Physical mechanisms of coherent acoustic phonons generation by ultrafast laser action.
Ruello, Pascal; Gusev, Vitalyi E
2015-02-01
In this review we address the microscopic mechanisms that are involved in the photogeneration processes of GHz-THz coherent acoustic phonons (CAP) induced by an ultrafast laser pulse. Understanding and describing the underlying physics is necessary indeed for improving the future sources of coherent acoustic phonons useful for the non-destructive testing optoacoustic techniques. Getting more physical insights on these processes also opens new perspectives for the emerging field of the opto-mechanics where lattice motions (surface and/or interfaces ultrafast displacements, nanostructures resonances) are controlled by light. We will then remind the basics of electron-phonon and photon-phonon couplings by discussing the deformation potential mechanism, the thermoelasticity, the inverse piezoelectric effect and the electrostriction in condensed matter. Metals, semiconductors and oxide materials will be discussed. The contribution of all these mechanisms in the photogeneration process of sound will be illustrated over several examples coming from the rich literature. PMID:25038958
The terahertz phonon laser a full quantum treatment
Camps, I; Pastawski, H M; Foà-Torres, L E F
2001-01-01
The aim of this work is to describe the behavior of a device capable to generate high frequency (~THz) acoustic phonons. This device consists in a GaAs-AlGaAs double barrier heterostructure that, when an external bias is applied, produces a high rate of longitudinal optical LO phonons. These LO phonons are confined and they decay by stimulated emission of a pair of secondary longitudinal optical (LO_2) and transversal acoustic (TA) phonons. The last ones form an intense beam of coherent acoustic phonons. To study this effect, we start from a tight binding Hamiltonian that take into account the electron-phonon (e-ph) and phonon-phonon (ph-ph) interactions. We calculate the electronic current through the double barrier and we obtain a set of five coupled kinetic equations that describes the electron and phonon populations. The results obtained here confirm the behavior of the terahertz phonon laser, estimated by rougher treatments.
Phonon superradiance and phonon laser effect in nanomagnets
Chudnovsky, E. M.; Garanin, D. A.
2004-01-01
We show that the theory of spin-phonon processes in paramagnetic solids must take into account the coherent generation of phonons by the magnetic centers. This effect should drastically enhance spin-phonon rates in nanoscale paramagnets and in crystals of molecular nanomagnets.
Nonequilibrium phonon effects in midinfrared quantum cascade lasers
International Nuclear Information System (INIS)
We investigate the effects of nonequilibrium phonon dynamics on the operation of a GaAs-based midinfrared quantum cascade laser over a range of temperatures (77–300?K) via a coupled ensemble Monte Carlo simulation of electron and optical-phonon systems. Nonequilibrium phonon effects are shown to be important below 200?K. At low temperatures, nonequilibrium phonons enhance injection selectivity and efficiency by drastically increasing the rate of interstage electron scattering from the lowest injector state to the next-stage upper lasing level via optical-phonon absorption. As a result, the current density and modal gain at a given field are higher and the threshold current density lower and considerably closer to experiment than results obtained with thermal phonons. By amplifying phonon absorption, nonequilibrium phonons also hinder electron energy relaxation and lead to elevated electronic temperatures.
Electron-phonon coupling in laser excited metals
Energy Technology Data Exchange (ETDEWEB)
Klett, Isabel; Mueller, Benedikt; Rethfeld, Baerbel [TU Kaiserslautern (Germany)
2011-07-01
Irradiation of metals with an ultrashort laser pulse leads to a hot electron gas while the lattice stays cold. The corresponding electron-phonon coupling has been calculated using a thermalized Fermi distribution function. However, after laser excitation, the electrons cannot be assumed in equilibrium, due to their relaxation time of tens of femtoseconds. In order to allow a nonequilibrium distribution function, the Boltzmann equation is applied. This model is extended by implementing the density of states of real metals into the Boltzmann collision terms. From the solution we extract the electron-phonon coupling in thermal nonequilibrium.
Nonequilibrium electron–phonon coupling after ultrashort laser excitation of gold
International Nuclear Information System (INIS)
Exciting a metal by an ultrashort laser pulse, the electrons are driven out of thermal equilibrium, while the phonon system remains almost unaffected. During and after the irradiation, the electrons thermalize and transfer energy to the phonons. In this work, we investigate the electron–phonon coupling in gold. The dependence of the coupling strength on the phonon properties as well as the nonequilibrium electrons has been taken into account. For the phonon system, we utilize several phonon temperatures. For the electrons we apply different excitation scenarios depending on the laser fluence and the photon energy. We observe that for gold at electron temperatures below 2000 K, the phonon distribution may affect the coupling slightly. However, the electron distribution, especially under nonequilibrium conditions, governs the electron–phonon coupling factor significantly.
International Nuclear Information System (INIS)
Laser cooling of semiconductors has been an elusive goal for many years, and while attempts to cool the narrow gap semiconductors such as GaAs are yet to succeed, recently, net cooling has been attained in a wider gap CdS. This raises the question of whether wider gap semiconductors with higher phonon energies and stronger electron-phonon coupling are better suitable for laser cooling. In this work, we develop a straightforward theory of phonon-assisted absorption and photoluminescence of semiconductors that involves more than one phonon and use to examine wide gap materials, such as GaN and CdS and compare them with GaAs. The results indicate that while strong electron-phonon coupling in both GaN and CdS definitely improves the prospects of laser cooling, large phonon energy in GaN may be a limitation, which makes CdS a better prospect for laser cooling.
Khurgin, Jacob B
2014-01-01
Laser cooling of semiconductors has been an elusive goal for many years, and while attempts to cool the narrow gap semiconductors such as GaAs are yet to succeed, recently, net cooling has been attained in a wider gap CdS. This raises the question of whether wider gap semiconductors with higher phonon energies and stronger electron-phonon coupling are better suitable for laser cooling. In this work we develop a straightforward theory of phonon-assisted absorption and 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.
Khurgin, Jacob B.
2014-06-01
Laser cooling of semiconductors has been an elusive goal for many years, and while attempts to cool the narrow gap semiconductors such as GaAs are yet to succeed, recently, net cooling has been attained in a wider gap CdS. This raises the question of whether wider gap semiconductors with higher phonon energies and stronger electron-phonon coupling are better suitable for laser cooling. In this work, we develop a straightforward theory of phonon-assisted absorption and photoluminescence of semiconductors that involves more than one phonon and use to examine wide gap materials, such as GaN and CdS and compare them with GaAs. The results indicate that while strong electron-phonon coupling in both GaN and CdS definitely improves the prospects of laser cooling, large phonon energy in GaN may be a limitation, which makes CdS a better prospect for laser cooling.
Khurgin, Jacob B.
2014-01-01
Laser cooling of semiconductors has been an elusive goal for many years, and while attempts to cool the narrow gap semiconductors such as GaAs are yet to succeed, recently, net cooling has been attained in a wider gap CdS. This raises the question of whether wider gap semiconductors with higher phonon energies and stronger electron-phonon coupling are better suitable for laser cooling. In this work we develop a straightforward theory of phonon-assisted absorption and photolu...
Inter-Landau level scattering and LO-phonon emission in Terahertz quantum cascade laser
Péré-Laperne, Nicolas; De Vaulchier, Louis-Anne; Guldner, Yves; Bastard, Gérald; Scalari, Giacomo; Giovannini, Marcella; Faist, Jérôme; Vasanelli, Angela; Dhillon, Sukhdeep; Sirtori, Carlo
2007-01-01
A Terahertz Quantum Cascade Laser (THz QCL) structure based on a bound to continuum and LO-phonon extraction stage is studied under a strong magnetic field. Two series of power oscillations as a function of magnetic field are observed. Comprehensive simulations of the lifetimes allow the first series to be assigned to interface roughness (elastic) and the second to LO phonon scattering (inelastic) of hot carriers in an excited Landau level, previously unobserved in terahertz QCL. We demonstra...
Phonon-mediated back-action of a charge readout on a double quantum dot
International Nuclear Information System (INIS)
Quantum point contacts are in use as an on-chip capacitative readout for the charge state of quantum dot systems. Here we investigate experimentally the back-action of quantum point contacts (QPCs) on a nearby double quantum dot (DQD). Driving current through a QPC influences the DQD state and leads to a measurable current flow in the DQD circuit with no bias voltage applied. The responsible mechanism is an indirect back-action process due to ohmic heating of the phonon bath. The system behaves like a thermoelectric engine, where a temperature gradient between the phonon bath and the electronic bath generates work observable as a measurable current flowing through the DQD.
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)
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.
Kudryashov, S I
2002-01-01
It is experimentally shown for the first time that by the effect of the feed-up laser pulse of 100 fs duration on the silicon target the consecutive structural transitions of the substance into the new crystalline and liquid metallic phase occur both during the laser pulse feed-up and after 0.1-10 sup 3 ps, depending on the material excitation conditions. The thresholds of the observed structural transitions are determined and the phonon nodes, responsible for therefore, are identified. The structural transitions dynamics in the silicon by the 01.-10 sup 3 ps times is described within the frames of the model of the phonon modes instability, originating due to the plasma electron-hole effect and also due to the intra- and intermode phonon-phonon anharmonic interactions
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.
Payne, Stephen A. (Castro Valley, CA); Page, Ralph H. (San Ramon, CA); Schaffers, Kathleen I. (Pleasanton, CA); Nostrand, Michael C. (Livermore, CA); Krupke, William F. (Pleasanton, CA); Schunemann, Peter G. (Malden, MA)
2000-01-01
The invention comprises a RE-doped MA.sub.2 X.sub.4 crystalline gain medium, where M includes a divalent ion such as Mg, Ca, Sr, Ba, Pb, Eu, or Yb; A is selected from trivalent ions including Al, Ga, and In; X is one of the chalcogenide ions S, Se, and Te; and RE represents the trivalent rare earth ions. The MA.sub.2 X.sub.4 gain medium can be employed in a laser oscillator or a laser amplifier. Possible pump sources include diode lasers, as well as other laser pump sources. The laser wavelengths generated are greater than 3 microns, as becomes possible because of the low phonon frequency of this host medium. The invention may be used to seed optical devices such as optical parametric oscillators and other lasers.
Wilson, T.; Kasper, E.; Oehme, M.; Schulze, J.; Korolev, K.
2014-11-01
We report on the direct excitation of 246 GHz longitudinal acoustic phonons in silicon doping superlattices by the resonant absorption of nanosecond-pulsed far-infrared laser radiation of the same frequency. A longitudinally polarized evanescent laser light field is coupled to the superlattice through a germanium prism providing total internal reflection at the superlattice interface. The ballistic phonon signal is detected by a superconducting aluminum bolometer. The sample is immersed in low-temperature liquid helium.
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
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)
Temperature performance of terahertz quantum-cascade lasers with resonant-phonon active-regions
Khanal, Sudeep; Zhao, Le; Reno, John L.; Kumar, Sushil
2014-09-01
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.
International Nuclear Information System (INIS)
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.
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.
Laser-enabled experimental wavefield reconstruction in two-dimensional phononic crystals
Celli, Paolo; Gonella, Stefano
2014-01-01
During the past two decades, noteworthy experimental investigations have been conducted on wave propagation in phononic crystals, with special emphasis on crystals for acoustic wave control, consisting of the repetition of cylindrical or spherical elements in a fluid medium. On the other hand, the experimental characterization of the elastic wave phenomena observed in the solid microstructure of phononic crystals designed for elastic wave control has been quite sparse and limited in scope. The related literature focuses mostly on steady-state analyses that aim at highlighting filtering properties, and are limited to out-of-plane measurements. The scope of this work is to address these limitations and provide a detailed experimental characterization of the transient wave phenomena observed in the cores of lattice-like phononic crystals. This is achieved using a 3D Scanning Laser Vibrometer, which allows measuring the in-plane velocity of material points belonging to the lattice topology. This approach is tested against the benchmark case of a regular honeycomb lattice. Specifically, the objective is to demonstrate the directional and dispersive nature of the S-mode at relatively low frequencies and characterize the P-mode below and above its veering frequency. The experimental results are compared against numerical simulations and unit cell Bloch analysis to highlight similarities and differences between the true response of finite crystals and the infinite lattice approximation. This study also intends to highlight the advantages of three-dimensional laser vibrometry as a tool for the characterization of complex structural materials, while carefully exposing some limitations of this methodology.
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.
Schwinger, J.
1991-01-01
The concepts of source and quantum action principle are used to produce the phonon Green's function appropriate for an initial phonon vacuum state. An application to the Mossbauer effect is presented.
Phonon-Assisted Population Inversion of a Single InGaAs/GaAs Quantum Dot by Pulsed Laser Excitation.
Quilter, J H; Brash, A J; Liu, F; Glässl, M; Barth, A M; Axt, V M; Ramsay, A J; Skolnick, M S; Fox, A M
2015-04-01
We demonstrate a new method to realize the population inversion of a single InGaAs/GaAs quantum dot excited by a laser pulse tuned within the neutral exciton phonon sideband. In contrast to the conventional method of inverting a two-level system by performing coherent Rabi oscillation, the inversion is achieved by rapid thermalization of the optically dressed states via incoherent phonon-assisted relaxation. A maximum exciton population of 0.67±0.06 is measured for a laser tuned 0.83 meV to higher energy. Furthermore, the phonon sideband is mapped using a two-color pump-probe technique, with its spectral form and magnitude in very good agreement with the result of path-integral calculations. PMID:25884136
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%.
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)
Makovetskii, D N
2011-01-01
This is a part of an overview of my early studies on nonlinear spin-phonon dynamics in solid state optical-wavelength phonon lasers (phasers) started in 1984. The main goal of this work is a short description and a qualitative analysis of experimental data on low-frequency nonlinear resonances revealed in a nonautonomous ruby phaser. Under phaser pumping modulation near these resonances, an unusual kind of self-organized motions in the ruby spin-phonon system was observed by me in 1984 for the first time. The original technique of optical-wavelength microwave-frequency acoustic stimulated emission (SE) detection and microwave-frequency power spectra (MFPS) analysis was used in these experiments (description of the technique see: D.N.Makovetskii, Cand. Sci. Diss., Kharkov, 1983). The real time evolution of MFPS was studied using this technique at scales up to several hours. The phenomenon of the self-organized periodic alternation of SE phonon modes was experimentally revealed at hyperlow frequencies from abou...
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)
Makovetskii, D N
2004-01-01
Two qualitatively different kinds of resonant destabilization of phonon stimulated emission (SE) are experimentally revealed for periodically forced multimode ruby phaser (phonon laser) operating at SE frequencies about 9 GHz, i.e. at microwave acoustic wavelengths of 1 micron. The inversion state of Cromium(3+) spin-system in ruby was created by electromagnetic pump at 23 GHz. Under deep modulation of pump power at low frequencies OMEGA_m = 70-200 Hz deterministic chaotic reconfigurations of the acoustic microwave power spectra (AMPS) were observed. This range of SE destabilization corresponds to the relaxational resonance that is well known for optical class-B lasers. Outside the relaxational resonance range, namely at ultra-low (infrasonic) frequencies OMEGA_m about 10 Hz, the other type of resonant destabilization of stationary phonon SE was observed by us for the first time. This new nonlinear resonance (we call it lambda-resonance) manifests itself as very slow and periodically repeated self-reconfigura...
Laser action in chromium-doped forsterite
Petricevic, V.; Gayen, S. K.; Alfano, R. R.; Yamagishi, Kiyoshi; Anzai, H.
1988-01-01
This paper reports on pulsed laser operation obtained in chromium-activated forsterite Cr(3+):Mg2SiO4 at room temperature. The spectrum of the free-running laser peaks at 1235 nm and a bandwidth of about 22 nm. The spectral range of the laser emission is expected to extend from 850 to 1300, provided the parasitic impurity absorption may be minimized by improved crystal growth techique.
Lanin, Aleksandr A; Fedotov, Andrei B; Zheltikov, Aleksei M
2012-05-01
An ultrafast three-dimensional readout of coherent optical-phonon oscillations from a diamond film is demonstrated using temporally and spectrally shaped ultrashort laser pulses, delivered by a compact, oscillator-only laser system. This system integrates a long-cavity ytterbium-fiber-laser-pumped 30?fs Cr:forsterite oscillator with a photonic-crystal-fiber soliton frequency shifter and a periodically poled lithium niobate spectrum compressor, providing coherent Raman excitation and time-delayed interrogation of optical phonons in diamond at a 20?MHz repetition rate with a submicrometer spatial resolution. PMID:22555720
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...
Theory of electron-optical phonon interactions in quantum wells and quantum well laser structures
International Nuclear Information System (INIS)
This thesis is concerned with the study of the quantum processes, including carder transitions and carrier capture, mediated by optical phonons in heterostructure quantum wells based on II-VI and III-V semiconductors and their alloys. The optical phonons are described by three different models namely, a model based on the bulk phonon approximation, the dielectric continuum (DC) model and the hybrid (HB) model. In order to create a discrete energy spectrum for the electrons with energies greater than the barrier energy and in order to reduce electron-phonon scattering rates, we concentrate on the situation in which the heterostructure is confined between metallic barriers. The essential features describing optical phonons are first discussed for the three models. In particular, in the case of the hybrid model we show that the hybridons form an orthogonal set of modes and are characterised by the property of non-locality, which is identified as the source of the mechanical boundary conditions. Calculations are then presented for the intersubband and intrasubband transition rates in the lowest electron subbands by the emission of DC and hybrid phonons in the case of the GaAs/AlAs heterostructure between two metal barriers. The dependence of the transition rates on the distance between the metallic barriers suggests that such, structures could be engineered so as to result in reduced scattering rates. A comparison of the predictions of total scattering rates via the hybrins of total scattering rates via the hybrid model with those via the DC model shows that the DC and the hybrid models are very close in this case. This near-agreement between the two models prompts an investigation on the existence of a sum-rule for the total scattering rates which we discuss in conjunction with a derivation of the rates in terms of Green functions. A sizeable part of this thesis is concerned with the evaluation of electron capture rates for electrons with energies at the bottom of the first and second subbands above the barrier energy which make transitions into the quantum well. We emphasise these calculations for the AlN/GaN quantum well system and for the alloy system GaAs/AlxGa1-xAs. The capture rate within the context of a given model is defined as the transition rate into all available subbands within the quantum well by the emission of either (a) bulk phonons of the well material or (b) the confined and interface phonons of the DC model or (c) the hybridons of the hybrid model (HB). The predictions of the three models are displayed and compared. We find that sharp peaks emerge at regular intervals of increasing well width corresponding to resonances in the electron states as a subband from above the barrier drops into the well. Other peaks arise when the electrons can begin to make transitions into the highest subband in the well. These peaks correspond to optical phonon emission thresholds and so depend on the model used to describe the optical phonon modes. The comparison between the DC model and hybrid model in the case of electron capture shows that the two models are in good agreement with regard to the magnitudes of the electron and phonon resonances and the regular intervals that occur. A different approach is required when the barrier thickness is much larger than the well width. In order to deal with this situation for the process of capture we consider an electron flux injected electrically with energy within the continuum above the barrier. This is subsequently captured into the AlN/GaN and II-VI quantum wells by the emission of bulk and DC phonons. The situation requires the identification of new capture parameters and we show that capture velocity is the appropriate parameter in this case. Calculations of capture velocities against the well width are presented for the DC and bulk phonons. (author)
Studies of random laser action in ?-conjugated polymers
International Nuclear Information System (INIS)
Laser action usually occurs within carefully configured resonant cavities. However, stimulated emission in disordered systems may also lead to coherent laser action above a certain threshold excitation intensity, Ith, which was dubbed as 'random lasing'. In random lasing a sequence of spectrally narrow emission lines, which are characteristic of laser modes, is superimposed on the amplified spontaneous emission band. We studied the statistical threshold distribution function, F(Ith) of Ith, of random lasers in ?-conjugated polymer films and its evolution with respect to the excitation area. The measurements were supported by pictures of the excited area taken while lasing occurs. We found that random lasing is accompanied by the appearance of lasing random cavities in the pictures, indicating that the sharp lines in the emission spectrum are, in fact, laser modes related to the random cavities formed in the disordered gain medium. Moreover a correlation exists between the cavity size extracted from the Fourier transform of the random lasing emission spectra and the size of the random resonators in the pictures obtained. In addition we also found that the measured F(Ith) has a marked asymmetry with respect to the average threshold, (Ith)ave, which decreases with the excitation area. An existing theoretical model based on random resonators in the polymer film is found to be in good agreement with the obtained F(Ith) function
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.
Textural Properties of Silicon Materials Produced by Laser Action.
Czech Academy of Sciences Publication Activity Database
D?ínek, Vladislav; Fajgar, Radek; Schneider, Petr; Šnajdaufová, Hana; Šolcová, Olga
Marseille : MADIREL, 2005. s.50. [International Symposium on the Characterisation of Porous Solids COPS VII /7./. 25.05.2005-28.05.2005, Aix-en-Provence] R&D Projects: GA ?R(CZ) GA104/04/0963; GA ?R(CZ) GD203/03/H140 Institutional research plan: CEZ:AV0Z40720504 Keywords : textural properties * laser action * experiments Subject RIV: CF - Physical ; Theoretical Chemistry
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.
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
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.
Plasma and Shock Generation by Indirect Laser Pulse Action
International Nuclear Information System (INIS)
To continue our investigation on crater formation in different conditions, we have carried out experiments with double targets consisted of a disk placed in front of a massive target with spacing of 200 ?m between them. Both elements of the targets were made of Al. The 6 ?m thick disks with a diameter of 300 ?m were covered by thin polyethylene foil (2.5 mm thick) to reduce X-ray radiation. The disks were supported by 10 ?m diameter carbon fibers. The following disk irradiation conditions were used: laser energy of 100 J, laser wavelength of 1.315 ?m, pulse duration of 0.4 ns, and laser spot diameter of 250 ?m. To measure some plasma parameters and accelerated disk velocity a three frame interferometric system was used. Efficiency of crater creation by a disk impact related to that for a direct laser action was determined using crater parameters, which were obtained by means of a crater replica technique. The experimental results concern the two main stages: (a) ablative plasma generation and disk acceleration and (b) disk impact and crater creation. Spatial density distributions at different moments of plasma generation and expansion, flyer disk motion, as well as shapes and dimensions of craters are shown. Discussion of the experimental results on the basis of the 2-D theoretical model of a laser-solid target interaction is carried out. (author)
Phonon-assisted lasing in ZnO microwires at room temperature
Michalsky, T.; Wille, M.; Dietrich, C. P.; Röder, R.; Ronning, C.; Schmidt-Grund, R.; Grundmann, M.
2014-11-01
We report on room temperature phonon-assisted whispering gallery mode (WGM) lasing in ZnO microwires. For WGM laser action on the basis of the low gain phonon scattering process high quality resonators with sharp corners and smooth facets are prerequisite. Above the excitation threshold power PTh of typically 100 kW/cm2, the recombination of free excitons under emission of two longitudinal optical phonons provides sufficient gain to overcome all losses in the microresonator and to result in laser oscillation. This threshold behavior is accompanied by a distinct change of the far and near field emission patterns, revealing the WGM related nature of the lasing modes. The spectral evolution as well as the characteristic behavior of the integrated photoluminescence intensity versus the excitation power unambiguously proves laser operation. Polarization-resolved measurements show that the laser emission is linear polarized perpendicular to the microwire axis (TE).
Schwinger, J.
1990-01-01
The gap between the nonlocalized lattice-phonon description and the localized Einstein oscillator treatment is filled by transforming the phonon Hamiltonian back to the particle variables. The particle-coordinate, normalized, wave function for the phonon vacuum state is exhibited.
Quenching of laser action in cresyl violet by 6943 A radiation
International Nuclear Information System (INIS)
Complete quenching of laser action in the dye when pumped by the second harmonic of a ruby laser is achieved in the presence of light of wavelength 6943 A. It is believed that the quenching is due to depletion of the upper laser level population by stimulated emission, and further that the unsatisfactory performance of flash-pumped cresyl violet rhodamine 6G lasers may stem from the quenching action of a red component in the pump light. (U.S.)
Random electric fields and coherent phonon excitation in C60 films by femtosecond laser pulses
Farztdinov, V. M.; Kovalenko, S. A.; Dobryakov, A. L.; Lozovik, Yurii E.; Matveets, Juru A.; Marowsky, Gerd
1998-04-01
The ultrafast relaxation of excitations in a C60 thin film was probed in the energy range 1.6 - 3.4 eV by pump- supercontinuum probe technique with 40 fs time resolution. The relaxation rate shows pronounced spectral dependence with maximum at 2 eV in the region of photoinduced darkening and at 2.4 eV in the region of photoinduced bleaching. It is found that the ultrafast relaxation rate decreases with increasing pumping pulse intensity. The shape of the optical density variation at zero time delay in the region of interband transitions at 2.3 - 3.4 eV is similar to the shape of the second derivative of the stationary absorption spectrum. We propose that this may indicate the creation of a random electric field in the sample during the absorption of the pump pulse. We suggest that the decrease of the relaxation rate with the increase of pumping pulse intensity results from extra-heating of the carriers in hu and t1u bands due to internal conversion from higher excited states, which are populated by two-step photon absorption of the intense pump pulse. Coherent excitation of phonons in the 60 - 300 cm-1 frequency range were detected over a wide spectral probe range. An oscillation with a frequency of 118 cm-1 indicates that the nonequilibrium dimerization of C60 molecules takes place following optical excitation. The full splitting of the Hg(1) intramolecular oscillation mode is observed clearly, which demonstrates that a strong deformation of the molecules upon photon absorption takes place.
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.
Marmon, Jason; Sheng, Tao; Zhang, Haitao; Zhang, Yong
2015-03-01
Electron-phonon coupling is typically studied as an intrinsic property for a given bulk material, and modifying the coupling has been explored in a nanostructure. We point out that the coupling strength can be easily perturbed both significantly and unintentionally. Nanowires, with their large surface-to-volume ratio, are more susceptible to extrinsic perturbations that affect coupling strength, although literature assumes that coupling is intrinsic. This work uses Raman spectroscopy under a near resonant condition to probe the coupling strength of individual ZnTe nanowires. Using the intensity ratio of the first and second order Raman peaks, R = I2LO/I1LO, as a measure of the electron-phonon coupling strength (proportional to the Huang-Rhys factor), we find that the ratio can change greatly when varying either the sample or measurement condition, for instance, the presence of defects in the as-grown sample and their removal though laser illumination.
Laser action in chromium-activated forsterite for near infrared excitation
Petricevic, V.; Gayen, S. K.; Alfano, R. R.
1988-01-01
This paper reports on laser action in chromium-doped forsterite (Cr:Mg2SiO4) for 1064-nm excitation of the crystal's double-hump absorption band spanning the 850-1200-nm wavelength range. The cavity arrangement used for obtaining laser action in Cr:Mg2SiO2 was similar to that described by Petricevic et al. (1988). The fundamental and second harmonic emissions from a Q-switched Nd:YAG laser operating at a 10-Hz repetition rate were used for excitation of the NIR and visible bands, respectively. Pulsed laser action was readily observed for both the 1064-nm and 532-nm pumping at or above the respective thresholds. The laser parameters of the 532-nm and 1064-nm excitations were similar, indicating that the IR band is responsible for laser action for both excitations.
Anharmonic Decay of Zone-Boundary Phonons Observed by a New Method of Phonon Detection
Lengfellner, Hans; Renk, Karl Friedrich
1981-01-01
A new method for detection of zone-boundary phonons is presented. Phonons generated by nonradiative transitions in thallium halide crystals are detected by phonon difference absorption with use of time-resolved far-infrared laser spectroscopy. Our experiments, performed at crystal temperatures between 3 and 20 K, give experimental evidence of strongly-temperature-dependent anharmonic lifetimes of transverse-acoustic zone-boundary phonons.
Wette, Frederik
1991-01-01
In recent years substantial progress has been made in the detection of surface phonons owing to considerable improvements in inelastic rare gas scattering tech niques and electron energy loss spectroscopy. With these methods it has become possible to measure surface vibrations in a wide energy range for all wave vectors in the two-dimensional Brillouin zone and thus to deduce the complete surface phonon dispersion curves. Inelastic atomic beam scattering and electron energy loss spectroscopy have started to play a role in the study of surface phonons similar to the one played by inelastic neutron scattering in the investigation of bulk phonons in the last thirty years. Detailed comparison between experimen tal results and theoretical studies of inelastic surface scattering and of surface phonons has now become feasible. It is therefore possible to test and to improve the details of interaction models which have been worked out theoretically in the last few decades. At this point we felt that a concise, co...
Melnikov, A A; Chekalin, S V
2010-01-01
We have applied femtosecond pump-probe technique with variable pump wavelength to study coherent lattice dynamics in Bi single crystal. Comparison of the coherent amplitude as a function of pump photon energy for two different in symmetry Eg and A1g phonon modes with respective spontaneous resonance Raman profiles reveals that their generation mechanisms are quite distinct. We show that displacive excitation, which is the main mechanism for the generation of coherent A1g phonons, cannot be reduced to the Raman scattering responsible for the generation of lower symmetry coherent lattice modes
Self-seeded forward lasing action from a femtosecond Ti:sapphire laser filament in air
International Nuclear Information System (INIS)
428 nm forward lasing action was observed from a femtosecond laser filament in air created by Ti:sapphire laser pulses. The 800 nm femtosecond laser filament not only provides a source for population inversion between two vibrational levels (B2?u+(0) and X2?g+(1)) of N2+ but also generates a 428 nm seed from filament-induced white light. This simple technique will find more applications in standoff spectroscopy. (letter)
Electron-Phonon and Phonon-Phonon Interactions
International Nuclear Information System (INIS)
1. Form of crystal Hamiltonian. 1.1. Adiabatic approximation and electron-phonon, interaction. 1.2. Harmonic approximation and phonon-phonon interaction. 1.3. Crystal momentum conservation. 2. Electron-phonon interaction in metals. 2.1. Real-time Green functions. Migdal's theorem. 2.2. Renormalization effects in normal state. 2.3. Pair interaction and superconductivity. 2.4. Hydro- dynamical limit and transport equation. 3. Phonon-phonon interaction in insulators. 3.1. Imaginary- time Green functions and perturbation theory. 3.2. Thermal and elastic properties. 3.3. Phonon renormalization effects. 3.4. Heat propagation and second sound. (author)
Mosaic structure peculiarities of laser action bands in silicon monocrystals
International Nuclear Information System (INIS)
Carried out is the investigation of structural imperfections, occurring in silicon monocrystals after laser irradiation of different light pulse power, different energy density in the irradiation zone and wave length. The methods of optical microscopy and roentgenography have been applied for obtaining information on the main peculiarities of the mosaic structure of laser effect zones in silicon monocrystals. The carried out investigation has made it possible to state, that in the laser effect zones the occurred mosaic blocks are formed by a net of cracks, obtained under the tensile stress effect. The dimensions of mosaic blocks and integral patchiness angles non-monotonously depend on the irradiation energy density
Schwinger, J.
1990-01-01
An atomic lattice in its ground state is excited by the rapid displacement and release of an atomic constituent. The time dependence of the energy transfer to other constituents is studied by using a phonon dispersion relation that is linear in frequency and propagation vector components.
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...
Controlling phonon squeezing and correlation via one- and two-phonon interference
International Nuclear Information System (INIS)
When ultrafast laser pulse strikes the crystal with a van Hove singularity in the phonon density of states, it can create a pair of anti-correlated in wave-vector phonons. As a result, the atomic fluctuations in either position or momentum become squeezed in such a way that their size might fall below the vacuum level. The ultrafast pulses can also generate a biphonon state in which the constituent phonons are correlated and/or entangled. Here we show that via the interplay between one- and two-phonon interference the bound and squeezed two-phonon state in (110) oriented ZnTe single crystal can be manipulated. -- Highlights: ? We use a pair of ultrafast laser pulses to manipulate squeezing and correlation of biphonons in ZnTe. ? We demonstrate that the strength of phonon squeezing and correlation can be controlled. ? We observe that a larger correlation comes at expense of a reduced squeezing.
Phonon localization in ultrathin layered structures
Döring, F.; Eberl, C.; Schlenkrich, S.; Schlenkrich, F.; Hoffmann, S.; Liese, T.; Krebs, H. U.; Pisana, S.; Santos, T.; Schuhmann, H.; Seibt, M.; Mansurova, M.; Ulrichs, H.; Zbarsky, V.; Münzenberg, M.
2015-04-01
An efficient way for minimizing phonon thermal conductivity in solids is to nanostructure them by means of reduced phonon mean free path, phonon scattering and phonon reflection at interfaces. A sophisticated approach toward this lies in the fabrication of thin multilayer films of different materials. In this paper, we show by femtosecond-pump-probe reflectivity measurements that in different multilayer systems with varying acoustic mismatch (consisting of metals, semiconductors, oxides and polymers), oscillations due to phonon localization can be observed. For the growth of multilayer films with well-defined layer thicknesses, we used magnetron sputtering, evaporation and pulsed laser deposition. By altering the material combinations and reducing the layer thicknesses down to 3 nm, we observed different mechanisms of phonon blocking, reaching in the frequency regime up to 360 GHz.
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...
