excited phonon m...
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.
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.
Bruchhausen, Axel; Lloyd-Hughes, James; Fischer, Milan; Beck, Mattias; Scalari, Giacomo; Faist, Jérôme; Dekorsy, Thomas
2010-01-01
We have investigated the time-resolved vibrational properties of terahertz quantum cascade lasers by means of ultra-fast laser spectroscopy. By the observation of the acoustic folded branches, and by analyzing the involved phonon modes it is possible to extract accurate structural information of these devices, which are essential for their design and performance.
Phonon generation in condensed ?He by laser-excited atomic bubbles
Moroshkin, Peter; Lebedev, Victor; Weis, Antoine
2012-01-01
We discuss the interaction between nanometer-sized defects (atomic bubbles) and elementary excitations (phonons) in quantum fluids and solids. We observe that optical excitations in embedded metal atoms induce bubble expansions/contractions that create strongly localized phonon wave packets in the quantum matrix. We derive the structure and dynamics of these vibronic excitations from the experimental laser-induced fluorescence spectra of Au and Cu atoms in liquid and solid He. The atomic vibr...
Hung, Nguyen Quoc; Nhan, Nguyen Vu; Bau, Nguyen Quang
2002-01-01
Based on the quantum transport equation for the electron-phonon system, the absorption coefficient of sound (acoustic phonons) by absorption of laser radiation in cylindrical quantum wires is calculated for the case of monophoton absorption process and the case of multiphoton absorption process. Analytical expressions and conditions for the absorption of sound are obtained. Differences between the two cases of monophoton absorption and of multiphoton absorption are discussed...
Dynamics of phonon mode in superradiance regime of laser cooling of crystals
International Nuclear Information System (INIS)
The kinetics of the impurity crystal in regime of anti-Stokes laser cooling has been considered taking into account the collective radiation effects. The system of master equations for impurities and pseudo-local phonons has been obtained. As would be expected, the collective radiation effects causes an acceleration in relaxation depletion of the phonon mode and therefore an increase of crystal cooling efficiency
Coherent optical phonons in different phases of Ge2 Sb 2 Te5 upon strong laser excitation
Hernández Rueda, Javier; Savoia, A; Gawelda, W.; Solís Céspedes, Javier; Mansart, B.; Boschetto, D.; Siegel, Jan
2011-01-01
The transient reflectivity response of phase-change Ge2 Sb 2 Te5 films to intense femtosecond laser pulses is studied by ultrafast coherent phonon spectroscopy. The three different phases (amorphous, fcc-, and hcp-crystalline), as well as laser-crystallized films, are investigated, featuring different photoexcited carrier and coherent optical phonon dynamics. At least two main phonon frequencies are identified for each phase/material and their evolution for increasing pump fluences is investi...
Laser heating versus phonon confinement effect in the Raman spectra of diamond nanoparticles
International Nuclear Information System (INIS)
Nanodiamond particles with typical diameters of 20 and 6 nm produced by high pressure high temperature or detonation processes have been studied by micro-Raman spectroscopy. We show that the frequency downshift and broadening of the first-order diamond phonon band is not uniquely related to phonon confinement, as commonly assumed. Local heating caused by the focused laser light must be also taken in account, since it may affect the Raman spectrum in a similar fashion, even at relatively low laser power levels. A combined theoretical model considering both effects (quantum confinement and local heating) on the excited phonon modes is presented and adopted for the simulation of the experimental data. We observe different heating behaviours upon laser illumination depending on the particles origin, thus underscoring the importance to compensate for this effect before retrieving structural parameters.
International Nuclear Information System (INIS)
The dynamics of coherent phonons in fluorine-containing crystals was investigated by pump-probe technique in the plasma production regime. Several phonon modes, whose frequencies are overtones of the 0.38-THz fundamental frequency, were simultaneously observed in a lithium fluoride crystal. Phonons with frequencies of 1 and 0.1 THz were discovered in a calcium fluoride crystal and coherent phonons with frequencies of 1 THz and 67 GHz were observed in a barium fluoride crystal. Furthermore, in the latter case the amplitudes of phonon mode oscillations were found to significantly increase 15 ps after laser irradiation. (interaction of laser radiation with matter)
Energy Technology Data Exchange (ETDEWEB)
Potemkin, F V; Mareev, E I [International Laser Center, M. V. Lomonosov Moscow State University, Moscow (Russian Federation); Khodakovskii, N G [A M Prokhorov General Physics Institute, Russian Academy of Sciences, Moscow (Russian Federation); Mikheev, P M
2013-08-31
The dynamics of coherent phonons in fluorine-containing crystals was investigated by pump-probe technique in the plasma production regime. Several phonon modes, whose frequencies are overtones of the 0.38-THz fundamental frequency, were simultaneously observed in a lithium fluoride crystal. Phonons with frequencies of 1 and 0.1 THz were discovered in a calcium fluoride crystal and coherent phonons with frequencies of 1 THz and 67 GHz were observed in a barium fluoride crystal. Furthermore, in the latter case the amplitudes of phonon mode oscillations were found to significantly increase 15 ps after laser irradiation. (interaction of laser radiation with matter)
Fourier transform inelastic x-ray scattering from phonons using Free Electron Laser pulses
Trigo, Mariano; Henighan, Thomas; Reis, David
2015-03-01
We demonstrate that ultrafast x-ray scattering at Free Electron Lasers (FELs) provides a new approach for measuring phonon dispersion relations spanning the entire Brillouin zone, without the need for complex monochromators and spectrometers. Our method uses an ultrafast optical laser as pump and the dynamics are probed using femtosecond x-ray pulses from an FEL. We obtain the entire transverse acoustic phonon dispersion in germanium with ~ 0.5 meV energy resolution by a simple Fourier transform of the oscillatory dynamics of the scattered x-ray intensity. Using coherent control with a pair of pump pulses, we show that the femtosecond laser couples to pairs of phonons, analogous to a second order Raman scattering mechanism, which also explains the excitation of large-wavevector phonons by the long wavelength (optical) pump pulse. This shows that the generation mechanism is quite general and thus this ultrafast approach could be applicable as a general spectroscopic tool of phonons near to and far from equilibrium.
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.
Manipulation of Squeezed Two-Phonon Bound States using Femtosecond Laser Pulses
Directory of Open Access Journals (Sweden)
Nakamura Kazutaka G.
2013-03-01
Full Text Available Two-phonon bound states have been excited exclusively in ZnTe(110 via impulsive stimulated second-order Raman scattering, essentially being squeezed states due to phase coherent excitation of two identical components anticorrelated in the wave vector. By using coherent control technique with a pair of femtosecond laser pulses, the manipulation of squeezed states has been demonstrated in which both the amplitude and lifetime of coherent oscillations of squeezed states are modulated, indicating the feasibility to control the quantum noise and the quantum nature of phonon squeezed states, respectively.
Experimental Study of Photon-Phonon Interactions in an Explosive by Laser Probe Mass Spectrography
Eloy, J.; Delpuech, A.
1995-01-01
We have shown in a series of previous papers the part of the molecular electronic structure played in the decomposition process of an explosive submitted to a shock wave. This part is important especially as regards energy transfer properties. This work is intented to investigate the process of these transfers by the study of photon-phonon interactions in this type of material. The experimental technique used for this purpose is laser probe mass spectrography. The first tested explosives are ...
International Nuclear Information System (INIS)
We study the scattering mechanisms driving electron-phonon relaxation in thin gold films via pump-probe time-domain thermoreflectance. Electron-electron scattering can enhance the effective rate of electron-phonon relaxation when the electrons are out of equilibrium with the phonons. In order to correctly and consistently infer electron-phonon coupling factors in films on different substrates, we must account for the increase in steady-state lattice temperature due to laser heating. Our data provide evidence that a thermalized electron population will not directly exchange energy with the substrate during electron-phonon relaxation, whereas this pathway can exist between a non-equilibrium distribution of electrons and a non-metallic substrate
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.
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...
Hung, Nguyen Quoc; Vuong, Dinh Quoc; Bau, Nguyen Quang
2002-01-01
Based on the quantum transport equation for the electron-phonon system, the absorption coefficient of sound (acoustic phonons) by absorption of a laser radiation in quantum wires with parabolic potential is calculated for the case of monophoton absorption and the case of multiphoton absorption. Analytical expressions and conditions for the absorption coefficient of sound are obtained. Differences between the two cases of monophoton absorption and of multiphoton absorption ar...
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 r...
Breaking the low phonon energy barrier for laser cooling in rare-earth doped hosts
Nemova, Galina; Kashyap, Raman
2011-03-01
A new approach to cool rare earth doped solids with optical super-radiance (SR) is presented. SR is the coherent, sharply directed spontaneous emission of photons by a system excited with a pulsed laser. We consider an Yb3+ doped ZBLAN sample pumped at the wavelength 1015nm with a rectangular pulsed source with a power of ~700W and duration of 20ns. The intensity of the SR is proportional to the square of the number of excited ions. This unique feature of SR permits an increase in the rate of the cooling process in comparison with the traditional laser cooling of the rare earth doped solids with anti-Stokes spontaneous incoherent radiation (fluorescence). This scheme overcomes the limitation of using only low phonon energy glasses for laser cooling.
Phonon-mediated off-resonant coupling effects in semiconductor quantum-dot lasers
International Nuclear Information System (INIS)
The impact of non-resonant background emitters in semiconductor quantum-dot microcavity lasers is addressed within theoretical investigations based on the solution of the von Neumann equation. Off-resonant coupling between emitter resonances and the cavity mode is enabled via phonons, which are included in the von Neumann dynamics by an effective Lindblad contribution. The results show enhanced coherent emission from non-resonantly coupled quantum dots, while the frequently used phenomenological cavity feeding mechanism only enhances the thermal component of the emission. (paper)
Adu, K. W.; Gutiérrez, H. R.; Kim, U. J.; Eklund, P. C.
2006-04-01
Results of a systematic set of micro-Raman experiments on the changes in the line shape of the ˜520cm-1 one-phonon band in Si nanowires with laser flux ? are presented. A complicated dependence of the 520cm-1 Raman band asymmetry (A) with ? is observed that depends both on the nanowire diameter and on the thermal anchoring of the wires to an indium foil substrate. With increasing power density in a ˜1? focal spot common to micro-Raman spectroscopy, we see a clear growth in A that has nothing to do with phonon confinement. In fact, we can explain the complex changes in A(?) by extending the model [H. Richter, Z. P. Wang, and Y. Ley, Solid State Commun. 39, 625 (1981)] to include an inhomogeneous heating in the Raman volume. The effects we observe in Si nanowires should be common to all semiconducting nanostructures and underscores the importance of demonstrating a flux-independent line shape when studying pure phonon confinement effects by Raman scattering.
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)
Li, Simian; Huang, Huan; Zhu, Weiling; Wang, Wenfang; Chen, Ke; Yao, Dao-Xin; Wang, Yang; Lai, Tianshu; Wu, Yiqun; Gan, Fuxi
2011-01-01
A femtosecond laser-irradiated crystallizing technique is tried to convert amorphous Sb2Te3 film into crystalline film. Sensitive coherent phonon spectroscopy (CPS) is used to monitor the crystallization of amorphous Sb2Te3 film at the original irradiation site. The CPS reveals that the vibration strength of two phonon modes that correspond to the characteristic phonon modes of crystalline Sb2Te3, enhances with increasing laser irradiation fluence (LIF), showing the rise of ...
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.
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.
International Nuclear Information System (INIS)
The terahertz (THz) frequency quantum cascade laser (QCL) is a semiconductor heterostructure laser that has attracted much research interest over the past decade. We report on the high performance of THz QCLs based on a three-well resonant-phonon (RP) depopulation active region (AR) and operating in the frequency range 2.7 THz to 4.0 THz. Devices, processed into surface-plasmon waveguides, lased up to 116 K in pulsed mode with threshold current densities as low as 840 Acm?2. The effects of the design frequency and laser cavity length on performance are discussed. We also report on the operation of QCLs with reduced AR thicknesses, and show, for the first time, that the AR thickness of RP QCLs processed in a surface plasmon waveguide can be reduced to as little as 5 µm. Finally, we demonstrate the use of an electrically tuneable THz QCL, based on a heterogeneous AR, for spectroscopic imaging of the high-explosive pentaerythritol tetranitrate. (paper)
Bruchhausen, Axel; Lloyd-Hughes, James; Hettich, Mike; Gebs, Raphael; Grossmann, Martin; Ristow, Oliver; Bartels, Albrecht; Fischer, Milan; Beck, Mattias; Scalari, Giacomo; Faist, Jérôme; Rudra, Alok; Gallo, Pascal; Kapon, Eli; Dekorsy, Thomas
2012-08-01
The dynamics of acoustic vibrations in terahertz quantum cascade laser structures (THz-QCLs) is studied by means of femtosecond pump-probe spectroscopy. The phonon modes are characterized by the folding of the acoustic dispersion into an effective reduced Brillouin zone. An accurate identification of this dispersion allows the sample structure and periodicity to be determined with high precision on the order of 0.1%. By temperature tuning the energy of the electronic levels of the system and performing wavelength dependent measurements, we are able to study the impulsive resonant generation and detection of coherent acoustic phonon modes. These results are supported by simulations of the electronic system that well explain the experimental observations. The effects of interface (IF) roughness on coherent acoustic phonon spectra are clearly observed for equal nominal THz-QCL structures but with different interface qualities.
Room-temperature laser action at 4.3--4.4 {micro}m in CaGa{sub 2}S{sub 4}:Dy{sup 3+}
Energy Technology Data Exchange (ETDEWEB)
Nostrand, M; Page, R H; Payne, S A; Krupke, W F; Schunemann
1999-04-22
The authors report room-temperature mid-IR laser operation in a new low-phonon-frequency, non-hygroscopic host crystal CaGa{sub 2}S{sub 4} (calcium thiogallate). Laser action at 4.31 {micro}m on the {sup 6}H{sub 11/2} {r_arrow}{sup 6}H{sub 13/2} transition of trivalent dysprosium was achieved with a slope efficiency of 1.6%.
Zhu, Weiling; Wang, Changzhou; Sun, Mingcheng; Li, Simian; Zhai, Jiwei; Lai, Tianshu
2012-01-01
The periodic number dependence of the femtosecond laser-induced crystallization threshold of [Si(5nm)/Sb80Te20(5nm)]x nanocomposite multilayer films has been investigated by coherent phonon spectroscopy. Coherent optical phonon spectra show that femtosecond laser-irradiated crystallization threshold of the multilayer films relies obviously on the periodic number of the multilayer films and decreases with the increasing periodic number. The mechanism of the periodic number dependence is also s...
Bruchhausen, A.; Lloyd-Hughes, J; Hettich, M.; Gebs, R; Grossmann, M; Ristow, O; Bartels, A.; Fischer, M.; Beck, M.; Scalari, G.; Faist, J.; Rudra, A.; Gallo, P; Kapon, E.; Dekorsy, T
2012-01-01
The dynamics of acoustic vibrations in terahertz quantum cascade laser structures (THz-QCLs) is studied by means of femtosecond pump-probe spectroscopy. The phonon modes are characterized by the folding of the acoustic dispersion into an effective reduced Brillouin zone. An accurate identification of this dispersion allows the sample structure and periodicity to be determined with high precision on the order of 0.1%. By temperature tuning the energy of the electronic levels of the system and ...
An excimer laser radiation action on DNA and chromatin
International Nuclear Information System (INIS)
The fluorimetric method for DNA strand breaks determination, the establishment of the lifetimes of the complexes ligand-DNA and ligand-chromatin and the Turbo Pascal program for the calculation of the number of molecules of the reaction product formed during a pulse are useful tools in the study of the laser radiation action on DNA and chromatin. DNA is protected by bound proteins against laser action. (authors)
Energy Technology Data Exchange (ETDEWEB)
Kobayashi, Takayoshi, E-mail: kobayashi@ils.uec.ac.jp [Advanced Ultrafast Laser Research Center, University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585 (Japan); JST, CREST, K' s Gobancho, 7, Gobancho, Chiyoda-ku, Tokyo, 102-0076 (Japan); Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (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 [Advanced Ultrafast Laser Research Center, University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585 (Japan); JST, CREST, K' s Gobancho, 7, Gobancho, Chiyoda-ku, Tokyo, 102-0076 (Japan); Du, Juan [Advanced Ultrafast Laser Research Center, University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585 (Japan); JST, CREST, K' s Gobancho, 7, Gobancho, Chiyoda-ku, Tokyo, 102-0076 (Japan); Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan); Kataura, Hiromichi [Nanosystem Research Institute, AIST, Higashi 1-1-1, Tsukuba, Ibaraki 305-8562 (Japan); Sakakibara, Youichi [Photonics Research Institute, AIST, Higashi 1-1-1, Tsukuba, Ibaraki 305-8562 (Japan); Miyata, Yasumitsu [Department of Chemistry, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8601 (Japan)
2013-01-15
Coherent phonon dynamics in single-walled carbon nanotubes with several chiralities is investigated by 7.1-fs pump-probe experiments. Vibrational wave-packets corresponding to the radial breathing mode (RBM) and G mode can be detected for four chiral systems, (6,4), (6,5), (7,5) and (8,3). Coherent phonon generation of RBMs is in-depth studied by analyzing the probe photon energy dependent amplitude profiles, which indicates that the real and imaginary parts of the third-order susceptibility can both contribute to the modulation of the probed difference absorbance. - Highlights: Black-Right-Pointing-Pointer We investigated coherent phonon dynamics in single-walled carbon nanotubes by 7.1-fs laser. Black-Right-Pointing-Pointer Vibrational wave-packets corresponding to the RBM and G mode can be detected. Black-Right-Pointing-Pointer Resonance conditions and mode frequencies lead to exact chirality assignments. Black-Right-Pointing-Pointer Both real and imaginary parts of the third order susceptibility contribute to the result.
Phoenix's Laser Beam in Action on Mars
2008-01-01
[figure removed for brevity, see original site] Click on image to view the animation The Surface Stereo Imager camera aboard NASA's Phoenix Mars Lander acquired a series of images of the laser beam in the Martian night sky. Bright spots in the beam are reflections from ice crystals in the low level ice-fog. The brighter area at the top of the beam is due to enhanced scattering of the laser light in a cloud. The Canadian-built lidar instrument emits pulses of laser light and records what is scattered back. The Phoenix Mission is led by the University of Arizona, Tucson, on behalf of NASA. Project management of the mission is by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Spacecraft development is by Lockheed Martin Space Systems, Denver.
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...
Energy Technology Data Exchange (ETDEWEB)
Li, Zhongyu; Wen, Ting; Lai, Tianshu, E-mail: stslts@mail.sysu.edu.cn, E-mail: jwzhai@tongji.edu.cn [State-Key Laboratory of Optoelectronic Materials and Technology, School of Physics and Engineering, Sun Yat-Sen University, Guangzhou 510275 (China); Hu, Yifeng; Zhai, Jiwei, E-mail: stslts@mail.sysu.edu.cn, E-mail: jwzhai@tongji.edu.cn [Functional Materials Research Laboratory, Tongji University, Shanghai 200092 (China)
2015-04-07
Femtosecond laser-irradiation-induced phase change of amorphous N-doped Ge{sub 8}Sb{sub 92} films is in situ studied by coherent phonon spectroscopy. We have observed that a new coherent optical phonon (COP) mode occurs as laser irradiation fluence reaches certain thresholds, indicating laser-induced phase changes. Additionally, this new phonon mode has also been verified in heat-annealing-crystallized N-doped Ge{sub 8}Sb{sub 92} films, confirming the emergence of laser-irradiation-induced crystallization. By measuring the pump fluence dependence of COP dynamics in laser-crystallized N-doped Ge{sub 8}Sb{sub 92} films, we found that the frequency and lifetime of COP decrease with the increasing of pump fluence, which suggests good crystallinity in laser-crystallized N-doped Ge{sub 8}Sb{sub 92} films. It has also been observed that the crystallization temperature of amorphous N-doped Ge{sub 8}Sb{sub 92} films increases with N-doping content. Our results indicate promising applications of N-doped Ge{sub 8}Sb{sub 92} films in optical phase-change memory devices.
Krupke, William F. (Pleasanton, CA); Payne, Stephen A. (Castro Valley, CA); Marshall, Christopher D. (Livermore, CA)
2001-01-01
The invention provides an efficient, compact means of generating blue laser light at a wavelength near .about.493+/-3 nm, based on the use of a laser diode-pumped Yb-doped laser crystal emitting on its zero phonon line (ZPL) resonance transition at a wavelength near .about.986+/-6 nm, whose fundamental infrared output radiation is harmonically doubled into the blue spectral region. The invention is applied to the excitation of biofluorescent dyes (in the .about.490-496 nm spectral region) utilized in flow cytometry, immunoassay, DNA sequencing, and other biofluorescence instruments. The preferred host crystals have strong ZPL fluorecence (laser) transitions lying in the spectral range from .about.980 to .about.992 nm (so that when frequency-doubled, they produce output radiation in the spectral range from 490 to 496 nm). Alternate preferred Yb doped tungstate crystals, such as Yb:KY(WO.sub.4).sub.2, may be configured to lase on the resonant ZPL transition near 981 nm (in lieu of the normal 1025 nm transition). The laser light is then doubled in the blue at 490.5 nm.
Hudert, Florian; Bruchhausen, Axel; Issenmann, Daniel; Schecker, Olivier; Waitz, Reimar; Erbe, Artur; Scheer, Elke; Dekorsy, Thomas; Mlayah, Adnen; Huntzinger, Jean-Roch
2009-05-01
In this Rapid Communication we report the first time-resolved measurements of confined acoustic phonon modes in free-standing Si membranes excited by fs laser pulses. Pump-probe experiments using asynchronous optical sampling reveal the impulsive excitation of discrete acoustic modes up to the 19th harmonic order for membranes of two different thicknesses. The modulation of the membrane thickness is measured with fm resolution. The experimental results are compared with a theoretical model including the electronic deformation potential and thermal stress for the generation mechanism. The detection is modeled by the photoelastic effect and the thickness modulation of the membrane, which is shown to dominate the detection process. The lifetime of the acoustic modes is found to be at least a factor of 4 larger than that expected for bulk Si.
Eisenmenger, Wolfgang
1980-01-01
Nonequilibrium phonon experiments with superconducting film tunneling junctions have demonstrated that phonon spectra produced by nonequilibrium quasiparticle distributions are well in accord with the predictions of theory. This is also demonstrated by the successful application of superconducting tunneling junctions for phonon absorption spectroscopy and recently also for phonon emission spectroscopy.
Enhanced laser action of Perylene-Red doped polymeric materials
Garcia-Moreno, I.; Costela, A.; Pintado-Sierra, Mercedes; Martin, Virginia; Sastre, Roberto
2009-01-01
The laser action of Perylene-Red doped in linear, crosslinked, fluorinated and sililated polymeric materials is reported. The purity of dye was found to be a key factor to enhance its solid-state laser behaviour. The samples were transversely pumped at 532 nm, with 5.5 mJ/pulse and 10 Hz repetition rate. Perylene-Red doped copolymers of methyl methacrylate with a 10 vol% proportion of 2,2,2-trifluoroethyl-methacrylate exhibited a lasing efficiency of 26% with a high photosta...
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.
International Nuclear Information System (INIS)
A femtosecond laser-irradiated crystallizing technique is tried to convert amorphous Sb2Te3 film into crystalline film. Sensitive coherent phonon spectroscopy (CPS) is used to monitor the crystallization of amorphous Sb2Te3 film at the original irradiation site. The CPS reveals that the vibration strength of two phonon modes that correspond to the characteristic phonon modes (A1g1 and Eg) of crystalline Sb2Te3 enhances with increasing laser irradiation fluence (LIF), showing the rise of the degree of crystallization with LIF and that femtosecond laser irradiation is a good post-treatment technique. Time-resolved circularly polarized pump-probe spectroscopy is used to investigate electron spin relaxation dynamics of the laser-induced crystallized Sb2Te3 film. Spin relaxation process indeed is observed, confirming the theoretical predictions on the validity of spin-dependent optical transition selection rule and the feasibility of transient spin-grating-based optical detection scheme of spin-plasmon collective modes in Sb2Te3-like topological insulators.
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.
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
Kozik, Evgeny; Svistunov, Boris
2005-01-01
Kelvin waves (kelvons)--helical waves on quantized vortex lines--are the normal modes of vortices in a superfluid. At zero temperature, the only dissipative channel of vortex dynamics is phonon emission. Starting with the hydrodynamic action, we derive the Hamiltonian of vortex-phonon interaction, thereby reducing the problem of the interaction of Kelvin waves with sound to inelastic elementary excitation scattering. On the basis of this formalism, we calculate the rate of s...
Nonadiabatic generation of coherent phonons
Shinohara, Y.; Sato, S. A.; Yabana, K.; Iwata, J. -I.; Otobe, T.; Bertsch, G. F.
2012-01-01
The time-dependent density functional theory (TDDFT) is the leading computationally feasible theory to treat excitations by strong electromagnetic fields. Here the theory is applied to coherent optical phonon generation produced by intense laser pulses. We examine the process in the crystalline semimetal antimony (Sb), where nonadiabatic coupling is very important. This material is of particular interest because it exhibits strong phonon coupling and optical phonons of diffe...
Coherent acoustic phonons in nanostructures
Dekorsy, T.; Taubert, R.; Hudert, F.; Bartels, A.; Habenicht, A.; Merkt, F.; Leiderer, P.; Köhler, K.; Schmitz, J.; Wagner, J.
2008-02-01
Phonons are considered as a most important origin of scattering and dissipation for electronic coherence in nanostructures. The generation of coherent acoustic phonons with femtosecond laser pulses opens the possibility to control phonon dynamics in amplitude and phase. We demonstrate a new experimental technique based on two synchronized femtosecond lasers with GHz repetition rate to study the dynamics of coherently generated acoustic phonons in semiconductor heterostructures with high sensitivity. High-speed synchronous optical sampling (ASOPS) enables to scan a time-delay of 1 ns with 100 fs time resolution with a frequency in the kHz range without a moving part in the set-up. We investigate the dynamics of coherent zone-folded acoustic phonons in semiconductor superlattices (GaAs/AlAs and GaSb/InAs) and of coherent vibration of metallic nanostructures of non-spherical shape using ASOPS.
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 energy sensitivity and temporal resolution with minimal back action. The prospect of phonon counting opens intriguing experimental possibilities with analogies in quantum optics. These include fluctuation-based phonon spectroscopy, phonon shot noise in the energy relaxation of nanoscale systems, and quantum statistical phenomena such as phonon bunching and anticorrelated electron-phonon exchange.
Impulsive softening of coherent phonons in tellurium
Hunsche, Stefan; Wienecke, K.; Dekorsy, Thomas; Kurz, Heinrich
1995-01-01
We investigate the dynamics of coherent optical phonons in tellurium after high-density excitation with femtosecond laser pulses. The data show a continuous redshift of the phonon frequency with increasing excitation density. Experiments with double-pulse excitation prove that the observed frequency shift is of purely electronic origin. We demonstrate that coherent phonons allow monitoring the pathway to nonthermal laser-induced melting of crystalline materials.
"Social Laser": Action Amplification by Stimulated Emission of Social Energy
Khrennikov, Andrei
2015-01-01
The problem of the "explanation" of recent social explosions, especially in the Middle East, but also in Southern Europe and the USA, have been debated actively in the social and political literature. We can mention the contributions of P. Mason, F. Fukuyama, E. Schmidt and J. Cohen, I. Krastev to this debate. We point out that the diversity of opinions and conclusions is really amazing. At the moment, there is no consistent and commonly acceptable theory of these phenomena. We present a model of social explosions based on a novel approach for the description of social processes, namely, the quantum-like approach. Here quantum theory is treated simply as an operational formalism - without any direct relation to physics. We explore the quantum-like laser model to describe the possibility of Action Amplification by Stimulated Emission of Social Energy (ASE).
'Social Laser': action amplification by stimulated emission of social energy.
Khrennikov, Andrei
2016-01-13
The problem of the 'explanation' of recent social explosions, especially in the Middle East, but also in Southern Europe and the USA, has been debated actively in the social and political literature. We can mention the contributions of P. Mason, F. Fukuyama, E. Schmidt, J. Cohen and I. Krastev to this debate. We point out that the diversity of opinions and conclusions is really amazing. At the moment, there is no consistent and commonly acceptable theory of these phenomena. We present a model of social explosions based on a novel approach for the description of social processes, namely the quantum-like approach. Here quantum theory is treated simply as an operational formalism-without any direct relation to physics. We explore the quantum-like laser model to describe the possibility of action amplification by stimulated emission of social energy. PMID:26621987
Misochko, O. V.; Andreev, S. V.; Kompanets, V. O.; Matveets, Yu. A.; Stepanov, A. G.; Chekalin, S. V.; Dekorsy, T.
2007-11-01
The effect of phase modulation (resulting in a chirp of an ultrashort laser pulse) on the generation of a coherent A 1 phonon in Te was studied. The amplitude of coherent oscillations was found to depend on the sign and value of the pulse chirp: the oscillation amplitude decreases as the chirp increases. For a positive chirp, this effect is twofold stronger than for a negative one. The frequency-resolved response of a bandwidth-limited pulse was studied, which revealed the difference of oscillations and the relaxation response for the Stokes and anti-Stokes frequencies. The detected phenomena can be used for coherent control of lattice dynamics.
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...
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 ...
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...
Carva, Karel; Battiato, Marco; Legut, Dominik; Oppeneer, Peter M.
2013-01-01
We report a computational theoretical investigation of electron spin-flip scattering induced by the electron-phonon interaction in the transition-metal ferromagnets bcc Fe, fcc Co and fcc Ni. The Elliott-Yafet electron-phonon spin-flip scattering is computed from first-principles, employing a generalized spin-flip Eliashberg function as well as ab initio computed phonon dispersions. Aiming at investigating the amount of electron-phonon mediated demagnetization in femtosecond...
Plasma formation on a metal surface under combined action of laser and microwave radiation
International Nuclear Information System (INIS)
By means of numerical modelling of the combined effect of laser (1.06 mm) and microwave (1010 – 1013 s-1) radiation on the aluminium surface in vacuum it is shown that the additional action of microwave radiation with the frequency 1012 s-1 provides complete ionisation of the metal vapour (for the values of laser radiation duration and intensity used in the calculations), while in the absence of microwave radiation the vapour remains weakly ionised. The mathematical model used accounts for the processes, occurring in the condensed phase (heat conduction, melting), the evaporation and the kinetic processes in the resulting vapour. (interaction of laser radiation with matter. laser plasma)
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.
International Nuclear Information System (INIS)
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 Bloch oscillations in acoustic-cavity structures
Kimura, N. D. Lanzillotti; Fainstein, A.; Jusserand, B.
2004-01-01
We describe a semiconductor multilayer structure based in acoustic phonon cavities and achievable with MBE technology, designed to display acoustic phonon Bloch oscillations. We show that forward and backscattering Raman spectra give a direct measure of the created phononic Wannier-Stark ladder. We also discuss the use of femtosecond laser impulsions for the generation and direct probe of the induced phonon Bloch oscillations. We propose a gedanken experiment based in an int...
The action of powerful laser radiation on 1-2-3 superconducting thin films and bulk materials
International Nuclear Information System (INIS)
Laser induced decomposition, evaporation, and ablation processes in 1-2-3 superconductors are experimentally and theoretically studied. A model of laser beam action on 1-2-3 superconductors is developed. This model explains the low-energy mechanism of ablation, the processes of the high temperature superconductor film modification under laser action and the origination of the drops on the film surface deposited by a laser ablation technique. The model is in good agreement with experimental results. (orig.)
