- Home
- ▪
- About
- ▪
- News
- ▪
- Advanced Search
- ▪
- Mobile
- ▪
- Contact Us
- ▪
- Site Map
- ▪
- Help

1

Phonon laser action in a tunable, two-level photonic molecule

The phonon analog of an optical laser has long been a subject of interest. We demonstrate a compound microcavity system, coupled to a radio-frequency mechanical mode, that operates in close analogy to a two-level laser system. An inversion produces gain, causing phonon laser action above a pump power threshold of around 50 $\\mu$W. The device features a continuously tunable, gain spectrum to selectively amplify mechanical modes from radio frequency to microwave rates. Viewed ...

Grudinin, Ivan S.; Painter, O.; Vahala, Kerry J.

2009-01-01

2

Physical mechanisms of coherent acoustic phonons generation by ultrafast laser action.

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

Ruello, Pascal; Gusev, Vitalyi E

2015-02-01

3

Polaron action for multimode dispersive phonon systems

Path-integral approach to the tight-binding polaron is extended to multiple optical phonon modes of arbitrary dispersion and polarization. The non-linear lattice effects are neglected. Only one electron band is considered. The electron-phonon interaction is of the density-displacement type, but can be of arbitrary spatial range and shape. Feynman's analytical integration of ion trajectories is performed by transforming the electron-ion forces to the basis in which the phonon dynamical matrix is diagonal. The resulting polaron action is derived for the periodic and shifted boundary conditions in imaginary time. The former can be used for calculating polaron thermodynamics while the latter for the polaron mass and spectrum. The developed formalism is the analytical basis for numerical analysis of such models by path-integral Monte Carlo methods.

Kornilovitch, P

2005-01-01

4

Polaron action for multimode dispersive phonon systems

Path-integral approach to the tight-binding polaron is extended to multiple optical phonon modes of arbitrary dispersion and polarization. The non-linear lattice effects are neglected. Only one electron band is considered. The electron-phonon interaction is of the density-displacement type, but can be of arbitrary spatial range and shape. Feynman's analytical integration of ion trajectories is performed by transforming the electron-ion forces to the basis in which the phonon...

Kornilovitch, Pavel

2005-01-01

5

Nonequilibrium phonon effects in midinfrared quantum cascade lasers

Energy Technology Data Exchange (ETDEWEB)

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.

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

2014-09-28

6

Lifetime of optical phonons in fs-laser excited bismuth

Energy Technology Data Exchange (ETDEWEB)

This paper presents experimental and theoretical results on the temperature-dependent optical response of a single crystal of bismuth to excitation by femtosecond laser pulses. We demonstrate that the measured damping rate of the transient reflectivity oscillations relates to the lifetime of optical phonons. The lifetime is the inverse rate of the decay of optical phonons into two acoustic phonons. This lifetime also indicates the approach to the vibration instability (catastrophe) threshold that manifests the beginning of the disordering of a solid crystal and transition to a liquid state. We observe the red shift of phonon frequency, which increases with the rise of the initial lattice temperature. The red shift is different from the previously observed red shift proportional to the electron temperature, and thus to the excitation laser fluence. The coherent phonon excitation process imprinted into the initial change in the reflectivity and the following reflectivity oscillations allowed us to uncover the temporal phonon history preceding the structural transformation of solid Bi. (orig.)

Boschetto, D.; Garl, T.; Rousse, A. [ENSTA/Ecole Polytechmique, Laboratoire d' Optique Appliquee, Palaiseau (France); Gamaly, E.G.; Rode, A.V. [The Australian National University, Laser Physics Centre, Canberra (Australia)

2008-09-15

7

Low energy electron-phonon effective action from symmetry analysis

Based on a detailed symmetry analysis, we state the general rules to build up the effective low energy field theory describing a system of electrons weakly interacting with the lattice degrees of freedom. The basic elements in our construction are what we call the "memory tensors", that keep track of the microscopic discrete symmetries into the coarse-grained action. The present approach can be applied to lattice systems in arbitrary dimensions and in a systematic way to any desired order in derivatives. We apply the method to the honeycomb lattice and re-obtain the by now well-known effective action of Dirac fermions coupled to fictitious gauge fields. As a second example, we derive the effective action for electrons in the kagom\\'e lattice, where our approach allows to obtain in a simple way the low energy electron-phonon coupling terms.

Cabra, D C; Silva, G A; Sturla, M B

2013-01-01

8

Electron-phonon equilibration in laser-heated gold films

By irradiating a thin metal foil with an intense short-pulse laser, we have created a uniform system far from equilibrium. The deposited energy is initially deposited only within the electronic subsystem, and the subsequent evolution of the system is determined by the details of the electron-phonon coupling. Here, we measure the time evolution of the lattice parameter through multilayer Bragg diffraction and compare the result to classical molecular dynamic simulations to determine the lattice temperature. The electron-ion coupling constant for gold is then determined by comparison with the evolution of a two-temperature electron-phonon system.

White, T. G.; Mabey, P.; Gericke, D. O.; Hartley, N. J.; Doyle, H. W.; McGonegle, D.; Rackstraw, D. S.; Higginbotham, A.; Gregori, G.

2014-07-01

9

Electron-phonon equilibration in laser-heated gold films

By irradiating a thin metal foil with an intense short-pulse laser, we have created a uniform system far from equilibrium. The deposited energy is initially deposited only within the electronic subsystem, and the subsequent evolution of the system is determined by the details of the electron-phonon coupling. Here, we measure the time evolution of the lattice parameter through multilayer Bragg diffraction and compare the result to classical molecular dynamic simulations to determine the lattic...

White, Tg; Mabey, P.; Gericke, Do; Hartley, Nj; Doyle, Hw; Mcgonegle, D.; Rackstraw, Ds; Higginbotham, A.; Gregori, G.

2014-01-01

10

Surface modification of semiconductors under the action of laser radiation

International Nuclear Information System (INIS)

The results of the experimental and theoretical studies of the heating mechanism of semiconductors under the action of laser radiation are presented. Time dependence of semiconductor heating is of a complex form: heating takes place in three stages, which are characterized by various heating rates. At certain irradiation energetic regimes the surface breaks up into an array of distinctly faceted molten segments separated by solid unmelted regions. It is shown that non-uniform surface heating and melting at the laser action is due to instability of uniform distribution of the carrier concentration and crystal lattice phonons temperature. (author)

11

Coherent optical phonon spectroscopy studies of femtosecond-laser modified Sb2Te3 films

International Nuclear Information System (INIS)

We performed time-resolved reflectivity measurements to monitor changes in optical phonon modes in Sb2Te3 thin films under femtosecond laser irradiation. We found that a phonon mode at 3.64 THz appears after high-fluence laser irradiation, in addition to the phonon modes of Sb2Te3. We determined that the additional mode is due to Te segregation as a result of laser-induced decomposition of the Sb2Te3 film. This experiment clearly illustrates the irreversible effects of femtosecond laser irradiation during the measurement of coherent optical phonon dynamics in Sb2Te3.

12

Energy Technology Data Exchange (ETDEWEB)

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., E-mail: jakek@jhu.edu [Johns Hopkins University, Baltimore, Maryland 21208 (United States)

2014-06-02

13

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

14

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

15

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.

16

All-electron theory of the coupling between laser-induced coherent phonons in bismuth

Using first principles, all-electron calculations and dynamical simulations we study the behavior of the A_1g and E_g coherent phonons induced in Bi by intense laser pulses. We determine the potential landscapes in the laser heated material and show that they exhibit phonon-softening, phonon-phonon coupling, and anharmonicities. As a consequence the E_g mode modulates the A_1g oscillations and higher harmonics of both modes appear, which explains recent isotropic reflectivity measurements. Our results offer a unified description of the different experimental observations performed so far on bismuth.

Zijlstra, E S; García, M E; Zijlstra, Eeuwe S.; Tatarinova, Larisa L.; Garcia, Martin E.

2006-01-01

17

International Nuclear Information System (INIS)

Full text: Recently, electrical generation of high-frequency ultrasonic phonons from low-dimensional semiconductor systems (LDSSs) has been studied both experimentally and theoretically by Australian research teams. It has been found that by electrical generation of the phonon emission from a LDSS device with fixed sample parameters, it is difficult to tune the frequency and the angle of the phonon emission. Here, we propose a novel scheme for generating tunable hypersonic phonon sources (i.e., the phonon frequency generated is far above 109 Hz) by optical means. This is motivated by recent availability of the free-electron laser radiations. In this work, a theoretical study of generation of high-frequency acoustic phonons by electrons in GaAs-based quantum wire (QWi) systems, subject to intense terahertz (THz) electromagnetic (EM) radiations, is conducted. We have studied the frequency and angular distribution of the phonon emission generated optically via deformation potential coupling. The distinctive nature for electron-photon-phonon interactions in a QWi device results in a strong dependence of the acoustic phonon emission on strength E0 and frequency ? of the THz EM field. Consequently, the frequency and the angle for THz phonon emission can be tuned by varying E0 and/or ?). We find that the tunable hypersonic generation from semiconductor QWi systems can be achieved by using recently developed free-electron laser radiationseloped free-electron laser radiations

18

Doping dependence of LO-phonon depletion scheme THz quantum-cascade lasers

International Nuclear Information System (INIS)

The effect of doping on terahertz quantum-cascade lasers (QCL) utilizing the longitudinal-optical (LO)-phonon depletion scheme of the lower laser state is investigated. Five identical 2.8 THz samples were grown with 2D equivalent doping ranging from 4.3 x 109 to 3.9 x 1010 cm-2. A linear dependence on doping is observed for both the threshold current density Jth and maximum current density Jmax. Only the sample doped to 3.9 x 1010 cm-2 shows the effects of free-carrier absorption with a nonlinear increase in Jth, while the Jmax remained linear. Since the applied field determines when the lasing action takes place, linearity is expected when the losses are independent of doping. All samples showed a similar Tmax of 140 K and T0 of 30 K

19

We have investigated the time-resolved vibrational properties of terahertz quantum cascade lasers by means of ultra-fast laser spectroscopy. By the observation of the acoustic folded branches, and by analyzing the involved phonon modes it is possible to extract accurate structural information of these devices, which are essential for their design and performance.

Bruchhausen, Axel; Lloyd-Hughes, James; Fischer, Milan; Beck, Mattias; Scalari, Giacomo; Faist, Jérôme; Dekorsy, Thomas

2010-01-01

20

Coherent optical phonons in different phases of Ge2 Sb 2 Te5 upon strong laser excitation

The transient reflectivity response of phase-change Ge2 Sb 2 Te5 films to intense femtosecond laser pulses is studied by ultrafast coherent phonon spectroscopy. The three different phases (amorphous, fcc-, and hcp-crystalline), as well as laser-crystallized films, are investigated, featuring different photoexcited carrier and coherent optical phonon dynamics. At least two main phonon frequencies are identified for each phase/material and their evolution for increasing pump fluences is investi...

Herna?ndez Rueda, Javier; Savoia, A.; Gawelda, W.; Soli?s Ce?spedes, Javier; Mansart, B.; Boschetto, D.; Siegel, Jan

2011-01-01

21

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)

22

The detection-energy dependence of a coherent phonon in a (001) CdTe crystal, generated by ultrashort laser pulses with the center energy transparent or opaque to the sample, is investigated using a spectrally resolved pump-probe method. At the excitation in the transparent region, the detection-energy dependence of the phonon amplitude has two peaks at the energy shifted by one times the phonon energy of CdTe from the center energy of the probe pulses. On the other hand, the amplitude in the opaque region shows two peaks at the energy shifted by about two times the phonon energy. This difference occurs even though the observed energies of the coherent phonons in both regions are the same as that of the longitudinal optical phonon of CdTe. The energy shifts in the detection-energy dependence imply that the emission and absorption of one phonon and two phonons in the transparent and opaque regions, respectively, are implicated in coherent phonon generation. In this study, the detection-energy dependence is examined from the viewpoint of the third-order nonlinear susceptibility based on the impulsive stimulated Raman scattering process under nonresonant and resonant conditions. PMID:25166406

Mizoguchi, K; Morishita, R; Oohata, G

2013-02-15

23

Effect of Pulse Width and Fluence of Femtosecond Laser on Electron—Phonon Relaxation Time

International Nuclear Information System (INIS)

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

24

Laser-Ultrasonic Investigation on Lamb Waves in Two-Dimensional Phononic Crystal Plates

In this paper, laser-ultrasonic non-destructive testing is used to investigate the propagation of Lamb waves in two-dimensional phononic crystal plates. The bandgaps are experimentally observed for low-order Lamb wave modes. The influence of crucial parameters such as the periodical arrangement of scatterers on bandgaps is discussed in detail. The finite element simulations further agree well with the results of the laser-ultrasonic investigation.

Wang, Jing Shi; Cheng, Ying; Xu, Xiao Dong; Liu, Xiao Jun

2014-06-01

25

Manipulation of Squeezed Two-Phonon Bound States using Femtosecond Laser Pulses

Directory of Open Access Journals (Sweden)

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.

Nakamura Kazutaka G.

2013-03-01

26

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.

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

27

Two-phonon bound state and phonon localization in ZnTe created by ultrashort laser pulses

A coherent two-phonon bound state has been impulsively generated in ZnTe(110) via second-order Raman scattering in the time domain for the first time. The state composed of two anti-correlated in wave vector acoustic phonons exhibits full {\\Gamma}1 symmetry and has energy higher than its corresponding overtone. By using two collinear pump pulses, we demonstrated the possibility to manipulate the localization degree of the two-phonon bound state. Furthermore, by suppressing two-phonon fluctuations, the coexistence of coherently excited bound and unbound two-phonon states has been observed.

Hu, Jianbo; Ohmori, Kenji; Nakamura, Kazutaka G

2010-01-01

28

Plasmon-phonon-assisted electron-hole recombination in silicon at high laser fluence

International Nuclear Information System (INIS)

We present both theoretical and experimental results in silicon which clearly demonstrate that at time scales of 20 to 40 ps, after the pump laser pulse and at fluences greater than 100 mJ/cm2, the carrier density of the electron-hole plasma drops for increasing fluence; this is not explained by Auger recombination. We show that this drop is specific to plasmon-phonon-assisted recombination, which naturally explains this behavior

29

Picosecond X-ray diffraction studies of laser-excited acoustic phonons in InSb

International Nuclear Information System (INIS)

We have employed time-resolved X-ray diffraction with picosecond temporal resolution to measure the time-dependent rocking curves of laser-irradiated asymmetrically cut single InSb crystals. Coherent acoustic phonons were excited in the crystals by irradiation with 800-nm, 100-fs laser pulses at irradiances between 0.25 and 12 mJ/cm2. The induced time-dependent strain profiles (corresponding to the coherent phonons) were monitored by diffracting collimated, monochromatic pulses of X-rays from the irradiated crystals. Recording of the diffracted radiation with a fast low-jitter X-ray streak camera resulted in an overall temporal resolution of better than 2 ps. The strain associated with the coherent phonons modifies the rocking curve of the crystal in a time-dependent manner, and the rocking curve is recorded by keeping the angle of incidence of the X-rays upon the crystal fixed, but varying the energy of the incident X-rays around a central energy of 8.453 keV (corresponding to the peak of the rocking curve of the unperturbed crystal). The observed time-dependent diffraction from the irradiated crystals is in reasonable agreement with simulations over a wide range of energies from the unperturbed rocking-curve peak. (orig.)

30

In this paper, we theoretically and experimentally study phononic band gaps and waveguiding for plate-mode acoustic waves in a square array of stepped cylinders coated on an aluminum thin plate. We show that the stepped cylinders shaped with a small segment of reduced diameter can change the phonon resonance frequencies and result in tailorable band gaps. We demonstrate the band-gap and waveguiding effects in the phononic plate utilizing finite-element method numerical calculations and pulse laser ultrasonic measurements. Experimental results agree well with the numerical predictions. The phononic band gaps, slow resonant acoustic waves, and waveguiding in the lower frequency range are experimentally observed. The results enable enhanced control over phononic metamaterial, which has applications in low-frequency guiding and isolation of acoustic waves, acoustic absorbers, and nondestructive evaluation.

Hsu, Jin-Chen; Wu, Tsung-Tsong; Hsu, Hua-Shien

2013-02-01

31

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

32

A femtosecond laser-irradiated crystallizing technique is tried to convert amorphous Sb2Te3 film into crystalline film. Sensitive coherent phonon spectroscopy (CPS) is used to monitor the crystallization of amorphous Sb2Te3 film at the original irradiation site. The CPS reveals that the vibration strength of two phonon modes that correspond to the characteristic phonon modes of crystalline Sb2Te3, enhances with increasing laser irradiation fluence (LIF), showing the rise of ...

Li, Simian; Huang, Huan; Zhu, Weiling; Wang, Wenfang; Chen, Ke; Yao, Dao-xin; Wang, Yang; Lai, Tianshu; Wu, Yiqun; Gan, Fuxi

2011-01-01

33

Energy Technology Data Exchange (ETDEWEB)

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.

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

34

Phonon-focusing effect with laser-generated ultrasonic surface waves

Surface-phonon focusing is examined with laser generation of pulsed surface acoustic waves (SAW's). Before presentation of the experimental results, the theory of the effect is summarized including both the ray approach and the stationary-phase analysis. To create a point source of SAW's the focused beam of a Q-switched Nd:YAG (yttrium aluminum garnet) laser is employed. To visualize the SAW amplitude distribution we use dust patterns arising as a result of SAW-induced dust-particle removal from the surface under investigation. The SAW amplitude measurements with the probe beam deflection technique show that the above patterns reflect adequately the SAW amplitude angular dependence. The strong SAW focusing is observed on cubic crystals such as Si, Ge, GaAs, as well as on LiNbO3 crystal. The results obtained are discussed in comparison with the theory.

Kolomenskii, Al. A.; Maznev, A. A.

1993-11-01

35

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.

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

2009-01-01

36

International Nuclear Information System (INIS)

This paper deals with the theoretical explanation of the experimental results reported in previous papers, demonstrating the anomalous melting of an Al surface layer upon energetic electron bombardment during electron microscopic observation, when the Al surface layer contains large-scale deuterium precipitates. The theory is based on the spin-flip-phonon-maser action of deuteron nucleus in a strong magnetic field as previously reported to explain the heating of heavy water on acoustic wave propagation, and gives large enough to explain the melting. (author)

37

Energy Technology Data Exchange (ETDEWEB)

Metals exposed to ultrafast laser irradiation close to ablative regimes show often a submicron-scale (near 0.5 {mu}m) periodic organization of the surface as ripples. Using two classes of metallic materials (transition and noble), we have determined that the ripples amplitude is strongly correlated to the material transport properties, namely electron-phonon relaxation strength, electronic diffusion, and to the energy band characteristics of the electronic laser excitation. This particularly depends on the topology of the electronic structure, including d-band effects on electronic excitation. Comparing the effects of electron-phonon nonequilibrium lifetimes for the different metals under similar irradiation conditions, we indicate how the electron-phonon coupling strength affects the electronic thermal diffusion, the speed of phase transformation and impacts on the ripples contrast. The highest contrast is observed for ruthenium, where the electron-phonon coupling is the strongest, followed by tungsten, nickel, and copper, the latter with the least visible contrast. The dependence of surface patterns contrast with fluence is linked to the dependence of the relaxation characteristics with the electronic temperature.

Colombier, J. P.; Garrelie, F.; Faure, N.; Reynaud, S.; Bounhalli, M.; Audouard, E.; Stoian, R.; Pigeon, F. [Universite de Lyon, Laboratoire Hubert Curien, UMR 5516 CNRS, Universite Jean Monnet, 42000 Saint-Etienne (France)

2012-01-15

38

Dissipationless Phonon Hall Viscosity

We study the acoustic phonon response of crystals hosting a gapped time-reversal symmetry breaking electronic state. The phonon effective action can in general acquire a dissipationless "Hall" viscosity, which is determined by the adiabatic Berry curvature of the electron wave function. This Hall viscosity endows the system with a characteristic frequency, \\omega_v; for acoustic phonons of frequency \\omega, it shifts the phonon spectrum by an amount of order (\\omega/\\omega_v...

Barkeshli, Maissam; Chung, Suk Bum; Qi, Xiao-liang

2011-01-01

39

International Nuclear Information System (INIS)

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

40

We have theoretically and numerically studied nitride-based quantum well (QW) laser structures. More specifically, we have used a QW made with III-nitride where the width of the barrier region is large relative to the electron mean free path, and we have calculated the electron surface capture velocities by considering an electron flux which is captured into the well region. The process is assisted by the emission of the longitudinal optical phonons as predicted by the hybri...

Stavrou, V. N.; Veropoulos, G. P.

2011-01-01

41

Random laser action from flexible biocellulose-based device

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

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

2014-02-01

42

International Nuclear Information System (INIS)

We have theoretically and numerically studied nitride-based quantum well (QW) laser structures. More specifically, we have used a QW made with III-nitride where the width of the barrier region is large relative to the electron mean free path, and we have calculated the electron surface capture velocities by considering an electron flux which is captured into the well region. The process is assisted by the emission of the longitudinal optical phonons as predicted by the hybrid (HB) model. The results of surface capture velocities via the emission of HB phonons are compared to the emission of the dielectric continuum phonons (Zakhleniuk et al 1999 Phys. Status Solidi a 176 79). Our investigation shows that the two different phonon models predict almost the same results for the non-retarded limit. Furthermore, the surface capture velocities strongly depend on the size of the structure and the heterostructure materials. Lastly, a comparison to the recent experimental values shows that our model could accurately describe the experimentally measured parameters of the quantum capture processes

43

Ultrafast dynamics and laser action of organic semiconductors

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...

Vardeny, Zeev Valy

2009-01-01

44

We report three-well, resonant-phonon depopulation terahertz quantum cascade lasers with semi-insulating surface-plasmon waveguides and reduced active region (AR) thicknesses. Devices with thicknesses of 10, 7.5, 6, and 5 {\\mu}m are compared in terms of threshold current density, maximum operating temperature, output power and AR temperature. Thinner ARs are technologically less demanding for epitaxial growth and result in reduced electrical heating of devices. However, it is found that 7.5-{\\mu}m-thick devices give the lowest electrical power densities at threshold, as they represent the optimal trade-off between low electrical resistance and low threshold gain.