Biological Effects of Contact Action of 1470 vs. 810 nm Semiconductor Lasers in vitro
Directory of Open Access Journals (Sweden)
N.A. Schumilova
2015-01-01
Full Text Available The aim of the investigation is to identify the character of biological effects of contact action of semiconductor laser with a wavelength of 1470 nm on the tissues with different optical and mechanical properties compared to the exposure to laser radiation with a wavelength of 810 nm. Materials and Methods. The study was performed on a chicken muscle tissue, liver of the cattle, nasal polyp, removed nasal septum cartilage. While making a linear incision of the tissues by the laser with a speed of 2 mm/s assessment of the width of ablation and coagulation zones, and the crater depth with the following measurement under the microscopy conditions were carried on. Weighing of the tissue specimens before and after the spot action was performed. Standardization of the operating speed was achieved by using uniformly moving recorder chart. Results. Radiation power increment of 1470 nm wavelength laser contributes to the increase of the ablation and coagulation zone width to a greater degree compared to 810 nm laser. Exposure to 1470 nm laser with a power of 1 W causes the tissue to stick to the fiber. When power is 2 W, coagulation zone of soft tissues is comparable, and in some cases exceeds it after treatment by 810 nm laser. In relation to the crater depth, 1470 nm radiation is inferior to 810 nm radiation, but is superior in relation to vaporization abilities. Conclusion. For tissue ablation with 1470 nm laser a power of 2 W is optimal, as it provides a sparing superficial effect, and in a number of cases exceeds the action of 810 nm 7 W laser by its coagulation properties. Generation of a crater with a less depth after application of 1470 nm laser allows it to be recommended for superficial coagulation of vascular lesions.
Plasma and Shock Generation by Indirect Laser Pulse Action
International Nuclear Information System (INIS)
In the paper the results of our experiment with flyer disks, accelerated to high velocities by the PALS iodine laser and subsequently creating craters when hitting massive targets , are presented. We have carried out experiments with the double targets consisted of a disk placed in front of a massive target part at distances of either 200 or 500 ?m. Both elements of the targets were made of Al. The following disk irradiation conditions were used: laser energy of 130 J, laser wavelength of 1.315 ?m, pulse duration of 0.4 ns, and laser spot diameter of 250 ?m. To measure some plasma parameters and accelerated disk velocity a three frame interferometric system was used. Efficiency of crater creation by a disk impact was determined from the crater parameters, which were obtained by means of a crater replica technique. The experimental results concern two main stages: (a) ablative plasma generation and disk acceleration and (b) disk impact and crater creation. Spatial density distributions at different moments of plasma generation and expansion are shown. Discussion of the experimental results on the basis of a 2-D theoretical model of the laser -- solid target interaction is carried out
Plasma and Shock Generation by Indirect Laser Pulse Action
Kasperczuk, A.; Borodziuk, S.; Demchenko, N. N.; Gus'kov, S. Yu.; Jungwirth, K.; Kalal, M.; Kralikova, B.; Krousky, E.; Limpouch, J.; Masek, K.; Pisarczyk, P.; Pisarczyk, T.; Pfeifer, M.; Rohlena, K.; Rozanov, V. B.; Skala, J.; Ullschmied, J.
2006-01-01
In the paper the results of our experiment with flyer disks, accelerated to high velocities by the PALS iodine laser and subsequently creating craters when hitting massive targets , are presented. We have carried out experiments with the double targets consisted of a disk placed in front of a massive target part at distances of either 200 or 500 ?m. Both elements of the targets were made of Al. The following disk irradiation conditions were used: laser energy of 130 J, laser wavelength of 1.315 ?m, pulse duration of 0.4 ns, and laser spot diameter of 250 ?m. To measure some plasma parameters and accelerated disk velocity a three frame interferometric system was used. Efficiency of crater creation by a disk impact was determined from the crater parameters, which were obtained by means of a crater replica technique. The experimental results concern two main stages: (a) ablative plasma generation and disk acceleration and (b) disk impact and crater creation. Spatial density distributions at different moments of plasma generation and expansion are shown. Discussion of the experimental results on the basis of a 2-D theoretical model of the laser — solid target interaction is carried out.
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.
Efficiency of a selective two-step laser action upon an atomic beam
International Nuclear Information System (INIS)
Efficiency of a selective two-step laser action upon an atomic beam has been considered on assumption that the interaction region is homogeneously illuminated and that the beam is an optically thin layer. Spontaneous and field-induced recombinations are regarded to be nonexistent. The analysis has been made for three energy levels. Formulae are derived which make it possible to analyze the efficience of a selective two-step laser action upon an atomic (molecular) beam depending on such parameters as radiation intensity, excited state lifetime and absorption cross sections, beam velocity and length
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
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 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)
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.
Modulated Laser Action from Dye Containing Holographic Polymer Dispersed Liquid Crystals
Jakubiak, Rachel; Brown, Dean; Urbas, Augustine; Tondigia, Vincent; Natarajan, Lalgudi; Sutherland, Richard; Vaia, Richard; Bunning, Timothy
2004-03-01
Holographic polymerization of liquid crystal containing photopolymerizable resins enables one-step, rapid formation of multi-phase structures that exhibit partial photonic band gaps. Holographic polymer dispersed liquid crystals (H-PDLCs) provide a versatile platform for diffractive optical elements because the structures are not limited by multi-phase equilibrium but are controlled by the interference of multiple lasers at discrete angles. By incorporating optically active components (coumarin, pyrromethene, quantum dots) into acrylate polymer and nematic liquid crystal H-PDLCs we create optically pumped distributed feedback lasers. The lattice structure of the H-PDLC determines the wavelength, number and propagation direction of laser action from the embedded chromophores. Unlike one-dimensional Bragg stacks made from H-PDLCs where just one propagation direction exists, higher dimensional structures generate multiple laser beams creating electric field modulated laser arrays.
Demonstration of laser action in a pseudo-random medium
Yang, Jin-Kyu; Boriskina, Svetlana V.; Noh, Heeso; Rooks, Michael J.; Solomon, Glenn S.; Dal Negro, Luca; Cao, Hui
2010-08-01
We demonstrated lasing in localized optical resonances of deterministic aperiodic structures with pseudo-random morphologies. The localized lasing modes in the Rudin-Shapiro arrays of air nanoholes in GaAs membranes occur at reproducible spatial locations and their frequencies are only slightly affected by the structural fluctuations in different samples. Numerical study on the resonances of the passive systems and optical imaging of lasing modes enabled us to interpret the observed lasing behavior in terms of distinctive localized resonances in the two-dimensional Rudin- Shapiro structures. The deterministic aperiodic media with controllable structural and optical properties provide a novel platform, alternative to random lasers and different from photonic crystals lasers, for the engineering of multi-frequency coherent light sources suitable for technological integration.
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
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.
El-Kady, Ihab F. (Albuquerque, NM); Olsson, Roy H. (Albuquerque, NM)
2012-01-10
Phononic crystals that have the ability to modify and control the thermal black body phonon distribution and the phonon component of heat transport in a solid. In particular, the thermal conductivity and heat capacity can be modified by altering the phonon density of states in a phononic crystal. The present invention is directed to phononic crystal devices and materials such as radio frequency (RF) tags powered from ambient heat, dielectrics with extremely low thermal conductivity, thermoelectric materials with a higher ratio of electrical-to-thermal conductivity, materials with phononically engineered heat capacity, phononic crystal waveguides that enable accelerated cooling, and a variety of low temperature application devices.
Yang, Yu; Lin, Guannan; Xu, Hui; Wang, Minquan; Qian, Guodong
2008-10-01
Laser dyes such as pyrromethene 567 (PM567), perylene red (P-red) and coumarin 540A (C540A) were doped into zirconia-organically modified silicate (ORMOSIL) materials prepared by low temperature sol-gel technique. Narrow line-width distributed feedback (DFB) laser actions were induced in the PM567 and/or P-red doped sol-gel planar waveguide. Tuning of the output wavelength was achieved by varying the period of the gain modulation generated by a nanosecond Nd:YAG laser at 532 nm. Compared with those of PM567 and P-red solely doped thin films, tuning range of C540A, PM567 and P-red co-doped sol-gel planar waveguide was greatly extended, from 564.5 nm to 635.1 nm.
Control of generation regimes of ring chip laser under the action of the stationary magnetic field
International Nuclear Information System (INIS)
We consider realisation of different generation regimes in an autonomous ring chip laser, which is a rather complicated problem. We offer and demonstrate a simple and effective method for controlling the radiation dynamics of a ring Nd:YAG chip laser when it is subjected to a stationary magnetic field producing both frequency and substantial amplitude nonreciprocities. The amplitude and frequency nonreciprocities of a ring cavity, arising under the action of this magnetic field, change when the magnet is moved with respect to the active element of the chip laser. Some self-modulation and stationary generation regimes as well as the regime of beatings and dynamic chaos regime are experimentally realised. Temporal and spectral characteristics of radiation are studied and conditions for the appearance of the generation regime are found. (control of laser radiation parameters)
International Nuclear Information System (INIS)
For the first time laser activity has been achieved in the low phonon energy, moisture-resistant bromide host crystals, neodymium-doped potassium lead bromide (Nd3+:KPb2Br5) and rubidium lead bromide (Nd3+:RbPb2Br5). 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 4F5/2 + 2H9/2 ? 4IJ 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 MPb2Br5 (M=K, Rb) is a promising candidate for long wavelength infrared applications because of its low phonon frequencies and other favorable features. In principle, Nd3+:MPb2Br5 has high potential for laser operation at new wavelengths as well as for the realization of short-wavelength lasing due to upconversion processes
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.
Features of nonstationary SHG of phase-modulated laser pulses under self-action conditions
International Nuclear Information System (INIS)
The influence of self-action effects on the efficiency of SHG of phase-modulated laser pulses in a nonstationary regime is analysed using a generalised method of strong interaction of nonlinear waves. An analytic solution for the SHG efficiency is obtained taking into account the depletion of pump radiation, the influences of the linear phase mismatch, mismatch of group velocities, and higher linearities. It is shown that the effects of self-action, mismatch of group velocities, and linear phase mismatch can compensate for each other, resulting in an increase in the efficiency of SHG of phase-modulated pulses. (nonlinear optical phenomena)
Study of Phonon Modes in Germanium Nanowires
Wang, Xi; Shakouri, Ali; Yu, Bin; Sun, Xuhui; Meyyappan, Meyya
2007-01-01
The observation of pure phonon confinement effect in germanium nanowires is limited due to the illumination sensitivity of Raman spectra. In this paper we measured Raman spectra for different size germanium nanowires with different excitation laser powers and wavelengths. By eliminating the local heating effect, the phonon confinement effect for small size nanowires was clearly identified. We have also fitted the Raman feature changes to estimate the size distribution of nan...
Study of Phonon Modes in Germanium Nanowires
Wang, X; Shakouri, A; Sun, X; Yu, B; Meyyappan, Meyya; Shakouri, Ali; Sun, Xuhui; Wang, Xi; Yu, Bin
2007-01-01
The observation of pure phonon confinement effect in germanium nanowires is limited due to the illumination sensitivity of Raman spectra. In this paper we measured Raman spectra for different size germanium nanowires with different excitation laser powers and wavelengths. By eliminating the local heating effect, the phonon confinement effect for small size nanowires was clearly identified. We have also fitted the Raman feature changes to estimate the size distribution of nanowires for the first time.
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...
Pavlopoulos, T G; Boyer, J H; Sathyamoorthi, G
1998-11-20
Some laser action properties of a new Pyrromethene-BF(2) complex, 1, 3, 5, 7-tetramethyl-8-ethyl-2, 6-dicyanopyrromethene-BF(2) complex are reported. This laser dye exhibits laser action in the green-yellow portion of the spectrum, and its laser action efficiency was ~350% higher compared with Coumarin 545. Exceptional photostability of the new laser dye was observed when a mixture of 1, 4-dioxane:heptane ratio of 1:4 was used as the solvent. Further, it is suggested that dye lasers can be upscaled to high average power output when surface-emitting laser diode arrays are used as pump (excitation) sources. PMID:18301620
Frequency stabilization of the zero-phonon line of a quantum dot via phonon-assisted active feedback
International Nuclear Information System (INIS)
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.
Frequency stabilization of the zero-phonon line of a quantum dot via phonon-assisted active feedback
Energy Technology Data Exchange (ETDEWEB)
Hansom, Jack; Schulte, Carsten H. H.; Matthiesen, Clemens; Stanley, Megan J.; Atatüre, Mete [Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE (United Kingdom)
2014-10-27
We report on the feedback stabilization of the zero-phonon emission frequency of a single InAs quantum dot. The spectral separation of the phonon-assisted component of the resonance fluorescence provides a probe of the detuning between the zero-phonon transition and the resonant driving laser. Using this probe in combination with active feedback, we stabilize the zero-phonon transition frequency against environmental fluctuations. This protocol reduces the zero-phonon fluorescence intensity noise by a factor of 22 by correcting for environmental noise with a bandwidth of 191?Hz, limited by the experimental collection efficiency. The associated sub-Hz fluctuations in the zero-phonon central frequency are reduced by a factor of 7. This technique provides a means of stabilizing the quantum dot emission frequency without requiring access to the zero-phonon emission.
International Nuclear Information System (INIS)
Nonlinear-laser properties of crystals of non-centrosymmetric orthorhombic semi-organic tris(glycine) zinc chloride Gly3?ZnCl2 are reported in this paper. Under one-micron picosecond pumping many-phonon high-order SRS, a more than two-octaves Stokes and anti-Stokes lasing frequency comb, ''Cherenkov''-type SHG, THG, and several cascaded parametric self-sum-frequency generation processes were observed. All recorded Raman-induced laser wavelengths were identified and attributed to the ?(3)-promoting vibration modes of the crystal. A brief review of nonlinear-laser properties of known SRS-active heterodesmic semi-organic crystals with partially ionic bonding character between structural units is given as well
Efficient laser action from two cw laser-pumped pyrromethene-BF(2) complexes.
Guggenheimer, S C; Boyer, J H; Thangaraj, K; Shah, M; Soong, M L; Paviopoulos, T G
1993-07-20
Two new pyrromethene-BF(2) dyes, P-556 and P-567, are tested for cw laser operation. P-556 demonstrates a significant advance in the 530-620-nm region over commercially currently available dyes, where the best cw dyes in any range have peak efficiencies of the order of 35% and dyes in this range typically have less then 25%. The P-556 has a cw efficiency of 45% at the peak. PMID:20830030
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...
Electron - Phonon Superconductivity
Marsiglio, F; Carbotte, J. P.
2001-01-01
In this chapter we review the essentials of conventional electron-phonon superconductivity, as provided through the Migdal-Eliashberg formalism. Signatures of the electron-phonon interaction, as they appear in conventional superconductors, are described in detail. An appendix briefly describes more recent attempts to understand the electron-phonon interaction for all coupling strengths.
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)
Dispersive effect on dual-color laser action from one-dimensional scattering gain media
International Nuclear Information System (INIS)
The dual-color laser action from the Rh6G solution with TiO2 scattering particles is investigated by solving Maxwell’s equations and rate equations of electronic population simultaneously. A one-dimensional (1D) dispersive model is proposed to explain the experiment results. The results indicate that, although the dispersion in optical domain is relatively small, the dispersion for both gain materials and scattering particles has significant influence on modes of random lasing, which lead to more lasing modes and lower spectral intensity. (paper)
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.
Phonon-phonon interactions and phonon damping in carbon nanotubes
De Martino, A.; Egger, R; Gogolin, A. O.
2009-01-01
We formulate and study the effective low-energy quantum theory of interacting long-wavelength acoustic phonons in carbon nanotubes within the framework of continuum elasticity theory. A general and analytical derivation of all three- and four-phonon processes is provided, and the relevant coupling constants are determined in terms of few elastic coefficients. Due to the low dimensionality and the parabolic dispersion, the finite-temperature density of noninteracting flexural...
Ultrafast optical generation of coherent phonons in CdTe1-xSex quantum dots
Bragas, A V; Costantino, S; Ingale, A; Zhao, J; Merlin, R; Ingale, Alka
2003-01-01
We report on the impulsive generation of coherent optical phonons in CdTe0.68Se0.32 nanocrystallites embedded in a glass matrix. Pump probe experiments using femtosecond laser pulses were performed by tuning the laser central energy to resonate with the absorption edge of the nanocrystals. We identify two longitudinal optical phonons, one longitudinal acoustic phonon and a fourth mode of a mixed longitudinal-transverse nature. The amplitude of the optical phonons as a function of the laser central energy exhibits a resonance that is well described by a model based on impulsive stimulated Raman scattering. The phases of the coherent phonons reveal coupling between different modes. At low power density excitations, the frequency of the optical coherent phonons deviates from values obtained from spontaneous Raman scattering. This behavior is ascribed to the presence of electronic impurity states which modify the nanocrystal dielectric function and, thereby, the frequency of the infrared-active phonons.
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...
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)
The heat-pipe resembling action of boiling bubbles in endovenous laser ablation.
van der Geld, Cees W M; van den Bos, Renate R; van Ruijven, Peter W M; Nijsten, Tamar; Neumann, H A Martino; van Gemert, Martin J C
2010-11-01
Endovenous laser ablation (EVLA) produces boiling bubbles emerging from pores within the hot fiber tip and traveling over a distal length of about 20 mm before condensing. This evaporation-condensation mechanism makes the vein act like a heat pipe, where very efficient heat transport maintains a constant temperature, the saturation temperature of 100 degrees C, over the volume where these non-condensing bubbles exist. During EVLA the above-mentioned observations indicate that a venous cylindrical volume with a length of about 20 mm is kept at 100 degrees C. Pullback velocities of a few mm/s then cause at least the upper part of the treated vein wall to remain close to 100 degrees C for a time sufficient to cause irreversible injury. In conclusion, we propose that the mechanism of action of boiling bubbles during EVLA is an efficient heat-pipe resembling way of heating of the vein wall. PMID:20644976
Characteristics of pulsed laser action due to transitions in barium atoms
Energy Technology Data Exchange (ETDEWEB)
Isaev, A.A.; Lemmerman, G.Yu.; Markova, S.V.; Petrash, G.G.
1979-09-01
Pulsed laser action has been studied at the 1.13- and 1.5-micron lines of the barium atom. A discharge tube 25 mm in diameter and 85 cm in length has been used. The supply power amounted to 2.5 kW at excitation pulse repetition rates of 8 and 13.3 kHz. Average lasing power has been investigated as a function of buffer gas pressure and supply power. Spectral and temporal characteristics have been studied. A maximum average lasing power of 12.5 W has been achieved, the efficiency being 0.5%, whereas the maximum efficiency was as high as 0.72%
Lasing action induced by femtosecond laser filamentation in ethanol flame for combustion diagnosis
Chu, Wei; Li, Helong; Ni, Jielei; Zeng, Bin; Yao, Jinping; Zhang, Haisu; Li, Guihua; Jing, Chenrui; Xie, Hongqiang; Xu, Huailiang; Yamanouchi, Kaoru; Cheng, Ya
2014-03-01
We experimentally demonstrate the generation of lasing action in the laminar ethanol/air flame on an alcohol burner array using femtosecond laser filament excitation. By probing the backward emissions of combustion species, it is found that as the interaction length of the filament in the flame increases, the signal's intensity at the 388 nm band for the B2? -X2? transition of CN increases exponentially, but that at the 474 nm band for A3?g-X'3?u transition of C2 increases linearly. The exponential behavior of the CN emissions is ascribed to amplified spontaneous emission, which opens up a way to overcome the quenching effect of specific species in combustion diagnosis.
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
ELECTRON-PHONON INTERACTIONS IN SEMICONDUCTORS : PHONON TRANSPORT AND DECAY
Ulbrich, R.
1981-01-01
Stationary charge transport in semiconductors implies steady flow of directed momentum and excess energy from the coupled system of electrons and phonons to the external heatsink. Bulk phonons mediate the momentum and energy transfer. This article will survey recent developments in phonon spectroscopy with special reference to those phonon transport and decay processes which are directly related to hot electron transport in semiconductors.
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
Squeezed Phonon Wave Packet Generation by Optical Manipulation of a Quantum Dot
Directory of Open Access Journals (Sweden)
Daniel Wigger
2015-02-01
Full Text Available In solid-state physics, the quantized lattice vibrations, i.e., the phonons, play a vital role. Phonons, much like photons, satisfy bosonic commutation relations, and therefore, various concepts well-known in quantum optics can be transferred to the emerging field of phononics. Examples are non-classical states and, in particular, squeezed states. We discuss the generation of phonon squeezing by optically exciting a quantum dot and show that by excitation with detuned continuous wave laser fields, sequences of squeezed phonon wave packets are created, which are emitted from the quantum dot region into the surrounding material.
Phonon-induced polariton superlattices
DEFF Research Database (Denmark)
de Lima, Jr., M. M.; Poel, Mike van der
2006-01-01
We show that the coherent interaction between microcavity polaritons and externally stimulated acoustic phonons forms a tunable polariton superlattice with a folded energy dispersion determined by the phonon population and wavelength. Under high phonon concentration, the strong confinement of the optical and excitonic polariton components in the phonon potential creates weakly coupled polariton wires with a virtually flat energy dispersion.
Phonon conduction in superlattices
Saini, Richa; Ashokan, Vinod; Indu, B. D.
2015-06-01
The lattice thermal conductivity of InAs/AlSb superlattices is investigated on the basis of modified Callaway model, which successfully explains the inadequacies of Matthiessen's rule. In the new formulation, the relaxation times of various contributing processes have been observed in terms of line widths. The evaluation of line widths is carried out by double time temperature dependent Green's function theory, using a comprehensive Hamiltonian which includes the contribution due to electrons, phonons, impurities, anharmonicities and interactions thereof. The frequency line widths are observed as an extremely sensitive quantity in the transport phenomena of superlattices, as it depends on large number of scattering events, namely; combined boundary, impurity, phonon-phonon and interference scattering processes. It is observed in the present work that the lattice thermal conductivity of superlattices is much less than that of a bulk sample. This can be attributed due to the reduction of phonon group velocity and strong phonon-phonon interactions, which in turn causes the decrease in relaxation times and phonon conductivity. Also, it is remarkable to note that the present theoretical model is equally application to all quantum well structures.
Tunable magnetoelastic phononic crystals
Robillard, J.-F.; Matar, O. Bou; Vasseur, J. O.; Deymier, P. A.; Stippinger, M.; Hladky-Hennion, A.-C.; Pennec, Y.; Djafari-Rouhani, B.
2009-09-01
The feasibility of tuning the band structure of phononic crystals is demonstrated by employing magnetostrictive materials and applying an external magnetic field. Band structures are calculated with a plane wave expansion method that accounts for coupling between the elastic behavior and the magnetic field through the development of elastic, piezomagnetic, and magnetic permeability effective tensors. We show the contactless tunability of the absolute band gaps of a two-dimensional phononic crystal composed of an epoxy matrix and Terfenol-D inclusions. The tunable phononic crystal behaves like a transmission switch for elastic waves when the magnitude of an applied magnetic field crosses a threshold.
Phonon Thermal Conduction in Graphene
Nika, D. L.; Pokatilov, E. P.; Askerov, A. S.; Balandin, A. A.
2008-01-01
We investigated theoretically the phonon thermal conductivity of single layer graphene. The phonon dispersion for all polarizations and crystallographic directions in graphene lattice was obtained using the valence-force field method. The three-phonon Umklapp processes were treated exactly using an accurate phonon dispersion and Brillouin zone, and accouting for all phonon relaxation channels allowed by the momentum and energy conservation laws. The uniqueness of graphene wa...
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
Directory of Open Access Journals (Sweden)
I. E. Psarobas
2014-12-01
Full Text Available Within the framework of elastic anisotropy, caused in a phononic crystal due to low crystallographic symmetry, we adopt a model structure, already introduced in the case of photonic metamaterials, and by analogy, we study the effect of birefringence and acoustical activity in a phononic crystal. In particular, we investigate its low-frequency behavior and comment on the factors which determine chirality by reference to this model.
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...
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.
International Nuclear Information System (INIS)
Large single crystals of the compound LaBO2MoO4, undoped and doped with Nd3+ ions, were grown. Their multi-wavelength Stokes and anti-Stokes picosecond generation, nonlinear-laser effects, and neodymium IR luminescence were investigated. We classify these crystals as a promising material for Raman frequency converters and gain medium for solid-state lasers
Phonon-Assisted Incoherent Excitation of a Quantum Dot and its Emission Properties
Weiler, S; Roy, C; Ulrich, S M; Richter, D; Jetter, M; Hughes, S; Michler, P
2012-01-01
We present a detailed study of a phonon-assisted incoherent excitation mechanism of single quantum dots. A spectrally-detuned laser couples to a quantum dot transition by mediation of acoustic phonons, whereby excitation efficiencies up to 20 % with respect to strictly resonant excitation can be achieved at T = 9 K. Laser frequency-dependent analysis of the quantum dot intensity distinctly maps the underlying acoustic phonon bath and shows good agreement with our polaron master equation theory. An analytical solution for the photoluminescence is introduced which predicts a broadband incoherent coupling process when electron-phonon scattering is in the strong phonon coupling (polaronic) regime. Additionally, we investigate the coherence properties of the emitted light and study the impact of the relevant pump and phonon bath parameters.
Temperature Dependence of Brillouin Light Scattering Spectra of Acoustic Phonons in Silicon
Somerville, Kevin; Klimovich, Nikita; An, Kyongmo; Sullivan, Sean; Weathers, Annie; Shi, Li; Li, Xiaoqin
2015-03-01
Thermal management represents an outstanding challenge in many areas of technology. Electrons, optical phonons, and acoustic phonons are often driven out of local equilibrium in electronic devices or during laser-material interaction processes. Interest in non-equilibrium transport processes has motivated the development of Raman spectroscopy as a local temperature sensor of optical phonons and intermediate frequency acoustic phonons, whereas Brillouin light scattering (BLS) has recently been explored as a temperature sensor of low-frequency acoustic phonons. Here, we report temperature dependent BLS spectra of silicon, with Raman spectra taken simultaneously for comparison. The origins of the observed temperature dependence of the BLS peak position, linewidth, and intensity are examined in order to evaluate their potential use as temperature sensors for acoustic phonons. We determine that the integrated BLS intensity can be used measure the temperature of specific acoustic phonon modes. This work is supported by National Science Foundation (NSF) Thermal Transport Processes Program under Grant CBET-1336968.
Unraveling the interlayer-related phonon self-energy renormalization in bilayer graphene
Araujo, Paulo T.; Mafra, Daniela L.; Sato, Kentaro; Saito, Riichiro; Kong, Jing; Dresselhaus, Mildred S.
2012-01-01
In this letter, we present a step towards understanding the bilayer graphene (2LG) interlayer (IL)-related phonon combination modes and overtones as well as their phonon self-energy renormalizations by using both gate-modulated and laser-energy dependent inelastic scattering spectroscopy. We show that although the IL interactions are weak, their respective phonon renormalization response is significant. Particularly special, the IL interactions are mediated by Van der Waals forces and are fun...
On liberation of anomalous large hydrogen volumes from metals under laser action
International Nuclear Information System (INIS)
Experiments on hydrogen isolation from the metal under laser effect are conducted. The experiments have shown that under the assigned parameters of laser pulse and focusing geometry the quantity of hydrogen, isolated from the samples investigated (titanium and aluminium alloys, steel) grows in a direct proportion to the number of flashes of evaporation laser. 12 refs., 2 figs., 1 tab
International Nuclear Information System (INIS)
Formation of non-stationary nonequilibrium distribution functions (DF) of electrons and phonons is investigated under the action of a strong pulse electric field on metal. For concreteness parameters were taken for nickel having reference temperature of 20 K. It is shown: isotropization of electron DF occurs as a result of impacts with lattice imperfections; electron DF does not become thermodynamically equilibrium as electron-electron impacts in the given situation give essentially smaller contribution than electron-phonon collisions and collisions with a 'another' subsystem do not result to thermalization; DF of electrons and phonons have high energy 'tails' as in electron-phonon impacts the momentum is transferred with sufficiently small transfer of energy; a lot of phonons with Debye energy are being born, i.e. phonon DF is being enriched by Debye phonons.
Influence of confined acoustic phonons on the Radioelectric field in a Quantum well
Long, Do Tuan; Quang Bau, Nguyen
2015-06-01
The influence of confined acoustic phonons on the Radioelectric field in a quantum well has been studied in the presence of a linearly polarized electromagnetic wave and a laser radiation. By using the quantum kinetic equation for electrons with confined electrons - confined acoustic phonons interaction, the analytical expression for the Radio electric field is obtained. The formula of the Radio electric field contains the quantum number m characterizing the phonons confinement and comes back to the case of unconfined phonons when m reaches to zero. The dependence of the Radio electric field on the frequency of the laser radiation, in case of confined acoustic phonons, is also achieved by numerical method for a specific quantum well AlGaAs/GaAs/AlGaAs. Results show that the Radio electric field has a peak and reaches saturation as the frequency of the laser radiation increases.
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.
Phonon dispersion of bcc cerium
International Nuclear Information System (INIS)
The phonon dispersion of the high temperature bcc or ?-phase of cerium has been measured by inelastic neutron scattering, growing the single crystals in situ on the spectrometer. The phonon dispersion shows a characteristic valley of low energy and strongly damped phonons along T 1[??0] and T 1[??2?]. From that the physical origin of the bcc-to-fcc martensitic phase transition is deduced. A mechanism involving long wavelength phonons is proposed. (orig.)
Spectrum and entanglement of phonons in quantum fluids of light
Busch, Xavier; Parentani, Renaud
2013-01-01
We study the quantum state of phonons propagating on top of a fluid of light coherently generated in a planar microcavity device by a quasi-resonant incident laser beam. In the steady-state under a monochromatic pump, because of the finite radiative lifetime of photons, a sizable incoherent population of low frequency phonons is predicted to appear. Their mean occupation number differs from a Planck distribution and is independent on the photon lifetime. When the photon fluid is subjected to a sudden change of its parameters, additional phonon pairs are created in the fluid with remarkable two-mode squeezing and entanglement properties. Schemes to assess non-separability of the phonon state from measurements of the correlation functions of the emitted light are discussed.
Highly efficient surface modification of solids by dual action of XUV/Vis-NIR laser pulses.
Czech Academy of Sciences Publication Activity Database
Mocek, Tomáš; Jakubczak, Krzysztof; Polan, Ji?í; Homer, Pavel; Rus, Bed?ich; Kim, I.J.; Kim, C. M.; Park, S.B.; Kim, T.K.; Lee, G.H.; Nam, C. H.; Chalupský, Jaromír; Hájková, V?ra; Juha, Libor
Dordrecht : Springer, 2009 - (Ciaran, L.; Riley, D.), s. 401-406 ISBN 978-1-4020-9923-6. [International Conference on X-Ray Lasers /11th./. Belfast (GB), 17.08.2008-22.08.2008] R&D Projects: GA ?R GC202/07/J008; GA AV ?R KAN300100702 Institutional research plan: CEZ:AV0Z10100523 Keywords : high - order harmonic generation * material processing * nanopatterning * laser induced periodic surface structures Subject RIV: BH - Optics, Masers, Lasers
Increased laser action in commercial dyes from fluorination regardless of their skeleton
International Nuclear Information System (INIS)
The direct and simple fluorination of representative organic laser dyes with emission covering the entire visible spectrum, from blue to red, including Coumarin 460, Pyrromethene 546, Rhodamine 6G and Perylene Red, enhances laser efficiencies by a factor up to 1.8 with respect to the corresponding non-fluorinated parent dyes. More importantly, fluorination also significantly enhances the photostability of the dyes, even under drastic laser pumping conditions. (letter)
Increased laser action in commercial dyes from fluorination regardless of their skeleton
Duran-Sampedro, G.; Agarrabeitia, A. R.; Arbeloa Lopez, T.; Bañuelos, J.; López-Arbeloa, I.; Chiara, J. L.; Garcia-Moreno, I.; Ortiz, M. J.
2014-11-01
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.
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.
Optical Investigations of Powerful Laser Actions on Massive and Flyer Targets
International Nuclear Information System (INIS)
In this paper we present experimental, theoretical, and computer simulation studies of craters formation produced by high power lasers in single and double layer targets. The experimental investigation was carried out using the PALS (Prague Asterix Laser System) facility working with two different laser beam wavelengths: ?1 = 1.315 ?m and ?3 0.438 ?m. Two types of targets made of Al were used: single massive targets, and double targets consisting of a foil or disk (6 ?m thick for both cases) placed in front of the massive target part at a distance of 200-500 ?m. Experiments with single massive targets were performed at laser intensities in the range of 1013-1015 W/cm2 by varying the laser beam diameters on the target surface from 70 ?m up to 1200 ?m (i.e. moving the target away from the focus). The double targets were illuminated by laser energies EL = 100-500 J focused always on a diameter of 250 ?m. In all experiments performed the laser pulse duration was equal to 400 ps. 3-frame interferometry was employed to investigate the plasma dynamics through measurements of the electron density distribution time development as well as of the disks and foil fragments velocities. The dimensions and shapes of craters were obtained by crater replica technology and microscopy measurement. The experiments were complemented by a 2-D analytical theory and computer simulations, which helped at interpretation of the results. This way the values of laser energy absorption coees of laser energy absorption coefficient, ablation loading efficiency and efficiency of energy transfer, as well as two-dimensional shock wave generation at the laser-driven macroparticle impact were obtained from the measured crater parameters for both the wavelengths of laser radiation
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.
PHONONS IN AMORPHOUS MATERIALS
Hunklinger, S.
1982-01-01
The study of the propagation of phonons is an important tool to investigate the sometimes unexpected and puzzling dynamic properties of amorphous solids. At first, as a typical example, we shall discuss the acoustic properties of vitreous silica. In the second part of the review emphasis will be given to the anomalous low temperature properties of amorphous materials.