International Nuclear Information System (INIS)
The dynamics of coherent phonons in fluorine-containing crystals under plasma formation were studied using a nonlinear pump–probe technique based on third harmonic generation. In LiF crystal more than one phonon mode was observed. The modes are the overtones of a fundamental wave with a frequency of 0.38 THz. In CaF2 crystal phonons with frequencies of 1 and 0.1 THz were observed. In BaF2 crystal, in addition to coherent phonons with frequencies of 1 THz and 67 GHz, a significant increase of amplitude in the phonon modes with a time delay of 15 ps was detected. (letter)
Decay processes of nonequilibrium phonons in Pr3+-doped yttrium aluminum garnet
Wang, Xiao-Jun; Ganem, Joseph; Dennis, W. M.; Yen, W. M.
1991-07-01
We have investigated the decay of nonequilibrium phonons in YAG:Pr3+ (1.0 at.%) at a temperature of 16 K. Nonequilibrium phonon populations are generated monochromatically with a high-power pulsed far-infrared laser using defect-induced one-phonon absorption and their temporal and spectral evolution determined using a time-resolved vibronic sideband spectrometer. We find that two decay mechanisms dominate the nonequilibrium phonon relaxation: anharmonic decay via three-phonon interactions and two-phonon-one-electron inelastic-scattering processes. The latter mechanism leads to the evolution of a highly peaked phonon distribution that persists for several phonon generations.
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.
Study on modes of energy action in laser-induction hybrid cladding
International Nuclear Information System (INIS)
The shape and microstructure in laser-induction hybrid cladding were investigated, in which the cladding material was provided by means of three different methods including the powder feeding, cold pre-placed coating (CPPC) and thermal pre-placed coating (TPPC). Moreover, the modes of energy action in laser-induction hybrid cladding were also studied. The results indicate that the cladding material supplying method has an important influence on the shape and microstructure of coating. The influence is decided by the mode of energy action in laser-induction hybrid cladding. During the TPPC hybrid cladding of Ni-based alloy, the laser and induction heating are mainly performed on coating. During the CPPC hybrid cladding of Ni-based alloy, the laser and induction heating are mainly performed on coating and substrate surface, respectively. In powder feeding hybrid cladding, a part of laser is absorbed by the powder particles directly, while the other part of laser penetrating powder cloud radiates on the molten pool. Meanwhile, the induction heating is entirely performed on the substrate. In addition, the wetting property on the interface is improved and the metallurgical bond between the coating and substrate is much easier to form. Therefore, the powder feeding laser-induction hybrid cladding has the highest cladding efficiency and the best bond property among three hybrid cladding methods.
Change of electrochromatic film properties under impulsive laser radiation action
International Nuclear Information System (INIS)
Effect of laser irradiation with pulse nanosecond duration on electrochromic film properties connected with their defectiveness has been investigated. Thin WO3, WS3, MoO3 films were investigated. It is shown that film irradiation with tau=80 ns results in considerable increase of colouring and decolouring rates, V, determined from change of optical density per time unit during electrocoloring of films. So V increase approximately three times is observed for WO3 films of 0.5-1 ?m thickness irradiated with laser at energy density E=4 Jxcmsup(-2). Analogous results have been obtained for MoO3 and WS3 films
Directory of Open Access Journals (Sweden)
Medvid Artur
2011-01-01
Full Text Available Abstract On the basis of the analysis of experimental results, a two-stage mechanism of nanocones formation on the irradiated surface of semiconductors by Nd:YAG laser is proposed for elementary semiconductors and solid solutions, such as Si, Ge, SiGe, and CdZnTe. Properties observed are explained in the frame of quantum confinement effect. The first stage of the mechanism is characterized by the formation of a thin strained top layer, due to redistribution of point defects in temperature-gradient field induced by laser radiation. The second stage is characterized by mechanical plastic deformation of the stained top layer leading to arising of nanocones, due to selective laser absorption of the top layer. The nanocones formed on the irradiated surface of semiconductors by Nd:YAG laser possessing the properties of 1D graded bandgap have been found for Si, Ge, and SiGe as well, however QD structure in CdTe was observed. The model is confirmed by "blue shift" of bands in photoluminescence spectrum, "red shift" of longitudinal optical line in Raman back scattering spectrum of Ge crystal, appearance of Ge phase in SiGe solid solution after irradiation by the laser at intensity 20 MW/cm2, and non-monotonous dependence of Si crystal micro-hardness as function of the laser intensity.
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.
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
Energy Technology Data Exchange (ETDEWEB)
Rademaker, K; Heumann, E; Payne, S A; Huber, G; Krupke, W F; Isaenko, L I; Burger, A
2004-09-15
For the first time laser activity has been achieved in the low phonon energy, moisture-resistant bromide host crystals, neodymium-doped potassium lead bromide (Nd{sup 3+}:KPb{sub 2}Br{sub 5}) and rubidium lead bromide (Nd{sup 3+}:RbPb{sub 2}Br{sub 5}). Laser activity at 1.07 {micro}m was observed for both crystalline materials. Laser operation at the new wavelengths 1.18 {micro}m and 0.97 {micro}m resulting from the {sup 4}F{sub 5/2} + {sup 2}H{sub 9/2} {yields} {sup 4}I{sub J} transitions (J=13/2 and 11/2) in Nd:RPB was achieved for the first time in a solid state laser material. Rare earth- doped MPb{sub 2}Br{sub 5} (M=K, Rb) is a promising candidate for long wavelength infrared applications because of its low phonon frequencies and other favorable features. In principle, Nd{sup 3+}:MPb{sub 2}Br{sub 5} has high potential for laser operation at new wavelengths as well as for the realization of short-wavelength lasing due to upconversion processes.
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.
Kamaraju, N.; Kumar, Sunil; Sood, A. K.
2010-01-01
Degenerate pump-probe reflectivity experiments have been performed on a single crystal of bismuth telluride (Bi$_2$Te$_3$) as a function of sample temperature (3K to 296K) and pump intensity using $\\sim$ 50 femtosecond laser pulses with central photon energy of 1.57 eV. The time resolved reflectivity data show two coherently generated totally symmetric A$_{1g}$ modes at 1.85 THz and 3.6 THz at 296K which blue shift to 1.9 THz and 4.02 THz, respectively at 3K. At high photoex...
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.
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...
Vertical cavity surface emitting laser action of an all monolithic ZnO-based microcavity
Kalusniak, S; Halm, S; Henneberger, F
2010-01-01
We report on room temperature laser action of an all monolithic ZnO-based vertical cavity surface emitting laser (VCSEL) under optical pumping. The VCSEL structure consists of a 2{\\lambda} microcavity containing 8 ZnO/Zn(0.92)Mg(0.08)O quantum wells embedded in epitaxially grown Zn(0.92)Mg(0.08)O/Zn(0.65)Mg(0.35)O distributed Bragg reflectors (DBRs). As a prerequisite, design and growth of high reflectivity DBRs based on ZnO and (Zn,Mg)O for optical devices operating in the ultraviolet and blue-green spectral range are discussed.
Vertical cavity surface emitting laser action of an all monolithic ZnO-based microcavity
Kalusniak, S.; Sadofev, S.; Halm, S.; Henneberger, F.
2010-01-01
We report on room temperature laser action of an all monolithic ZnO-based vertical cavity surface emitting laser (VCSEL) under optical pumping. The VCSEL structure consists of a 2{\\lambda} microcavity containing 8 ZnO/Zn(0.92)Mg(0.08)O quantum wells embedded in epitaxially grown Zn(0.92)Mg(0.08)O/Zn(0.65)Mg(0.35)O distributed Bragg reflectors (DBRs). As a prerequisite, design and growth of high reflectivity DBRs based on ZnO and (Zn,Mg)O for optical devices operating in the ...
Laser action generation by atomic transitions in xenon in the afterglow during electron-beam pumping
Sereda, O. V.; Tarasenko, V. F.; Fedenev, A. V.
1991-02-01
Data are presented characterizing the generation of laser action due to five atomic transitions in Xe (with the most intensive ones at 2.026, 1.733, and 2.651 microns) in the afterglow produced by pumping an Ar-Xe gas mixture by an electron beam of about 5 ns duration. It is shown that it is possible to achieve a preferential generation of any one of these lines.
Laser action generation by atomic transitions in xenon in the afterglow during electron-beam pumping
Energy Technology Data Exchange (ETDEWEB)
Sereda, O.V.; Tarasenko, V.F.; Fedenev, A.V. (AN SSSR, Institut Sil' notochnoi Elektroniki, Tomsk (USSR) AN SSSR, Institut Obshchei Fiziki, Moscow (USSR))
1991-02-01
Data are presented characterizing the generation of laser action due to five atomic transitions in Xe (with the most intensive ones at 2.026, 1.733, and 2.651 microns) in the afterglow produced by pumping an Ar-Xe gas mixture by an electron beam of about 5 ns duration. It is shown that it is possible to achieve a preferential generation of any one of these lines. 12 refs.
Efficient and stable dye laser action from modified dipyrromethene BF2 complexes
Costela González, Ángel; Garcia-Moreno, I.; Gómez, C; Amat-Guerri, Francisco; Sastre Muñoz, Roberto
2001-01-01
We report on the lasing action of modified dipyrromethene BF2 complexes in air-equilibrated liquid solutions. All recent dyes share a common chromophore core and were dissolved in apolar, polar nonprotic, and polar protic solvents. When pumped transversely at 534 nm, nearly solvent-independent laser emission was obtained with efficiencies well over 40% in most cases. Highest lasing efficiency was 59%. Under continuous ultraviolet irradiation some of these dyes demonstrated improved photostabi...
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.
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.
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...
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...
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.
Hase, Muneaki; Hayashi, Daisuke; Lee, J.D.
2011-01-01
We demonstrate optical control of the LO phonon-plasmon coupled (LOPC) modes in GaAs by using a femtosecond pump-pulse pair. The relaxation time of the plasmon-like LOPC mode significantly depends on the separation time (\\Delta t) of the pump-pulse pair. Especially it is maximized when \\Delta t becomes simultaneously comparable to the half period of the longitudinal optical (LO) phonon oscillation and resonant to the 3/4 period of the plasmon-like LOPC oscillation. We attrib...
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)
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)
Long-time correlated quantum dynamics of phonon cooling
Carlig, Sergiu; Macovei, Mihai A.
2014-01-01
We investigate the steady-state cooling dynamics of vibrational degrees of freedom related to a nanomechanical oscillator coupled with a laser-pumped quantum dot in an optical resonator. Correlations between phonon-cooling and quantum-dot photon emission processes occur respectively when a photon laser absorption together with a vibrational phonon absorption is followed by photon emission in the optical resonator. Therefore, the detection of photons generated in the cavity m...
Impulsive Excitation of Phonon-Pair Combination States by Second-Order Raman Scattering
Bartels, Albrecht; Dekorsy, Thomas; Kurz, Heinrich
2000-01-01
The excitation of (100)-oriented KTaO3 with 25-fs laser pulses impulsively drives phonon-pair combination states via second-order Raman scattering. Oscillations in the phonon-amplitude covariance at the sum and difference frequency of the two involved phonons are observed in a spectrally and temporally resolved pump-probe experiment. Transmission changes of the sample are dominated by contributions of wave vector conserving phonon-pair combinations from the entire Brillouin zone that have max...
Long-time correlated quantum dynamics of phonon cooling
Carlig, Sergiu; Macovei, Mihai A.
2014-07-01
We investigate the steady-state cooling dynamics of vibrational degrees of freedom related to a nanomechanical oscillator coupled with a laser-pumped quantum dot in an optical resonator. Correlations between phonon-cooling and quantum-dot photon emission processes occur, respectively, when a photon laser absorption together with a vibrational phonon absorption is followed by photon emission in the optical resonator. Therefore, the detection of photons generated in the cavity mode concomitantly contributes to phonon cooling detection of the nanomechanical resonator.
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)
Energy Technology Data Exchange (ETDEWEB)
Andrianov, S.N.; Samartsev, V.V.; Sheibut, Y.E. [Zavoiskii Physicotechnical Institute, Tatarstan (Russian Federation)
1995-09-01
The theory of photon-phonon superradiation in extended samples of impurity molecular crystals was developed within the framework of the nonequilibrium statistical operator method. Optical superradiation on indirect transitions of anisotropic impurity molecules involving resonant phonons under conditions of their hermodynamic equilibrium was studied. Two-quantum superradiation on a Stokes indirect transition accompanied by emission of coherent photons and phonons with nonequilibrium initial phonon subsystem was also examined. Prerequisites to the effect were analyzed and its main properties were described. 16 refs., 3 figs.
Energy Technology Data Exchange (ETDEWEB)
Ashitkov, Sergei I; Komarov, P S; Ovchinnikov, A V; Struleva, E V; Agranat, Mikhail B [Joint Institute for High Temperatures, Russian Academy of Sciences, Moscow (Russian Federation)
2013-03-31
An interferometric method is developed and realised using a frequency-modulated pulse for diagnosing a dynamics of fast deformations with a spatial and temporal resolution under the action of a single laser pulse. The dynamics of a free surface of a submicron-thick aluminium film is studied under an action of the ultrashort compression pulse with the amplitude of up to 14 GPa, excited by a femtosecond laser heating of the target surface layer. The spallation strength of aluminium was determined at a record high deformation rate of 3 Multiplication-Sign 10{sup 9} s{sup -1}. (extreme light fields and their applications)
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.
Action of the 216-nm fifth harmonic of a Nd:YAP laser on photosensitive germanosilicate glass films
International Nuclear Information System (INIS)
The absorption spectrum, refractive index, and relief of the surface of a germanosilicate glass film are studied upon the non-destructive action of the 216-nm (5.75-eV) fifth harmonic of a repetitively pulsed Nd:YAP laser. It is shown that laser irradiation of films induces a strong photorefractive effect despite the relatively low absorption coefficient. For the 100-mJ cm-2 energy density and above, two-photon process make a noticeable contribution to the absorption of laser radiation at 216 nm. The diffraction efficiency of photoinduced phase gratings achieved ?7x10-3 for the exposure dose ?6 kJ cm-2, which corresponds to the induced refractive index 1.5x10-3. At higher exposure doses, a relief appears on a film surface and the diffraction efficiency of a phase grating is reduced. (interaction of laser radiation with matter. laser plasma)
International Nuclear Information System (INIS)
Self-consistent phonon scheme given by S. Takeno and M. Goda involving multiple scattering and phonon eigen frequencies which are expressed in terms of many body correlation function of atoms as well as of interatomic potential in the solids, has been employed for calculating the collective modes in liquid rubidium. Simplified numerical calculations of the eigen frequencies of longitudinal and transverse phonons in this liquid metal are made within the framework of 'quasi-crystalline approximation'. The model potential used in these calculations is the potential of D.L. Price for liquid rubidium. An attempt has also been made to estimate the phonon damping (phonon lifetime) in terms of a cut-off parameter q0 in this liquid metal. (author)
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)
Coherent excitation and control of surface phonons
Matsumoto, Yoshiyasu
2006-03-01
The excitation and control of nuclear wavepackets using tailored laser pulses have attracted a lot of interest recently and being realized mainly in gas-phase molecules. In contrast, there have been little studies on the coherent excitation and control for adsorbates particularly on metal surfaces. This is because dephasing is substantially rapid on metal surfaces due to efficient couplings between adsorbates and metals. Recently, we have demonstrated the time-domain observation of nuclear wavepacket dynamics of monolayer adsorbate by femtosecond time-resolved second harmonic generation (TRSHG). When metal surfaces covered with alkali metal atoms are irradiated by ultrafast laser pulses, coherent surface phonon modes are excited. The formation and dissipation processes of coherent surface phonons are probed by time-resolved second harmonic generation. SHG signal intensities are enhanced by alkali atoms adsorption by various resonant transitions in the adsorbate-substrate system. However, not all resonant electronic transitions lead to the generation of coherent stretching vibrations of alkali atoms. The measurements of TRSHG traces as a function of the excitation photon energy at a fixed alkali coverage indicate that resonant transitions between adsorbate-induced surface states is responsible for the coherent vibrational motions. By carefully examining the Cs coverage dependence of the TRSHG waveform, we found that TR-SHG traces show beating structures. This indicates that the oscillatory TR-SHG traces are contributed by at least two kinds of coherent surface phonon modes: the Cs-Pt stretching mode (2.3 THz) and the Rayleigh phonon mode (2.6 or 2.9 THz, depending on the Cs coverage). We used fs pulse trains with the repetition frequencies of 2.0 - 2.9 THz that are synthesized by using a spatial-light modulator as an excitation source for the coherent phonons. By tuning the pulse train frequency, we succeed in the selective excitation of a coherent phonon mode.
Prospects afforded in the field of electrotechnics by the action of laser waves on matter
International Nuclear Information System (INIS)
The laser, a new light source discovered in 1960, permits high power concentrations to be attained, both in space and time, considerably larger than those obtained by the conventional optical sources. It results accordingly in a method of production of hot and dense plasma thanks to the interaction of the optical wave and a solid deuterium-tritium sphere. These phenomena open a new way to the control of thermonuclear fusion. Coherent waves are transmitted in a narrow band, often tunable. They permit the selective excitation of atoms or molecules of a gas and give a new means of separating the isotopes which might possibly be of great economical interest. The Laboratories de Marcoussis, in close co-operation with the Atomic Energy Board - C.E.A. and under its sponsorship, were the originators of the work carried out in this field from 1962. The results they recorded have marked some important steps in research development. The author describes the prospects opened up by the action of laser waves on matter. He discloses the research work done on the control of fusion and the improvement of isotope separation methods which will probably have a great impact on the evolution of electrotechnics
Impulsive excitation of phonon-pair combination states by second-order raman scattering
Bartels; Dekorsy; Kurz
2000-03-27
The excitation of (100)-oriented KTaO3 with 25-fs laser pulses impulsively drives phonon-pair combination states via second-order Raman scattering. Oscillations in the phonon-amplitude covariance at the sum and difference frequency of the two involved phonons are observed in a spectrally and temporally resolved pump-probe experiment. Transmission changes of the sample are dominated by contributions of wave vector conserving phonon-pair combinations from the entire Brillouin zone that have maxima in their combined density of states. For low temperatures the temperature dependence of the covariance oscillations of different phonon combinations is reproduced by a quantum-mechanical model. PMID:11018991
Emission of submillimeter electromagnetic waves by coherent phonons
Dekorsy, Thomas; Auer, Holger; Waschke, Christian; Bakker, Huib J.; Roskos, Hartmut G.; Kurz, Heinrich; Wagner, Veit; Grosse, Peter
1995-01-01
We report on the first observation of the emission of electromagnetic radiation from coherent lattice vibrations in a semiconductor. Coherent optical phonons are excited by ultrashort laser pulses in single-crystal tellurium. THz frequency radiation emitted by the Dember-field-driven phonons is detected by time-resolved THz-emission spectroscopy. The measurements are complemented by optical pump-probe experiments with a polarization-sensitive detection scheme utilizing the symmetry of the Ram...
Coherent control of acoustic phonons in semiconductor superlattices
Bartels, Albrecht; Dekorsy, Thomas; Kurz, Heinrich; Köhler, Klaus
1998-01-01
Coherent acoustic phonons are generated in GaAs/AlAs superlattices by excitation with femtosecond laser pulses. Several modes of the acoustic phonon spectrum are observed, in agreement with the effect of zone folding in the mini-Brillouin zone of the superlattice. By applying successive pump pulses we are able to silence the first back-folded mode near q=0, while selectively enhancing the coherent amplitude of higher order backfolded modes. This increase in the spectroscopic sensitivity opens...
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 ...
Perrin, Bernard
2007-06-01
The conference PHONONS 2007 was held 15-20 July 2007 in the Conservatoire National des Arts et Métiers (CNAM) Paris, France. CNAM is a college of higher technology for training students in the application of science to industry, founded by Henri Grégoire in 1794. This was the 12th International Conference on Phonon Scattering in Condensed Matter. This international conference series, held every 3 years, started in France at Sainte-Maxime in 1972. It was then followed by meetings at Nottingham (1975), Providence (1979), Stuttgart (1983), Urbana-Champaign (1986), Heidelberg (1989), Ithaca (1992), Sapporo (1995), Lancaster (1998), Dartmouth (2001) and St Petersburg (2004). PHONONS 2007 was attended by 346 delegates from 37 different countries as follows: France 120, Japan 45, Germany 25, USA 25, Russia 21, Italy 13, Poland 9, UK 9, Canada 7, The Netherlands 7, Finland 6, Spain 6, Taiwan 6, Greece 4, India 4, Israel 4, Ukraine 4, Serbia 3, South Africa 3, Argentina 2, Belgium 2, China 2, Iran 2, Korea 2, Romania 2, Switzerland 2, and one each from Belarus, Bosnia-Herzegovina, Brazil, Bulgaria, Egypt, Estonia, Mexico, Moldova, Morocco, Saudi Arabia, Turkey. There were 5 plenary lectures, 14 invited talks and 84 oral contributions; 225 posters were presented during three poster sessions. The first plenary lecture was given by H J Maris who presented fascinating movies featuring the motion of a single electron in liquid helium. Robert Blick gave us a review on the new possibilities afforded by nanotechnology to design nano-electomechanical systems (NEMS) and the way to use them to study elementary and fundamental processes. The growing interest for phonon transport studies in nanostructured materials was demonstrated by Arun Majumdar. Andrey Akimov described how ultrafast acoustic solitons can monitor the optical properties of quantum wells. Finally, Maurice Chapellier told us how phonons can help tracking dark matter. These 328 presentations gave rise to 185 articles 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
Manipulation of thermal phonons
Hsu, Chung-Hao
Developing materials that can conduct electricity easily, but block the motion of phonons is necessary in the applications of thermoelectric devices, which can generate electricity from temperature differences. In converse, a key requirement as chips get faster is to obtain better ways to dissipate heat. Controlling heat transfer in these crystalline materials devices --- such as silicon --- is important. The heat is actually the motion or vibration of atoms known as phonons. Finding ways to manipulate the behavior of phonons is crucial for both energy applications and the cooling of integrated circuits. A novel class of artificially periodic structured materials --- phononic crystals --- might make manipulation of thermal phonons possible. In many fields of physical sciences and engineering, acoustic wave propagation in solids attracts many researchers. Wave propagation phenomena can be analyzed by mathematically solving the acoustic wave equation. However, wave propagation in inhomogeneous media with various geometric structures is too complex to find an exact solution. Hence, the Finite Difference Time Domain method is developed to investigate these complicated problems. In this work, the Finite-Difference Time-Domain formula is derived from acoustic wave equations based on the Taylor's expansion. The numerical dispersion and stability problems are analyzed. In addition, the convergence conditions of numerical acoustic wave are stated. Based on the periodicity of phononic crystal, the Bloch's theorem is applied to fulfill the periodic boundary condition of the FDTD method. Then a wide-band input signal is used to excite various acoustic waves with different frequencies. In the beginning of the calculation process, the wave vector is chosen and fixed. By means of recording the displacement field and taking the Fourier transformation, we can obtain the eigenmodes from the resonance peaks of the spectrum and draw the dispersion relation curve of acoustic waves. With the large investment in silicon nanofabrication techniques, this makes tungsten/silicon phononic crystal a particularly attractive platform for manipulating thermal phonons. Phononic crystal makes use of the fundamental properties of waves to create band gap over which there can be no propagation of acoustic waves in the crystal. This crystal can be applied to deterministically manipulate the phonon dispersion curve affected by different crystal structures and to modify the phonon thermal conductivity accordingly. We can expect this unique metamaterial is a promising route to creating unprecedented thermal properties for highly-efficient energy harvesting and thermoelectric cooling.
Birefringent phononic structures
Psarobas, I. E.; Exarchos, D. A.; Matikas, T. E.
2014-12-01
Within the framework of elastic anisotropy, caused in a phononic crystal due to low crystallographic symmetry, we adopt a model structure, already introduced in the case of photonic metamaterials, and by analogy, we study the effect of birefringence and acoustical activity in a phononic crystal. In particular, we investigate its low-frequency behavior and comment on the factors which determine chirality by reference to this model.
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...
Ultrafast spectroscopy of propagating coherent acoustic phonons in GaN/InGaN heterostructures
Liu, R; Sanders, G D; Stanton, C J; Yahng, J S; Jho, Y D; Yee, K J; Oh, E; Kim, D S; Liu, Rongliang; Kim, Chang Sub
2003-01-01
We show that large amplitude, coherent acoustic phonon wavepackets can be generated and detected in In$_x$Ga$_{1-x}$N/GaN epilayers and heterostructures in femtosecond pump-probe differential reflectivity experiments. The amplitude of the coherent phonon increases with increasing Indium fraction $x$ and unlike other coherent phonon oscillations, both \\textit{amplitude} and \\textit{period} are strong functions of the laser probe energy. The amplitude of the oscillation is substantially and almost instantaneously reduced when the wavepacket reaches a GaN-sapphire interface below the surface indicating that the phonon wavepackets are useful for imaging below the surface. A theoretical model is proposed which fits the experiments well and helps to deduce the strength of the phonon wavepackets. Our model shows that localized coherent phonon wavepackets are generated by the femtosecond pump laser in the epilayer near the surface. The wavepackets then propagate through a GaN layer changing the local index of refract...
Observation of coherent zone-folded acoustic phonons generated by Raman scattering in a superlattice
Hawker, Philip; Kent, Anthony J.; Challis, Lawrence J.; Bartels, Albrecht; Dekorsy, Thomas; Kurz, Heinrich; Köhler, Klaus
2000-01-01
We have used pulse time-of-flight techniques to examine the phonon emission from an optically excited GaAs/AlAs superlattice structure. For laser excitation wavelengths shorter than 767 nm (the energy of E1HH1 transition), we detect a significant longitudinal acoustic phonon component directed in a narrow beam normal to the structure. Under identical excitation conditions, generation of coherent longitudinal acoustic phonons has previously been observed in this structure. We suggest that the ...
Infrared-Phonon Polariton Resonance of the Nonlinear Susceptibility in GaAs
Dekorsy, Thomas; Yakovlev, Vladislav A.; Seidel, Wolfgang; Helm, Manfred; Keilmann, Fritz
2003-01-01
Nonlinear probing of the fundamental lattice vibration of polar crystals is shown to reveal insight into higher-order cohesive lattice forces. With a free-electron laser tunable in the far infrared we experimentally investigate the dispersion of the second-order susceptibility due to the phonon resonance in GaAs. We observe a strong resonance enhancement of second harmonic light generation at half the optical phonon frequency, and in addition a minimum at a higher frequency below the phonon f...
International Nuclear Information System (INIS)
By the method of laser probing the velocity of Pb laser jet front under acting of powerful 20 ns pulses of YAG:Nd laser was estimated. The peculiar properties of probing irradiation absorption and scattering processes were established for application of nanosecond pulses with high level of power density on Pb targets. The main mechanism of Pb drop-liquid phase formation was defined for mentioned conditions of laser acting as condensation process. (authors)
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
Phonon waveguides for electromechanical circuits
Hatanaka, D.; Mahboob, I.; Onomitsu, K.; Yamaguchi, H.
2014-07-01
Nanoelectromechanical systems (NEMS), utilizing localized mechanical vibrations, have found application in sensors, signal processors and in the study of macroscopic quantum mechanics. The integration of multiple mechanical elements via electrical or optical means remains a challenge in the realization of NEMS circuits. Here, we develop a phonon waveguide using a one-dimensional array of suspended membranes that offers purely mechanical means to integrate isolated NEMS resonators. We demonstrate that the phonon waveguide can support and guide mechanical vibrations and that the periodic membrane arrangement also creates a phonon bandgap that enables control of the phonon propagation velocity. Furthermore, embedding a phonon cavity into the phonon waveguide allows mobile mechanical vibrations to be dynamically switched or transferred from the waveguide to the cavity, thereby illustrating the viability of waveguide-resonator coupling. These highly functional traits of the phonon waveguide architecture exhibit all the components necessary to permit the realization of all-phononic NEMS circuits.
International Nuclear Information System (INIS)
In this paper are presented theoretical calculations of the linewidth of the Rayleigh phonon propagating along high symmetry directions of the (111) surface of aluminium both for different temperatures and for different values of the phonon momentum. The interatomic potential of the crystal contains both a harmonic part which describes the normal vibrations of the crystal and a cubic anharmonic part which is the dominant term of the lifetimes of the vibrations. The calculations show a rapid decay when either the temperature or the momentum transfer decreases, and a large anisotropy with the direction of the momentum transfer. (author). 10 refs, 6 figs, 2 tabs
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.
Benmadani, Y.; Kermaoui, A.; Chalal, M.; Khemici, W.; Kellou, A.; Pellé, F.
2013-10-01
The influence of composition on the thermal stability of tellurite glasses was investigated by using differential scanning calorimetry (DSC). The studied glasses were synthesized by conventional melting quenching method. The best thermal stability and poor crystallization tendency were obtained for the glass composed of 65TeO2-15ZnO-10Na2O-5BaO-3La2O3 doped with Er2O3 (2 mol %). This glass will be referred, in this article, as TZNBL: Er3+ glass. The spectroscopic properties of the above glass are investigated based on the Judd-Ofelt and McCumber theories. The calculated intensity parameters (?2,4,6) are compared to those obtained for Er3+ in other glasses. The radiative emission rate has been calculated for the different Er3+emitting levels. The high values of ?4 and ?6 confirm the results of the DSC experiment concerning the rigidity of the studied glass. Absorption, emission and gain cross section of the 4I13/2 ? 4I15/2 (Er3+) transition in the studied glass are reported and the results are compared to those of other glasses. The 4I13/2 ? 4I15/2 (Er3+) absorption and emission cross sections derived by the application of the Mc Cumber's theory corroborate the Judd-Ofelt results. The whole of results demonstrate that the new composition leads to good thermal and mechanical properties as well efficient Er3+ absorption, emission cross sections, which make this glass as a promising candidate for laser action and amplification.
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.
Xie, Hongqiang; LI Guihua; 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 intens...
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)
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.
Phononic crystals fundamentals and applications
Adibi, Ali
2016-01-01
This book provides an in-depth analysis as well as an overview of phononic crystals. This book discusses numerous techniques for the analysis of phononic crystals and covers, among other material, sonic and ultrasonic structures, hypersonic planar structures and their characterization, and novel applications of phononic crystals. This is an ideal book for those working with micro and nanotechnology, MEMS (microelectromechanical systems), and acoustic devices. This book also: Presents an introduction to the fundamentals and properties of phononic crystals Covers simulation techniques for the analysis of phononic crystals Discusses sonic and ultrasonic, hypersonic and planar, and three-dimensional phononic crystal structures Illustrates how phononic crystal structures are being deployed in communication systems and sensing systems.
Temperature dependence of Brillouin light scattering spectra of acoustic phonons in silicon
International Nuclear Information System (INIS)
Electrons, optical phonons, and acoustic phonons are often driven out of local equilibrium in electronic devices or during laser-material interaction processes. The need for a better understanding of such non-equilibrium transport processes has motivated the development of Raman spectroscopy as a local temperature sensor of optical phonons and intermediate frequency acoustic phonons, whereas Brillouin light scattering (BLS) has recently been explored as a temperature sensor of low-frequency acoustic phonons. Here, we report the measured BLS spectra of silicon at different temperatures. The origins of the observed temperature dependence of the BLS peak position, linewidth, and intensity are examined in order to evaluate their potential use as temperature sensors for acoustic phonons
Magnons and Phonons Driven out of Equilibrium in a Magnetic Insulator
An, Kyongmo; Olsson, Kevin; Klimovich, Nikita; Sullivan, Sean; Weathers, Annie; Marshall, Luke; Chen, Xi; Zhou, Jianshi; Shi, Li; Li, Xiaoqin
2015-03-01
We investigate magnons and phonons in a bulk Y3Fe5O12(YIG) under a large temperature gradient created by laser radiation. YIG is a good playground to study the interaction between phonons and magnons. Because of its absence of itinerant electrons, energy transport is only carried by magnons and phonons. Understanding the coupling between them is a key to the thermally driven spin transport such as Spin Seebeck Effect. We use Brillouin light scattering technique to measure phonon and magnon temperature. We found that they can be driven out of equilibrium under a large temperature gradient. We numerically simulate the phonon and magnon temperatures using two-temperature model. Our results suggest a lower bound of magnon phonon relaxation time in YIG. We acknowledge support from DOE, AOR under Contract W911NF-14-1-0016 and NSF via Grant CBET-1336968.