Salih, M; Valavanis, A; Khanna, S P; Li, L H; Cunningham, J E; Davies, A G; Linfield, E H

2013-01-01

45

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

International Nuclear Information System (INIS)

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

46

Enhanced laser action of Perylene-Red doped polymeric materials

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

Garcia-moreno, I.; Costela, A.; Pintado-sierra, Mercedes; Martin, Virginia; Sastre, Roberto

2009-01-01

47

Triboluminescence of tungsten initiated by termodeformations under laser action

The paper presents the results of a study on spectral composition of non-thermal glow from tungsten surface (mechanoluminescence--ML), that is initiated by thermal deformations under laser pulse action. Spectral relationships of glow intensity have been obtained. It has been shown that ML of tungsten exhibits a wide spectrum and is present throughout the spectral range under study ((lambda) equals 460 - 760 nm).

Banishev, Alexander F.; Panchenko, Vladislav Y.; Shishkov, Alexei V.

2001-05-01

48

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

49

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.

Krupke, William F. (Pleasanton, CA); Payne, Stephen A. (Castro Valley, CA); Marshall, Christopher D. (Livermore, CA)

2001-01-01

50

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.

Eisenmenger, Wolfgang

1980-01-01

51

Nonthermal luminescence of the tungsten surface under the action of pulse laser radiation

International Nuclear Information System (INIS)

Laser-induced radiation outlet of defects on the surface and W surface destruction are studied. Nonthermal luminescence on the samples opposite side terms of laser pulse action has been recorded. Outlet of defects to the surface arising from thermoelastic strain, appearing in laser action area, can be among the reasons of the luminescence

52

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

Eisenmenger, W.

1981-01-01

53

Phonon engineering for nanostructures.

Energy Technology Data Exchange (ETDEWEB)

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.

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

54

International Nuclear Information System (INIS)

A femtosecond laser-irradiated crystallizing technique is tried to convert amorphous Sb2Te3 film into crystalline film. Sensitive coherent phonon spectroscopy (CPS) is used to monitor the crystallization of amorphous Sb2Te3 film at the original irradiation site. The CPS reveals that the vibration strength of two phonon modes that correspond to the characteristic phonon modes (A1g1 and Eg) of crystalline Sb2Te3 enhances with increasing laser irradiation fluence (LIF), showing the rise of the degree of crystallization with LIF and that femtosecond laser irradiation is a good post-treatment technique. Time-resolved circularly polarized pump-probe spectroscopy is used to investigate electron spin relaxation dynamics of the laser-induced crystallized Sb2Te3 film. Spin relaxation process indeed is observed, confirming the theoretical predictions on the validity of spin-dependent optical transition selection rule and the feasibility of transient spin-grating-based optical detection scheme of spin-plasmon collective modes in Sb2Te3-like topological insulators.

55

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.)

56

Phonon-assisted lasing in ZnO microwires at room temperature

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).

Michalsky, T.; Wille, M.; Dietrich, C. P.; Röder, R.; Ronning, C.; Schmidt-Grund, R.; Grundmann, M.

2014-11-01

57

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.

Schwinger, J.

1990-01-01

58

It has been well-known that VO2 undergoes both a structural phase transition (SPT) (electron-phonon interaction) from monoclinic (insulator phase) to tetragonal (metal phase) and of a discontinuous first-order metal-insulator transition (MIT) (Jump) (electron-electron interaction) near 68^oC. Peierls transiton and Mott transition in VO2 remain controversial. We have investigated a relation of the MIT and the SPT in VO2 by observing coherent phonons using a laser with a femtosecond pulse width (10˜20 ft). A coherent phonon indicating a metal phase is measured after MIT. This indicates that the SPT does not affect the MIT. This is confirmed by a micro-Raman scattering experiment and XRD. The speed of the first-order MIT is interpreted as about 100 femtosecond. This is different from a well-known analysis in which the SPT and the MIT simultaneously occur. (References on the MIT: New J. Phys. 6 (1994) 52 (http://www.njp.org), Appl. Phys. Lett. 86 (2005) 242101, Physica B 369 (2005) 76; cond-mat/0607577; cond-mat/0608085; cond-mat/0609033)

Kim, Hyun-Tak; Chae, Byung-Gyu; Kim, Bong-Jun; Lee, Yong Wook; Yun, Sun Jin; Kang, Kwang-Yong; Han, Kang-Jeon; Lee, Ki-Ju; Lim, Yong-Sik

2007-03-01

59

International Nuclear Information System (INIS)

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. - Highlights: ? We have studied coherent phonons of A1g and Eg symmetry in bismuth. ? Amplitudes of both modes were measured in visible and near infrared ranges. ? Obtained data were compared to spontaneous Raman cross sections. ? We show that displacive excitation cannot be reduced for Bi to Raman scattering.

60

The effect of pore formation on the reflectance of aluminum alloy 1421 during laser pulse action

It is shown that the appearance of micropores leads to an increase in the reflectance of aluminum-based alloy 1421 irradiated by laser pulses. The waveform of a reflected signal bears information on the onset and duration of the pore-formation process in the near-surface material layer during the action of a laser pulse.

Kikin, P. Yu.; Perevezentsev, V. N.; Rusin, E. E.

2014-05-01

61

The paper presents the results of study of thin plates and films mechanoluminescence initiated by thermal deformations resulting from high-power laser pulse action. The dependence of excitation threshold and intensity of mechanoluminescence on plates thickness and the dependence of intensity of mechanoluminescence on laser pulse power density were investigated.

Banishev, Alexander F.; Panchenko, Vladislav Y.; Shishkov, Alexei V.

2002-04-01

62

Frequency stabilization of the zero-phonon line of a quantum dot via phonon-assisted active feedback

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 fluore...

Hansom, Jack; Schulte, Carsten H. H.; Matthiesen, Clemens; Stanley, Megan; Atature, Mete

2014-01-01

63

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

Melnikov, A A; Chekalin, S V

2010-01-01

64

Crater formation in a target under the action of a high-power laser pulse

International Nuclear Information System (INIS)

The formation of craters in targets of various materials under the action of a high-power neodymium-laser pulse at radiation intensities from 1010 to 1014 W/cm2 was studied experimentally and theoretically. The interaction between the laser beam and solid targets is investigated to determine the efficiency of the ablation loading of various materials and the transformation of the laser energy into the energy of a shock wave

65

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)

66

Laser light: its nature and its action on the eye.

Lasers produce a coherent, focused, monochromatic, high-energy form of light. Because laser surgery is more versatile and precise and is freer of complications than conventional surgery it has become widely accepted in ophthalmology over the past 10 years. Applications range from routine procedures in the fundus to recent, more delicate interventions in the cornea. The argon laser is the most widely used to treat extrafoveal chorioretinal diseases such as age-related macular degeneration and ...

Bessette, F. M.; Nguyen, L. C.

1989-01-01

67

Tunable vacuum ultraviolet laser action by argon excimers

Energy Technology Data Exchange (ETDEWEB)

Vacuum ultraviolet lasing was achieved in electron-beam-pumped high-density argon gas (25--65 bars). With a diffraction grating, the argon excimer laser (126 nm) could be tuned between 123.2 and 127.4 nm. The line width of the tuned laser was 0.6 nm and the output power approx.1 kW.

Wrobel, W.; Roehr, H.; Steuer, K.

1980-01-15

68

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

Directory of Open Access Journals (Sweden)

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.

N.A. Schumilova

2015-01-01

69

Cautionary note concerning the CuSO4 X-ray laser. [alternative to lasing action

For the so far unconfirmed lasing action claimed by Kepros et al. (1972) to have been obtained by focusing a 1.06-micron radiation of a q-switched Nd(3+) glass laser to a small cylindrical volume inside a CuSO4-doped gelatin medium supported between two glass plates, an alternate explanation is proposed that does not depend on the assumption of laser action in copper. The proposed explanation shows how collimated X-ray beams might be created under the experimental conditions described by Kepros et al.

Billman, K. W.; Mark, H.

1973-01-01

70

An investigation was made of the damage to the surface of silicon and copper by pulsed and pulse-periodic action of an Nd : YAG laser. Anomalies were found in a probe Ne — He laser beam scattered by the surface of silicon when it was irradiated by a series of Nd : YAG pulses of I < Imelt intensity (I melt is the surface melting threshold). These anomalies were attributed tentatively to the formation of a defect-saturated surface layer.

Banishev, A. F.; Balykina, E. A.

1997-06-01

71

An investigation was made of solid-phase damage to the surface of silicon by Nd:YAG laser pulses. The results made it possible to postulate particle emission when the surface of silicon was subjected to laser pulses with the threshold power density Imelt corresponding to the onset of surface melting. Such emission was attributed to the formation of surface microcracks as a result of condensation of nonequilibrium defects under the action of elastic stresses.

Banishev, A. F.; Golubev, V. S.; Kremnev, A. Yu

1998-10-01

72

Surface motion induced by laser action on opaque anisotropic crystals

International Nuclear Information System (INIS)

Analytical solutions for the acoustic wave equations obtained by temporal Fourier and spatial Laplace transformations directly provide a description of the motion of the crystal surface caused by the spatially distributed laser heating of a semi-infinite crystal. Evaluation of the acoustic field in the bulk of the material is not needed here. In general, all three acoustic modes are excited due to the laser-induced thermoelastic effect and contribute to each of the three components of the transient surface displacement. Numerical simulations of the surface displacement as a function of time and crystal surface orientation are performed with the use of the analytical formulae derived in the case of a hexagonal crystal, for which only two modes are excited. The formulae obtained make it possible to optimize the orientation of the surface of the crystal in order to improve the efficiency of the excitation of the in-plane motion of the surface

73

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.

74

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)

75

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

Medvid, Artur; Onufrijevs, Pavels; Mychko, Alexander

2011-01-01

76

Structure, phase composition, and properties of aluminum-oxide ceramic in the laser action zone

International Nuclear Information System (INIS)

We investigated the microstructure of the irradiated material and its effect on the mechanical properties of the ceramic, as well as the mechanism responsible for the appearance of thermal stresses and, as a consequence, for the formation of microcracks. When a ceramic is exposed to laser radiation the exposed zone becomes amorphous, and in addition at the top of the channel of the opening. In a group of materials both with and without the same starting content of the glassy form the degree of formation of the amorphous phase depends on the laser pulse duration. Laser treatment sharply lowers the microhardness in a laser action zone of the order of the grain sizes. In this case radial microcracks up to 40-50 ?m long form. When the ceramic interacts with x-rays colored sections appear on the surface

77

The lasing properties of pyrromethene 567 (PM567) dissolved in solid poly-trimethylsilyl-methacrylate (TMSMA) cross-linked with ethylene glycol dimethacrylate (EGDMA) and copolymerized with methyl methacrylate (MMA) have been investigated. The vol/vol proportion of the different comonomers in each copolymer formulation was systematically varied, and the effect of each composition on the laser action of PM567 was evaluated. The laser samples were transversely pumped at 534 nm with 5.5 mJ/pulse from a frequency doubled Q-switched Nd:KGW laser. Lasing efficiencies of up to 14% and good stability with no sign of degradation after 10,000 pump pulses at 1 Hz in the copolymer P(TMSMA:MMA 50:50) were demonstrated. Pumping this sample at 10 Hz, the laser emission of PM567 remained at 45% of its initial value after 40,000 pulses.

Costela, A.; García-Moreno, I.; Carrascoso, M. L.; Sastre, R.

2002-01-01

78

Polaritons in cuprous oxide perturbed by LA-phonons

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

Roslyak, Oleksiy; Birman, Joseph L.

2007-01-01

79

Studies of Phonon Anharmonicity in Solids

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.

Lan, Tian

80

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.

El-Kady, Ihab F. (Albuquerque, NM); Olsson, Roy H. (Albuquerque, NM)

2012-01-10

81

International Nuclear Information System (INIS)

Structural features of the laser radiation self-focusing dynamics in the electromagnetic induced transparency (EIT) band are studied for an atomic system with a ?-type energy level diagram. Effective nonlinearity of an EIT medium is manifested primarily as nonlinear dispersion (dependence of the group velocity on the wave amplitude). Qualitative analysis of the dynamics of self-action of laser pulses, which is confirmed by numerical simulation, shows that nonlinear evolution of a 3D wave packet follows the scenario of self-focusing, which serves as the background on which the envelope profile turnover and the formation of a shock wave occur at an advanced rate

82

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

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 ...

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

2010-01-01

83

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

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.

Kalusniak, S; Halm, S; Henneberger, F

2010-01-01

84

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

85

Phonon Bloch oscillations in acoustic-cavity structures

We describe a semiconductor multilayer structure based in acoustic phonon cavities and achievable with MBE technology, designed to display acoustic phonon Bloch oscillations. We show that forward and backscattering Raman spectra give a direct measure of the created phononic Wannier-Stark ladder. We also discuss the use of femtosecond laser impulsions for the generation and direct probe of the induced phonon Bloch oscillations. We propose a gedanken experiment based in an integrated phonon source-structure-detector device, and we present calculations of pump and probe time dependent optical reflectivity that evidence temporal beatings in agreement with the Wannier-Stark ladder energy splitting.

Kimura, N D L; Jusserand, B

2004-01-01

86

The Features of Craters Formation on the Target under the Action of Powerful Laser Pulse

International Nuclear Information System (INIS)

The results of experimental and theoretical investigations of craters originating in solid targets of different materials when powerful Nd:glass laser pulse irradiates the surface at flux densities in the range of 1010-1014 W/cm2 are presented. The experimentally observed dependencies of crater depth and ablated mass on laser pulse energy and target material properties are analysed employing the theory of shock wave initiation and propagation under the action of the plasma-producing laser beam. From the comparison of the theoretically deduced and experimentally observed dependencies, a simple formula is derived allowing to determine the pressures in the shock wave and in the plasma corona using the measurements for the crater depth and ablated mass

87

Degenerate pump-probe reflectivity experiments have been performed on a single crystal of bismuth telluride (Bi$_2$Te$_3$) as a function of sample temperature (3K to 296K) and pump intensity using $\\sim$ 50 femtosecond laser pulses with central photon energy of 1.57 eV. The time resolved reflectivity data show two coherently generated totally symmetric A$_{1g}$ modes at 1.85 THz and 3.6 THz at 296K which blue shift to 1.9 THz and 4.02 THz, respectively at 3K. At high photoex...

Kamaraju, N.; Kumar, Sunil; Sood, A. K.

2010-01-01

88

Abstract On the basis of the analysis of experimental results, a two-stage mechanism of nanocones formation on the irradiated surface of semiconductors by Nd:YAG laser is proposed for elementary semiconductors and solid solutions, such as Si, Ge, SiGe, and CdZnTe. Properties observed are explained in the frame of quantum confinement effect. The first stage of the mechanism is characterized by the formation of a thin strained top layer, due to redistribution of point defects in tempe...

Medvid Artur; Onufrijevs Pavels; Mychko Alexander

2011-01-01

89

On Theory of the Phonon Perturbed Superradiance

The paper examines superradiance in impurity crystals in the field of a coherent phonon wave excited by two ultrashort laser pulses via Raman scattering processes at the moment of preparation of the initial state of an ensemble of emitters. It is shown that by varying the power of the excitation pulses and their mutual direction of propagation, one can control the superradiance parameters and extract data on the electron-phonon coupling constant and its anisotropy.

Saiko, A. P.

2004-01-01

90

DYE LASER SOURCE OF MONOCHROMATIC UV-B AND UV-C RADIATIONS FOR BIOLOGICAL ACTION SPECTROSCOPY

The authors have used a flashlamp driven tunable dye laser as a radiation source for observing UV-C and UV-B action spectra of two eukaryotic microorganisms. The general nature of the irradiation system and various operating parameters are described. The laser produces the high p...

91

Destruction of silicon and copper surface under pulsed and pulse periodic action of YAG:Nd laser

The paper presents the results of the study of silicon and copper surface destruction under pulsed and pulse-periodic action of YAG:Nd laser radiation. The anomalies have been discovered in the probe beam of He-Ne laser scattered from the silicon surface under its irradiation with a series of YAG:Nd laser pulses at I less than Imelt. (where Imelt. is the surface melting threshold). These anomalies are supposedly related to formation of surface layer saturated with defects.

Banishev, Alexander F.; Baliikina, Elena A.

1997-04-01

92

Electron scattering and hybrid phonons in low-dimensional laser structures made with GaAs/AlxGa1?xAs

International Nuclear Information System (INIS)

We theoretically and numerically present the hybrid phonon modes for the double heterostructure GaAs/AlxGa1-xAs and their interactions with electrons. More specifically, we have calculated the electron capture within a symmetric quantum well via the emission of hybrid phonons. Our investigation shows that the capture rates via the hybrid phonons are matched to the rates predicted by the dielectric continuum (DC) model and the concentration of aluminium which is an important parameter for controlling the electron capture process in light-emitting diodes (LED)

93

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

94

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)

95

Spontaneous emission of phonons by coupled quantum dots

We find an interference effect for electron-phonon interactions in coupled semiconductor quantum dots that can dominate the nonlinear transport properties even for temperatures close to zero. The intradot electron tunnel process leads to a `shake up' of the phonon system and is dominated by a double-slit-like interference effect of spontaneously emitted phonons. The effect is closely related to subradiance of photons (Dicke effect) in a laser-trapped two-ion system and expla...

Brandes, Tobias; Kramer, Bernhard

1999-01-01

96

Phonon lasing in transport through double quantum dots

Energy Technology Data Exchange (ETDEWEB)

An optical phonon laser is proposed using a double quantum dot (DQD) fabricated on semiconductor substrates. The DQD couples to two modes of LO phonons which work as a natural cavity. The pumping is realized by the electric current under a finite bias. We show that lasing takes place when the tunneling rate to external leads is much larger than the decay rate of phonons.

Okuyama, Rin; Eto, Mikio [Faculty of Science and Technology, Keio University, Yokohama 223-8522 (Japan); Brandes, Tobias [Institut für Theoretische Physik, Technische Universität Berlin, D-10623 Berlin (Germany)

2013-12-04

97

Phonon lasing in transport through double quantum dots

International Nuclear Information System (INIS)

An optical phonon laser is proposed using a double quantum dot (DQD) fabricated on semiconductor substrates. The DQD couples to two modes of LO phonons which work as a natural cavity. The pumping is realized by the electric current under a finite bias. We show that lasing takes place when the tunneling rate to external leads is much larger than the decay rate of phonons

98

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)

99

Damage to the surface of silicon in the solid phase by the action of Nd:YAG laser pulses

International Nuclear Information System (INIS)

An investigation was made of solid-phase damage to the surface of silicon by Nd:YAG laser pulses. The results made it possible to postulate particle emission when the surface of silicon was subjected to laser pulses with the threshold power density Imelt corresponding to the onset of surface melting. Such emission was attributed to the formation of surface microcracks as a result of condensation of nonequilibrium defects under the action of elastic stresses. (interaction of laser radiation with matter. laser plasma)

100

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

Nika, Denis L.; Balandin, Alexander A.

2012-01-01

101

Length-scale dependent phonon interactions

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...

Srivastava, Gyaneshwar

2014-01-01

102

Electron - Phonon Superconductivity

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.

Marsiglio, F.; Carbotte, J. P.

2001-01-01

103

Non-equilibrium Phonons in CaWO4: Issues for Phonon Mediated Particle Detectors

The CRESST experiment looks for evidence of dark matter particles colliding with nuclei in CaWO4, using cryogenic bolometers sensitive to energy deposition ˜ 10 keV with a few percent accuracy. Calibration of the energy deposited in the phonon system depends upon the details of the evolution of the non-equilibrium energy in the CaWO4 absorber. Our phonon images sensitively measure variations in angular phonon flux, providing key information about the elastic constants and scattering rates that determine the energy evolution. Phonon pulses, created by focused photoexcitation of a 150 nm Cu film, are detected after propagation through 3 mm of CaWO4. The 20 ns Ar-ion laser pulse creates a localized (10-3 mm^2) source of 10-20 K blackbody phonons. The sample is at 2 K. Our images show that the elastic constants derived from ultrasonic velocities along high symmetry axes do not accurately predict the total phonon flux along non-symmetry directions. We present new data on the dependence of phonon flux on excitation level and discuss the influence of isotope and anharmonic decay on the shape of phonon pulses in these ultrapure samples. Thanks to J.P. Wolfe and the Frederick Seitz Materials Research Laboratory, Urbana, IL, for partial support of this work.

Msall, Madeleine; Head, Timothy; Jumper, Daniel

2009-03-01

104

??????????? ?????? ??? ????????? ??? ????????? ??? ????????????? laser ?? ???????

1)?????? ???????????? ??? ???????????? ?????????? ????????? ??? ????????? ??? ????????????? laser ?? ?????? ??????? ?? ???????????? ????? ??? ?? ????????. 2)?????? ???????? ???????????? ?? ??? ?????? LIBS ?? ??? ??????? ??????????????? ????????? ??????? ???????? ??? ?????...

????????, ??????

2007-01-01

105

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)

106

Non-equilibrium phonon dynamics

International Nuclear Information System (INIS)

This book presents information on the following topics: studies of nonequilibrium dynamics in the time domain; studies on nonequilibrium phonons by optical techniques; generation, propagation and detection of terahertz phonons in gallium arsenide; monochromatic phonon generation by superconductiong tunnel junctions; phonon imaging-theory and applications; an introduction to crossing effects in phonon scattering; phonon echoes, polarization echoes, and acoustic phase conjugation in solids; introduction to phonon hydrodynamics; electron-phonon interacti, screening and phonon-generation; surface acoustic waves; vibrational energy exchange between gases and solids; and the gas/phonon interface - desorption and other phenomena

107

Continuous-wave diode-pumped laser action of Nd³?-doped photo-thermo-refractive glass.