Optical investigations of powerful laser actions on massive and flyer targets
International Nuclear Information System (INIS)
In this paper we present experimental, theoretical, and computer simulation studies of craters formation produced by high power lasers in single and double layer targets. The experimental investigation was carried out using the PALS (Prague Asterix Laser System) facility working with two different laser beam wavelengths: ?1 = 1.315 ?m and ?3 0.438 ?m. Two types of targets made of Al were used: single massive targets and double targets consisting of a foil or disk (6 ?m and 11 ?m thick for both cases) placed in front of the massive target at the distance of 200-500 ?m. Experiments with single massive targets were performed at laser intensities in the range of 1013-1015 W/cm2 by varying the laser beam diameter on the target surface from 70 ?m up to 1200 ?m (moving the target away from the focus). The double targets were illuminated by laser energies EL = 100-500 J always focused on diameter of 250 ?m. In all experiments performed the laser pulse duration was equal to 400 ps. The 3-frame interferometry was employed to investigate the plasma dynamics by means of the electron density distribution time development as well as the disks and foil fragments velocity measurements. Dimensions and shapes of craters were obtained by crater replica technology and microscopy measurement. Experimental results were complemented by two-dimensional analytical theory and computer simulations to help their interpretation. This way the values of laser energy absorption coefficient, ablation loading efficiency and efficiency of energy transfer as well as two-dimensional shock wave generation at the laser-driven macro-particle impact were obtained from measured craters' parameters for both wavelengths of laser radiation. (author)
Optical Investigations of Powerful Laser Actions on Massive and Flyer Targets
Pisarczyk, T.; Borodziuk, S.; Demchenko, N. N.; Gus'kov, S. Yu.; Jungwirth, K.; Kalal, M.; Kasperczuk, A.; Kralikova, B.; Krousky, E.; Limpouch, J.; Masek, K.; Pisarczyk, P.; Pfeifer, M.; Rohlena, K.; Rozanov, V. B.; Skala, J.; Ullschmied, J.
2006-01-01
In this paper we present experimental, theoretical, and computer simulation studies of craters formation produced by high power lasers in single and double layer targets. The experimental investigation was carried out using the PALS (Prague Asterix Laser System) facility working with two different laser beam wavelengths: ?1 = 1.315 ?m and ?3 = 0.438 ?m. Two types of targets made of Al were used: single massive targets, and double targets consisting of a foil or disk (6 ?m thick for both cases) placed in front of the massive target part at a distance of 200-500 ?m. Experiments with single massive targets were performed at laser intensities in the range of 1013-1015 W/cm2 by varying the laser beam diameters on the target surface from 70 ?m up to 1200 ?m (i.e. moving the target away from the focus). The double targets were illuminated by laser energies EL = 100-500 J focused always on a diameter of 250 ?m. In all experiments performed the laser pulse duration was equal to 400 ps. 3-frame interferometry was employed to investigate the plasma dynamics through measurements of the electron density distribution time development as well as of the disks and foil fragments velocities. The dimensions and shapes of craters were obtained by crater replica technology and microscopy measurement. The experiments were complemented by a 2-D analytical theory and computer simulations, which helped at interpretation of the results. This way the values of laser energy absorption coefficient, ablation loading efficiency and efficiency of energy transfer, as well as two-dimensional shock wave generation at the laser-driven macroparticle impact were obtained from the measured crater parameters for both the wavelengths of laser radiation.
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. 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.
Optical investigation of powerful laser actions on massive and flyer targets.
Czech Academy of Sciences Publication Activity Database
Pisarczyk, T.; Borodziuk, S.; Demchenko, N. N.; Gus´kov, S.Y.; Jungwirth, Karel; Kálal, M.; Kasperzcuk, A.; Králiková, Božena; Krouský, Eduard; Limpouch, Ji?í; Mašek, Karel; Pisarczyk, P.; Pfeifer, Miroslav; Rohlena, Karel; Rozanov, V. B.; Skála, Ji?í; Ullschmied, Ji?í
Melville : American Institut of Physics, 2005 - (Sadowski, M.; Dudeck, M.; Hartfus, H.; Pawelec, E.), 64-71 ISBN 0-7354-0304-X. ISSN 0094-243X. - (AIP Conference Proceedings. 812). [PLASMA 2005. Opole-Turawa (PL), 06.09.2005-09.09.2005] R&D Projects: GA MŠk(CZ) LC528 Grant ostatní: EC - LASERLAB-EUROPE(XE) RII3-CT-2003-506350 Institutional research plan: CEZ:AV0Z10100523; CEZ:AV0Z20430508 Keywords : plasma heating by laser * plasma diagnostics * laser ablation * laser fusion Subject RIV: BL - Plasma and Gas Discharge Physics http://dx.doi.org/10.1063/1.2168799
Vasil'chenko, Zh V.; Azharonok, V. V.; Filatova, I. I.; Shimanovich, V. D.; Golubev, V. S.; Zabelin, A. M.
1996-09-01
Emission spectroscopy methods were used in an investigation of thermodynamic parameters of a surface plasma formed by the action of cw CO2 laser radiation of (2-5)×106 W cm-2 intensity on stainless steel in a protective He or Ar atmosphere. The spatiotemporal structure and pulsation characteristics of the plasma plume were used to determine the fields of the plasma electron density and temperature.
Berry curvature and the phonon Hall effect
Qin, Tao; Zhou, Jianhui; Shi, Junren
2012-09-01
We show that an effective magnetic field acting on phonons naturally emerges in the phonon dynamics of magnetic solids, giving rise to the phonon Hall effect. A general formula for the intrinsic phonon Hall conductivity is derived by using the corrected Kubo formula with the energy magnetization contribution incorporated properly. We thus establish a direct connection between the phonon Hall effect and the intrinsic phonon band structure, i.e., the phonon Berry curvature and phonon dispersion. Based on the formalism, we predict that phonons could also display the quantum Hall effect in certain topological phonon systems. In the low-temperature regime, we predict that the phonon Hall conductivity is proportional to T3 for ordinary phonon systems, while that for the topological phonon system has a linear T dependence with a quantized temperature coefficient.
Electron-phonon interaction and coupled phonon--plasmon modes
Falkovsky, L.
2003-01-01
The theory of Raman scattering by the electron--phonon coupled system in metals and heavily doped semiconductors is developed taking into account the Coulomb screening and the electron--phonon deformation interaction. The Boltzmann equation for carriers is applied. Phonon frequencies and optic coupling constants are renormalized due to interactions with carriers. The $k-$dependent semiclassical dielectric function is involved instead of the Lindhard-Mermin expression. The re...
Superconductivity without phonons.
Monthoux, P; Pines, D; Lonzarich, G G
2007-12-20
The idea of superconductivity without the mediating role of lattice vibrations (phonons) has a long history. It was realized soon after the publication of the Bardeen-Cooper-Schrieffer (BCS) theory of superconductivity 50 years ago that a full treatment of both the charge and spin degrees of freedom of the electron predicts the existence of attractive components of the effective interaction between electrons even in the absence of lattice vibrations--a particular example is the effective interaction that depends on the relative spins of the electrons. Such attraction without phonons can lead to electronic pairing and to unconventional forms of superconductivity that can be much more sensitive than traditional (BCS) superconductivity to the precise details of the crystal structure and to the electronic and magnetic properties of a material. PMID:18097398
Action of a 904-nm diode laser in orthopedics and traumatology: a clinical study on 447 cases
Tam, Giuseppe
2001-10-01
Objective: The evidence in medical literature is that a beneficial analgesic effect can only be obtained by employing laser radiation of relatively low power density and wavelengths which are able to penetrate tissue. For this reason the semiconductor, or laser diode (GaAs, 904 nm), is the most appropriate choice in pain-reduction therapy. Summary Background Data: Low power laser (or LLL) acts on the Prostaglandins synthesis, increases the endorphins synthesis in the Rolando gelatinous substance and in the dorsal horn of the spinal cord. The L-Arginine, which is the classic substrate of nitric oxide, carries on vasodilatory and anti- inflammatory action. Methods: Treatment was carried out on 447 cases and 435 patients (250 women and 185 men) between 20th May 1987 and 31st December 1999. The patients, whose age ranged from 25 to 70, were suffering from rheumatic, degenerative and traumatic pathologies as well as cutaneous ulcers. The majority of patients had been seen by orthopaedists and rheumatologists and had undergone x-ray, ultrasound scan, etc. All patients had previously received drug-based treatment and/or physiotherapy, with poor results. Two thirds were experiencing acute symptomatic pain, while the others presented a chronic pathology with recurrent crises. We used a pulsed IR diode laser, GaAs emitting at 904 nm. Frequency of treatment: 1 application per day for 5 consecutive days, followed by a 2-day interval. The percentage reduction in symptoms or improvement in functional status were determined on the basis of objective analysis as it happens in the Legal and Insurance Medicine field. Results: Very good results were achieved especially with cases of symptomatic osteoarthritis of the cervical vertebrae, with sport-related injuries, epicondylitis, osteoarthritis of the knee, periarthritis and with cutaneous ulcers. The beneficial action of the LLLT in the latter pathology is linked to the increase in collagen and to fibroblast proliferation. The total relief of the pain was achieved in 80% of acute and 65% of chronic cases. Conclusions: Treatment with 904 nm IR diode laser has substantially reduced the symptoms as well as improved the quality of life of the patient, thus postponing the need for surgery.
Analysis of the stress raising action of flaws in laser clad deposits
International Nuclear Information System (INIS)
Highlights: ? Laser clad defects are 0D-pores/inclusions, 1D-clad waviness or 2D-planar defects. ? Surface pore of laser clad bar initiates fatigue cracks. ? Side edge surface pores are more critical than in-clad surface pores. ? Smaller notch radius and angle of as-laser clad surface raises stress significantly. ? Planar inner defects grow faster towards surface. - Abstract: Fatigue cracking of laser clad cylindrical and square section bars depends upon a variety of factors. This paper presents Finite Element Analysis (FEA) of the different macro stress fields generated as well as stress raisers created by laser cladding defects for four different fatigue load conditions. As important as the defect types are their locations and orientations, categorized into zero-, one- and two-dimensional defects. Pores and inclusions become critical close to surfaces. The performance of as-clad surfaces can be governed by the sharpness of surface notches and planar defects like hot cracks or lack-of-fusion (LOF) are most critical if oriented vertically, transverse to the bar axis. The combination of the macro stress field with the defect type and its position and orientation determines whether it is the most critical stress raiser. Based on calculated cases, quantitative and qualitative charts were developed as guidelines to visualize the trends of different combinations
Phonon operators in deformed nuclei
International Nuclear Information System (INIS)
For the description of the excited states in deformed nuclei new phonon operators are introduced, which depend on the sign of the angular momentum projection onto the symmetry axis of a deformed nucleus. In the calculations with new phonons the Pauli principle is correctly taken into account in the two-phonon components of the wave functions. There is a difference in comparison with the calculation with phonons independent of the sign of the angular momentum projection. The new phonons should be used in deformed nuclei if the Pauli principle is consistently taken into account and in the calculations with the excited state wave functions having the components with more than one phonon operator
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 .
Efficient materials processing by dual action of XUV/Vis-NIR ultrashort laser pulses.
Czech Academy of Sciences Publication Activity Database
Jakubczak, Krzysztof; Mocek, Tomáš; Polan, Ji?í; Homer, Pavel; Rus, Bed?ich; Kim, I.J.; Kim, C. M.; Park, S.B.; Kim, T.K.; Lee, G.H.; Nam, C. H.; Chalupský, Jaromír; Hájková, V?ra; Juha, Libor; Sobota, Jaroslav; Fo?t, Tomáš
Bellingham : SPIE, 2009 - (Juha, L.; Bajt, S.; Sobierajski, R.), 73610A/1-73610A/5 ISBN 9780819476357. ISSN 0277-786x. - (Proceedings of SPIE. 7361). [Damage to VUV, EUV, and X-Ray Optics II. Prague (CZ), 21.04.2009-23.04.2009] R&D Projects: GA AV ?R KAN300100702; GA MŠk LC510; GA MŠk(CZ) LC528; GA MŠk LA08024; GA ?R GC202/07/J008 Institutional research plan: CEZ:AV0Z10100523; CEZ:AV0Z20650511 Keywords : High-order Harmonic Generation ( HHG ) * materials machining * nanopatterning * femtosecond laser pulses * Laser Induced Periodic Surface Structures (LIPSS) Subject RIV: BH - Optics, Masers, Lasers http://dx.doi.org/10.1117/12.822433
Bacterial action of carbon dioxide laser radiation in experimental dental root canals
International Nuclear Information System (INIS)
The ability of a carbon dioxide laser to sterilize the root canal of human teeth has been investigated. Three oral bacteria, Streptococcus sanguis, Streptococcus mutans, and Actinomyces viscosus, and three other bacteria, Bacillus cereus, Staphyloccus aureus, and Pseudomonoas aeruginosa were used as experimental organisms. Exposure of cells on glass slides to laser radiation showed there was little difference in the exposure required to kill these six organisms. Complete recovery of bacteria from the root canal was initially a problem and was only achieved when bacterial manipulations and removal were carried out in rapid succession, within 5 min of inoculation. However, the geometry of the instrumented canal and the laser alignment were major factors in achieving consistent cell death of oral bacteria in the root canals. Using sets of 10 teeth, four repeated exposures of 10 W for 1 s was found to sterilize 4 or more of the teeth
Low intensity red laser action on Escherichia coli cultures submitted to stress conditions
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.
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 tress. Thus, our results suggest that therapies based on low intensity red lasers could take into account physiologic conditions and genetic characteristics of cells. (paper)
International Nuclear Information System (INIS)
Formation of a liquid phase with a transition to a homogeneous amorphous state under the surface layer solidification is detected under picosecond laser pulse effect on the microcrystalline graphite. A periodic surface structure is produced in the heating region with the period of the order of the length of the heating pulse wave, its strokes following the direction of this pulse polarization. Study of the probing laser pulse reflection kinetics has shown, that the typical time of liquid phase and solidification life makes up ? 10-10 s
Phonon effects in molecular transistors
Mitra, A.; Aleiner, I.; Millis, A. J.
2003-01-01
A rate equation formalism is used to determine the effect of electron-phonon coupling on the conductance of a molecule. Interplay between the phonon-induced renormalization of the density of states on the quantum dot and the phonon-induced renormalization of the dot-lead coupling is found to be important. Whether or not the phonons are able to equilibrate in a time rapid compared to the transit time of an electron through the dot is found to affect the conductance. Observabl...
Detecting phonon blockade with photons
Didier, Nicolas; Blanter, Yaroslav M; Fazio, Rosario
2010-01-01
By proper designing the coupling between a Cooper pair box and a nano-mechanical resonator, it is possible to reach a sufficient level on non-linearity as to make the experimental observation of phonon blockade possible. We show that phonon blockade can be observed by measuring the statistics of the light in a superconducting microwave resonator capacitively coupled to the mechanical mode. The underlying reason is the formation of an entangled state between the two resonators, ensuring a perfect match between the phonon dynamics and the photon statistics. Our scheme does also offer a way to prepare and detect entangled states between phonons and photons.
Mukhamedgalieva, Anel F.; Bondar', Anatolii M.; Ionin, Andrei A.; Klimachev, Yurii M.; Sinitsyn, Dmitrii V.; Zvorykin, Vladimir D.
2004-09-01
The laser ablation of fused and crystal silica and natural silicates induced by pulsed CO2 laser irradiation (total pulse time of 35 ?s, pulse increase time of 0,1 ?s, pulse energy of 10 J) has been studied. By action of focused laser radiation at the surface of samples the appearance of erosion plume at the irradiated surface take place. For study of ablation regimes the frame image of laser induced plume by use of high speed photography method with 2 microsecond expose of each frame have been made. It has been observed the formation of two different type of laser plume during laser pulse action. First type plume represents a long narrow plume with the onset close to start of laser pulse. The maximal length of this plume is about of 20 millimeter. The second type of plume represents a conical plume with the onset, which is late from laser pulse start for a few microsecond. The first type plume expands in to laser beam direction. The second type plume expands normal to the surface. The velocity of laser plume particles by means of measurements of moment transferred into samples during laser pulse action has been measured. It has been obtained, that value of this velocity varies in region of 1-3×103 m/s in dependence of laser fluency value. The appearance of first time plume have a threshold which equal to 0,15 kJ/cm2 whereas the appearance of second type plume have not a such threshold and may take place at low laser fluency. We believe, that the first type plume connects with the selective ablation of SimOn complexes whereas second type plume connects with the thermal heating caused by dissipation of laser energy in to system of low frequency acoustics phonons.
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)
Condensation kinetics of microcavity polaritons with scattering by phonons and polaritons
Doan, T. D.; Cao, Huy Thien; Tran Thoai, D. B.; Haug, H.
2005-08-01
We present numerical studies of the exciton polariton condensation kinetics in microcavities for the combined action of polariton-polariton and polariton-acoustic phonon scattering both for quasi-stationary and picosecond pulse excitation, respectively. For excitations of nearly resonant polaritons mainly the polariton-polariton scattering mechanism results in a condensation on the minimum of the lower polariton branch at relatively low areal polariton densities of the order of 109-1010cm-2 . The simultaneously acting polariton-phonon scattering increases the number of condensed particles considerably by providing a heat dissipation from the polariton gas to the lattice. For nonresonant excitations at large k values the considered scattering mechanisms cannot support a polariton condensation. Above (below) laser threshold there exists a (no) polariton condensate and the polariton distribution of the noncondensed particles can be fitted by a Bose-Einstein (Maxwell-Boltzmann) distribution. Our results for 3ps pulse excitation are in very good agreement with recent experimental observations of Yamamoto
International Nuclear Information System (INIS)
Defects in semiconductors introduce vibrational modes that are distinct from bulk modes because they are spatially localized in the vicinity of the defect. Light impurities produce high-frequency modes often visible by Fourier-transform infrared absorption or Raman spectroscopy. Their vibrational lifetimes vary by orders of magnitude and sometimes exhibit unexpectedly large isotope effects. Heavy impurities introduce low-frequency modes sometimes visible as phonon replicas in photoluminescence bands. But other defects such as surfaces or interfaces exhibit spatially localized modes (SLMs) as well. All of them can trap phonons, which ultimately decay into lower-frequency bulk phonons. When heat flows through a material containing defects, phonon trapping at localized modes followed by their decay into bulk phonons is usually described in terms of phonon scattering: defects are assumed to be static scattering centers and the properties of the defect-related SLMs modes are ignored. These dynamic properties of defects are important. In this paper, we quantify the concepts of vibrational localization and phonon trapping, distinguish between normal and anomalous decay of localized excitations, discuss the meaning of phonon scattering in real space at the atomic level, and illustrate the importance of phonon trapping in the case of heat flow at Si/Ge and Si/C interfaces
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.
Golubev, V B
2001-01-01
The hydrodynamic model of the periodical lamination of the heterogeneous condensed systems from the immiscible components under the effect of the powerful laser beams in the mode of canalized permittivity is presented. The model accounts for the motion of the immiscible components particles in the melt vortex flows under the effect of the centrifugal forces. The conditions for origination of the periodical concentration lamination and their spatial scale are determined
The heat-pipe resembling action of boiling bubbles in endovenous laser ablation
Geld, C. W. M.; Bos, R. R. Den; Ruijven, P. W. M.; Nijsten, T. E. C.; Neumann, H. A. M.; Gemert, M. J. C.
2010-01-01
Endovenous laser ablation (EVLA) produces boiling bubbles emerging from pores within the hot fiber tip and traveling over a distal length of about 20 mm before condensing. This evaporation-condensation mechanism makes the vein act like a heat pipe, where very efficient heat transport maintains a constant temperature, the saturation temperature of 100A degrees C, over the volume where these non-condensing bubbles exist. During EVLA the above-mentioned observations indicate that a venous cylind...
Nemtsev, I Z; Luzhnikov, E A; Lapshin, V P; Gol'dfarb, Iu S; Badalian, A V
1997-01-01
Extracorporeal exposure to LG-79 He-Ne laser of 12 mWt power was used in 57 patients hospitalized at the intoxication reanimation department with acute poisonings with psychotropic drugs. The clinical result was a decrease of the incidence of pneumonia in the patients with x-ray signs of venous congestion from 52% among those administered to physiochemotherapy to 24% after this treatment modality. Laser hemotherapy brought about a temporary normalization of the erythrocyte membrane permeability, which was changed biophysically by means of a diffractometer. Red cell aggregation was approximating the norm, decreasing by 20%, and platelet aggregation decreased by 17%. Analysis of the results brought as to a conclusion that He-Ne laser exposure is an effective source of singlet stimulation of molecular O2 evenly dissolved in the blood, which causes resonance oscillations of water difields. This leads to membrane depolarization, which is probably responsible for purification of polarized membranes from toxic agents fixed by them. PMID:9382223
Jet formation in spallation of metal film from substrate under action of femtosecond laser pulse
Inogamov, N. A.; Zhakhovskii, V. V.; Khokhlov, V. A.
2015-01-01
It is well known that during ablation by an ultrashort laser pulse, the main contribution to ablation of the substance is determined not by evaporation, but by the thermomechanical spallation of the substance. For identical metals and pulse parameters, the type of spallation is determined by film thickness d f . An important gauge is metal heating depth d T at the two-temperature stage, at which electron temperature is higher than ion temperature. We compare cases with d f film) and d f ? d T (bulk target). Radius R L of the spot of heating by an optical laser is the next (after d f ) important geometrical parameter. The morphology of film bulging in cases where d f blistering) changes upon a change in radius R L in the range from diffraction limit R L ˜ ? to high values of R L ? ?, where ? ˜ 1 ?m is the wavelength of optical laser radiation. When d f F m, gold film deposited on the glass target acquires a cupola-shaped blister with a miniature frozen nanojet in the form of a tip on the circular top of the cupola ( F abs and F m are the absorbed energy and the melting threshold of the film per unit surface area of the film). A new physical mechanism leading to the formation of the nanojet is proposed.
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.
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.
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.
Anomalous effect of phonon wind on lateral migration of excitons in ultrathin quantum CdTe/ZnTe well
Onishchenko, E E; Zajtsev, V V
2001-01-01
The effect of the acoustic phonons nonequilibrium flux on the photoluminescence of the CdTe/ZnTe thin quantum well, excited quasi-resonantly by the He-Ne-laser is studied. It is established that the phonon flux leads to the change in the form of the quantum well luminescence band even by low generation capacities. It is assumed that the nonequilibrium phonons flux stimulates the excitons migration in the quantum well plane, conditioned by the tunnel transitions between the potential local minima, which are accompanied by the phonons induced emission
Spectral self-action of THz emission from ionizing two-color laser pulses in gases
Cabrera-Granado, Eduardo; 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 of the generated THz field. Diffraction limits the achievable THz bandwidth by efficiently depleting the low frequency amplitudes in the propagating field.
Distributions of phonon lifetimes in Brillouin zones
Togo, Atsushi; Chaput, Laurent; Tanaka, Isao
2015-03-01
Lattice thermal conductivities of zincblende- and wurtzite-type compounds with 33 combinations of elements are calculated with the single-mode relaxation-time approximation and a full solution of the linearized phonon Boltzmann equation from first-principles anharmonic lattice dynamics calculations. In nine zincblende-type compounds, distributions of phonon linewidths (inverse phonon lifetimes) are discussed in detail. The phonon linewidths vary nonsmoothly with respect to wave vector, which is explained from the imaginary parts of the self-energies. It is presented that detailed combination of phonon-phonon interaction strength and three-phonon selection rule is critically important to determine phonon lifetime for these compounds. This indicates difficulty to predict phonon lifetime quantitatively without anharmonic force constants. However, it is shown that joint density of states weighted by phonon numbers, which is calculated only from harmonic force constants, can be potentially used for a screening of the lattice thermal conductivity of materials.
Berry Curvature and Phonon Hall Effect
Qin, Tao; Shi, Junren
2012-02-01
We establish the general phonon dynamics of magnetic solids by incorporating the Mead-Truhlar correction in the Born-Oppenheimer approximation. The effective magnetic-field acting on the phonons naturally emerges, giving rise to the phonon Hall effect. A general formula of the intrinsic phonon Hall conductivity is obtained by using the corrected Kubo formula with the energy magnetization contribution properly incorporated. The resulting phonon Hall conductivity is fully determined by the phonon Berry curvature and the dispersions. Based on the formula, the topological phonon system could be rigorously defined. In the low temperature regime, we predict that the phonon Hall conductivity is proportional to T^3 for the ordinary phonon systems, while that for the topological phonon systems has the linear T dependence with the quantized temperature coefficient. [4pt] [1] Tao Qin and Junren Shi, arXiv:1111.1322 (2011) [0pt] [2] Tao Qin, Qian Niu and Junren Shi, Phys. Rev. Lett., Accepted, (2011).
Dephasing times in quantum dots due to elastic LO phonon-carrier collisions
DEFF Research Database (Denmark)
Uskov, A. V.; Jauho, Antti-Pekka
2000-01-01
Interpretation of experiments on quantum dot (QD) lasers presents a challenge: the phonon bottleneck, which should strongly suppress relaxation and dephasing of the discrete energy states, often seems to be inoperative. We suggest and develop a theory for an intrinsic mechanism for dephasing in QDs: second-order elastic interaction between quantum dot charge carriers and LO phonons. The calculated dephasing times are of the order of 200 fs at room temperature, consistent with experiments. The phonon bottleneck thus does not prevent significant room temperature dephasing.
Phonon dispersion curves and phonon lifetimes in crystalline ammonia
International Nuclear Information System (INIS)
The theory of lattice dynamics of molecular crystals using atom-atom and multipole-multipole potentials developed in previous papers is extended to take account of anharmonic effects. Calculations of the dispersion curves and the density of states for the harmonic phonons in solid ammonia are presented. The finite phonon lifetimes due to anharmonicity are calculated for the zero wave vector modes and compared with experiment. (orig.)
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...
Phonon lineshapes in atom-surface scattering
Martínez Casado, R.; Sanz, Ángel S.; Miret-Artés, Salvador
2010-01-01
Phonon lineshapes in atom-surface scattering are obtained from a simple stochastic model based on the so-called Caldeira-Leggett Hamiltonian. In this single-bath model, the excited phonon resulting from a creation or annihilation event is coupled to a thermal bath consisting of an infinite number of harmonic oscillators, namely the bath phonons. The diagonalization of the corresponding Hamiltonian leads to a renormalization of the phonon frequencies in terms of the phonon fr...
Electron-phonon bound state in graphene
S. M. Badalyan; Peeters, F. M.
2012-01-01
The fine structure of the Dirac energy spectrum in graphene induced by electron-optical phonon coupling is investigated in the portion of the spectrum near the phonon emission threshold. The derived new dispersion equation in the immediate neighborhood below the phonon threshold corresponds to an electron-phonon bound state. We find that the singular vertex corrections beyond perturbation theory increase strongly the electron-phonon binding energy. The predicted enhancement ...
Berry Curvature and Phonon Hall Effect
Qin, Tao; Zhou, Jianhui; Shi, Junren
2011-01-01
We establish the general phonon dynamics of magnetic solids by incorporating the Mead-Truhlar correction in the Born-Oppenheimer approximation. The effective magnetic-field acting on the phonons naturally emerges, giving rise to the phonon Hall effect. A general formula of the intrinsic phonon Hall conductivity is obtained by using the corrected Kubo formula with the energy magnetization contribution incorporated properly. The resulting phonon Hall conductivity is fully dete...
Hot Phonons in an Electrically Biased Graphene Constriction
Chae, Dong-Hun; Krauss, Benjamin; von Klitzing, Klaus; Smet, Jurgen H.
2010-01-01
Phonon carrier interactions can have significant impact on device performance. They can be probed by measuring the phonon lifetime, which reflects the interaction strength of a phonon with other quasi-particles in particular charge carriers as well as its companion phonons. The carrier phonon and phonon-phonon contributions to the phonon lifetime can be disentangled from temperature dependent studies. Here, we address the importance of phonon carrier interactions in Joule-he...
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.
Wave front dislocations appearance under the laser beam self-action in liquid crystal
Energy Technology Data Exchange (ETDEWEB)
Subota, Svitlana [Physics Faculty, Kyiv Taras Shevchenko University, Prosp. Glushkova, 6, Kyiv 03680 (Ukraine)]. E-mail: subota@univ.kiev.ua
2005-07-15
We present theoretical study of optical singularity birth and behaviour in an initially smooth wave front of the incident astigmatic Gaussian light beam. Linearly polarised light beam illuminates a homeotropically aligned nematic liquid crystal cell. Strong director anchoring at the cell walls is assumed. Director reorientation profile is found numerically solving Euler-Lagrange equations. We found the threshold intensity for light induced Fredeericksz-type transition. The threshold intensity of light beam is appeared to increase with increasing of beam asymmetry under the constant value of laser beam area and cell thickness. The results are compared with those calculated using Gaussian-like trial function. Utilizing the Huygens-Fresno principle we calculate the propagation of the distorted light beam after the liquid crystal cell. It is found that with distance increasing we can observe at first the dipole, then the quadrupole and then again the dipole of optical vortices whis unit charge. Thus, the trajectory of zero amplitude resembles a deformed rubber ring symmetrical in the xz-, yz-planes and stretched along z-axis.
Phonon scattering at siliconcrystal surfaces
Marx, Dieter; Eisenmenger, Wolfgang
1982-01-01
Our observations of the reflection or backscattering of high-frequency phonons (v =280 GHz to 1 THz) at silicon-solid interfaces disagree significantly with predictions from the acoustic mismatch model. Interfaces composed of materials theoretically wellmatched, show high scattering experimentally. In contrast, interfaces theoretically poorly matched, show less phonon scattering than expected. Generally, this is best expressed by the fact that the interface scattering ranges from roughly 30?6...
International Nuclear Information System (INIS)
A numerical technique for calculating the time-dependent multimode lasing in an electron-beam-controlled CO2 laser at significant optical inhomogeneities caused by radiation self-action is presented. The reported calculations for subatmospheric pressure yield a sequence of involvement of transverse modes in lasing, the evolution of their characteristics (which is self-consistent with the evolution of gain and optical inhomogeneities of the active medium), and the exclusion of output modes from lasing. This calculation technique can be used when the radiation round-trip time around the cavity is shorter than the characteristic time of change in the active-medium characteristics. (lasers)
Zhang, S. H.; Xu, W.; Badalyan, S. M.; Peeters, F.M.
2012-01-01
We study the mobility of Dirac fermions in monolayer graphene on a GaAs substrate, restricted by the combined action of the extrinsic potential of piezoelectric surface acoustical phonons of GaAs (PA) and of the intrinsic deformation potential of acoustical eigen-phonons in graphene (DA). In the high temperature ($T$) regime the momentum relaxation rate exhibits the same linear dependence on $T$ but different dependences on the carrier density $n$, corresponding to the mobil...
Wang, Cih-Su; Liau, Chi-Shung; Sun, Tzu-Ming; Chen, Yu-Chia; Lin, Tai-Yuan; Chen, Yang-Fang
2015-03-01
A new approach is proposed to light up band-edge stimulated emission arising from a semiconductor with dipole-forbidden band-gap transition. To illustrate our working principle, here we demonstrate the feasibility on the composite of SnO2 nanowires (NWs) and chicken albumen. SnO2 NWs, which merely emit visible defect emission, are observed to generate a strong ultraviolet fluorescence centered at 387 nm assisted by chicken albumen at room temperature. In addition, a stunning laser action is further discovered in the albumen/SnO2 NWs composite system. The underlying mechanism is interpreted in terms of the fluorescence resonance energy transfer (FRET) from the chicken albumen protein to SnO2 NWs. More importantly, the giant oscillator strength of shallow defect states, which is served orders of magnitude larger than that of the free exciton, plays a decisive role. Our approach therefore shows that bio-materials exhibit a great potential in applications for novel light emitters, which may open up a new avenue for the development of bio-inspired optoelectronic devices.
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.
Bykovskii, N. E.; Zavedeev, E. V.; Senatskii, Yu. V.
2015-04-01
Craters on the surface of an yttrium-aluminum garnet crystal plate under irradiation by nanosecond laser pulses with an intensity of 109-1010 W/cm2 and a wide (˜500Å) spectrum have been studied. The mechanism of crater formation as a result of plastic deformation of the surface during the laser action has been discussed. The proposed mechanism takes into account specific features of nonlinear effects under the action of a broadband radiation on the medium. In the stimulated Brillouin scattering of pumping radiation, acoustic waves transform into shock waves, on the fronts of which stimulated Raman scattering develops. As a result, crystal lattice defects formed on the shock-wave fronts are dragged in the direction of pumping, which leads to a high-rate deformation of the crystal surface.