Bactericidal action of 308 nm excimer-laser radiation: an in vitro investigation.
Folwaczny, M; Liesenhoff, T; Lehn, N; Horch, H H
1998-12-01
The aim of the present study was to investigate the influence of 308 nm excimer-laser radiation on bacterial growth. Six different bacterial strains (Staphylococcus aureus, Escherichia coli, Streptococcus faecalis, Lactococcis lactis, Salmonella typhimurium, and Deinococcus radiodurans) were exposed in vitro to various doses and energy densities of laser radiation. To exclude bacterial killing by supraphysiological heating, the temperature change in the samples during irradiation was measured. Extended antimicrobial effects of XeCl excimer-laser radiation depending on the time of radiation, the energy density of the laser beam, and the irradiated bacterial strain were observed. Reduction of bacterial growth is independent of temperature and not linked to any ablative tissue removal. In almost all cases, a 99.9% reduction of bacteria was reached by total radiation times laser radiation may be of significant clinical importance in endodontics and periodontology in the future. PMID:10023253
Wang, Cih-Su; Liau, Chi-Shung; Sun, Tzu-Ming; Chen, Yu-Chia; Lin, Tai-Yuan; Chen, Yang-Fang
2015-01-01
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 f...
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
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 .
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.
Tunable topological phononic crystals
Chen, Ze-Guo
2015-01-01
Topological insulators, first observed in electronic systems, have inspired many analogues in photonic and phononic crystals in which remarkable one-way propagation edge states are supported by topologically nontrivial bandgaps. Such bandgaps can be achieved by breaking the time-reversal symmetry to lift the degeneracy associated with Dirac cones at the corners of the Brillouin zone. Here, we report on our construction of a phononic crystal exhibiting a Dirac-like cone in the Brillouin zone center. We demonstrate that simultaneously breaking the time-reversal symmetry and altering the geometric size of the unit cell result in a topological transition that is verified by the Chern number calculation and edge mode analysis. The topology of the bandgap is tunable by varying both the velocity field and the geometric size; such tunability may dramatically enrich the design and use of acoustic topological insulators.
Dielectricity and Hard Phonons
Weger, M.; Birman, J. I.
2002-01-01
The maximum value of the superconducting transition temperature Tc due to a phonon-mediated interaction was estimated by Cohen and Anderson in 1972 from ab initio considerations, and found to be about 10 K. McMillan's semi empirical estimate from 1968 gives a value of about 40 K. We consider these estimates on the basis of subsequent theoretical and experimental evidence, and pay attention in particular to the inhomogeneity of the electron gas. This inhomogeneity gives rise ...
A magnetically field-controllable phononic crystal
Bayat, Alireza; Gordaninejad, Faramarz
2014-04-01
Phononic crystals are periodic structures consist of different materials in an elastic medium designed to interact with elastic waves. These crystals have practical applications, such as, frequency filters, beam splitters, sound or vibration protectors, acoustic lasers, acoustic mirrors and elastic waveguides. In this study, the wave propagation in a tunable phononic crystal is investigated. The magnetically controllable phononic crystal consists of a soft magnetorheological elastic medium undergoing large deformations upon the application of a magnetic field. Finite deformations and induced magnetic fields influence wave propagation characteristics in the periodic structure. The soft matrix is modeled as a hyperelastic elastomer to take into account the material nonlinearity. The integrated effects of material properties, transformation of the geometry of the unit cell, and the induced magnetic field, are used to tune the band structure of the periodic structure. Both analytical and finite element methods are employed to evaluate the dispersion diagrams considering Bloch boundary conditions. Results show that the applied magnetic field significantly affect the width and the position of band-gaps.
Phonons within two adsorbed slabs
Sylla, B.; More, M.; Dobrzynski, L.
1989-04-01
The existence of localized phonons within two different slabs adsorbed on a substrate is reported here. A closed form expression giving the frequencies of these phonons as function of the propagation vector parallel to the interfaces was obtained within a simple model. This expression is also a function of the respective force constants and masses and depends on the number of atomic layers present in each slab. A few specific examples illustrate this result. A comparison is made also with the sandwich phonons, localized phonons within a slab situated between two semi-infinite crystals.
Monochromatic phonon generation by the Josephson effect
Energy Technology Data Exchange (ETDEWEB)
Berberich, P.; Buemann, R.; Kinder, H.
1982-11-15
ac-Josephson junctions of tin and lead were found to emit monochromatic phonons with Josephson frequency, rather than thermal phonons. This is a new tunable phonon source with high efficiency and prospectively extremely high-frequency resolution.
Monochromatic phonon generation by the Josephson effect
International Nuclear Information System (INIS)
ac-Josephson junctions of tin and lead were found to emit monochromatic phonons with Josephson frequency, rather than thermal phonons. This is a new tunable phonon source with high efficiency and prospectively extremely high-frequency resolution
THz electromagnetic emission by coherent infrared-active phonons
Dekorsy, Thomas; Auer, Holger; Bakker, Huib J.; Roskos, Hartmut G.; Kurz, Heinrich
1996-01-01
Coherent phonons are excited in single-crystal tellurium by above-band-gap excitation with femtosecond laser pulses. Coherent infrared-active lattice vibrations give rise to the emission of electromagnetic waves at the phonon frequency. The excitation mechanism is based on the ultrafast buildup of a photo-Dember field and the coupling of a polar lattice mode to this field. The dynamics of the Dember field is obtained from a numerical simulation of the electron-hole plasma dynamics close to th...
[Reaction of peripheric immune organ on action of low-energy red spectrum lasers].
Va?nahi?, O M
2001-01-01
Influence of low-energy laser irradiation of red diapason on the popliteal lymph nodes (LN) structure of sexually matured white rats depending on the given locally irradiation dose, using light conductor of laser apparatus ALOK-1, was investigated. In the irradiated LN the regular dose-dependent quantitative and qualitative changes in parenchyma were observed. In contralateral LN the same, but less pronounced, changes were observed, witnessing about systemic character of peripheral immune organs reactions on the laser irradiation influence. During irradiation in 0.3 and 3 J/cm2 doses the activation of processes in the LN parenchyma, and in 30 J/cm2 dose the destruction processes of LN were observed. PMID:11503337
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)
Low intensity red laser action on Escherichia coli cultures submitted to stress conditions
Santos, J. N.; Roos, C.; Barboza, L. L.; Paoli, F.; Fonseca, A. S.
2014-12-01
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.
DYNAMICS OF PHONON INTERACTIONS IN ORGANIC SOLIDS
Prasad, P.
1981-01-01
Investigations carried out on three aspects of phonon interactions are presented in this paper. The phonon dephasing induced by anharmonic phonon-phonon scattering is investigateci by temperature dependence of linewidths, lineshapes and frequencies in the Raman spectra. The dephasing of phonons in organic solids is found to be primarily caused by a T1-relaxation involving a three-phonon inelastic scattering. Second, a similar investigation on dephasing of vibrations within the molecule sugges...
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)
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.
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.
Coherent acoustic phonons in nanostructures investigated by asynchronous optical sampling
Dekorsy, T.; Hudert, F.; Cerna, R.; Schäfer, H.; Janke, C.; Bartels, A.; Köhler, K.; Braun, S.; Wiemer, M.; Mantl, S.
2006-10-01
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 and decay dynamics are investigated in semiconductor heterostructures, layered nanoscale materials of relevance for microelectronics, and X-ray mirrors. Changes of the optical properties of tailored semiconductor heterostructures associated with coherent phonon dynamics open the pathway for the modulation of optical signals at up to THz frequencies.
Ursu, I.; Apostol, I.; Mihâilescu, I. N.; Nistor, L. C.; Teodorescu, V. S.; Turcu, E.; Prokhorov, A. M.; Chapliev, N. I.; Konov, V. I.; Ralchenko, V. G.; Tokarev, V. N.
1982-12-01
The compounds induced on the surface of titanium and copper targets by a breakdown plasma produced by focused TEA-CO2 high-repetition frequency laser pulses was studied by transmission electron microscopy and selected area diffraction in correlation with absorptivity data determined before and after laser irradiation. The possibility of using TEA-CO2 lasers to produce complex thermal treatments was demonstrated for metallic surfaces by the modification of the physico-chemical properties at the sites of plasma action on these surfaces.
Phonon-cavity electromechanics
Mahboob, I.; Nishiguchi, K.; Okamoto, H.; Yamaguchi, H.
2012-05-01
Photonic cavities have emerged as an indispensable tool to control and manipulate harmonic motion in opto/electromechanical systems. Invariably, in these systems a high-quality-factor photonic mode is parametrically coupled to a high-quality-factor mechanical oscillation mode. This entails the demanding challenges of either combining two physically distinct systems, or else optimizing the same nanostructure for both mechanical and optical properties. In contrast to these approaches, here we show that the cavity can be realized by the second oscillation mode of the same mechanical oscillator. A piezoelectric pump generates strain-induced parametric coupling between the first and the second mode at a rate that can exceed their intrinsic relaxation rate. This leads to a mechanically induced transparency in the second mode which plays the role of the phonon cavity, the emergence of parametric normal-mode splitting and the ability to cool the first mode. Thus, the mechanical oscillator can now be completely manipulated by a phonon cavity.
International Nuclear Information System (INIS)
The subject of phonons and polaritons is introduced by a discussion of the formalism of lattice dynamics based on the Born-Oppenheimer approximation. The classical equations of motion for the displacements of the atoms of a crystal from their equilibrium positions are set up. Invariance conditions on the coupling constants are derived, and the equations of motion are solved in the harmonic approximation using a normal coordinate transformation. The procedures are illustrated by means of three simple examples. The lattice specific heat is then examined using the Debye elastic continuum model. This leads to a discussion of the frequency distribution function for the normal modes of vibration. Attention is then turned to the calculation of optical properties due to the photon-phonon interaction. A simple model is used to derive expressions for the dielectric constant and the absorption and reflectivity coefficients. These results are then applied to the discussion of polaritons. The dispersion curves for polaritons are derived from a macroscopic approach based on Maxwell's equations. The use of Raman scattering in the study of polaritons is examined in detail. The effect of a free surface is then considered, and the theory of surface polaritons is developed. The determination of surface polariton dispersion curves by means of attenuated total reflection is discussed. The presentation is concluded by a brief survey of effects due to anharmonicity. A calculation of the linear thermal expansion coefficient is presented for a simple model. (author)
Piezoelectric surface acoustical phonon amplification in graphene on a GaAs substrate
International Nuclear Information System (INIS)
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 RPA,DA scales with TBGS?1 (S=PA,DA), TBGS being the Block?Gru¨neisen temperature. In the high-T Block?Gru¨neisen regime, extrinsic PA phonon scattering is suppressed by intrinsic DA phonon scattering, where the ratio RPA/RDA scales with ?1/?(n), n being the carrier concentration. We found that only for carrier concentration n?1010cm?2, RPA/RDA>1. In the low-T Block?Gru¨neisen regime, and for n=1010cm?2, the ratio RPA/RDA scales with TBGDA/TBGPA?7.5 and RPA/RDA>1. In this regime, PA phonon dominates the electron scattering and RPA/RDA<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.
Strength of synthetic diamonds under tensile stresses produced by picosecond laser action
Abrosimov, S. A.; Bazhulin, A. P.; Bolshakov, A. P.; Konov, V. I.; Krasiuk, I. K.; Pashinin, P. P.; Ralchenko, V. G.; Semenov, A. Yu.; Sovyk, D. N.; Stuchebryukhov, I. A.; Fortov, V. E.; Khishchenko, K. V.; Khomich, A. A.
2015-01-01
Results of an experimental-theoretical study of spallation in synthetic diamonds are presented. In this study, data were first obtained on dynamic tensile strength of poly- and singlecrystal diamond samples at mechanical loads of up to 0.34 TPa and strain rates of 10-100 µs-1. Shock-wave loading was performed by 70 ps laser pulses on a Kamerton-T facility using a Nd:glass laser (second harmonics ? = 527 nm, pulse energy of up to ?3 J) at intensities of ?8 TW/cm2. The obtained maximal value of the spall strength ?16.4 GPa is 24% of the theoretical ultimate strength of diamond. Raman scattering experiments showed that a small amount of diamond was graphitized in the spall area on the backside of the sample.
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.
A METHOD FOR THE SELECTION OF DYES STABLE UNDER THE ACTION OF LASER RADIATION AND HEATING
Planner, A; Lion, Y.
1987-01-01
In this paper, we proposed a simple method of studying the dye stability by solving the dye in a transparent polymer matrix and observing the changes in colour, transparency and free radical contents appearing as a result of laser irradiation either heating in platelets of the solidified solution. Our study proves that PMMA platelets tinted with methyl red can be applied, among others, to modulate, mix and detect light beams.
Anomalous effect of phonon wind on lateral migration of excitons in ultrathin quantum CdTe/ZnTe well
International Nuclear Information System (INIS)
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
Phonon Scattering Mechanisms in Thermoelectrics
Delaire, Olivier; Ma, Jie; Li, Chen; May, Andrew; Singh, David; Ehlers, Georg; Abernathy, Doug; Sales, Brian
2014-03-01
Improving our current microscopic understanding of thermal conductivity is needed to design more efficient thermoelectric materials. Thus, establishing a complete picture of phonon dispersions and mean-free-paths is crucial to provide a realistic microscopic characterization of phonon transport, against which theories can be tested. Thanks to recent advances in instrumentation, inelastic neutron scattering can map phonon dispersions and lifetimes across the entire Brillouin zone. As our studies illustrate, such measurements provide key insights about phonon scattering mechanisms, including phonon anharmonicity, electron-phonon coupling, and scattering by point defects or nanostructures. In addition, we perform first-principles simulations of atomic dynamics, including effects of anharmonicity and electron-phonon coupling, to quantitatively model the large experimental datasets. We present results from several studies of important thermoelectric materials, illustrating how this integrated approach can be used to reach a new level of microscopic understanding of thermal conductivity. We acknowledge funding from the US Department of Energy, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, and the S3TEC Energy Frontier Research Center.
Sharp resonant phonons in two adsorbed slabs
Akjouj, A.; El Boudouti, E. H.; Sylla, B.; Djafari-Rouhani, B.; Dobrzynski, L.
1996-02-01
The existence of sharp resonant phonons in a slab separated from its semi-infinite substrate by a buffer layer is reported here. These resonant phonons appear as well-defined peaks in the phonon density of states. Such sharp resonant phonons are obtained here by a Green's function method both in the continuum elastic and in atomic approaches.
Spectral self-action of THz emission from ionizing two-color laser pulses in gases
Cabrera-Granado, Eduardo; Chen, Yxing; Babushkin, Ihar; Bergé, Luc; Skupin, Stefan
2014-01-01
The spectrum of terahertz (THz) emission in gases via ionizing two-color femtosecond pulses is analyzed by means of a semi-analytic model and finite-difference-time-domain simulations in 1D and 2D geometries. We show that produced THz signals interact with free electron trajectories and thus influence significantly further THz generation upon propagation, i.e., make the process inherently nonlocal. This self-action plays a key role in the observed strong spectral broadening ...
Antipov, A. A.; Arakelyan, S. M.; Kutrovskaya, S. V.; Kucherik, A. O.; Nogtev, D. S.; Prokoshev, V. G.
The paper deals with the techniques of creating metal-carbon components while the mixture of nanotubes (medium radius is about 70 nm) and metal nanopowders (particles radius is about 100 nm) is under the influence of laser radiation. The experiments on forming metal-carbon compounds out of mixture of nanotubes and nickel nanopowders, iron, titanium oxide. It has been shown that there is a possibility to obtain nanostructured material by sintering the target material and by forming complex coverings in the process of depositing ablation products on the cold substrate surface.
Phonon properties of plutonium pnictides
International Nuclear Information System (INIS)
The phonon properties of plutonium pnictides (PuX; X= As, Sb ) have been studied by using rigid ion (RIM) and breathing shell models (BSM) which includes breathing motion of electron 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 f-electron. Dominant ionic nature of bonding has been predicted for PuX compounds from the large LO-TO phonon splitting at zone center. We also report, for the first time specific heat for these compounds. (author)
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
Infrared-phonon-polariton resonance of the nonlinear susceptibility in GaAs.
Dekorsy, T; Yakovlev, V A; Seidel, W; Helm, M; Keilmann, F
2003-02-01
Nonlinear probing of the fundamental lattice vibration of polar crystals is shown to reveal insight into higher-order cohesive lattice forces. With a free-electron laser tunable in the far infrared we experimentally investigate the dispersion of the second-order susceptibility due to the phonon resonance in GaAs. We observe a strong resonance enhancement of second harmonic light generation at half the optical phonon frequency, and in addition a minimum at a higher frequency below the phonon frequency. Measuring this frequency and comparison to a theoretical model allows the determination of competing higher-order lattice forces. PMID:12633374
Fine Structure of the Low-Frequency Raman Phonon Bands of Single-Wall Carbon Nanotubes
Iliev, M. N.; Litvinchuk, A. P.; Arepalli, S.; Nikolaev, P.; Scott, C. D.
1999-01-01
The Raman spectra of singled-wall carbon nanotubes (SWNT) produced by laser and are process were studied between 5 and 500 kappa. The line width vs. temperature dependence of the low-frequency Raman bands between 150 and 200/ cm deviates from that expected for phonon decay through phonon-phonon scattering mechanism. The experimental results and their analysis provided convincing evidence that each of the low-frequency Raman lines is a superposition of several narrower Raman lines corresponding to tubes of nearly the same diameter. The application of Raman spectroscopy to probe the distribution of SWNT by both diameter and chirality is discussed.
Acoustic phonon dynamics in thin-films of the topological insulator Bi2Se3
Glinka, Yuri D.; Babakiray, Sercan; Johnson, Trent A.; Holcomb, Mikel B.; Lederman, David
2015-01-01
Transient reflectivity traces measured for nanometer-sized films of the topological insulator Bi2Se3 revealed GHz-range oscillations driven within the relaxation of hot carriers photoexcited with ultrashort laser pulses of 1.51 eV photon energy. These oscillations have been suggested to result from acoustic phonon dynamics, including coherent longitudinal acoustic phonons in the form of standing acoustic waves. An increase of oscillation frequency from ~35 to ~70 GHz with de...
Effect of intense chirped pulses on the coherent phonon generation in Te
Misochko, O. V.; Dekorsy, T.; Andreev, S. V.; Kompanets, V. O.; Matveets, Yu. A.; Stepanov, A. G.; Chekalin, S. V.
2007-02-01
The authors have studied the influence of chirped laser pulses on the coherent phonon generation in single crystal Te. They have shown that the pulse chirp affects the amplitude of coherent phonons with A1 symmetry in the case of intense excitation only. By varying the chirp of an intense exciting pulse, the authors demonstrated that negatively chirped pulses are almost twice more effective in the creation of lattice coherence than positively chirped pulses.
Theory of coherent acoustic phonons in InGaN/GaN multi-quantum wells
Sanders, G. D.; Stanton, C. J.; Kim, Chang-Sub
2001-01-01
A microscopic theory for the generation and propagation of coherent LA phonons in pseudomorphically strained wurzite (0001) InGaN/GaN multi-quantum well (MQW) p-i-n diodes is presented. The generation of coherent LA phonons is driven by photoexcitation of electron-hole pairs by an ultrafast Gaussian pump laser and is treated theoretically using the density matrix formalism. We use realistic wurzite bandstructures taking valence-band mixing and strain-induced piezo- electric ...
Phonon-drag effects on thermoelectric power
Wu, M. W.; Horing, N. J. M.; Cui, H. L.
1995-01-01
We carry out a calculation of the phonon-drag contribution $S_g$ to the thermoelectric power of bulk semiconductors and quantum well structures for the first time using the balance equation transport theory extended to the weakly nonuniform systems. Introducing wavevector and phonon-mode dependent relaxation times due to phonon-phonon interactions, the formula obtained can be used not only at low temperatures where the phonon mean free path is determined by boundary scatteri...
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.
Coherent phonons in condensed media
Dekorsy, Thomas; Cho, Gyu Cheon; Kurz, Heinrich
2000-01-01
The impulsive excitation and phase-sensitive detection of coherent phonons and phonon-polaritons provide a detailed insight into the dynamical properties of matter. The experiments are based on optical pump-probe techniques with femtosecond time resolution. These techniques enable the detection of amplitude and phase of the coherent lattice motion simultaneously. Frequencies in the terahertz range and dephasing times in the picosecond range can be obtained with high accuracy. Especially in se...
Thermal effects on electron-phonon interaction in silicon nanostructures
Kumar, Rajesh; Kumar, Vivek; Shukla, A. K.
2009-01-01
Raman spectra from silicon nanostructures, recorded using excitation laser power density of 1.0 kW/cm^2, is employed here to reveal the dominance of thermal effects at temperatures higher than the room temperature. Room temperature Raman spectrum shows only phonon confinement and Fano effects. Raman spectra recorded at higher temperatures show increase in FWHM and decrease in asymmetry ratio with respect to its room temperature counterpart. Experimental Raman scattering data...
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.
Establishment of correlated states in a quantum dot interacting with an acoustic phonon reservoir
HUANG Hui; Li, Gao-Xiang; Gu, Wen-ju; Ficek, Zbigniew
2014-01-01
We investigate the effects of a low frequency (acoustic) phonon bath on the dynamics of a quantum dot modelled as a cascade three-level system. We show that the phonon bath appears to the upper transition of the cascade system as a broadband reservoir of inverted rather than conventional harmonic oscillators. The action of the annihilation and creation operators of the inverted oscillator are interchanges relative to those of the usual harmonic oscillator that it serves as a...
PHONON SOFTENING IN ULTRA HEAVILY DOPED Si AND Ge
Compaan, A.; G. Contreras; Cardona, M.; Axmann, A.
1983-01-01
Multiple pulse annealing with a XeCl laser (308 nm, 10nsec, ~0.8J/cm2) has been used to produce flat concentration profiles following heavy implantations of Ga, B, P, and As at energies up to 350 keV. The influence of the free carrier concentration on the zone center phonon frequency has been studied by Raman scattering with violet and ultra-violet cw laser lines to ensure that only the implanted region was sampled. We find a softening of the zone center optic mode in Si : As (Ne ? 3 x 1021 c...
Wang, Cih-Su; Liau, Chi-Shung; Sun, Tzu-Ming; Chen, Yu-Chia; Lin, Tai-Yuan; Chen, Yang-Fang
2015-01-01
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. PMID:25758749
Scattering of phonons by dislocations
International Nuclear Information System (INIS)
By 1950, an explicit effort had been launched to use lattice thermal conductivity measurements in the investigation of defect structures in solids. This technique has been highly successful, especially when combined with the measurements of other properties such as optical absorption. One exception has been the study of dislocations. Although dislocations have a profound effect on the phonon thermal conductivity, the mechanisms of the phonon-dislocation interaction are poorly understood. The most basic questions are still debated in the literature. It therefore is pointless to attempt a quantitative comparison between an extensive accumulation of experimental data on the one hand, and the numerous theoretical models on the other. Instead, this chapter will attempt to glean a few qualitative conclusions from the existing experimental data. These results will then be compared with two general models which incorporate, in a qualitative manner, most of the proposed theories of the phonon-dislocation interaction. Until very recently, measurement of thermal conductivity was the only means available to probe the interaction between phonons and defects at phonon frequencies above the standard ultrasonic range of approx. = 109 Hz. The introductory paragraphs provide a brief review of the thermal-conductivity technique and the problems which are encountered in practice. There is also a brief presentation of the theoretical models and the complications that may occur in more realistic situations
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
Electron - phonon interaction influence on electron and phonon excitations in amorphous metals
International Nuclear Information System (INIS)
The influence of electron-phonon interaction on electron and phonon excitations in amorphous metals is examined. The equation for the gap in the electron spectrum for the transition to the superconducting state is obtained. The renormalization of the energy spectrum and damping of electron and phonon excitations due to electron-phonon interaction is considered. (orig.)
Phonon spectra in quantum wires
Directory of Open Access Journals (Sweden)
Ili? Dušan
2007-01-01
Full Text Available Green's function method, adjusted to bound crystalline structures, was applied to obtain the phonon dispersion law in quantum wires. The condition of the existence of small mechanical atom movements defining phonon spectra can be found by solving the secular equation. This problem was presented graphically for different boundary parameters. The presence of boundaries, as well as the change of boundary parameters, leads to the appearance of new properties of the layered structure. The most important feature is that, beside the allowed energy zones (which are continuous as in the bulk structure, zones of forbidden states appear. Different values of the boundary parameters lead to the appearance of lower and upper energy gaps, or dispersion branches spreading out of the bulk energy zone. The spectra of phonons in corresponding unbound structures were correlated to those in bound structures.
First principles phonon calculations in materials science
Togo, Atsushi; Tanaka, Isao
2015-01-01
Phonon plays essential roles in dynamical behaviors and thermal properties, which are central topics in fundamental issues of materials science. The importance of first principles phonon calculations cannot be overly emphasized. Phonopy is an open source code for such calculations launched by the present authors, which has been world-widely used. Here we demonstrate phonon properties with fundamental equations and show examples how the phonon calculations are applied in mate...
Ultrafast Electron-Phonon Decoupling in Graphite
Ishioka, Kunie; Hase, Muneaki; Kitajima, Masahiro; Wirtz, Ludger; Rubio Secades, Ángel; Petek, Hrvoje
2007-01-01
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...
Wide-Stopband Aperiodic Phononic Filters
Rostem, K.; Chuss, D. T.; Denis, K. L.; Wollack, E. J.
2015-01-01
We demonstrate that an aperiodic phononic structure comprising a discrete set of unit cells of different size can exhibit a complete phonon stopband. Each geometrically finite element of the set has a dispersion relation that contains bandgaps when calculated under a Bloch boundary condition. Hence, the stopband width in an aperiodic phononic filter (PnF) may readily exceed the bandgap width of a phononic crystal with a well-defined lattice constant, or a single coherence le...
Ab initio calculations of phonon dispersion and lattice dynamics in TlGaTe{sub 2}
Energy Technology Data Exchange (ETDEWEB)
Jafarova, Vusala; Orudzhev, Guseyn; Alekperov, Oktay; Mamedov, Nazim; Abdullayev, Nadir; Najafov, Arzu [Institute of Physics (Innovation Sector), 33 H. Javid ave, Baku 1143 (Azerbaijan); Paucar, Raul [Institute of Physics (Innovation Sector), 33 H. Javid ave, Baku 1143 (Azerbaijan); Chiba Institute of Technology, 2-17-1 Tsudanuma, Narashino, Chiba 275-0016 (Japan); Shim, YongGu [Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531 (Japan); Wakita, Kazuki [Chiba Institute of Technology, 2-17-1 Tsudanuma, Narashino, Chiba 275-0016 (Japan)
2015-06-15
This work reports the results of DFT-based calculations of phonon spectra of TlGaTe{sub 2}. The dispersion of phonon bands was calculated along the directions of Brillouin zone (BZ) that include symmetry points. The calculated phonon frequencies at the centre of BZ were compared with those obtained by Raman spectroscopy with the aid of a confocal laser microscopy system. A fairly good agreement between the calculated and experimental data was found. Complimentary, molar heat capacity at constant volume and Debye temperature were calculated in the range 5/500 K on the base of the obtained phonon density of states. The obtained temperature dependencies were compared with available experimental data.The results of comparison were satisfactory. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Phonon creation by gravitational waves
Sabín, Carlos; Ahmadi, Mehdi; Fuentes, Ivette
2014-01-01
We show that gravitational waves create phonons in a Bose-Einstein condensate (BEC). A traveling spacetime distortion produces particle creation resonances that correspond to the dynamical Casimir effect in a BEC phononic field contained in a cavity-type trap. We propose to use this effect to detect gravitational waves. The amplitude of the wave can be estimated applying recently developed relativistic quantum metrology techniques. We provide the optimal precision bound on the estimation of the wave's amplitude. Finally, we show that the parameter regime required to detect gravitational waves with this technique is within experimental reach.
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.
Phonon creation by gravitational waves
International Nuclear Information System (INIS)
We show that gravitational waves create phonons in a Bose-Einstein condensate (BEC). A traveling spacetime distortion produces particle creation resonances that correspond to the dynamical Casimir effect in a BEC phononic field contained in a cavity-type trap. We propose to use this effect to detect gravitational waves. The amplitude of the wave can be estimated applying recently developed relativistic quantum metrology techniques. We provide the optimal precision bound on the estimation of the wave's amplitude. Finally, we show that the parameter regime required to detect gravitational waves with this technique could be, in principle, within experimental reach in a medium-term timescale. (paper)
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.
Tunneling current induced phonon generation in nanostructures
Arseyev, P. I.; Maslova, N. S.
2006-01-01
We analyze generation of phonons in tunneling structures with two electron states coupled by electron-phonon interaction. The conditions of strong vibration excitations are determined and dependence of non-equilibrium phonon occupation numbers on the applied bias is found. For high vibration excitation levels self consistent theory for the tunneling transport is presented.
Phonon bands shapes and electron-phonon interaction in high-temperature superconductors
International Nuclear Information System (INIS)
It is reported on investigations of the phonon spectra of the high-temperature superconductors by the IR radiation reflection method. Within the framework of the model of resonance interaction of IR phonons with electron excitation spectra are analyzed phonon band shapes and is estimated contribution concrete phonon branches in the dimensionless constant of electron-phonon interaction (EPI). It is shown that the polar oscillation contribution in EPI is approximately one order higher than the nonpolar oscillation one
Kinetic description of an electron--LO-phonon system with finite phonon lifetime
International Nuclear Information System (INIS)
We study the cooling of an electron plasma from a kinetic point of view. For this purpose, a quantum theory of fluctuations is applied to derive the kinetic equations for an electron--LO-phonon system from various model Hamiltonians. A polarization approximation is provided that goes beyond perturbation theory of the electron-phonon interaction. The description of electron-phonon energy exchange is shown to be impossible with the interacting Hamiltonian in Froehlich's one-phonon form unless dissipation of the bare LO phonon is included. For a Hamiltonian including effects of the scattering of LO phonons by acoustic phonons, kinetic equations are derived. The equation for LO phonons is shown to describe the collective excitations with finite lifetime, in the limiting case of weak damping of the plasmon-phonon coupled modes. A reduction of the cooling rate similar to the ''hot-phonon'' effect is shown to occur for the case of weak coupling without assuming a steady state of the LO phonons. Finally, an electron-phonon interaction Hamiltonian in two-phonon form is considered and it is shown that electron-phonon energy exchange may be described in the polarization approximation without introducing a finite phonon lifetime
Otelaja, O. O.; Robinson, R. D.
2015-10-01
In this work, the mechanism for enhanced phonon backscattering in silicon is investigated. An understanding of phonon propagation through substrates has implications for engineering heat flow at the nanoscale, for understanding sources of decoherence in quantum systems, and for realizing efficient phonon-mediated particle detectors. In these systems, phonons that backscatter from the bottom of substrates, within the crystal or from interfaces, often contribute to the overall detector signal. We utilize a microscale phonon spectrometer, comprising superconducting tunnel junction emitters and detectors, to specifically probe phonon backscattering in silicon substrates (˜500 ?m thick). By etching phonon "enhancers" or deep trenches (˜90 ?m) around the detectors, we show that the backscattered signal level increases by a factor of ˜2 for two enhancers versus one enhancer. Using a geometric analysis of the phonon pathways, we show that the mechanism of the backscattered phonon enhancement is due to confinement of the ballistic phonon pathways and increased scattering off the enhancer walls. Our result is applicable to the geometric design and patterning of substrates that are employed in phonon-mediated detection devices.