Laser action of the photo-thermo-refractive (PTR) glass, which is the photosensitive material for holographic recording of volume Bragg gratings (VBGs), was demonstrated for the first time by introducing Nd³?. Nd:PTR glass has a bandwidth of 27.8 nm and 16.0 nm for luminescence and absorption, respectively. An uncoated 2 mm thick Nd:PTR element generated cw laser output of 124 mW, with a slope efficiency of 25%, by laser diode pumping. This Nd:PTR glass also performed wide bandwidth laser action at 1053.9-1063.3 nm, where the decrease of the pump-absorption efficiency was held off below 30%, even under a 3.5 nm shift of pump wavelength from its absorption center. PMID:21685985

Sato, Yoichi; Taira, Takunori; Smirnov, Vadim; Glebova, Larissa; Glebov, Leonid

2011-06-15

108

Introduction to phonon hydrodynamics

International Nuclear Information System (INIS)

The study of phonon hydrodynamics is the study of the collective behavior of the interacting phonon system at low frequencies and long wavelengths. The author presents a short outline of the phenomenological approach and lists a few results. The microscopic theory is examined and results of that approach are used to demonstrate the importance of phonon transport. It is shown that the singular behavior of the self-energy of a long-wavelength phonon is Z and 'omega go to zero' is important in order to understand the thermodynamics of the interacting phonon system, such as the difference between adiabatic and isothermal elastic constants

109

Probing Phonons in Nonpolar Semiconducting Nano wires with Raman Spectroscopy

International Nuclear Information System (INIS)

We present recent developments in Raman probe of confined optical and acoustic phonons in nonpolar semiconducting nano wires, with emphasis on Si and Ge. First, a review of the theoretical spatial correlation phenomenological model widely used to explain the downshift and asymmetric broadening to lower energies observed in the Raman profile is given. Second, we discuss the influence of local inhomogeneous laser heating and its interplay with phonon confinement on Si and Ge Raman line shape. Finally, acoustic phonon confinement, its effect on thermal conductivity, and factors that lead to phonon damping are discussed in light of their broad implications on nano device fabrication

110

Coherent phonon-induced optical modulation in semiconductors at terahertz frequencies

International Nuclear Information System (INIS)

The coherent modulation of electronic and vibrational nonlinearities in atoms and molecular gases by intense few-cycle pulses has been used for high-harmonic generation in the soft x-ray and attosecond regime, as well as for Raman frequency combs that span multiple octaves from the terahertz to petahertz frequency regions. In principle, similar high-order nonlinear processes can be excited efficiently in solids and liquids on account of their high nonlinear polarizability densities. In this paper, we demonstrate the phononic modulation of the optical index of Si and GaAs for excitation and probing near their direct band gaps, respectively at ?3.4 and ?3.0 eV. The large amplitude coherent longitudinal optical (LO) polarization due to the excitation of LO phonons of Si (001) and LO phonon–plasmon coupled modes in GaAs (001) excited by 10 fs laser pulses induces effective amplitude and phase modulation of the reflected probe light. The combined action of the amplitude and phase modulation in Si and GaAs generates phonon frequency combs with more than 100 and 60 THz bandwidth, respectively. (paper)

111

Coherent phonon-induced optical modulation in semiconductors at terahertz frequencies

The coherent modulation of electronic and vibrational nonlinearities in atoms and molecular gases by intense few-cycle pulses has been used for high-harmonic generation in the soft x-ray and attosecond regime, as well as for Raman frequency combs that span multiple octaves from the terahertz to petahertz frequency regions. In principle, similar high-order nonlinear processes can be excited efficiently in solids and liquids on account of their high nonlinear polarizability densities. In this paper, we demonstrate the phononic modulation of the optical index of Si and GaAs for excitation and probing near their direct band gaps, respectively at ˜3.4 and ˜3.0 eV. The large amplitude coherent longitudinal optical (LO) polarization due to the excitation of LO phonons of Si (001) and LO phonon-plasmon coupled modes in GaAs (001) excited by 10 fs laser pulses induces effective amplitude and phase modulation of the reflected probe light. The combined action of the amplitude and phase modulation in Si and GaAs generates phonon frequency combs with more than 100 and 60 THz bandwidth, respectively.

Hase, Muneaki; Katsuragawa, Masayuki; Monia Constantinescu, Anca; Petek, Hrvoje

2013-05-01

112

Ultrafast optical generation of coherent phonons in CdTe1-xSex quantum dots

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.

Bragas, A V; Costantino, S; Ingale, A; Zhao, J; Merlin, R; Ingale, Alka

2003-01-01

113

Ultrafast optical generation of coherent phonons in CdTe1-xSex quantum dots

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.

Bragas, A. V.; Aku-Leh, C.; Costantino, S.; Ingale, Alka; Zhao, J.; Merlin, R.

2004-05-01

114

Size effects on the phonon spectra of quantum dots in CdTe-doped glasses

We studied the confinement effects on the phonon spectra of CdTe quantum dots by means of resonant Raman scattering measurements. The spectra show clearly longitudinal optical phonons, surface phonons and some of their overtone combinations. We show that the scattering due to surface phonons increases as the quantum dot size decreases. The results are obtained by tuning the laser excitation energy to resonance for quantum dots of different sizes inside the broad size distribution in CdTe-doped glasses.

de Paula, A. M.; Barbosa, L. C.; Cruz, C. H. B.; Alves, O. L.; Sanjurjo, J. A.; Cesar, C. L.

1996-07-01

115

Lifetime of sub-THz coherent acoustic phonons in a GaAs-AlAs superlattice

We measure the lifetime of the zone-center 340 GHz longitudinal phonon mode in a GaAs-AlAs superlattice excited and probed with femtosecond laser pulses. By comparing measurements conducted at room temperature and liquid nitrogen temperature, we separate the intrinsic (phonon-phonon scattering) and extrinsic contributions to phonon relaxation. The estimated room temperature intrinsic lifetime of 0.95 ns is compared to available calculations and experimental data for bulk GaAs. We conclude tha...

Maznev, Aa; Hofmann, F.; Jandl, A.; Esfarjani, K.; Bulsara, Mt; Fitzgerald, Ea; Chen, G.; Nelson, Ka

2012-01-01

116

International Nuclear Information System (INIS)

A theory of the transport and localisation of spherical dielectric particles in a liquid under the action of a gradient force in a laser-radiation field with a periodically modulated intensity is developed. An expression for the gradient force is derived in the Rayleigh - Hans approximation. The Langevin equation of motion is numerically solved using this expression. The transport and localisation of particles are investigated depending on their properties, the viscosity of the liquid, and the parameters of laser radiation. (laser applications and other topics in quantum electronics)

117

Spin dynamics of antiferromagnets under action of femtosecond laser pulses (Review Article)

Investigations of excitation of spin dynamics in transparent antiferromagnets (AFM) under the action of femtosecond laser pulses are reviewed. A variety of observed effects is considered in the context of a unified approach. The analysis is based on the nonlinear sigma model for the antiferromagnetism vector L with taking into account effective fields induced in a magnetic material due to the interaction between light and the spin system of the magnetic material. The contributions of various magneto-optical effects (both standard Faraday or Cotton-Mouton (Voigt) effects and specific L-dependent effects for AFM) are considered as characteristic contributions to the effective field within the sigma model. The most typical experimental data for real AFM are discussed.

Ivanov, B. A.

2014-02-01

118

The paper presents an investigation of deformation response of monocrystalline silicon surface to the action of short laser pulses in the air and in vacuum P approximately equals 10-2 Torr. An anomalously continuous change of the surface relief was identified on irradiation in the air. The observable phenomenon is explained by oxidation of surface layer, enriched with defects.

Banishev, Alexander F.; Golubev, Vladimir S.; Kremnev, Alexei Y.

2000-02-01

119

International Nuclear Information System (INIS)

We discovered several new nonlinear-laser ?(3)-properties in tetragonal YVO4 vanadate, which is well-known birefringent optical material, host-crystal for lanthanide lasant ions, and attractive gain media for Raman laser converters. We hope that observed many-phonon SRS, almost sesqui-octave Stokes and anti-Stokes lasing comb, cascaded self-frequency ''tripling'' and self-sum-frequency generation in the blue spectral range could significantly enriche applied potential of this crystal

120

Growth and erosion of a discrete breather interacting with Rayleigh-Jeans distributed phonons

The interaction of a discrete breather with Rayleigh-Jeans distributed low-amplitude phonons is studied for the discrete nonlinear Schrödinger equation. A statistical analysis gives a criterion for growth or decay of the breather, depending on its phase frequency, and on the chemical potential of the phonons. If the breather exceeds a critical amplitude, the breather accumulates wave action from the phonons and grows. If the breather amplitude is smaller, the phonons erode the breather.

Rumpf, B.

2007-04-01

121

In this Letter we propose the use of hypersonic phononic crystals to control the emission and propagation of high frequency phonons. We report the fabrication of high quality, single crystalline hypersonic crystals using interference lithography and show that direct measurement of their phononic band structure is possible with Brillouin light scattering. Numerical calculations are employed to explain the nature of the observed propagation modes. This work lays the foundation for experimental studies of hypersonic crystals and, more generally, phonon-dependent processes in nanostructures. PMID:15903869

Gorishnyy, T; Ullal, C K; Maldovan, M; Fytas, G; Thomas, E L

2005-03-25

122

If phonons are particles, they must be attached to absolute space through their proper masses, which depend on the absolute velocities. In such a case one should be able to register with phonons the Sagnac and Marinov effects which have been observed with massless and massive particles (photons and neutrons). The experimental possibilities for such experiments are analyzed.

Marinov, Stefan

1982-05-01

123

Microscopic model of a phononic refrigerator

We analyze a simple microscopic model to pump heat from a cold to a hot reservoir in a nanomechanical system. The model consists of a one-dimensional chain of masses and springs coupled to a back gate through which a time-dependent perturbation is applied. The action of the gate is to modulate the coupling of the masses to a substrate via additional springs that introduce a moving phononic barrier. We solve the problem numerically using non-equilibrium Green function techniques. For low driving frequencies and for sharp traveling barriers, we show that this microscopic model realizes a phonon refrigerator.

Arrachea, Liliana; Chamon, Claudio; Capaz, Rodrigo

2012-01-01

124

Origin of coherent G -band phonon spectra in single-wall carbon nanotubes

Coherent phonons in single-wall carbon nanotubes (SWNTs) are observed as oscillations of the differential absorption coefficient as a function of time by means of pump-probe spectroscopy. For the radial breathing mode (RBM) of a SWNT, the coherent phonon signal is understood to be a result of the modulated diameter-dependent energy gaps due to the coherent RBM phonon oscillations. However, this mechanism might not be the dominant contribution to other phonon modes in the SWNT. In particular, for the G -band phonons, which correspond to bond-stretching motions, we find that the modulation of the interatomic optical dipole (electron-photon) matrix element gives rise to a strong coherent G -band phonon intensity comparable to the coherent RBM phonon intensity. We also further discuss the dependence of coherent G -band and RBM phonon amplitudes on the laser excitation pulse width.

Nugraha, A. R. T.; Hasdeo, E. H.; Sanders, G. D.; Stanton, C. J.; Saito, R.

2015-01-01

125

Periodical structures created by Ag nanoparticles in AgCl film under action of violet laser beam

International Nuclear Information System (INIS)

A periodic structure (PS) was obtained in thin light-sensitive AgCl-Ag film composition under action of single violet laser beam at normal incidence. The PS period is d? 266nm. Appearance of the structure is associated with excitation of waveguide modes. PS grooves consist of Ag nanoparticles. Grooves are oriented mainly along direction of laser beam polarization Eo. Existence of linear dichroism and absorption gap at beam wavelength was shown on absorption spectra at polarized illumination. It was found for the first time that dichroism remains after AgCl removal from film by chemical fixation

126

ELECTRON-PHONON INTERACTIONS IN SEMICONDUCTORS : PHONON TRANSPORT AND DECAY

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.

Ulbrich, R.

1981-01-01

127

Transverse optical phonon dispersion for multi-layer graphene

The Raman spectra were measured with different wavelength excitation lasers for multi-layer graphene samples obtained by mechanical and electrostatic exfoliation of highly oriented pyrolytic graphite on a silicon substrate. Phonon frequencies depending on the laser energy value are constructed, and the average distance between defects in the resulting multi-layer graphene calculated using G and D lines intensity ratio.

Kurkina, I.; Smagulova, S.

2014-10-01

128

Phonon-induced polariton superlattices

DEFF Research Database (Denmark)

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.

de Lima, Jr., M. M.; Poel, Mike van der

2006-01-01

129

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

130

Manipulation of thermal phonons

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.

Hsu, Chung-Hao

131

Inelastic neutron time-of-flight spectra from polycrystalline cesium were measured at 50, 100, and 290 K for a large variety of momentum transfers Q and energy transfers ?. Born-von Kármán models were fitted to the resulting (Q,?) topography. These models were used to calculate the phonon dispersion curves and the phonon densities of states. The results confirm theoretical predictions. The elastic constants c44 and c' determined from the measured data agree with ultrasonic results.

Nücker, N.; Buchenau, U.

1985-04-01

132

Birefringent phononic structures

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.

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

2014-12-01

133

Birefringent phononic structures

Directory of Open Access Journals (Sweden)

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.

I. E. Psarobas

2014-12-01

134

We report the investigation of surface acoustic waves (SAWs) propagating on a 1D phononic surface (PS) by the heterodyne-detected transient reflecting grating technique. A suitable experimental configuration enables the excitation of traveling SAWs with variable wave numbers and the measurement of their propagation with temporal and spatial resolution. Using the full characterization of the band diagram of this PS, as reported previously (Malfanti I., Taschin A., Bartolini P., Bonello B. and Torre R., J. Mech. Phys. Solids, 59 (2011) 2370), we studied the dispersion properties of the SAWs as the wave number approaches the Brillouin zone edge. SAW-packet group velocities show a clear slowing-down process approaching the BZ edge, with a measurable minimum velocity of about 140?m/s

Malfanti, I.; Taschin, A.; Bartolini, P.; Torre, R.

2012-02-01

135

Phonon Thermodynamics versus Electron-Phonon Models

Applying the path integral formalism we study the equilibrium thermodynamics of the phonon field both in the Holstein and in the Su-Schrieffer-Heeger models. The anharmonic cumulant series, dependent on the peculiar source currents of the {\\it e-ph} models, have been computed versus temperature in the case of a low energy oscillator. The cutoff in the series expansion has been determined, in the low $T$ limit, using the constraint of the third law of thermodynamics. In the H...

Zoli, Marco

2004-01-01

136

Phonon-Assisted Incoherent Excitation of a Quantum Dot and its Emission Properties

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.

Weiler, S; Roy, C; Ulrich, S M; Richter, D; Jetter, M; Hughes, S; Michler, P

2012-01-01

137

Resonance phenomena connected with the action of CO2-laser radiation on a germanium surface

Mass spectroscopy is used to study the desorption of CO2 and H2O molecules from the surfaces of germanium and oxidized germanium stimulated by IR radiation from a CO2 laser. A comparison with the thermodesorption process is made, and resonance effects in the photodesorption mechanism are hypothesized. The enhanced CO2 desorption under laser irradiation as compared with thermodesorption is due to the resonance excitation of surface adsorption complexes whose local oscillation modes are in resonance with the laser radiation.

Zoteev, A. V.; Kiselev, V. F.

1987-04-01

138

Crater formation in a target under the action of a high-power laser pulse

International Nuclear Information System (INIS)

The results of the experiments and theoretical studies on the craters formation in the targets from different materials under the effect of the powerful neodymium laser within the intensities range from 1010 up to 1014 W/cm2 are presented. The studies on the laser beam interaction with solid targets are carried out with the purpose of determining the efficiency of the materials ablation loading and laser transformation into the shock wave energy

139

Hot phonon dynamics in graphene.

The dynamics of hot phonons in supported, suspended, and gated monolayer graphene was studied by using time-resolved anti-Stokes Raman spectroscopy. We found that the hot phonon relaxation is dominated by phonon-phonon interaction in graphene, and strongly affected by the interaction between graphene and the substrate. Relaxation via carrier-phonon coupling, known as Landau damping, is ineffective for hot phonons which are in thermal equilibrium with excited carriers. Our findings provide a basis for better management of energy dissipation in graphene devices. PMID:23106146

Wu, Shiwei; Liu, Wei-Tao; Liang, Xiaogan; Schuck, P James; Wang, Feng; Shen, Y Ron; Salmeron, Miquel

2012-11-14

140

INSTABILITIES IN THERMAL BATH : PHONON ENHANCEMENT AND SATURATION IN A THREE-LEVEL SYSTEM

The equations, determining temporal behavior of coupled electronic and phonon subsystems in the electromagnetic field, are analyzed. The steady state solution describing saturation of the three level in such a system is achieved. It is shown that laser-like self-excitation of phonons cannot be obtained though essential phonon enhancement may be gained provided certain conditions are fulfilled. Field induced transparency is predicted between first two levels when the field saturates ground and...

Fain, B.

1981-01-01

141

Unraveling the interlayer-related phonon self-energy renormalization in bilayer graphene

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...

Araujo, Paulo T.; Mafra, Daniela L.; Sato, Kentaro; Saito, Riichiro; Kong, Jing; Dresselhaus, Mildred S.

2012-01-01

142

Observation of coherent zone-folded acoustic phonons generated by Raman scattering in a superlattice

We have used pulse time-of-flight techniques to examine the phonon emission from an optically excited GaAs/AlAs superlattice structure. For laser excitation wavelengths shorter than 767 nm (the energy of E1HH1 transition), we detect a significant longitudinal acoustic phonon component directed in a narrow beam normal to the structure. Under identical excitation conditions, generation of coherent longitudinal acoustic phonons has previously been observed in this structure. We suggest that the ...

Hawker, Philip; Kent, Anthony J.; Challis, Lawrence J.; Bartels, Albrecht; Dekorsy, Thomas; Kurz, Heinrich; Ko?hler, Klaus

2000-01-01

143

Infrared-Phonon Polariton Resonance of the Nonlinear Susceptibility in GaAs

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

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

2003-01-01

144

Continuous mode cooling and phonon routers for phononic quantum networks

We study the implementation of quantum state transfer protocols in phonon networks, where in analogy to optical networks, quantum information is transmitted through propagating phonons in extended mechanical resonator arrays or phonon waveguides. We describe how the problem of a non-vanishing thermal occupation of the phononic quantum channel can be overcome by implementing optomechanical multi- and continuous mode cooling schemes to create a 'cold' frequency window for tran...

Habraken, S. J. M.; Stannigel, K.; Lukin, Mikhail D.; Zoller, P.; Rabl, P.

2012-01-01

145

Behaviour of neutron irradiated silicon under the action of powerful laser pulses

International Nuclear Information System (INIS)

The behaviour of defects in silicon irradiated by neutrons under the effect of powerful ruby laser pulses (tau approximately 1.0 ms) is studied. Combinations of laser and isochronous annealing at different energies in impulse and annealing temperatures are used. The irradiated layer characteristics are judged by the measurements of electric conductivity and the Hall effe.ct. It is shown that a single laser impulse operating in the regime of free generation can be sufficient for total restoration of the initial crystal properties along the whole depth (300 ?m). It is found that under the laser effect the decay processes and reconstruction of defects have the character different from the case of annealing in a furnace. The conditions for formation of specific defect types are created, annealing of a vacancy nucleus of a disordering region has an explosive character. The great possibilities of utilization of the laser effect in investigation of defect structures are pointed out

146

Spectrum and entanglement of phonons in quantum fluids of light

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.

Busch, Xavier; Parentani, Renaud

2013-01-01

147

Phonons in Ge/Si superlattices with Ge quantum dots

Ge/Si superlattices with Ge quantum dots obtained by means of molecular-beam epitaxy were investigated by means of light Raman scattering under resonance conditions. These structures are shown to have oscillation properties of both two-dimensional and zero-dimensional objects. Within spectrum low-frequency range one observes twisted acoustic phonons (up to 15 order) typical for planar superlattices. Lines of acoustic phonons are overlapped with a wide band of continuous emission. Analysis of frequencies of Ge and Ge-Si optical phonons shows that Ge quantum dots are pseudoamorphous ones and mixing of Ge and Si atoms is a negligible one. One detected low-frequency shift of longitudinal optical phonons at laser excitation energy increase (2.54-2.71 eV)

Milekhin, A G; Pchelyakov, O P; Schulze, S; Zahn, D R T

2001-01-01

148

Structure, phase composition and properties of aluminoxide ceramics in the action zone of laser beam

International Nuclear Information System (INIS)

The microstructure of material irradiated by a laser beam and its effect on mechanical properties of ceramics, as well as the mechanism of generation of thermal stresses and, as a result, formation of microcracks are investigated. When ceramics is irradiated by a laser beam, it is observed that the radiation affected zone becomes amorphous in the upper part of the hole. In a group of materials with or without equal initial content of the glass-like form the degree of amorphous state depends on the laser pulse duration. In laser treatment microhardness is sharply reduced in the radiation affected zone within the limits of grain sizes. In this case radial microcracks of up to 40-50 ?m length are developed. When ceramics is interacting with X rays, colored spots appear on the surface

149

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.

Vasil'chenko, Zh V.; Azharonok, V. V.; Filatova, I. I.; Shimanovich, V. D.; Golubev, V. S.; Zabelin, A. M.