Photonic and phononic quasicrystals
International Nuclear Information System (INIS)
This review focuses on the peculiarities of quasiperiodic order for the properties of photonic and phononic (sonic) heterostructures. The most beneficial feature of quasiperiodicity is that it can combine perfectly ordered structures with purely point-diffractive spectra of arbitrarily high rotational symmetry. Both are prerequisites for the construction of isotropic band gap composites, in particular from materials with low index contrast, which are required for numerous applications. Another interesting property of quasiperiodic structures is their scaling symmetry, which may be exploited to create spectral gaps in the sub-wavelength regime. This review covers structure/property relationships of heterostructures based on one-dimensional (1D) substitutional sequences such as the Fibonacci, Thue-Morse, period-doubling, Rudin-Shapiro and Cantor sequence as well as on 1D modulated structures, further on 2D tilings with 8-, 10-, 12- and 14-fold symmetry as well as on the pinwheel tiling, the Sierpinski gasket and on curvilinear tilings and, finally, on the 3D icosahedral Penrose tiling. (topical review)
Photonic and phononic quasicrystals
Energy Technology Data Exchange (ETDEWEB)
Steurer, Walter; Sutter-Widmer, Daniel [Laboratory of Crystallography, Department of Materials, ETH Zurich, Wolfgang-Pauli-Strasse 10, CH-8093 Zurich (Switzerland)
2007-07-07
This review focuses on the peculiarities of quasiperiodic order for the properties of photonic and phononic (sonic) heterostructures. The most beneficial feature of quasiperiodicity is that it can combine perfectly ordered structures with purely point-diffractive spectra of arbitrarily high rotational symmetry. Both are prerequisites for the construction of isotropic band gap composites, in particular from materials with low index contrast, which are required for numerous applications. Another interesting property of quasiperiodic structures is their scaling symmetry, which may be exploited to create spectral gaps in the sub-wavelength regime. This review covers structure/property relationships of heterostructures based on one-dimensional (1D) substitutional sequences such as the Fibonacci, Thue-Morse, period-doubling, Rudin-Shapiro and Cantor sequence as well as on 1D modulated structures, further on 2D tilings with 8-, 10-, 12- and 14-fold symmetry as well as on the pinwheel tiling, the Sierpinski gasket and on curvilinear tilings and, finally, on the 3D icosahedral Penrose tiling. (topical review)
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
Polymorphism, phonon dynamics and carrier-phonon coupling in pentacene
Della Valle, R G; Farina, L; Venuti, E; Masino, M; Girlando, A; Brillante, Aldo; Farina, Luca; Girlando, Alberto; Masino, Matteo; Valle, Raffaele G. Della; Venuti, Elisabetta
2003-01-01
The crystal structure and phonon dynamics of pentacene is computed with the Quasi Harmonic Lattice Dynamics (QHLD) method, based on atom-atom potential. We show that two crystalline phases of pentacene exist, rather similar in thermodynamic stability and in molecular density. The two phases can be easily distinguished by Raman spectroscopy in the 10-100 cm-1 spectral region. We have not found any temperature induced phase transition, whereas a sluggish phase change to the denser phase is induced by pressure. The bandwidths of the two phases are slightly different. The charge carrier coupling to low-frequency phonons is calculated.
PHONON PULSES FRQM A RELAXING SYSTEM
Englman, R.
1981-01-01
The spread of polychromatic phonon pulses, following optical absorption by a defect, is calculated up to ~102 lattice-spacings far. Phonon dispersion attenuates the pulse. The angular variation of the pulse peak position reflects the spectral anisotropy.
Damping of coupled phonon--plasmon modes
Falkovsky, L. A.
2002-01-01
The effect of free carriers on dispersion and damping of coupled phonon-plasmon modes is considered in the long-wave approximation. The electron and phonon scattering rate as well as Landau damping are taken into account.
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.
Phonon dispersions of cluster crystals
Neuhaus, Tim
2010-01-01
We analyze the ground states and the elementary collective excitations (phonons) of a class of systems, which form cluster crystals in the absence of attractions. Whereas the regime of moderate-to-high-temperatures in the phase diagram has been analyzed in detail by means of density functional considerations (Likos C N, Mladek B M, Gottwald D and Kahl G 2007 {\\it J.~Chem.~Phys.}\\ {\\bf 126} 224502), the present approach focuses on the complementary regime of low temperatures. We establish the existence of an infinite cascade of isostructural transitions between crystals with different lattice site occupancy at $T=0$ and we quantitatively demonstrate that the thermodynamic instabilities are bracketed by mechanical instabilities arising from long-wavelength acoustical phonons. We further show that all optical modes are degenerate and flat, giving rise to perfect realizations of Einstein crystals. We calculate analytically the complete phonon spectrum for the whole class of models as well as the Helmholtz free en...
Phonon Mapping in Flowing Equilibrium
Ruff, J. P. C.
2015-03-01
When a material conducts heat, a modification of the phonon population occurs. The equilibrium Bose-Einstein distribution is perturbed towards flowing-equilibrium, for which the distribution function is not analytically known. Here I argue that the altered phonon population can be efficiently mapped over broad regions of reciprocal space, via diffuse x-ray scattering or time-of-flight neutron scattering, while a thermal gradient is applied across a single crystal sample. When compared to traditional transport measurements, this technique offers a superior, information-rich new perspective on lattice thermal conductivity, wherein the band and momentum dependences of the phonon thermal current are directly resolved. The proposed method is benchmarked using x-ray thermal diffuse scattering measurements of single crystal diamond under transport conditions. CHESS is supported by the NSF & NIH/NIGMS via NSF Award DMR-1332208.
Phonons from neutron powder diffraction
Dimitrov, D A; Röder, H
1998-01-01
The spherically averaged structure function $\\soq$ obtained from pulsed neutron powder diffraction contains both elastic and inelastic scattering via an integral over energy. The Fourier transformation of $\\soq$ to real space, as is done in the pair density function (PDF) analysis, regularizes the data, i.e. it accentuates the diffuse scattering. We present a technique which enables the extraction of off--center phonon information from powder diffraction experiments by comparing the experimental PDF with theoretical calculations based on standard interatomic potentials and the crystal symmetry. This procedure (dynamics from powder diffraction(DPD)) has been successfully implemented for two systems, a simple metal, fcc Ni, and an ionic crystal, CaF$_{2}$. Although computationally intensive, this data analysis allows for a phonon based modeling of the PDF, and additionally provides off-center phonon information from powder neutron diffraction.
Topological Nature of the Phonon Hall Effect
Zhang, Lifa; Ren, Jie; WANG, JIAN-SHENG; Li, Baowen
2010-01-01
We provide a topological understanding on phonon Hall effect in dielectrics with Raman spinphonon coupling. A general expression for phonon Hall conductivity is obtained in terms of the Berry curvature of band structures. We find a nonmonotonic behavior of phonon Hall conductivity as a function of magnetic field. Moreover, we observe a phase transition in phonon Hall effect, which corresponds to the sudden change of band topology, characterized by the altering of integer Che...
Polaron with disordered electron-phonon interaction
Yavidov, Bakhrom
2014-01-01
A single electron in one dimensional lattice is considered within the framework of extended Holstein model at strong-coupling limit. Disordered density-displacement type electron-phonon interaction is proposed. Basic parameters of small polaron formed due to disordered electron-phonon interaction are calculated. It is shown that disordered electron-phonon interaction substantially influences all properties of the polaron. Depending on disordered electron-phonon intera...
Unconventional plasmon-phonon coupling in graphene
Jablan, M.; Soljac?ic?, M.; Buljan, H.
2010-01-01
We calculate hybridization of plasmons and intrinsic optical phonons in graphene by using the self-consistent linear response formalism. We find that longitudinal plasmons (transverse magnetic modes) couple exclusively to transverse optical phonons, whereas graphene's transverse plasmons (transverse electric modes) couple only to longitudinal optical phonons. This mixing of polarizations is in contrast to the usual plasmon-phonon coupling in other systems. The resulting chan...
International Nuclear Information System (INIS)
We have studied phonons in UCoGa5, an isostructural compound of the heavy fermion superconductor PuCoGa5. Our neutron inelastic scattering experiment revealed very clear longitudinal and transverse acoustic phonons and low energy optical phonons along the high symmetry directions. The phonon frequencies measured at room temperature are in good agreement with ab initio calculation assuming a Coulomb repulsion U=0
Distribution of phonon lifetime in Brillouin zone
Togo, Atsushi; Chaput, Laurent; Tanaka, Isao
2015-01-01
Lattice thermal conductivities of zincblende- and wurtzite-type compounds with 33 combinations of elements are calculated with the single-mode relaxation-time approximation and linearized phonon Boltzmann equation from first-principles anharmonic lattice dynamics calculations. In 9 zincblende-type compounds, distributions of phonon linewidths (inverse phonon lifetimes) are discussed in detail. The phonon linewidths vary non-smoothly with respect to wave vector, which is expl...
Ultrafast electron-phonon decoupling in graphite
Ishioka, Kunie; Hase, Muneaki; Kitajima, Masahiro; Wirtz, Ludger; Rubio Secades, Ángel; Petek, Hrvoje
2008-01-01
We report the ultrafast dynamics of the 47.4 THz coherent phonons of graphite interacting with a photoinduced non-equilibrium electron-hole plasma. Unlike conventional materials, upon photoexcitation the phonon frequency of graphite upshifts, and within a few picoseconds relaxes to the stationary value. Our first-principles density functional calculations demonstrate that the phonon stiffening stems from the light-induced decoupling of the non-adiabatic electron-phonon inter...
Phonon Theory of Martensitic Transformation Precursors
Jin, Yongmei M.; Wang, Yu U.
2014-01-01
A phonon theory of precursor phenomena in martensitic phase transformations is developed. Extending Gr\\"uneisen theory of thermal expansion, this theory addresses the effects of deformation-dependent low-energy phonons on the structural, thermal, and elastic behaviors of pre-martensitic cubic crystals that undergo incomplete phonon softening. It reveals spontaneous symmetry breaking, pre-martensitic transformation, phonon domains, and tweed structure. The theory naturally ex...
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
Phonons in an entropic crystal
Cheng; Zhu; Russel; Chaikin
2000-08-14
Hard spheres crystallize due to purely entropic forces. The underlying excluded-volume interaction is completely anharmonic and the nature of the phonon spectrum is therefore of interest. To measure the single-particle motion and the phonon spectrum by dynamic light scattering we have used a collection of novel techniques including multispeckle cross correlation on a CCD chip and the growth of large single crystals using a temperature gradient. The random hexagonal close packed crystal has a dispersion relation closer to hcp than to fcc. PMID:10970529
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 tunnels from a sonic black hole
Fang, Hengzhong; Zhou, Kaihu
2011-01-01
We investigate the phonon radiation from a spherically symmetrical, stationary, viscid-free son-ic black hole by using a semi-classical method. The backreaction of the radiated phonon is taken into account. We obtain the phonon emission temperature, and it is consistent with the Hawking's formula.
Phonon propagation dynamics in band-engineered one-dimensional phononic crystal waveguides
Hatanaka, Daiki; Dodel, Amaury; Mahboob, Imran; Onomitsu, Koji; Yamaguchi, Hiroshi
2015-01-01
The phonon propagation dynamics in a phononic crystal waveguide, realized via a suspended one-dimensional membrane array with periodic air holes, is investigated as function of its geometry. The bandstructure of the phononic crystal can be engineered by modifying the characteristics of the phonon standing waves in the waveguide by varying the waveguide width and the pitch of the air holes. This enables the phonon transmission bands, the bandgaps, the velocity and the nonline...
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.
Firas J. Al-Maliki
2012-01-01
The synthesis, structural characterization, and amplified spontaneous emission spectroscopy of dye-scattering particles in inorganic medium based on Rhodamine 610-TiO2 nanoparticles confined in silica xerogel matrix have been reported. Optimum concentrations have been determined depending on the normal fluorescence spectra for laser dye, in order to provide amplification, and TiO2 nanoparticals as scatter center. Random Laser has been studied under second harmonic Nd: YAG laser excitation. At...
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.
Experimental investigation of magneto-photo-phonon resonance
International Nuclear Information System (INIS)
Full text: Recently, Xu and Zhang proposed that magneto-photo-phonon resonances (MPPR) may appear in two-dimensional semiconductor systems driven by terahertz electromagnetic radiation. The resonance condition may be written as ? + N?C = ?LO, where N is an integer and ?, ?C and ?LO are the photon, cyclotron and longitudinal-optic phonon frequencies, respectively. Physically, an increase in longitudinal resistivity, pxx, is expected when an inter-Landau-level transition, coupled with optical absorption, leads to resonant scattering via LO-phonon emission. The MPPR may be investigated either by sweeping magnetic field at a fixed photon energy or by scanning photon energy (i.e. spectroscopy) at a fixed magnetic field. Our experiments embrace both approaches. We have examined a variety of GaAs-based two-dimensional electron gases. In GaAs, ?LO ? 56 THz, corresponding to a magnetic field of ?21 T. Using a filtered 'globar' (broadband) source of THz radiation, no shift in the usual magneto-phonon resonance (MPR) was observed. At a fixed magnetic field corresponding to an MPR, the resistivity modulation due to the THz radiation was so small that no zero-path difference maximum could be detected in the interferogram of the Fourier spectrometer. Measurements using a much stronger source of radiation, an optically-pumped molecular laser, yielded sharp cyclotron resonance at low temperature (4 K), but nat low temperature (4 K), but no optical effects were detected at the high temperatures (150 K) required for MPPR, although the usual MPR was again observed. Use of a still stronger source, a free-electron laser, permitted observation of cyclotron resonance features at 150 K, but again no shift in the usual MPR which might be attributed to MPPR. We conclude from these experiments that the direct optical process of cyclotron resonance is at least 100 times stronger than the proposed indirect process which would lead to MPPR
The graphene phonon dispersion with C{sup 12} and C{sup 13} isotopes
Energy Technology Data Exchange (ETDEWEB)
Whiteway, Eric; Bernard, Simon; Yu, Victor; Hilke, Michael [Department of Physics, McGill University, Montréal H3A 2T8 (Canada); Austing, D. Guy [National Research Council of Canada, Ottawa, Ontario K1A 0R6 (Canada)
2013-12-04
Using very uniform large scale chemical vapor deposition grown graphene transferred onto silicon, we were able to identify 15 distinct Raman lines associated with graphene monolayers. This was possible thanks to a combination of different carbon isotopes and different Raman laser energies and extensive averaging without increasing the laser power. This allowed us to obtain a detailed experimental phonon dispersion relation for many points in the Brillouin zone. We further identified a D+D' peak corresponding to a double phonon process involving both an inter- and intra-valley phonon. In order to both eliminate substrate effects and to probe large areas, we undertook to study Raman scattering for large scale chemical vapor deposition (CVD) grown graphene using two different isotopes (C12 and C13) so that we can effectively exclude and subtract the substrate contributions, since a heavier mass downshifts only the vibrational properties, while keeping all other properties the same.
Nanoscale control of phonon excitations in graphene.
Kim, Hyo Won; Ko, Wonhee; Ku, JiYeon; Jeon, Insu; Kim, Donggyu; Kwon, Hyeokshin; Oh, Youngtek; Ryu, Seunghwa; Kuk, Young; Hwang, Sung Woo; Suh, Hwansoo
2015-01-01
Phonons, which are collective excitations in a lattice of atoms or molecules, play a major role in determining various physical properties of condensed matter, such as thermal and electrical conductivities. In particular, phonons in graphene interact strongly with electrons; however, unlike in usual metals, these interactions between phonons and massless Dirac fermions appear to mirror the rather complicated physics of those between light and relativistic electrons. Therefore, a fundamental understanding of the underlying physics through systematic studies of phonon interactions and excitations in graphene is crucial for realising graphene-based devices. In this study, we demonstrate that the local phonon properties of graphene can be controlled at the nanoscale by tuning the interaction strength between graphene and an underlying Pt substrate. Using scanning probe methods, we determine that the reduced interaction due to embedded Ar atoms facilitates electron-phonon excitations, further influencing phonon-assisted inelastic electron tunnelling. PMID:26109454
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
Signature of spin-phonon coupling in Sr2CoO4 thin film: A Raman spectroscopic study
Pandey, Pankaj K.; Choudhary, R. J.; Mishra, Dileep K.; Sathe, V. G.; Phase, D. M.
2013-04-01
We have investigated the phonon spectra of pulsed laser deposited Sr2CoO4 thin film and its evolution with temperature using Raman spectroscopy. The magnetic measurement reveals magnetic transition at temperature TC = 255 K. No structural phase transition is observed in the investigated temperature range (100-300 K). Close correlation between the frequency shift and the magnetization across TC establishes that the anomaly in the vicinity of TC is owing to spin-phonon coupling in the material. Using two different approaches, we have calculated spin-phonon coupling strength to be in the range of 2-3.5 cm-1.
International Nuclear Information System (INIS)
Phonon-induced fluorescence changes have been obtained in the shape of the spectra of selectively laser-excited dye molecules in noncrystalline organic solids, e.g. perylene molecules in Langmuir films of Cd arachidate. The changes in the zero-phonon lines and in the sidebands are observed after heat pulse irradiation (phonon memory), and by realtime phonon detection. The results are explained by electron-phonon interaction and by the model of matrix-shift variations caused by phonon-induced transitions in two-level systems in amorphous solids. (orig.)
Dudetskiy, V. Yu; Lariontsev, E. G.; Chekina, S. N.
2014-09-01
The effect of pump noise on the synchronisation of selfmodulation oscillations in a solid-state ring laser with periodic pump modulation is studied numerically and experimentally. It is found that, in contrast to desynchronisation that usually occurs under action of noise in the case of 1/1 synchronisation of self-oscillations by a periodic signal, the effect of noise on 1/2 synchronisation may be positive, namely, at a sufficiently low intensity, pump noise is favourable for synchronisation of self-oscillations, for narrowing of their spectrum, and for increasing the signal-to-noise ratio.
Mechanisms of nonequilibrium electron-phonon coupling and thermal conductance at interfaces
Giri, Ashutosh; Gaskins, John T.; Donovan, Brian F.; Szwejkowski, Chester; Warzoha, Ronald J.; Rodriguez, Mark A.; Ihlefeld, Jon; Hopkins, Patrick E.
2015-03-01
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 (Te ? Tp) does electron-phonon scattering at an interface contribute to thermal boundary conductance.
Ultrafast coupling of coherent phonons with a nonequilibrium electron-hole plasma in GaAs
Basak, Amlan Kumar; Petek, Hrvoje; Ishioka, Kunie; Thatcher, Evan M.; Stanton, Christopher J.
2015-03-01
We present a joint experimental theoretical study of the coupling of coherent phonons in bulk GaAs with a nonequilibrium electron-hole plasma following photoexcitation at the E1 gap by ultrafast laser pulses. In contrast to prior coherent phonon experiments where photoexcitation across the E0 gap generated electrons in the ? valley, for the E1 gap excitation, the majority of the electrons are generated in the satellite L valleys. This leads to a drastically different situation from the previous studies because the damping of electrons is now faster due to the higher scattering rates in the L valley, and, in addition, the diffusion of carriers has a significant effect on the plasma response due to the shorter optical absorption depth of the pump-probe light. Reflectivity measurements show coherent phonon-plasmon oscillations, whose frequencies lie between the transverse and longitudinal optical phonon frequencies due to the heavy damping and change with time due to the diffusion of the plasma. We analyze the experimental data with a theoretical model that describes the time and density-dependent coupling of the coherent phonon and the electron-hole plasma as the photoexcited carriers diffuse into the sample on a subpicosecond time scale. The calculated phonon-plasmon dynamics qualitatively reproduce the experimentally observed time-dependent frequency.
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
Sensitivity of the system of cytochrome P-450 of poultry liver to the action of red laser light
International Nuclear Information System (INIS)
It is detected that irradiation of poultry embryos by red laser light (? = 633 nm) at a doze of 1 - 6 mJ can influence a level of the cytochrome P-450 oxidized form in poultry liver. It is supposed that this level is changed due to variations in the content of lipid peroxide compounds in tissue under low-level red laser radiation and is one of the factors of regulation of the intensity of peroxide processes in tissues
Phonon dispersions of cluster crystals
Neuhaus, Tim; Likos, Christos N.
2010-01-01
We analyze the ground states and the elementary collective excitations (phonons) of a class of systems, which form cluster crystals in the absence of attractions. Whereas the regime of moderate-to-high-temperatures in the phase diagram has been analyzed in detail by means of density functional considerations (Likos C N, Mladek B M, Gottwald D and Kahl G 2007 {\\it J.~Chem.~Phys.}\\ {\\bf 126} 224502), the present approach focuses on the complementary regime of low temperatures....
Phonons from neutron powder diffraction
Dimitrov, D. A.; Louca, D.; Ro?der, H.
1998-01-01
The spherically averaged structure function $\\soq$ obtained from pulsed neutron powder diffraction contains both elastic and inelastic scattering via an integral over energy. The Fourier transformation of $\\soq$ to real space, as is done in the pair density function (PDF) analysis, regularizes the data, i.e. it accentuates the diffuse scattering. We present a technique which enables the extraction of off-center phonon information from powder diffraction experiments by compar...
Phonon dispersions of cluster crystals.
Neuhaus, Tim; Likos, Christos N
2011-06-15
We analyze the ground states and the elementary collective excitations (phonons) of a class of systems, which form cluster crystals in the absence of attractions. Whereas the regime of moderate-to-high temperatures in the phase diagram has been analyzed in detail by means of density functional considerations (Likos et al 2007 J. Chem. Phys. 126 224502), the present approach focuses on the complementary regime of low temperatures. We establish the existence of an infinite cascade of isostructural transitions between crystals with different lattice site occupancies at T = 0 and we quantitatively demonstrate that the thermodynamic instabilities are bracketed by mechanical instabilities arising from long-wavelength acoustical phonons. We further show that all optical modes are degenerate and flat, giving rise to almost perfect realizations of Einstein crystals. We calculate analytically the complete phonon spectrum for the whole class of models as well as the Helmholtz free energy of the systems. On the basis of the latter, we demonstrate that the aforementioned isostructural phase transitions must terminate at an infinity of critical points at low temperatures, brought about by the anharmonic contributions in the Hamiltonian and the hopping events in the crystals. PMID:21613703
Observation of coherent phonon generation in C60 films
Dobryakov, A. L.; Farztdinov, V. M.; Kovalenko, S. S.; Letokhov, Vladilen S.; Lozovik, Yurii E.; Matveets, Juru A.
1996-05-01
By studying the temporal behavior of the optical density of C60 thin film with the help of femtosecond laser spectroscopy the coherent phonon oscillations in the frequency region 10 - 400 cm-1 (including with odd symmetry) in the wide spectral region of probing h(omega) pr equals 1.78 divided by 2.34 eV was detected. Spectral dependence of photoinduced response permits to observe selectively the relaxation of electrons in different bands. The possibility of reversible polymerization in excited state is discussed.
Interconversion of photon-phonon in a silica optomechanical microresonator
Dong, ChunHua; Shen, Zhen; Zou, ChangLing; Guo, GuangCan
2015-05-01
In an optomechanical resonator, the optical and mechanical excitations can be coherently converted, which induces a transparency window for a weak probe laser beam. Here, we report an experimental study of transient optomechanically induced transparency (OMIT) using the silica microsphere with the breathing modes. The transient OMIT behavior obtained are in good agreement with theoretical calculations. In addition, the coherent interconversion between optical and mechanical excitations that can be used for light storage and readout has also been studied here. Our experimental results indicate that the light storage is closely related to the process of OMIT, and the photon-phonon conversion can be further applied to optical wavelength or optical mode conversion.
Thermal conductance boost in phononic crystal nanostructures
Anufriev, Roman; Nomura, Masahiro
2015-06-01
A theoretical study of coherent phonon scattering in thin-film phononic-crystal nanostructures (also called thermocrystals) is presented. It is commonly assumed that phononic crystals may only reduce thermal conductivity of materials. In this theoretical paper, contrary to this assumption, we demonstrate that phononic nanopatterning can enhance the thermal conductance of thin films under certain conditions. That is to say, it is shown that a thin membrane with many holes can have a higher thermal conductance than an unpatterned membrane. This effect originates from the increase in the density of states due to the coherent modifications of phonon dispersion. This counterintuitive phenomenon, called the thermal conductance boost effect, can be used for applications involving phonon management.
Phonon surface mapping of graphite: Disentangling quasi-degenerate phonon dispersions
Grüneis, Alexander; Lazzeri, Michele; Wirtz, Ludger; Attaccalite, Claudio; Rubio Secades, Ángel; Mauri, Francesco; Pichler, Thomas
2009-01-01
The two-dimensional mapping of the phonon dispersions around the K point of graphite by inelastic x-ray scattering is provided. The present work resolves the longstanding issue related to the correct assignment of transverse and longitudinal phonon branches at K.We observe an almost degeneracy of the three TO-, LA-, and LO-derived phonon branches and a strong phonon trigonal warping. Correlation effects renormalize the Kohn anomaly of the TO mode, which exhibits a trigonal warping effect o...
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 surface mapping of graphite: disentangling quasi--degenerate phonon dispersions
Grueneis, A.; Serrano, J.; Bosak, A.; Lazzeri, M.; Molodtsov, S. L.; Wirtz, Ludger; Attaccalite, C.; Krisch, M.; Rubio, A.; Mauri, F; Pichler, T.
2009-01-01
The two-dimensional mapping of the phonon dispersions around the $K$ point of graphite by inelastic x-ray scattering is provided. The present work resolves the longstanding issue related to the correct assignment of transverse and longitudinal phonon branches at $K$. We observe an almost degeneracy of the three TO, LA and LO derived phonon branches and a strong phonon trigonal warping. Correlation effects renormalize the Kohn anomaly of the TO mode, which exhibits a trigonal...
Phonon Coherence and New Set of Sidebands in Phonon-Assisted Photoluminescence
Xu, SJ; Xiong, SJ
2005-01-01
We investigate excitonic polaron states comprising a local exciton and phonons in the longitudinal optical (LO) mode by solving the Schrödinger equation. We derive an exact expression for the ground state (GS), which includes multi-phonon components with coefficients satisfying the Huang-Rhys factors. The recombination of GS and excited polaron states gives one set of sidebands in photoluminescence (PL): the multi-phonon components in the GS produce the Stokes lines and the zero-phonon compo...
A variational approach to the optimized phonon technique for electron-phonon problems
Cataudella, V.; De Filippis, G.; Martone, F.; Perroni, C. A.
2004-01-01
An optimized phonon approach for the numerical diagonalization of interacting electron-phonon systems is proposed. The variational method is based on an expansion in coherent states that leads to a dramatic truncation in the phonon space. The reliability of the approach is demonstrated for the extended Holstein model showing that different types of lattice distortions are present at intermediate electron-phonon couplings as observed in strongly correlated systems. The connec...
Phonon-mediated Superconductivity in Silicene
Wan, Wenhui; Ge, Yanfeng; Yang, Fan; Yao, Yugui
2013-01-01
We predict that electron-doped silicene is a good two-dimensional electron-phonon superconductor under biaxial tensile strain by first-principles calculations within rigid band approximation. Superconductivity transition temperature of electron-doped silicene can be increased to be above 10 K by 5% tensile strain. Band structures, phonon dispersive relations, and Eliashberg functions are calculated for detailed analysis. The strong interaction between acoustic phonon modes n...
Nonlinear phononics using atomically thin membranes
Midtvedt, Daniel; Isacsson, Andreas; Croy, Alexander
2014-01-01
Phononic crystals and acoustic meta-materials are used to tailor phonon and sound propagation properties by facilitating artificial, periodic structures. Analogous to photonic crystals, phononic band gaps can be created, which influence wave propagation and, more generally, allow engineering of the acoustic properties of a system. Beyond that, nonlinear phenomena in periodic structures have been extensively studied in photonic crystals and atomic Bose-Einstein Condensates in...
Influence of the electron-phonon iinteraction on phonon heat conduction in a molecular nanowire
Directory of Open Access Journals (Sweden)
Galovi? Slobodanka P.
2006-01-01
Full Text Available A model for phonon heat conduction in a molecular nanowire is developed. The calculation takes into account modification of the acoustic phonon dispersion relation due to the electron-phonon interaction. The results obtained are compared with models based upon a simpler, Callaway formula.
Phonon Bose-Einstein condensation in a Hubbard-phonon interacting system with infrared divergence
Sekine, Yoshitsugu
2013-01-01
We show that a finite Hubbard-phonon interacting system exhibits phonon BEC at sufficiently low temperature. We also have the gauge symmetry breaking for phonons. The key tools are a unitary transformation introduced by Arai and Hirokawa \\protect{\\cite{AH1}} and the Araki-Woods representation. This system is essentially the same as a free system or the van Hove model.
Influence of the electron-phonon iinteraction on phonon heat conduction in a molecular nanowire
Galovi? Slobodanka P.; ?evizovi? D.; Zekovi? S.; Ivi? Z.
2006-01-01
A model for phonon heat conduction in a molecular nanowire is developed. The calculation takes into account modification of the acoustic phonon dispersion relation due to the electron-phonon interaction. The results obtained are compared with models based upon a simpler, Callaway formula.
International Nuclear Information System (INIS)
It is shown that the low lying excitations of glasses, the so called two level systems (TLS), being in a virtual state induce indirect phonon-phonon interactions of a coherent type. These indirect 3-phonon interactions are responsible for the plateau in temperature dependence of thermal conductivity followed by a linear increase in x at higher temperatures (x(T)?T). (orig.)
Phonon-assisted transient electroluminescence in Si
Energy Technology Data Exchange (ETDEWEB)
Cheng, Tzu-Huan, E-mail: f94943139@ntu.edu.tw [Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei, Taiwan (China); Chu-Su, Yu [Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan and Department of Laboratory Medicine, National Taiwan University Hospital, Taipei, Taiwan (China); Liu, Chien-Sheng [Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan (China); Lin, Chii-Wann [Institute of Biomedical Engineering and Institute of Electrical Engineering, National Taiwan University, Taipei, Taiwan (China)
2014-06-30
The phonon-replica infrared emission is observed at room temperature from indirect band gap Si light-emitting diode under forward bias. With increasing injection current density, the broadened electroluminescence spectrum and band gap reduction are observed due to joule heating. The spectral-resolved temporal response of electroluminescence reveals the competitiveness between single (TO) and dual (TO?+?TA) phonon-assisted indirect band gap transitions. As compared to infrared emission with TO phonon-replica, the retarder of radiative recombination at long wavelength region (?1.2??m) indicates lower transition probability of dual phonon-replica before thermal equivalent.
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].
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
Phonon-assisted transient electroluminescence in Si
International Nuclear Information System (INIS)
The phonon-replica infrared emission is observed at room temperature from indirect band gap Si light-emitting diode under forward bias. With increasing injection current density, the broadened electroluminescence spectrum and band gap reduction are observed due to joule heating. The spectral-resolved temporal response of electroluminescence reveals the competitiveness between single (TO) and dual (TO?+?TA) phonon-assisted indirect band gap transitions. As compared to infrared emission with TO phonon-replica, the retarder of radiative recombination at long wavelength region (?1.2??m) indicates lower transition probability of dual phonon-replica before thermal equivalent.
Ballistic phonon transport in holey silicon.
Lee, Jaeho; Lim, Jongwoo; Yang, Peidong
2015-05-13
When the size of semiconductors is smaller than the phonon mean free path, phonons can carry heat with no internal scattering. Ballistic phonon transport has received attention for both theoretical and practical aspects because Fourier's law of heat conduction breaks down and the heat dissipation in nanoscale transistors becomes unpredictable in the ballistic regime. While recent experiments demonstrate room-temperature evidence of ballistic phonon transport in various nanomaterials, the thermal conductivity data for silicon in the length scale of 10-100 nm is still not available due to experimental challenges. Here we show ballistic phonon transport prevails in the cross-plane direction of holey silicon from 35 to 200 nm. The thermal conductivity scales linearly with the length (thickness) even though the lateral dimension (neck) is as narrow as 20 nm. We assess the impact of long-wavelength phonons and predict a transition from ballistic to diffusive regime using scaling models. Our results support strong persistence of long-wavelength phonons in nanostructures and are useful for controlling phonon transport for thermoelectrics and potential phononic applications. PMID:25861026
Phonon counting and intensity interferometry of a nanomechanical resonator.
Cohen, Justin D; Meenehan, Seán M; MacCabe, Gregory S; Gröblacher, Simon; Safavi-Naeini, Amir H; Marsili, Francesco; Shaw, Matthew D; Painter, Oskar
2015-04-23
In optics, the ability to measure individual quanta of light (photons) enables a great many applications, ranging from dynamic imaging within living organisms to secure quantum communication. Pioneering photon counting experiments, such as the intensity interferometry performed by Hanbury Brown and Twiss to measure the angular width of visible stars, have played a critical role in our understanding of the full quantum nature of light. As with matter at the atomic scale, the laws of quantum mechanics also govern the properties of macroscopic mechanical objects, providing fundamental quantum limits to the sensitivity of mechanical sensors and transducers. Current research in cavity optomechanics seeks to use light to explore the quantum properties of mechanical systems ranging in size from kilogram-mass mirrors to nanoscale membranes, as well as to develop technologies for precision sensing and quantum information processing. Here we use an optical probe and single-photon detection to study the acoustic emission and absorption processes in a silicon nanomechanical resonator, and perform a measurement similar to that used by Hanbury Brown and Twiss to measure correlations in the emitted phonons as the resonator undergoes a parametric instability formally equivalent to that of a laser. Owing to the cavity-enhanced coupling of light with mechanical motion, this effective phonon counting technique has a noise equivalent phonon sensitivity of 0.89 ± 0.05. With straightforward improvements to this method, a variety of quantum state engineering tasks using mesoscopic mechanical resonators would be enabled, including the generation and heralding of single-phonon Fock states and the quantum entanglement of remote mechanical elements. PMID:25903632
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.