Gastaud, C.; Redon, M.; Belland, P.; Fourrier, M.
1984-06-01
This paper reports the first use of a N2O laser for optically pumping vinyl halides, to obtain new cw submillimeter laser lines. Eighteen far-infrared (FIR) emissions have been observed in vinyl chloride, twenty five in vinyl bromide and thirty eight in vinyl flouride.
Acoustic phonon dispersion at hypersonic frequencies in Si and Ge
Kuok, M. H.; Ng, S. C.; Rang, Z. L.; Lockwood, D. J.
2000-11-01
Brillouin spectra of the longitudinal acoustic (LA) mode, traveling along the [001] direction, in silicon and germanium have been recorded in 180° backscattering using 457.9-514.5-nm laser lines. The wave velocity of the LA phonon propagating in the [001] direction was determined at hypersonic frequencies, from the measured acoustic phonon dispersion in silicon and germanium. The elastic modulus c11 of the two semiconductors has been calculated from the respective measured hypersonic wave velocities and the results are compared with values determined from lower-frequency ultrasonic and other measurements. Interestingly, the hypersonic velocities are consistently lower by ~1-2 % than the ultrasonic ones, but they generally agree within the present experimental accuracy.
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.
A source of terahertz coherent phonons
Makler, Sergio; Vasilevskiy, Mikhail; Tuyarot, Diana; Weberszpil, José; Anda, Enrique; Pastawski, Horacio
1998-01-01
Resonant tunnelling in a double-barrier heterostructure (DBHS) designed in order to produce an intense coherent emission of phonons is studied theoretically. Thisemission is achieved when the energy difference between the first excited level and the ground state in the well is close to the LO-phonon energy. The LO phonons emitted during the electron transition decay into a pair of (fLO and TA) phonons that leave the well in the [111] direction. These secondary TA phonons are coherent and f...
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.
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.
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
International Nuclear Information System (INIS)
The analysis of the local heating role in the processes of the degradation of the antireflection coatings of the nonlinear crystals when they have been used in the CW and quasi-CW YAG lasers was carried out. The broad sample range of the oxide, nitride and fluoride films deposited on the LiNbO3, BaNaNbO5, LiIO3 KTP and BBO crystals was considered. Investigation of these samples was carried out under the intense heating of their surfaces by the action of the CO2 laser pulses. The analysis of the obtained results with account for the chemical reaction thermodynamics, thermotension and other factors is presented
Mechanisms of nonequilibrium electron-phonon coupling and thermal conductance at interfaces
Energy Technology Data Exchange (ETDEWEB)
Giri, Ashutosh; Gaskins, John T.; Donovan, Brian F.; Szwejkowski, Chester; Hopkins, Patrick E., E-mail: phopkins@virginia.edu [Department of Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, Virginia 22904 (United States); Warzoha, Ronald J. [Department of Mechanical Engineering, United States Naval Academy, Annapolis, Maryland 21401 (United States); Rodriguez, Mark A.; Ihlefeld, Jon [Sandia National Laboratories, Albuquerque, New Mexico 87123 (United States)
2015-03-14
We study the electron and phonon thermal coupling mechanisms at interfaces between gold films with and without Ti adhesion layers on various substrates via pump-probe time-domain thermoreflectance. The coupling between the electronic and the vibrational states is increased by more than a factor of five with the inclusion of an ?3?nm Ti adhesion layer between the Au film and the non-metal substrate. Furthermore, we show an increase in the rate of relaxation of the electron system with increasing electron and lattice temperatures induced by the laser power and attribute this to enhanced electron-electron scattering, a transport channel that becomes more pronounced with increased electron temperatures. The inclusion of the Ti layer also results in a linear dependence of the electron-phonon relaxation rate with temperature, which we attribute to the coupling of electrons at and near the Ti/substrate interface. This enhanced electron-phonon coupling due to electron-interface scattering is shown to have negligible influence on the Kapitza conductances between the Au/Ti and the substrates at longer time scales when the electrons and phonons in the metal have equilibrated. These results suggest that only during highly nonequilibrium conditions between the electrons and phonons (T{sub e} ? T{sub p}) does electron-phonon scattering at an interface contribute to thermal boundary conductance.
Phonon anharmonicity of iron monosilicide
International Nuclear Information System (INIS)
A self-consistent thermodynamic model of the crystal lattice of FeSi is developed. In the framework of this model calculations of the heat capacity, coefficient of thermal expansion and bulk modulus of FeSi in a wide temperature range are carried out. On the basis of comparison with the experimental data, electronic contribution to the heat capacity of FeSi is obtained, the temperature dependence of which is caused by the insulator to metal transition, accompanied by disappearance of the energy gap in the electronic spectrum. We have found strong phonon anharmonicity of FeSi, which is manifested in substantial reduction of the Debye temperature and Gruneisen parameter with increasing temperature. The obtained values for the Gruneisen parameter of the crystal lattice of FeSi correlate with the estimations of the Gruneisen parameters for individual branches of the phonon spectrum of FeSi measured in neutron and synchrotron experiments
New facets of quadrupole phonon
International Nuclear Information System (INIS)
A systematic approach to even-even, odd-even, and odd-odd nuclei, based on spherical quadrupole phonons, is discussed. The truncated quadrupole-phonon model (TQM), based on SU(6) symmetry, describes even-even nuclei in the collective approximation. In the particle-TQM interaction model (PTQM), an odd single particle is coupled to the TQM core. In the SU(number) limit of the PTQM, analogs of Nilsson states appear. In the cluster-vibration model, even-even, odd-even, and odd-odd nuclei are described by coupling a few selected shell-model single particles to the quadrupole vibration (harmonic or TQM). The quasicluster-vibration model (QCVM) is an approximation of the CVM in the sense that the cluster consists of a few quasiparticles. Both the diagonalization and the diagrammatic approaches are discussed. The latter leads to generalized vibrational rules (GVR), as a consequence of the nuclear Ward identity. 106 references, 2 tables
Spectral collapse via two-phonon interactions in trapped ions
Felicetti, S.; Pedernales, J. S.; Egusquiza, I. L.; Romero, G.; Lamata, L.; Braak, D.; Solano, E.
2015-09-01
Two-photon processes have so far been considered only as resulting from frequency-matched second-order expansions of light-matter interaction, with consequently small coupling strengths. However, a variety of novel physical phenomena arises when such coupling values become comparable to the system characteristic frequencies. Here, we propose a realistic implementation of two-photon quantum Rabi and Dicke models in trapped-ion technologies. In this case, effective two-phonon processes can be explored in all relevant parameter regimes. In particular, we show that an ion chain under bichromatic laser drivings exhibits a rich dynamics and highly counterintuitive spectral features, such as interaction-induced spectral collapse.
Topologically protected elastic waves in phononic metamaterials
Mousavi, S. Hossein; Khanikaev, Alexander B.; Wang, Zheng
2015-11-01
Surface waves in topological states of quantum matter exhibit unique protection from backscattering induced by disorders, making them ideal carriers for both classical and quantum information. Topological matters for electrons and photons are largely limited by the range of bulk properties, and the associated performance trade-offs. In contrast, phononic metamaterials provide access to a much wider range of material properties. Here we demonstrate numerically a phononic topological metamaterial in an elastic-wave analogue of the quantum spin Hall effect. A dual-scale phononic crystal slab is used to support two effective spins for phonons over a broad bandwidth, and strong spin-orbit coupling is realized by breaking spatial mirror symmetry. By preserving the spin polarization with an external load or spatial symmetry, phononic edge states are shown to be robust against scattering from discrete defects as well as disorders in the continuum, demonstrating topological protection for phonons in both static and time-dependent regimes.
Topologically protected elastic waves in phononic metamaterials.
Mousavi, S Hossein; Khanikaev, Alexander B; Wang, Zheng
2015-01-01
Surface waves in topological states of quantum matter exhibit unique protection from backscattering induced by disorders, making them ideal carriers for both classical and quantum information. Topological matters for electrons and photons are largely limited by the range of bulk properties, and the associated performance trade-offs. In contrast, phononic metamaterials provide access to a much wider range of material properties. Here we demonstrate numerically a phononic topological metamaterial in an elastic-wave analogue of the quantum spin Hall effect. A dual-scale phononic crystal slab is used to support two effective spins for phonons over a broad bandwidth, and strong spin-orbit coupling is realized by breaking spatial mirror symmetry. By preserving the spin polarization with an external load or spatial symmetry, phononic edge states are shown to be robust against scattering from discrete defects as well as disorders in the continuum, demonstrating topological protection for phonons in both static and time-dependent regimes. PMID:26530426
Phonon-phonon interaction in CdGa{sub 2}Se{sub 2} single crystals
Energy Technology Data Exchange (ETDEWEB)
Kerimova, T.G.; Abdullayev, N.A.; Kengerlinski, L.Y.; Mamedova, I.A.; Ibragimov, N.I. [Institute of Physics, Azerbaijan National Academy of Sciences, H. Javid ave. 131, Baku-1143 (Azerbaijan)
2015-06-15
Raman scattering spectra of CdGa{sub 2}Se{sub 4} single crystals were measured in temperature range 8-300 K. From the temperature dependence of optical phonons of B (196 cm{sup -1}) and E (246 cm{sup -1}) symmetry type, the lattice deformation and phonon-phonon interaction contributions to the temperature coefficient of phonon shift were calculated. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Phonon-assisted resonant tunneling through a triple-quantum-dot: a phonon-signal detector
Shen, X. Y.; DONG Bing; Lei, X. L.
2007-01-01
We study the effect of electron-phonon interaction on current and zero-frequency shot noise in resonant tunneling through a series triple-quantum-dot coupling to a local phonon mode by means of a nonperturbative mapping technique along with the Green function formulation. By fixing the energy difference between the first two quantum dots to be equal to phonon frequency and sweeping the level of the third quantum dot, we find a largely enhanced current spectrum due to phonon ...
Phonon generation by current-carrying nanostructures
Totland, H.; Galperin, Y M; Gurevich, V. L.
1998-01-01
We calculate the rate of acoustic phonon generation by a current-carrying, ballistic quantum channel, defined in a two-dimensional electron gas by a split-gate. Both uniform and nonuniform channels are considered. The generation rate of acoustic phonons of a particular frequency and direction of propagation is a steplike function of the applied bias voltage, with threshold voltages that are calculated in the paper. The emitted phonons have a characteristic angular distributi...
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 ...
Maximizing phonon thermal conductance for ballistic membranes
Kühn, T; Maasilta, I. J.
2007-01-01
At low temperatures, phonon scattering can become so weak that phonon transport becomes ballistic. We calculate the ballistic phonon conductance G for membranes using elasticity theory, considering the transition from three to two dimensions. We discuss the temperature and thickness dependence and especially concentrate on the issue of material parameters. For all membrane thicknesses, the best conductors have, counter-intuitively, the lowest speed of sound.
Phonon drag effects for polyvalent metals: Aluminium
International Nuclear Information System (INIS)
The theory of the phonon-drag contribution to the electron-phonon scattering resistivity is generalized to the polyvalent metals, taking explicit account of the multiple-planewave character of the pseudo-wavefunction and the non-sphericity of the Fermi surface. It is shown that, in marked contrast to the situation for the alkali metals, phonon-drag effects are negligible for the polyvalent metals. (orig.)
Phonon drag effects for polyvalent metals: aluminium
Energy Technology Data Exchange (ETDEWEB)
Brody, M.; Kaveh, M.; Wiser, N. (Bar-Ilan Univ., Ramat-Gan (Israel). Dept. of Physics)
The theory of the phonon-drag contribution to the electron-phonon scattering resistivity is generalized to the polyvalent metals, taking explicit account of the multiple-planewave character of the pseudo-wavefunction and the non-sphericity of the Fermi surface. It is shown that, in marked contrast to the situation for the alkali metals, phonon-drag effects are negligible for the polyvalent metals.
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)
Maximizing phonon thermal conductance for ballistic membranes
Kühn, T.; Maasilta, I. J.
2007-12-01
At low temperatures, phonon scattering can become so weak that phonon transport becomes ballistic. We calculate the ballistic phonon conductance G for membranes using elasticity theory, considering the transition from three to two dimensions. We discuss the temperature and thickness dependence and especially concentrate on the issue of material parameters. For all membrane thicknesses, the best conductors have, counter-intuitively, the lowest speed of sound.
Maximizing phonon thermal conductance for ballistic membranes
Energy Technology Data Exchange (ETDEWEB)
Kuehn, T; Maasilta, I J [Department of Physics, Nanoscience Center, P. O. Box 35, FIN-40014, University of Jyvaeskylae (Finland)
2007-12-15
At low temperatures, phonon scattering can become so weak that phonon transport becomes ballistic. We calculate the ballistic phonon conductance G for membranes using elasticity theory, considering the transition from three to two dimensions. We discuss the temperature and thickness dependence and especially concentrate on the issue of material parameters. For all membrane thicknesses, the best conductors have, counter-intuitively, the lowest speed of sound.
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)
Polaronic Signatures in Phonon Isotopic Shifts
International Nuclear Information System (INIS)
The effect of O(16) by O(18) isotopic substitution in the excitation spectrum of a model electron-phonon Hamiltonian, previously used to describe the dynamics of the O(4)-Cu(1)-O(4) cluster in YBa2Cu3O7, is presented. This model includes electronic correlations and electron-phonon interactions, exhibiting the presence of polaron tunneling. The calculated isotopic shifts of phonon excitations differ from those found using harmonic or anharmonic potentials, and are consistent results of optical measurements of c-axis phonons. The isotopic substitution changes the dynamics of polaron tunneling and produces a change in the local structure
Polaronic signatures in phonon isotopic shifts
International Nuclear Information System (INIS)
The effect of O(16) by O(18) isotopic substitution in the excitation spectrum of a model electron-phonon Hamiltonian, previously used to describe the dynamics of the O(4)-Cu(1)-O(4) cluster in YBa2Cu3O7, is presented. This model includes electronic correlations and electron-phonon interactions, exhibiting the presence of polaron tunneling. The calculated isotopic shifts of phonon excitations differ from those found using harmonic or anharmonic potentials, and are consistent results of optical measurements of c-axis phonons. The isotopic substitution changes the dynamics of polaron tunneling and produces a change in the local structure
Polaronic signatures in phonon isotopic shifts
Energy Technology Data Exchange (ETDEWEB)
Mustre de Leon, J.; Coss, R. de; Rubio-Ponce, A. [Inst. Politecnico Nacional, Merida (Mexico). Centro de Investigacion y de Estudios Avanzados; Bishop, A.R.; Trugman, S.A. [Los Alamos National Lab., NM (United States)
1998-12-31
The effect of O(16) by O(18) isotopic substitution in the excitation spectrum of a model electron-phonon Hamiltonian, previously used to describe the dynamics of the O(4)-Cu(1)-O(4) cluster in YBa{sub 2}Cu{sub 3}O{sub 7}, is presented. This model includes electronic correlations and electron-phonon interactions, exhibiting the presence of polaron tunneling. The calculated isotopic shifts of phonon excitations differ from those found using harmonic or anharmonic potentials, and are consistent results of optical measurements of c-axis phonons. The isotopic substitution changes the dynamics of polaron tunneling and produces a change in the local structure.
Polaronic Signatures in Phonon Isotopic Shifts
Energy Technology Data Exchange (ETDEWEB)
de Leon, J.M.; de Coss, R.; Rubio-Ponce, A.; Bishop, A.R.; Trugman, S.A.
1998-06-01
The effect of O(16) by O(18) isotopic substitution in the excitation spectrum of a model electron-phonon Hamiltonian, previously used to describe the dynamics of the O(4)-Cu(1)-O(4) cluster in YBa{sub 2}Cu{sub 3}O{sub 7}, is presented. This model includes electronic correlations and electron-phonon interactions, exhibiting the presence of polaron tunneling. The calculated isotopic shifts of phonon excitations differ from those found using harmonic or anharmonic potentials, and are consistent results of optical measurements of c-axis phonons. The isotopic substitution changes the dynamics of polaron tunneling and produces a change in the local structure.
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
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].
International Nuclear Information System (INIS)
In order to fully understand nanoscale heat transport it is necessary to spectrally characterize phonon transmission in nanostructures. Toward this goal we have developed a microfabricated phonon spectrometer. We utilize microfabricated superconducting tunnel junction (STJ)-based phonon transducers for the emission and detection of tunable, non-thermal and spectrally resolved acoustic phonons, with frequencies ranging from ?100 to ?870 GHz, in silicon microstructures. We show that phonon spectroscopy with STJs offers a spectral resolution of ?15–20 GHz, which is ?20 times better than thermal conductance measurements, for probing nanoscale phonon transport. The STJs are Al–AlxOy–Al tunnel junctions and phonon emission and detection occurs via quasiparticle excitation and decay transitions that occur in the superconducting films. We elaborate on the design geometry and constraints of the spectrometer, the fabrication techniques and the low-noise instrumentation that are essential for successful application of this technique for nanoscale phonon studies. We discuss the spectral distribution of phonons emitted by an STJ emitter and the efficiency of their detection by an STJ detector. We demonstrate that the phonons propagate ballistically through a silicon microstructure, and that submicron spatial resolution is realizable in a design such as ours. Spectrally resolved measurements of phonon transport in nanoscale structures and nanomaterials will further the engineering and exploitation of phonons, and thus have important ramifications for nanoscale thermal transport as well as the burgeoning field of nanophononics. (paper)
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.
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.
International Nuclear Information System (INIS)
The author creates an experimental complex for studying the physics and mechanism of destruction of carbon-graphite heat-shielding coatings in a nitrogen-plasma flow under the action of pulsed-laser radiation of moderate power enabling the evaluation of physicochemical nonequilibrium processes in the gaseous and condensed phases and the effect of the latter on the ablation stability of the material as a whole. A diagram of the experimental complex is shown. The optical scheme for laser sounding of the boundary layer on the surface of destruction, performed in order to evaluate the coefficient of absorption of the radiant component, consisted of a smoothly tunable narrow-band LZhI-402 dye laser. The effect of condensation of carbon vapor and hardening of the surface by the products of condensation in the region of burned spots as well as maximum absorption of the radiant component of the incident flux on the polyatomic molecules of the type C3 were observed
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.
International Nuclear Information System (INIS)
We report the spatio-temporal separation of electron and phonon thermal transports in nanostructured magnetic L10 FePt films at the nanometer length scale and the time domain of tens of picosecond, when heated with a pulsed laser. We demonstrate that lattice dynamics measured using the picosecond time-resolved laser pump/X-ray probe method on the FePt (002) and Ag (002) Bragg reflections from different layers provided the information of nanoscale thermal transport between the layers. We also describe how the electron and phonon thermal transports in nanostructured magnetic thin films were separated.
Dynamical stabilization by phonon-phonon interaction exemplified in cubic zirconia
Energy Technology Data Exchange (ETDEWEB)
Souvatsos, [etrps G [Los Alamos National Laboratory; Rudin, Sven P [Los Alamos National Laboratory
2008-01-01
Cubic zirconia exhibits a soft phonon mode (X{sup -}{sub 2}), which becomes dynamically unstable at low temperatures. Previous ab initio invest.igations into the temperature-induced stabilization of the soft mode treated it as an independent anharmonic oscillator. Calculations presented here, using the self consistent ab initio lattice dynamical (SCAILD) method to evaluate the phonons at 2570 K, show that the soft mode should not be treated independently of other phonon modes. Phonon-phonon interactions stabilize the X{sup -}{sub 2} mode. Furthermore, the effective potential experienced by the mode takes on a quadratic form.
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.
Energy Technology Data Exchange (ETDEWEB)
Tuchina, E S; Petrov, P O; Kozina, K V; Tuchin, V V [N.G. Chernyshevsky Saratov State University, Saratov (Russian Federation); Ratto, F; Pini, R [Institute of Applied Physics ' Nello Carrara' , National Research Council, via Madonna del Piano 10 50019 Sesto Fiorentino (Italy); Centi, S [University of Florence, Dept. Experimental and Clinical Biomedical Sciences, viale Morgagni 50, 50134 Firenze (Italy)
2014-07-31
The effect of NIR laser radiation (808 nm) and gold nanorods on the cells of two strains of Staphylococcus aureus, one of them being methicillin-sensitive and the other being methicillinresistant, is studied. Nanorods having the dimensions 10 × 44 nm with the absorption maximum in the NIR spectral region, functionalised with human immunoglobulins IgA and IgG, are synthesised. It is shown that the use of nanoparticles in combination with NIR irradiation leads to killing up to 97% of the population of microorganisms. (laser biophotonics)
Improved cw laser action on the 118.6- and 220-?m H20 transitions using helium and hydrogen
International Nuclear Information System (INIS)
The power of a cw water-vapor laser operating on the far-infrared transitions of 118.6 and 220 ?m has been considerably improved by the use of helium and hydrogen gas additives. The laser power on the 118.6-?m transition has been increased by an order of magnitude from 1.5 to 15 mW in a nonoptimized cavity. For the same discharge current of 1.8 A, the power on the 220-?m line has been increased from 0.26 to 1.3 mW
International Nuclear Information System (INIS)
The effect of NIR laser radiation (808 nm) and gold nanorods on the cells of two strains of Staphylococcus aureus, one of them being methicillin-sensitive and the other being methicillinresistant, is studied. Nanorods having the dimensions 10 × 44 nm with the absorption maximum in the NIR spectral region, functionalised with human immunoglobulins IgA and IgG, are synthesised. It is shown that the use of nanoparticles in combination with NIR irradiation leads to killing up to 97% of the population of microorganisms. (laser biophotonics)
International Nuclear Information System (INIS)
Within the framework of the macroscopic dielectric continuum model the longitudinal (LO) phonon model are derived for a cylindrical semiconductor quantum wire made of semiconductor 1 (well material) embedded in another finite semiconductor 2 (barrier material). The phonon states of models are given by solving the generalized Born-Huang equation. It is shown that there may exist four types of longitudinal optical phonon model according to the concrete materials forming the wire. The dispersion equations for phonon frequencies with wave-vector components parallel to the wire are obtained. After having quantized the phonon field we derive the Frohlich Hamiltonian describing the electron-LO-phonon interaction. The influence of the thickness of the barrier layer as well as the thin metallic shell on the phonon frequencies and their interaction with electrons is studied. (author)
Enhanced electron-phonon coupling for a semiconductor charge qubit in a surface phonon cavity
Chen, J. C. H.; Sato, Y.; Kosaka, R.; Hashisaka, M.; Muraki, K.; Fujisawa, T.
2015-10-01
Electron-phonon coupling is a major decoherence mechanism, which often causes scattering and energy dissipation in semiconductor electronic systems. However, this electron-phonon coupling may be used in a positive way for reaching the strong or ultra-strong coupling regime in an acoustic version of the cavity quantum electrodynamic system. Here we propose and demonstrate a phonon cavity for surface acoustic waves, which is made of periodic metal fingers that constitute Bragg reflectors on a GaAs/AlGaAs heterostructure. Phonon band gap and cavity phonon modes are identified by frequency, time and spatially resolved measurements of the piezoelectric potential. Tunneling spectroscopy on a double quantum dot indicates the enhancement of phonon assisted transitions in a charge qubit. This encourages studying of acoustic cavity quantum electrodynamics with surface phonons.
Enhanced electron-phonon coupling for a semiconductor charge qubit in a surface phonon cavity.
Chen, J C H; Sato, Y; Kosaka, R; Hashisaka, M; Muraki, K; Fujisawa, T
2015-01-01
Electron-phonon coupling is a major decoherence mechanism, which often causes scattering and energy dissipation in semiconductor electronic systems. However, this electron-phonon coupling may be used in a positive way for reaching the strong or ultra-strong coupling regime in an acoustic version of the cavity quantum electrodynamic system. Here we propose and demonstrate a phonon cavity for surface acoustic waves, which is made of periodic metal fingers that constitute Bragg reflectors on a GaAs/AlGaAs heterostructure. Phonon band gap and cavity phonon modes are identified by frequency, time and spatially resolved measurements of the piezoelectric potential. Tunneling spectroscopy on a double quantum dot indicates the enhancement of phonon assisted transitions in a charge qubit. This encourages studying of acoustic cavity quantum electrodynamics with surface phonons. PMID:26469629
Probing phonon surface scattering in nanostructures
Robinson, Richard; Hertzberg, Jared; Otelaja, Obafemi
2012-02-01
In insulating materials, heat is transmitted by atomic vibrations (``phonons''). In nanostructured materials such as nanowires and nanosheets, the characteristic length scale of a material can be less than the mean free path of a phonon. The phonon transport is then drastically altered and becomes dominated by scattering from surfaces. We demonstrate a method to assess the scattering rate and transmission factor of phonons traversing a silicon nanosheet. Generation and detection of phonons is accomplished by a superconducting tunnel junction attached to the silicon nanostructure and operated at a temperature of 0.3K. Decay of excited states in the superconductor is employed as a tunable narrow-band source of phonons [1,2]. This tunable source enables investigation of the phonon mean free path as a function of phonon frequency and surface roughness, for frequencies from ˜100 GHz to ˜500 GHz in nanosheets 100 to 200 nm thick. This work is supported by DOE (DE-SC0001086). [4pt] [1] H. Kinder. Phys. Rev. Lett. 28, 1564 (1972)[0pt] [2] J. B. Hertzberg et al, Rev. Sci. Inst. 82, 104905 (2011).
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.
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.
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-drag effects on thermoelectric power
Wu Ming Wei; Cui, H L
1995-01-01
We carry out a calculation of the phonon-drag contribution S_g to the thermoelectric power of bulk semiconductors and quantum well structures for the first time using the balance equation transport theory extended to the weakly nonuniform systems. Introducing wavevector and phonon-mode dependent relaxation times due to phonon-phonon interactions, the formula obtained can be used not only at low temperatures where the phonon mean free path is determined by boundary scattering, but also at high temperatures. In the linear transport limit, S_g is equivalent to the result obtained from the Boltzmann equation with a relaxation time approximation. The theory is applied to experiments and agreement is found between the theoretical predictions and experimental results. The role of hot-electron effects in S_g is discussed. The importance of the contribution of S_g to thermoelectric power in the hot-electron transport condition is emphasized.
Calibration of a Microfabricated Phonon Spectrometer
Hertzberg, Jared; Otelaja, Obafemi; Robinson, Richard
2012-02-01
Non-thermal distributions of phonons may be locally excited and detected in silicon micro- and nanostructures by decay of quasiparticles injected into an adjacent superconducting tunnel junction [1]. Using this technique, narrow frequency bands of phonons may be isolated and applied to investigate phonon transport through nanostructures at sub-kelvin temperatures [2]. In our prototype phonon spectrometer we have demonstrated spatial resolution below 1 micron and frequency resolution of 10 GHz. We describe ways to control the spatial resolution, frequency resolution, frequency range, dynamic range and signal-to-noise ratio in this technique, by using different superconducting materials in the tunnel junctions and by inserting absorber materials into the phonon transmission path. This work is supported by DOE (DE-SC0001086). [4pt] [1] H. Kinder. Phys. Rev. Lett. 28, 1564 (1972)[0pt] [2] J. B. Hertzberg et al, Rev. Sci. Inst. 82, 104905 (2011).
Phonon dynamics of plutonium chalcogenides and pnictides
Energy Technology Data Exchange (ETDEWEB)
Arya, Balwant S., E-mail: bsarya13@yahoo.co [Department of Physics, Govt. Narmada College, Hoshangabad 461001 (India); Department of Physics, University of Bhopal, Bhopal 462026 (India); Aynyas, Mahendra [Department of Physics, S.V. College, Bhopal 462030 (India); Sanyal, S.P. [Department of Physics, University of Bhopal, Bhopal 462026 (India)
2009-09-15
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.
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.
Characterization of phononic heterostructures by infrared thermography
Exarchos, D. A.; Tragazikis, I.; Psarobas, I.; Matikas, T. E.
2015-06-01
This work deals with the development of a new class of metamaterials based on phononic composite structures that can offer vibration protection in a wide range of applications. Such phononic heterostructures is a class of phononic crystals that exhibit spectral gaps with lattice constants of a few orders of magnitude smaller than the relevant acoustic wavelength. The design of a phononic composite metamaterial is based on the formation of omnidirectional frequency gaps. This is very much relevant to the dimensionality of a finite slab of the crystal. In this respect, two dimensional structures are used to cut off acoustic waves. In this study, different infrared thermography techniques were used in order to assess the phononic structure's geometry, as well as to determine the thermal properties of the metamaterial.
Phononic crystals and elastodynamics: Some relevant points
International Nuclear Information System (INIS)
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
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
Ryabykh, T. P.; Karu, Tiina I.
1996-01-01
Luminol-amplified chemiluminescence was recorded after irradiation with laser radiation at 632.8 and 820 nm. The following cellular systems were used as objects of irradiation: blood of healthy donors, blood of patients with colon cancer or acute respiratory illness, blast cells of patients with acute leukemia. The irradiation was suppressing the oxidative metabolism of cellular systems under study.
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)
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)
Coherent gigahertz phonons in Ge2Sb2Te5 phase-change materials.
Hase, Muneaki; Fons, Paul; Kolobov, Alexander V; Tominaga, Junji
2015-12-01
Using [Formula: see text]40 fs ultrashort laser pulses, we investigate the picosecond acoustic response from a prototypical phase change material, thin Ge2Sb2Te5 (GST) films with various thicknesses. After excitation with a 1.53 eV-energy pulse with a fluence of [Formula: see text]5 mJ cm(-2), the time-resolved reflectivity change exhibits transient electronic response, followed by a combination of exponential-like strain and coherent acoustic phonons in the gigahertz (GHz) frequency range. The time-domain shape of the coherent acoustic pulse is well reproduced by the use of the strain model by Thomsen et al 1986 (Phys. Rev. B 34 4129). We found that the decay rate (the inverse of the relaxation time) of the acoustic phonon both in the amorphous and in the crystalline phases decreases as the film thickness increases. The thickness dependence of the acoustic phonon decay is well modeled based on both phonon-defect scattering and acoustic phonon attenuation at the GST/Si interface, and it is revealed that those scattering and attenuation are larger in crystalline GST films than those in amorphous GST films. PMID:26570991
Coherent gigahertz phonons in Ge2Sb2Te5 phase-change materials
Hase, Muneaki; Fons, Paul; Kolobov, Alexander V.; Tominaga, Junji
2015-12-01
Using ? 40 fs ultrashort laser pulses, we investigate the picosecond acoustic response from a prototypical phase change material, thin Ge2Sb2Te5 (GST) films with various thicknesses. After excitation with a 1.53 eV-energy pulse with a fluence of ? 5 mJ cm?2, the time-resolved reflectivity change exhibits transient electronic response, followed by a combination of exponential-like strain and coherent acoustic phonons in the gigahertz (GHz) frequency range. The time-domain shape of the coherent acoustic pulse is well reproduced by the use of the strain model by Thomsen et al 1986 (Phys. Rev. B 34 4129). We found that the decay rate (the inverse of the relaxation time) of the acoustic phonon both in the amorphous and in the crystalline phases decreases as the film thickness increases. The thickness dependence of the acoustic phonon decay is well modeled based on both phonon-defect scattering and acoustic phonon attenuation at the GST/Si interface, and it is revealed that those scattering and attenuation are larger in crystalline GST films than those in amorphous GST films.
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.
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.
Q-switch pumped InSb spin-flip Raman laser action under pulsed electric field conditions
International Nuclear Information System (INIS)
Temporal synchronization of a Q-switch spin-flip Raman laser pulse (SFR) with a voltage pulse across an InSb sample leads to an enhancement of the Stokes output and to a shortening of the spin-flip pulse duration. During the end of the voltage pulse with a fall time <= 30 ns, the Stokes output power increased by a factor 2-3 while the SFR pulse duration decreased to 50 ns. (orig.)