1996-09-01

150

International Nuclear Information System (INIS)

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

151

International Nuclear Information System (INIS)

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

152

The effect of electron–phonon energy exchange on thermal pulse propagation in semiconductors

International Nuclear Information System (INIS)

In this work, the nonequilibrium electron and phonon temperature distributions in semiconductors, initially heated on the surface with a short laser pulse, are calculated as a function of position and time. The transient temperatures of both quasiparticle systems are calculated self-consistently with the electron–phonon energy interaction taken into account. The electron and phonon temperature distributions are calculated using the Fourier integral and the coupled time-dependent one-dimensional heat diffusion equations for electron and phonon systems with special boundary conditions according to the experimental set-up

153

International Nuclear Information System (INIS)

Full text: This paper presents results of researches of optical hardness of ? -irradiated with doze 104- 109 rad alkali-silicate (K, GLS, LGS) and quartz (KU, KV, KSG) glasses against influence of radiation neodymium laser with intensity q = 0,1-1000 GWt/cm2. It is observed, that the laser produces damage of surface and volume of investigated glasses before and after ?-irradiation. This damage has threshold character and is always accompanied by a bright luminescence of plasma. Definition of threshold values of intensity superficial qs and volumetric qd laser produced damage was made by the complex method - fixing the moment of damage of transparent dielectric by simultaneous registration of the laser impulse which has passed through plasma of breakdown, mass-charge spectrum of ions of plasma and measuring the energy falling on the glass, and of penetrated and mirror-image radiations; and by optical microscopy. This method of research of influence ?-induced in transparent dielectric radiating defects on its optical stability against influence of laser radiation allows not only to define values qs and qd in the investigated interval of dozes, but also to investigate in details physical phenomena taking place in this process of interaction. On the basis of the received data quantitative characteristics of optical durability of the investigated glasses on wave length of ?1,06 microns depending on dozes of ?-irradiation and intensity of laser radiation are made. Doze dependences of charge and power spectra and quantitative characteristics of ions of plasma of breakdown were investigated at q? qs. In the investigated interval of dozes of ?- irradiation and intensity of laser radiation by a method of optical microscopy the morphology of occurring laser damage as surfaces, and volume of glass is also studied. It is found, that ? -induced defects in investigated glasses strongly effect on thresholds of damage qs and qd and on characteristics of ions of plasma. Significant growth of total number of ions of all frequency rates of charge N? reduction of maximal energy Emax and frequency rates of a charge Zmax ions are observed. Correlation between parameters of superficial damage - threshold qs and the size of damage d and characteristics of ion plasma - N?, Zmax and Emax are also observed. Damages, as microscopic researches have shown, looked like the micro crater representing the fused layer with a flat bottom and melted edges. Such structure of craters is consequences of the thermal action accompanying damages by plasma. With growth of a doze ? -irradiations of investigated glasses the sizes of damage grow considerably with the increase in diameter d of formed the craters received at the same values q. It is shown that the increase in intensity of a laser radiation up to 1000 GWt/cm2 leads to the catastrophic damage of the surface leading to breaking of glass. Results of microscopic researches show that the damage of surface and volume of the investigated non- irradiated glasses begins locally in the separate from each other small size parts where the congestion of the absorbing defects breaking the structure of glass was formed. Those are initially present in structure of glass alien impurity inclusions, dislocations and vacancies, bubbles and pores and others of heterogeneity. Concentration of absorbing defects in glass considerably increases due to formation of the radiating defects caused by ? - irradiation. This leads to an additional power consumption of a laser radiation on heating and evaporation of substance of a target, and consequently to reduction of a part of laser radiation, too, which is spent for heating and ionization of plasma. This seems to be a reason for reduction Z max and Emax of emitted ion by plasma and strong growth of output of ions from plasma of ? - irradiated glass connected with recombined processes taking place in plasma. (author)

154

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

155

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

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.

Tam, Giuseppe

2001-10-01

156

Laser action of ionized and neutral atomic lines in electron-beam-produced rare gas plasmas

International Nuclear Information System (INIS)

Rare gas plasmas (He through Xe) were produced by a short-pulsed, high-current electron beam (600 kV, 10 kA peak, 3 ns FWHM) in a drift tube without external field over a wide pressure range (0.1 -- 80 Torr). The emission spectra of the plasmas were observed between 2500 and 8500A with a spectrograph and bandpass filters from both end- and side-views. Self-terminating laser emissions (3 ns FWHM, 10 -- 400 W peak) travelling along with the electron-beam pulse were found for 20 spectral lines of singly-ionized and neutral Ne, Ar, Kr, and Xe atoms through the end window of the drift tube, and the small-signal gain coefficients were measured. The temporal behaviours of the emission intensity were measured for the laser lines and for many other spontaneous lines through the side window, and the atomic processes of the laser excitations were examined. (author)

157

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

158

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

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

Santos, J. N.; Roos, C.; Barboza, L. L.; Paoli, F.; Fonseca, A. S.

2014-12-01

159

The behaviour of a magnetized plasma under the action of laser with high pulse energy

International Nuclear Information System (INIS)

Simple magnetic traps, such as a cusp and field-reversed configuration are considered for application in high density regime. Magneto-inertial fusion with laser compression of magnetized spherical target and features of laser driven magneto-inertial fusion (LDMIF) are presented. A new fusion scheme which can avoid some of the major difficulties faced in the present approaches in magnetic and inertial confinement fusion is shown. Different schemes of magnetized discharges for LDMIF are discussed. Contributions (fusion power, charged particles and neutrons deposition, thermal conduction, radiation and mechanical work) to a power balance of compressed plasma target are calculated.

160

Spectroscopy and laser action of Cr3+, Nd3+ codoped crystal with Ca-Gallogermanate structure

Energy transfer between Cr3+ and Nd3+ ions has been investigated in the 4.2K-300K temperature range by using steady-state and time-resolved laser spectroscopy. Nonradiative energy transfer has been studied from the time-resolved emission spectra and the donor fluorescence decays. The transfer efficiency was calculated as a function of temperature by using the Cr3+ lifetimes of the single doped and codoped samples. Laser experiments were carried out in a diffusive cavity by pumping with Xenon ...

Azkargorta, J.; Iparraguirre, I.; Balda, R.; Ferna?ndez, J.; Kaminskii, A.

1994-01-01

161

Anomalous Hall effect in the phonon thermal conductivity of paramagnetic dielectrics

International Nuclear Information System (INIS)

A theory of the phonon Hall effect during heat transfer in a paramagnetic dielectric discovered by Strohm et al. [Phys. Rev. 95, 155901 (2005)] is developed. The heat flux emerging in the direction perpendicular to the magnetic field and to the temperature gradient is associated with the interaction of magnetic ions with the oscillating crystal field. In crystals with an arbitrary phonon spectrum, this interaction induces elliptic polarization of phonons. On the other hand, for any type of scattering, the temperature gradient forms part of the phonon density matrix, which is nondiagonal in modes. The combined action of these factors leads to the anomalous Hall effect

162

Spectroscopy and laser action of the "red perylimide dye" in various solvents

Optical properties of the red perylimide laser dye in various solvents are studied. The absorption spectrum exhibits two main bands, in the ranges 480-600 and 400-460 nm, due to the S 0-S 1 and S 0-S 2 transition. The fluorescence spectrum is a mirror image of the S 0-S 1 absorption (shift of ˜ 30-50 nm). The Stokes shift increases with solvent polarity. Such dye-solvent interactions are compared to theoretical predictions. The fluorescence quantum yields approaches unity in all the solvents studied. Laser tunability around 30 nm was obtained each time, covering the spectral range 580-640 nm. This interval is important for medical applications in photodynamic therapy and fluorescence diagnostics. The laser threshold energy varied from 0.35 mJ/pulse in cyclohexane to 1.87 mJ/pulse in methanol, and the slope efficiency from about 6.6% in methanol to 14% in xylenes. The laser output was stable for several hours of operation under an average pump energy of about 20 mJ/pulse at 1 Hz repetition rate, without flow.

Gvishi, R.; Reisfeld, R.; Burshtein, Z.

1993-10-01

163

Experimental study on the thin foil acceleration under the action of power laser pulses

International Nuclear Information System (INIS)

It is shown that the major physical processes occurring on irradiation of thin foils by intense laser pulses with flux densities between 1013 and 3x1014 W/cm2 are in agreement with the results of two-dimensional hydrodynamic calculations. Thin metal foils of different materials, organic films, thin two-layer targets as were used as targets in the experiments. To study plasma motion on the back side of the target and from the sid incident laser beam, interferometric and shadow methods have been applied. For a laser pulse energy of 100 J the maximum velocity of the matter at the back side of a 6 ?m aluminium foil is 5x106 cm/s. The calculated value of the hydrodynamic efficiency in this case is approximately 5%. For a laser pulse energy of approximately 100 J the kinetic energy of the accelerated part of the target is between 4.5 and 4.8 J. No restrictions on the heat fluxes as compared to the predictions of the classical theory are observed in the range of laser radiation intensities studied. A strong effect of the X-rays from the plasma corona on the state of the accelerated part of the foil is observed. An analysis of the X-ray spectra shows that under conditions studied and light flux densities of 1014 W/cm2 the amount of ''hot'' electrons with an effective temperature of approximately 5 keV does not exceed 10-4 of the total number of electrons in the plasma coronahe plasma corona

164

International Nuclear Information System (INIS)

The dependence of the strength of the electron-phonon coupling and the electron heat capacity on the electron temperature is investigated for eight representative metals, Al, Cu, Ag, Au, Ni, Pt, W, and Ti, for the conditions of strong electron-phonon nonequilibrium. These conditions are characteristic of metal targets subjected to energetic ion bombardment or short-pulse laser irradiation. Computational analysis based on first-principles electronic structure calculations of the electron density of states predicts large deviations (up to an order of magnitude) from the commonly used approximations of linear temperature dependence of the electron heat capacity and a constant electron-phonon coupling. These thermophysical properties are found to be very sensitive to details of the electronic structure of the material. The strength of the electron-phonon coupling can either increase (Al, Au, Ag, Cu, and W), decrease (Ni and Pt), or exhibit nonmonotonic changes (Ti) with increasing electron temperature. The electron heat capacity can exhibit either positive (Au, Ag, Cu, and W) or negative (Ni and Pt) deviations from the linear temperature dependence. The large variations of the thermophysical properties, revealed in this work for the range of electron temperatures typically realized in femtosecond laser material processing applications, have important implications for quantitative computational analysis of ultrafast processes associated with laser interaction with metalsiated with laser interaction with metals

165

Berry curvature and the phonon Hall effect

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.

Qin, Tao; Zhou, Jianhui; Shi, Junren

2012-09-01

166

Electron-phonon interaction and coupled phonon--plasmon modes

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...

Falkovsky, L.

2003-01-01

167

Taking into account the constraints imposed by the lattice symmetry, the phonon dispersion is calculated for graphene with interactions between the first and second nearest neighbors in the framework of the Born-von Karman model. Analytical expressions are obtained for the out-of-plane (bending) modes determined only by two force constants as well as for the in-plane modes with four force constants. Values of the force constants are found in fitting to elastic constants and ...

Falkovsky, L. A.

2007-01-01

168

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

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

Mostafazadeh, Ali

2014-01-01

169

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

We study optical spectral singularities of a weakly nonlinear PT-symmetric bilinear planar slab of optically active material. In particular, we derive the lasing threshold condition and calculate the laser output intensity. These reveal the following unexpected features of the system: 1. For the case that the real part of the refractive index $\\eta$ of the layers are equal to unity, the presence of the lossy layer decreases the threshold gain; 2. For the more commonly encoun...

Mostafazadeh, Ali

2014-01-01

170

A magnetically field-controllable phononic crystal

Phononic crystals are periodic structures consist of different materials in an elastic medium designed to interact with elastic waves. These crystals have practical applications, such as, frequency filters, beam splitters, sound or vibration protectors, acoustic lasers, acoustic mirrors and elastic waveguides. In this study, the wave propagation in a tunable phononic crystal is investigated. The magnetically controllable phononic crystal consists of a soft magnetorheological elastic medium undergoing large deformations upon the application of a magnetic field. Finite deformations and induced magnetic fields influence wave propagation characteristics in the periodic structure. The soft matrix is modeled as a hyperelastic elastomer to take into account the material nonlinearity. The integrated effects of material properties, transformation of the geometry of the unit cell, and the induced magnetic field, are used to tune the band structure of the periodic structure. Both analytical and finite element methods are employed to evaluate the dispersion diagrams considering Bloch boundary conditions. Results show that the applied magnetic field significantly affect the width and the position of band-gaps.

Bayat, Alireza; Gordaninejad, Faramarz

2014-04-01

171

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

172

Phonon Softening in Superconducting Diamond

We observe strong softening of optical phonon modes in superconducting (Tc = 4.2 K) boron doped diamond near the Brillouin zone center using inelastic x-ray scattering from a CVD-grown highly oriented sample. The magnitude of the softening, and our observation that it becomes stronger approaching zone center, supports theoretical models suggesting a phonon-mediated pairing mechanism via coupling of optical phonon modes to Fermi surfaces around the zone center. The electron-p...

Hoesch, M.; Fukuda, T.; Takenouchi, T.; Sutter, J. P.; Tsutsui, S.; Baron, A. Q. R.; Nagao, M.; Takano, Y.; Kawarada, H.; Mizuki, J.

2005-01-01

173

Phonon-induced topological insulation

We develop an approximate theory of phonon-induced topological insulation in Dirac materials. In the weak coupling regime, long wavelength phonons may favor topological phases in Dirac insulators with direct and narrow bandgaps. This phenomenon originates from electron-phonon matrix elements, which change qualitatively under a band inversion. A similar mechanism applies to weak Coulomb interactions and spin-independent disorder; however, the influence of these on band topolo...

Saha, Kush; Garate, Ion

2014-01-01

174

Phonon imaging: theory and applications

International Nuclear Information System (INIS)

This paper examines the propagation of thermal energy through crystalline solids at low temperatures. Thermal energy emanating from a point source of heat is strongly channeled into various directions in the crystal. The effect is caused by the elastic anisotropy of the crystal and is known as phonon focusing. This paper reviews phonon imaging techniques which graphically demonstrate phonon focusing and the information gained from these techniques is used here to study the scattering of high frequency phonon in the crystals. A general discussion is presented of ballistic heat propagation in real crystals

175

International Nuclear Information System (INIS)

Experiments were made on irradiation of annealed tantalum foils by millisecond pulses of various energies and beam defocusing. Changes in structure, composition and properties were studied as a result of irradiation based on X-ray structural methods and microhardness measurements. Revealed are effect of plastic deformation, oxidation, crack formation, destruction and hardening under the action of light pulses. The dependence of the effects observed on irradiation conditions is investigated

176

International Nuclear Information System (INIS)

Trigonal Na3Li(MoO4)2?6H2O was found to be an attractive, simultaneously ?(2)- and ?(3)-active nonlinear optical crystal. We investigated its basic optical properties and observed several nonlinear effects, namely many-phonon SRS, almost two-octave Stokes and anti-Stokes lasing combs, SHG, THG, and efficient cascaded (?(3) ? ?(2))-generation, as well as SRS arising from nonlinear interaction of two different ?(3)-active vibrations. All recorded nonlinear-lasing components were identified and attributed to SRS-promoting vibration modes. A short review of nonlinear-laser molybdates is given

177

Kinetic processes in the overdense plasma under the action of ultra-intense laser pulses

International Nuclear Information System (INIS)

The results of numerical and analytical investigation of the ultra-intense laser pulse's interaction with overdense plasma are presented. The mechanisms of the wave field energy transformation into the overdense plasma energy are discussed. The effects of radiation propagation deep into plasma as well as long-living vortex formation, plasma boundary instability, and the surface structures formation are obtained. The basic mechanisms for the absorption of incident radiation and the role played by polarization of the radiation are studied. Nonlinear theory of plasma surface instability in the field of the strong electromagnetic wave is developed. (author)

178

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)

179

Energy Technology Data Exchange (ETDEWEB)

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.

Estreicher, S. K., E-mail: Stefan.Estreicher@ttu.edu; Gibbons, T. M.; Kang, By.; Bebek, M. B. [Physics Department, Texas Tech University, Lubbock, Texas 79409-1051 (United States)

2014-01-07

180

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

181

Spectral self-action of THz emission from ionizing two-color laser pulses in gases

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.

Cabrera-Granado, Eduardo; Babushkin, Ihar; Bergé, Luc; Skupin, Stefan

2014-01-01

182

Acoustic Metamaterials and Phononic Crystals

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.

2013-01-01

183

Photon control of phonons in mixed crystal quantum dots

International Nuclear Information System (INIS)

Coherent phonon oscillations in solids can be excited impulsively by a single femtosecond laser pulse whose duration is shorter than a phonon period. In the impulsive stimulated Raman scattering (ISRS) experiment, scattering of probe is monitored as a function of time with respect to pump to generate time domain spectra of coherent phonons. In this paper, we present one such study of CdSe0.68Te0.32 (d?80 A) quantum dots in glass matrix, i.e semiconductor-doped glass (SDG) RG780 from Schott, USA and the experiment was performed at Prof. Merlin's laboratory at the University of Michigan, USA. Here, we present first report of selectively driving only CdSe-like modes in these mixed crystal quantum dots using photon control with two pump beams

184

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.

185

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

Energy Technology Data Exchange (ETDEWEB)

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.

Subota, Svitlana [Physics Faculty, Kyiv Taras Shevchenko University, Prosp. Glushkova, 6, Kyiv 03680 (Ukraine)]. E-mail: subota@univ.kiev.ua

2005-07-15

186

Quantum confinement effects on the optical phonons of CdTe quantum dots

We present Raman-scattering results for CdTe nanocrystals in doped glasses which clearly show the confinement effects on the phonon spectra as a function of the quantum-dot size. We observed optical phonon modes, surface phonons and some of their overtone combinations. We show that the surface-phonon scattering intensity increases as the quantum-dot size decreases. Our results also show a decrease in the electron-phonon coupling as the nanocrystal size is decreased. These confinement effects are observed by changing the laser excitation energy, and thus by tuning to resonance with the optical transitions for quantum dots of different sizes within their broad size distribution in semiconductor-doped glasses.

de Paula, A. M.; Barbosa, L. C.; Cruz, C. H. B.; Alves, O. L.; Sanjurjo, J. A.; Cesar, C. L.

1998-05-01

187

Phonon Linewidths and Electron Phonon Coupling in Nanotubes

We prove that Electron-phonon coupling (EPC) is the major source of broadening for the Raman G and G- peaks in graphite and metallic nanotubes. This allows us to directly measure the optical-phonon EPCs from the G and G- linewidths. The experimental EPCs compare extremely well with those from density functional theory. We show that the EPC explains the difference in the Raman spectra of metallic and semiconducting nanotubes and their dependence on tube diameter. We dismiss the common assignment of the G- peak in metallic nanotubes to a Fano resonance between phonons and plasmons. We assign the G+ and G- peaks to TO (tangential) and LO (axial) modes.

Lazzeri, M; Mauri, F; Ferrari, A C; Robertson, J; Lazzeri, Michele; Mauri, Francesco

2006-01-01

188

Studies of electron-phonon and phonon-phonon interactions in InN using ultrafast Raman spectroscopy

International Nuclear Information System (INIS)

Subpicosecond time-resolved Raman spectroscopy has been employed to investigate electron-phonon interactions and phonon dynamics in InN. The electron-longitudinal optical phonon scattering rate and the decay dynamics of longitudinal optical phonons in InN have been directly measured. Our results indicate that hot-phonon effects can play an important role in the electron relaxation and transport in InN. The carrier dependence of the lifetime of the longitudinal optical phonons has also been measured. The results suggest that more theoretical work is needed to account for the dependence of the lifetime of longitudinal optical phonons on the photoexcited carrier density.

189

Energy Technology Data Exchange (ETDEWEB)

The characteristics of laser action due to a self-terminating 4p(1)P1-3d(1)D2 transition of the calcium atom at a wavelength of 5.544 microns in a quasi-steady hollow-cathode discharge were studied experimentally. The maximumn lasing power was 10.5 mW and the specific laser power was not less than 30 mW/cu cm. The active-medium efficiency was estimated to be 0.21-0.59 percent, and the gain was estimated to be not less than 0.36/cm. 14 references.

Batenin, V.M.; Kalinin, S.V.; Klimovskii, I.I.; Ospanov, K.M.

1987-11-01

190

Double-resonant LA phonon scattering in defective graphene and carbon nanotubes

We present measurements of the D'' Raman mode in graphene and carbon nanotubes at different laser excitation energies. The Raman mode around 1050-1150 cm-1 originates from a double-resonant scattering process of longitudinal acoustic (LA) phonons with defects. We investigate its dependence on laser excitation energy, on the number of graphene layers, and on the carbon nanotube diameter. We assign this Raman mode to so-called inner processes with resonant phonons mainly from the ? -K high-symmetry direction. The asymmetry of the D'' mode is explained by additional contributions from phonons next to the ? -K line. Our results demonstrate the importance of inner contributions in the double-resonance scattering process and add a fast method to investigate acoustic phonons in graphene and carbon nanotubes by optical spectroscopy.

Herziger, Felix; Tyborski, Christoph; Ochedowski, Oliver; Schleberger, Marika; Maultzsch, Janina

2014-12-01

191

Berry Curvature and Phonon Hall Effect

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).

Qin, Tao; Shi, Junren

2012-02-01

192

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

Energy Technology Data Exchange (ETDEWEB)

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.

Nostrand, M

2000-09-01

193

Fine Structure of the Low-Frequency Raman Phonon Bands of Single-Wall Carbon Nanotubes

The Raman spectra of singled-wall carbon nanotubes (SWNT) produced by laser and are process were studied between 5 and 500 kappa. The line width vs. temperature dependence of the low-frequency Raman bands between 150 and 200/ cm deviates from that expected for phonon decay through phonon-phonon scattering mechanism. The experimental results and their analysis provided convincing evidence that each of the low-frequency Raman lines is a superposition of several narrower Raman lines corresponding to tubes of nearly the same diameter. The application of Raman spectroscopy to probe the distribution of SWNT by both diameter and chirality is discussed.

Iliev, M. N.; Litvinchuk, A. P.; Arepalli, S.; Nikolaev, P.; Scott, C. D.

1999-01-01

194

Theory of coherent acoustic phonons in InGaN/GaN multi-quantum wells

A microscopic theory for the generation and propagation of coherent LA phonons in pseudomorphically strained wurzite (0001) InGaN/GaN multi-quantum well (MQW) p-i-n diodes is presented. The generation of coherent LA phonons is driven by photoexcitation of electron-hole pairs by an ultrafast Gaussian pump laser and is treated theoretically using the density matrix formalism. We use realistic wurzite bandstructures taking valence-band mixing and strain-induced piezo- electric ...

Sanders, G. D.; Stanton, C. J.; Kim, Chang-sub

2001-01-01

195

Berry Curvature and Phonon Hall Effect

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...