International Nuclear Information System (INIS)
The analytical theory for the directivity patterns of ultrasounds emitted from laser-irradiated interface between two isotropic solids is developed. It is valid for arbitrary combinations of transparent and opaque materials. The directivity patterns are derived both in two-dimensional and in three-dimensional geometries, by accounting for the specific features of the sound generation by the photo-induced mechanical stresses distributed in the volume, essential in the laser ultrasonics. In particular, the theory accounts for the contribution to the emitted propagating acoustic fields from the converted by the interface evanescent photo-generated compression-dilatation waves. The precise analytical solutions for the profiles of longitudinal and shear acoustic pulses emitted in different directions are proposed. The developed theory can be applied for dimensional scaling, optimization, and interpretation of the high-pressure laser ultrasonics experiments in diamond anvil cell
The effect of Landau–Zener dynamics on phonon lasing
International Nuclear Information System (INIS)
Optomechanical systems couple light to the motion of nanomechanical objects. Intriguing new effects are observed in recent experiments that involve the dynamics of more than one optical mode. There, mechanical motion can stimulate strongly driven multi-mode photon dynamics that acts back on the mechanics via radiation forces. We show that even for two optical modes Landau–Zener–Stueckelberg oscillations of the light field drastically change the nonlinear attractor diagram of the resulting phonon lasing oscillations. Our findings illustrate the generic effects of Landau–Zener physics on back-action induced self-oscillations. (paper)
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.
Symmetry dependence of phonon lineshapes in superconductors with anisotropic gaps
Devereaux, T. P.
1994-01-01
The temperature dependence below $T_{c}$ of the lineshape of optical phonons of different symmetry as seen in Raman scattering is investigated for superconductors with anisotropic energy gaps. It is shown that the symmetry of the electron-phonon vertex produces non-trivial couplings to an anisotropic energy gap which leads to unique changes in the phonon lineshape for phonons of different symmetry. The phonon lineshape is calculated in detail for $B_{1g}$ and $A_{1g}$ phonon...
Angular Momentum of Phonons and Einstein-de Haas Effect
Zhang, Lifa; Niu, Qian
2013-01-01
We study angular momentum of phonons in a magnetic crystal. In the presence of a spin-phonon interaction, we obtain a nonzero angular momentum of phonons, which is an odd function of magnetization. At zero temperature, phonon has a zero-point angular momentum besides a zero-point energy. With increasing temperature, the total phonon angular momentum diminishes and approaches to zero in the classical limit. The nonzero phonon angular momentum can have a significant impact on ...
Phonon coupling effect upon transport in nanoscale polymers
International Nuclear Information System (INIS)
In an environmental coupled polymer, a variation of the conductivity is evaluated, which results from the external electron–phonon interaction coupling with the internal one. A quantized current appears under the external phonon coupling. The resonant tunnelling in the nanoscale polymer driven by the internal electron–phonon interaction is enhanced by the external phonon coupling. In addition, the external electron–phonon interaction softens the stiffness of the polymer. -- Highlights: ? A quantized current appearing under the external phonon coupling is evaluated. ? The resonant tunnelling is enhanced by the external phonon coupling. ? The external electron–phonon interaction softens the stiffness of the polymer.
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.
Splash, pop, sizzle: Information processing with phononic computing
Sklan, Sophia R.
2015-05-01
Phonons, the quanta of mechanical vibration, are important to the transport of heat and sound in solid materials. Recent advances in the fundamental control of phonons (phononics) have brought into prominence the potential role of phonons in information processing. In this review, the many directions of realizing phononic computing and information processing are examined. Given the relative similarity of vibrational transport at different length scales, the related fields of acoustic, phononic, and thermal information processing are all included, as are quantum and classical computer implementations. Connections are made between the fundamental questions in phonon transport and phononic control and the device level approach to diodes, transistors, memory, and logic.
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.
International Nuclear Information System (INIS)
This work was achieved in vivo and in vitro to evaluate the efficiency of Er:YAG laser in the cervical dentinal hypersensitivity treatment (HSDC). The Clinical study was achieved in patients with HSDC. The treatment was realized in five sessions: the first for selection, the second for exams (clinic and X-Ray) and trying to remove the etiologic factors that could cause the HSDC. The third and fourth sessions were subjected to the radiation with that protocol: 60 mJ energy ,2 Hz frequency, 6 mm out of focus, under air cooling, 20 seconds each application which the same was repeated four times with one minute breaks, which scanning movements and without using anaesthetics. The fifth was evaluation. The patients were evaluated and registered in a subject scale of pain 0 to 3, in the beginning and end of each session of irradiation, and one month after the last session. The results showed that for the irradiated group occurs significant differences in the beginning of each session and between. For the control group did not occur significant differences in the beginning and after each session, but did show a difference between the sessions. As the control group as the irradiated group, had reduction of sensibility between the session. For the morphologic study nine teeth were selected, 7 molars and 2 pre-molars from operative dentistry discipline. Half of the surface was irradiated with Er:YAG laser, the same protocol used in vivo, and the other half was used as a control without receiving any laser irradiation. Subsequently, specimens were prepared for SEM examinations. The results showed that laser treated surfaces showed a reduction of dentine tubular diameter with partial or total closure of the dentine tubules. For the control group, it was observed bigger amounts smear layer and open dentine tubular. The results obtained indicated that the Er:YAG laser can contribute to the HSDC treatment. (author)
International Nuclear Information System (INIS)
In this research, it was analyzed the acceleration of the healing process of cutaneous lesions in mice, using a diode laser emitting in 830 nm. The 64 selected animals in this study were randomically divided into four groups of 16 animals each (G1, G2, G3 and G4). Biometric and histological comparisons were accomplished in the following periods: 3, 7 and 14 days after the surgery and laser application. Three laser irradiation configurations were used: a punctual contact (G2) and two non-contact and uniform (G3 and G4). For group G2, the laser intensity was 428 mW/cm2 , and for groups G3 and G4 it was 53 mW/cm2. The total doses were D = 3 J/cm2 for groups G2 and G4, and D = 1,3 J/cm2 for G3. The first group, G1, was considered control and thus not submitted to any treatment after the surgery. All irradiated lesions presented acceleration of the healing process with regard to the control group. However, our results clearly indicate that the smaller laser intensity (uniform irradiation) leaded to the best results. On the other hand, the smaller used dose also leaded to the more significant and expressive results. The combination of the intensity value of 53 mW/cm2 and the dose of 1,3 J/cm2 leaded to optimal results, regarding the Biometric and histological analysis, presenting faster lesion contraction, quicker neoformation of epithelial and conjunctive tissue (with more collagen fibers ). (author)
Phonon spectrum and electron-phonon coupling in zigzag graphene nanoribbons
Zhang, Ting; Heid, Rolf; Bohnen, Klaus-Peter; Sheng, Ping; Chan, C. T.
2014-05-01
In this paper, we report a first-principles study of the lattice dynamics of small graphene nanoribbon with zigzag edges. Our investigation is based on spin polarized density functional calculations (DFT). Nesting properties in the electronic band structure are very different for nanoribbons with unpolarized, ferromagnetic, and antiferromagnetic configurations. As a result, the phonon spectrum and nesting related softening in phonon frequencies differ in these cases. The unpolarized and ferromagnetic structures show nesting related phonon softening and considerable electron phonon linewidth, while for the antiferromagnetic structure, a band gap at the Fermi energy eliminates these effects. Saturating the nanoribbon edge with hydrogen has negligible effect on the phonon spectra for the magnetic structures while for the unpolarized configuration all structures without hydrogen are unstable due to soft phonon modes. The electron-phonon coupling coefficients have also been calculated and implications for Peierls transition and superconductivity are discussed.
Strong squeezing via phonon mediated spontaneous generation of photon pairs
Qu, Kenan; Agarwal, G. S.
2014-11-01
We propose a scheme for generating squeezed light by using a double-cavity optomechanical system driven by a blue detuned laser in one cavity and by a red detuned laser in the other. This double-cavity system is shown to effectively mimic an interaction that is similar to the one for a downconverter, which is known to be a source of strong squeezing for light fields. There are however distinctions, as the phonons which lead to such an interaction can contribute to the quantum noise. We show that squeezing of the output fields, of the order of 10 dB, can be achieved even for an effective mechanical mode occupation number of about 4, which for the chosen parameters corresponds to 10 mK. Our results are generic and applicable to a wide class of electromechanical and optomechanical systems involving the interaction of two electromagnetic modes and one mechanical mode.
Resonant Tunneling with Electron-Phonon Interaction.
Wingreen, Ned Scott
An exactly solvable model for resonant tunneling with electron-phonon interaction is presented and the results are compared with experimentally observed phonon-assisted resonant tunneling. While an electron tunnels through a localized state, it can exchange energy with the phonon system and thereby move closer to or farther from the resonance condition. As a result, the total transmission probability as a function of incident energy will depend on the electron -phonon interaction during tunneling. The transmission probability through a single resonant site coupled to phonons is solved for in the limit of a uniform density of states in the leads. To carry out the solution we employ S-matrix scattering theory and a Green function analysis of a localized state coupled to phonons. The presence of phonons alters the transmission spectrum by generating inelastic sidebands and suppressing the elastic tunneling resonance, but does not change the overall transmissivity of the tunneling structure. Contact is made with experiment by calculating the current transmitted through the resonant site including interaction with an Einstein band of optic phonons. The structure in the current-voltage characteristic for a coupling strength appropriate to GaAs reproduces the experimentally observed structure in the current for a GaAs/AlGaAs double -barrier heterostructure.
Microfabricated phononic crystal devices and applications
International Nuclear Information System (INIS)
Phononic crystals are the acoustic wave analogue of photonic crystals. Here a periodic array of scattering inclusions located in a homogeneous host material forbids certain ranges of acoustic frequencies from existence within the crystal, thus creating what are known as acoustic bandgaps. The majority of previously reported phononic crystal devices have been constructed by hand, assembling scattering inclusions in a viscoelastic medium, predominantly air, water or epoxy, resulting in large structures limited to frequencies below 1 MHz. Recently, phononic crystals and devices have been scaled to VHF (30–300 MHz) frequencies and beyond by utilizing microfabrication and micromachining technologies. This paper reviews recent developments in the area of micro-phononic crystals including design techniques, material considerations, microfabrication processes, characterization methods and reported device structures. Micro-phononic crystal devices realized in low-loss solid materials are emphasized along with their potential application in radio frequency communications and acoustic imaging for medical ultrasound and nondestructive testing. The reported advances in batch micro-phononic crystal fabrication and simplified testing promise not only the deployment of phononic crystals in a number of commercial applications but also greater experimentation on a wide variety of phononic crystal structures. (topical review)
PHONONS IN GRAPHITE INTERCALATED WITH BROMINE
Batallan, F.; Rosenman, I.; Simon, C.; Furdin, G.; Lauter, H.
1981-01-01
We have investigated the phonon spectrum in stage 2 graphite intercalate with bromine by using inelastic neutron scattering. We have observed longitudinal and transverse phonons along the c direction as well as in the layer plane. Results are presented for energies up to 15 THz at 300 K. A linear chain model explains most of our results.
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
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.
Temperature-dependent nonlinear phonon shifts in a supported MoS2 monolayer.
Taube, Andrzej; Judek, Jaros?aw; Jastrz?bski, Cezariusz; Duzynska, Anna; ?witkowski, Krzysztof; Zdrojek, Mariusz
2014-06-25
We report Raman spectra measurements on a MoS(2) monolayer supported on SiO(2) as a function of temperature. Unlike in previous studies, the positions of the two main Raman modes, E(2g)(1) and A(1g) exhibited nonlinear temperature dependence. Temperature dependence of phonon shifts and widths is explained by optical phonon decay process into two acoustic phonons. On the basis of Raman measurements, local temperature change under laser heating power at different global temperatures is derived. Obtained results contribute to our understanding of the thermal properties of two-dimensional atomic crystals and can help to solve the problem of heat dissipation, which is crucial for use in the next generation of nanoelectronic devices. PMID:24897497
Li, Chen; Delaire, Olivier; Chen, Xin; Singh, David; May, Andrew; Ma, Jie; McGuire, Michael; Ehlers, Georg; Christianson, Andrew; Huq, Ashfia
2013-03-01
Thermoelectric materials can convert waste heat into electrical energy, and have attracted much attention in recent years for power generation. IV-VI compounds in rock salt structure include some of the most efficient thermoelectric materials and giant phonon anharmonicity is believed to contribute to the low thermal conductivity. In this work, phonon dispersions and linewidths in single-crystalline SnTe were measured at a series of temperatures using time-of-flight and triple-axis neutron spectrometers to study the temperature dependence of the phonon dynamics and phonon anharmonicity. Phonon calculations and molecular dynamics simulations with first-principles methods were used to identify the anomalies in phonon modes and the results were compared to the measurements. Because the phonons involved have an important contribution to the lattice thermal conductivity in this system, the anharmonic coupling is likely to provide a key insight in understanding the surprisingly low thermal conductivity of the rocksalt tellurides in general. Thermoelectric materials can convert waste heat into electrical energy, and have attracted much attention in recent years for power generation. IV-VI compounds in rock salt structure include some of the most efficient thermoelectric materials and giant phonon anharmonicity is believed to contribute to the low thermal conductivity. In this work, phonon dispersions and linewidths in single-crystalline SnTe were measured at a series of temperatures using time-of-flight and triple-axis neutron spectrometers to study the temperature dependence of the phonon dynamics and phonon anharmonicity. Phonon calculations and molecular dynamics simulations with first-principles methods were used to identify the anomalies in phonon modes and the results were compared to the measurements. Because the phonons involved have an important contribution to the lattice thermal conductivity in this system, the anharmonic coupling is likely to provide a key insight in understanding the surprisingly low thermal conductivity of the rocksalt tellurides in general. Funding from the US DOE, Office of Basic Energy Sciences, Materials Science and Engineering Division, and from the S3TEC Energy Frontier Research Center, DOE DE-SC0001299.
Phononic crystals and elastodynamics: Some relevant points
Directory of Open Access Journals (Sweden)
N. Aravantinos-Zafiris
2014-12-01
Full Text Available In the present paper we review briefly some of the first works on wave propagation in phononic crystals emphasizing the conditions for the creation of acoustic band-gaps and the role of resonances to the band-gap creation. We show that useful conclusions in the analysis of phononic band gap structures can be drawn by considering the mathematical similarities of the basic classical wave equation (Helmholtz equation with Schrödinger equation and by employing basic solid state physics concepts and conclusions regarding electronic waves. In the second part of the paper we demonstrate the potential of phononic systems to be used as elastic metamaterials. This is done by demonstrating negative refraction in phononic crystals and subwavelength waveguiding in a linear chain of elastic inclusions, and by proposing a novel structure with close to pentamode behavior. Finally the potential of phononic structures to be used in liquid sensor applications is discussed and demonstrated.
Phononic crystals and elastodynamics: Some relevant points
Aravantinos-Zafiris, N.; Sigalas, M. M.; Kafesaki, M.; Economou, E. N.
2014-12-01
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.
Laser performance at 1064 nm in Nd3+ doped oxi-tellurite glasses
Bell, Maria Jose; Anjos, Virgílio; Moreira, Lyane; Falci, Rodrigo; Kassab, Luciana; Silva, D.; Doualan, Jean Louis; Camy, Patrice; Moncorge, Richard
2015-03-01
The search for Nd3+ doped new solid-state laser hosts having specific thermo-mechanical and optical properties is very active. Among tellurites, the TeO2-ZnO glass combines good mechanical stability, chemical durability, high linear and nonlinear refractive indices, low phonon energies (~750 cm-1) and a wide transmission window (0.4-6 ?m). Their high nonlinear optical properties can be used for the development of Kerr-lens mode-locked subpicosecond lasers. The present work concentrates on the luminescence properties and the laser performance of a TeO2-ZnO tellurite glasses doped with Nd3+. True continuous-wave laser action is achieved by pumping the sample with a CW Ti:Sapphire laser inside a standard two-mirror laser cavity. A low laser threshold of 8 mW and a laser slope efficiency of 21% could be obtained for an output coupler transmission of 2.7%, which is an encouraging improvement compared to what was reported in the past with other Nd-doped tellurite bulk glasses. Authors acknowledge the support of agencies CAPES, FAPEMIG National Institute of Photonics (INCT Project/CNPQ) and COFECUB.
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.
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
Lantukh, Yu. D.; Ketsle, G. A.; Pashkevich, S. N.; Letuta, S. N.; Razdobreev, D. A.
2006-07-01
This paper discusses the mechanism of amplitude holographic recording in polyvinyl alcohol films with additives of thiazine dyes (thionine, methylene blue) under the action of a helium-neon laser. It is proposed to describe the photochemical transformations of the dye by a sequential reaction scheme with one reversible stage. It is shown that the presence of associates (dimers) of the dyes in the films has a substantial effect on the bleaching kinetics. Plasticization of the polymer makes it possible to control the ratio of the rate constants of the reaction scheme and also results in complete breakdown of the holographic gratings after the recording is completed. The kinetics of spontaneous erasure of the holograms in the test medium are compared with those of the thiazine-dye-deoxyribonucleic-acid (DNA) film system.
Critical-point phonon frequencies of diamond
Klein, Claude A.; Hartnett, Thomas M.; Robinson, Clifford J.
1992-06-01
The phonon-dispersion curves derived from neutron-scattering experiments performed on diamond [J. Warren et al., Phys. Rev. 158, 805 (1967)] are not accurate enough to yield the exact frequencies of critical-point (CP) phonons and, thus, to provide a satisfactory interpretation of second-order optical spectra. A self-consistent analysis of such spectra [S. Solin and A. Ramdas, Phys. Rev. B 1, 1687 (1970)] was not fully successful because of ambiguities that arise in assigning second-order infrared absorptions and features in the Raman spectra to specific two-phonon summations. A more effective method for obtaining accurate CP phonon frequencies involves investigating defect-activated one-phonon absorptions; in this paper, we take advantage of the availability of chemically vapor-deposited (CVD) diamond for the purpose of locating and assigning infrared (ir) absorption features in the one-phonon region to CP phonons at the Brillouin-zone boundary. Fourier-transform ir absorbance spectra of CVD diamond exhibit a complex structure at wave numbers below the 1332.5-cm-1 lattice-mode cutoff, which is induced by impurity-associated defect centers and yields the exact positions of 16 zone-edge CP phonons. In conjunction with the triply degenerate zone-center mode, this set of phonons then provides the basis for predicting the positions of second-order optical features through simple summations. When the selection rules are taken into account, the procedure yields excellent results, not only in terms of CVD-diamond ir spectra, but also in regard to earlier measurements of the intrinsic two-phonon absorption coefficient of type-IIa natural diamond [J. Hardy and S. Smith, Philos. Mag. 6, 1163 (1961)] and the second-order polarization-dependent Raman spectra recorded by Solin and Ramdas.
Phonon mediated quantum spin simulator made from a two-dimensional Wigner crystal in Penning traps
Wang, Joseph; Keith, Adam; Freericks, J. K.
2013-03-01
Motivated by recent advances in quantum simulations in a Penning trap, we give a theoretical description for the use of two-dimensional cold ions in a rotating trap as a quantum emulator. The collective axial phonon modes and planar modes are studied in detail, including all effects of the rotating frame. We show the character of the phonon modes and spectrum, which is crucial for engineering exotic spin interactions. In the presence of laser-ion coupling with these coherent phonon excitations, we show theoretically how the spin-spin Hamiltonian can be generated. Specifically, we notice certain parameter regimes in which the level of frustration between spins can be engineered by the coupling to the planar modes. This may be relevant to the quantum simulation of spin-glass physics or other disordered problems. Motivated by recent advances in quantum simulations in a Penning trap, we give a theoretical description for the use of two-dimensional cold ions in a rotating trap as a quantum emulator. The collective axial phonon modes and planar modes are studied in detail, including all effects of the rotating frame. We show the character of the phonon modes and spectrum, which is crucial for engineering exotic spin interactions. In the presence of laser-ion coupling with these coherent phonon excitations, we show theoretically how the spin-spin Hamiltonian can be generated. Specifically, we notice certain parameter regimes in which the level of frustration between spins can be engineered by the coupling to the planar modes. This may be relevant to the quantum simulation of spin-glass physics or other disordered problems. This work was supported under ARO grant number W911NF0710576 with funds from the DARPA OLE Program. J. K. F. also acknowledges the McDevitt bequest at Georgetown University. A. C. K. also acknowledges support of the National Science Foundation under grant
Longitudinal polar optical phonons in InN/GaN single and double het- erostructures
International Nuclear Information System (INIS)
Longitudinal optical phonon energy in InN epi-layers has been determined independently from the Raman spectroscopy and temperature dependent Hall mobility measurements. Raman spectroscopy technique can be used to obtain directly the LO energy where LO phonon scattering dominates transport at high temperature. Moreover, the Hall mobility is determined by the scattering of electrons with LO phonons so the data for the temperature dependence of Hall mobility have been used to calculate the effective energy of longitudinal optical phonons.The samples investigated were (i) single heterojunction InN with thicknesses of 1.08, 2.07 and 4.7 ?m grown onto a 40 nm GaN buffer and (ii) GaN/InN/AlN double heterojunction samples with InN thicknesses of 0.4, 0.6 and 0.8 ?m. Hall Effect measurements were carried out as a function of temperature in the range between T = 1.7 and 275 K at fixed magnetic and electric fields. The Raman spectra were obtained at room temperature. In the experiments, the 532 nm line of a nitrogen laser was used as the excitation source and the light was incident onto the samples along of the growth direction (c-axis). The results, obtained from the two independent techniques suggest the following: (1) LO phonon energies obtained from momentum relaxation experiments are generally slightly higher than those obtained from the Raman spectra. (2) LO phonon energy for the single heterojunctions does not depend on the InN thickness. (3) In double heterostructures,ickness. (3) In double heterostructures, with smaller InN thicknesses and hence with increased strain, LO phonon energy increases by 3% (experimental accuracy is < 1%) when the InN layer thickness increases from 400 to 800 nm (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Rotational Modes in Phononic Crystals
Wu, Ying; Peng, Pai; Mei, Jun
2014-03-01
We propose a lumped model for the rotational modes in two-dimensional phononic crystals comprised of square arrays of solid cylindrical scatterers in solid hosts. The model not only can reproduce the dispersion relations in a certain range with one fitted parameter, but also gives simple analytical expressions for the frequencies of the eigenmodes at the high symmetry points in the Brillouin zone. These expressions provide physical understandings of the rotational modes as well as certain translational and hybrid mode, and predict the presence of accidental degeneracy of the rotational and dipolar modes, which leads to a Dirac-like cone in the Brillouin zone center. We propose a lumped model for the rotational modes in two-dimensional phononic crystals comprised of square arrays of solid cylindrical scatterers in solid hosts. The model not only can reproduce the dispersion relations in a certain range with one fitted parameter, but also gives simple analytical expressions for the frequencies of the eigenmodes at the high symmetry points in the Brillouin zone. These expressions provide physical understandings of the rotational modes as well as certain translational and hybrid mode, and predict the presence of accidental degeneracy of the rotational and dipolar modes, which leads to a Dirac-like cone in the Brillouin zone center. Supported by KAUST Baseline Research Fund, National Natural Science Foundation of China (Grants No. 10804086 and No. 11274120), and the Fundamental Research Funds for the Central Universities (Grant No. 2012ZZ0077).
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.)
International Nuclear Information System (INIS)
We report on the theoretical and the experimental investigations of the coherent phonon dynamics in sapphire crystal using the femtosecond time-resolved coherent anti-Stokes Raman scattering (fs-CARS) technique. The temporal chirped white-light continuum (WLC) is used for the Stokes pulse, therefore we can perform the selective excitation of the phonon modes without using a complicated laser system. The expected quantum beat phenomenon is clearly observed. The theoretical formulas consist very well with the experimental results. The dephasing times of the excited phonon modes, the wavenumber difference, and the phase shift between the simultaneously excited modes are obtained and discussed. This work opens up a way to study directly high-frequency coherent phonon dynamics in bulk crystals on a femtosecond time scale and is especially helpful for understanding the nature of coherent phonons. (condensed matter: structural, mechanical, and thermal properties)
Fainstein, A; Lanzillotti-Kimura, N D; Jusserand, B; Perrin, B
2013-01-18
We show that distributed Bragg reflector GaAs/AlAs vertical cavities designed to confine photons are automatically optimal to confine phonons of the same wavelength, strongly enhancing their interaction. We study the impulsive generation of intense coherent and monochromatic acoustic phonons by following the time evolution of the elastic strain in picosecond-laser experiments. Efficient optical detection is assured by the strong phonon backaction on the high-Q optical cavity mode. Large optomechanical factors are reported (~THz/nm range). Pillar cavities based in these structures are predicted to display picogram effective masses, almost perfect sound extraction, and threshold powers for the stimulated emission of phonons in the range ?W-mW, opening the way for the demonstration of phonon "lasing" by parametric instability in these devices. PMID:23373951
Coherent phonon and surface-enhanced Raman scattering dynamics in solids
International Nuclear Information System (INIS)
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
Carrier relaxation with LO phonon decay in semiconductor quantum dots
Levetas, S. A.; Godfrey, M. J.; Dawson, P
2000-01-01
Analysis of an exactly soluble model of phonons coupled to a carrier in a quantum dot provides a clear illustration of a phonon bottleneck to relaxation. The introduction of three-phonon interactions leads to a broad window for relaxation by the processes of LO phonon scattering and decay.
The Phonon Drag Effect in Single-Walled Carbon Nanotubes
V. W. Scarola; Mahan, G. D.
2002-01-01
A variational solution of the coupled electron-phonon Boltzmann equations is used to calculate the phonon drag contribution to the thermopower in a 1-D system. A simple formula is derived for the temperature dependence of the phonon drag in metallic, single-walled carbon nanotubes. Scattering between different electronic bands yields nonzero values for the phonon drag as the Fermi level varies.
Electron-Phonon Interaction and Raman Linewidth in Superconducting Fullerides
Aksenov, V. L.; V. V. Kabanov
1997-01-01
We propose a microscopic theory of interaction of long wave molecular phonons with electrons in fullerides in the presence of disorder. Phonon relaxation rate and frequency renormalization are discussed. Finite electronic bandwidth reduces phonon relaxation rate at $q=0$. Electron-phonon coupling constants with molecular modes in fullerides are estimated. The results are in good agreement with photoemission experiments.
Electron-Phonon Interaction and Raman Linewidth in Superconducting Fullerides
Aksenov, V L
1998-01-01
We propose a microscopic theory of interaction of long wave molecular phonons with electrons in fullerides in the presence of disorder. Phonon relaxation rate and frequency renormalization are discussed. Finite electronic bandwidth reduces phonon relaxation rate at $q=0$. Electron-phonon coupling constants with molecular modes in fullerides are estimated. The results are in good agreement with photoemission experiments.
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
Energy resolved phonon scattering in thin film amorphous solids
International Nuclear Information System (INIS)
Energy resolved phonon scattering measurements were performed using a novel heat pulse technique. Two thin film phonon generators were deposited on one face of a sapphire crystal substrate and two phonon detectors were deposited on the opposite face, under one of which a thin film amorphous material was deposited. The phonon detectors were superconducting tunnel heterojunctions. A comparison of the number of phonons detected at each junction gave information on the fraction of phonons transmitted through the amorphous film as a function of energy from which the phonon mean free path as a function of energy could be deduced. Materials investigated were silicon monoxide and germanium. (author)
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
Phonons dispersions in auxetic lattices
International Nuclear Information System (INIS)
The modes of vibrations in auxetic structures are studied, with models where the two-dimensional lattice is represented by a planar mesh with rod-like particles connected by strings. An auxetic membrane can be obtained modifying a honeycomb one, according to a model proposed by Evans et al. in 1991 and used to explain a negative elastic Poisson's ratio. This property means that auxetic materials have a lateral extension, instead to shrink, when they are stretched. The models here proposed with rod-like particles inserted in the structure have interesting behaviour of acoustic and rotational branches of phonon dispersions. Complete bandgaps of vibrations can be obtained for a proper choice of lattice coupling parameters and distribution of masses in the unit cell of the lattice
Effects of phonon-phonon coupling on properties of pygmy resonance in $^{124-132}$Sn
Voronov V.V.; Severyukhin A. P.; Arsenyev N. N.; Van Giai Nguyen
2012-01-01
Starting from an effective Skyrme interaction we study effects of phonon-phonon coupling on the low-energy electric dipole response in $^{124-132}$Sn. The QRPA calculations are performed within a finite rank separable approximation. The inclusion of two-phonon configurations gives a considerable contribution to low-lying strength. Comparison with available experimental data shows a reasonable agreement for the low-energy $E1$ strength distribution.
Phonon confinement and plasmon-phonon interaction in nanowire-based quantum wells
Ketterer, Bernt; Arbiol, Jordi; Fontcuberta I Morral, Anna
2011-01-01
Resonant Raman spectroscopy is realized on closely spaced nanowire based quantum wells. Phonon quantization consistent with 2.4 nm thick quantum wells is observed, in agreement with cross-section transmission electron microscopy measurements and photoluminescence experiments. The creation of a high density plasma within the quantized structures is demonstrated by the observation of coupled plasmon-phonon modes. The density of the plasma and thereby the plasmon-phonon interac...
Dynamical stabilization of the bcc phase in lanthanum and thorium by phonon-phonon interaction
Souvatzis, P.; Bjorkman, T.; Eriksson, O.; P. Andersson; Rudin, M. I. Katsnelson S- P
2009-01-01
The recently developed self consistent {\\it ab initio} lattice dynamical method (SCAILD) has been applied to the high temperature bcc phase of La and Th which are dynamically unstable at low temperatures. The bcc phase of these metals is found to be stabilized by phonon-phonon interactions. The calculated high temperature phonon frequencies for La are found to be in good agreement with the corresponding experimental data.
Effects of phonon-phonon coupling on properties of pygmy resonance in 124-132Sn
Directory of Open Access Journals (Sweden)
Voronov V. V.
2012-12-01
Full Text Available Starting from an effective Skyrme interaction we study effects of phonon-phonon coupling on the low-energy electric dipole response in 124-132Sn. The QRPA calculations are performed within a finite rank separable approximation. The inclusion of two-phonon configurations gives a considerable contribution to low-lying strength. Comparison with available experimental data shows a reasonable agreement for the low-energy E1 strength distribution.
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...
Phonon Bandgap Engineering of Strained Monolayer MoS2
Jiang, Jin-wu
2014-01-01
The phonon band structure of monolayer MoS2 is characteristic for a large energy gap between acoustic and optical branches, which protects the vibration of acoustic modes from being scattered by optical phonon modes. Therefore, the phonon bandgap engineering is of practical significance for the manipulation of phonon-related mechanical or thermal properties in monolayer MoS2. We perform both phonon analysis and molecular dynamics simulations to investigate the tension effect...
BEDT-TTF organic superconductors: the entangled role of phonons
Girlando, Alberto; Masino, Matteo; Brillante, Aldo; Della Valle, Raffaele G.; Venuti, Elisabetta
2002-01-01
We calculate the lattice phonons and the electron-phonon coupling of the organic superconductor \\kappa-(BEDT-TTF)_2 I_3, reproducing all available experimental data connected to phonon dynamics. Low-frequency intra-molecular vibrations are strongly mixed to lattice phonons. Both acoustic and optical phonons are appreciably coupled to electrons through the modulation of the hopping integrals (e-LP coupling). By comparing the results relevant to superconducting \\kappa- and \\be...
Thermal phonon resonance observed with millisecond optical beating Brillouin spectroscopy
Minami, Yasuo; Sakai, Keiji
2008-11-01
We observed resonating thermal phonons in a cavity. The combination of our millisecond Brillouin scattering technique and this phonon resonance observation enables the determination of phonon velocity with an accuracy of 10-4 within an observation time of 30 ms. In the experiment, phonon propagation in a confined space filled with liquid toluene was observed. The observed phonon resonance spectra agree with theoretical predictions.
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.
Plasmon-Phonon Interaction and Phonon Induced Transparency in Graphene Plasmonic Nanostructures
Chan, Wei Min; Nene, Parinita; Strait, Jared; Manolatou, Christina; Sandip, Tiwari; McEuen, Paul; Rana, Farhan
2014-03-01
Electrons in graphene interact via Coulomb forces but also via an optical phonon-mediated interaction. As a result of the chiral nature of electrons, these two interactions are additive. This phonon-mediated interaction results in strong coupling between the plasmons and phonons. Plasmons in graphene also interact strongly with the substrate optical phonons. In this talk we will present experimental results on plasmon-phonon interactions. We patterned disc-shaped plasmon resonators in CVD grown graphene with radii varying from 16-80 nm and studied plasmon resonances using IR spectroscopy. Sharp features appear in the plasmon absorption spectra when the plasmon frequencies are close to the phonon frequencies. When the plasmon frequency matches the zone-center optical phonon frequency, a narrow transparency dip appears in the plasmon absorption spectra. This transparency, which resembles EIT in optics, can be explained in terms of the cancellation between the Coulomb and the phonon-mediated electron-electron interactions. Our theoretical model, based on the eigenvalue equation for confined plasmon modes, explains the data well and enables us to extract parameters related to the plasmon-phonon interaction in graphene.
Single electron-phonon interaction in a suspended quantum dot phonon cavity
Höhberger, E M; Brandes, T; Kirschbaum, J; Wegscheider, W; Bichler, M; Kotthaus, J P
2003-01-01
An electron-phonon cavity consisting of a quantum dot embedded in a free-standing GaAs/AlGaAs membrane is characterized in Coulomb blockade measurements at low temperatures. We find a complete suppression of single electron tunneling around zero bias leading to the formation of an energy gap in the transport spectrum. The observed effect is induced by the excitation of a localized phonon mode confined in the cavity. This phonon blockade of transport is lifted at magnetic fields where higher electronic states with nonzero angular momentum are brought into resonance with the phonon energy.