Indian Academy of Sciences (India)
R K Khanna; R C Chouhan
2003-10-01
A somewhat more general analysis for solving spatial propagation characteristics of intense Gaussian beam is presented and applied to the laser beam propagation in step-index pro?le as well as parabolic pro?le dielectric ?bers with Kerr non-linearity. Considering self-action due to saturating and non-saturating non-linearity in the refractive index, a general theory has been developed without any kind of power series expansion for the dielectric constant as is usually done in other theories that make use of paraxial approximation. Result of the steady state self-focusing analysis indicates that the Kerr non-linearity acts as a perturbation on the radial inhomogeneity due to ?ber geometry. Analysis indicates that the paraxial rays and peripheral rays focus at different points, indicating aberration effect. Calculated critical power matches with the experimentally reported result.
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 localization in ion-irradiated semiconductors
Energy Technology Data Exchange (ETDEWEB)
Ishioka, K.; Nakamura, K.G.; Kitajima, M. [National Research Inst. for Metals, Tsukuba, Ibaraki (Japan)
1996-03-01
We have carried out real-time Raman measurements on the (100) surfaces of GaAs and Ge under 5 keV He{sup +} irradiation, and investigated the kinetics of the lattice disordering during ion irradiation by estimating the correlation length of the longitudinal optical phonon from the Raman spectra. The phonon correlation length of GaAs has been seen to decrease inversely proportional to the cubic root of ion fluence. The result implies a linear correspondence of the phonon correlation length to the mean distance between the defects in GaAs, and indicates localization of phonon due to defect formation induced by ion irradiation. The Raman spectral change of Ge also suggests phonon localization while under ion irradiation. We have performed real-time Raman measurements on a Si(111) surface under irradiation by 5 keV He{sup +}, Ar{sup +}, and Kr{sup +} ions. Little change has been observed in the Raman line shape, resulting from the optical penetration depth too large compared with the projected range of ions in the present experimental condition. The intensity of the optical phonon peak has been seen to decrease with increasing ion fluence. The reduction of the phonon line intensity is interpreted as an increase in the absorption of the light in the damaged region near the surface, being dominated by the total number of the defects within the optical penetration depth. (author)
Nonlinear response function for two-phonon polaritons
International Nuclear Information System (INIS)
A nonlinear response function describing three-polariton processes (two single-phonon polaritons and two-phonon polariton) is derived for a system of interaction phonons and photons. The main features of the nonlinear optical spectra in the two-phonon polariton region are analyzed. (author). 17 refs
International Nuclear Information System (INIS)
Coherent phononic oscillations in Bi and Ag nanowires were studied with a femtosecond pump-probe technique. In Bi nanowires laser pulses of 50 fs excited simultaneously acoustic oscillations at a frequency of about 9.5 GHz and optical phonons in the THz range. The transmission of nanowires on a glass substrate and the light scattered from free standing nanowires were measured. In Ag nanowires laser-induced acoustic oscillations at different excitation levels were studied. The observed reduction of the oscillation frequency at higher pump energy was related to a transient softening of the material. This was directly confirmed for optical phonons by experiments with a pre-pump pulse of variable energy, producing different excitation densities.
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...
Acoustic superfocusing by solid phononic crystals
Energy Technology Data Exchange (ETDEWEB)
Zhou, Xiaoming [CNRS, Institut Jean Lamour, Vandoeuvre-lès-Nancy F-54506 (France); Institut Jean Lamour, University of Lorraine, Boulevard des Aiguillettes, BP 70239, Vandoeuvre-lès-Nancy 54506 (France); Key Laboratory of Dynamics and Control of Flight Vehicle, Ministry of Education and School of Aerospace Engineering, Beijing Institute of Technology, Beijing 100081 (China); Assouar, M. Badreddine, E-mail: Badreddine.Assouar@univ-lorraine.fr; Oudich, Mourad [CNRS, Institut Jean Lamour, Vandoeuvre-lès-Nancy F-54506 (France); Institut Jean Lamour, University of Lorraine, Boulevard des Aiguillettes, BP 70239, Vandoeuvre-lès-Nancy 54506 (France)
2014-12-08
We propose a solid phononic crystal lens capable of acoustic superfocusing beyond the diffraction limit. The unit cell of the crystal is formed by four rigid cylinders in a hosting material with a cavity arranged in the center. Theoretical studies reveal that the solid lens produces both negative refraction to focus propagating waves and surface states to amplify evanescent waves. Numerical analyses of the superfocusing effect of the considered solid phononic lens are presented with a separated source excitation to the lens. In this case, acoustic superfocusing beyond the diffraction limit is evidenced. Compared to the fluid phononic lenses, the solid lens is more suitable for ultrasonic imaging applications.
The hot phonon spot in the film
International Nuclear Information System (INIS)
The possibility of hot phonon spot (HPS) formation and the further study of dynamics of HPS development at the excitation of phonon system as a result of cooling down of the photoexcited current carriers in the semiconductor films are discussed. The adequately defective and thick films are considered. It is assumed that the loss of energy via boundaries may be neglected and the density of states of excited phonons through the depth of film will be uniform. (author). 3 refs, 2 figs, 3 tabs
Phonon bandshapes and electron-phonon interaction in high-Tc superconductors
International Nuclear Information System (INIS)
Phonon spectra of the single-crystal high-Tc superconductors were studied by means of IR-reflection spectroscopy, with the incident radiation polarized perpendicularly to the conducting cuprate planes. A model of the infrared phonons resonantly interacting with the electron-excitation spectrum is used to analyze the phonon bandshapes and to estimate the contributions from the particular phonon branches to the dimensionless electron-photon coupling constant ? (EPI). Comparison of the obtained data with the results of Raman studies of the electron-phonon interaction (EPI) shows that the contribution to EPI from the polar vibrations is almost an order of magnitude higher than that from the nonpolar modes. Based on this, the conclusion is made that EPI has a long-range character. An estimate given for the total ? magnitude confirms the strong electron-phonon coupling (? > 2). 12 refs., 10 figs., 3 tabs
Garmire, Elsa; Rebane, Karl K
2012-01-01
Session 1 Elementary Excitations and Excitation Transport.- Picosecond Resolved Optically Driven Phonon Dynamics.- Relaxation and Propagation of High Frequency Phonons in Thin Crystalline Plates After Intense Laser Pumping.- Evolution in Real Time and Space of Short Polariton Pulses in Crystals.- Quasielastic Electronic Light Scattering in Semiconductors at Low Concentrations of Current Carriers.- Condensed Matter Science With Far Infra Red Free Electron Lasers (Abstract).- Nonequilibrium Terahertz Range Acoustic Phonons and Luminescence of Excitons in Semiconductors.- Session II Optical Prope
Coupled Bloch-Phonon Oscillations in Semiconductor Superlattices
Dekorsy, Thomas; Bartels, Albrecht; Kurz, Heinrich; Köhler, Klaus; Hey, Rudolf; Ploog, Klaus
2000-01-01
We investigate coherent Bloch oscillations in GaAs/AlxGa1-xAs superlattices with electronic miniband widths larger than the optical phonon energy. In these superlattices the Bloch frequency can be tuned into resonance with the optical phonon. Close to resonance a direct coupling of Bloch oscillations to LO phonons is observed which gives rise to the coherent excitation of LO phonons. The density necessary for driving coherent LO phonons via Bloch oscillations is about 2 orders of magnitude sm...
Tailoring the Phonon Band Structure in Binary Colloidal Mixtures
Fornleitner, J.; Kahl, G; Likos, C. N.
2010-01-01
We analyze the phonon spectra of periodic structures formed by two-dimensional mixtures of dipolar colloidal particles. These mixtures display an enormous variety of complex ordered configurations [J. Fornleitner {\\it et al.}, Soft Matter {\\bf 4}, 480 (2008)], allowing for the systematic investigation of the ensuing phonon spectra and the control of phononic gaps. We show how the shape of the phonon bands and the number and width of the phonon gaps can be controlled by chang...
Monolithic Phononic Crystals with a Surface Acoustic Band Gap from Surface Phonon-Polariton Coupling
Yudistira, D.; Boes, A.; Djafari-Rouhani, B.; Pennec, Y.; Yeo, L. Y.; Mitchell, A.; Friend, J. R.
2014-11-01
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.
Energy Technology Data Exchange (ETDEWEB)
Richardson, Martin; Hammons, Dennis; Eichenholz, Jason [Laser Energetics inc., Oviedo (United States); Chai, Bruce [Crystal Photonics Inc., Sandford (United States); Ye, Qing [Corning Research Laboratories, Corning (United States); Jang, Won [Hanseo University, Seosan (Korea, Republic of); Shah, Lawrence [University of Central Florida, Orlando (United States)
1999-07-01
We review new developments with a new laser host material, YCa{sub 4}O(BO{sub 3}){sub 3} or YCOB. Lasers based on this host material will open new opportunities for the development of compact, high-power, frequency-agile visible and near IR laser sources, as well as sources for ultrashort pulses. Efficient diode-pumped laser action with both Nd-doped and Yb-doped YCOB has already been demonstrated. Moreover, since these materials are biaxial, and have high nonlinear optical coefficients, they have become the first laser materials available as efficient self-frequency-doubled lasers, capable of providing tunable laser emission in several regions of the visible spectrum. Self-frequency doubling eliminates the need for inclusion of a nonlinear optical element within or external to the laser resonator. These laser materials possess excellent thermal and optical properties, have high laser-damage thresholds, and can be grown to large sizes. In addition they are non-hygroscopic. They therefore possess all the characteristics necessary for laser materials required in rugged, compact systems. Here we summarize the rapid progress made in the development of this new class of lasers, and review their potential for a number of applications. (author)
Phonon-Drag Thermopower at High Temperatures
Vdovenkov, V A
1999-01-01
The adiabatic cristal model is offered. It is shown that springy nuclei oscillations relatively electronic envelops and waves of such oscillations (inherent oscillations and waves) may exist in crystals. The analysis of experimental temperature dependencies of resistivity in semiconductors with electron-vibrational centres has shown that inherent oscillations effectively interact with crystalline phonons as well as with electrons and holes, creating powerful interaction of electrons and holes with phonons. The experimental narrow peaks of phonon-drag thermoelectric power at Debye temperatures from 77K to 700K confirm existence of inherent oscillations waves in crystals. Inherent oscillations and waves gives rise to strong electron-phonon interaction and probably can bring about superconductivity at temperatures as below so and well above room temperature.
Pressure-enabled phonon engineering in metals.
Lanzillo, Nicholas A; Thomas, Jay B; Watson, Bruce; Washington, Morris; Nayak, Saroj K
2014-06-17
We present a combined first-principles and experimental study of the electrical resistivity in aluminum and copper samples under pressures up to 2 GPa. The calculations are based on first-principles density functional perturbation theory, whereas the experimental setup uses a solid media piston-cylinder apparatus at room temperature. We find that upon pressurizing each metal, the phonon spectra are blue-shifted and the net electron-phonon interaction is suppressed relative to the unstrained crystal. This reduction in electron-phonon scattering results in a decrease in the electrical resistivity under pressure, which is more pronounced for aluminum than for copper. We show that density functional perturbation theory can be used to accurately predict the pressure response of the electrical resistivity in these metals. This work demonstrates how the phonon spectra in metals can be engineered through pressure to achieve more attractive electrical properties. PMID:24889627
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...
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
Phonon dispersion relation of liquid metals
Indian Academy of Sciences (India)
P B Thakor; P N Gajjar; A R Jani
2009-06-01
The phonon dispersion curves of some liquid metals, viz. Na $(Z = 1)$, Mg $(Z = 2)$, Al $(Z = 3)$ and Pb $(Z = 4)$, have been computed using our model potential. The charged hard sphere (CHS) reference system is applied to describe the structural information. Our model potential along with CHS reference system is capable of explaining the phonon dispersion relation for monovalent, divalent, trivalent and tetravalent liquid metals.
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.
Electron and Phonon Transport in Molecular Junctions
DEFF Research Database (Denmark)
Li, Qian
2015-01-01
Molecular electronics provide the possibility to investigate electron and phonon transport at the smallest imaginable scale, where quantum effects can be investigated and exploited directly in the design. In this thesis, we study both electron transport and phonon transport in molecular junctions. The system we are interested in here are ?-stacked molecules connected with two semi-infinite leads. ?-stacked aromatic rings, connected via ?-? electronic coupling, provides a rather soft mechanical b...
Heat capacity of suspended phonon cavities
Gusso, Andre; Rego, Luis G. C.
2006-01-01
We present a detailed analysis of the vibrational spectrum and heat capacity of suspended mesoscopic dielectric plates, for various thickness-to-side ratios at sub-Kelvin temperatures. The vibrational modes of the suspended cavity are accurately obtained from the three-dimensional (3D) elastic equations in the small strain limit and their frequencies assigned to the cavity phonon modes. The calculations demonstrate that the heat capacity of realistic quasi-2D phonon cavities...
Symmetry-Adapted Phonon Analysis of Nanotubes
Aghaei, Amin; Dayal, Kaushik; Elliott, Ryan S.
2012-01-01
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 th...
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 therefor...
Investigation of the Phonon Spectrum of Nickel
International Nuclear Information System (INIS)
Using a neutron spectrometer and time- of-flight data, the authors have made a study of the inelastic scattering of cold neutrons in nickel. The sample used was an alloy of nickel isotopes and the amplitude of coherent neutron scattering was zero. From the spectrum of inelastically-scattered neutrons, the phonon spectrum of the face-centred cubic lattice of nickel was obtained and a comparison made with the phonon spectrum of the body-centred cubic lattice of vanadium. (author)
Bartels, Albrecht; Dekorsy, Thomas; Kurz, Heinrich; Köhler, Klaus
1999-01-01
Coherent zone-folded acoustic phonons are excited in GaAs/AlAs superlattices by femtosecond laser pulses via resonant impulsive stimulated Raman scattering in both forward and backward scattering directions. The relative amplitudes of three distinct modes of first and second backfolded order match well with scattering intensities calculated within an elastic continuum model. The detection of the coherent acoustic modes is based on the modulation of the interband transitions via the acoustic d...
Upconversion cooling of Er-doped low-phonon fluorescent solids
Garcia-Adeva, Angel J.; Balda, Rolindes; Fernandez, Joaquin
2008-01-01
We report on a novel mechanism for laser cooling of fluorescent solids based on infrared-to-visible upconversion often found in rare-earth-doped low-phonon materials. This type of optical cooling presents some advantages with regards to conventional anti-Stokes cooling. Among them, it allows to obtain cooling in a broader range of frequencies around the barycenter of the infrared emitting band.
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 ...
Phonons in Yukawa lattices and liquids
Energy Technology Data Exchange (ETDEWEB)
Sullivan, Thomas [Department of Physics, Boston College, Chestnut Hill, MA 02467 (United States); Kalman, Gabor J [Department of Physics, Boston College, Chestnut Hill, MA 02467 (United States); Kyrkos, Stamatios [Department of Physics, Boston College, Chestnut Hill, MA 02467 (United States); Department of Chemistry and Physics, Le Moyne College, 1419 Salt Springs Rd, Syracuse, NY 13214 (United States); Bakshi, Pradip [Department of Physics, Boston College, Chestnut Hill, MA 02467 (United States); Rosenberg, Marlene [Department of Electrical and Computer Engineering, University of California, San Diego, La Jolla, CA 92093 (United States); Donko, Zoltan [Research Institute for Solid State Physics and Optics, Hungarian Academy of Sciences, PO Box 49, H-1525 Budapest (Hungary)
2006-04-28
The understanding of the theoretical structure of phonon dispersion in Yukawa lattices and the relationship between these perfect lattice phonons on the one hand, and the excitations in the disordered and liquid states on the other, is an important issue in analysing experimental and simulation results on plasma crystals. As the first step in this programme, we have numerically calculated the full phonon spectrum for 2D triangular Yukawa lattices, for a wide range of {kappa}-bar (screening parameter) values and along different propagation angles. Earlier calculations of the excitation spectra of the 2D and 3D Yukawa liquids were based on the quasilocalized charge approximation (QLCA), whose implicit premise is that the spectrum of an average distribution (governed by the isotropic liquid pair correlation function) is a good representation of the actual spectrum. To see the implications of this model more clearly, we compare the high {gamma} (near crystallization) QLCA phonon spectra with the angle-averaged phonon spectra of the lattice phonons.
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
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
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.
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.)
Electron-phonon contribution to the phonon and excited electron (hole) linewidths in bulk Pd
International Nuclear Information System (INIS)
We present an ab initio study of the electron-phonon (e-ph) coupling and its contribution to the phonon linewidths and to the lifetime broadening of excited electron and hole states in bulk Pd. The calculations, based on density-functional theory, were carried out using a linear-response approach in the plane-wave pseudopotential representation. The obtained results for the Eliashberg spectral function ?2F(?), e-ph coupling constant ?, and the contribution to the lifetime broadening, ?e-ph, show strong dependence on both the energy and momentum of an electron (hole) state. The calculation of phonon linewidths gives, in agreement with experimental observations, an anomalously large broadening for the transverse phonon mode T1 in the ? direction. In addition, this mode is found to contribute most strongly to the electron-phonon scattering processes on the Fermi surface
International Nuclear Information System (INIS)
SU(6) quadrupole phonon model (TQM) is equivalent to IBM and SU(6) particle-quadrupole phonon coupling model (PTQM) is equivalent to IBFM; these models are simply embedded in the Bohr-Mottelson quadrupole-phonon model and particle-quadrupole phonon coupling model, respectively. Due to this equivalence, dynamical symmetries (SU(3), SU(5), O(6)) and supersymmetries for TQM/PTQM are the same as for IBM/IBFM. The author discusses the quadrupole-phonon structure for the SU(3) limit, the coherent state, the analogs of Nilsson states and the supersymmetries. A new approximate supersymmetry is proposed which could appear for the situation with even nucleus of SU(3) type and the unique-parity bands in the neighbouring odd nucleus. (Auth.)
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
Generation mechanism for coherent LO phonons in surface-space-charge fields of III-V-compounds
Pfeifer, Torsten; Dekorsy, Thomas; Kütt, Waldemar; Kurz, Heinrich
1992-01-01
We report on details of coherent LO phonon generation in surface-space-charge regions of III-V-compounds by optical injection of free carriers with laser pulses of 50 fs duration at 2 eV. Both the dynamics of the transient surface field, as well as the coherent lattice vibration, are measured via electro-optic sampling techniques under different experimental conditions. The driving force for the coherent phonon vibration is the sudden depolarization of the crystal lattice due to ultrafast scr...
Marques, M. S.; Menezes, L. de S.; Lozano B., W.; Kassab, L. R. P.; de Araújo, C. B.
2013-02-01
Changing the sample's temperature from 200 K to 535 K, we observed 670-fold enhancement of a phonon-assisted upconversion emission at ?754 nm obtained from a Nd3+-doped tellurite glass excited by 5 ns laser pulses at 805 nm. A rate-equation model, including the relevant energy levels and temperature dependent transition rates, is proposed to describe the process. The results fit well with the data when one considers the nonradiative transitions contributing for the 754 nm luminescence are promoted by an effective phonon mode with energy of 700 cm-1.
Wilson, Thomas
2010-03-01
Intense pulses of coherent 246-GHz longitudinal acoustic phonons have been produced in n-i-p-i silicon doping superlattices by the resonant absorption of pulsed far-infrared (FIR) laser radiation. A niobium small-period grating-coupler has been used to convert the incident transverse electric field into an evanescent longitudinal field over the thickness of the superlattice. Si:B piezo-phonon spectroscopy is used, in conjunction with a fast granular aluminum/palladium microbolometer, to verify that the phonons exist in a narrow frequency band (˜10-GHz) around the FIR laser frequency at 246-GHz (1.22 mm). Time-of-flight across the thin (0.5-mm) substrate is used to verify that the phonons are longitudinal. The laser radiation is coupled onto the grating-coupler via a corrugated waveguide and a hyper-hemispherical silicon lens. Potential applications include the development of a novel terahertz cryogenic acoustic microscope for sub-surface imaging and sub-nanometer lateral resolution.
Ionizing particle detection based on phononic crystals
Aly, Arafa H.; Mehaney, Ahmed; Eissa, Mostafa F.
2015-08-01
Most conventional radiation detectors are based on electronic or photon collections. In this work, we introduce a new and novel type of ionizing particle detector based on phonon collection. Helium ion radiation treats tumors with better precision. There are nine known isotopes of helium, but only helium-3 and helium-4 are stable. Helium-4 is formed in fusion reactor technology and in enormous quantities during Big Bang nucleo-synthesis. In this study, we introduce a technique for helium-4 ion detection (sensing) based on the innovative properties of the new composite materials known as phononic crystals (PnCs). PnCs can provide an easy and cheap technique for ion detection compared with conventional methods. PnC structures commonly consist of a periodic array of two or more materials with different elastic properties. The two materials are polymethyl-methacrylate and polyethylene polymers. The calculations showed that the energies lost to target phonons are maximized at 1 keV helium-4 ion energy. There is a correlation between the total phonon energies and the transmittance of PnC structures. The maximum transmission for phonons due to the passage of helium-4 ions was found in the case of making polyethylene as a first layer in the PnC structure. Therefore, the concept of ion detection based on PnC structure is achievable.
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
Second Harmonic Generation of Nanoscale Phonon Wave Packets.
Bojahr, A; Gohlke, M; Leitenberger, W; Pudell, J; Reinhardt, M; von Reppert, A; Roessle, M; Sander, M; Gaal, P; Bargheer, M
2015-11-01
Phonons are often regarded as delocalized quasiparticles with certain energy and momentum. The anharmonic interaction of phonons determines macroscopic properties of the solid, such as thermal expansion or thermal conductivity, and a detailed understanding becomes increasingly important for functional nanostructures. Although phonon-phonon scattering processes depicted in simple wave-vector diagrams are the basis of theories describing these macroscopic phenomena, experiments directly accessing these coupling channels are scarce. We synthesize monochromatic acoustic phonon wave packets with only a few cycles to introduce nonlinear phononics as the acoustic counterpart to nonlinear optics. Control of the wave vector, bandwidth, and consequently spatial extent of the phonon wave packets allows us to observe nonlinear phonon interaction, in particular, second harmonic generation, in real time by wave-vector-sensitive Brillouin scattering with x-rays and optical photons. PMID:26588396
Anharmonic phonons in type I clathrates
Tanigaki, Katsumi; Wu, Jiazhen; Shimotani, Hidekazu
2015-03-01
A systematic study on the anharmonicity of phonons is made for thermoelectric single crystal type-I clathrates based on their heat capacity Cp at low temperatures (T) down to 360 mK. The low-T linear terms obs ?T of Cp, including the tunneling-term of the atoms accommodated in the host cages (?ph T = ?T), and the Sommerfeld itinerant-electron term (?e T) are successfully separated through careful measurements of sigle crystals with various carrier concentrations. The values of the density of anharmonic potentials are deduced. The effective mass (m *) enhancement is also determined from ?e values and the electron-phonon interaction strength (?) can be evaluated from these values. It is shown that both the thermal conductivities (?'s) and the electron-phonon interaction strengths (?'s) are quantitatively in good agreement with the ? parameters deduced from the present experiments. The boson peaks observed at low energy excitations are disucssued in relation to the ? values.
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 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. PMID:26099716
Phonon transport properties in pillared silicon film
Wei, Zhiyong; Yang, Juekuan; Bi, Kedong; Chen, Yunfei
2015-10-01
The phonon transport property of pillared silicon film is systematically investigated by molecular dynamics simulation and lattice dynamics calculation. It is found that the thermal conductivity can be reduced to as low as 28.6% of the conductivity of plain ones. Although the reduced thermal conductivity can be explained qualitatively by increased surface roughness, our calculations show that the pillars modify the phonon dispersion relation and reduce the phonon group velocity due to the local resonance effects. Furthermore, by analyzing the participation ratio spectra, it is shown that the pillars reduce the mode participation ratio over the whole range of frequency. We found that the mode localization around the pillars is another important factor to reduce the thermal conductivity of pillared film. The present investigations indicate that the pillared film may have potential application in thermoelectric energy conversion.
Phonon heat transport in gallium arsenide
Indian Academy of Sciences (India)
Richa Saini; Vinod Ashokan; B D Indu; R Kumar
2012-03-01
The lifetimes of quantum excitations are directly related to the electron and phonon energy linewidths of a particular scattering event. Using the versatile double time thermodynamic Green’s function approach based on many-body theory, an ab-initio formulation of relaxation times of various contributing processes has been investigated with newer understanding in terms of the linewidths of electrons and phonons. The energy linewidth is found to be an extremely sensitive quantity in the transport phenomena of crystalline solids as a collection of large number of scattering processes, namely, boundary scattering, impurity scattering, multiphonon scattering, interference scattering, electron–phonon processes and resonance scattering. The lattice thermal conductivities of three samples of GaAs have been analysed on the basis of modi?ed Callaway model and a fairly good agreement between theory and experimental observations has been reported.
Coherent phonon heat conduction in superlattices.
Luckyanova, Maria N; Garg, Jivtesh; Esfarjani, Keivan; Jandl, Adam; Bulsara, Mayank T; Schmidt, Aaron J; Minnich, Austin J; Chen, Shuo; Dresselhaus, Mildred S; Ren, Zhifeng; Fitzgerald, Eugene A; Chen, Gang
2012-11-16
The control of heat conduction through the manipulation of phonons as coherent waves in solids is of fundamental interest and could also be exploited in applications, but coherent heat conduction has not been experimentally confirmed. We report the experimental observation of coherent heat conduction through the use of finite-thickness superlattices with varying numbers of periods. The measured thermal conductivity increased linearly with increasing total superlattice thickness over a temperature range from 30 to 150 kelvin, which is consistent with a coherent phonon heat conduction process. First-principles and Green's function-based simulations further support this coherent transport model. Accessing the coherent heat conduction regime opens a new venue for phonon engineering for an array of applications. PMID:23161996
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.
Electron-Phonon Coupling in Boron-Doped Diamond Superconductor
H.J. Xiang; Li, Zhenyu; Yang, * Jinlong; Hou, J. G.; Zhu, Qingshi
2004-01-01
The electronic structure, lattice dynamics, and electron-phonon coupling of the boron-doped diamond are investigated using the density functional supercell method. Our results indicate the boron-doped diamond is a phonon mediated superconductor, con rming previous theoretical conclusions deduced from the calculations employing the virtual crystal approximation. We show that the optical phonon modes involving B vibrations play an important role in the electron-phonon coupling...
Phonon nanocapacitor for storage and lasing of terahertz lattice waves
Han, Haoxue; Li, Baowen; Volz, Sebastian; Kosevich, Yuriy A.
2014-01-01
We introduce a novel ultra-compact nanocapacitor of coherent phonons formed by high-finesse interference mirrors based on atomic-scale semiconductor metamaterials. Our molecular dynamics simulations show that the nanocapacitor stores THz monochromatic lattice waves, which can be used for phonon lasing - the emission of coherent phonons. Either one- or two-color phonon lasing can be realized depending on the geometry of the nanodevice. The two color regimes of the capacitor o...
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 depende...
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...
Ding, Yujie J
2015-03-01
Raman oscillation, frequency upconversion, and Raman amplification can be achieved in a second-order nonlinear medium at the phonon-polariton resonance. By beating two optical fields, a second-order nonlinear polarization is generated inside the medium. Such a polarization induces a spatially uniform nonpropagating electric field at the beat frequency, which in turn mixes with the input optical field at the lower frequency to generate or amplify the anti-Stokes optical field. Raman oscillation can be efficiently reached for the copropagating configuration. In comparison, efficient frequency upconversion and large amplifications are achievable for the counterpropagating configuration. These Raman processes can be used to effectively remove transverse-optical phonons before decaying to lower-frequency phonons, achieve laser cooling, and significantly enhance coherent anti-Stokes Raman scattering. The counterpropagating configuration offers advantages for amplifying extremely weak signals. PMID:25723418
Lattice parameters and Raman-active phonon modes of ?-(AlxGa1?x)2O3
International Nuclear Information System (INIS)
We present X-ray diffraction and Raman spectroscopy investigations of a (100)-oriented (AlxGa1–x)2O3 thin film on MgO (100) and bulk-like ceramics in dependence on their composition. The thin film grown by pulsed laser deposition has a continuous lateral composition spread allowing to determine precisely the dependence of the phonon mode properties and lattice parameters on the chemical composition. For x?phonon energies depend linearly on the composition. We determined the slopes of these dependencies for the individual lattice parameters and for nine Raman lines, respectively. While the lattice parameters of the ceramics follow Vegard's rule, deviations are observed for the thin film. This deviation has only a small effect on the phonon energies, which show a reasonably good agreement between thin film and ceramics
Först, Michael; Kurz, Heinrich; Dekorsy, Thomas; Leavitt, Richard P.
2003-01-01
The coupling of Bloch oscillations to longitudinal optical phonons is investigated in a narrow-well In0.53Ga0.47As/In0.52Al0.48As superlattice. A strong increase of coherent phonon amplitudes is observed when the Bloch oscillations are subsequently tuned into resonance with different optical phonon modes. The rapid dephasing of the Bloch oscillations due to field induced tunneling from the weakly bound miniband into above-barrier continuum states leads to an additional and new excitation proc...
Electronic structure, phonon spectra and electron-phonon interaction in ScB2
International Nuclear Information System (INIS)
The electronic structure, Fermi surface, angle dependence of the cyclotron masses and extremal cross sections of the Fermi surface, phonon spectra, electron-phonon Eliashberg and transport spectral functions, temperature dependence of electrical resistivity of the ScB2 diboride were investigated from first principles using the fully relativistic and full potential linear muffin-tin orbital methods. The calculations of the dynamic matrix were carried out within the framework of the linear response theory. A good agreement with experimental data of electron-phonon spectral functions, electrical resistivity, cyclotron masses and extremal cross sections of the Fermi surface was achieved.
Phonon dispersion curves of CsCN
Indian Academy of Sciences (India)
N K Gaur; Preeti Singh; E G Rini; Jyotsna Galgale; R K Singh
2004-08-01
The motivation for the present work was gained from the recent publication on phonon dispersion curves (PDCs) of CsCN from the neutron scattering technique. We have applied the extended three-body force shell model (ETSM) by incorporating the effect of coupling between the translation modes and the orientation of cyanide molecules for the description of phonon dispersion curves of CsCN between the temperatures 195 and 295 K. Our results on PDCs in symmetric direction are in good agreement with the experimental data measured with inelastic neutron scattering technique.
Angular momentum in spin-phonon processes
Garanin, D. A.; Chudnovsky, E. M.
2015-07-01
Quantum theory of spin relaxation in the elastic environment is revised with account of the concept of a phonon spin recently introduced by Zhang and Niu [L. Zhang and Q. Niu, Phys. Rev. Lett. 112, 085503 (2014), 10.1103/PhysRevLett.112.085503]. Similar to the case of the electromagnetic field, the division of the angular momentum associated with elastic deformations into the orbital part and the part due to phonon spins proves to be useful for the analysis of the balance of the angular momentum. Such analysis sheds important light on microscopic processes leading to the Einstein-de Haas effect.
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.
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.
Eklund, Peter C.
2005-03-01
Results of Raman experiments that investigate the influence of laser flux and thermal anchoring on the asymmetric line profile ˜520 cm-1 optical phonon scattering from small diameter Si nanowires are presented. At low laser flux ?= 100 ?W/?m^2, the Raman band takes on even higher asymmetry that is likely due to inhomogenous heating. The data at low and high laser flux can be explained quantitatively on the basis of fundamental Raman scattering theory. ^1 H.^ Richter, Z. P. Wang, and L. Ley, Solid State Communcations, 39, 625 (1981) ^Work supported by the NSF NIRT program (DMR- 0304178).