Qin, Tao; Zhou, Jianhui; Shi, Junren

2011-01-01

196

Optical phonons of aluminum nitride

International Nuclear Information System (INIS)

Oriented polycrystalline films of AlN on Si(111) substrates and amorphous AlN films on sapphire substrates have been prepared by sputter deposition of aluminum in a nitrogen plasma. Phonons at 303, 426, 514, 614, 663, and 831 cm-1 ( +- 3%) have been observed in the Raman spectra of the crystalline films. The 303-cm-1 phonon shifts to 288 cm-1 and the 663-cm-1 phonon to 650 cm-1 in the amorphous sample. By means of infrared absorption measurements with the electric field perpendicular to the c axis we have tentatively identified E1(LO) and E1(TO) modes near 800 and 610 cm-1, respectively. A tentative assignment of the other modes is made from partial data from orientation dependent scattering and results for other wurtzite structure compounds. A comparison of the AlN phonon frequencies with those of other known wurtzite structure compounds shows that Martin's scaling equation is satisfied

197

Electron-phonon and phonon-phonon interactions in low-dimensional nanostructures

The electron-phonon interaction gives rise to a number of physically measurable quantities in solid state physics, perhaps most notably the heat capacity and the finite electrical resistivity in metals. The effect of extreme quantum confinement on the electron-phonon interaction is investigated for single-atom thick, infinitely long chains of metallic Al, Cu, Ag and Au atoms using density functional perturbation theory. In these atomic wires, the minimum energy geometries are distinct from the bulk configurations and the resulting changes in the inter-atomic force constants quantitatively change the phonon spectrum. The character of the electronic states at the Fermi level determines whether electrons will couple to longitudinal or transverse phonons, and in case of Al the overall strength of the interaction is reduced by two orders of magnitude relative to the bulk. The phonon-phonon interaction gives rise to the observed temperature-dependence of vibrational quantities, including phonon band structure and Raman spectra. Using finite-temperature molecular dynamics simulations based on density functional theory, an accurate description of the phonon-phonon interaction is made possible by considering anharmonic terms in the lattice potential energy. This technique is applied to the strict two-dimensional geometry in monolayer MoS2, where it is found that the Raman active E2g and A1g phonon modes show a non-uniform redshift with increasing temperature due to the distinct symmetries of these vibrational modes. In both cases, experimental evidence is presented to compliment the predictions made by the theoretical calculations. For monolayer MoS2 , experimental Raman measurements confirm a non-uniform redshift of the E2g and A1g modes. In order to confirm the predicted reduction in electron-phonon coupling strength in aluminum, we consider a bulk structure subject to pressure, which allows us to mimic the shorter inter-atomic separation observed in the atomic wires. Experiments confirm a reduction in the electrical resistivity as a function of pressure, due to weakened electron-phonon coupling. These studies suggest new ways of manipulating quantum transport in atomic scale materials.

Lanzillo, Nicholas Anthony

198

radiofrequency filters using phononic crystals

In the straight line of photonic and microwave meta-materials, phononic crystals are foreseen to enable novel acoustic applications that existing technologies cannot reach. These phononic crystals are periodic organisation of acoustically different materials exhibiting, for example, qtop bands, which means frequency ranges in which no wave can propagate in the structure. In this thesis we target RF frequencies in order to investigate applications complementary to the conventional resonators o...

Gorisse, Marie

2011-01-01

199

Phonon Raman scattering in superconductors

International Nuclear Information System (INIS)

If a superconductor has a Raman-active phonon mode of low frequency (larger but of the order of magnitude of the superconducting energy gap 2?), we show that electron-phonon coupling leads to a complex bound excitation, also Raman active, with a discrete frequency lower than 2? and with intensity which can be appreciable. We propose that these are the lines found by Sooryakumar and Klein at approximately the energy-gap frequency in superconducting 2H-NbSe2

200

Towards Phonon Spectrum of Graphene

It is shown that the nearest neighbor coupling between the carbon atoms is not enough to reproduce the phonon spectrum as observed in graphene, the second neighbor force constant is essential. For completeness we have rederived the phonon spectrum of one dimensional chains and two dimensional lattices like square lattice and triangular lattice with nearest and next nearest neighbor coupling among the atoms. This article is essentially an account of the technical details of a...

Kundu, Rupali

2007-01-01

201

Surface phonons in graphite (001)

He scattering data from the (001) surface of graphite reveal the dispersion of three acoustic surface phonon branches. They are clearly associated with the three bulk phonon bands, but appreciable deviations from the respective bulk and edges are observed. In particular the Rayleigh wave is close to the band edge only in the long-wave limit, as expected from the continuum theory, and displays an anomalous stiffening starting from about one third of the Brillouin zone in the direction.

Benedek, G.; Brusdeylins, G.; Heimlich, C.; Toennies, J. P.; Valbusa, U.

1986-12-01

202

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

Passeron, Thierry

2012-01-01

203

International Nuclear Information System (INIS)

The author examined the effects of electron-phonon interactions on the optical phonons of high-Tc superconductors of the type YBa2Cu3O7-? by applying the Raman scattering technique. The self-energy of the Ag phonons depending on their wave vector was measured in the material in the state of normal conductivity. The wave vector of the phonons was varied by using different laser wave lengths between 476 and 800 nm for excitation. In the state of superconductivity of the material, anomalous frequency and line width changes were observed for most of the Ag phonons, and these effects could be interpreted to result from the interaction of the phonons with electronic excitations via the superconducting energy gap. Experiments made with YBa2Cu3O7-? specimens doped with small amounts of gold, praseodymium, or iron also measured the phonon self-energy effects in the superconducting state. (orig./MM)

204

DEFF Research Database (Denmark)

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.

Nysteen, Anders; Nielsen, Per Kær

2012-01-01

205

Phonons and electron-phonon coupling in A15's

International Nuclear Information System (INIS)

A short summary is given on the phonon results obtained by inelastic neutron scattering on polycrystalline samples. Detailed results are reported for recent measurements on single crystals of Nb3Sb (Tsub(c)=0.2 K), which is the first A15 compound for which a complete determination of the phonon dispersion curves has been achieved. The results for Nb3Sb are compared to data taken on Nbsub(3.2)Gesub(0.8) (Tsub(c)=6 K) and Nbsub(3.1)Gasub(0.9) (Tsub(c)=12 K), as well to the limited data available for Nb3Sn. It is found, that in high Tsub(c) A15's the average phonon frequency is somewhat lower than in low Tsub(c) reference compounds. In particular those modes which involve a buckling of the chains are strongly depressed. On the other hand it turned out that the softening on cooling of the shear mode TA110 and of the GAMMA12 mode, as observed in Nb3Sb and V3Si is not a general phenomenon. A brief survey is given on the results of current theoretical investigations of phonons in the A15's. These calculations look promising to explain the observed differences of the phonon spectra in the A15 family. (orig.)

206

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

207

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...

Al-maliki, Firas J.

2012-01-01

208

The purpose of the study is to evaluate the effect of various laser techniques for bleaching teeth in office vital whitening. Hydrogen peroxide (30% concentration) and carbamide peroxide (10% solution) were used for chemical activation of bleaching process. Extracted non-carcious upper central incisors were exposed to laser radiation. Four different laser systems (Nd:YAG laser SHG, wavelength 0.53 ?m, CTE:YAG laser, wavelength 2.7 ?m, Nd:YAG laser, wavelength 1.06 ?m, and alexandrite laser, wavelength 0.75 ?m) were applied to accelerate the speed of the process. The end of chemical exposition was verified by the change of bleaching agent color. The color change was determined by stereomicroscope (Nikon SMZ 2T, Japan), the quality of surface structure was checked by scanning electron microscope Joel, Japan). The speed of bleaching rnaged from 630 s (chemical methods only) to 250-340 s (chemicals + alexandrite laser radiation). The Alexandrite laser application was considered an elective process to decrease the time of bleaching without modifying the surface.

Dostalova, Tatjana; Jelinkova, Helena; Koranda, Pavel; Nemec, Michal; Sulc, Jan; Housova, Devana; Miyagi, Mitsunobu; Kokta, Milan R.

2003-06-01

209

Coherent phonon dynamics at the martensitic phase transition of Ni_2MnGa

We use time-resolved optical reflectivity to study the laser stimulated dynamics in the magnetic shape memory alloy Ni_2MnGa. We observe two coherent optical phonons, at 1.2 THz in the martensite phase and at 0.7 THz in the pre-martensite phase, which we interpret as a zone-folded acoustic phonon and a heavily damped amplitudon respectively. In the martensite phase the martensitic phase transition can be induced by a fs laser pulse on a timescale of a few ps.

Mariager, S. O.; Caviezel, A.; Beaud, P.; Quitmann, C.; Ingold, G.

2012-01-01

210

Coherent phonon dynamics at the martensitic phase transition of Ni2MnGa

We use time-resolved optical reflectivity to study the laser stimulated dynamics in the magnetic shape memory alloy Ni2MnGa. We observe two coherent optical phonons, at 1.2 THz in the martensite phase and at 0.7 THz in the pre-martensite phase, which we interpret as a zone-folded acoustic phonon and a heavily damped amplitudon, respectively. In the martensite phase the martensitic phase transition can be induced by a fs laser pulse on a timescale of a few ps.

Mariager, S. O.; Caviezel, A.; Beaud, P.; Quitmann, C.; Ingold, G.

2012-06-01

211

Temperature dependence of the anharmonic decay of optical phonons in carbon nanotubes and graphite

We report on the temperature dependence of the anharmonic decay rate of zone-center optical phonons in both single-walled carbon nanotubes and graphite from cryogenic temperatures to 650K. The measurements are performed using a pump-probe Raman scattering scheme with femtosecond (fs) laser pulses [Song et al. PRL 100,225503(2008)]. A nonequilibrium population of the zone-center (G-mode) optical phonons is created by an initial fs laser pulse. A subsequent fs probe pulse generates both Stokes and antiStokes Raman scattering, from which we infer the mode population of the G-mode phonons. We observe a large nonequilibrium phonon population in both systems, together with a room-temperature population lifetime of 1-2ps. The population decay is attributed to anharmonic coupling to lower-energy phonons [Bonini et al. PRL 99,176802(2007)]. We observe little T dependence of the decay rate below room temperature, but find a component growing roughly linearly with increasing T for >300K. We compare the behavior observed in nanotubes and graphite and discuss the implications of our results for the mechanism of the anharmonic decay of optical phonons in both systems.

Chatzakis, Ioannis; Yan, Hugen; Song, Daohua; Berciaud, Stephane; Heinz, Tony F.

2009-03-01

212

Phonon-induced electrical conductance in semiconductors

The bath of thermal phonons is a well-known source of impedance to electronic conduction in solids. Turning the tables, a change in electronic conductance may be used for phonon detection, as will be discussed in the following.

Lassmann, Kurt; Burger, Wilfried

1986-01-01

213

Nanoscale phononic interconnects in THz frequencies.

Phononic computing is emerging as an alternative computing paradigm to the conventional electronic and optical computing. In this study, we propose and analyze various phononic interconnects, such as nano-scaled phononic resonators, waveguides and switches, on the ?111? surface of 3C-SiC and 3C-GeSi with substitutional and vacancy defects. This is achieved by simultaneously introducing defects of various types, and by varying their specific locations on the surface. To calculate the intrinsic and the defect-induced vibrational properties, such as the phononic bandgap and the variation in the phonon spectra, the total phonon density of states (TPDOS) and the partial phonon density of states (PPDOS) were calculated using molecular dynamics simulations with semi-empirical potentials. The proposed phononic interconnects, in conjunction with electronic and/or photonic interconnects, can be used in the current and future devices. PMID:25260120

Sgouros, Aris P; Neupane, Mahesh R; Sigalas, M M; Aravantinos-Zafiris, N; Lake, Roger K

2014-11-14

214

Damping of coupled phonon--plasmon modes

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.

Falkovsky, L. A.

2002-01-01

215

Phonon-induced topological insulation

We develop an approximate theory of phonon-induced topological insulation in Dirac materials. In the weak-coupling regime, long-wavelength phonons may favor topological phases in Dirac insulators with direct and narrow band gaps. This phenomenon originates from electron-phonon matrix elements, which change qualitatively under a band inversion. A similar mechanism applies to weak Coulomb interactions and spin-independent disorder; however, the influence of these on band topology is largely independent of temperature. As applications of the theory, we evaluate the temperature dependence of the critical thickness and the critical stoichiometric ratio for the topological transition in CdTe/HgTe quantum wells and in BiTl(S1-?Se?)2, respectively.

Saha, Kush; Garate, Ion

2014-05-01

216

Phonon dispersions of cluster crystals

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...

Neuhaus, Tim

2010-01-01

217

Phonon confinement and electron transport in GaAs-based quantum cascade structures

We present a detailed investigation of the effects that optical-phonon confinement has on the electronic transport properties of GaAs-based midinfrared multiple-quantum-well (MQW) quantum cascade lasers (QCLs). The macroscopic dielectric continuum model is used to describe the interface (IF) and confined (CF) optical phonon modes. Dispersions of the IF modes are obtained by using the transfer matrix method with periodic boundary conditions. Normalization coefficients of the IF and CF potentials are derived in detail for MQW structures consisting of arbitrary combinations of binary and ternary alloys. Interstage and intrastage scattering rates due to all the IF and CF modes are calculated for both ?- and X-valley electrons. The IF and CF scattering processes, in addition to the electron-electron and intervalley phonon scattering, are fully incorporated into the multivalley Monte Carlo simulation of a deep-active-well 6.7?m GaAs-based MQW QCL. At both 77K and room temperature, we find that phonon confinement enhances the electron-polar optical phonon scattering rates to a relatively small extent and induces minor corrections to the current, population inversion, and the electronic temperature with respect to the results obtained in the bulk-phonon approximation. Therefore, the bulk-phonon approximation in transport simulations of GaAs-based QCLs remains valuable due to its simplicity and high accuracy.

Gao, X.; Botez, D.; Knezevic, I.

2008-04-01

218

Unconventional plasmon-phonon coupling in graphene

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...

Jablan, M.; Soljac?ic?, M.; Buljan, H.

2010-01-01

219

Relativistic electron-phonon interaction

International Nuclear Information System (INIS)

The theory of Gaspari and Gyorffy of the electron-phonon interaction is generalized to the relativistic case. Starting from the Dirac equation an expression for the Hopfield parameter eta is derived in the rigid muffin-tin approximation. As an example the Hopfield parameter is calculated for Nb and Ta by the relativistic APW method. The numerical results show that relativistic effects are important in Ta. However the direct influence of spin-orbit interaction on the electron-phonon interaction is neglegible both, in Nb and Ta. (author)

220

Phononic crystals and acoustic metamaterials

Directory of Open Access Journals (Sweden)

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.

Ming-Hui Lu

2009-12-01

221

Resonances in ferroelectric phononic superlattice

The periodically poled ferroelectric wafer is a two-dimensional phononic superlattice. The important applications of such a solid include ultrasonic transducers at the micro/nano-scale for low intensity ultra-sonography, ferroelectric data storage, and development of very high frequency chips for next generation communication and information technologies, and others. In this work, we show theoretically and experimentally that a ferroelectric phononic superlattice has two distinctive resonances in acousto-electric transformation. They are associated with a split acoustic mode at the boundary between the first and second acoustic Brillouin zone.

Ostrovskii, Igor; Cremaldi, Lucien

2012-10-01

222

Introduction to phonons and electrons

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

Lou, Liang-fu

2003-01-01

223

Phonon dynamics of americium telluride

We report for the first time the complete phonon dispersion curves for Americium telluride (AmTe) using a breathing shell models (BSM) to establish their predominant ionic nature. The results obtained in the present study show the general features of the phonon spectrum. We could not compare our results with the experimental measurements as they are not available so far. We emphasize the need of neutron scattering measurements to compare our results. We also report, for the first time specific heat for this compound.

Arya, B. S.; Aynyas, Mahendra; Ahirwar, Ashok K.; Sanyal, S. P.

2013-06-01

224

Unraveling the interlayer-related phonon self-energy renormalization in bilayer graphene

In this work, we present a step towards further understanding of 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 fundamental for understanding low-energy phenomena such as transport and infrared optics. Our approach opens up a new route to understanding fundamental properties of IL interactions which can be extended to any graphene-like material, such as MoS2, WSe2, oxides and hydroxides. Furthermore, we report a previously elusive crossing between IL-related phonon combination modes in 2LG, which might have important technological applications.

Araujo, Paulo; Mafra, Daniela; Sato, Kentaro; Saito, Richiiro; Kong, Jing; Dresselhaus, Mildred

2013-03-01

225

We consider a multi-qubit system consisting of two trapped ions coupled in a laser field. The ions are identical three-level electronic systems which interact with one another through the phonon modes of their relative or center of mass motions, and the system is tuned so that two-phonon processes dominate the electronic transitions. The resulting evolution of the system is studied theoretically with a focus on the entanglement properties of the system. A method of quantifying the entanglement is discussed, and the time dependence of these quantifications is determined. The cases of the two ions coupled to the same phonon field and to two different isolated phonon fields are compared for Fock cavity modes. Instances of the entanglement sudden death recovery are identified in these various systems.

Abdel-Aty, M.; Bouchene, M.; McGurn, A. R.

2014-09-01

226

Coherent Longitudinal Acoustic Phonon Approaching THz Frequency in Multilayer Molybdenum Disulphide

Coherent longitudinal acoustic phonon is generated and detected in multilayer Molybdenum Disulphide (MoS2) with number of layers ranging from 10 to over 1300 by femtosecond laser pulse. For thin MoS2, the excited phonon frequency exhibits a standing wave nature and shows linear dependence on the sample thickness. The frequency varies from 40 GHz to 0.2 THz (10 layers), which promises possible application in THz frequency mechanical resonators. This linear thickness dependence gradually disappears in thicker samples above about 150 layers, and the oscillation period shows linear dependence on the probe wavelength. From both the oscillation period of the coherent phonon and the delay time of acoustic echo, we can deduce a consistent sound velocity of 7.11*103 m/s in MoS2. The generation mechanisms of the coherent acoustic phonon are also discussed through pump power dependent measurement.

Ge, Shaofeng; Liu, Xuefeng; Qiao, Xiaofen; Wang, Qinsheng; Xu, Zhen; Qiu, Jun; Tan, Ping-Heng; Zhao, Jimin; Sun, Dong

2014-07-01

227

Electron-phonon coupling dynamics in very small (between 2 and 8 nm diameter) Au nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Ultrafast laser experiments were used to study electron-phonon coupling in Au nanoparticles in the 2.5 to 8 nm size range in aqueous solution. The electron-phonon coupling constants for these samples were found to be independent of the particle size. This is attributed to a weak interaction between the electron gas and the surface phonon modes in Au. Calculations were performed which show that the coupling between the hot electrons and the surface accounts for less than 10% of the total electron energy losses for these particles. Thus, bulk electron-phonon coupling dominates the relaxation of excited electrons in Au particles, for particles as small as several hundred atoms. (c) 2000 American Institute of Physics.

Hodak, Jose H. [Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556-5670 (United States); Henglein, Arnim [Notre Dame Radiation Laboratory, University of Notre Dame, Notre Dame, Indiana 46556-5670 (United States); Hartland, Gregory V. [Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556-5670 (United States)

2000-04-01

228

Electron-phonon coupling dynamics in very small (between 2 and 8 nm diameter) Au nanoparticles

International Nuclear Information System (INIS)

Ultrafast laser experiments were used to study electron-phonon coupling in Au nanoparticles in the 2.5 to 8 nm size range in aqueous solution. The electron-phonon coupling constants for these samples were found to be independent of the particle size. This is attributed to a weak interaction between the electron gas and the surface phonon modes in Au. Calculations were performed which show that the coupling between the hot electrons and the surface accounts for less than 10% of the total electron energy losses for these particles. Thus, bulk electron-phonon coupling dominates the relaxation of excited electrons in Au particles, for particles as small as several hundred atoms. (c) 2000 American Institute of Physics

229

Phonon tunnels from a sonic black hole

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.

Fang, Hengzhong; Zhou, Kaihu

2011-01-01

230

Phonon drag in ballistic quantum wires

The acoustic phonon-mediated drag-contribution to the drag current created in the ballistic transport regime in a one-dimensional nanowire by phonons generated by a current-carrying ballistic channel in a nearby nanowire is calculated. The threshold of the phonon-mediated drag current with respect to bias or gate voltage is predicted.

Muradov, M. I.

2001-01-01

231

Energy Technology Data Exchange (ETDEWEB)

The parameters of the CW laser action due to the 2p1-1s4 transition in NeI and the 3d2-2p2 transition in ArI were calculated as functions of the electronic n(e) and atomic n(a) concentrations for conditions of a positive low-pressure column. For these transitions and for the 2p8-1s5 transition in the Kr atom, the parameters of the arbitrarily produced nonequilibrium plasma were determined. 17 references.

Batenin, V.M.; Kalinin, S.V.; Klimovskii, I.I.; Ospanov, K.M.

1988-10-01

232

Yoctocalorimetry: phonon counting in nanostructures

It appears feasible with nanostructures to perform calorimetry at the level of individual thermal phonons. Here I outline an approach employing monocrystalline mesoscopic insulators, which can now be patterned from semiconductor heterostructures into complex geometries with full, three- dimensional relief. Successive application of these techniques also enables definition of integrated nanoscale thermal transducers; coupling these to a dc SQUID readout yields the requisite e...

Roukes, M. L.

1998-01-01

233

Nonlinear phononics using atomically thin membranes

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.

Midtvedt, Daniel; Isacsson, Andreas; Croy, Alexander

2014-09-01

234

International Nuclear Information System (INIS)

The effects of nanocavities embedded in a narrow constriction on ballistic phonon transport in a semiconductor nanowire are investigated. It is shown that when more than one nanocavity is embedded in a narrow constriction with a fixed length, the nanowire has selective transmission and filter actions for the ballistic phonon. The number of resonant transmission peaks increases with the number n of cavities, while the frequencies of the main peaks are independent of n. The thermal conductance can be enhanced significantly, and the enhancement alters in different temperature ranges with the number n of cavities, depending on the competition between the transmission enhancement and scatter enhancement of the ballistic phonon. This structure may be a promising candidate for selective frequency generator and filter for the ballistic phonon in nanophononics.

235

International Nuclear Information System (INIS)

A numerical investigation was made of the structure of thermocapillary convection of a laser melt formed by radiation with various parameters in the specific case of SS304 stainless steel. A critical Reynolds number was found: above this number a single-vortex structure of the melt flow changed to two vortices. A comparison of the shape of the molten pool predicted by numerical calculations with experiments confirmed the existence of a two-vortex structure initiated solely by thermocapillary forces on the melt surface. A correlative dependence was proposed for relating the laser radiation parameters to those of the molten pool when a two-vortex flow structure appeared. (interaction of laser radiation with matter. laser plasma)

236

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

237

Heralded Single-Phonon Preparation, Storage, and Readout in Cavity Optomechanics

We show how to use the radiation pressure optomechanical coupling between a mechanical oscillator and an optical cavity field to generate in a heralded way a single quantum of mechanical motion (a Fock state). Starting with the oscillator close to its ground state, a laser pumping the upper motional sideband produces correlated photon-phonon pairs via optomechanical parametric down-conversion. Subsequent detection of a single scattered Stokes photon projects the macroscopic oscillator into a single-phonon Fock state. The nonclassical nature of this mechanical state can be demonstrated by applying a readout laser on the lower sideband to map the phononic state to a photonic mode and performing an autocorrelation measurement. Our approach proves the relevance of cavity optomechanics as an enabling quantum technology.