Toward stimulated interaction of surface phonon polaritons
International Nuclear Information System (INIS)
Thermal emission spectra mediated by surface phonon polariton are examined by using a theoretical model that accounts for generation processes. Specifically, the acoustic phonon fusion mechanism is introduced to remedy theoretical deficiencies of the near thermal equilibrium treatments. The model clarifies the thermal excitation mechanism of surface phonon polaritons and the energy transfer path under non-zero energy flow. When applied to GaAs and SiC semi-infinite surfaces, the nonequilibrium model predicts that the temperature dependence of the quasi-monochromatic peak can exhibit distinctly different characteristics of either sharp increase or slow saturation depending on the materials, which is in direct contrast with the estimate made by the near-equilibrium model. The proposed theoretical tool can accurately analyze the nonequilibrium steady states, potentially paving a pathway to demonstrate stimulated interaction/emission of thermally excited surface phonon polaritons
Phonon-mediated detection of particles
International Nuclear Information System (INIS)
Over the past five years particle physicists, nuclear physicists and astrophysicists have been increasingly interested in using phonons to detect particle interactions. In these detection attempts it is obviously critical to integrate the understanding that the phonon physicists have accumulated on the mechanisms governing the production, propagation and detection of those phonons. Vice versa, some of the issues raised by the particle detection problem may be of significant interest and the high sensitivity methods being developed may become important for phonon physics investigations. These were the motivations for a round table discussion between members of the two communities. This report attempts to summarize the themes of a very interesting discussion. 24 refs., 2 figs., 1 tab
Phononic crystals: Entering an acoustic phase
Barreiro, Julio T.
2015-03-01
Electrons moving in a one-dimensional crystal can acquire a geometrical phase. Sound waves in phononic crystals are now shown to display the same effect -- underlining the similarity between conventional solids and acoustic metamaterials.
Strong Coupling between Nanoscale Metamaterials and Phonons
Energy Technology Data Exchange (ETDEWEB)
Shelton, David J.; Brener, Igal; Ginn, James C.; Sinclair, Michael B.; Peters, David W.; Coffey, Kevin R.; Boreman, Glenn D.
2011-01-01
We use split ring resonators (SRRs) at optical frequencies to study strong coupling between planar metamaterials and phonon vibrations in nanometer-scale dielectric layers. A series of SRR metamaterials were fabricated on a semiconductor wafer with a thin intervening SiO{sub 2} dielectric layer. The dimensions of the SRRs were varied to tune the fundamental metamaterial resonance across the infrared (IR) active phonon band of SiO{sub 2} at 130 meV (31 THz). Strong anticrossing of these resonances was observed, indicative of strong coupling between metamaterial and phonon excitations. This coupling is very general and can occur with any electrically polarizable resonance including phonon vibrations in other thin film materials and semiconductor band-to-band transitions in the near to far IR. These effects may be exploited to reduce loss and to create unique spectral features that are not possible with metamaterials alone.
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
Design of phonon detectors for neutrinos
International Nuclear Information System (INIS)
Several alternative neutrino detection schemes are described briefly and compared. It is suggested that a ballistic-phonon experiment might be promising. In such an experiment the amplitude received at a bolometer would depend on the distance it is from the neutrino event, and also on the direction because of phonon focusing, so several bolometers suggested to locate the event position from the difference in arrival times. The design of such an experiment is discussed assuming the phonons are detected by conventional superconducting bolometers. Determination of the direction of neutrino flux would be obtained from a study of the distribution of direction of the tracks of recoiling electrons or nuclei. The problem of smearing out the effective source over a distance of approximately a mean free path is addressed, and the need for high-resolution phonon focusing studies is expressed
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.)
Acoustic and optical phonons in metallic diamond
Directory of Open Access Journals (Sweden)
M. Hoesch, T. Fukuda, T. Takenouchi, J.P. Sutter, S. Tsutsui, A.Q.R. Baron, M. Nagao, Y. Takano, H. Kawarada and J. Mizuki
2006-01-01
Full Text Available The dispersion of acoustic and optical phonons in highly boron-doped diamond has been measured by inelastic X-ray scattering at an energy resolution of 6.4 meV. The sample is doped in the metallic regime and shows superconductivity below 4.2 K (midpoint. The data are compared to pure and nitrogen-doped diamond that represent the non-metallic state. No difference is found for the acoustic phonons in the three samples, while the optical phonons show a shift of the dispersion (softening in qualitative agreement with earlier results from Raman spectroscopy. The presence of boron and nitrogen incorporated into the diamond lattice leads to structural disorder. Evidence for this is found both in the observation of otherwise symmetry-forbidded Bragg intensity at (0 0 2 and intensity from acoustic phonon modes in the vicinity of (0 0 2.
PHONON ECHOES IN BULK AND POWDERED MATERIALS
Kajimura, K.
1981-01-01
Experimental and theoretical studies of phonon echoes in bulk and powdered materials are reviewed. Phonon echoes have been observed in many materials such as bulk piezoelectric crystals, paramagnets, glasses, doped semiconductors, and piezoelectric, magnetic, and metallic powders, etc. The echoes arise from a time reversal of the phase, like spin echoes, of a primary pulsed acoustic excitation due to a second acoustic or rf pulse. The phase reversal occurs through the nonlinear interactions o...
Forward Electron-Phonon Scattering and HTS
Kulic, M L; Kulic, Miodrag L.; Dolgov, Oleg V.
1999-01-01
Tunneling and point contact spectroscopy show clear phonon features and together with optic measurements give strong support that the electron-phonon interaction (EPI) is large in HTS oxides. Strong correlations in HTS oxides renormalize the EPI (and interaction with impurities) so that the forward scattering peak (FSP) develops for small hole doping \\delta<<1. The FSP mechanism explains important properties of the normal and superconducting state.
Surface phonon propagation in topological insulators
Thalmeier, Peter
2011-01-01
The effect of helical Dirac states on surface phonons in a topological insulators is investigated. Their coupling is derived in the continuum limit by assuming displacement dependent Dirac cones. The resulting renormalisation of sound velocity and attenuation and its dependence on chemical potential and wave vector is calculated. At finite wave vectors a Kohn anomaly in the renormalized phonon frequency is caused by intraband-transitions. It appears at wave vectors q
Phonon Overlaps: Polyacetylene, Polarons, and Molecular Size
Chang, Connie Te-ching; Sethna, James P
2006-01-01
We provide a theory for the effects of polarons and phonons in mediating and suppressing the quantum tunneling of electrons into single molecules of conducting polymers, motivated by experiments on molecular quantum dots. The effects of both phonons and excitations of the polaron particle-in-a-box excitations are calculated. Using both the Su-Schrieffer-Heeger (SSH) model of polyacetylene and direct density-functional theory (DFT) calculations, we calculate the suppression o...
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.
Generation of coherent acoustic phonons in GaN-based p-n junction
Energy Technology Data Exchange (ETDEWEB)
Lin, Kung-Hsuan; Yu, Cheng-Ta; Sun, Chi-Kuang [Department of Electrical Engineering and Graduate Institute of Electro-Optical Engineering, National Taiwan University, Taipei, 10617 (Taiwan); Keller, Stacia; Mishra, Umesh; DenBaars, Steven P. [Department of Electrical and Computer Engineering, University of California, Santa Barbara, CA 93106 (United States)
2004-11-01
Coherent acoustic phonons were generated in the piezoelectric bulk semiconductor through inverse piezoelectric effect by femtosecond laser pulses. While the photocarriers are generated in the depletion region of the piezoelectric semiconductor, the electrons and holes sweep in counter-directions due to the built-in electric field and result in strain pulses through the piezoelectric effect. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
LO-phonon-assisted polariton lasing in a ZnO-based microcavity
Orosz, L.; Réveret, F.; Médard, F.; Disseix, P.; Leymarie, J.; Mihailovic, M.; Solnyshkov, D.; Malpuech, G.; Zuniga-Pérez, J.; Semond, F.; Leroux, M.; Bouchoule, S.; Lafosse, X.; Mexis, M.; Brimont, C.; Guillet, T.
2012-03-01
Polariton relaxation mechanisms are analyzed experimentally and theoretically in a ZnO-based polariton laser. A minimum lasing threshold is obtained when the energy difference between the exciton reservoir and the bottom of the lower polariton branch is resonant with the LO phonon energy. Tuning off this resonance increases the threshold, and exciton-exciton scattering processes become involved in the polariton relaxation. These observations are qualitatively reproduced by simulations based on the numerical solution of the semiclassical Boltzmann equations.
Coherent anti-Stokes Raman metrology of phonons powered by photonic-crystal fibers.
Savvin, A D; Lanin, A A; Voronin, A A; Fedotov, A B; Zheltikov, A M
2010-04-01
Coherent anti-Stokes Raman scattering (CARS) is used to measure the amplitude, the dephasing lifetime, and parameters of optical nonlinearities of optical phonons in a synthetic diamond film. A compact CARS apparatus demonstrated in this work relies on the use of an unamplified 70 fs 340 mW Cr:forsterite laser output and photonic-crystal fibers optimized for the generation of wavelength-tunable Stokes field and the spectral compression of the probe pulse. PMID:20364169
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.
Frequency dependence of dispersive phonon images
Scientific Electronic Library Online (English)
K., Jakata; A.G., Every.
2008-10-01
Full Text Available In the past, lattice dynamics models have been used in interpreting dispersive phonon focusing patterns of crystals. They have had mixed success in accounting for observed images and, moreover, different models applied to the same crystal tend to differ significantly in their predictions. In this pa [...] per we interpret observed phonon focusing images of two cubic crystals, germanium and silicon, through an extension of continuum elasticity theory that takes into account the first deviation from linearity of the phonon dispersion relation. This is done by incorporating fourth-order spatial derivatives of the displacement field in the wave equation. The coefficients of the higher-order derivatives are determined by fitting to phonon dispersion relations for the acoustic branches measured by neutron scattering in the [100], [111] and [110] symmetry directions. With this model we simulate phonon images of Si and Ge projected onto the (100), (110) and (111) observation planes. These are able to account well for the observed phonon images.
Toward quantitative modeling of silicon phononic thermocrystals
Lacatena, V.; Haras, M.; Robillard, J.-F.; Monfray, S.; Skotnicki, T.; Dubois, E.
2015-03-01
The wealth of technological patterning technologies of deca-nanometer resolution brings opportunities to artificially modulate thermal transport properties. A promising example is given by the recent concepts of "thermocrystals" or "nanophononic crystals" that introduce regular nano-scale inclusions using a pitch scale in between the thermal phonons mean free path and the electron mean free path. In such structures, the lattice thermal conductivity is reduced down to two orders of magnitude with respect to its bulk value. Beyond the promise held by these materials to overcome the well-known "electron crystal-phonon glass" dilemma faced in thermoelectrics, the quantitative prediction of their thermal conductivity poses a challenge. This work paves the way toward understanding and designing silicon nanophononic membranes by means of molecular dynamics simulation. Several systems are studied in order to distinguish the shape contribution from bulk, ultra-thin membranes (8 to 15 nm), 2D phononic crystals, and finally 2D phononic membranes. After having discussed the equilibrium properties of these structures from 300 K to 400 K, the Green-Kubo methodology is used to quantify the thermal conductivity. The results account for several experimental trends and models. It is confirmed that the thin-film geometry as well as the phononic structure act towards a reduction of the thermal conductivity. The further decrease in the phononic engineered membrane clearly demonstrates that both phenomena are cumulative. Finally, limitations of the model and further perspectives are discussed.
THE PHONON ANOMALY IN b.c.c. He4 : A PHONON SELF-TRAPPING ?
Héritier, M.
1981-01-01
It is proposed that a longitudinal phonon in b.c.c. He4, at wavevector |[MATH]| ?2.3 Å-1can be self-trapped in a liquid drop and form a roton-like excitation. This can account for anomalies observed in the phonon spectrum, in a sphere of momentum space.
Phonon Frequency Distribution of Vanadium
International Nuclear Information System (INIS)
The phonon frequency distribution of vanadium has been measured several times using the beryllium filter time-of-flight method. The results of the various authors agree more or less satisfactorily. But there have been objections against this method; for instance it does not start with monochromatic neutrons, and multiphonon processes are corrected only in a crude way. It seems worth while to determine the frequency distribution of vanadium by a different method. In the present work the authors tried to obtain this frequency distribution by a method which covers a larger part of the energy-transfer, momentum-transfer plane. Using the rotating crystal time-of-flight spectrometer at Karlsruhe with incident neutron energies between 0.018 and 0.08 eV energy transfers in the range from 0 to 2kBT and Q-values between 0 and 14Å-1 (where nQ is the momentum transfer) have been measured. Scattering-law values have been calculated and the frequency distribution was determined with the extrapolation method proposed by Egelstaff in an iterative way with the help of LEAP calculations. Taking into account the experimental errors the results agree very satisfactorily with the cold neutron work for energy transfers greater than 0.5 kBT. Below 0.5 kBT we have found an additional peak, the origin of which is not yet explained. Results are discussed and compared with existing theoretical calculations. (author)
Phonon spectrum of copper oxide
International Nuclear Information System (INIS)
It is customarily assumed that the superconducting properties of high-Tc cuprates are strongly associated with the presence of CuO conducting planes in the structure of these systems as well as structural fragments (planes or chains) which supply free carriers. In the binary copper oxide CuO, which has a monoclinic lattice (space group C 2/c) and is a Mott insulator, the same structural motifs, namely, CuO planes, in which copper is surrounded by four oxygen atoms can be distinguished. In addition, as in many high-Tc superconductors, antiferromagnetic ordering is observed in CuO (TN = 229.5 K). For this reason, CuO can be regarded as a simpler model system for high-Tc cuprate superconductors. Here, the partial spectra of vibrations of copper atoms and oxygen in CuO were obtained experimentally using isotopic contrast in inelastic neutron scattering. The phonon spectrum of the compound is constructed based on these data. The obtained spectrum is compared with calculations based on the rigid-ion model
International Nuclear Information System (INIS)
As predicted by harmonic theory the coherent inelastic spectrums of neutrons, scattered by a single, non-conducting crystal, for a particular angle of scattering consists of a number of delta-function peaks superposed on a continuous background. The peaks correspond to one-phonon processes in which one phonon is absorbed or emitted by the neutron; the background arises from multi-phonon processes. When anharmonic forces (phonon-phonon interactions) are present, the delta-function peaks are broadened into finite peaks, while their central frequencies are shifted with respect to the harmonic values. In the case of a metal there is in addition to phonon-phonon interactions an interaction between phonons and conduction electrons, which also gives a contribution to the displacement and broadening oftheone-phononpeaks. Continuing earlier work of Van Hove (sho considered the relatively simple case of a non-conductin crystal in its ground state (T = 0oK) ), we have studied the shifts and widths of the scattering peaks as a 'result of the above-mentioned interactions by means of many particle perturbation theory, making extensive use of diagram techniques. Prerequisite to the entire discussion is the assumption that, independent of the strength of the interactions, the width of each peak is small compared to the value of the frequency at its centre; only then the peaks can be considered as being well defined with respect to the background to higher order in the intethe background to higher order in the interactions. This condition is expected to be fulfilled for temperatures which are not too high and values of the phonon wave vector which are not too large. Our procedure yields closed formulae for the partial scattering function describing the peaks, which can be evaluated to arbitrarily high accuracy. In particular an expansion for calculating the line shift and line width in powers of u/d and in terms of simple connected diagrams is obtained (u is an average atomic or ionic displacement, d is the smallest interatomic or interionic distance in the crystal). Approximate calculations are performed to give some insight into the orders of magnitude of the effects under study. (author)
Dispersive phonon linewidths: the E2 phonons of ZnO.
Serrano, J; Manjón, F J; Romero, A H; Widulle, F; Lauck, R; Cardona, M
2003-02-01
Phonon linewidths can exhibit a large variation when either pressure or isotopic masses are changed. These effects yield detailed information about the mechanisms responsible for linewidths and lifetimes, e.g., anharmonicity or isotopic disorder. We report Raman measurements of the linewidth of the upper E2 phonons of ZnO crystals with several isotopic compositions and their dependence on pressure. Changes by a factor of 12 are observed at a given temperature. Comparison with calculated densities of one-phonon states, responsible for isotope scattering, and of two-phonon states, responsible for anharmonic decay, yields a consistent picture of these phenomena. Isotopic disorder broadening by 7 cm(-1) is found in samples with mixed 16O-18O content, whereas the anharmonic processes involve decay into sums and differences of two phonons. PMID:12633376
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
Theoretical study of phonon spectra in ferromagnetic nanoparticles
International Nuclear Information System (INIS)
Based on the spin-phonon model we analyze the influence of surface and size effects on the phonon properties of ferromagnetic nanoparticles. A Green's function technique in real space enables us to calculate the renormalized phonon energy and its damping depending on the temperature and the anharmonic spin-phonon interaction constants. With decreasing particle size the phonon energy can decrease or increase for different surface spin-phonon interaction constants, whereas the damping increases always. The influence of an external magnetic field is discussed, too. The theoretical results are in reasonable accordance to experimental data
Origin of the acoustic phonon frequency shifts in semiconducting nanoparticles
International Nuclear Information System (INIS)
The surface and size effects on the acoustic phonon properties of semiconducting nanoparticles, such as ZnO, are studied using the s-d model and a Green's function technique. We have shown that the electron-phonon and anharmonic phonon-phonon interactions play an important role in ZnO nanoparticles and must be taken into account in order to explain the experimental data. Due to surface and size effects on the electron-phonon constants, the acoustic phonon frequency and their damping increase with decreasing of particle size.
Cooling carbon nanotubes to the phononic ground state with constant electron current
Zippilli, Stefano; Morigi, Giovanna; Bachtold, Adrian
2008-01-01
We present a quantum theory of cooling of a mechanical resonator using back-action with constant electron current. The resonator device is based on a doubly clamped nanotube, which mechanically vibrates and acts as a double quantum dot for electron transport. Mechanical vibrations and electrons are coupled electrostatically using an external gate. The fundamental eigenmode is cooled by absorbing phonons when electrons tunnel through the double quantum dot. We identify the re...
Coherent acoustic phonon generation in GaAs1?xBix
International Nuclear Information System (INIS)
We have used femtosecond laser pulses to generate coherent acoustic phonons in the dilute Bismide alloy, GaAs1?xBix. The observed oscillation periods match well with the oscillation periods calculated using the propagating strain pulse model. We attribute the generation process predominantly to electronic stress due to the absorption of the laser pulse at the surface of the GaAs1?xBix layer. Our initial estimates suggest that the incorporation of Bi in GaAs causes an enhancement of the hydrostatic deformation potential because of the resonant state in the valence band due to isolated Bi impurities
International Nuclear Information System (INIS)
The influence of normal processes of electron-electron and phonon-phonon scattering on thermohalvanomagnetic effects in metals is under consideration. For electron and phonon distribution functions the kinetic equation system is solved. Component of kinetic coefficient tensors for metals in magnetic field are calculated in linear approximation by a degradation parameter. The effects of mutual entrainment of electrons and phonons as well as normal processes of electron-electron and phonon-phonon scattering on thermomagnetic effects in metals under isothermal conditions are analyzed
Situation with collective two-phonon states in deformed nuclei
International Nuclear Information System (INIS)
Within the quasiparticle-phonon nuclear model with the operators of phonons depending on the sign of the angular momentum projection, the Pauli principle is taken into account in the two-phonon components of the wave functions. The centroid energies of the collective two-phonon states in even-even deformed nuclei are calculated. It is shown that the inclusion of the Pauli principle leads to their shift by 1-3 MeV towards high energies. The shifts of three-phonon poles due to the Pauli principle are calculated in the three-phonon components of the wave functions. The collective two-phonon states, the centroid energies of which are 3-5 MeV, are expected to be strongly fragmented. The conclusion is confirmed that the collective two-phonon states should not exist in deformed nuclei. The situation in 168Er and in the 228Th isotopes is analysed
Ong, Zhun-Yong; Zhang, Gang; Zhang, Yong-Wei
2015-03-01
Using the nonequilibrium Green's function method, we compute the the thermal boundary conductance of a monolayer graphene-boron-nitride (Gr-BN) lateral heterostructure with an armchair interface. At 300 K, the thermal conductance of the Gr-BN interface is computed to be 3.5 nW/nm2 or equivalent to approximately 200 nm of BN. The application of a strain, parallel or normal to the interface, also reduces the interfacial thermal resistance by improving the transmission of acoustic phonons. We do a modal decomposition of the phonon transmission spectrum and identify the phonon scattering channels responsible for heat transfer at the interface. We show that at low frequencies, interfacial heat transfer is dominated by the longitudinal, transverse and flexural acoustic phonons while at higher frequencies, it is mostly by longitudinal acoustic and optical phonons. Our work sheds light on the mechanism of phonon-phonon conversion at the interface of 2D lateral heterostructures and how it can be modified via the application of strain.
Revision of the statistical mechanics of phonons to include phonon line widths
International Nuclear Information System (INIS)
Zubarev in 1960 obtained the smeared Bose-Einstein (B-E) function in order to take into account the fact that the eigenenergy associated with a fixed phonon wave vector q and fixed polarization index j is not precisely defined but instead, is smeared by phonon-phonon and phonon-electron interactions. The ratio GAMMA(qj)/?(qj) is often quite small, i.e., of the order of 0.01 or less, where GAMMA is the phonon linewidth and h-bar ? is the eigenenergy. However, in strongly anharmonic crystals GAMMA/? may be as large as 0.3 at certain points of the Brillouin zone. In such dramatic cases one would suspect that such phonon linewidths would have some observable effect on the thermodynamic properties. The purpose of this work is to derive the expression for the average free energy per mode for a crystal having large phonon linewidths and to test the properties of the thermodynamic functions derivable from the average free energy per mode
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
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.
Phonons and Lattice Dielectric Properties of Zirconia
Zhao, X; Zhao, Xinyuan; Vanderbilt, David
2001-01-01
We have performed a first-principles study of the structural and vibrational properties of the three low-pressure (cubic, tetragonal, and especially monoclinic) phases of ZrO2, with special attention to the computation of the zone-center phonon modes and related dielectric properties. The calculations have been carried out within the local-density approximation using ultrasoft pseudopotentials and a plane-wave basis. The fully relaxed structural parameters are found to be in excellent agreement with experimental data and with previous theoretical work. The total-energy calculations correctly reproduce the energetics of the ZrO2 phases, and the calculated zone-center phonon frequencies yield good agreement with the infrared and Raman experimental frequencies in the monoclinic phase. The Born effective charge tensors are computed and, together with the mode eigenvectors, used to decompose the lattice dielectric susceptibility tensor into contributions arising from individual infrared-active phonon modes. This w...
Phonon transmission across an interface between two crystals
Meilakhs, Aleksandr
2015-01-01
The new model of phonon transmission across the interface between two crystals is proposed featured by taking into account the mismatch of crystal lattices. It has been found that the mismatch of lattices results in phonon scattering at the interface even in the absence of defects. As it has been shown, at the normal incidence, longitudinally polarized phonons have much larger transmission coefficient than that of transversely polarized phonons, excluding the special resonan...
Hopping-resolved electron-phonon coupling in bilayer graphene
E. Cappelluti; Profeta, G.
2012-01-01
In this paper we investigate the electron-phonon coupling in bilayer graphene, as a paradigmatic case for multilayer graphenes where interlayer hoppings are relevant. Using a frozen-phonon approach within the context of Density Functional Theory (DFT) and using different optical phonon displacements we are able to evaluate quantitatively the electron-phonon coupling $\\alpha_i$ associated with each hopping term $\\gamma_i$. This analysis also reveals a simple scaling law betwe...
One-phonon ionization of neutral donors in germanium
Gienger, Martin; Groß, Peter; Lassmann, Kurt
1989-01-01
Here we show by phonon spectroscopy with superconducting tunnelling junctions that one-phonon excitations from the ground state to the conduction band (CB) are measurable as phonon induced conductivity (PIC) changes in the special case of donors in Ge. For the conductivity thresholds we find somewhat smaller binding energies than evaluated from optical measurements whereas for the 1s-singlet to 1s-triplet ground state splitting as seen by elastic phonon scattering we obtain the optical values.
Calculations of the A_1 phonon frequency in photoexcited Tellurium
Tangney, P.; Fahy, S
1998-01-01
Calculations of the A_1 phonon frequency in photoexcited tellurium are presented. The phonon frequency as a function of photoexcited carrier density and phonon amplitude is determined. Recent pump probe experiments are interpreted in the light of these calculatons. It is proposed that, in conjunction with measurements of the phonon period in ultra-fast pump-probe reflectivity experiments, the calculated frequency shifts can be used to infer the evolution of the density of ph...
Correlation induced phonon softening in low density coupled bilayer systems
Hwang, E. H.; Sarma, S. Das
2000-01-01
We predict a possible phonon softening instability in strongly correlated coupled semiconductor bilayer systems. By studying the plasmon-phonon coupling in coupled bilayer structures, we find that the renormalized acoustic phonon frequency may be softened at a finite wave vector due to many-body local field corrections, particularly in low density systems where correlation effects are strong. We discuss experimental possibilities to search for this predicted phonon softening...
Squeezed Phonon States: Modulating Quantum Fluctuations of Atomic Displacements
Hu, X; Nori, Franco
1996-01-01
We study squeezed quantum states of phonons, which allow the possibility of modulating the quantum fluctuations of atomic displacements below the zero-point quantum noise level of coherent phonon states. We calculate the corresponding expectation values and fluctuations of both the atomic displacement and the lattice amplitude operators, and also investigate the possibility of generating squeezed phonon states using a three-phonon parametric amplification process based on ph...
Relaxation between electrons and surface phonons in nanoscale metal films
Singh, Navinder
2006-01-01
The Two Temperature model of M I Kaganov, I M Lifshitz and L V Tanatarov (Sov. Phys. JETP 4, 173 (1957)) about relaxation between electrons and bulk phonons is extended to the case of surface phonons. The state of electrons and phonons is described by equilibrium Fermi and Bose functions with different temperatures. The new feature added is the geometric constraint of surface phonons. We obtain expressions for the energy transfer rate from degenerate hot electrons to surface...
Band structure characteristics of T-square fractal phononic crystals
International Nuclear Information System (INIS)
The T-square fractal two-dimensional phononic crystal model is presented in this article. A comprehensive study is performed for the Bragg scattering and locally resonant fractal phononic crystal. We find that the band structures of the fractal and non-fractal phononic crystals at the same filling ratio are quite different through using the finite element method. The fractal design has an important impact on the band structures of the two-dimensional phononic crystals
Imaging of acoustic phonon stop bands in superlattices
International Nuclear Information System (INIS)
Phonon-imaging experiments reveal the angular distribution of high-frequency acoustic-phonon transmission through an In/sub 0.15/Ga/sub 0.85/As/AlAs superlattice. Phonon stop bands due to Bragg reflection at the folded-zone boundary are observed for both longitudinal and fast transverse phonons. A newly predicted intrazone stop band due to coupling between acoustic modes is detected
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...
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...
Thermal characterization of nanoscale phononic crystals using supercell lattice dynamics
Bruce L. Davis; Hussein, Mahmoud I.
2011-01-01
The concept of a phononic crystal can in principle be realized at the nanoscale whenever the conditions for coherent phonon transport exist. Under such conditions, the dispersion characteristics of both the constitutive material lattice (defined by a primitive cell) and the phononic crystal lattice (defined by a supercell) contribute to the value of the thermal conductivity. It is therefore necessary in this emerging class of phononic materials to treat the lattice dynamics at both periodicit...
Phonon-assisted intersubband transitions in wurtzite GaN/InxGa1?xN quantum wells
International Nuclear Information System (INIS)
A detailed numerical calculation on the phonon-assisted intersubband transition rates of electrons in wurtzite GaN/InxGa1?xN quantum wells is presented. The quantum-confined Stark effect, induced by the built-in electric field, and the ternary mixed crystal effect are considered. The electron states are obtained by iteratively solving the coupled Schrödinger and Poisson equations. The dispersion properties of each type of phonon modes are considered in the derivation of Fermi's golden rule to evaluate the transition rates. It is indicated that the interface and half-space phonon scattering play an important role in the process of 1–2 radiative transition. The transition rate is also greatly reduced by the built-in electric field. This work can be helpful for the structural design and simulation of new semiconductor lasers
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
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.
On calculating the radiated ballistic phonon power in phononic crystal membranes
Puurtinen, T. A.; Maasilta, I. J.
2012-12-01
Phononic crystals are periodically modified structures, where the phonon spectra (dispersion relations) are strongly modified due to interference, or Bragg reflections. In all practical cases, the resulting dispersion relations have to be calculated numerically, using for example the finite difference or the finite element method. We show that if one uses the results of finite element modeling directly in the calculation of phonon group velocities, a sizeable numerical error in the calculation of thermal conductance or radiated power can easily follow. We introduce here a sorting algorithm for the eigenfrequency surfaces to reduce this error, which arises from the discretization of the k-space points.
Raman line shapes of anharmonic phonons
International Nuclear Information System (INIS)
Anharmonic effects in crystals typically result in the symmetric broadening of the single-phonon Lorentzian line shape. However, a simple model, based on consideration of a highly anharmonic potential, shows that anharmonicity can lead not only to asymmetric line shapes but also to line shapes composed of multiple subpeaks. Experimental Raman data on the soft A1(TO) phonon in ferroelectric PbTiO3 indicates that this mode does indeed consist of a series of subpeaks whose intensities are accurately predicted (with no fitting parameters) by our model
Phonon interference effects in molecular junctions
DEFF Research Database (Denmark)
Markussen, Troels
2013-01-01
We study coherent phonon transport through organic, p-conjugated molecules. Using first principles calculations and Green's function methods, we find that the phonon transmission function in cross-conjugated molecules, like meta-connected benzene, exhibits destructive quantum interference features very analogous to those observed theoretically and experimentally for electron transport in similar molecules. The destructive interference features observed in four different cross-conjugated molecules significantly reduce the thermal conductance with respect to linear conjugated analogues. Such control of the thermal conductance by chemical modifications could be important for thermoelectric applications of molecular junctions.
Phonon spectra in one-dimensional quasicrystals
International Nuclear Information System (INIS)
The propagation of phonons in one-dimensional quasicrystals is investigated. The authors use the projection method which has been recently proposed to generate almost periodic tilings of the line. They define a natural Laplace operator on these structures which models phonon (and also tight-binding electron) propagation. The self-similarity properties of the spectrum are discussed, as well as some characteristic features of the eigenstates, which are neither extended nor localized. The long-wavelength limit is examined in more detail; it is argued that one is the lower critical dimension for this type of models
Phonon thermal conductivity in single layered manganites
International Nuclear Information System (INIS)
We present measurements of the thermal transport in single crystals of single-layered manganites La1-xSr1+xMnO4 with 0=ph upon hole-doping. The suppression of ?ph originates from scattering of phonons by polaronic holes. The suppression is particularly strong when charge and orbital degrees of freedom are disordered and rather weak in the case of long-range charge and orbital ordering. Moreover, slight anomalies are found in the vicinity of antiferromagnetic phase transitions, probably due to scattering of phonons by magnetic fluctuations
Phonon Overlaps: Polyacetylene, Polarons, and Molecular Size
Chang, C T; Chang, Connie Te-ching; Sethna, James P.
2006-01-01
We provide a theory for the effects of polarons and phonons in mediating and suppressing the quantum tunneling of electrons into single molecules of conducting polymers, motivated by experiments on molecular quantum dots. The effects of both phonons and excitations of the polaron particle-in-a-box excitations are calculated. Using both the Su-Schrieffer-Heeger (SSH) model of polyacetylene and direct density-functional theory (DFT) calculations, we calculate the suppression of ground--state to ground--state transitions and the position and strength of the side-bands.
Electron Phonon Superconductivity in LaNiOP
Subedi, A; Singh, D. J.; Du, M. H.
2008-01-01
We report first principles calculations of the electronic structure, phonon dispersions and electron phonon coupling of LaNiPO. These calculations show that this material can be explained as a conventional electron phonon superconductor in contrast to the FeAs based high temperature superconductors.
Phonon spectroscopy through the electronic density of states in graphene
Nicol, E. J.; Carbotte, J. P.
2009-01-01
We study how phonon structure manifests itself in the electronic density of states of graphene. A procedure for extracting the value of the electron-phonon renormalization $\\lambda$ is developed. In addition, we identify direct phonon structures. With increasing doping, these structures, along with $\\lambda$, grow in amplitude and no longer display particle-hole symmetry.
O. V. Dolgov; Andersen, O.K.; Mazin, I.I.
2007-01-01
We show that the usual expression for evaluating electron-phonon coupling and the phonon linewidth in 2D metals with a cylindrical Fermi surface cannot be applied near the wave vector corresponding to the Kohn singularity. Instead, the Dyson equation for phonons has to be solved self-consistently. If a self-consistent procedure is properly followed, there is no divergency in either the coupling constant or the phonon linewidth near the offending wave vectors, in contrast to ...
Exciton-LO-phonon dynamics in InAs/GaAs quantum dots: Effects of zone-edge phonon damping
Machnikowski, Pawel; Jacak, Lucjan
2003-01-01
The dynamics of an exciton-LO-phonon system after an ultrafast optical excitation in an InAs/GaAs quantum dot is studied theoretically. Influence of anharmonic phonon damping and its interplay with the phonon dispersion is analyzed. The signatures of the zone-edge decay process in the absorption spectrum and time evolution are highlighted, providing a possible way of experimental investigation on phonon anharmonicity effects.
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''
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.