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
PHONON RELAXATION IN CRYSTALS STUDIED BY HOT LUMINESCENCE
Saari, P.; Rebane, K.
1981-01-01
We have developed a method for studying phonon interactions in picosecond timescale, which manifest themselves in optical emission spectra. In sodium nitrite transition rates between high-frequency internal and lattice phonon states have been evaluated and their correlation with the order of anharmonicity has been observed. For anthracene the kinetics of vibron relaxation up to acoustic phonons has been revealed.
International Nuclear Information System (INIS)
This paper presents a calculation of the linewidths of phonons in Pd owing to decay into electron-hole pairs. Korringa-Kohn-Rostoker energies and wave functions are used with the rigid-muffin-tin approximation (for the electron-phonon matrix element). The linewidths of the longitudinal [zeta00] phonons show a sharp maximum which is in qualitative agreement with the recent experimental observations of Youngblood et al. Relatively large linewidths are calculated for a transverse mode (T1) along the [110] direction, which are in good agreement with the previous experiment of Miiller. Both the matrix element and the joint density of states at the Fermi energy contribute to the magnitude of the calculated linewidths. The electron-phonon contribution to the electronic mass enhancement is calculated to be 0.41. This result is used to estimate the contribution due to paramagnetic fluctuations
Coherent acoustic phonons in phonon cavities investigated by asynchronous optical sampling
Energy Technology Data Exchange (ETDEWEB)
Hudert, F [University of Constance and Center of Applied Photonics, 78464 Constance (Germany); Bartels, A [University of Constance and Center of Applied Photonics, 78464 Constance (Germany); Janke, C [University of Constance and Center of Applied Photonics, 78464 Constance (Germany); Dekorsy, T [University of Constance and Center of Applied Photonics, 78464 Constance (Germany); Koehler, K [Fraunhofer Institut fuer angewandte Festkoerperphysik, Freiburg (Germany)
2007-12-15
Using a recently introduced measurement technique, called asynchronous optical sampling (ASOPS), we have investigated the dynamics of coherent acoustic phonons in a semiconductor heterostructure composed of a GaAs film between two GaAs/AlAs superlattices, serving as a cavity for acoustic phonons. Measurements were performed at liquid helium temperatures. The possibility to perform two-color pump-probe spectroscopy allowed us to tune the probe pulse energy to the cavity band gap, while sweeping the pump pulse energy over the superlattice resonance. The large measurement window of 1 ns in combination with a resolution of about 150 fs made a detailed analysis of the observed phonon dynamics possible. We observed a long lived oscillation in the gap of the phonon dispersion at 466 GHz, which we attribute to a cavity mode.
Coherent acoustic phonons in phonon cavities investigated by asynchronous optical sampling
International Nuclear Information System (INIS)
Using a recently introduced measurement technique, called asynchronous optical sampling (ASOPS), we have investigated the dynamics of coherent acoustic phonons in a semiconductor heterostructure composed of a GaAs film between two GaAs/AlAs superlattices, serving as a cavity for acoustic phonons. Measurements were performed at liquid helium temperatures. The possibility to perform two-color pump-probe spectroscopy allowed us to tune the probe pulse energy to the cavity band gap, while sweeping the pump pulse energy over the superlattice resonance. The large measurement window of 1 ns in combination with a resolution of about 150 fs made a detailed analysis of the observed phonon dynamics possible. We observed a long lived oscillation in the gap of the phonon dispersion at 466 GHz, which we attribute to a cavity mode
Coherent acoustic phonons in phonon cavities investigated by asynchronous optical sampling
Hudert, F.; Bartels, A.; Janke, C.; Dekorsy, T.; Köhler, K.
2007-12-01
Using a recently introduced measurement technique, called asynchronous optical sampling (ASOPS), we have investigated the dynamics of coherent acoustic phonons in a semiconductor heterostructure composed of a GaAs film between two GaAs/AlAs superlattices, serving as a cavity for acoustic phonons. Measurements were performed at liquid helium temperatures. The possibility to perform two-color pump-probe spectroscopy allowed us to tune the probe pulse energy to the cavity band gap, while sweeping the pump pulse energy over the superlattice resonance. The large measurement window of 1 ns in combination with a resolution of about 150 fs made a detailed analysis of the observed phonon dynamics possible. We observed a long lived oscillation in the gap of the phonon dispersion at 466 GHz, which we attribute to a cavity mode.
Low frequency phononic band structures in two-dimensional arc-shaped phononic crystals
Energy Technology Data Exchange (ETDEWEB)
Xu, Zhenlong, E-mail: zhenlongxu1000@163.com [Faculty of Electro Mechanical Engineering, Guangdong University of Technology, Guangzhou, 510006 (China); Meizhouwan Vocational Technology College, Putian, 351254 (China); Wu, Fugen [Department of Experiment Education, Guangdong University of Technology, Guangzhou, 510006 (China); Guo, Zhongning [Faculty of Electro Mechanical Engineering, Guangdong University of Technology, Guangzhou, 510006 (China)
2012-07-02
The low frequency phononic band structures of two-dimensional arc-shaped phononic crystals (APCs) were studied by the transfer matrix method in cylindrical coordinates. The results showed the first phononic band gaps (PBGs) of APCs from zero Hz with low modes. Locally resonant (LR) gaps were obtained with higher-order rotation symmetry, due to LR frequencies corresponding to the speeds of acoustic waves in the materials. These properties can be efficiently used in a structure for low frequencies that are forbidden, or in a device that permits a narrow window of frequencies. -- Highlights: ? We report a new class of quasi-periodic hetero-structures, arc-shaped phononic crystals (APCs). ? The results show the first PBGs start with zero Hz with low modes. ? Locally resonant (LR) gaps were obtained with higher-order rotation symmetry, due to LR frequencies corresponding to the speeds of acoustic waves in the materials.
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''
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...
High-speed asynchronous optical sampling for high-sensitivity detection of coherent phonons
Dekorsy, T.; Taubert, R.; Hudert, F.; Schrenk, G.; Bartels, A.; Cerna, R.; Kotaidis, V.; Plech, A.; Köhler, K.; Schmitz, J.; Wagner, J.
2007-12-01
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 acquisition time signal-to-noise ratios better than 107 are achieved. We present examples of the high-sensitivity detection of coherent phonons in superlattices and of the coherent acoustic vibration of metallic nanoparticles.
High-speed asynchronous optical sampling for high-sensitivity detection of coherent phonons
International Nuclear Information System (INIS)
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 acquisition time signal-to-noise ratios better than 107 are achieved. We present examples of the high-sensitivity detection of coherent phonons in superlattices and of the coherent acoustic vibration of metallic nanoparticles
High-speed asynchronous optical sampling for high-sensitivity detection of coherent phonons
Energy Technology Data Exchange (ETDEWEB)
Dekorsy, T [Physics Department and Center for Applied Photonics, University Constance, Box M700, D-78457 Constance (Germany); Taubert, R [Physics Department and Center for Applied Photonics, University Constance, Box M700, D-78457 Constance (Germany); Hudert, F [Physics Department and Center for Applied Photonics, University Constance, Box M700, D-78457 Constance (Germany); Schrenk, G [Physics Department and Center for Applied Photonics, University Constance, Box M700, D-78457 Constance (Germany); Bartels, A [Physics Department and Center for Applied Photonics, University Constance, Box M700, D-78457 Constance (Germany); Cerna, R [Physics Department and Center for Applied Photonics, University Constance, Box M700, D-78457 Constance (Germany); Kotaidis, V [Physics Department and Center for Applied Photonics, University Constance, Box M700, D-78457 Constance (Germany); Plech, A [Physics Department and Center for Applied Photonics, University Constance, Box M700, D-78457 Constance (Germany); Koehler, K [Fraunhofer Institute fuer Angewandte Festkoerperphysik, Tullastr. 72, D-79108 Freiburg (Germany); Schmitz, J [Fraunhofer Institute fuer Angewandte Festkoerperphysik, Tullastr. 72, D-79108 Freiburg (Germany); Wagner, J [Fraunhofer Institute fuer Angewandte Festkoerperphysik, Tullastr. 72, D-79108 Freiburg (Germany)
2007-12-15
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 acquisition time signal-to-noise ratios better than 10{sup 7} are achieved. We present examples of the high-sensitivity detection of coherent phonons in superlattices and of the coherent acoustic vibration of metallic nanoparticles.
Theory of coherent acoustic phonons in InGaN/GaN multi-quantum wells
Sanders, G D; Kim, C S; Kim, Chang-Sub
2001-01-01
A microscopic theory for the generation and propagation of coherent LA phonons in pseudomorphically strained wurzite (0001) InGaN/GaN multi-quantum well (MQW) p-i-n diodes is presented. The generation of coherent LA phonons is driven by photoexcitation of electron-hole pairs by an ultrafast Gaussian pump laser and is treated theoretically using the density matrix formalism. We use realistic wurzite bandstructures taking valence-band mixing and strain-induced piezo- electric fields into account. In addition, the many-body Coulomb ineraction is treated in the screened time-dependent Hartree-Fock approximation. We find that under typical experimental conditions, our microscopic theory can be simplified and mapped onto a loaded string problem which can be easily solved.
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.
Patrick, CE; Giustino, F.
2014-01-01
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 le...
Electronic structure, phonon spectra and electron-phonon interaction in HfB2
Sichkar, S. M.; V. N. Antonov
2013-01-01
The electronic structure, Fermi surface, angle dependence of the cyclotron masses and extremal cross sections of the Fermi surface, phonon spectra, electron-phonon Eliashberg and transport spectral functions, temperature dependence of electrical resistivity of the HfB2 diboride were investigated from first principles using the fully relativistic and full potential linear muffin-tin orbital methods. The calculations of the dynamic matrix were carried out within the framework ...
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...
Generalized Kinetic Theory of Electrons and Phonons
Rossani, A.
2002-01-01
A Generalized Kinetic Theory was proposed in order to have the possibility to treat particles which obey a very general statistics. By adopting the same approach, we generalize here the Kinetic Theory of electrons and phonons. Equilibrium solutions and their stability are investigated.
LO-phonon overheating in quantum dots.
Czech Academy of Sciences Publication Activity Database
Král, Karel
2006-01-01
Ro?. 56, ?. 1 (2006), s. 33-40. ISSN 0011-4626. [Symposium on Surface Physics /10./. Praha, 11.07.2005-15.07.2005] Institutional research plan: CEZ:AV0Z10100520 Keywords : quantum dots * electron-phonon interaction Subject RIV: BE - Theoretical Physics Impact factor: 0.568, year: 2006
Anomalous Doppler effects in bulk phononic crystal
International Nuclear Information System (INIS)
Doppler effects in simple cubic phononic crystal are studied theoretically and numerically. In addition to observing Doppler shifts from a moving source's frequencies inside the gap, we find that Doppler shifts can be multi-order, anisotropic, and the dominant order of shift depends on the band index that the source's frequency is in.
Electron-phonon coupling in nanodevices.
Czech Academy of Sciences Publication Activity Database
Král, Karel; Lin, C. Y.
2009-01-01
Ro?. 42, ?. 3 (2009), s. 618-621. ISSN 1386-9477 R&D Projects: GA MŠk ME 866 Institutional research plan: CEZ:AV0Z10100520 Keywords : nanodevice * electron-phonon interaction * nonequilibrium quantum transport Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.177, year: 2009
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 dot s * electron - phonon interaction * polarons Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.964, year: 2009
Tuning phonon properties in thermoelectric materials.
Srivastava, G P
2015-02-01
This review article presents a discussion of theoretical progress made over the past several decades towards our understanding of thermoelectric properties of materials. Particular emphasis is placed upon describing recent progress in 'tuning' phonon properties of nanocomposite materials for gaining enhancement of the thermoelectric figure of merit. PMID:25583032
Thermal memory: a storage of phononic information
WANG, Lei; LI, Baowen
2008-01-01
Memory is an indispensable element for computer besides logic gates. In this Letter we report a model of thermal memory. We demonstrate via numerical simulation that thermal (phononic) information stored in the memory can be retained for a long time without being lost and more importantly can be read out without being destroyed. The possibility of experimental realization is also discussed.
Large-amplitude coherent phonons in semimetals
Misochko, Oleg V.; Lebedev, Michael V.; Ishioka, Kunie; Kitajima, Masahiro; Chekalin, Sergey V.; Dekorsy, Thomas
We report on the time-resolved dynamics of two, different in symmetry, largeamplitude coherent phonons in Bi and Sb. A systematic study was made of the variation of the nonlinear ultrafast lattice dynamics with pulse duration, excitation strength, temperature, and probe wavelength.
LOW FREQUENCY PHONONS IN SINTERED COPPER
Frisken, B.; Guillon, F.; Harrison, J; Page, J.
1981-01-01
Measurements of Young's Modulus and sound velocity of a range of sintered copper powder samples have demonstrated the existence of low frequency soft phonon modes that could explain the low temperature anomaly in the Kapitza resistance between liquid 3He and sintered metal heat exchangers below 10 mK.
Temperature dependent phonon renormalization in metallic nanotubes
Scardaci, V.; S. Piscanec; Lazzeri, Michele; Krupke, R.; Mauri, Francesco; Ferrari, A. C.
2007-01-01
We measure the temperature dependence of the Raman spectra of metallic and semiconducting nanotubes. We show that the different trend in metallic tubes is due to phonon re-normalization induced by the variation in electronic temperature, which is modeled including non-adiabatic contributions to account for the dynamic, time dependent nature
Electron-phonon interactions in correlated systems
International Nuclear Information System (INIS)
There exist attempts to describe the superconducting mechanism operating in HTS as based on antiferromagnetic fluctuations. It is not our intention to dwell on the superconducting mechanism, even though this is very a important issue. The main aim is to discuss the problem of interplay between electron-phonon and electron-electron interactions in correlated systems. We believe such analysis can be of importance for various materials and not only HTS'S. We shall however mainly refer to experiments on this last class of superconductors. Severe complications are to be expected by studying the problem. As is well known electron correlations are very important in narrow band systems, where the relevant electronic scale EF is quite small. In those circumstances, the phonon energy scale ?D is of comparable magnitude, with the ratio ?D/EF of order 1 signalling a possible break down of the Migdal - Eliashberg description of the electron-phonon interaction in metals. Here we shall assume the validity of the Migdal-Eliashberg approximation and concentrate on the mutual influence of electron and phonon subsystems. In the next section we shall discuss experimental motivation for and theoretical work related to the present problem. Section 3 contains a brief discussion of our theory. It is a self-consistent theory a la Migdal with strong correlations treated with an auxiliary boson technique. We conclude with results and their discussion. (orig.)
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)
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
Phonon density of states in nanocrystalline 57Fe
Indian Academy of Sciences (India)
Ranber Singh; S Prakash; R Meyer; P Entel
2003-03-01
The Born–von Karman model is used to calculate phonon density of states (DOS) of nanocrystalline bcc Fe. It is found that there is an anisotropic stiffening in the interatomic force constants and hence there is shrinking in the nearest-neighbour distances in the nanophase. This leads to additional vibrational modes above the bulk phonons near the bottom of the phonon band. It is found that the high energy phonon modes of nanophase Fe are the surface modes. The calculated phonon DOS closely agree with the experimental data except a peak at 37 meV. The calculated phonon dispersion relations are also compared with those of the bulk phonons and anomalous behaviour is discussed in detail. The speci?c heat in nanophase enhances as compared to bulk phase at low temperatures and the calculated Debye temperature $\\Theta_{D}$ agrees with the experimental results. It is predicted that the nanocrystalline Fe may consist of about 14 GPa pressure.
Establishment of correlated states in a quantum dot interacting with an acoustic-phonon reservoir
Huang, Hui; Li, Gao-xiang; Gu, Wen-ju; Ficek, Zbigniew
2014-08-01
We investigate the effects of a low-frequency (acoustic) phonon bath on the dynamics of a quantum dot modeled as a cascade three-level system. We show that the phonon bath appears to the upper transition of the cascade system as a broadband reservoir of inverted rather than conventional harmonic oscillators. The action of the annihilation and creation operators of the inverted oscillator are interchanges relative to those of the usual harmonic oscillator that it serves as a linear amplifier to the system, and thereby gives rise to unusual features in the dynamics of the quantum dot. We find that the phonon bath, although being in a thermal state, affects the quantum dot as a correlated-type reservoir which results in the decay of the system to a correlated two-photon state with the population distribution no longer obeying a Boltzmann distribution. It is particularly interesting that even for a zero-temperature phonon reservoir, the steady state is a correlated state which, under appropriate conditions on the Rabi frequencies and the damping rates, can reduce to a strongly correlated pure state. It is shown that the two-photon correlations result in a significant squeezing and strong two-photon correlations in the radiation field emitted by the quantum dot. The presence of the correlations in the system is manifest in the presence of quantum beats in the time evolution of the populations and the radiation intensity. The effect of the ordinary spontaneous emission on the features induced by the phonon bath is also discussed.
International Nuclear Information System (INIS)
A microscopic theory to study the combined dynamics of a quantum dot exciton coupled to a single cavity mode as well as acoustic phonons is presented. By considering the phonon subsystem in the coherent state representation, the phonon’s impact on the emitted photons is investigated. The single photon emission probability and phonon effects on this quantity are studied. On the other hand, we illustrate that while a quantum dot interacts with a single cavity mode, the collapse and revival phenomenon will occur. It is demonstrated that acoustic phonons have a pronounced impact on the collapse and revival of the quantum dot exciton. Our finding reveals that at elevated temperatures the phonon interaction decreases the Rabi frequency. Moreover, the cavity mode possesses non-classical features such as sub-Poissonian statistics. (paper)
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
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.
Electron and Phonon Transport in Molecular Junctions
DEFF Research Database (Denmark)
Li, Qian
2015-01-01
Molecular electronics provide the possibility to investigate electron and phonon transport at the smallest imaginable scale, where quantum effects can be investigated and exploited directly in the design. In this thesis, we study both electron transport and phonon transport in molecular junctions. The system we are interested in here are ?-stacked molecules connected with two semi-infinite leads. ?-stacked aromatic rings, connected via ?-? electronic coupling, provides a rather soft mechanical bridge while maintaining high electronic conductivity. We investigate electron transport and the thermoelectric response of five representative ?-stacked systems. We find that the transmission and power factor are both enhanced by increasing the conjugation length or adding substituent groups. The local transmission shows that several extra paths are added by cyano groups, which increases the total transmission at the Fermi energy. We propose and analyze a way of using ? stacking to design molecular junctions to control heat transport. We develop a simple model system to identify optimal parameter regimes and then use density functional theory (DFT) to extract model parameters for a number of specific ?-stacked systems. It is found that the proposed mechanism can indeed signicantly reduce the phonon conductance but also increase it depending on the specific molecules and stackings used. Furthermore, we study how a molecule's conformation influence phonon transport by mechanically compressing an alkane chain in the junction with graphene leads, using DFT combined with scattering matrix approach. We find that the thermal conductance of the compressed junction drops by half in comparison to the extended junction, making it possible to turn on and o the heat current. The reduced thermal conductance in the compressed junction mainly stems from a large suppression of the transmission coefficients of the longitudinal and the in-plane transverse channels of the leads. Finally, we return and investigate phonon transport through ?-stacked molecules connected to graphene leads including all modes of the system using DFT method. It is found that the thermal conductance of ?-stacked systems can be reduced by 95%, compared with that in a single-molecule junction. Phonon transmission of ?-stacked systems is reduced dramatically in the whole frequency range and the left transmission mainly remains below 5 THz.
A quantum formalism for a terahertz acoustic laser
Scientific Electronic Library Online (English)
Ihosvany, Camps Rodríguez; Sergio Saul, Makler; Enrique Victoriano, Anda.
1999-12-01
Full Text Available The aim of this work is to improve the study of a phonon laser (saser) proposed by us several years ago[1]. This is a device capable to generate an intense coherent beam of acoustical phonons. Our acoustic laser consists in a double barrier heterostructure tailored such the energy difference between [...] the ground and the first excited state in the well is close to the energy of the LO phonon. The electrons are directly injected into the excited level. Therefore they decay producing a high rate of LO phonons. These phonons are confined inside the well and decay into a pair of phonons[2]: LO -> + TA. The TA phonons escape the well in the [111] direction constituting an intense coherent beam. Recently were studied (and sometimes realized experimentally) several kinds of phonon lasers. Up to our knowledge our saser is the only that has a very short wavelength (smaller than 25 Å) and a very long range (greater than 1000 mum). Because of that, such beam could have applications to acoustic nanoscopy, acoustic nanolithography and phonoelectronics. In early articles[1, 3, 4, 5, 6] we get the kinetic equations for the averaged electron and phonon populations. Quantum fluctuations were not taken into account. The system Hamiltonian is H = He + Hph + He-ph + Hph-ph + He-e. To solve this Hamiltonian we expand their eigenfunctions in the basis of the eigenstates¦jn1n2n3ñ of the single particle part of it. We obtain a set of coupled equations for the expansion coefficients that can be solved with some approximations. The results are qualitatively similar to those obtained previously.
Indian Academy of Sciences (India)
L Pintschovius; F Weber; W Reichardt; A Kreyssig; R Heid; D Reznik; O Stockert; K Hradil
2008-10-01
Phonons in a metal interact with conduction electrons which give rise to a finite linewidth. In the normal state, this leads to a Lorentzian shape of the phonon line. Density functional theory is able to predict the phonon linewidths as a function of wave vector for each branch of the phonon dispersion. An experimental verification of such predictions is feasible only for compounds with very strong electron–phonon coupling. YN2B2C was chosen as a test example because it is a conventional superconductor with a fairly high $T_{c}$ (15.2 K). Inelastic neutron scattering experiments did largely confirm the theoretical predictions. Moreover, they revealed a strong temperature dependence of the linewidths of some phonons with particularly strong electron–phonon coupling which can as yet only qualitatively be accounted for by theory. For such phonons, marked changes of the phonon frequencies and linewidths were observed from room temperature down to 15 K. Further changes were observed on entering into the superconducting state. These changes can, however, not be described simply by a change of the phonon linewidth.
Valley contrasting chiral phonons in monolayer hexagonal systems
Zhang, Lifa; Niu, Qian
2015-03-01
In monolayer haxagonal lattice systems, two inequivalent valleys appear in the reciprocal lattice space. With inversion symmetry breaking, we find valley dependent chiral phonons which are circularly polarized with carrying spin angular momentum and ionic magnetic moment. At valleys, light and heavy phonons are found and evolve in intervalley electronic scattering. Under three-fold rotation operation, phonons have pseudo angular momentum, which include spin and orbital parts. From conservation of pseudo angular momentum, momentum and energy, the selection rules in valleytronics are obtained. Due to chiral valley phonons, one can observe polarized infrared photoluminescence and phonon valley coherence by infrared excitation. There is also a valley dependent phonon Berry curvature which can result a valley phonon Hall effect. The valley-dependent chiral phonon, together with its spin angular momentum, pseudo angular momentum, infrared polarized photoluminescence, phonon valley coherence and valley Hall effect, will form a basis for valley-based phononics applications. We acknowledge support from DOE-DMSE (DE-FG03-02ER45958),NBRPC (2012CB-921300), NSFC (91121004), and the Welch Foundation (F-1255).
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 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)
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
Spectroscopy of the two Lowest Exciton Zero-Phonon Lines in Single CdSe/ZnS Nanocrystals
Energy Technology Data Exchange (ETDEWEB)
Louyer, Y; Biadala, L; Tamarat, Ph; Lounis, B, E-mail: y.louyer@cpmoh.u-bordeaux1.f [Centre de Physique Moleculaire Optique et Hertzienne, University of Bordeaux and CNRS, 351 cours de la Liberation, Talence, F-33405 (France)
2010-09-01
We study the optical properties of the lowest-energy exciton states in highly photostable individual CdSe/ZnS nanocrystals at low temperatures. We observe two sharp zero-phonon lines which we attribute to the radiative recombination from the two lowest-energy levels of the band-edge exciton fine structure. By using resonant laser excitation on these two lines we measure a spectral broadening of 10 {mu}eV over integration times of 100 ms.
Twofold decoherence brought on by the phonon bath in a quantum-dot two-state system
Chen, Zhi-De
2015-10-01
Because of the inherent coupling, the influence from the phonon bath on the coherent energy exchange between a quantum-dot (QD) two-state system (TSS) and a resonant optical mode is a twofold action. One action is the influence on the construction of the coherence, and the other is on the constructed coherence. The latter has been extensively studied by the master-equation approach, whereas the former has been ignored so far. In the present paper, the influence from the phonon bath on the construction of the coherence is studied by using the small-polaron theory. It is found that in the presence of phonon coupling, the construction of the coherence depends on the state evolution of the phonon bath during the energy exchange. The coherence construction probability is calculated and found to be a decreasing function of both temperature and coupling strength. The spectrum including the twofold decoherence effect is calculated and the obtained result can help one to understand some peculiar observations in the photoluminescence spectrum of a QD TSS system, including the additional cavity line in the strong-coupling regime and the additional coherent scattering in the case of the Mollow triplet.
International Nuclear Information System (INIS)
Laser cooling of solids, sometimes also known as optical refrigeration, is a fast developing area of optical science, investigating the interaction of light with condensed matter. Apart from being of fundamental scientific interest, this topic addresses a very important practical issue: design and construction of laser pumped solid-state cryocoolers, which are compact, free from mechanical vibrations, moving parts, fluids and can cause only low electromagnetic interference in the cooled area. The optical cryocooler has a broad area of applications such as in the development of magnetometers for geophysical sensors, in biomedical sensing and can be beneficial for satellite instrumentations and small sensors, where compactness and the lack of vibrations are very important. Simply, a laser cooler works on the conversion of low energy pump photons into high-energy anti-Stokes fluorescence photons by extracting some of the phonons (heat energy) in a material. That is, the process of laser cooling of solids is based on anti-Stokes fluorescence also known as luminescence upconversion, when light quanta in the red tail of the absorption spectrum are absorbed from a pump laser, and blue-shifted photons are spontaneously emitted. The extra energy extracted from the solid-state lattice in the form of the phonons is the quanta of vibrational energy which generates heat. The idea to cool solids with anti-Stokes fluorescence was proposed in 1929 by Peter Pringsheim and first demonstrated experimentally by Epstein's research team in 1995. In 1999, Steven Bowman proposed to use the optical refrigeration by anti-Stokes fluorescence within the laser medium to balance the heat generated by the Stokes shifted stimulated emission in a high-power solid-state bulk laser. Such a laser without internal heating named radiation-balanced or athermal laser was experimentally demonstrated for the first time in 2002. At the present time laser cooling of solids can be largely divided into three main areas: laser cooling of rare-earth doped solids, laser cooling in semiconductors and radiation-balanced lasers. All three areas are very interesting and important and will be considered in this paper.
A step closer to visualizing the electron___phonon interplay
Energy Technology Data Exchange (ETDEWEB)
Chen, Y.L.; Lee, W.S.; Shen, Z.X.; /Stanford U., Appl. Phys. Dept. /Stanford U., Phys. Dept. /SLAC, PULSE
2011-01-04
The origin of the very high superconducting transition temperature (Tc) in ceramic copper oxide superconductors is one of the greatest mysteries in modern physics. In the superconducting state, electrons form pairs (known as Cooper pairs) and condense into the superfluid state to conduct electric current with zero resistance. For conventional superconductors, it is well established that the 2 electrons in a Cooper pair are 'bonded' by lattice vibrations (phonons), whereas in high-Tc superconductors, the 'glue' for the Cooper pairs is still under intense discussion. Although the high transition temperature and the unconventional pairing symmetry (d-wave symmetry) have led many researchers to believe that the pairing mechanism results from electron-electron interaction, increasing evidence shows that electron-phonon coupling also significantly influences the low-energy electronic structures and hence may also play an important role in high-Tc superconductivity. In a recent issue of PNAS, Carbone et al. use ultrafast electron diffraction, a recently developed experimental technique, to attack this problem from a new angle, the dynamics of the electronic relaxation process involving phonons. Their results provide fresh evidence for the strong interplay between electronic and atomic degrees of freedom in high-Tc superconductivity. In general, ultrafast spectroscopy makes use of the pump-probe method to study the dynamic process in material. In such experiments, one first shoots an ultrafast (typically 10-100 fs) 'pumping' pulse at the sample to drive its electronic system out of the equilibrium state. Then after a brief time delay ({Delta}t) of typically tens of femtoseconds to tens of picoseconds, a 'probing' pulse of either photons or electrons is sent in to probe the sample's transient state. By varying {Delta}t, one can study the process by which the system relaxes back to the equilibrium state, thus acquiring the related dynamic information. This pump-probe experiment is reminiscent of the standard method used by bell makers for hundreds of years to judge the quality of their products (hitting a bell then listening to how the sound would fade away), albeit the relevant time scale here is way beyond tens of femtoseconds. Traditionally, ultrafast spectroscopy was carried out to study gas-phase reactions, but it has also been applied to study condensed phase systems since the development of reliable solid-state ultrafast lasers approximately a decade ago. In addition, the ability to control pulse width, wavelength, and amplification of the output of Ti:Sapphire lasers has further increased the capability of this experimental method. During the past decade, many ultrafast pump-probe experiments have been carried out in various fields by using different probing methods, such as photo-resistivity, fluorescence yield, and photoemission, and they have revealed much new information complementary to the equilibrium spectroscopy methods used before. Carbone et al. used the photon-pump, electron (diffraction)-probe method. The pumping photon pulse first drives the electrons in the sample into an oscillating mode along its polarization direction. Then during the delay time, these excited electrons can transfer excess energy to the adjacent nuclei and cause crystal lattice vibration on their way back to the equilibrium state. An ultrashort electron pulse is shot at the sample at various time delays {Delta}t and the diffraction pattern is collected. Because the electron diffraction pattern is directly related to the crystal lattice structure and its motion, this technique provides a natural way to study the electron-phonon coupling problem. Furthermore, by adjusting the pump pulse's relative polarization with respect to the Cu-O bond direction, Carbone et al. were able to acquire the electron-phonon coupling strength along different directions. Focusing on the lattice dynamic along the c axis, Carbone et al. found that the c-axis phonons in the optimally-doped Bi{sub 2}Sr{sub 2}CaCu{sub
Influence of isotopic disorder on phonon frequencies and phonon linewidths of an anharmonic crystal
International Nuclear Information System (INIS)
Based on a perturbation theory using Matsubara functions and a diagrammatic treatment, it is shown that the phonon linewidths of an anharmonic crystal with isotopic impurities include two different contributions, a disorder-induced temperature-independent part, caused by harmonic scattering processes of phonons at isotopic impurities, and a disorder-influenced temperature-dependent part, caused by anharmonic decay processes. Whereas in case of an anharmonic ideal crystal it is usual to restrict the corresponding self-energy on diagonal elements only, this is no longer sufficient in the presence of impurities. For that reason it is shown that only nondiagonal elements of the effective vertex function of the harmonic phonon propagator contribute to the disorder-induced contribution to the phonon linewidth, whereas the corresponding harmonic and the anharmonic frequency shifts are determined by diagonal and nondiagonal elements as well. As an application, numerical results of the disorder-induced temperature-independent as well as the disorder-influenced temperature-dependent contribution to the phonon linewidths of a diatomic linear chain with a single mass defect are presented. copyright 1996 The American Physical Society
Anharmonicity and necessity of phonon eigenvectors in the phonon normal mode analysis
International Nuclear Information System (INIS)
It is well known that phonon frequencies can shift from their harmonic values when elevated to a finite temperature due to the anharmonicity of interatomic potential. Here, we show that phonon eigenvectors also have shifts, but only for compound materials in which each atom has at least two types of anharmonic interactions with other atoms. Using PbTe as the model material, we show that the shifts in some phonon modes may reach as much as 50% at 800?K. Phonon eigenvectors are used in normal mode analysis (NMA) to predict phonon relaxation times and thermal conductivity. We show, from both analytical derivations and numerical simulations, that the eigenvectors are unnecessary in frequency-domain NMA, which gives a critical revision of previous knowledge. This simplification makes the calculation in frequency-domain NMA more convenient since no separate lattice dynamics calculations are needed. On the other hand, we expect our finding of anharmonic eigenvectors may make difference in time-domain NMA and other areas, like wave-packet analysis
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.