Galland, Christophe; Sangouard, Nicolas; Piro, Nicolas; Gisin, Nicolas; Kippenberg, Tobias J.

2014-04-01

238

The graphene phonon dispersion with C{sup 12} and C{sup 13} isotopes

Energy Technology Data Exchange (ETDEWEB)

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.

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

239

The graphene phonon dispersion with C12 and C13 isotopes

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.

Whiteway, Eric; Bernard, Simon; Yu, Victor; Austing, D. Guy; Hilke, Michael

2013-12-01

240

The graphene phonon dispersion with C12 and C13 isotopes

International Nuclear Information System (INIS)

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

241

Waveguide laser arrays operating at 1.5 micrometers have been fabricated on Er:Yb-doped glass substrates by a two-step silver-sodium ion-exchange process based on thermal diffusion followed by a field-assisted burial step. The fabrication parameters have been optimized to achieve low propagation losses and good mode matching between waveguide channels and standard single-mode output fibers. Each laser cavity is formed by two Bragg gratings butt-coupled to the two ends of the channel waveguide. Fiber-coupled output power in excess of 10 mW is readily available from a single channel, when pumped from both sides by two 980-nm laser diodes providing a maximum power of ~300 mW. Single-longitudinal mode operation with output power of the order of 1 mW has been achieved using narrow reflectivity band (<30 GHz) Bragg gratings with different laser configurations. The laser operating wavelength can be selected across the whole C-band of optical communications (1530-1565 nm) by changing the Bragg grating peak reflectivity wavelength. A relative intensity noise lower than -150 dB/Hz has been measured for frequencies larger than 2 MHz. Stability of single-frequency operation, low intensity noise and flexibility in the choice of the operating wavelength make this laser array particularly attractive for wavelength division multiplexing optical transmissions.

Sorbello, Gino; Taccheo, Stefano; Ramponi, Roberta; Foglietti, Vittorio; Jiang, Shibin; Peyghambarian, Nasser; Laporta, Paolo

2002-04-01

242

Piezoelectric surface acoustical phonon amplification in graphene on a GaAs substrate

Energy Technology Data Exchange (ETDEWEB)

We study the interaction of Dirac Fermions in monolayer graphene on a GaAs substrate in an applied electric field by the combined action of the extrinsic potential of piezoelectric surface acoustical phonons of GaAs (piezoelectric acoustical (PA)) and of the intrinsic deformation potential of acoustical phonons in graphene (deformation acoustical (DA)). We find that provided the dc field exceeds a threshold value, emission of piezoelectric (PA) and deformation (DA) acoustical phonons can be obtained in a wide frequency range up to terahertz at low and high temperatures. We found that the phonon amplification rate R{sup PA,DA} scales with T{sub BG}{sup S?1} (S=PA,DA), T{sub BG}{sup S} being the Block?Gru{sup ¨}neisen temperature. In the high-T Block?Gru{sup ¨}neisen regime, extrinsic PA phonon scattering is suppressed by intrinsic DA phonon scattering, where the ratio R{sup PA}/R{sup DA} scales with ?1/?(n), n being the carrier concentration. We found that only for carrier concentration n?10{sup 10}cm{sup ?2}, R{sup PA}/R{sup DA}>1. In the low-T Block?Gru{sup ¨}neisen regime, and for n=10{sup 10}cm{sup ?2}, the ratio R{sup PA}/R{sup DA} scales with T{sub BG}{sup DA}/T{sub BG}{sup PA}?7.5 and R{sup PA}/R{sup DA}>1. In this regime, PA phonon dominates the electron scattering and R{sup PA}/R{sup DA}<1 otherwise. This study is relevant to the exploration of the acoustic properties of graphene and to the application of graphene as an acoustical phonon amplifier and a frequency-tunable acoustical phonon device.

Nunes, O. A. C., E-mail: oacn@unb.br [Institute of Physics, University of Brasilia, Brasilia, 70910-900 DF (Brazil)

2014-06-21

243

Using the G' Raman cross-section to understand the phonon dynamics in bilayer graphene systems.

The G' (or 2D) Raman band of AB stacked bilayer graphene comes from a double resonance Raman (DRR) process and is composed of four peaks (P(11), P(12), P(21), and P(22)). In this work, the integrated areas (IA) of these four peaks are analyzed as a function of the laser power for different laser lines. We show that the dependence of the IA of each peak on temperature is different for each distinct laser excitation energy. This special dependence is explained in terms of the electron-phonon coupling and the relaxation of the photon-excited electron. In this DRR process, the electron is scattered by an iTO phonon from a K to an inequivalent K' point of the Brillouin zone. Here, we show that this electron relaxes while in the conduction band before being scattered by an iTO phonon due to the short relaxation time of the excited electron, and the carrier relaxation occurs predominantly by emitting a low-energy acoustic phonon. The different combinations of relaxation processes determine the relative intensities of the four peaks that give rise to the G' band. Some peaks show an increase of their IA at the expense of others, thereby making the IA of the peaks both different from each other and dependent on laser excitation energy and on power level. Also, we report that the IA of the G' mode excited at 532 nm, shows a resonance regime involving ZO' phonons (related to the interlayer breathing mode in bilayer graphene systems) in which a saturation of what we call the P(12) process occurs. This effect gives important information about the electron and phonon dynamics and needs to be taken into account for certain applications of bilayer graphene in the field of nanotechnology. PMID:22620978

Mafra, D L; Kong, J; Sato, K; Saito, R; Dresselhaus, M S; Araujo, P T

2012-06-13

244

Generation and detection of incoherent phonons in picosecond ultrasonics.

In picosecond ultrasonics experiments the absorption of a femtosecond laser pulse in a thin metallic transducer is used to generate very short acoustic pulses. These pulses are made of coherent longitudinal waves with a frequency spectrum that can reach 100-200 GHz. The laser pulse absorption gives rise to a heating of the film of a few Kelvin within a typical time of 1 ps. Later on, the heat goes in the substrate through an interface thermal resistance and is diffused by thermal conduction. At very low temperature and in pure crystals the thermal phonons emitted by the heated metallic film can propagate ballistically over large distances and produce a so-called heat pulse. We report on the experimental evidence of the coexistence of the coherent acoustic pulse and the incoherent heat pulse generated and detected by laser ultrasonics. PMID:16814828

Perrin, B; Péronne, E; Belliard, L

2006-12-22

245

Direct Measurement of the D-Mode and G-Mode Optical Phonon Lifetimes in Single Wall Carbon Nanotubes

Time-resolved Raman spectroscopy has been applied to determine the population lifetime of both zone-center and zone-edge optical phonons. Non-equilibrium populations of these phonons were produced by the rapid relaxation of charge carriers following photoexcitation of the nanotube sample with a femtosecond laser pulse. The temporal evolution of these phonon populations was recorded using the strength of antiStokes Raman scattering in G-mode (for the zone-center phonons) and D-mode (for the zone-edge phonons) as a function of the time delay of the fs probe pulse. A longer lifetime was found for the D-mode than for the G-mode phonons, a result consistent with recent ab-initio calculations of the anharmonic decay of these phonons [1]. We also report on the transient mode populations for the zone-center and zone-edge phonons that result from carrier cooling. [1] N. Bonini, M. Lazzeri, N. Marzari, and F. Mauri, Phys. Rev. Lett. 99, 176802 (2007).

Yan, Hugen; Song, Daohua; Heinz, Tony

2009-03-01

246

Energy Technology Data Exchange (ETDEWEB)

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.

Nikitin, Sergey M., E-mail: sergey.nikitin.Etu@univ-lemans.fr, E-mail: vitali.goussev@univ-lemans.fr [LAUM, UMR-CNRS 6613, Université du Maine, 72085 Le Mans (France); IMMM, UMR-CNRS 6283, Université du Maine, 72085 Le Mans (France); LSPM, UPR-CNRS 3407, Université Paris Nord, 93430 Villetaneuse (France); Tournat, Vincent; Chigarev, Nikolay; Castagnede, Bernard; Gusev, Vitalyi, E-mail: sergey.nikitin.Etu@univ-lemans.fr, E-mail: vitali.goussev@univ-lemans.fr [LAUM, UMR-CNRS 6613, Université du Maine, 72085 Le Mans (France); Bulou, Alain [IMMM, UMR-CNRS 6283, Université du Maine, 72085 Le Mans (France); Zerr, Andreas [LSPM, UPR-CNRS 3407, Université Paris Nord, 93430 Villetaneuse (France)

2014-01-28

247

Theory of spherical and two-stage target compression and heating under the action of a laser pulse

International Nuclear Information System (INIS)

A theory is developed of acceleration, heating and compression of a two-stage cladding target on exposure to a laser pulse. Under hydrodynamic conditions it is shown that the inner cladding can be accelerated up to the speed of approximately 200 km/s, energy concentration in the central stage of the target can be increased upon retention of high plasma density and inhomogeneous laser plasma configuration required for the development of a self-sustaining wave of synthesis reactions can be achieved in the end. Depending on the purpose of experimental studies (achievement of high plasma density or temperature) various schemes are suggested to match parameters of the two-stage target with laser pulse characteristics

248

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

249

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: Portuguese Abstract in portuguese 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.

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.

250

Phonon anharmonicity of iron monosilicide

A self-consistent thermodynamic model of the crystal lattice of FeSi is developed. In the framework of this model calculations of the heat capacity, coefficient of thermal expansion and bulk modulus of FeSi in a wide temperature range are carried out. On the basis of comparison with the experimental data, electronic contribution to the heat capacity of FeSi is obtained, the temperature dependence of which is caused by the insulator to metal transition, accompanied by disappearance of the energy gap in the electronic spectrum. We have found strong phonon anharmonicity of FeSi, which is manifested in substantial reduction of the Debye temperature and Gruneisen parameter with increasing temperature. The obtained values for the Gruneisen parameter of the crystal lattice of FeSi correlate with the estimations of the Gruneisen parameters for individual branches of the phonon spectrum of FeSi measured in neutron and synchrotron experiments.

Povzner, A. A.; Filanovich, A. N.

2015-01-01

251

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

252

Lattice phonon mediation of solid state photo reactions in organic crystals

International Nuclear Information System (INIS)

Physical or chemical change in a crystal lattice manifests itself as a change in its phonon spectrum. Laser Raman spectroscopic technique is being successfully used to study crystalline state photo reactions in organic materials. The main thrust of such study has been to investigate the role of phonons in such reactions. Electronic spectroscopy has generally been used to determine the extent of reaction progress and also to determine the nature of the photo processes involved. Infrared and Raman spectroscopy have been used to characterize the reactants and the products. Raman phonon spectroscopic study has been used to investigate whether the reaction occurs by homogeneous mechanism where the product form solid solution in the reactant lattice or by heterogeneous mechanism where the reactant and the product form separate lattices. Phonon participation in such reactions are shown to occur through strong exciton-phonon coupling or through a mode softening. In some reactions, however lattice phonons do not influence reactivity and topochemical controls is sufficient to explain crystalline state reactivity. (author). 69 refs., 11 figs

253

Photon-absorption-induced intersubband optical-phonon scattering of electrons in quantum wells

International Nuclear Information System (INIS)

In the presence of a normally incident intense mid-IR pulsed laser field, both photon-absorption-induced intrasubband and intersubband phonon-scattering of electrons are found by including the photon-assisted phonon-scattering process in a Boltzmann equation for phonon energies that are smaller than the energy separation between two electron subbands in a quantum well. The ultrafast dynamics of the electron distributions for different subbands is studied with various lattice temperatures, photon energies, field strengths, and quantum-well widths. Upward steps found in the differences between the electron distributions with/without the photon-assisted process are attributed to either photon-absorption-induced phonon scattering of electrons via intrasubband transitions or the photon-absorption-induced phonon scattering of electrons via intersubband transitions in quantum wells. The photon-absorption-induced phonon absorption by intersubband transitions of electrons from the first to the second subband is a unique feature in quantum-well systems and is found to have a significant effect on the electron populations in both subbands

254

Phonons from neutron powder diffraction

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...

Dimitrov, D. A.; Louca, D.; Ro?der, H.

1998-01-01

255

Phonon Transport Across Mesoscopic Constrictions

Phonon transport across constrictions formed by a nanowire or a nanoparticle on a substrate is studied by a numerical solution of the gray Boltzmann transport equation (BTE) resolving the effects of two length scales that govern problems of practical importance. Predictions of total thermal resistance for wire/substrate and particle/substrate combinations are made for the entire range of Knudsen number, with an emphasis on resolving transport in the mesoscopic regime where ballistic-diffusive...

Singh, Druv; Murthy, Jayathi Y.; Fisher, Timothy S.

2011-01-01

256

Phonon dispersions of cluster crystals

Energy Technology Data Exchange (ETDEWEB)

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.

Neuhaus, Tim [Institute of Theoretical Physics, Heinrich Heine University of Duessedorf, Universitaetsstrasse 1, D-40225 Duesseldorf (Germany); Likos, Christos N, E-mail: christos.likos@univie.ac.at [Faculty of Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna (Austria)

2011-06-15

257

International Nuclear Information System (INIS)

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

258

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)

259

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)

260

Phonon-Assisted Resonant Tunnelling through a Triple-Quantum-Dot: a Phonon-Signal Detector

International Nuclear Information System (INIS)

We study the effect of electron-phonon interaction on current and zero-frequency shot noise in resonant tunnelling 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 effect, and in particular we predict current peaks corresponding to phonon-absorption and phonon-emission assisted resonant tunnelling processes, which show that this system can be acted as a sensitive phonon-signal detector or as a cascade phonon generator

261

Phonons in Yukawa lattices and liquids

International Nuclear Information System (INIS)

The understanding of the theoretical structure of phonon dispersion in Yukawa lattices and the relationship between these perfect lattice phonons on the one hand, and the excitations in the disordered and liquid states on the other, is an important issue in analysing experimental and simulation results on plasma crystals. As the first step in this programme, we have numerically calculated the full phonon spectrum for 2D triangular Yukawa lattices, for a wide range of ?-bar (screening parameter) values and along different propagation angles. Earlier calculations of the excitation spectra of the 2D and 3D Yukawa liquids were based on the quasilocalized charge approximation (QLCA), whose implicit premise is that the spectrum of an average distribution (governed by the isotropic liquid pair correlation function) is a good representation of the actual spectrum. To see the implications of this model more clearly, we compare the high ? (near crystallization) QLCA phonon spectra with the angle-averaged phonon spectra of the lattice phonons

262

Hydrodynamic states of phonons in insulators

The Chapman-Enskog method is generalized for accounting the effect of kinetic modes on hydrodynamic evolution. Hydrodynamic states of phonon system of insulators have been studied in a small drift velocity approximation. For simplicity, the investigation was carried out for crystals of the cubic class symmetry. It has been found that in phonon hydrodynamics, local equilibrium is violated even in the approximation linear in velocity. This is due to the absence of phonon momen...

Sokolovsky, S. A.

2012-01-01

263

Nonlinear phononics using atomically thin membranes

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...

Midtvedt, Daniel; Isacsson, Andreas; Croy, Alexander

2014-01-01

264

Electron-phonon coupling in one dimension

International Nuclear Information System (INIS)

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

265

Plasmon-phonon coupling in graphene

Collective excitations of coupled electron-phonon systems are calculated for both monolayer and bilayer graphene, taking into account the non-perturbative Coulomb coupling between electronic excitations in graphene and the substrate longitudinal optical phonon modes. We find that the plasmon-phonon coupling in monolayer graphene is strong at all densities, but in bilayer graphene the coupling is significant only at high densities satisfying the resonant condition $\\omega_{pl...

Hwang, E. H.; Sensarma, Rajdeep; Sarma, S. Das

2010-01-01

266

Controlling phonon emission with plasmonic metamaterials

It is shown, that plasmonic metamaterial nanostructures could be used to reduce the electron-phonon scattering rate, by providing an alternative, fast electron-plasmon scattering channel. Since the plasmon-phonon and plasmon-photon scattering processes are relatively slow, this provides a mechanism for a hot-electron plasmonic protection against the phonon emission. The stored/protected energy can be returned to the single particle channel by processes similar to the Rabi os...

Kempa, Krzysztof

2012-01-01

267

Relativistic Kinetics of Phonon Gas in Superfluids

The relativistic kinetic theory of the phonon gas in superfluids is developed. The technique of the derivation of macroscopic balance equations from microscopic equations of motion for individual particles is applied to an ensemble of quasi-particles. The necessary expressions are constructed in terms of a Hamilton function of a (quasi-)particle. A phonon contribution into superfluid dynamic parameters is obtained from energy-momentum balance equations for the phonon gas tog...

Popov, Vladimir

2006-01-01

268

Maximizing phonon thermal conductance for ballistic membranes

At low temperatures, phonon scattering can become so weak that phonon transport becomes ballistic. We calculate the ballistic phonon conductance G for membranes using elasticity theory, considering the transition from three to two dimensions. We discuss the temperature and thickness dependence and especially concentrate on the issue of material parameters. For all membrane thicknesses, the best conductors have, counter-intuitively, the lowest speed of sound.

Ku?hn, T.; Maasilta, I. J.

2007-01-01

269

Phonon-mediated Superconductivity in Silicene

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...

Wan, Wenhui; Ge, Yanfeng; Yang, Fan; Yao, Yugui

2013-01-01

270

Phonon anharmonicities in graphite and graphene

We determine from first-principles the finite-temperature properties--linewidths, line shifts, and lifetimes--of the key vibrational modes that dominate inelastic losses in graphitic materials. In graphite, the phonon linewidth of the Raman-active E2g mode is found to decrease with temperature; such anomalous behavior is driven entirely by electron-phonon interactions, and does not appear in the nearly-degenerate infrared-active E1u mode. In graphene, the phonon anharmonic l...

Bonini, Nicola; Lazzeri, Michele; Marzari, Nicola; Mauri, Francesco

2007-01-01

271

Phonon drag of electrons at high temperatures

Temperature-dependent thermoelectric power (TEP) in semiconductor crystals and crystal structures containing an electron-vibrational centers (EVC) was investigated in this article. The TEP contain narrow pius at Debye temperatures for different phonons. In thin epitaxial layers on substrates such pius exist at Debye temperatures of substrates phonons. These pius existence imposable to explain on basis of known TEP theory but it may be explained by the phonon drag of electron...

Vdovenkov, V. A.

2002-01-01

272

Twisted phonons in Bose-Einstein condensates

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

Mendonça, J. T.; Gammal, A.

2014-03-01

273

Phonon-phonon interaction is systematically studied by nonequilibrium Green's function (NEGF) formulism in momentum space at finite temperatures. Within the quasi-particle approximation, phonon frequency shift and lifetime are obtained from the retarded self-energy. The lowest order NEGF provides the same phonon lifetime as Fermi's golden rule. Thermal conductance is predicted by the Landauer formula with a phenomenological transmission function. The main advantage of our me...

Xu, Yong; Wang, Jian-sheng; Duan, Wenhui; Gu, Bing-lin; Li, Baowen

2008-01-01

274

Phonon surface mapping of graphite: Disentangling quasi-degenerate phonon dispersions

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...

Gru?neis, Alexander; Lazzeri, Michele; Wirtz, Ludger; Attaccalite, Claudio; Rubio Secades, A?ngel; Mauri, Francesco; Pichler, Thomas

2009-01-01

275

Phonon coherence and new set of sidebands in phonon-assisted photoluminescence

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...

Xu, Sj; Xiong, Sj

2005-01-01

276

A variational approach to the optimized phonon technique for electron-phonon problems

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...

Cataudella, V.; Filippis, G.; Martone, F.; Perroni, C. A.

2004-01-01

277

Phonon-assisted resonant tunneling through a triple-quantum-dot: a phonon-signal detector

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 ...

Shen, X. Y.; Dong, Bing; Lei, X. L.

2007-01-01

278

Two-dimensional phonon transport in graphene.

Properties of phonons-quanta of the crystal lattice vibrations-in graphene have recently attracted significant attention from the physics and engineering communities. Acoustic phonons are the main heat carriers in graphene near room temperature, while optical phonons are used for counting the number of atomic planes in Raman experiments with few-layer graphene. It was shown both theoretically and experimentally that transport properties of phonons, i.e. energy dispersion and scattering rates, are substantially different in a quasi-two-dimensional system such as graphene compared to the basal planes in graphite or three-dimensional bulk crystals. The unique nature of two-dimensional phonon transport translates into unusual heat conduction in graphene and related materials. In this review, we outline different theoretical approaches developed for phonon transport in graphene, discuss contributions of the in-plane and cross-plane phonon modes, and provide comparison with available experimental thermal conductivity data. Particular attention is given to analysis of recent results for the phonon thermal conductivity of single-layer graphene and few-layer graphene, and the effects of the strain, defects, and isotopes on phonon transport in these systems. PMID:22562955

Nika, Denis L; Balandin, Alexander A

2012-06-13

279

Electromagnetic decay of two-phonon states

International Nuclear Information System (INIS)

The electromagnetic decay of two-phonon states corresponding to the multi-excitation of giant resonances is studied. The calculations are performed within a boson expansion approach and the elementary modes are constructed in random phase approximation (RPA). The rates for direct transition of two-phonon states to the ground state turn out to be not negligibly smaller than those from the (single) giant resonances. The former transitions are accompanied by a ?-ray whose energy is equal to the sum of the two phonon energies. Thus the detection of such high energy ?-rays could provide a signature of the excitation of two-phonon states. (author) 9 refs., 3 tabs

280

Electron-phonon interaction effects in tantalum

International Nuclear Information System (INIS)

The results of calculations for a number of electron-phonon interaction effects for tantalum are presented. The calculations are based on Korringa-Kohn-Rostoker energy bands, Born--von Karman phonons, and the rigid-muffin-tin approximation for the electron-phonon matrix element. The calculated Eliashberg spectral function ?2F is compared with the earlier tunneling data of Shen and the proximity tunneling data of Wolf et al. The calculated and tunneling transverse-phonon peaks agree well, but the height of the tunneling longitudinal-phonon peak is smaller than the calculated results. The calculated electron-phonon coupling parameter ? is 0.88, which is larger than the ? determined from superconducting tunneling and superconducting T/sub c/ measurements, but is slightly smaller than the ? determined from electronic specific-heat measurements. Calculated phonon linewidths along various symmetry directions are presented. The temperature dependence of the electrical resistivity due to phonon scattering is calculated in the lowest-order variational approximation and it agrees with experiment. The point-contact spectral function of Kulik, G(?), is determined and compared with ?2F(?). The agreement between calculated and measured electronic specific heat and high-temperature electrical resistivity gives strong support to the validity of the rigid-muffin-tin approximation for electron-phonon matrix elements

281

Resonant tunneling in a pulsed phonon field

DEFF Research Database (Denmark)

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].