Towards a Quantum Interface between Diamond Spin Qubits and Phonons in an Optical Trap
Ji, Peng; Momeen, M. Ummal; Hsu, Jen-Feng; D'Urso, Brian; Dutt, Gurudev
2014-05-01
We introduce a method to optically levitate a pre-selected nanodiamond crystal in air or vacuum. The nanodiamond containing nitrogen-vacancy (NV) centers is suspended on a monolayer of graphene transferred onto a patterned substrate. Laser light is focused onto the sample, using a home-built confocal microscope with a high numerical aperture (NA = 0.9) objective, simultaneously burning the graphene and creating a 3D optical trap that captures the falling nano-diamond at the beam waist. The trapped diamond is an ultra-high-Q mechanical oscillator, allowing us to engineer strong linear and quadratic coupling between the spin of the NV center and the phonon mode. The system could result in an ideal quantum interface between a spin qubit and vibrational phonon mode, potentially enabling applications in quantum information processing and sensing the development of quantum information storage and processing.
The phonon and thermal properties of a ladder nanostructure
Directory of Open Access Journals (Sweden)
M Mardaani
2011-12-01
Full Text Available In this paper, we study the phonon thermal properties of a ladder nanostructure in harmonic approximation. We present a model consisting of two infinite chains with different masses. Then, we investigate the effect of different masses on the phonon spectrum. Moreover, as a specific case, in the absence of the second neighbor interaction, we calculate the phonon density of states/modes. Finally, we consider the thermal conductivity of the system. The results show that the phonon spectrum shifts down to the lower frequencies by increasing the masses. Furthermore, a frequency gap appears in the phonon spectrum. By increasing the springs constants, the thermal conductance decreases.
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.
LEED Kikuchi pattern: phonon and plasmon contributions
International Nuclear Information System (INIS)
Detailed properties of LEED Kikuchi patterns for MgO and Al are studied experimentally and theoretically. The Kikuchi line disappearance, the intensity change of various Kikuchi bands, the temperature dependence of Kikuchi band intensity etc., are studied experimentally with an energy analyser, and the results are interpreted theoretically by phonon and plasmon excitations. (Auth.)
Phononic crystals for liquid sensor applications
International Nuclear Information System (INIS)
Acoustic band gap materials, so-called phononic crystals, are introduced as a new platform for sensing material properties in small cavities. The sensor employs specific transmission windows within the band gap to determine properties of one component that builds the phononic crystal. The dependence of the frequency where transmission takes place is correlated to material properties, specifically to the sound velocity of a liquid. This value is related to several parameters of practical interest like the concentration of one component in a mixture or conversion rate in a microreactor. The capability of the concept will be demonstrated with a one-dimensional arrangement of solid plates and liquid-filled cavities and a two-dimensional periodic arrangement of liquid-filled holes in a solid matrix. The properties of 1D phononic crystals will be analysed in terms of the effective acoustic impedance and the resulting transmission behaviour and experimentally verified. The transmission properties of the 2D phononic crystal will be modelled with the layer multiple-scattering theory. Similar features which can be employed for sensing purposes will be discussed
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
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...
PHONONS IN THE DNA DOUBLE HELIX
Prohofsky, E.; Zandt, L.; Kohli, M.; Lu, K.; Mei, M.; Putman, B.
1981-01-01
We have calculated a model for the phonon modes of the DNA double helix. We have used these modes in a number of applications to biological problems which use lattice concepts such as soft modes, local modes and quasi-momentum.
Phonon affected transport through molecular quantum.
Czech Academy of Sciences Publication Activity Database
Loos, Jan; Koch, T.; Alvermann, A.; Bishop, A. R.; Fehske, H.
2009-01-01
Ro?. 21, ?. 39 (2009), 395601/1-395601/18. ISSN 0953-8984 Institutional research plan: CEZ:AV0Z10100521 Keywords : quantum dots * electron - phonon interaction * polarons Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.964, year: 2009
Synthetic thermoelectric materials comprising phononic crystals
El-Kady, Ihab F; Olsson, Roy H; Hopkins, Patrick; Reinke, Charles; Kim, Bongsang
2013-08-13
Synthetic thermoelectric materials comprising phononic crystals can simultaneously have a large Seebeck coefficient, high electrical conductivity, and low thermal conductivity. Such synthetic thermoelectric materials can enable improved thermoelectric devices, such as thermoelectric generators and coolers, with improved performance. Such synthetic thermoelectric materials and devices can be fabricated using techniques that are compatible with standard microelectronics.
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)
Baimuratov, Anvar S; Rukhlenko, Ivan D; Leonov, Mikhail Yu; Shalkovskiy, Alexey G; Baranov, Alexander V; Fedorov, Anatoly V
2014-08-11
We present a theory of phonon-assisted photoluminescence from a semiconductor quantum dot (QD) whose electron and phonon subsystems are resonantly coupled via the polar electron-phonon interaction. We show that the resonance-induced renormalization of the QD energy spectrum, leading to the formation of the polaron-like states, can be performed exactly in terms of the arbitrarily degenerate states of electron-hole pairs and the phonon modes of equal energies. Using the model of QDs with finite potential barriers for electron and holes leads to new selection rules of interband optical transitions and the three-particle interaction describing simultaneous absorption and/or emission of a photon and a phonon. We also derive a simple expression for the differential cross section of the stationary, low-temperature photoluminescence, which allows the fundamental parameters of the polaron-like excitations to be readily extracted from the frequency-resolved experimental spectra. In particular, the energies of the excitations and the coherence relaxation rates of the optical transitions resulting in their generation and recombination are shown to be directly given by the positions and widths of the photoluminescence peaks. The developed theory complements the existing experimental techniques of studying the phonon-assisted photoluminescence from individual nanocrystals. PMID:25321054
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
Magnetic-Field-Assisted Terahertz Quantum Cascade Laser Operating up to 225 K
Wade, A.; Fedorov, G.; Smirnov, D.; Kumar, S.; Williams, B. S.; Hu, Q.; Reno, J. L.
2008-01-01
Advances in semiconductor bandgap engineering have resulted in the recent development of the terahertz quantum cascade laser1. These compact optoelectronic devices now operate in the frequency range 1.2-5 THz, although cryogenic cooling is still required2.3. Further progress towards the realization of devices operating at higher temperatures and emitting at longer wavelengths (sub-terahertz quantum cascade lasers) is difficult because it requires maintaining a population inversion between closely spaced electronic sub-bands (1 THz approx. equals 4 meV). Here, we demonstrate a magnetic-field-assisted quantum cascade laser based on the resonant-phonon design. By applying appropriate electrical bias and strong magnetic fields above 16 T, it is possible to achieve laser emission from a single device over a wide range of frequencies (0.68-3.33 THz). Owing to the suppression of inter-landau-level non-radiative scattering, the device shows magnetic field assisted laser action at 1 THz at temperatures up to 215 K, and 3 THz lasing up to 225 K.
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
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)
Nanoscale heat transport via electrons and phonons by molecular dynamics simulations
Lin, Keng-Hua
Nanoscale heat transport has become a crucial research topic due to the growing importance of nanotechnology for manufacturing, energy conversion, medicine and electronics. Thermal transport properties at the nanoscale are distinct from the macroscopic ones since the sizes of nanoscale features, such as free surfaces and interfaces, are comparable to the wavelengths and mean free paths of the heat carriers (electrons and phonons), and lead to changes in thermal transport properties. Therefore, understanding how the nanoscale features and energy exchange between the heat carriers affect thermal transport characteristics are the goals of this research. Molecular dynamics (MD) is applied in this research to understand the details of nanoscale heat transport. The advantage of MD is that the size effect, anharmonicity, atomistic structure, and non-equilibrium behavior of the system can all be captured since the dynamics of atoms are described explicitly in MD. However, MD neglects the thermal role of electrons and therefore it is unable to describe heat transport in metal or metal-semiconductor systems accurately. To address this limitation of MD, we develop a method to simulate electronic heat transport by implementing electronic degrees of freedom to MD. In this research, nanoscale heat transport in semiconductor, metal, and metal-semiconductor systems is studied. Size effects on phonon thermal transport in SiGe superlattice thin films and nanowires are studied by MD. We find that, opposite to the macroscopic trend, superlattice thin films can achieve lower thermal conductivity than nanowires at small scales due to the change of phonon nature caused by adjusting the superlattice periodic length and specimen length. Effects of size and electron-phonon coupling rate on thermal conductivity and thermal interface resistivity in Al and model metal-semiconductor systems are studied by MD with electronic degrees of freedom. The results show that increasing the specimen length or the electron-phonon coupling rate increases the electronic contribution in thermal transport and therefore increases the thermal conductivity; moreover, the thermal interface resistivity in metal-semiconductor systems is observed to depend on the heat flux direction due to the direction-dependent energy transfer pathways between electrons and phonons at the interface. MD with electronic degrees of freedom is also applied to simulate heat transport across the metal-semiconductor interface under the non-equilibrium conditions, mimicking the ultrafast laser heating in transient thermoreflectance measurements. The effect of local and non-local electron-phonon coupling across the interface are examined, since the experimental evidence suggests that non-local electron-phonon coupling occurs under the non-equilibrium conditions. Our results show that non-local electron-phonon coupling not only facilitates energy transfer across the interface but also enhances ballistic transport of the high frequency phonon modes in a semiconductor. In summary, our study provides an insight into the details of nanoscale heat transport in various systems by MD and MD with electronic degrees of freedom.
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.
Controlling of exciton condensate by external fields and phonon laser
Lozovik, Yu E.; Ovchinnikov, I. V.
2000-01-01
The novel method of observation and controlling of Bose-Einstein condensation in the system of spatially and momentum-space indirect excitons in coupled quantum wells using in-plane magnetic and normal electric fields is proposed. Fields are used for exciton dispersion engeneering. In the presence of in-plane magnetic field ground state of spatially indirect exciton becomes also indirect in the momentum space. Manipulation of electric field magnitude is used for tuning to re...
Theory of coherent phonons in carbon nanotubes and graphene nanoribbons.
Sanders, G D; Nugraha, A R T; Sato, K; Kim, J-H; Kono, J; Saito, R; Stanton, C J
2013-04-10
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. PMID:23478856
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
International Nuclear Information System (INIS)
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 ?eV over integration times of 100 ms.
Multi-phonon dynamics of the ultra-fast photoinduced transition of (EDO-TTF)2SbF6
International Nuclear Information System (INIS)
We report here the first observation of the photoinduced insulating-to-metal phase transition in the (EDO-TTF)2SbF6 salt, which occurs on the picosecond time-scale. The time-resolved optical experiments performed with 80 fs time-resolution demonstrate that the dynamical process involves several low-frequency phonons, as the crystalline structure is destabilized upon laser excitation.
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)
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.
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
Structural Properties and Phonon dispertion of NACl
Directory of Open Access Journals (Sweden)
R. Khoda-Bakhsh
2001-06-01
Full Text Available Although many phenomena in condensed matter Physics can be understood on the basis of a model, there are also considerable number of physical properties of solid which can not be explained except in the framework of lattice dynamics. We have calculated the phonon frequencies of Na Cl, using an approach which is a combination of frozen phonon and force constants methods in the framework of density functional pseudopotential theory. The dispersion relation curves, were calculated along symmetry direction ?, ? and Ù. We also calculated Grunesein parameters for all modes at X and L points in Brillion zone. The calcutions are made in the framework of density functional and pseudopotential theory, using super cell method, with the valence orbitals expanded in plane waves.
Phonon-tunneling dissipation in mechanical resonators
International Nuclear Information System (INIS)
Full text: Micro- and nanoscale mechanical resonators have emerged as ubiquitous devices for application in a wide range of technical disciplines including communications, sensing, metrology, and fundamental scientific endeavors. In many instances, the performance of these devices is limited by the deleterious effects of mechanical damping. To further compound this limitation, the quantitative understanding of many damping mechanisms remains elusive. Here, we report a significant advancement towards predicting and controlling support-induced losses, a key dissipation mechanism in high quality- factor mechanical resonators. We have developed an efficient finite-element-enabled numerical solver, employing the recently introduced 'phonon tunneling' approach. Exploiting this solver we demonstrate the ability to predict the design-limited damping of generic mechanical resonators, yielding excellent agreement with experimental measurements on custom-fabricated monocrystalline resonators. Thus, our phonon-tunneling solver represents a major step towards accurate prediction of the mechanical quality factor in micro- and nanomechanical resonators. (author)
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.))
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 spectroscopy with superconducting tunnel junctions
International Nuclear Information System (INIS)
Superconducting tunnel junctions can be used as generators and detectors of monochromatic phonons of frequency larger than 80 GHz, as was first devised by Eisenmenger and Dayem (1967) and Kinder (1972a, 1973). In this report, we intend to give a general outline of this type of spectroscopy and to present the results obtained so far. The basic physics underlying phonon generation and detection are described in chapter I, a wider approach being given in the references therein. In chapter II, the different types of junctions are considered with respect to their use. Chapter III deals with the evaporation technique for the superconducting junctions. The last part of this report is devoted to the results that we have obtained on ?-irradiated LiF, pure Si and Phosphorous implanted Si. In these chapters, the limitations of the spectrometer are brought out and suggestions for further work are given
Phonon 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.
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.
Electron-phonon interaction in nanodevices.
Czech Academy of Sciences Publication Activity Database
Král, Karel
Warrendale : TMS (The Minerals, Metals & Materials Society), 2008, s. 81-86. ISBN 978-0-87339-716-2. [ TMS 2008 Annual Meeting & Exhibition. New Orleans, Louisiana (US), 09.03.2008-13.03.2008] R&D Projects: GA MŠk OC08001 Institutional research plan: CEZ:AV0Z10100520 Keywords : nanomaterials * electron-phonon interaction * quantum dots * nanodevice Subject RIV: BM - Solid Matter Physics ; Magnetism
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)Six(30)Si1-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)Six(30)Si1-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)Six(30)Si1-x nanowires is ?30% lower than that of isotopically pure (29)Si nanowires in agreement with theoretical predictions. PMID:25993500
Phonon heat conduction in layered anisotropic crystals
Minnich, A. J.
2014-01-01
The thermal properties of anisotropic crystals are of both fundamental and practical interest, but transport phenomena in anisotropic materials such as graphite remain poorly understood because solutions of the Boltzmann equation often assume isotropy. Here, we extend an analytical solution of the Boltzmann equation to highly anisotropic solids and examine its predictions for graphite. We show that the phonon mean free paths in the cross-plane direction can be comparable to ...
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...
Geometric aspects of phonon polarization transport
Mehrafarin, Mohammad; Torabi, Reza
2009-01-01
We study the polarization transport of transverse phonons by adopting a new approach based on the quantum mechanics of spin-orbit interactions. This approach has the advantage of being apt for incorporating fluctuations in the system. The formalism gives rise to Berry effect terms manifested as the Rytov polarization rotation law and the polarization-dependent Hall effect. We derive the distribution of the Rytov rotation angle in the presence of thermal noise and show that t...
LEED Kikuchi pattern, phonon and plasmon contributions
International Nuclear Information System (INIS)
Detailed properties of LEED Kikuchi patterns for MgO and Al are studied experimentally and theoretically. The diffraction effects of the primary beam, the Kikuchi lines non-appearance, the intensity change of Kikuchi bands with indexes, the temperature dependence and the contrast change of the band with energy losses are studied with an energy analyser and the results are interpreted theoretically by phonon and plasmon excitations. (Auth.)
PHONON RAMAN SPECTROSCOPY IN GRAPHITE INTERCALATION COMPOUNDS
Hwang, D.; Solin, S.
1981-01-01
The atoms or molecules intercalated in a graphite intercalation compound are correlated spatially among themselves, resulting in a static structure factor with sharp peaks. Graphite phonons with momenta corresponding to these structure factor peaks have a higher probability of being scattered into the Brillouin zone center and becoming Raman active. With this momentum selection scheme, we can interpret the observed Raman features of graphite intercalation compounds with various in-plane struc...
Electron-Phonon Interaction in Tetrahedral Semiconductors
Cardona, Manuel
2004-01-01
Effects of electron-phonon interactions on the band structure can be experimentally investigated in detail by measuring the temperature dependence of energy gaps or critical points (van Hove singularities) of the optical excitation spectra. These studies have been complemented in recent years by observing the dependence of such spectra on isotopic mass whenever different stable isotopes of a given atom are available at affordable prices. In crystals composed of different ato...
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 e...
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...
Phononic properties of hexagonal chiral lattices
Spadoni, Alessandro; Ruzzene, Massimo; Gonella, Stefano; Scarpa, Fabrizio
2009-01-01
The manuscript reports the outcome of investigations on the phononic properties of a chiral cellular structure. The considered geometry features in-plane hexagonal symmetry, whereby circular nodes are connected through six ligaments tangent to the nodes themselves. in-plane wave propagation is analyzed through the application of Bloch theorem, which is employed to predict two-dimensional dispersion relations as well as illustrate dispersion properties unique to the considered chiral configura...
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...
Robinson, Richard; Otelaja, Obafemi; Hertzberg, Jared; Aksit, Mahmut; Stewart, Derek
2013-03-01
Phonons are the dominant heat carriers in dielectrics and a clear understanding of their behavior at the nanoscale is important for the development of efficient thermoelectric devices. In this work we show how acoustic phonon transport can be directly probed by the generation and detection of non-equilibrium phonons in microscale and nanoscale structures. Our technique employs a scalable method of fabricating phonon generators and detectors by forming Al-AlxOy-Al superconducting tunnel junctions on the sidewalls of a silicon mesa etched with KOH and an operating temperature of 0.3K [1]. In the line-of-sight path along the width of these mesas, phonons with frequency ˜100 GHz can propagate ballistically The phonons radiate into the mesa and are observed by the detector after passing through the mesa. We fabricated silicon nanosheets of width 100 to 300 nm along the ballistic path and observe surface scattering effects on phonon transmission when the characteristic length scale of a material is less than the phonon mean free path. We compare our results to the Casimir-Ziman theory. Our methods can be adapted for studying phonon transport in other nanostructures and will improve the understanding of phonon contribution to thermal transport. The work was supported in part by the National Science Foundation under Agreement No. DMR-1149036.[4pt] [1] J. B. Hertzberg et al, Rev. Sci. Inst. 82, 104905 (2011).
Robinson, Richard; Otelaja, Obafemi; Hertzberg, Jared; Aksit, Mahmut; Stewart, Derek
2013-03-01
Phonons are the dominant heat carriers in dielectrics and a clear understanding of their behavior at the nanoscale is important for the development of efficient thermoelectric devices. In this work we show how acoustic phonon transport can be directly probed by the generation and detection of non-equilibrium phonons in microscale and nanoscale structures. Our technique employs a scalable method of fabricating phonon generators and detectors by forming Al-AlxOy-Al superconducting tunnel junctions on the sidewalls of a silicon mesa etched with KOH and an operating temperature of 0.3K. In the line-of-sight path along the width of these mesas, phonons with frequency ~100 GHz can propagate ballistically The phonons radiate into the mesa and are observed by the detector after passing through the mesa. We fabricated silicon nanosheets of width 100 to 300 nm along the ballistic path and observe surface scattering effects on phonon transmission when the characteristic length scale of a material is less than the phonon mean free path. We compare our results to the Casimir-Ziman theory. Our methods can be adapted for studying phonon transport in other nanostructures and will improve the understanding of phonon contribution to thermal transport. The work was supported in part by the National Science Foundation under Agreement No. DMR-1149036.
Nasieka, Iu.; Boyko, M.; Strelchuk, V.; Danilchenko, B.; Rashkovetskyi, L.; Fochuk, P.
2014-10-01
An impact of different doses (10-500 kGy) of ?-irradiation on electron-phonon coupling in Ge-doped CdTe (CdTe:Ge) single crystals was investigated via low-temperature (T=5 K) photoluminescence (LTPL) and resonant Raman scattering (RRS). In the present work electron-phonon coupling concerns longitudinal optical (LO) phonons and was described in terms of Huang-Rhys factor. It was obtained ?-irradiation in such dose range leads to the increases in the value of Huang-Rhys factor. At high doses (equal to 200 kGy) the saturation of the increased at low doses Huang-Rhys factor was observed. Based on the features of radiation-stimulated changes in LTPL, increasing of electron-LO-phonon coupling can be explained by radiation-induced defect compensation process involving, with the great probability, Ge dopant atoms filling of native cadmium vacancies (VCd) and by other related mechanisms such as radiation-induced Ge clusters dissociation. Such compensation is resulted in the proving of the crystalline perfection of irradiated crystals. The latter was confirmed by resonant Raman scattering measurements. Resonant Raman conditions for near E0+?0 gap (2,54 eV at 80 K) were obtained by temperature tuning of the band gap keeping the excitation energy fixed for laser excitation energies near E0+?0. It was found good agreement in the dose dependencies of the values of Huang-Rhys factors and 2LO/1LO phonon modes ratio obtained from resonant Raman spectra. The increasing in the intensity of Fröhlich-induced 2LO-phonon modes with the increase of the irradiation dose and decreasing in impurity-induced 1LO-phonon intensity indicates about decreasing in the defect concentration in studied crystals. Relatively high saturation dose corresponding to the 2LO/1LO phonon modes ratio indicates high radiation strength of studied material.
Laminated piezoelectric phononic crystal with imperfect interfaces
Lan, Man; Wei, Peijun
2012-01-01
Dispersive characteristics of elastic waves propagating through laminated piezoelectric phononic crystal with imperfect interfaces are studied in this paper. First, the transfer matrix method and the Bloch theorem are used to derive the dispersion equation. Next, the imperfect interfaces with the jump of mechanical quantity across interface are considered. In the spring model of imperfect interface, the tractions are continuous, but displacements are discontinuous across the interface. In the mass model of imperfect interface, displacements are continuous, but tractions are discontinuous. In the spring-mass model, both traction and displacement are discontinuous. The effect of imperfect interface is introduced by inserting an additional interface transfer matrix in the calculation of total transfer matrix. Finally, the dispersion equation is solved numerically and the dispersive curves are shown in the Brillouin zone. Band gaps of phononic crystal with imperfect interface are compared with that of phononic crystal with perfect interface. The influences of the imperfect interface on the dispersive curves and the band gaps of periodic laminated piezoelectric composite are discussed.
Nonharmonic phonons in ?-iron at high temperatures
Mauger, L.; Lucas, M. S.; Muñoz, J. A.; Tracy, S. J.; Kresch, M.; Xiao, Yuming; Chow, Paul; Fultz, B.
2014-08-01
Phonon densities of states (DOS) of bcc ?-Fe57 were measured from room temperature through the 1044 K Curie transition and the 1185 K fcc ?-Fe phase transition using nuclear resonant inelastic x-ray scattering. At higher temperatures all phonons shift to lower energies (soften) with thermal expansion, but the low transverse modes soften especially rapidly above 700 K, showing strongly nonharmonic behavior that persists through the magnetic transition. Interatomic force constants for the bcc phase were obtained by iteratively fitting a Born-von Kármán model to the experimental phonon spectra using a genetic algorithm optimization. The second-nearest-neighbor fitted axial force constants weakened significantly at elevated temperatures. An unusually large nonharmonic behavior is reported, which increases the vibrational entropy and accounts for a contribution of 35 meV/atom in the free energy at high temperatures. The nonharmonic contribution to the vibrational entropy follows the thermal trend of the magnetic entropy, and may be coupled to magnetic excitations. A small change in vibrational entropy across the ?-? structural phase transformation is also reported.
Optimization of phononic filters via genetic algorithms
International Nuclear Information System (INIS)
A phononic crystal is commonly characterized by its dispersive frequency spectrum. With appropriate spatial distribution of the constituent material phases, spectral stop bands could be generated. Moreover, it is possible to control the number, the width, and the location of these bands within a frequency range of interest. This study aims at exploring the relationship between unit cell configuration and frequency spectrum characteristics. Focusing on 1D layered phononic crystals, and longitudinal wave propagation in the direction normal to the layering, the unit cell features of interest are the number of layers and the material phase and relative thickness of each layer. An evolutionary search for binary- and ternary-phase cell designs exhibiting a series of stop bands at predetermined frequencies is conducted. A specially formulated representation and set of genetic operators that break the symmetries in the problem are developed for this purpose. An array of optimal designs for a range of ratios in Young's modulus and density are obtained and the corresponding objective values (the degrees to which the resulting bands match the predetermined targets) are examined as a function of these ratios. It is shown that a rather complex filtering objective could be met with a high degree of success. Structures composed of the designed phononic crystals are excellent candidates for use in a wide range of applications including sound and vibration filteringand vibration filtering
Correlation-enhanced electron-phonon coupling
Yin, Zhiping
2015-03-01
Electron-phonon coupling (EPC) plays an important role in many material properties such as resistivity and conventional superconductivity. Accurate theoretical calculations of EPC in solids is essential for computational design, discovery and optimization of many functional materials. The widely used density functional theory (DFT) in the local density approximation (LDA) and generalized gradient approximation (GGA) can reasonably compute the EPC in weakly correlated materials but suffers from important shortcomings in strongly correlated materials. The self-energy of the quasiparticles in correlated materials modifies the LDA/GGA electronic structures hence the phonon frequencies and EPC. In this talk, I will discuss two types of underestimation of the EPC by LDA/GGA and propose a simple yet efficient methodology to evaluate the realistic EPC by using advanced electronic structure method beyond LDA/GGA. The extraordinarily high superconducting temperatures that are observed in two distinct classes of compounds-the bismuthates and the transition-metal chloronitrides can be readily accounted for by the correlation-enhanced EPC. Further impact of electronic correlation on the coupling of phonons and electronic degrees of freedom will also be discussed. This work was supported by the AFOSR-MURI Program.
Phonons in graphene with point defects
International Nuclear Information System (INIS)
The phonon density of states (DOS) of graphene with different types of point defects (carbon isotopes, substitution atoms, vacancies) is considered. Using a solvable model which is based on the harmonic approximation and the assumption that the elastic forces act only between nearest neighboring ions we calculate corrections to the graphene DOS dependent on the type and concentration of defects. In particular the correction due to isotopic dimers is determined. It is shown that a relatively small concentration of defects may lead to significant and specific changes in the DOS, especially at low frequencies, near the Van Hove points and in the vicinity of the K points of the Brillouin zone. In some cases defects generate one or several narrow gaps near the critical points of the phonon DOS as well as resonance states in the Brillouin zone regular points. All types of defects are characterized by the appearance of one or more additional Van Hove peaks near the (Dirac) K points and their singular contribution may be comparable with the effect of electron-phonon interaction. Besides, for low frequencies and near the critical points the relative change in density of states may be many times higher than the concentration of defects.
International Nuclear Information System (INIS)
Nonlinear radiation dynamics of a solid-state ring laser is studied in the region of laser parameters corresponding to the parametric resonance between the self-modulation and relaxation oscillations. Bistable regions are found in which, apart from the self-modulation regime of the first kind, a stable quasi-periodic self-modulation regime exists. Temporal and spectral emission parameters of counterpropagating waves are considered in the bistable self-modulation generation regimes. The effect of noise on the bistable self-modulation oscillations is studied. It is shown that during the interaction of noise, spectral peaks split at relaxation and self-modulation frequencies. (control of laser radiation parameters)
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.
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.
Phonon energy inversion in graphene during transient thermal transport
International Nuclear Information System (INIS)
This work reports on the phonon energy inversion in graphene nanoribbons: after initial localized thermal excitation, the energy of initial cold phonons (flexural mode: FM) becomes higher than that of local hot phonons (longitudinal and transverse modes: LM/TM). Such energy inversion holds for about 50 picoseconds. Two physical factors combine together to give rise of this phenomenon: one is the much faster heat conduction by FM phonons than that by LM/TM phonons, and the other factor is the strongly temperature-dependent energy exchange rate between FM and LM/TM phonons: 3.7×1010 s?1 at 84 K to 20.3×1010 s?1 at around 510 K.
Reduction of Thermal Conductivity by Nanoscale 3D Phononic Crystal
Yang, Lina; Yang, Nuo; Li, Baowen
2013-01-01
We studied how the period length and the mass ratio affect the thermal conductivity of isotopic nanoscale three-dimensional (3D) phononic crystal of Si. Simulation results by equilibrium molecular dynamics show isotopic nanoscale 3D phononic crystals can significantly reduce the thermal conductivity of bulk Si at high temperature (1000?K), which leads to a larger ZT than unity. The thermal conductivity decreases as the period length and mass ratio increases. The phonon dispersion curves show an obvious decrease of group velocities in 3D phononic crystals. The phonon's localization and band gap is also clearly observed in spectra of normalized inverse participation ratio in nanoscale 3D phononic crystal. PMID:23378898
Reduction of Thermal Conductivity by Nanoscale 3D Phononic Crystal
Yang, Lina; Li, Baowen
2013-01-01
The thermal conductivity of nanostructures needs to be as small as possible so that it will have a greater efficiency for solid-state electricity generation/refrigeration by thermoelectrics. We studied how the period length and the mass ratio affect the thermal conductivity of isotopic nanoscale 3D phononic crystal of Si. Simulation results by equilibrium molecular dynamics show isotopic nanoscale 3D phononic crystal can make a significance reduction on the thermal conductivity of bulk Si at high temperature,1000 K. Size and mass effects are obvious in manipulating thermal conductivity. The thermal conductivity decreases as the period length and mass ratio increases. The phonon dispersion curves show the decrease of group velocities in 3D phononic crystals. The phonon's localization and band gap is clearly shown in spectra of normalized inverse participation ratio in nanoscale 3D phononic crystal structure.
NATO Advanced Study Institute on Nonequilibrium Phonon Dynamics
1985-01-01
Phonons are always present in the solid state even at an absolute temperature of 0 K where zero point vibrations still abound. Moreover, phonons interact with all other excitations of the solid state and, thereby, influence most of its properties. Historically experimental information on phonon transport came from measurements of thermal conductivity. Over the past two decades much more, and much more detailed, information on phonon transport and on many of the inherent phonon interaction processes have come to light from experiments which use nonequilibrium phonons to study their dynamics. The resultant research field has most recently blossomed with the development of ever more sophisticated experimental and theoretical methods which can be applied to it. In fact, the field is moving so rapidly that new members of the research community have difficulties in keeping up to date. This NATO Advanced Study Institute (ASI) was organized with the objective of overcoming the information barrier between those expert...
Electron-phonon interaction in small-radius carbon nanotubes
Barnett, R; Kaxiras, E; Barnett, Ryan; Demler, Eugene; Kaxiras, Efthimios
2003-01-01
We perform analysis of the band structure, phonon dispersion, and electron-phonon interactions in ultrasmall (5,0) nanotubes. The large curvature makes these tubes metallic with a large density of states at the Fermi energy and leads to unusual electron-phonon interactions, with the dominant coupling coming from the out-of-plane phonons modes. By combining the frozen-phonon approximation with the RPA analysis of the giant Kohn anomaly in 1d we find parameters of the effective Fröhlich Hamiltonian for the conduction electrons and discuss possible instabilities of the electron-phonon system. We argue that the $2k_F$ charge-density wave dominates over the superconducting electron pairing and should open a pseudogap for quasiparticles at a temperature around 160 K.
Acoustic phonon transmission spectra in piezoelectric AlN/GaN Fibonacci phononic crystals
Sesion, P. D., Jr.; Albuquerque, E. L.; Chesman, C.; Freire, V. N.
2007-08-01
We study the acoustic-phonon transmission spectra in periodic and quasiperiodic (Fibonacci type) superlattices made up from the III-V nitride materials AlN and GaN. The phonon dynamics is described by a coupled elastic and electromagnetic equations within the static field approximation model, stressing the importance of the piezoelectric polarization field in a strained condition. We use a transfer-matrix treatment to simplify the algebra, which would be otherwise quite complicated, allowing a neat analytical expressions for the phonon transmission coefficients. Numerical results, for the normal incidence case, show a strike self-similar pattern for both hexagonal (class 6 mm) and cubic symmetries crystalizations of the nitrides.
Control of Dephasing and Phonon Emission in Coupled Quantum Dots
Debald, S.; Brandes, T.; Kramer, 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 eit...
Phonon-assisted tunneling through a double quantum dot system
Tagani, M. Bagheri; Soleimani, H. Rahimpour
2012-01-01
Electron transport through a double quantum dot system is studied with taking into account electron-phonon interaction. The Keldysh nonequilibrium Green function formalism is used to compute the current and transmission coefficient of the system. The influence of the electron-phonon interaction, interdot tunneling, and temperature on the density of states and current is analyzed. Results show that although the electron-phonon interaction results in the appearance of side pea...
Phonon Hall thermal conductivity from Green-Kubo formula
Wang, Jian-sheng; Zhang, Lifa
2009-01-01
We derive a formula for the thermal conductivity tensor of a ballistic phonon Hall model. It is found that, although the diagonal elements of the conductivity tensor diverge to infinite, the off-diagonal elements are finite,antisymmetric, and odd in magnetic field. The off-diagonal elements are non-zero only if the dynamic matrix of the phonon system breaks mirror reflection symmetry. The results are obtained without perturbative assumptions about the spin-phonon interactions.
Nanophotonic cavity optomechanics with propagating phonons in microwave Ku band
Li, Huan; Liu, Qiyu; Li, Mo
2015-01-01
Sideband-resolved coupling between multiple photonic nanocavities and propagating mechanical waves in microwave Ku-band is demonstrated. Coherent and strong photon-phonon interaction is manifested with optomechanically induced transparency and absorption, and phase-coherent interaction in multiple cavities. Inside an echo chamber it is shown that a phonon pulse can interact with an embedded nanocavity for multiple times. Our device provides a scalable platform to optomechanically couple phonons and photons for microwave photonics and quantum photonics.