Surface waves in granular phononic crystals
Pichard, Helene; Groby, Jean-Philippe; Tournat, Vincent; Zheng, Li-Yang; Gusev, Vitali
2015-01-01
The existence of surface elastic waves at a mechanically free surface of granular phononic crystals is studied. The granular phononic crystals are made of spherical particles distributed periodically on a simple cubic lattice. It is assumed that the particles are interacting by means of normal, shear and bending contact rigidities. First, Rayleigh-type surface acoustic waves, where the displacement of the particles takes place in the sagittal plane while the particles possess one rotational and two translational degrees of freedom, are analyzed. Second, shear-horizontal-type waves, where the displacement of the particles is normal to the sagittal plane while the particles possess one translational and two rotational degrees of freedom are studied. The existence of zero-group velocity surface acoustic waves of Rayleigh-type is theoretically predicted and interpreted. A comparison with surface waves predicted by the Cosserat theory is performed, and its limitations are established.
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.
Interaction of Thermal Phonons with Interfaces
Energy Technology Data Exchange (ETDEWEB)
David H. Hurley; Subhash Shinde; Edward Piekos
2013-11-01
In this chapter we will first explore the connection between interface scattering and thermal transport using the Boltzmann transport equation (BTE). It will be shown that Boltzmann transport provides a convenient method for considering boundary scattering in nanochannel structures. For internal interfaces such as grain boundaries found in polycrystals, it is more natural to consider transmission and reflection across a single boundary. In this regard we will discuss theories related to interface thermal resistance. Our qualitative discussion of the theories of phonon transport will be followed by a discussion of experimental techniques for measuring thermal transport. We end this chapter by giving a detailed description of two complimentary experimental techniques for measuring the influence of interfaces on thermal phonon transport.
Phonon Squeezing in a Superconducting Molecular Transistor
Zazunov, A; Martin, T; Martin, Thierry
2006-01-01
Josephson transport through a double junction formed by a single molecule or carbon nanotube is considered in the presence of a local vibrational mode which is linearly coupled to the charge on the molecule. An exact solution is obtained in the limit of a large superconducting gap, and it is complemented by a variational analysis in the general case. Coherent charge fluctuations involve polaron dressing and are entangled with non-classical phonon states. The flow of a Josephson current induces squeezing of the phonon mode, controlled by the superconducting phase difference and by the junction asymmetry. Squeezing is maximal in the polaron crossover regime, where a nearly minimum-uncertainty state with about 40 per cent squeezing can be obtained. Optical probes of non-classical states are briefly discussed.
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
Design and characterization of bubble phononic crystals
Leroy, Valentin; Bretagne, Alice; Fink, Mathias; Willaime, Herve; Tabeling, Patrick; Tourin, Arnaud
2009-01-01
We report the practical realization of phononic crystals with gas inclusions, using soft lithography techniques. Ultrasonic experiments from 0.3 to 5 MHz confirm the existence of deep and wide minima of transmission through the crystal. We show that the first gap is due to the combined effects of Bragg reflections and bubble resonances. We propose a simple layered model that gives a reasonable prediction of the ultrasonic transmission. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3...
Anharmonic phonon excitations in subbarrier fusion reactions
Hagino, . K.; Takigawa, N.; Kuyucak, S.
1997-01-01
Recently measured high precision data of fusion excitation function have enabled a detailed study on the effects of nuclear collective excitations on fusion reactions. Using such highly accurate data of the $^{16}$O + $^{144,148}$Sm reactions, we discuss the anharmonic properties of collective phonon excitations in $^{144,148}$Sm nuclei. It is shown that subbarrier fusion reactions are strongly affected by the anharmonic effects and thus offer an alternative method to extrac...
Thermal Logic Gates: Computation with phonons
WANG, Lei; LI, Baowen
2007-01-01
Logic gates are basic digital elements for computers. We build up thermal logic gates that can perform similar operations as their electronic counterparts. The thermal logic gates are based on the nonlinear lattices, which exhibit very intriguing phenomena due to their temperature dependent power spectra. We demonstrate that phonons, the heat carriers, can be also used to carry information and processed accordingly. The possibility of nanoscale experiment is discussed.
Sub-wavelength phononic crystal liquid sensor
Ke M.; Zubtsov M.; Lucklum R.
2011-01-01
We introduce an acoustic liquid sensor based on phononic crystals consisting of steel plate with an array of holes filled with liquid. We both theoretically and experimentally demonstrate sensor properties considering the mechanism of the extraordinary acoustic transmission as underlying phenomenon. The frequency of this resonant transmission peak is shown to rely on the speed of sound of the liquid, and the resonant frequency can be used as a measure of speed of sound and rela...
Pressure-enabled phonon engineering in metals
Lanzillo, Nicholas A.; 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
Multiple doppleron-phonon resonances in indium
Energy Technology Data Exchange (ETDEWEB)
Gudkov, V.V. [Institute for Metal Physics, Ural Department of the Russian Academy of Sciences, 18, Kovalevskaya st., 620219 Ekaterinburg (Russian Federation); Russian State Vocational Pedagogical University, 11, Mashinostroitelei st., 620012 Ekaterinburg (Russian Federation)
2004-11-01
Magnetic field dependences of absorption and phase velocity of circularly polarized ultrasonic waves were studied in super pure crystal of indium at the temperatures 1.28-4.2 K. Geometry of experiment corresponded to acoustic analogy of the Faraday effect. Multiple doppleron-phonon resonances were observed, as well as sharp peaks of Doppler-shifted acoustic cyclotron resonance and ultrasonic wave-field transport. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Pseudogap in the optical phonon spectra
Proville, L.
2004-01-01
The energy spectrum of the quantum Klein-Gordon lattice is computed numerically for different nonlinear contributions to the Hamiltonian. In agreement with the studies on the effective Hubbard Hamiltonian for boson quasi-particles (see for instance Refs.\\onlinecite{AGRANOVICH,Eilbeck}) a pairing of the phonon states is found when the nonlinearity of the lattice is significant. On the opposite, when the nonlinear contribution is weak or moderate, which is common in materials ...
Phonon scattering in graphene over substrate steps
DEFF Research Database (Denmark)
Sevincli, Haldun; Brandbyge, Mads
2014-01-01
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 su...
Novel information theory techniques for phonon spectroscopy
International Nuclear Information System (INIS)
The maximum entropy method (MEM) and spectral reverse Monte Carlo (SRMC) techniques are applied to the determination of the phonon density of states (PDOS) from heat-capacity data. The approach presented here takes advantage of the standard integral transform relating the PDOS with the specific heat at constant volume. MEM and SRMC are highly successful numerical approaches for inverting integral transforms. The formalism and algorithms necessary to carry out the inversion of specific heat curves are introduced, and where possible, I have concentrated on algorithms and experimental details for practical usage. Simulated data are used to demonstrate the accuracy of the approach. The main strength of the techniques presented here is that the resulting spectra are always physical: Computed PDOS is always positive and properly applied information theory techniques only show statistically significant detail. The treatment set out here provides a simple, cost-effective and reliable method to determine phonon properties of new materials. In particular, the new technique is expected to be very useful for establishing where interesting phonon modes and properties can be found, before spending time at large scale facilities
Heat capacity of suspended phonon cavities
Gusso, A; Gusso, Andre; Rego, Luis G. C.
2006-01-01
We present a detailed analysis of the vibrational spectrum and heat capacity of suspended mesoscopic dielectric plates, for various thickness-to-side ratios at sub-Kelvin temperatures. The vibrational modes of the suspended cavity are accurately obtained from the three-dimensional (3D) elastic equations in the small strain limit and their frequencies assigned to the cavity phonon modes. The calculations demonstrate that the heat capacity of realistic quasi-2D phonon cavities approach the linear dependence on T at sub-Kelvin temperatures. The behavior is more pronounced for the thinnest cavities, but takes place also for moderately thick structures, with thickness-to-side ratios $\\gamma$=0.1 to 0.2. It is also demonstrated that the heat capacity of the suspended phonon cavities is invariant under the product of the temperature (T) with a characteristic lateral dimension (L) of the sample. The present results establish a lower bound for the heat capacity of suspended mesoscopic structures and indicate the emerg...
Phonon drag thermopower and weak localization
Miele, A; Zaremba, E; Feng, Y; Foxon, C T; Harris, J J
1998-01-01
Previous experimental work on a two-dimensional (2D) electron gas in a Si-on-sapphire device led to the conclusion that both conductivity and phonon drag thermopower $S^g$ are affected to the same relative extent by weak localization. The present paper presents further experimental and theoretical results on these transport coefficients for two very low mobility 2D electron gases in $\\delta-$doped GaAs/Ga$_x$Al$_{1-x}$As quantum wells. The experiments were carried out in the temperature range 3-7K where phonon drag dominates the thermopower and, contrary to the previous work, the changes observed in the thermopower due to weak localization were found to be an order of magnitude less than those in the conductivity. A theoretical framework for phonon drag thermopower in 2D and 3D semiconductors is presented which accounts for this insensitivity of $S^g$ to weak localization. It also provides transparent physical explanations of many previous experimental and theoretical results.
Coherent phonon spectroscopy of non-fully symmetric modes using resonant terahertz excitation
Huber, T.; Ranke, M.; Ferrer, A.; Huber, L.; Johnson, S. L.
2015-08-01
We use intense terahertz (THz) frequency electromagnetic pulses generated via optical rectification in an organic crystal to drive vibrational lattice modes in single crystal Tellurium. The coherent modes are detected by measuring the polarization changes of femtosecond laser pulses reflecting from the sample surface, resulting in a phase-resolved detection of the coherent lattice motion. We compare the data to a model of Lorentz oscillators driven by the near-single-cycle broadband THz pulse. The demonstrated technique of optically probed coherent phonon spectroscopy with THz frequency excitation could prove to be a viable alternative to other time-resolved spectroscopic methods like standard THz time domain spectroscopy.
Photo-acoustic terahertz phonon detection and generation within a semiconductor superlattice
LEGRAND, Romain; Huynh, Agnes; Perrin, Bernard
2012-01-01
Currently, the development of compact opto-acoustic transducers able to generate and detect acoustic wave in the terahertz wavelength is an active research subject. Superlattice made with a periodic stacking of AlAs/GaAs layers has shown the ability to be used as high frequency acoustic generators and detectors. The excitation by a femtosecond laser leads to a temporally short strain in the pattern which produces quasi-monochromatic coherent phonons up to a frequency of 1 THz related to the m...
Illg, Christian; Haag, Michael; Mueller, Benedikt Y.; Czycholl, Gerd; Fähnle, Manfred
2015-11-01
Transition matrix elements for electron-phonon scattering are discussed. The approximate expression for the matrix element derived by the combination of a phenomenological theory of electronic and ionic screening of the electron-electron interaction with a microscopic perturbation theory for the matrix element is compared with unscreened matrix elements from the ab initio electron theory. The matrix elements calculated in these two ways differ very strongly. A situation is investigated (ultrafast demagnetization of a ferromagnetic film after excitation with a femtosecond laser pulse) in which nevertheless both types of matrix elements yield similar results for the demagnetization rate.
Acoustic phonon dynamics in thin-films of the topological insulator Bi2Se3
Glinka, Yuri D.; Babakiray, Sercan; Johnson, Trent A.; Holcomb, Mikel B.; Lederman, David
2015-04-01
Transient reflectivity traces measured for nanometer-sized films (6-40 nm) of the topological insulator Bi2Se3 revealed GHz-range oscillations driven within the relaxation of hot carriers photoexcited with ultrashort (˜100 fs) laser pulses of 1.51 eV photon energy. These oscillations have been suggested to result from acoustic phonon dynamics, including coherent longitudinal acoustic phonons in the form of standing acoustic waves. An increase of oscillation frequency from ˜35 to ˜70 GHz with decreasing film thickness from 40 to 15 nm was attributed to the interplay between two different regimes employing traveling-acoustic-waves for films thicker than 40 nm and the film bulk acoustic wave resonator (FBAWR) modes for films thinner than 40 nm. The amplitude of oscillations decays rapidly for films below 15 nm thick when the indirect intersurface coupling in Bi2Se3 films switches the FBAWR regime to that of the Lamb wave excitation. The frequency range of coherent longitudinal acoustic phonons is in good agreement with elastic properties of Bi2Se3.
Acoustic phonon dynamics in thin-films of the topological insulator Bi2Se3
International Nuclear Information System (INIS)
Transient reflectivity traces measured for nanometer-sized films (6–40?nm) of the topological insulator Bi2Se3 revealed GHz-range oscillations driven within the relaxation of hot carriers photoexcited with ultrashort (?100 fs) laser pulses of 1.51?eV photon energy. These oscillations have been suggested to result from acoustic phonon dynamics, including coherent longitudinal acoustic phonons in the form of standing acoustic waves. An increase of oscillation frequency from ?35 to ?70?GHz with decreasing film thickness from 40 to 15?nm was attributed to the interplay between two different regimes employing traveling-acoustic-waves for films thicker than 40?nm and the film bulk acoustic wave resonator (FBAWR) modes for films thinner than 40?nm. The amplitude of oscillations decays rapidly for films below 15?nm thick when the indirect intersurface coupling in Bi2Se3 films switches the FBAWR regime to that of the Lamb wave excitation. The frequency range of coherent longitudinal acoustic phonons is in good agreement with elastic properties of Bi2Se3
Phonons in ZnTe/CdSe superlattices with interchange of cation layers across interfaces
Energy Technology Data Exchange (ETDEWEB)
Xu Zhizhong; Dowd, H.; Ren Shangfen [Department of Physics, Illinois State University, Normal, IL (United States); Gu Zong Quan [State Key Laboratory for Surface Physics, Institute of Physics and Center for Condensed Matter Physics, Academia Sinica, Beijing (China)
1998-02-23
The ZnTe/CdSe superlattice is one of the wide-gap semiconductor superlattices grown successfully in recent years which have potential applications in blue-green diode lasers. There exists experimental evidence of interchange of entire atom layers across the interfaces of ZnTe/CdSe superlattices in spite of the resulting interface strain. First-principles pseudopotential calculations of the total energy of such systems confirmed the possibility of such interchanges. By using the combination of a first-principles pseudopotential method and an empirical method with parameters extracted from the available experimental data and pseudopotential calculations, we studied phonons in ZnTe/CdSe superlattices with interchange of atom layers across the interface. The results are compared with phonons in ZnTe/CdSe superlattices with ideal interfaces. Several unique features of phonon modes in superlattices with interchange of atomic layers across interfaces are identified and discussed. These results provide more information about interface structures in such heterostructures, and we hope that they will stimulate more experimental measurements in these materials. (author)
Phonons in ZnTe/CdSe superlattices with interchange of cation layers across interfaces
International Nuclear Information System (INIS)
The ZnTe/CdSe superlattice is one of the wide-gap semiconductor superlattices grown successfully in recent years which have potential applications in blue-green diode lasers. There exists experimental evidence of interchange of entire atom layers across the interfaces of ZnTe/CdSe superlattices in spite of the resulting interface strain. First-principles pseudopotential calculations of the total energy of such systems confirmed the possibility of such interchanges. By using the combination of a first-principles pseudopotential method and an empirical method with parameters extracted from the available experimental data and pseudopotential calculations, we studied phonons in ZnTe/CdSe superlattices with interchange of atom layers across the interface. The results are compared with phonons in ZnTe/CdSe superlattices with ideal interfaces. Several unique features of phonon modes in superlattices with interchange of atomic layers across interfaces are identified and discussed. These results provide more information about interface structures in such heterostructures, and we hope that they will stimulate more experimental measurements in these materials. (author)
Akkerman, Avraham; Murat, Michael
2015-05-01
The mean free path (MFP) for electron-phonon interactions in pure silicon is an important characteristic needed both for low energy electron transport calculations using Boltzmann transport equation, and for Monte Carlo simulations. Full band calculations present a basic (though complicated) approach to the solution of the problem. Simpler approaches based on analytical presentation of the scattering rates have also been used; however they are valid for a restricted range of electron energies, below 2 eV. In this paper we introduce a hybrid method that utilizes the density of energy states calculated from the full band calculations for electron energies larger than 2 eV, allowing to extend the analytical approach for energies up to 5 eV, where the impact ionization becomes the dominant mechanism of electron interactions within bulk silicon. The resulting MFPs as function of electron energy and lattice temperature, together with the integral probability distribution for given energy losses by phonon emission (or energy gain by absorption of phonons) form the database for Monte Carlo calculations. Using this method, we calculate the electron diffusivity and mobility as function of the electron and lattice temperatures. These parameters are important for solution of the two temperature model, used for calculations of the track structure created by swift ions and nanosecond laser beams.
Anharmonicity due to Electron-Phonon Coupling in Magnetite
Hoesch, Moritz; Piekarz, Przemys?aw; Bosak, Alexey; Le Tacon, Mathieu; Krisch, Michael; Koz?owski, Andrzej; Ole?, Andrzej M.; Parlinski, Krzysztof
2013-05-01
We present the results of inelastic x-ray scattering for magnetite and analyze the energies and widths of the phonon modes with different symmetries in a broad range of temperature 125Verwey transition is approached. It is found that the maxima of phonon widths occur away from high-symmetry points, which suggests the incommensurate character of critical fluctuations. Strong phonon anharmonicity induced by electron-phonon coupling is discovered by a combination of these experimental results with ab initio calculations which take into account local Coulomb interactions at Fe ions. It (i) explains observed anomalous phonon broadening and (ii) demonstrates that the Verwey transition is a cooperative phenomenon which involves a wide spectrum of phonons coupled to the electron charge fluctuations condensing in the low-symmetry phase.
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.
Coupled bloch-phonon oscillations in semiconductor superlattices
Dekorsy; Bartels; Kurz; Kohler; Hey; Ploog
2000-07-31
We investigate coherent Bloch oscillations in GaAs/AlxGa1-xAs superlattices with electronic miniband widths larger than the optical phonon energy. In these superlattices the Bloch frequency can be tuned into resonance with the optical phonon. Close to resonance a direct coupling of Bloch oscillations to LO phonons is observed which gives rise to the coherent excitation of LO phonons. The density necessary for driving coherent LO phonons via Bloch oscillations is about 2 orders of magnitude smaller than the density necessary to drive coherent LO phonons in bulk GaAs. The experimental observations are confirmed by the theoretical description of this phenomenon [A.W. Ghosh et al., Phys. Rev. Lett. 85, 1084 (2000)]. PMID:10991479
Acoustic phonon spectrum and thermal transport in nanoporous alumina arrays
Kargar, Fariborz; Ramirez, Sylvester; Debnath, Bishwajit; Malekpour, Hoda; Lake, Roger K.; Balandin, Alexander A.
2015-10-01
We report results of a combined investigation of thermal conductivity and acoustic phonon spectra in nanoporous alumina membranes with the pore diameter decreasing from D = 180 nm to 25 nm. The samples with the hexagonally arranged pores were selected to have the same porosity ? ? 13%. The Brillouin-Mandelstam spectroscopy measurements revealed bulk-like phonon spectrum in the samples with D = 180-nm pores and spectral features, which were attributed to spatial confinement, in the samples with 25-nm and 40-nm pores. The velocity of the longitudinal acoustic phonons was reduced in the samples with smaller pores. Analysis of the experimental data and calculated phonon dispersion suggests that both phonon-boundary scattering and phonon spatial confinement affect heat conduction in membranes with the feature sizes D < 40 nm.
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...
International Nuclear Information System (INIS)
In this paper, exact analytical expressions for the entire phonon spectra in single-walled carbon nanotubes with zigzag geometry are presented by using a new approach, originally developed by Kandemir and Altanhan. This approach is based on the concept of construction of a classical lattice Hamiltonian of single-walled carbon nanotubes, wherein the nearest and next nearest neighbor and bond bending interactions are all included, then its quantization and finally diagonalization of the resulting second quantized Hamiltonian. Furthermore, within this context, explicit analytical expressions for the relevant electron-phonon interaction coefficients are also investigated for single-walled carbon nanotubes having this geometry, by the phonon modulation of the hopping interaction
Energy Technology Data Exchange (ETDEWEB)
Kandemir, B S; Keskin, M [Department of Physics, Faculty of Sciences, Ankara University, 06100 Tandogan, Ankara (Turkey)
2008-08-13
In this paper, exact analytical expressions for the entire phonon spectra in single-walled carbon nanotubes with zigzag geometry are presented by using a new approach, originally developed by Kandemir and Altanhan. This approach is based on the concept of construction of a classical lattice Hamiltonian of single-walled carbon nanotubes, wherein the nearest and next nearest neighbor and bond bending interactions are all included, then its quantization and finally diagonalization of the resulting second quantized Hamiltonian. Furthermore, within this context, explicit analytical expressions for the relevant electron-phonon interaction coefficients are also investigated for single-walled carbon nanotubes having this geometry, by the phonon modulation of the hopping interaction.
Conductivity of strongly pumped superconductors. An electron-phonon system far from equilibrium
International Nuclear Information System (INIS)
The study of nonequilibrium physics is of great interest, because one can capture novel phenomena and properties which are hidden at equilibrium, e.g., one can study relaxation processes. A common way to study the nonequilibrium dynamics of a sample is a pump-probe experiment. In a pump probe experiment an intense laser pulse, the so called pump pulse, excites the sample and takes it out of equilibrium. After a certain delay time a second pulse, the probe pulse, measures the actual state of the sample. In this thesis, we theoretically study the pump-probe response of superconductors. On the one hand we are interest in the effect of a pump pulse and on the other hand we want to provide the pump-probe response, such that experimental measurement can be easily interpreted. In order to do this, we use the density matrix formalism to compute the pump-probe response of the system. In the density matrix formalism equations of motion are set up for expectation values of interest. In order to study the dynamics induced by a pump pulse, we compute the temporal evolution of the quasiparticle densities and the mean phonon amplitude. We find that the induced dynamics of the system depends on characteristics of the pump pulse. For short pulses, the system is pushed into the nonadiabatic regime. In this regime, the order parameter is lowered during the pump pulse and shows a 1/(?(t))-decaying oscillation afterwards. In addition, coherent phonons are generated, which is resonantly enhanced if the frequency of the order parameter oscillation is equal to the phonon frequency. For long pulses, the system is pushed into the adiabatic regime. In this regime, the order parameter is lowered during the pulse and remains almost constant afterwards. Further, there is almost no generation of coherent phonons. For the pump-probe response we compute the conductivity induced by the probe pulse. The conductivity is a typical observable in real pump-probe experiments. Hence, it is possible to compare the theoretical conductivity with a measured one. We find that the dynamics of the superconductor is reflected in oscillation of the conductivity as function of delay time between pump and probe pulse. This oscillation provides information of the frequency and decay time of the algebraically decaying order-parameter oscillations. Further, the dynamics of the coherent phonons is reflected by an oscillation of conductivity as function of delay time at the phonon frequency.
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)
Transmission de phonons acoustiques dans des cristaux phononiques asymétriques
Nghiem, Trang; Chapuis, Pierre-Olivier
2014-01-01
Les propriétés de conduction thermique des solides cristallins dépendent de la géométrie des matériaux. Les phonons acoustiques transportent l'essentiel de la chaleur : il est donc possible de contrôler les flux de chaleur si la dispersion de ces phonons est modifiée. Nous montrons que pour un réseau périodique bidimensionnel de triangles creux dans une matrice de silicium la conduction n'est plus isotrope. Nous déterminons aussi les directions privilégiées lorsque les phonons traversent un r...
Lifetimes of confined acoustic phonons in ultrathin silicon membranes
Cuffe, John; Chávez, E.; Chapuis, P.-O.; Alzina, F.; Sotomayor Torres, C. M.
2013-01-01
We study the relaxation of coherent acoustic phonon modes with frequencies up to 500 GHz in ultrathin free-standing silicon membranes. Using an ultrafast pump-probe technique of asynchronous optical sampling, we observe that the decay time of the first-order dilatational mode decreases significantly from ~4.7 ns to 5 ps with decreasing membrane thickness from ~194 to 8 nm. The experimental results are compared with theories considering both intrinsic phonon-phonon interactions and extrinsic s...
Phonon counting and intensity interferometry of a nanomechanical resonator
Cohen, Justin D.; Meenehan, Sean M.; 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 l...
Phonon Drag Effect in Nanocomposite FeSb2
Pokharel, Mani; Zhao, Huaizhou; Lukas, Kevin; Mihaila, Bogdan; Ren, Zhifeng; Opeil, Cyril
2012-01-01
We study the temperature dependence of thermoelectric transport properties of four FeSb2 nanocomposite samples with different grain sizes. The comparison of the single crystals and nanocomposites of varying grain size indicates the presence of substantial phonon drag effects in this system contributing to a large Seebeck coefficient at low temperature. As the grain size decreases, the increased phonon scattering at the grain boundaries leads to a suppression of the phonon-dr...
Electron-Phonon Mass Enhancement in Multi-Layers
Bergmann, Gerd
2006-01-01
A strong electron-phonon interaction in a metal increases the electron density of states in the vicinity of the Fermi energy dramatically. This phenomenon is called electron-phonon mass enhancement. In this paper the question is investigated whether the mass enhancement can be manipulated in multi-layers of two metals with strong and weak electron-phonon interaction. A rich behavior is observed for different thickness ranges of the layers. For thin layers one observes a rath...
Subpicosecond coherent carrier-phonon dynamics in semiconductor heterostructures
Dekorsy, Thomas; Kim, A. M. T.; Cho, Gyu Cheon; Kurz, Heinrich; Kuznetsov, Alex V.; Förster, Arno
1996-01-01
Coherent longitudinal-optical phonons are generated in semiconductor heterostructures. The coupling of the coherent, longitudinal-optic (LO) phonons to collective carrier excitations oscillating parallel to the growth direction of GaAs/Al0.36Ga0.64As quantum wells is investigated with femtosecond time-resolution. This coupling is found to be weak for small well widths and evolves towards the bulk plasmon phonon coupling at increased well widths. We present a theory for the dielectric function...
Control of Dephasing and Phonon Emission in Coupled Quantum Dots
Debald, S.; Brandes, T.; B.; Kramer
2002-01-01
We predict that phonon subband quantization can be detected in the non-linear electron current through double quantum dot qubits embedded into nano-size semiconductor slabs, acting as phonon cavities. For particular values of the dot level splitting $\\Delta$, piezo-electric or deformation potential scattering is either drastically reduced as compared to the bulk case, or strongly enhanced due to phonon van Hove singularities. By tuning $\\Delta$ via gate voltages, one can eit...
Thermal drag in spin ladders coupled to phonons
Bartsch, Christian; Brenig, Wolfram
2013-01-01
We study the spin-phonon drag effect in the magnetothermal transport of spin-1/2 two-leg ladders coupled to lattice degrees of freedom. Using a bond operator description for the triplon excitations of the spin ladder and magnetoelastic coupling to acoustic phonons, we employ the time convolutionless projection operator method to derive expressions for the diagonal and off-diagonal thermal conductivities of the coupled two-component triplon-phonon system. We find that for mag...
Phonon Effects on Spin-Charge Separation in One Dimension
Ning, W. Q.; Zhao, Hui; Wu, C. Q.; H. Q. Lin
2005-01-01
Phonon effects on spin-charge separation in one dimension are investigated through the calculation of one-electron spectral functions in terms of the recently developed cluster perturbation theory together with an optimized phonon approach. It is found that the retardation effect due to the finiteness of phonon frequency suppresses the spin-charge separation and eventually makes it invisible in the spectral function. By comparing our results with experimental data of TTF-TCN...
Width of phonon states on defects of various dimensions
Falkovsky, L. A
2001-01-01
We consider the localized phonon states created by defects of various geometries near the edge of an optical-phonon branch. The averaged Green's function is calculated to study the Raman line shape. The phonon scattering by the defects induces broadening and line shape asymmetry. The contribution of localized states to Raman spectra has a form of shoulder with a width proportional to the square root of defect concentration.
Direct observation of the superconducting gap in phonon spectra
Weber, F.; Kreyssig, A.; Pintschovius, L.; Heid, R.; Reichardt, W; Reznik, D.; Stockert, O.; K. Hradil
2008-01-01
We show that the superconducting energy gap $\\Delta$ can be directly observed in phonon spectra, as predicted by recent theories. In addition, since each phonon probes the gap on only a small part of the Fermi surface, the gap anisotropy can be studied in detail. Our neutron scattering investigation of the anisotropic conventional superconductor YNi$_2$B$_2$C demonstrates this new application of phonon spectroscopy.
Interface Phonons and Polaron Effect in Quantum Wires
Maslov A; Proshina OV
2010-01-01
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 o...
Lifetime of the phonons in the PLT ceramic
Energy Technology Data Exchange (ETDEWEB)
Barba-Ortega, J., E-mail: jjbarba@unal.edu.co; Joya, M. R., E-mail: mrinconj@unal.edu.co [Departamento de Física, Universidad Nacional de Colombia, carrera 30 # 45-03, Bogotá 1149 (Colombia); Londoño, F. A., E-mail: flondono@fisica.udea.edu.co [Instituto de Física, Universidad de Antioquia, Calle 67 #53-108 Of.6-105, Medellin (Colombia)
2014-11-05
The lifetimes at higher temperatures on lanthanum-modified lead titanate (PLT) are mainly due to the anharmonic decay of optical phonons into low-energy phonons. The temperature-independent contributions from inherent crystal defects and from boundary scattering become comparable to the phonon scattering contribution at lower temperatures. The thermal interaction is large at higher temperatures which decreases the phonon mean free path, and so the decay lifetime decreases as the temperature of the system is increased. This leads to the increased line width at higher temperatures. We made an estimate of the lifetimes for different concentrations and temperatures in PLT.
Representative longitudinal optical phonon modes in polar semiconductor quantum dots
International Nuclear Information System (INIS)
Highlights: ? We model the exciton-longitudinal optical phonon coupling for cylinder quantum dot. ? We predict a representative optical phonon mode for GaAs/AlAs quantum dot. ? Huang–Rhys factors increases with radius decreasing of GaAs/AlAs quantum dot. - Abstract: Existence of representative longitudinal optical (LO) phonon modes is theoretically discussed for the case of polar semiconductor cylindrical quantum dots embedded in a semiconductor matrix. The approach is developed within the dielectric continuum model considering the Fröhlich interaction between electrons and the confined LO phonons. The theory is applied to cylindrical GaAs/AlAs quantum dots within an adiabatic treatment.
Phonon dynamics of multiferroics: (Er, TM) MnO3
International Nuclear Information System (INIS)
The phonon dynamics of orthorhombic multiferroic perovskite RMnO3 (R = Er, Tm) using a shell model with pairwise interionic interaction potential has been investigated. The present work includes the computation of the structural parameters, phonon frequencies and the specific heat curves. The symmetry vectors obtained through detailed group - theoretical analysis for Pnma space group at the zone center point were employed to classify the phonon frequencies obtained into their irreducible representations. The evaluated phonon dynamical properties are in good agreement with the available experimental data. (author)
Control of Dephasing and Phonon Emission in Coupled Quantum Dots
Debald, S; Krämer, B
2002-01-01
We predict that phonon subband quantization can be detected in the non-linear electron current through double quantum dot qubits embedded into nano-size semiconductor slabs, acting as phonon cavities. For particular values of the dot level splitting $\\Delta$, piezo-electric or deformation potential scattering is either drastically reduced as compared to the bulk case, or strongly enhanced due to phonon van Hove singularities. By tuning $\\Delta$ via gate voltages, one can either control dephasing, or strongly increase emission into phonon modes with characteristic angular distributions.