Kral, P.; Jauho, Antti-Pekka

1999-01-01

282

Phonon-assisted transient electroluminescence in Si

Energy Technology Data Exchange (ETDEWEB)

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.

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

283

Phonon-phonon coupling and the stability of the high-temperature bcc phase of Zr

International Nuclear Information System (INIS)

Phonon-phonon coupling strengths have been derived from first-principles total energy calculations for bcc Zr. It is shown that the instability leading to the bcc-hcp first-order phase transition in Zr is overcome at high temperatures by the strong interactions between the T1 N-point phonon and other low-lying (110) T1 vibrational modes

284

Comparison of electron-phonon and hole-phonon energy loss rates in silicon

The hole-phonon energy loss rate in silicon is measured at phonon temperatures ranging from 300 mK to 700 mK. We demonstrate that it is approximately an order of magnitude higher than the corresponding electron-phonon energy loss rate over an identical temperature range.

Richardson-Bullock, J. S.; Prest, M. J.; Shah, V. A.; Gunnarsson, D.; Prunnila, M.; Dobbie, A.; Myronov, M.; Morris, R. J. H.; Whall, T. E.; Parker, E. H. C.; Leadley, D. R.

2015-01-01

285

Phonon Bose-Einstein condensation in a Hubbard-phonon interacting system with infrared divergence

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.

Sekine, Yoshitsugu

2013-01-01

286

Influence of the electron-phonon iinteraction on phonon heat conduction in a molecular nanowire

Directory of Open Access Journals (Sweden)

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.

Galovi? Slobodanka P.

2006-01-01

287

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.)

288

The time varying ratio of intensities of resonance lines of H- and He-like ions in laser irradiated cylindrical fibre targets is analysed using a hydro/atomic physics code. Correspondence between the ratio and gain on the Balmer ? transition of H-like ions in the adiabatically cooling and recombining plasma is found. The line ratios and absorbed energies corresponding to maximum gains for carbon, oxygen and fluorine plasmas are calculated. A useful diagnostic method is proposed for infering ...

Zhang, J.; Key, Mh; Norreys, P.; Tallents, Gj

1993-01-01

289

Dynamics of internal electric and phonon fields in n-GaAs pumped with ultrashort pulses

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english 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.

Fabrício M., Souza; J. Carlos, Egues.

1999-12-01

290

Lamb waves in plates covered by a two-dimensional phononic film

The propagation of Lamb waves in silicon plates coated by a very thin two-dimensional phononic film is studied experimentally. The dispersion curves are measured using a laser ultrasonics technique. The data are then compared to the calculated dispersion curves of the uncoated silicon plate. The overall shapes of the lower-order symmetric and antisymmetric Lamb modes are not altered by the thin phononic film, except by the appearing of frequency band gaps at the edges of both the first and the second Brillouin zone. The influence of the filling fraction on the magnitude of the gaps is investigated experimentally.

Bonello, Bernard; Charles, Christine; Ganot, François

2007-01-01

291

Phonon dynamics of UO2 at high temperature

Inelastic neutron scattering and numerical simulations are being used to investigate the fundamental aspects of phonons and thermal transport in UO2 as part of a DOE-EFRC "Center for Materials Science of Nuclear Fuel" project. Understanding thermal transport associated with nuclear fuel environments requires a correct accounting for a wide range of phonon scattering processes, including anharmonic phonon-phonon, phonon-fission product, and phonon-defect cluster. Reactor and spallation neutron measurements of phonon dispersion, phonon linewidths and density of states in UO2 at room and high temperature are in progress for direct comparison with atomic potential lattice-dynamics simulations of phonon dispersion, phonon group velocity, phonon linewidth, and phonon density of states. Direct comparisons between experimental measurements and numerical simulations in UO2 as a function of temperature will be presented.

Pang, J. W. L.; Chernatynskiy, A.; Larson, B. C.; Phillpot, S. R.; Buyers, W. J. L.

2011-03-01

292

Structural origin and laser performance of thulium-doped germanate glasses.

The structural origin and laser performance of thulium-doped germanate glasses have been studied. The investigation includes two main sections. The first part discusses the Raman spectroscopic and thermal stability of the host glass structure. The low value of the largest phonon energy (850 cm(-1)) reduces the probability of nonradiative relaxation. The large emission cross section of the Tm(3+) : (3)F(4) level (8.69 × 10(-21) cm(2)), the high quantum efficiency of the (3)F(4) level (71%), and the low nonradiative relaxation rate of the (3)F(4) ? (3)H(6) transition (0.09 ms(-1)) illustrate good optical properties of the germanate glass. In the second part, the room-temperature laser action from the thulium-doped germanate glass is demonstrated when pumped by a 790 nm laser diode. The maximum output power of 346 mW and slope efficiency of 25.6% are achieved. PMID:22085213

Xu, Rongrong; Xu, Lin; Hu, Lili; Zhang, Junjie

2011-12-15

293

Sound-Particles and Phonons with Spin 1

Directory of Open Access Journals (Sweden)

Full Text Available We present a new model for solids which is based on the stimulated vibration of independent neutral Fermi-atoms, representing independent harmonic oscillators with natural frequencies, which are excited by actions of the longitudinal and transverse elastic waves. Due to application of the principle of elastic wave-particle duality, we predict that the lattice of a solid consists of two type Sound Boson-Particles with spin 1 with finite masses. Namely, these lattice Boson-Particles excite the longitudinal and transverse phonons with spin 1. In this letter, we estimate the masses of Sound Boson-Particles which are around 500 times smaller than the atom mass.

Samoilov V.

2011-01-01

294

Chalcogenide glass microsphere laser.

Laser action has been demonstrated in chalcogenide glass microsphere. A sub millimeter neodymium-doped gallium lanthanum sulphide glass sphere was pumped at 808 nm with a laser diode and single and multimode laser action demonstrated at wavelengths between 1075 and 1086 nm. The gallium lanthanum sulphide family of glass offer higher thermal stability compared to other chalcogenide glasses, and this, along with an optimized Q-factor for the microcavity allowed laser action to be achieved. When varying the pump power, changes in the output spectrum suggest nonlinear and/or thermal effects have a strong effect on laser action. PMID:21165022

Elliott, Gregor R; Murugan, G Senthil; Wilkinson, James S; Zervas, Michalis N; Hewak, Daniel W

2010-12-01

295

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.

296

Dynamical stabilization by phonon-phonon interaction exemplified in cubic zirconia

Energy Technology Data Exchange (ETDEWEB)

Cubic zirconia exhibits a soft phonon mode (X{sup -}{sub 2}), which becomes dynamically unstable at low temperatures. Previous ab initio invest.igations into the temperature-induced stabilization of the soft mode treated it as an independent anharmonic oscillator. Calculations presented here, using the self consistent ab initio lattice dynamical (SCAILD) method to evaluate the phonons at 2570 K, show that the soft mode should not be treated independently of other phonon modes. Phonon-phonon interactions stabilize the X{sup -}{sub 2} mode. Furthermore, the effective potential experienced by the mode takes on a quadratic form.

Souvatsos, [etrps G [Los Alamos National Laboratory; Rudin, Sven P [Los Alamos National Laboratory

2008-01-01

297

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.

298

Strong squeezing via phonon mediated spontaneous generation of photon pairs

We propose a scheme generating robust squeezed light by using double cavity optomechanical system driven by blue detuned laser in one cavity and by red detuned laser in the other. This double cavity system is shown to mimic effectively an interaction that is similar to the one for the downconverter, which is known to be a source of strong squeezing for the light fields. There are however distinctions as the phonons, which lead to such an interaction, can contribute to the quantum noise. We show that the squeezing of the output fields of the order of $10$dB can be achieved even at mirror temperature of the order $10$mK.

Qu, Kenan

2014-01-01

299

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

Tuchina, E. S.; Petrov, P. O.; Kozina, K. V.; Ratto, F.; Centi, S.; Pini, R.; Tuchin, V. V.

2014-07-01

300

We show that the self-consistent dynamics of both phonons and electrons is the necessary ingredient for the reliable description of the hot phonons generation during electron transport in metallic single-wall carbon nanotubes (SWNTs). We solve the coupled Boltzmann transport equations to determine in a consistent way the current vs. voltage (IV) curve and the phonon occupation in metallic SWNTs which are lying on a substrate. We find a good agreement with measured IV curves and we determine an optical phonon occupation which corresponds to an effective temperature of several thousands K (hot phonons), for the voltages typically used in experiments. We show that the high-bias resistivity strongly depends on the optical phonon thermalization time. This implies that a drastic improvement of metallic nanotubes performances can be achieved by increasing the coupling of the optical phonons with a thermalization source.

Lazzeri, M; Lazzeri, Michele; Mauri, Francesco

2006-01-01

301

Electron-phonon scattering in topological insulators

We formulate and apply a theory of electron-phonon interactions for the surface state of a strong topological insulator. Phonons are modelled using an isotropic elastic continuum theory with stress-free boundary conditions and interact with the Dirac surface fermions via the deformation potential. We discuss the temperature dependence of the quasi-particle lifetime in photoemission and of the surface resistivity.

Giraud, Se?bastien; Egger, Reinhold

2011-01-01

302

Phonon Interference Effects in Molecular Junctions

We study coherent phonon transport through organic, \\pi-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 cr...

Markussen, Troels

2013-01-01

303

Phonon mediated quantum spin simulator made from a two-dimensional Wigner crystal in Penning traps

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.

Wang, Joseph; Keith, Adam; Freericks, J. K.

2013-03-01

304

Coherent phonon frequency comb generated by few-cycle femtosecond pulses in Si

Directory of Open Access Journals (Sweden)

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.

Petek Hrvoje

2013-03-01

305

International Nuclear Information System (INIS)

We present a microscopic theory of the light emission dynamics of an electrically pumped quantum dot emitter below laser threshold. The structure consists of a bulk semiconductor and Stranski-Krastanov grown InGaAs/GaAs quantum dot layers, operating at room temperature. Involving quantum wells and quantum dots Transport through the structure is driven by scattering with longitudinal-optical phonons, including nonequilibrium phonons. The calculations are momentum resolved and include the contacts, the bulk material and the quantum wells as well as the quantum dots. The emission of photons from the structure is included in our description as well. The system involves 15 Stranski-Krastanov grown InGaAs/GaAs quantum dot layers and operates at room temperature. It appears that even though the phonon distribution remains thermal, there is a substantial carrier heating in the quantum wells.

306

Phononic crystals and elastodynamics: Some relevant points

Directory of Open Access Journals (Sweden)

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.

N. Aravantinos-Zafiris

2014-12-01

307

Phononic crystals and elastodynamics: Some relevant points

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

Aravantinos-Zafiris, N.; Sigalas, M. M.; Kafesaki, M.; Economou, E. N.

2014-12-01

308

Phonon-drag effects on thermoelectric power

We carry out a calculation of the phonon-drag contribution S_g to the thermoelectric power of bulk semiconductors and quantum well structures for the first time using the balance equation transport theory extended to the weakly nonuniform systems. Introducing wavevector and phonon-mode dependent relaxation times due to phonon-phonon interactions, the formula obtained can be used not only at low temperatures where the phonon mean free path is determined by boundary scattering, but also at high temperatures. In the linear transport limit, S_g is equivalent to the result obtained from the Boltzmann equation with a relaxation time approximation. The theory is applied to experiments and agreement is found between the theoretical predictions and experimental results. The role of hot-electron effects in S_g is discussed. The importance of the contribution of S_g to thermoelectric power in the hot-electron transport condition is emphasized.

Wu Ming Wei; Cui, H L

1995-01-01

309

The phonon Hall effect: theory and application.

We present a systematic theory of the phonon Hall effect in a ballistic crystal lattice system, and apply it on the kagome lattice which is ubiquitous in various real materials. By proposing a proper second quantization for the non-Hermitian in the polarization-vector space, we obtain a new heat current density operator with two separate contributions: the normal velocity responsible for the longitudinal phonon transport, and the anomalous velocity manifesting itself as the Hall effect of transverse phonon transport. As exemplified in kagome lattices, our theory predicts that the direction of Hall conductivity at low magnetic field can be reversed by tuning the temperatures, which we hope can be verified by experiments in the future. Three phonon-Hall-conductivity singularities induced by phonon-band-topology change are discovered as well, which correspond to the degeneracies at three different symmetric center points, ?, K, X, in the wavevector space of the kagome lattice. PMID:21753242

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

2011-08-01

310

Plasphonics: local hybridization of plasmons and phonons.

We show that the interaction between localized surface plasmons sustained by a metallic nano-antenna and delocalized phonons lying at the surface of an heteropolar semiconductor can generate a new class of hybrid electromagnetic modes. These plasphonic modes are investigated using an analytical model completed by accurate Green dyadic numerical simulations. When surface plasmon and surface phonon frequencies match, the optical resonances exhibit a large Rabi splitting typical of strongly interacting two-level systems. Based on numerical simulations of the electric near-field maps, we investigate the nature of the plaphonic excitations. In particular, we point out a strong local field enhancement boosted by the phononic surface. This effect is interpreted in terms of light harvesting by the plasmonic antenna from the phononic surface. We thus introduce the concept of active phononic surfaces that may be exploited for far-infared optoelectronic devices and sensors. PMID:23481988

Marty, Renaud; Mlayah, Adnen; Arbouet, Arnaud; Girard, Christian; Tripathy, Sudhiranjan

2013-02-25

311

Propagating phonons coupled to an artificial atom.

Quantum information can be stored in micromechanical resonators, encoded as quanta of vibration known as phonons. The vibrational motion is then restricted to the stationary eigenmodes of the resonator, which thus serves as local storage for phonons. In contrast, we couple propagating phonons to an artificial atom in the quantum regime and reproduce findings from quantum optics, with sound taking over the role of light. Our results highlight the similarities between phonons and photons but also point to new opportunities arising from the characteristic features of quantum mechanical sound. The low propagation speed of phonons should enable new dynamic schemes for processing quantum information, and the short wavelength allows regimes of atomic physics to be explored that cannot be reached in photonic systems. PMID:25213379

Gustafsson, Martin V; Aref, Thomas; Kockum, Anton Frisk; Ekström, Maria K; Johansson, Göran; Delsing, Per

2014-10-10

312

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.)

313

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2011-05-15

314

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)

315

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

Fainstein, A; Lanzillotti-Kimura, N D; Jusserand, B; Perrin, B

2013-01-18

316

DEFF Research Database (Denmark)

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.

Angelsky, O. V.; Bekshaev, A. Ya.

2014-01-01

317

The method of local interferometry with a spatial resolution of ~ 5 ?m was used in an investigation of the dynamics of the development of small-scale deformations and periodic relief of the surface of silicon in the zone of irradiation with laser pulses. During the initial stage of such irradiation the changes in the surface relief were of random nature. Ordered surface fluctuations (surface wave) appeared in the molten phase. The initial period of the surface wave was ~ 20 ?s and it increased after the end of a laser pulse. Complete damping (i.e., formation of a periodic relief) was observed in these experiments in ~ 5 ms from the end of a laser pulse.

Banishev, A. F.; Chistyakov, I. M.

1992-05-01

318

International Nuclear Information System (INIS)

The dispersion relations for aluminium have been determined fairly completely at 80°K by measurements with a new three-axis crystal spectrometer at the 30-MW research reactor R2 at Studsvik. Complete dispersion curves have been obtained for the three symmetry directions, together with interpolation points on the zone boundaries and elsewhere. The results are presented as dispersion curves and as contour maps of dispersion surfaces. The series of measurements was the first undertaken with the spectrometer, and to establish a sound experimental routine, considerable attention was devoted to details such as resolution, reproducibility and the avoidance of disturbing effects, A focusing technique was used throughout to optimize resolution. The results consequently were of a rather high degree of accuracy and were utilized to search for Kohn anomalies, but no clear examples were found. Such effects are evidently small in aluminium, but there are indications that a moderate improvement of experimental technique may render them discernible. Phonon widths at 80°K could often be determined from the widths of observed resonances via a calculated resolution width. In another series of measurements at 300°K - not yet completed - widths could always be determined. Examples are given of broadenings and energy shifts in passing from 80 to 300°K. A noteworthy effect was found at q = (0.8,0,0) : the phonon width there increased in an anomalous fashion in passing from 80 to 300°K. Another observation is that points for small q on transverse branches tend to lie significantly above the lines through the origin having slopes corresponding to the velocity of 10-Mc/s sound waves. (author)

319

Improved Monte Carlo algorithm of phonon transport in semiconductor nanodevices

International Nuclear Information System (INIS)

In this work, we present the main features of an algorithm of phonon transport based on the particle Monte Carlo solution of the Boltzmann Transport Equation. In particular, we have developed an injection technique which consists in replacing a costly reservoir of phonons at thermodynamic equilibrium by an equivalent interface injecting in the device the appropriate phonon distribution. Additionally, we have derived a formulation of phonon-phonon scattering rates which includes realistic phonon dispersion of the material giving accurate frequency-dependence. An algorithm is proposed to improve the treatment of phonon interaction

320

Interface optical phonons in spheroidal quantum dots

Energy Technology Data Exchange (ETDEWEB)

Interface optical phonons are studied in the case of a quantum dot (QD) with prolate and oblate spheroidal geometries within the dielectric continuum approach. We considered CdSe or CdS QDs imbedded in a host material which is modelled as an infinite medium. The surface optical phonon modes, the corresponding frequencies, and the electron-phonon interaction Hamiltonian are reported. Comparison is made with previous works which only considered strictly spherical dots. We conclude that deviations from the perfect spherical shape could be responsible for observable physical effects in Raman spectra. (author)

Comas, F.; Trallero-Giner, C. [Departamento de Fisica Teorica, Universidad de la Habana, Vedado (Cuba); Studart, N.; Marques, G.E. [Departamento de Fisica, Universidade Federal de Sao Carlos, Sao Paulo (Brazil)

2002-07-01

321

Interface optical phonons in spheroidal quantum dots

International Nuclear Information System (INIS)

Interface optical phonons are studied in the case of a quantum dot (QD) with prolate and oblate spheroidal geometries within the dielectric continuum approach. We considered CdSe or CdS QDs imbedded in a host material which is modelled as an infinite medium. The surface optical phonon modes, the corresponding frequencies, and the electron-phonon interaction Hamiltonian are reported. Comparison is made with previous works which only considered strictly spherical dots. We conclude that deviations from the perfect spherical shape could be responsible for observable physical effects in Raman spectra. (author)

322

Acoustic superfocusing by solid phononic crystals

We propose a solid phononic crystal lens capable of acoustic superfocusing beyond the diffraction limit. The unit cell of the crystal is formed by four rigid cylinders in a hosting material with a cavity arranged in the center. Theoretical studies reveal that the solid lens produces both negative refraction to focus propagating waves and surface states to amplify evanescent waves. Numerical analyses of the superfocusing effect of the considered solid phononic lens are presented with a separated source excitation to the lens. In this case, acoustic superfocusing beyond the diffraction limit is evidenced. Compared to the fluid phononic lenses, the solid lens is more suitable for ultrasonic imaging applications.

Zhou, Xiaoming; Assouar, M. Badreddine; Oudich, Mourad

2014-12-01

323

Superconductivity and phonon softening in instable systems

International Nuclear Information System (INIS)

The effect of softening of phonon modes on the coupling parameter ? for superconductors with strong electron-phonon interaction is considered by taking into account electron effects. New formulae are derived which relates the increase in coupling parameter with optical phonons ?sub(opt) for the Pd-H system and the increase in the parameter ? for A3B-superconductors with A15-structure to changes in the density of states at the Fermi level. Using these formulae the role of electron factor N(O) 2> in the increasing of superconductive transition temperature Tsub(c) is discussed for the most high temperature superconductors. (author)

324

Acoustic and optical phonons in metallic diamond

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 qua...

M Hoesch, T. Fukuda

2006-01-01

325

Phonon dynamics of uranium chalcogenides (US)

International Nuclear Information System (INIS)

In this paper, we have investigated the phonon dynamics of US solids in NaCl phase using a Rigid Shell model with pair wise interionic interaction potential. The potential consists of the long-range Coulomb and three-body interactions and the short-range van der Waals interaction and the Hafemeister and Flygare type overlap repulsion extended up to the second neighbor ions. The elastic constants obtained from the model have been used to calculate the phonon dispersion relation in the symmetry direction. The phonon dispersion curves of US compound, calculated from the present model, agree with the neutron scattering data. (author)

326

One-dimensional hypersonic phononic crystals.

We report experimental observation of a normal incidence phononic band gap in one-dimensional periodic (SiO(2)/poly(methyl methacrylate)) multilayer film at gigahertz frequencies using Brillouin spectroscopy. The band gap to midgap ratio of 0.30 occurs for elastic wave propagation along the periodicity direction, whereas for inplane propagation the system displays an effective medium behavior. The phononic properties are well captured by numerical simulations. The porosity in the silica layers presents a structural scaffold for the introduction of secondary active media for potential coupling between phonons and other excitations, such as photons and electrons. PMID:20141118

Gomopoulos, N; Maschke, D; Koh, C Y; Thomas, E L; Tremel, W; Butt, H-J; Fytas, G

2010-03-10

327

Dynamical stabilization of the bcc phase in lanthanum and thorium by phonon-phonon interaction

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.