Phonon energy in an anharmonic quasi-one-dimensional solid
Grado-Caffaro, M.A.; M. Grado-Caffaro
2011-01-01
For the first time, the phonon energy per unit volume in a large anharmonic quasi-one-dimensional solid is determined by considering all polarizations of the various modes of phonon propagation and by assuming the solid as a lattice of atoms behaving as Morse oscillators. In this context, the equilibrium phonon occupation number, which is given by the Bose distribution, replaces formally the vibrational quantum number into the expression for the Morse-oscillator energy. In addition, the quasi...
Fluid phonons, protoinflationary dynamics and large-scale gravitational fluctuations
Giovannini, Massimo
2013-01-01
We explore what can be said on the effective temperature and sound speed of a statistical ensemble of fluid phonons present at the onset of a conventional inflationary phase. The phonons are the actual normal modes of the gravitating and irrotational fluid that dominates the protoinflationary dynamics. The bounds on the tensor to scalar ratio result in a class of novel constraints involving the slow roll parameter, the sound speed of the phonons and the temperature of the pl...
Observation of Anomalous Phonon Softening in Bilayer Graphene
Yan, Jun; Henriksen, Erik A.; Kim, Philip; Pinczuk, Aron
2007-01-01
The interaction of electron-hole pairs with lattice vibrations exhibits a wealth of intriguing physical phenomena. The Kohn anomaly is a renowned example where electron-phonon coupling leads to non-analytic phonon dispersion at specific momentum nesting the Fermi surface. Here we report evidence of another type of phonon anomaly discovered by low temperature Raman spectroscopy in bilayer graphene where the charge density is modulated by the electric field effect. This anomal...
Phonon-assisted tunneling and its dependence on pressure
International Nuclear Information System (INIS)
First the mechanism of phonon-assisted tunneling has been investigated. The indirect tunnel current density has been computed after taking the amplitude of the time dependent perturbation as the energy of the lattice vibration. Later the pressure dependence of the phonon-assisted tunnel current has been computed using Payne's expression for the dependence of phonon frequency on pressure. Very good qualitative agreements are obtained between predicted and observed characteristics. (author)
Periodic Anderson model with electron-phonon correlated conduction band
Zhang, Peng; Reis, Peter; Tam, Ka-Ming; Jarrell, Mark; Moreno, Juana; Assaad, Fakher; McMahan, Andy
2012-01-01
This paper reports dynamical mean field calculations for the periodic Anderson model in which the conduction band is coupled to phonons. Motivated in part by recent attention to the role of phonons in the $\\gamma$-$\\alpha$ transition in Ce, this model yields a rich and unexpected phase diagram which is of intrinsic interest. Specifically, above a critical value of the electron-phonon interaction, a first order transition with two coexisting phases develops in the temperature...
Theory of phonon dynamics in an ion trap
Dutta, T.; Mukherjee, M.; 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 ra...
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 demons 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.
Phonons and electron-phonon coupling in graphene-h-BN heterostructures
International Nuclear Information System (INIS)
First principle calculations of the phonons of graphene-h-BN heterostructures are presented and compared to those of the constituents. It is shown that AA and AB' stacking are not only energetically less favoured than AB but also dynamically unstable. Low energy flat phonon branches of h-BN character with out of plane displacement have been identified and their coupling to electrons in graphene has been evaluated. (copyright 2014 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Phonons and electron-phonon coupling in graphene-h-BN heterostructures
Energy Technology Data Exchange (ETDEWEB)
Slotman, Guus J.; Wijs, Gilles A. de; Fasolino, Annalisa; Katsnelson, Mikhail I. [Institute for Molecules and Materials, Radboud University Nijmegen (Netherlands)
2014-10-15
First principle calculations of the phonons of graphene-h-BN heterostructures are presented and compared to those of the constituents. It is shown that AA and AB' stacking are not only energetically less favoured than AB but also dynamically unstable. Low energy flat phonon branches of h-BN character with out of plane displacement have been identified and their coupling to electrons in graphene has been evaluated. (copyright 2014 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Phonon dispersion and lifetimes in MgB2
Daghero, Dario
2003-01-01
We measure phonon dispersion and linewidth in a single crystal of MgB2 along the Gamma-A, Gamma-M, and A-L directions using inelastic x-ray scattering. We use density functional theory to compute the effect of both electron-phonon coupling and anharmonicity on the linewidth, obtaining excellent agreement with experiment. Anomalous broadening of the E(2g) phonon mode is found all along Gamma-A. The dominant contribution to the linewidth is always the electron-phonon coupling
Phonon dispersion and lifetimes in MgB2
Shukla, A; D'Astuto, M; Lazzeri, M; Mauri, F; Bellin, C; Krisch, M H; Karpinski, J; Kazakov, S M; Jun, J; Daghero, D; Parlinski, K; Shukla, Abhay; Calandra, Matteo; Astuto, Matteo d'; Lazzeri, Michele; Mauri, Francesco; Bellin, Christophe; Krisch, Michael
2003-01-01
We measure phonon dispersion and linewidth in a single crystal of MgB_2 along the Gamma-A and Gamma-M directions using inelastic X-Ray scattering. Anomalous broadening of the E_2g phonon mode is found along Gamma-A only. We use Density Functional Theory to compute the effect of both electron-phonon coupling and anharmonicity on the linewidth, obtaining excellent agreement with experiment. The dominant contribution to the linewidth is always the electron-phonon coupling.
Theory of the phonon Hall effect in paramagnetic dielectrics.
Sheng, L; Sheng, D N; Ting, C S
2006-04-21
Based upon Raman spin-lattice interaction, we propose a theoretical model for the phonon Hall effect in paramagnetic dielectrics, which was discovered recently in an experiment [C. Strohm, G. L. J. A. Rikken, and P. Wyder, Phys. Rev. Lett. 95, 155901 (2005).]. The phonon Hall effect is revealed to be a phonon analogue to the anomalous Hall effect in electron systems. The thermal Hall conductivity is calculated by using the Kubo formula. Our theory reproduces the essential experimental features of the phonon Hall effect, including the sign, magnitude, and linear magnetic field dependence of the thermal Hall conductivity. PMID:16712169
Calculations of the $A_{1}$ phonon frequency in photoexcited Tellurium
Tangney, P
1999-01-01
Calculations of the A_1 phonon frequency in photoexcited tellurium are presented. The phonon frequency as a function of photoexcited carrier density and phonon amplitude is determined. Recent pump probe experiments are interpreted in the light of these calculatons. It is proposed that, in conjunction with measurements of the phonon period in ultra-fast pump-probe reflectivity experiments, the calculated frequency shifts can be used to infer the evolution of the density of photoexcited carriers on a sub-picosecond time-scale.
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
Phonon dynamics and Urbach energy studies of MgZnO alloys
Huso, Jesse; Che, Hui; Thapa, Dinesh; Canul, Amrah; McCluskey, M. D.; Bergman, Leah
2015-03-01
The MgxZn1-xO alloy system is emerging as an environmentally friendly choice in ultraviolet lighting and sensor technologies. Knowledge of defects which impact their optical and material properties is a key issue for utilization of these alloys in various technologies. The impact of phase segregation, structural imperfections, and alloy inhomogeneities on the phonon dynamics and electronic states of MgxZn1-xO thin films were studied via selective resonant Raman scattering (SRRS) and Urbach analyses, respectively. A series of samples with Mg composition from 0-68% were grown using a sputtering technique, and the optical gaps were found to span a wide UV range of 3.2-5.8 eV. The extent of the inherent phase segregation was determined via SRRS using two UV-laser lines to achieve resonance with the differing optical gaps of the embedded cubic and wurtzite structural domains. The occurrence of Raman scattering from cubic structures is discussed in terms of relaxation of the selection rules due to symmetry breaking by atomic substitutions. The Raman linewidth and Urbach energy behavior indicate the phase segregation region occurs in the range of 47-66% Mg. Below the phase segregation, the longitudinal optical phonons are found to follow the model of one-mode behavior. The phonon decay model of Balkanski et al. indicates that the major contributor to Raman linewidth arises from the temperature-independent term attributed to structural defects and alloy inhomogeneity, while the contribution from anharmonic decay is relatively small. Moreover, a good correlation between Urbach energy and Raman linewidth was found, implying that the underlying crystal dynamics affecting the phonons also affect the electronic states. Furthermore, for alloys with low Mg composition structural defects are dominant in determining the alloy properties, while at higher compositions alloy inhomogeneity cannot be neglected.
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
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...
Zero-phonon linewidth and phonon satellites in the optical absorption of nanowire-based quantum dots
Lindwall, Greta; Wacker, Andreas; Weber, Carsten; Knorr, Andreas
2007-01-01
The optical properties of quantum dots embedded in a catalytically grown semiconductor nanowire are studied theoretically. In comparison to dots in a bulk environment, the excitonic absorption is strongly modified by the one-dimensional character of the nanowire phonon spectrum. In addition to pronounced satellite peaks due to phonon-assisted absorption, we find a finite width of the zero-phonon line already in the lowest-order calculation.
Effects of phonon-phonon coupling on low-lying states in neutron-rich Sn isotopes
Severyukhin, A. P.; V. V. Voronov; Van Giai, Nguyen
2004-01-01
Starting from an effective Skyrme interaction we present a method to take into account the coupling between one- and two-phonon terms in the wave functions of excited states. The approach is a development of a finite rank separable approximation for the quasiparticle RPA calculations proposed in our previous work. The influence of the phonon-phonon coupling on energies and transition probabilities for the low-lying quadrupole and octupole states in the neutron-rich Sn isotop...
International Nuclear Information System (INIS)
A recently developed self-consistent ab initio lattice dynamical method has been applied to the high temperature body centered cubic (bcc) phase of La and Th, which are dynamically unstable at low temperatures. The bcc phase of these metals is found to be stabilized by phonon-phonon interactions. The calculated high temperature phonon frequencies for La are found to be in good agreement with the corresponding experimental data.
Cooling carbon nanotubes to the phononic ground state with constant electron current
Zippilli, Stefano; Bachtold, Adrian
2008-01-01
We present a quantum theory of cooling of a mechanical resonator using back-action with constant electron current. The resonator device is based on a doubly clamped nanotube, which mechanically vibrates and acts as a double quantum dot for electron transport. Mechanical vibrations and electrons are coupled electrostatically using an external gate. The fundamental eigenmode is cooled by absorbing phonons when electrons tunnel through the double quantum dot. We identify the regimes in which ground state cooling can be achieved for realistic experimental parameters.
Quantifying electron-phonon coupling in CdTe1?xSex nanocrystals via coherent phonon manipulation
International Nuclear Information System (INIS)
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.
Energy Technology Data Exchange (ETDEWEB)
Raetsep, Margus [Institute of Physics, University of Tartu, Riia 142, 51014 Tartu (Estonia); Freiberg, Arvi [Institute of Physics, University of Tartu, Riia 142, 51014 Tartu (Estonia) and Institute of Molecular and Cell Biology, University of Tartu, Tartu (Estonia)]. E-mail: arvi.freiberg@ut.ee
2007-11-15
The electron-phonon and vibronic couplings governing the spectral properties have been studied in the Fenna-Matthews-Olson (FMO) bacteriochlorophyll a (BChl a)-protein complex at 4.5 K using a spectrally selective difference fluorescence line-narrowing technique. The complex is a part of the light-harvesting system of green photosynthetic bacteria. Its lowest-energy absorption band, peaking at 826 nm and responsible for the fluorescence, is believed to be due to Q{sub y} transitions of largely isolated molecules. One of the main merits of the used method compared with the more common fluorescence line narrowing is that the zero-phonon lines (ZPL) resonant with the excitation laser can be accurately measured, allowing precise determination of the Huang-Rhys (HR) factors, the main characteristics of the linear electron-phonon and vibronic coupling strengths. Over 60 individual vibrational modes of intra- and intermolecular origin have been resolved in the energy range of 45-1600 cm{sup -1}. The small HR factors for these modes, ranging between 0.001 and 0.018, add up to a value of S {sub vib}=0.38{+-}0.07. The effective HR factor for the phonons, S {sub ph}, was found clearly wavelength-dependent, varying from {approx}0.7 at short wavelengths to {approx}0.3 at the long-wavelength tail of the absorption spectrum. Coupling between the BChl a molecules is likely responsible for this wavelength dependence.
International Nuclear Information System (INIS)
The electron-phonon and vibronic couplings governing the spectral properties have been studied in the Fenna-Matthews-Olson (FMO) bacteriochlorophyll a (BChl a)-protein complex at 4.5 K using a spectrally selective difference fluorescence line-narrowing technique. The complex is a part of the light-harvesting system of green photosynthetic bacteria. Its lowest-energy absorption band, peaking at 826 nm and responsible for the fluorescence, is believed to be due to Qy transitions of largely isolated molecules. One of the main merits of the used method compared with the more common fluorescence line narrowing is that the zero-phonon lines (ZPL) resonant with the excitation laser can be accurately measured, allowing precise determination of the Huang-Rhys (HR) factors, the main characteristics of the linear electron-phonon and vibronic coupling strengths. Over 60 individual vibrational modes of intra- and intermolecular origin have been resolved in the energy range of 45-1600 cm-1. The small HR factors for these modes, ranging between 0.001 and 0.018, add up to a value of S vib=0.38±0.07. The effective HR factor for the phonons, S ph, was found clearly wavelength-dependent, varying from ?0.7 at short wavelengths to ?0.3 at the long-wavelength tail of the absorption spectrum. Coupling between the BChl a molecules is likely responsible for this wavelength dependence
Czech Academy of Sciences Publication Activity Database
Jakubczak, Krzysztof; Mocek, Tomáš; Rus, Bed?ich; H?ebí?ek, J.; Sawicka, Magdalena; Kim, I.J.; Park, S.B.; Kim, T.K.; Lee, G.H.; Nam, C. H.; Chalupský, Jaromír; Hájková, V?ra; Juha, Libor; Sobota, Jaroslav; Fo?t, Tomáš
Bellingham : SPIE, 2009 - (Khounsary, A.; Morawe, C.; Goto, S.), 736010/1-736010/11 ISBN 978-0-8194-7738-5. ISSN 0277-786X. - (Proceedings of SPIE. 7448). [Advances in X-Ray/EUV Optics and Components IV. San Diego (US), 03.08.2009-05.08.2009] R&D Projects: GA AV ?R KAN300100702; GA MŠk LC510; GA MŠk(CZ) LC528; GA MŠk LA08024; GA ?R GC202/07/J008 Institutional research plan: CEZ:AV0Z10100523; CEZ:AV0Z20650511 Keywords : High-order Harmonic Generation ( HHG ) * materials machining * nanopatterning * femtosecond laser pulses * Laser Induced Periodic Surface Structures (LIPSS) Subject RIV: BH - Optics, Masers, Lasers http://dx.doi.org/10.1117/12.826404
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 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
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.
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
The Role of Phonon Mechanism in Electron Coupling
Joukovskaya, L.
2002-01-01
In this article in the framework of generalized Frolich model we consider electron-spin-phonon system. A parameter of electron-spin-phonon interaction is found. It is shown its interrelation with experiments on isotope-effect on high temperature superconductors and asymptotic transformation to BCS theory.
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
International Nuclear Information System (INIS)
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 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.
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 density of states in V3Si
International Nuclear Information System (INIS)
The observation by inelastic neutron scattering techniques of a high energy peak in the phonon spectrum (14 THz) of V3Si is reported, and is attributed to a peak in the phonon density of states due to vanadium motions by the incoherent inelastic neutron scattering process
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.
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)
Robust and optimal laser cooling of trapped ions
Cerrillo, J.; 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...
Fast and robust laser cooling of trapped systems.
Cerrillo, J; Retzker, A; Plenio, M B
2010-01-29
We present a robust and fast laser cooling scheme suitable for trapped ions, atoms, or cantilevers. 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 applications. PMID:20366705
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
Resonance enhancement of electron-phonon interaction in nanostructures
International Nuclear Information System (INIS)
The theory of electron-phonon interaction in quantum well is developed taking into account the influence of interface optical phonons. A detailed analysis of the dependence of polaron effective mass on the quantum well size and dielectric characteristics of barrier material is performed. It is shown that quasi-two-dimensional polaron may arise in narrow quantum wells. However, the interaction parameters are determined by effective mass of carriers in the quantum well and interface optical phonons frequencies. If the barriers are made of non-polar material, the polaron effective mass depends on the quantum well width. By increasing the quantum well width, a new mechanism of amplification of the electron-phonon interaction is realized. It occurs in the case of coincidence of the optical phonon energy with the energy of one of the electronic transitions. This leads to a nonmonotonic dependence of polaron effective mass on the quantum well width
Phonon anharmonicity of monoclinic zirconia and yttrium-stabilized zirconia
Li, C. W.; Smith, H. L.; Lan, T.; Niedziela, J. L.; Muñoz, J. A.; Keith, J. B.; Mauger, L.; Abernathy, D. L.; Fultz, B.
2015-04-01
Inelastic neutron scattering measurements on monoclinic zirconia (ZrO2 ) and 8 mol% yttrium-stabilized zirconia were performed at temperatures from 300 to 1373 w K . Temperature-dependent phonon densities of states (DOS) are reported, as are Raman spectra obtained at elevated temperatures. First-principles lattice dynamics calculations with density functional theory gave total and partial phonon DOS curves and mode Grüneisen parameters. These mode Grüneisen parameters were used to predict the experimental temperature dependence of the phonon DOS with partial success. However, substantial anharmonicity was found at elevated temperatures, especially for phonon modes dominated by the motions of oxygen atoms. Yttrium-stabilized zirconia (YSZ) was somewhat more anharmonic and had a broader phonon spectrum at low temperatures, owing in part to defects in its structure. YSZ also has a larger vibrational entropy than monoclinic zirconia.
Phonon Squeezed States Quantum Noise Reduction in Solids
Hu, X; Hu, Xuedong; Nori, Franco
1999-01-01
This article discusses quantum fluctuation properties of a crystal lattice, and in particular, phonon squeezed states. Squeezed states of phonons allow a reduction in the quantum fluctuations of the atomic displacements to below the zero-point quantum noise level of coherent phonon states. Here we discuss our studies of both continuous-wave and impulsive second-order Raman scattering mechanisms. The later approach was used to experimentally suppress (by one part in a million only, which might be noise) fluctuations in phonons (and it has not been clearly reproduced by other experimental groups). We calculate the expectation values and fluctuations of both the atomic displacement and the lattice amplitude operators, as well as the effects of the phonon squeezed states on macroscopically measurable quantities, such as changes in the dielectric constant. These results are compared with recent experiments. Further information, including preprints and animations, are available in http://www-personal.engin.umich.ed...
Phonon dispersion measured directly from molecular dynamics simulations
Kong, Ling Ti
2011-10-01
A method to measure the phonon dispersion of a crystal based on molecular dynamics simulation is proposed and implemented as an extension to an open source classical molecular dynamics simulation code LAMMPS. In the proposed method, the dynamical matrix is constructed by observing the displacements of atoms during molecular dynamics simulation, making use of the fluctuation-dissipation theory. The dynamical matrix can then be employed to compute the phonon spectra by evaluating its eigenvalues. It is found that the proposed method is capable of yielding the phonon dispersion accurately, while taking into account the anharmonic effect on phonons simultaneously. The implementation is done in the style of fix of LAMMPS, which is designed to run in parallel and to exploit the functions provided by LAMMPS; the measured dynamical matrices could be passed to an auxiliary postprocessing code to evaluate the phonons.
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.
Dang, N. C.; Hayes, J. M.; Reinot, T.; Small, G. J.
2004-02-01
A detailed treatment of the relationship between the dispersive growth kinetics of the zero-phonon hole (ZPH) of an impurity molecule in an amorphous host and burn fluence broadening of the ZPH is presented. Focus is on non-photochemical hole burning (NPHB). The equation used for simulations accounts for dispersion due to a distribution of tunneling parameters ( ?-distribution), the angle between the laser polarization and the transition dipole ( ?-distribution), and off-resonant absorption of the zero-phonon line ( ?-distribution). Two cases are considered: burned laser linewidth narrow relative to the homogeneous width of the zero-phonon line; and the reverse situation. Results are presented for two model systems whose parameter values are similar to those of aluminum phthalocyanine tetrasulphonate (APT) in hyperquenched glassy water and in hyperquenched glassy ethanol. For comparison, results are presented for the case where the hole growth kinetics are non-dispersive (single-exponential). It is found that at the early stage of burning fluence broadening is considerably more severe for a dispersive system than for a non-dispersive system. A straightforward explanation for this is given. The results are compared with those of earlier works on dispersive hole growth kinetics and fluence broadening. The results reveal the types of experiment needed to understand the aforementioned relationship, a requirement for determination of the homogeneous width of the ZPH that reflects the dynamics of the system.
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.
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...
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.
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)
Hamiltonian of Acoustic Phonons in Inhomogeneous Solids
Directory of Open Access Journals (Sweden)
Vladimir Labas
2013-03-01
Full Text Available Theoretical solid-state physicists formulate their models usually in the form of a Hamiltonian. In quantum mechanics, the Hamilton operator (Hamiltonian is of fundamental importance in most formulations of quantum theory. Mentioned operator corresponds to the total energy of the system and its spectrum determines the set of possible outcomes when one measures the total energy. Interpretation of results obtained by the applying of models based on the Hamiltonian indicates very specific mechanisms of some observed phenomena that are not fully consistent with the experience. Such approach may occasionally lead to surprises when obtained results are confronted with expectations. The aim of this work is to find Hamilton operator of acoustic phonons in inhomogeneous solids. The transport of energy in the vibrating crystal consisting of ions whose properties differ over long distances is described in the work. We modeled crystal lattice by 1D “inhomogeneous” ionic chain vibrating by acoustic frequencies and found the Hamiltonian of such system in the second quantization. The influence of long-distance inhomogeneities on the acoustic phonons quantum states can be discussed on basis of our results.
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)
Palmer, A. J.; Hess, L. D.; Stephens, R. R.; Pepper, D. M.
1977-01-01
The results of a two-year investigation into the possibility of developing continuous wave excimer lasers are reported. The program included the evaluation and selection of candidate molecular systems and discharge pumping techniques. The K Ar/K2 excimer dimer molecules and the xenon fluoride excimer molecule were selected for study; each used a transverse and capillary discharges pumping technique. Experimental and theoretical studies of each of the two discharge techniques applied to each of the two molecular systems are reported. Discharge stability and fluorine consumption were found to be the principle impediments to extending the XeF excimer laser into the continuous wave regime. Potassium vapor handling problems were the principal difficulty in achieving laser action on the K Ar/K2 system. Of the four molecular systems and pumping techniques explored, the capillary discharge pumped K Ar/K2 system appears to be the most likely candidate for demonstrating continuous wave excimer laser action primarily because of its predicted lower pumping threshold and a demonstrated discharge stability advantage.
Phonon line shapes in the vortex state of the phonon-mediated superconductor YNi2B2C
International Nuclear Information System (INIS)
We present an inelastic neutron-scattering study of phonon line shapes in the vortex state of the type II superconductor YNi2B2C. In a previous study [1] we showed that certain phonons exhibit a clear signature of the superconducting gap 2? on entering the superconducting state. Our interest was to find out whether or not the line shape of such phonons reflects the inhomogeneous nature of the vortex state induced by a magnetic field smaller than the upper critical field Bc2.We found that this is indeed the case because the observed phonon line shapes can be well described by a model considering the phonon as a local probe of the spatial variation of the superconducting gap.
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)
Phong, Tran Cong; Phuong, Le Thi Thu; Hien, Nguyen Dinh; Lam, Vo Thanh
2015-07-01
We investigate the influence of phonon confinement on the optically detected magneto-phonon resonance (ODMPR) effect and ODMPR line-width in quantum wells. The ODMPR conditions as functions of the well's width and the photon energy are also obtained. The shifts of ODMPR peaks caused by the confined phonon are discussed. The numerical result for the GaAs/AlAs quantum well shows that in the two cases of confined and bulk phonons, the line-width (LW) decreases with increasing well's width and increases with increasing temperature. Furthermore, in the small range of the well's width, the influence of phonon confinement plays an important role and cannot be neglected in reaching the ODMPR line-width.
Electron–phonon coupling in quantum-well states of the Pb/Si(1?1?1) system
International Nuclear Information System (INIS)
The electron–phonon coupling parameters in the vicinity of the ?-bar point, ?( ?-bar ), for electronic quantum well states in epitaxial lead films on a Si(1?1?1) substrate are measured using 5, 7 and 12 ML films and femtosecond laser photoemission spectroscopy. The ?( ?-bar ) values in the range of 0.6–0.9 were obtained by temperature-dependent line width analysis of occupied quantum well states and found to be considerably smaller than the momentum averaged electron–phonon coupling at the Fermi level of bulk lead, (? = 1.1–1.7). The results are compared to density functional theory calculations of the lead films with and without interfacial stress. It is shown that the discrepancy can not be explained by means of confinement effects or simple structural modifications of the Pb films and, thus, is attributed to the influence of the substrate on the Pb electronic and vibrational structures. (fast track communication)
Makovetskii, D N
2001-01-01
The microwave phonon stimulated emission (SE) has been experimentally and numerically investigated in a nonautonomous microwave acoustic quantum generator, called also microwave phonon laser or phaser (see previous works arXiv:cond-mat/0303188 ; arXiv:cond-mat/0402640 ; arXiv:nlin.CG/0703050) Phenomena of branching and long-time refractority (absence of the reaction on the external pulses) for deterministic chaotic and regular processes of SE were observed in experiments with various levels of electromagnetic pumping. At the pumping level growth, the clearly depined increasing of the number of coexisting SE states has been observed both in real physical experiments and in computer simulations. This confirms the analytical estimations of the branching density in the phase space. The nature of the refractority of SE pulses is closely connected with the pointed branching and reflects the crises of strange attractors, i.e. their collisions with unstable periodic components of the higher branches of SE states in t...
Mollow triplet for cavity-mediated laser cooling
Kim, Oleg; Beige, Almut
2013-01-01
Here we analyse cavity-mediated laser cooling for an experimental setup with an external trap which strongly confines the motion of a particle in the direction of the cavity axis. It is shown that the stationary state phonon number exhibits three sharp minima as a function of the atom-cavity detuning due to a direct atom-phonon-photon coupling term in the system Hamiltonian. These resonances have the same origin as the Mollow triplet in the resonance fluorescence of a laser-...
Czech Academy of Sciences Publication Activity Database
Cihelka, Jaroslav; Matulková, Irena; Sovová, Kristýna; Kamas, Michal; Kubelík, Petr; Ferus, Martin; Juha, Libor; Civiš, Svatopluk
2009-01-01
Ro?. 39, 3-4 (2009), s. 227-227. ISSN 0169-6149 R&D Projects: GA MŠk LC510; GA MŠk(CZ) LC528; GA ?R GA203/06/1278; GA MŠk LA08024 Institutional research plan: CEZ:AV0Z40400503; CEZ:AV0Z10100523 Keywords : planetary atmosphere * lasers * spectroscopy Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.053, year: 2009
International Nuclear Information System (INIS)
The therapy with laser emitting low intensity has been currently used in the most diverse fields of medicine as therapeutic conduct for pain. It is a non invasive, painless, non-thermal and aseptic type therapy, without any collateral effects, having a good cost/benefit relationship. However, for the therapy with low-intensity laser to result in positive effects, a correct diagnosis is fundamental, as well as a protocol of adequate application. n odontology, the majority of patients diagnosed with temporomandibular disorders (TMD), present pain and limitations in the movements of the jaw. In this work, a GaAlAs laser emitting low intensity, was used, ?=785 nm, in patients having a dysfunction of the temporomandibular joint with a complaint of pain. Twenty patients were divided into two groups. The group treated received laser therapy in the temporomandibular articulations and in the muscles affected. The dose applied was 45 J/cm2, while the ten patients in the control group received 0 J/cm2, in a total of nine applications, carried out three times a week, during three weeks. he evaluation of the patients was made through clinical examinations of manual palpation of the masseter, temporal, cervical, posterior neck and sternocleidomastoid muscles, and measurements of opening and laterality of the mouth. The results obtained showed a diminishing of the pain and an increase of the mandibular mobility in the patients treated, when compared to the control group. These results point to this therapy as being an important tool in the treatment of pain in patients with a dysfunction in the TMJ, indicating this therapeutic modality as a co-adjuvant in these treatments. (author)
Laser action from 2,6,8-trisubstituted-1,3,5,7-tetramethyl-pyrromethene-BF(2) complexes: part 2.
Boyer, J H; Haag, A; Soong, M L; Thangaraj, K; Pavlopoulos, T G
1991-09-20
In laser activity 1,3,5,7-tetramethyl-2,6-dicarboethoxy-8- cyanopyrromethene-BF(2)complex 5 under flash-lamp excitation was approximately 1.8 times more energy efficient than Rhodamine-B; about the same efficiency of Rhodamine-575 was found for 1,3,5, 7-tetramethyl-2,6,8-triethylpyrromethene- BF(2) complex 2. PMID:20706458
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)
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)
Emergent Chern-Simons excitations due to electron--phonon interaction
Sinner, Andreas
2015-01-01
We address the problem of Dirac fermions interacting with longitudinal phonons. A gap in the spectrum of fermions leads to the emergence of the Chern--Simons excitations in the spectrum of phonons. We study the effect of those excitations on observable quantities: the phonon dispersion, the phonon spectral density, and the Hall conductivity.
Bulk viscosity coefficients due to phonons in superfluid neutron stars
International Nuclear Information System (INIS)
We calculate the three bulk viscosity coefficients as arising from the collisions among phonons in superfluid neutron stars. We use effective field theory techniques to extract the allowed phonon collisional processes, written as a function of the equation of state of the system. The solution of the dynamical evolution of the phonon number density allows us to calculate the bulk viscosity coefficients as function of the phonon collisional rate and the phonon dispersion law, which depends on the neutron pairing gap. Our method of computation is rather general, and could be used for different superfluid systems, provided they share the same underlying symmetries. We find that the behavior with temperature of the bulk viscosity coefficients is dominated by the contributions coming from the collinear regime of the 2?3 phonon processes. For typical star radial pulsation frequencies of ? ? 104s?1, we obtain that the bulk viscosity coefficients at densities n?>4n0 are within 10% from its static value for T?9 K and for the case of strong neutron superfluidity in the core with a maximum value of the 3P2 gap above 1 MeV, while, otherwise, the static solution is not a valid approximation to the bulk viscosity coefficients. Compared to previous results from Urca and modified Urca reactions, we conclude that at T ? 109K phonon collisions give the leading contribution to the bulk viscosities in the core of the neutron stars, except for n ? 2n0 when the opening of the Urca processes takes place
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)
Perrin, N.
1980-01-01
We study the steady state of the coupled-quasiparticle pair phonon system in a superconducting film in the présence of an optical irradiation for various strengths of the light. A numerical solution of the coupled equations is performed, the quasiparticle distribution being represented by a Fermi-Dirac distribution with an effective temperature T*. It is shown that the quantitative response of the superconducting film to the drive depends strongly on the imposed conditions : intensity of the...
Khelif, Abdelkrim
2012-01-01
We present in this paper a theoretical and an experimental study of surface acoustic wave propagations in pillars-based phononic crystal. This artificial crystal is made up of cylindrical pillars deposited on a semi- infinite medium and arranged in a square array. With appropriate choice of the geometrical parameters, this structure can display two kinds of complete band gaps for surface guided waves, a low frequency gap based on locally resonant mode of pillars as well as a higher frequency ...
Influence of anharmonic phonon decay on self-heating in Si nanowire transistors
International Nuclear Information System (INIS)
Anharmonic phonon-phonon scattering is incorporated into an electro-thermal quantum transport approach based on the nonequilibrium Green's function formalism. Electron-phonon and phonon-phonon interactions are taken into account through scattering self-energies solved in the self-consistent Born approximation. While studying self-heating effects in ultra-scaled Si nanowire transistors, it is found that the phonon decay process softens the artificial accumulation of high energy phonons caused by electron relaxations close to the drain region. This leads to an increase of the device current in the ON-state and a reduction of the effective lattice temperature
Dynamics of the development of high-frequency nonequilibrium phonons in a thin film
International Nuclear Information System (INIS)
The propagation, in a semiconductor film, of high-frequency nonequilibrium phonons that have been formed as a result of cooling of a photoexcited electron-hole plasma is investigated. The only anharmonic process for the nonequilibrium phonons is assumed to be spontaneous decay. Scattering of phonons by impurities is neglected. The film thickness is assumed to be a small quantity ??l (?), where ? if the phonon group velocity and ?l(?) is the decay time for a longitudinal phonon. It is established that energy is transported in space by phonons moving almost parallel to the film surfaces, and the characteristic length scale of the phonon nonequilibrium is anti r ? ?t
Tunneling in suspended carbon nanotubes assisted by longitudinal phonons
Sapmaz, S; Blanter, Y M; Dekker, C; Van der Zant, H S J; Blanter, Ya.M.
2006-01-01
Current-voltage characteristics of suspended single-wall carbon nanotube quantum dots show a series of steps equally spaced in voltage. The energy scale of this harmonic, low-energy excitation spectrum is consistent with that of the longitudinal low-k phonon mode (stretching mode) in the nanotube. Agreement is found with a Franck-Condon-based model in which the phonon-assisted tunneling process is modeled as a coupling of electronic levels to underdamped quantum harmonic oscillators. Comparison with this model indicates a rather strong electron-phonon coupling factor of order unity.