SU(6) limit of the quasiparticle-phonon nuclear model
International Nuclear Information System (INIS)
Quasiparticle-phonon nuclear model is considered. It is shown that the Hamiltonian of the quasiparticle-phonon nuclear model has the SU(6) limit. Under some conditions this Hamiltonian can be represented as a rotational invariant which is constructed of the generators of the SU(6) algebra. The collective quadrupole random phase approximation phonon operators and their commutators form a closed algebra. The microscopic expressions for the parameters of the quadrupole phonon model are derived. The calculation of maximal numbers of bosons and the test of the conditions giving the SU(6) limit for some Zn isotopes have been performed
Directory of Open Access Journals (Sweden)
Keiko Kato
2015-09-01
Full Text Available We determine phonon decay rate by measuring the temperature dependence of coherent phonons in p-type Si under Fano resonance, where there is interference between the continuum and discrete states. As the temperature decreases, the decay rate of coherent phonons decreases, whereas that evaluated from the Raman linewidth increases. The former follows the anharmonic decay model, whereas the latter does not. The different temperature dependences of the phonon decay rate of the two methods originate from the way that the continuum state, which originates from the Fano resonance, modifies the time- and frequency-domain spectra. The observation of coherent phonons is useful for evaluating the phonon decay rate free from the interaction with the continuum state and clarifies that the anharmonic decay is dominant in p-type Si even under Fano resonance.
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...
Coherent phonon optics in a chip with an electrically controlled active device
Poyser, Caroline L.; Akimov, Andrey V.; Campion, Richard P.; Kent, Anthony J.
2015-02-01
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 external control. Here we fabricate a phononic chip, which includes a generator of coherent monochromatic phonons with frequency 378 GHz, a sensitive coherent phonon detector, and an active layer: a doped semiconductor superlattice, with electrical contacts, inserted into the phonon propagation path. In the experiments, we demonstrate the modulation of the coherent phonon flux by an external electrical bias applied to the active layer. Phonon optics using external control broadens the spectrum of prospective applications of phononics on the nanometer scale.
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 external control. Here we fabricate a phononic chip, which includes a generator of coherent monochromatic phonons with frequency 378?GHz, a sensitive coherent phonon detector, and an active layer: a doped semiconductor superlattice, with electrical contacts, inserted into the phonon propagation path. In the experiments, we demonstrate the modulation of the coherent phonon flux by an external electrical bias applied to the active layer. Phonon optics using external control broadens the spectrum of prospective applications of phononics on the nanometer scale. PMID:25652241
Energy Technology Data Exchange (ETDEWEB)
Ursu, I.; Miha-breveilescu, I.N.; Nistor, L.C.; Teodorescu, V.S.; Prokhorov, A.M.; Konov, V.I.; Uglov, S.A.
1986-08-15
New experimental data are reported supporting the conclusion that the formation of surface compound layers by high-intensity multipulse laser irradiation is determined by a critical value of the oxygen impurities concentration in the ambient nitrogen atmosphere.
Howard, Colin; El-Batanouny, M.
2013-01-01
Photoemission and phonon spectroscopies have yielded widely varying estimates of the electron-phonon coupling constant \\lambda\\ on the surfaces of topological insulators, even for a particular material and technique. We connect the results of these experiments by determining the Dirac fermion quasiparticle spectral function using information from measured spectra of a strongly-interacting, low-lying optical surface phonon band. The manifest spectral features resulting from t...
Quantifying electron-phonon coupling in CdTe1-xSex nanocrystals via coherent phonon manipulation
Spann, B. T.; Xu, X.
2014-08-01
We employ ultrafast transient absorption spectroscopy with temporal pulse shaping to manipulate coherent phonon excitation and quantify the strength of electron-phonon coupling in CdTe1-xSex nanocrystals (NCs). Raman active CdSe and CdTe longitudinal optical phonon (LO) modes are excited and probed in the time domain. By temporally controlling pump pulse pairs to coherently excite and cancel coherent phonons in the CdTe1-xSex NCs, we estimate the relative amount of optical energy that is coupled to the coherent CdSe LO mode.
Measurement and control of electron-phonon interactions in graphene
Remi, Sebastian
Despite the weak interaction between electrons and atomic vibrations (phonons) in the one-atom thick crystal of carbon called graphene, the scattering of electrons off phonons limits coherent electron transport in pristine devices over mesoscopic length scales. The future of graphene as a replacement to silicon and other materials in advanced electronic devices will depend on the success of controlling and optimizing electronic transport. In this dissertation, we explore the electron-phonon interaction via Raman scattering, elucidating the effects of filling and emptying charge states on the phonons in both the metallic state and when levels are quantized by an applied perpendicular magnetic field. In zero magnetic field, the phonon energy shifts due to electronic screening by charge carriers. Previously, a logarithmic divergence of the phonon energy was predicted as a function of the charge carrier density. For the first time, we observe signatures of this logarithmic divergence at liquid He temperatures after vacuum annealing on single layers. We also measure the electron-phonon coupling strength, Fermi velocity, and broadening of electronic quantum levels from Raman scattering and correlate these parameters to electronic transport. In a strong perpendicular magnetic field, the energy bands split into discrete Landau levels. Here, we observe kinks and splitting of the optical phonon energy, even when the Landau level transitions are far from resonant with the phonons. We discover that the kinks are attributed to charge filling of Landau levels, as understood from a linearized model based on electron-phonon interactions. Moreover, we show that material parameters determined without magnetic fields also describe phonon behavior in high magnetic fields.
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.
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.
Influence of laser heating on the X-ray diffraction intensity of InSb
International Nuclear Information System (INIS)
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 ?-, 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
International Nuclear Information System (INIS)
In this paper, we introduce an improvement of the Debye model for the phonon spectrum in a quantum box at low temperatures. This improvement is a direct consequence of the consideration of the discrete phonon spectrum in some special quantum boxes, names in this paper, quantum cubic cells (QCC in which the highest significant level, qT, is smaller than 100). We show that a discrete Planck spectrum may occur in nanometric QCC around the temperature 1K. Furthermore, we demonstrate that the total energy density and the heat capacity become functions of the product of cell size by temperature Pq, which are clear and measurable quantum effects in solid QCC. The limits of this quantum regime of the cubic cell are set as Pq is an element of [0.1, 1] and a reciprocity rule for the cell size and temperature is given. The thermodynamic functions for the phonon gas in QCC are recalculated taking into account their dependency on Pq. The calculation of the phonon average velocity, which plays a key role in the Debye model, is also reconsidered and simplified for quasi-isotropic cubic crystals. Finally, the theoretical formula of the Debye temperature for quasi-isotropic cubic solids is corrected (at low temperatures) and put in a form which depends on a single elastic constant. We show that this correction reduces the errors between the calculated and experimental Debye temperatures of some elements which crystallize in the cubic system. (author)
Robust and optimal laser cooling of trapped ions
J. Cerrillo; Retzker, A.; Plenio, M. B.
2009-01-01
We present a robust and fast laser cooling scheme suitable for trapped atoms and ions. Based on quantum interference, generated by a special laser configuration, it is able to rapidly cool the system such that the final phonon occupation vanishes to zeroth order in the Lamb-Dicke parameter in contrast to existing cooling schemes. Furthermore, it is robust under conditions of fluctuating laser intensity and frequency, thus making it a viable candidate for experimental applica...
Polaronic Signatures in Phonon Isotopic Shifts
Mustre de Leon, J.; de Coss, R.; Pali, J.; Rubio-Ponce, A.; Bishop, A. R.
1998-03-01
Recent optical studies in YBCO have shown that under oxygen substitution specific phonon modes associated with the axial oxygen vibrations, i.e., (505 cm-1 (G. Ruani, C. Taliani, M. Muccini, K. Conder, E. Kaldis, and K. A. M=FCller, Physica C 226 101-105 (1994).) Raman active mode and 565 cm-1 Infrared Active (R. Heen, T. Strach, E. Sch=F6nherr, and M. Cardona, Phys. Rev. B 55, 3285 (1997).) exhibit an isotopic shift that differs from that obtained assuming harmonic motion of this atom. We present calculations of the Isotope shifts in those phonon modes using rigid double well potentials, similar to those used in the interpretation of early XAFS (J. Mustre de Leon, S.D. Conradson, I. Batistic and A.R. Bishop, Phys. Rev. Lett. 65, 1675 (1990).) experiments. We find that the predictions of these models differ from the experimental values even more than those found using harmonic potentials. Using a three site model electron-phonon Hamiltonian, which exhibits polaron tunelling, (J. Mustre de Leon, I. Batistic, A. Bishop, S. Trugman, and S.D. Conradson. Phys. Rev. Lett. 68, 3236 (1992).) we calculate Isotope shifts for the excitation spectra of this model. =46or excitations identified with the optical modes mentioned above we find isotpic shifts consistent with the experimental values, suggesting polaronic behavior associated with this mode. We note that the lowest exitacion moce of this model identified with polaronic tunelling exhibits opposite behavior to that observed for the other excitations or modes derived from rigid potentials.
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...
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.
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
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.
Phonon scattering in graphene over substrate steps
Energy Technology Data Exchange (ETDEWEB)
Sevinçli, H., E-mail: haldunsevincli@iyte.edu.tr [Department of Materials Science and Engineering, Izmir Institute of Technology, Gülbahçe Kampüsü, 35430 Urla, Izmir (Turkey); Department of Micro- and Nano-technology (DTU Nanotech), Technical University of Denmark, DK-2800 Kongens Lyngby (Denmark); Brandbyge, M., E-mail: mads.brandbyge@nanotech.dtu.dk [Department of Micro- and Nano-technology (DTU Nanotech), Technical University of Denmark, DK-2800 Kongens Lyngby (Denmark); Center for Nanostructured Graphene(CNG), Department of Micro- and Nano-technology, Technical University of Denmark, DK-2800 Kongens Lyngby (Denmark)
2014-10-13
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.
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.
Phonon frequency spectrum in random binary alloys
International Nuclear Information System (INIS)
Starting from the augmented space formalism (Mookerjee 1973 a,b), a cluster CPA calculation for the phonon density of states is presented for linear chains as well as three-dimensional lattices. Off-diagonal disorder has been taken into account, and a self-consistent medium has been generated. Unlike earlier work, the Green function does not suffer from analytical difficulties in any concentration range. At the same time, the self-consistent medium gives a superior estimate of the band edges and the structures near them. (author)
Electron-Acoustic Phonon Interaction in Graphene
Mo?ulkoc, Aybey
2014-01-01
Özet. Bu çal??mada, elektronlar?n akustik fononlar ile etkile?mesinden kaynaklanan kiral polaron olu?umu incelenmi?tir. Elektron-fonon sistemlerinin taban durumunu hesaplayabilmek için Lee-Low-Pines teorisi çerçevesinde analitik bir metot geli?tirilmi?tir. Grafenin dejenere band yap?s?n?n kiral polaron olu?umunu destekledi?i tespit edilmi?tirAbstract. In this study, chiral polaron formation due to interactions of the electrons with acoustic phonon was investigated. In order to calculate froun...
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.
Ultralow-threshold laser and blue shift cooperative luminescence in a Yb3+ doped silica microsphere
Directory of Open Access Journals (Sweden)
Yantang Huang
2014-02-01
Full Text Available An experimental investigation on ultralow threshold laser and blue shift cooperative luminescence (CL in a Yb3+ doped silica microsphere (YDSM with continuous-wave 976 nm laser diode pumping is reported. The experimental results show that the YDSM emits laser oscillation with ultralow threshold of 2.62 ?W, and the laser spectrum is modulated by the microsphere morphology characteristics. In addition, blue emission of YDSM is also observed with the increase of pump power, which is supposed to be generated by CL of excited Yb ion-pairs with the absorption of 976 nm photons and Si-O vibration phonons, and the process is explained with an energy level diagram. This property of the blue shift CL with phonons absorption in the Yb3+doped microcavity makes it attractive for the application of laser cooling based on anti-Stokes fluorescence emission, if the Yb3+doped microcavity made from with low phonon energy host materials.
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
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)
Representative longitudinal optical phonon modes in polar semiconductor quantum dots
Cheche, Tiberius O.; Barna, Valentin; Stamatin, Ioan
2012-01-01
Existence of representative longitudinal optical (LO) phonon modes is theoretically discussed for the case of polar semiconductor cylindrical quantum dots embedded in a semiconductor matrix. The approach is developed within the dielectric continuum model considering the Fr\\"ohlich interaction between electrons and the confined LO phonons. The theory is applied to cylindrical GaAs/AlAs quantum dots within an adiabatic treatment.
PHONON MECHANISM OF THE MAGNETOVOLUME EFFECT IN ITINERAN ELECTRON FERROMAGNETS
D.; Kim
1988-01-01
We show the possibility of having a negative phonon Grüneisen constant in the ferromagnetic state of a metal. With such behavior of Grüneisen constant, we propose phonons can be playing an important role in causing zero or negative thermal volume expansion often observed in ferromagnetic metals.
Phonon thermal transport through tilt grain boundaries in strontium titanate
Zheng, Zexi; Chen, Xiang; Deng, Bowen; Chernatynskiy, Aleksandr; Yang, Shengfeng; Xiong, Liming; Chen, Youping
2014-08-01
In this work, we perform nonequilibrium molecular dynamics simulations to study phonon scattering at two tilt grain boundaries (GBs) in SrTiO3. 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 SrTiO3 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.
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 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.
Properties of interface phonon spectra in complicated cylindrical nanosystem
O.M. Voitsekhivska; A.M.Gryschyk
2007-01-01
The spectra of two types of interface phonons (top and side optical) are studied within the framework of dielectric continuum model for combined nanoheterosystems consisting of semiconductor cylindrical quantum dots inside the cylindrical quantum wire placed into dielectric or semiconductor medium. The dependencies of both types of interface phonon energies on the quasiwave numbers and geometric parameters of nanosystem are calculated and analysed.
Electron-phonon interaction on optical spectra of nanoelectronic devices
Kim, Q.
2002-01-01
Information obtained on the solid-state lattice dynamics by electron-phonon interaction between lattice phonons and electrons could open up to learn more about lattice dynamics and to apply it in nanoelectronic devices including software reliability, nano-size capacitors, master clock sources, as well as non-contact temperature probes on nano-electronic and photonicdevices.
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.
International Nuclear Information System (INIS)
We describe a general method to determine the relative phase difference between the complex components of a phononic Raman tensor from the measured angular dependence of the intensity of light scattered inelastically by the phonon in a Raman process. The method is applied to Raman spectra of a (110)-oriented SmBa2Cu3O7-? thin film obtained at room temperature. From our spectra we derive for the A1g-like phonons the anisotropy ratio and the relative phase difference between the two independent components of the Raman tensor as a function of laser energy ??. We point out that our results can be used to verify theoretical calculations of Raman tensors and compare our data with values calculated for the related compound YBa2Cu4O8. copyright 1998 The American Physical Society
International Nuclear Information System (INIS)
We have investigated the terahertz (THz) radiation from the coherent GaAs-like longitudinal optical (LO) phonons at room temperature in GaAs/AlAs multiple quantum wells utilizing an optical gating method with an ultrashort pulse laser. It has been found that the intensity of the THz radiation with a long dephasing time is markedly enhanced under the condition that the energy spacing between the fundamental heavy-hole and light-hole excitons is almost equal to the LO-phonon energy. This fact demonstrates that the impulsive excitonic interference, which produces no beating oscillation at room temperature owing to a very fast dephasing time, acts as a driving force for the coherent LO phonon emitting the intense THz radiation
Lattice parameters and Raman-active phonon modes of ?-(Al{sub x}Ga{sub 1?x}){sub 2}O{sub 3}
Energy Technology Data Exchange (ETDEWEB)
Kranert, Christian, E-mail: christian.kranert@uni-leipzig.de; Jenderka, Marcus; Lenzner, Jörg; Lorenz, Michael; Wenckstern, Holger von; Schmidt-Grund, Rüdiger; Grundmann, Marius [Institut für Experimentelle Physik II, Universität Leipzig, Halbleiterphysik, Linnéstr. 5, 04103 Leipzig (Germany)
2015-03-28
We present X-ray diffraction and Raman spectroscopy investigations of a (100)-oriented (Al{sub x}Ga{sub 1–x}){sub 2}O{sub 3} thin film on MgO (100) and bulk-like ceramics in dependence on their composition. The thin film grown by pulsed laser deposition has a continuous lateral composition spread allowing to determine precisely the dependence of the phonon mode properties and lattice parameters on the chemical composition. For x?phonon energies depend linearly on the composition. We determined the slopes of these dependencies for the individual lattice parameters and for nine Raman lines, respectively. While the lattice parameters of the ceramics follow Vegard's rule, deviations are observed for the thin film. This deviation has only a small effect on the phonon energies, which show a reasonably good agreement between thin film and ceramics.
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.
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.
Surface anharmonicity: Temperature dependence of phonon energies on Cu(110)
International Nuclear Information System (INIS)
The temperature dependence of surface phonons on Cu(110) has been determined with high resolution electron energy loss spectroscopy between 21 and 766 K. Phonons at bar ? and at bar Y, both with atomic motion perpendicular to the surface, have been examined to assess the importance of anharmonicity at the surface. As the temperature is increased the observed phonon energies decrease and the linewidths increase. The same percentage decrease is observed at bar ? and bar Y. A simple model using an anharmonic potential can reproduce the magnitude and shape of the temperature dependence of the phonon at bar ?. Direct comparison with bulk phonon studies shows that the anharmonicity at the surface is 4.1--4.8 times greater. 18 refs., 5 figs
Controlling elastic waves with small phononic crystals containing rigid inclusions
Peng, Pai; Qiu, Chunyin; Liu, Zhengyou; Wu, Ying
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.
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.
Acoustic beamwidth compressor using gradient-index phononic crystals
International Nuclear Information System (INIS)
We report a novel approach to effectively couple acoustic energy into a two-dimensional phononic-crystal waveguide by an acoustic beamwidth compressor using the concept of a gradient-index phononic crystal (GRIN PC). The GRIN PC-based beamwidth compressor is composed of a square array of solid scatterers embedded in epoxy. By gradually modulating the density and elastic modulus of the scatterers along the direction transverse to the phononic propagation, the beamwidth compressor can efficiently compress the wide acoustic beam to the scale of the phononic-crystal waveguide. This acoustic beamwidth compressor is investigated through a finite-difference time-domain method. A beam-size conversion ratio of 6.5 : 1 and a transmission efficiency of up to 90% is obtained over the working frequency range of the phononic-crystal waveguide. Potential applications for this device include acoustic biosensors and signal processors.
Heterobarrier for converting hot-phonon energy to electric potential
Shin, Seungha; Melnick, Corey; Kaviany, Massoud
2013-02-01
We show that hot phonons emitted in energy conversion or resistive processes can be converted to electric potential in heterobarrier structures. Using phonon and electron interaction kinetics and self-consistent ensemble Monte Carlo, we find the favorable conditions for unassisted absorption of hot phonons and design graded heterobarriers for their direct conversion into electric energy. Tandem barriers with nearly optical-phonon height allow for substantial potential gain without current loss. We find that 19% of hot phonons can be harvested with an optimized GaAs/AlxGa1-xAs barrier structure over a range of current and electron densities, thus enhancing the overall energy conversion efficiency and reducing waste heat.
Persson, A. I. H.; Enquist, H.; Jurgilaitis, A.; Andreasson, B. P.; Larsson, J.
2015-11-01
The spectrum of laser-generated acoustic phonons in indium antimonide coated with a thin nickel film has been studied using time-resolved x-ray diffraction. Strain pulses that can be considered to be built up from coherent phonons were generated in the nickel film by absorption of short laser pulses. Acoustic reflections at the Ni-InSb interface leads to interference that strongly modifies the resulting phonon spectrum. The study was performed with high momentum transfer resolution together with high time resolution. This was achieved by using a third-generation synchrotron radiation source that provided a high-brightness beam and an ultrafast x-ray streak camera to obtain a temporal resolution of 10 ps. We also carried out simulations, using commercial finite element software packages and on-line dynamic diffraction tools. Using these tools, it is possible to calculate the time-resolved x-ray reflectivity from these complicated strain shapes. The acoustic pulses have a peak strain amplitude close to 1%, and we investigated the possibility to use this device as an x-ray switch. At a bright source optimized for hard x-ray generation, the low reflectivity may be an acceptable trade-off to obtain a pulse duration that is more than an order of magnitude shorter.
Resonant and nonlocal properties of phononic metasolids
Torrent, Daniel; Pennec, Yan; Djafari-Rouhani, Bahram
2015-11-01
We derive a general theory of effective properties in metasolids based on phononic crystals with low frequency resonances. We demonstrate that in general these structures need to be described by means of a frequency-dependent and nonlocal anisotropic mass density, stiffness tensor and a third-rank coupling tensor, which shows that they behave like a nonlocal Willis medium. The effect of nonlocality and coupling tensor manifest themselves for some particular resonances, whereas they become negligible for other resonances. Considering the example of a two-dimensional phononic crystal, consisting of triangular arrangements of cylindrical shells in an elastic matrix, we show that its mass density tensor is strongly resonant and anisotropic presenting both positive and negative divergent values, while becoming scalar in the quasistatic limit. Moreover, it is found that the negative value of transverse component of the mass density is induced by a dipolar resonance, while that of the vertical component is induced by a monopolar one. Finally, the dispersion relation obtained by the effective parameters of the crystal is compared with the band structure, showing good agreement for the low-wave-number region, although the nonlocal effects are important given the existence of some resonant values of the wave number.
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
Size effects in thermal conduction by phonons
Allen, Philip B.
2014-08-01
Heat transport in nanoscale systems is both hard to measure microscopically, and hard to interpret. Ballistic and diffusive heat flow coexist, adding confusion. This paper looks at a very simple case: a nanoscale crystal repeated periodically. This is a popular model for simulation of bulk heat transport using classical molecular dynamics (MD), and is related to transient thermal grating experiments. Nanoscale effects are seen in perhaps their simplest form. The model is solved by an extension of standard quasiparticle gas theory of bulk solids. Both structure and heat flow are constrained by periodic boundary conditions. Diffusive transport is fully included, while ballistic transport by phonons of a long mean free path is diminished in a specific way. Heat current J (x) and temperature gradient ?T (x') have a nonlocal relationship, via ? (x-x'), over a distance |x-x'| determined by phonon mean free paths. In MD modeling of bulk conductivity, finite computer resources limit system size. Long mean free paths, comparable to the scale of heating and cooling, cause undesired finite-size effects that have to be removed by extrapolation. The present model allows this extrapolation to be quantified. Calculations based on the Peierls-Boltzmann equation, using a generalized Debye model, show that extrapolation involves fractional powers of 1/L. It is also argued that heating and cooling should be distributed sinusoidally [??cos(2?x/L)] to improve convergence of numerics.
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)
Quasi-bound exiton-LO phonon intermediate state in multi-phonon Raman scattering of semiconductors
International Nuclear Information System (INIS)
A new model is proposed to understand multi-phonon Raman spectrum (MRS) of II-VI semiconductors. A quasibound state of exciton-LO phonon complex (EPQBS) in the intermediate state is shown to be responsible for the observed overtone series. The observation of MRS is a natural consequence of our model in which the EPQBS lies in the absorption continuum. (author)
Ultrafast X-ray diffraction of laser-irradiated crystals
Heimann, P A; Kang, I; Johnson, S; Missalla, T; Chang, Z; Falcone, R W; Schönlein, R W; Glover, T E; Padmore, H A
2001-01-01
Coherent acoustic phonons have been observed in the X-ray diffraction of a laser-excited InSb crystal. Modeling based on time-dependent dynamical diffraction theory has allowed the extraction of fundamental constants, such as the electron-acoustic phonon coupling time. A dedicated beamline for time-resolved studies has been developed at the Advanced Light Source with special considerations toward high transmission, low scattering and a wide photon energy range. The facility combines a bend magnet beamline, time-resolved detectors and a femtosecond laser system.
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)
Bagheri Harouni, M.
2014-11-01
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.
Frozen phonon calculations for the L(2/3, 2/3, 2/3) phonon of niobium and molybdenum
International Nuclear Information System (INIS)
Materials with high superconducting transition temperatures frequently exhibit anomalous features in their phonon dispersion curves. The origin of these anomalies and their significance for superconductivity has been the subject of much debate. Two seemingly different models have been proposed to explain these anomalies in terms of the electron-phonon interaction. The first model focuses on real space charge-density distortions (CDD's), while the second emphasizes the states in reciprocal space near the Fermi energy. To test the assumptions in these models and to better understand the details of the electronic response to lattice vibrations in transition metals self-consistent frozen phonon calculations were performed for the (2/3, 2/3, 2/3) phonon in Nb and Mo. Initial results are reported for the CDD's associated with this phonon and discuss the differences between Nb and Mo
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
Balin, Victor N.; Guk, Alexey S.; Jordanishwily, A. K.; Kropotov, Sergey P.; Maday, Dimitry Y.; Kusovkova, Tatyana A.; Serebryakov, Victor A.; Frolov, Sergey V.
1995-04-01
The paper presents the investigation results of the morphofunctional state of the mouth cavity tissues after teeth processing by the laser radiation with the wavelength 2.69 micrometers . Teeth preparation down to the state of the deep or intermediate caries as well as pulp trepanation cases are discussed. No pulp necrosis was observed.
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.
Iskandar, A.; Abou-Khalil, A.; Kazan, M.; Kassem, W.; Volz, S.
2015-03-01
This paper provides theoretical understanding of the interplay between the scattering of phonons by the boundaries and point-defects in SiGe thin films. It also provides a tool for the design of SiGe-based high-efficiency thermoelectric devices. The contributions of the alloy composition, grain size, and film thickness to the phonon scattering rate are described by a model for the thermal conductivity based on the single-mode relaxation time approximation. The exact Boltzmann equation including spatial dependence of phonon distribution function is solved to yield an expression for the rate at which phonons scatter by the thin film boundaries in the presence of the other phonon scattering mechanisms. The rates at which phonons scatter via normal and resistive three-phonon processes are calculated by using perturbation theories with taking into account dispersion of confined acoustic phonons in a two dimensional structure. The vibrational parameters of the model are deduced from the dispersion of confined acoustic phonons as functions of temperature and crystallographic direction. The accuracy of the model is demonstrated with reference to recent experimental investigations regarding the thermal conductivity of single-crystal and polycrystalline SiGe films. The paper describes the strength of each of the phonon scattering mechanisms in the full temperature range. Furthermore, it predicts the alloy composition and film thickness that lead to minimum thermal conductivity in a single-crystal SiGe film, and the alloy composition and grain size that lead to minimum thermal conductivity in a polycrystalline SiGe film.
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)
Cross-plane phonon transport properties of molybdenum disulphide
Wei, Zhiyong; Liu, Biao; Liu, Chenhan; Bi, Kedong; Yang, Juekuan; Chen, Yunfei
2015-11-01
The cross-plane thermal conductivity of a molybdenum disulphide (MoS2) film is calculated from the nonequilibrium molecular dynamics simulation. The results show that, unlike graphite which has a slow convergent speed, the thermal conductivity of MoS2 tends to a convergent value when the film thickness is beyond about 40?nm. We also construct the cross-plane thermal conductivity of bulk MoS2 as an accumulation function of the phonon mean free path (MFP). It is found that phonons with MFPs below 40?nm contribute ~90% of the MoS2 cross-plane thermal conductivity at room temperature. This critical size of the phonon MFP is about two orders of magnitude smaller than that of graphite. Further calculations show that the shorter cross-plane phonon MFPs in bulk MoS2 may result from the lower phonon cut-off frequency and the mismatch of phonon density of state between Mo and S due to the mass difference. The phonon transport properties obtained would be helpful in the design and optimization of MoS2-based devices.
Experimental studies of electron-phonon interactions in gallium nitride
International Nuclear Information System (INIS)
This thesis presents an experimental investigation of the electron-phonon interaction in GaN. Bulk epilayers, grown by MBE, and AIGaN/GaN heterostructure grown by MOCVD, have been studied. The energy relaxation rate for hot electrons has been measured over a wide range of temperatures, allowing both acoustic and optic phonon emission to be studied in GaN epilayers. Direct phonon measurements, both studying the emission and absorption processes, have been performed. Detection of phonons emitted when hot electrons relax their excess energy complements the measurements of relaxation rates. Absorption of acoustic phonons by the epilayers, using both fixed and extended metal film phonon sources, allowed investigation into the effectiveness of the 2kF cutoff in the low mobility layers. The experimental findings are compared with the predictions of theory. AIGaN/GaN heterostructures were characterised and measurements of the energy relaxation rate in the temperature range 4K-40K obtained. Excellent agreement with theory is observed. A preliminary study of phonon absorption by the 2DEG system is presented, which allowed experimental determination of the 'thickness' of the 2DEG and demonstrated the applicability of the technique in the study of low dimensional systems. (author)
International Nuclear Information System (INIS)
Here we present a theoretical work on short pulse laser interaction with metal targets. With the help of Two Temperature Model we consider in detail the interplay of two competitive mechanism of the laser deposited energy dissipation: the fast electron heat conduction and the electron-phonon interaction processes. For a range of pulse durations the modelling included a complex description of these processes as the functions of the electron and phonon temperatures. It was shown that for transitional type of metals the maximum surface temperature determined for a range of pulse durations at fixed fluence exhibits peak behavior and the corresponding pulse duration is close to the electron-phonon relaxation time. In contrast, having complex deviation of heat conductivity from its linear growth with the electronic temperature, the group of noble metals shows different behavior in maximum surface temperature depending on the fluence regime. Based on the results, an experimental approach in measuring the electron-phonon relaxation time is suggested and a general tendency of photo-mechanical versus photo-thermal damage of metal targets is deduced.
Role of phonon dispersion in studying phonon mean free paths in skutterudites
Zebarjadi, Mona; Yang, Jian; Lukas, Kevin; Kozinsky, Boris; Yu, Bo; Dresselhaus, Mildred; Opeil, Cyril; Ren, Zhifeng; Chen, Gang
2012-01-01
Experimental thermal conductivity of bulk materials are often modeled using Debye approximation together with functional forms of relaxation time with fitting parameters. While such models can fit the temperature dependence of thermal conductivity of bulk materials, the Debye approximation leads to large error in the actual phonon mean free path, and consequently, the predictions of the thermal conductivity of the nanostructured materials using the same relaxation time are not correct even af...
TWO-PHONON BOUND STATES IN AMMONIUM CHLORIDE AT FINITE TEMPERATURES
Anikiev, A.; Umarov, B.; Gorelik, V.; Vetelino, J.
1981-01-01
Two-phonon density of states in 2[MATH]4 band of ammonium chloride crystal was calculated by the method of Green's temperature functions considering anharmonic phonon-phonon interaction. Theoretically calculated temperature dependence of quasibound two-phonon state is compared to the Raman scattering experiments.
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)
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.
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.
International Nuclear Information System (INIS)
The first measurements were made of the energy threshold for air breakdown on metallic and dielectric targets when a plasma was formed in the tail of a TEA CO2 laser pulse. A study was made of the dependences of the threshold characteristics on the dimensions of the illuminated spot and on the angle of incidence of the radiation on the target. A qualitative interpretation of the results is given
Energy Technology Data Exchange (ETDEWEB)
Ageev, V.P.; Burdin, S.G.; Goncharov, I.N.; Goncharov, Y.N.; Konov, V.I.; Skvortsov, Y.A.; Tokarev, V.N.; Chapliev, N.I.
1983-04-01
The first measurements were made of the energy threshold for air breakdown on metallic and dielectric targets when a plasma was formed in the tail of a TEA CO/sub 2/ laser pulse. A study was made of the dependences of the threshold characteristics on the dimensions of the illuminated spot and on the angle of incidence of the radiation on the target. A qualitative interpretation of the results is given.
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)