Souvatzis, P.; Bjorkman, T.; Eriksson, O.; Andersson, P.; Rudin, M. I. Katsnelson S- P.

2009-01-01

328

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

Directory of Open Access Journals (Sweden)

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.

Voronov V. V.

2012-12-01

329

We investigate in the framework of linear response theory the complete phonon dispersion, phonon induced electronic charge response, electron-phonon interaction and dielectric and infrared properties of the high-temperature superconductors (HTSC's). In particular the experimentally observed strong renormalization of the in-plane oxygen bond-stretching modes (OBSM) which appear upon doping in the HTSC's is discussed. It is shown that the characteristic softening, indicating a...

Falter, Claus

2004-01-01

330

We study, theoretically and experimentally, a new type of a multi-phonon Bragg light scattering in an optically anisotropic medium. A four-phonon Bragg anomalous light scattering in a tellurium dioxide crystal was observed using a light-blue optical beam of about 1 W in power from an argon gas-laser. Just the Bragg regime of light scattering was assured experimentally and a pentet of the light orders was distinguished and investigated.

Shcherbakov, Alexandre S.; Sanchez Perez, Karla Janeth; Sanchez Lucero, Daniel; Nemov, Sergey A.

2011-09-01

331

Phonon Properties of CoSb2 Single Crystals

Energy Technology Data Exchange (ETDEWEB)

The phonon properties of CoSb{sub 2} have been investigated by Raman scattering spectroscopy and lattice dynamics calculations. Sixteen out of eighteen Raman active modes predicted by factor-group analysis are experimentally observed and assigned. The calculated and measured phonon energies at the {Lambda} point are in very good agreement. The temperature dependence of the A{sub g} symmetry modes is well represented by phonon-phonon interactions without contribution from any other phonon or electron related interactions.

Petrovic C.; Lazarevic, N.; Radonjic, M.M.; Hu, R.; Tanaskovic, D.; Popovic, Z.V.

2012-04-04

332

Phonon properties of CoSb2 single crystals

International Nuclear Information System (INIS)

The phonon properties of CoSb2 have been investigated by Raman scattering spectroscopy and lattice dynamics calculations. Sixteen out of eighteen Raman active modes predicted by factor-group analysis are experimentally observed and assigned. The calculated and measured phonon energies at the ? point are in very good agreement. The temperature dependence of the Ag symmetry modes is well represented by phonon-phonon interactions without contribution from any other phonon or electron related interactions. (paper)

333

Toward engineered quantum many-body phonon systems

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

Soykal, O? O.; Tahan, Charles

2013-01-01

334

Screening effects in the electron-optical phonon interaction

We show that recently reported unusual hardening of optical phonons renormalized by the electron-phonon interaction is due to the neglect of screening effects. When the electron-ion interaction is properly screened optical phonons soften in three dimension. It is important that for short-wavelength optical phonons screening is static while for long-wavelength optical phonons screening is dynamic. In two-dimensional and one-dimensional cases due to crossing of the nonperturbe...

Reizer, M.

1999-01-01

335

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

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

2014-11-21

336

Monolithic Phononic Crystals with a Surface Acoustic Band Gap from Surface Phonon-Polariton Coupling

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.

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

2014-11-01

337

Phonon dynamics of the Heisenberg chain with finite-frequency phonons.

Since the discovery of the inorganic Spin-Peierls compound CuGeO3, one dimensional spin systems coupled to phonons have been studied intensively. While static properties are well understood, the dynamic phonon behavior is still unclear. We have studied the phonon dynamics of the spin 12 Heisenberg chain with bond phonons, around the structural phase transition which occurs as a function of spin-phonon coupling. We have employed Quantum Monte Carlo simulations based on stochastic series expansion (SSE), at almost zero and at finite temperature. The dynamic properties have been obtained by mapping the SSE to a continuous time path integral. At zero temperature we find that the quantum phase transition is of the central peak type as inferred before by Sandvik et al[1]. The renormalisation of the main phonon branch, however, depends strongly on the phonon frequency. As a function of temperature at fixed coupling, we find both a central peak for lower and phonon softening for higher spin-phonon coupling. This behavior is similar to the 3 dimensional case. [1] A. W. Sandvik et al., Phys. Rev. Lett. 83, 195 (1999)

Michel, Franz; Evertz, Hans Gerd

2005-03-01

338

Constants of Electron-Phonon Interaction for Optical and Intervalley Phonons in n-Ge

Directory of Open Access Journals (Sweden)

Full Text Available The electron scattering in case four-ellipsoidal, two-ellipsoidal and single-ellipsoidal L1-model of conduction band of Germanium is investigated. The constants of electron-phonon interaction for optical ?430 = 4·108 eV/cm and intervalley phonon ?320 = 1,4·108 eV/cm on base of the theory of anisotropy scattering and experimental temperature dependences resistivity are defined. The scattering by optical and intervalley phonon is significant in four-ellipsoidal L1-model of conduction band of n-Ge is shown. The scattering by acoustic phonons is dominated in two and single-valley L1-model.

S.V. Luniov

2014-04-01

339

Raman scattering from phonons and magnons in magnetic semiconductors, MnTe

Comparisons are made between theoretical and experimental data on laser Raman scattering by phonons and two-magnons in antiferromagnetic and paramagnetic phases of MnTe. The study was performed specifically to characterize the magnetic exchange coupling constants of the Mn ions in the samples. Crystal MnTe samples were bombarded with an Ar ion laser beam to obtain spectrometer and photon counter data. One E(2g) phonon with a room temperature energy of 178/cm and a two-magnon peak of 360/cm were observed in the Raman spectrum. A spin wave dispersion relation is presented for the spectrum. Finally, a Monte Carlo technique was used to calculate the two-magnon joint density of states that best fits the experimental data.

Mobasser, S. R.; Hart, T. R.

1985-01-01

340

Phonon density of states of model ferroelectrics

Energy Technology Data Exchange (ETDEWEB)

First principles density functional calculations and inelastic neutron scattering measurements have been used to study the variations of the phonon density of states of PbTiO3 and SrTiO3 as a function of temperature. The phonon spectra of the quantum paraelectric SrTiO3 is found to be fundamentally distinct from those of ferroelectric PbTiO3 and BaTiO3. SrTiO3 has a large 70-90 meV phonon band-gap in both the low temperature antiferrodistortive tetragonal phase and in the high temperature cubic phase. Key bonding changes in these perovskites lead to spectacular differences in their observed phonon density of states.

Choudhury, Narayani [University of Arkansas; Kolesnikov, Alexander I [ORNL; Schober, Helmut [Institut Laue-Langevin (ILL); Walter, Eric J. [College of William and Mary, Williamsburg, VA; Johnson, Mark [Institut Laue-Langevin (ILL); Abernathy, Douglas L [ORNL; Lucas, [ORNL

2010-01-01

341

Phonon-induced dynamic resonance energy transfer

In a network of interacting quantum systems, achieving fast coherent energy transfer is a challenging task. While quantum systems are susceptible to a wide range of environmental factors, in many physical settings their interactions with quantized vibrations, or phonons, of a supporting structure are the most prevalent. This leads to noise and decoherence in the network, ultimately impacting the energy-transfer process. In this work, we introduce a novel type of coherent energy-transfer mechanism for quantum systems, where phonon interactions are able to actually enhance the energy transfer. Here, a shared phonon interacts with the systems and dynamically adjusts their resonances, providing remarkable directionality combined with quantum speed-up. We call this mechanism phonon-induced dynamic resonance energy transfer and show that it enables long-range coherent energy transport even in highly disordered systems.

Lim, James; Tame, Mark; Yee, Ki Hyuk; Lee, Joong-Sung; Lee, Jinhyoung

2014-05-01

342

Phonon spectra of a Fibonacci chain

Energy Technology Data Exchange (ETDEWEB)

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.

Li Liqin [MOE Key Laboratory of Laser Life Science and Institute of Laser Life Science, South China Normal University, Guangzhou 510631 (China); Yang Xiangbo [MOE Key Laboratory of Laser Life Science and Institute of Laser Life Science, South China Normal University, Guangzhou 510631 (China); Laboratory of Photonic Information Technology, South China Normal University, Guangzhou 510631 (China)], E-mail: xbyang@scnu.edu.cn

2008-08-01

343

Acoustic and optical phonons in metallic diamond

Directory of Open Access Journals (Sweden)

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.

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

344

Phonon drag of electrons at high temperatures

Temperature-dependent thermoelectric power (TEP) in semiconductor crystals and crystal structures containing an electron-vibrational centers (EVC) was investigated in this article. The TEP contain narrow pius at Debye temperatures for different phonons. In thin epitaxial layers on substrates such pius exist at Debye temperatures of substrates phonons. These pius existence imposable to explain on basis of known TEP theory but it may be explained by the phonon drag of electrons (PDE) effect. In this connection there is the necessity to change traditional point of view on the PDE effect existence only at low temperatures and expand the PDE theory on case of strong electron-phonon coupling provided by EVC at high temperatures.

Vdovenkov, V A

2002-01-01

345

Strong Coupling between Nanoscale Metamaterials and Phonons

Energy Technology Data Exchange (ETDEWEB)

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.

Shelton, David J.; Brener, Igal; Ginn, James C.; Sinclair, Michael B.; Peters, David W.; Coffey, Kevin R.; Boreman, Glenn D.

2011-01-01

346

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

347

Hot phonons in a single heterostructure

International Nuclear Information System (INIS)

The lifetime of long-wavelength optical phonons in bulk semiconductors is known to be a function of electron density, decreasing with increasing density. An explanation of this has been given in terms of the effect of plasmon coupling on the anharmonic decay route. This explanation is limited to small wave-vectors and is not applicable to the case of phonons in general, since their interaction with electrons involves larger wave-vectors for which the plasma coupling is Landau damped. Nevertheless, a similar decrease of lifetime with density is observed for hot phonons in the channel of a GaN HFET. We offer an explanation of this in terms of a lifetime of interface modes significantly shorter than that of bulk modes. Our explanation also applies qualitatively to the observation of the non-monotonic behaviour of phonon lifetime with electron density

348

Toward stimulated interaction of surface phonon polaritons

Energy Technology Data Exchange (ETDEWEB)

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.

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

2013-12-21

349

Phonon-Drag Thermopower at High Temperatures

The adiabatic cristal model is offered. It is shown that springy nuclei oscillations relatively electronic envelops and waves of such oscillations (inherent oscillations and waves) may exist in crystals. The analysis of experimental temperature dependencies of resistivity in semiconductors with electron-vibrational centres has shown that inherent oscillations effectively interact with crystalline phonons as well as with electrons and holes, creating powerful interaction of electrons and holes with phonons. The experimental narrow peaks of phonon-drag thermoelectric power at Debye temperatures from 77K to 700K confirm existence of inherent oscillations waves in crystals. Inherent oscillations and waves gives rise to strong electron-phonon interaction and probably can bring about superconductivity at temperatures as below so and well above room temperature.

Vdovenkov, V A

1999-01-01

350

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

351

Influence of phonons on semiconductor quantum emission

Energy Technology Data Exchange (ETDEWEB)

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.)

Feldtmann, Thomas

2009-07-06

352

Heat capacity of suspended phonon cavities

We present a detailed analysis of the vibrational spectrum and heat capacity of suspended mesoscopic dielectric plates, for various thickness-to-side ratios at sub-Kelvin temperatures. The vibrational modes of the suspended cavity are accurately obtained from the three-dimensional (3D) elastic equations in the small strain limit and their frequencies assigned to the cavity phonon modes. The calculations demonstrate that the heat capacity of realistic quasi-2D phonon cavities...

Gusso, Andre; Rego, Luis G. C.

2006-01-01

353

Surface phonon propagation in topological insulators

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<2k_F du...

Thalmeier, Peter

2011-01-01

354

Forward Electron-Phonon Scattering and HTS

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.

Kulic, Miodrag L.; Dolgov, Oleg V.

1999-01-01

355

Inelastic Phonon Scattering in Graphene FETs

Inelastic phonon scattering in graphene field-effect transistors (FETs) is studied by numerically solving the Boltzmann transport equation in three dimensional real and phase spaces (x, kx, ky). A kink behavior due to ambipolar transport agreeing with experiments is observed. While low field behavior has previously been mostly attributed to elastic impurity scattering in earlier studies, it is found in the study that even low field mobility is affected by inelastic phonon sc...

Chauhan, Jyotsna; Guo, Jing

2011-01-01

356

Electron-phonon interaction using Wannier functions

We introduce a technique based on the spatial localization of electron and phonon Wannier functions to perform first-principles calculations of the electron-phonon interaction with an ultradense sampling of the Brillouin zone. After developing the basic theory, we describe the practical implementation within a density-functional framework. The proposed method is illustrated by considering a virtual crystal model of boron-doped diamond. For this test case, we first discuss the spatial localiza...

Giustino, F.; Cohen, Ml; Louie, Sg

2007-01-01

357

Phonon-assisted robust and deterministic two-photon biexciton preparation in a quantum dot

We investigate both experimentally and theoretically a simple yet more robust and flexible alternative to Rabi oscillation-type biexciton preparation protocols traditionally used for semiconductor quantum dots. The quantum dot is excited by a strong laser pulse positively detuned from the two-photon resonance yielding an on demand initialization of the biexciton state by making use of the phonon-induced thermalization of the photon dressed states. It is shown that for excita...

Bounouar, S.; Mu?ller, M.; Barth, A. M.; Gla?ssl, M.; Axt, V. M.; Michler, P.

2014-01-01

358

Coherent zone-folded acoustic phonons are excited in GaAs/AlAs superlattices by femtosecond laser pulses via resonant impulsive stimulated Raman scattering in both forward and backward scattering directions. The relative amplitudes of three distinct modes of first and second backfolded order match well with scattering intensities calculated within an elastic continuum model. The detection of the coherent acoustic modes is based on the modulation of the interband transitions via the acoustic d...

Bartels, Albrecht; Dekorsy, Thomas; Kurz, Heinrich; Ko?hler, Klaus

1999-01-01

359

Frequency dependence of dispersive phonon images

Scientific Electronic Library Online (English)

Full Text Available SciELO South Africa | Language: English Abstract in english 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.

K., Jakata; A.G., Every.

2008-10-01

360

High-frequency coherent phonons resonantly excited in metallic single-walled carbon nanotubes (M-SWCNTs) were investigated via spectrally resolved pump-probe spectroscopy using 7.5-fs laser pulses. In addition to first-order coherent phonons such as radial breathing mode (RBM) and M and G modes, we clearly observed second-order high-frequency coherent phonons of 2 D and 2 G modes, which can be regarded as squeezed phonons. We found that the amplitudes of the RBM, G and 2 D modes were resonantly enhanced at specific wavelengths: the maximum resides at a wavelength whose energy is smaller than that of the van Hove singularities in M-SWCNTs by an amount corresponding to the phonon energy. Furthermore, the 2 D mode has stronger enhancement than the other first-order Raman modes. These results indicate that the enhancement originates from a Stokes-stimulated Raman-scattering process at van Hove singularities and that efficient resonance enhancement occurs for the 2 D mode, possibly through double resonance due to the trigonal warping effect and strong electron-phonon coupling due to the Kohn anomaly.

Sato, K.; Tahara, K.; Minami, Y.; Katayama, I.; Kitajima, M.; Kawai, H.; Yanagi, K.; Takeda, J.

2014-12-01

361

Spectral properties of blue upconversion luminescences in Tm3+ doped tellurite (PWT, PbF2-WO3-TeO2) glasses and germanate (PWG, PbF2-WO3-GeO2) glasses pumped by a tunable dye laser were studied at room temperature. Two emission bands centered at 453 and 477 nm, corresponding to the 1D2?3H4 and 1G4?3H6 transitions of Tm3+ ions respectively, were observed. The two-photon absorption mechanism responsible for the 477 nm luminescence was confirmed by a quadratic dependence of luminescent intensities on the excitation power. Tellurite glasses showed a weaker upconversion luminescence than germanate glasses. This observation was inconsistent with the prediction from the phonon sideband measurement. In this article, Raman spectroscopy and transmittance measurement were employed to investigate the origin of the difference in upconversion luminescences in the two glasses. Compared with phonon sideband spectroscopy, Raman spectroscopy extracts more information, including both phonon energy and phonon density, and therefore, is a more effective analytical tool for understanding upconversion luminescence. Our results showed that the phonon energy as well as phonon density of the host glass is important in determining the upconversion efficiency.

Tsang, W. S.; Yu, W. M.; Mak, C. L.; Tsui, W. L.; Wong, K. H.; Hui, H. K.

2002-02-01

362

Raman studies of surface phonons in CdSe and CdS quantum dots embedded in dielectric media

Energy Technology Data Exchange (ETDEWEB)

Contribution of surface phonons strongly affects Raman spectra of quantum dots (QDs). In spite of a number of studies for CdSe and CdS, there is still no unique opinion on the behaviour of surface phonon parameters on the QD size. Moreover, since surface phonons are localized near the QD / host matrix interface, they can be sensitive to the type of host media as well as to the shell type for capped QDs. Here we present resonant micro-Raman studies of surface phonons of bare and capped colloidal CdSe and CdS QDs in different organic media (gelatine, polyvinyl alcohol, polyacrylamide) as well as those grown in silicate glass. Measurements were performed using a Dilor XY 800 spectrometer and different Ar laser lines for excitation. The dependences obtained for the surface phonon frequency, halfwidth as well as surface-to-LO phonon intensity ratio on the QD size, excitation wavelength, type of host media, passivating shell are analyzed. The results are compared with the calculations in the framework of a dielectric continuum model. The differences observed can be related to the QD surface reconstruction.

Azhniuk, Yuriy [Institute of Electron Physics, Uzhhorod (Ukraine); Dzhagan, Volodymyr; Valakh, Mykhailo [Institute of Semiconductor Physics, Kyiv (Ukraine); Kuchmii, Stepan; Raevskaya, Alexandra; Stroyuk, Alexandr [Institute of Physical Chemistry, Kyiv (Ukraine); Zahn, Dietrich [Chemnitz University of Technology, Chemnitz (Germany)

2007-07-01

363

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)

364

Electron-phonon coupling in CdSe nanocrystals from an atomistic phonon model.

Phonon frequencies and eigenvectors, electron-phonon couplings, and the associated resonance Raman spectra have been calculated for approximately spherical, wurtzite form CdSe nanocrystals having radii of 1.4 to 2.3 nm and containing 318 to 1498 atoms. Calculations of the equilibrium geometries and phonon modes are carried out using an empirical force field, and the electron and hole wave functions are calculated as particle-in-a-sphere envelope functions multiplying the Bloch functions, with valence-band mixing included for the hole functions. The coupling of each phonon mode to the 1S(e)-1S(3/2) and 1S(e)-2S(3/2) excitations is evaluated directly from the change in Coulombic energy along the phonon coordinate. Ten to 50 different modes in each crystal have significant Huang-Rhys factors, clustered around two frequency regions: acoustic phonons at 20-40 cm(-1) depending on crystal size, and optical phonons at 185-200 cm(-1). The Huang-Rhys factors are larger for the acoustic modes than for the optical modes and decrease with increasing crystal size, and the Huang-Rhys factors for each group of modes are smaller for the 1S(e)-2S(3/2) than for the 1S(e)-1S(3/2) excitation. These results are compared with measurements of electron-phonon coupling in CdSe nanocrystals using different experimental techniques. PMID:21598957

Kelley, Anne Myers

2011-06-28

365

THE PHONON ANOMALY IN b.c.c. He4 : A PHONON SELF-TRAPPING ?

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.

He?ritier, M.

1981-01-01

366

Coherent acoustic phonon generation in GaAs1-xBix

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.

Joshya, R. S.; Ptak, A. J.; France, R.; Mascarenhas, A.; Kini, R. N.

2014-03-01

367

Coherent acoustic phonon generation in GaAs{sub 1?x}Bi{sub x}

Energy Technology Data Exchange (ETDEWEB)

We have used femtosecond laser pulses to generate coherent acoustic phonons in the dilute Bismide alloy, GaAs{sub 1?x}Bi{sub x}. The observed oscillation periods match well with the oscillation periods calculated using the propagating strain pulse model. We attribute the generation process predominantly to electronic stress due to the absorption of the laser pulse at the surface of the GaAs{sub 1?x}Bi{sub x} layer. Our initial estimates suggest that the incorporation of Bi in GaAs causes an enhancement of the hydrostatic deformation potential because of the resonant state in the valence band due to isolated Bi impurities.

Joshya, R. S.; Kini, R. N., E-mail: rajeevkini@iisertvm.ac.in [Indian Institute of Science Education and Research Thiruvananthapuram (IISER-TVM), CET Campus, Thiruvananthapuram, Kerala 695016 (India); Ptak, A. J.; France, R.; Mascarenhas, A. [National Renewable Energy Laboratory (NREL), 1617 Cole Blvd., Golden, Colorado 80401 (United States)

2014-03-03

368

Directory of Open Access Journals (Sweden)

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

Nianbei Li

2012-12-01

369

Electron-Phonon Coupling and the Soft Phonon Mode in TiSe2

We report high-resolution inelastic x-ray measurements of the soft phonon mode in the charge-density-wave compound TiSe2. We observe a complete softening of a transverse optic phonon at the L point, i.e., q=(0.5,0,0.5), at T?TCDW. Detailed ab initio calculations for the electronic and lattice dynamical properties of TiSe2 are in quantitative agreement with experimental frequencies for the soft phonon mode. The observed broad range of renormalized phonon frequencies, (0.3,0,0.5)?q?(0.5,0,0.5), is directly related to a broad peak in the electronic susceptibility stabilizing the charge-density-wave ordered state. Our analysis demonstrates that a conventional electron-phonon coupling mechanism can explain a structural instability and the charge-density-wave order in TiSe2 although other mechanisms might further boost the transition temperature.

Weber, F.; Rosenkranz, S.; Castellan, J.-P.; Osborn, R.; Karapetrov, G.; Hott, R.; Heid, R.; Bohnen, K.-P.; Alatas, A.

2011-12-01

370

Anisotropic phonon anomaly in Bi2212 manifested by electron-phonon coupling

Electron-phonon coupling (EPC) is one of the important issues in condensed matter physics. Angle-resolved photoemission spectroscopy has been recognized as a powerful tool for the study of EPC by determining the renormalization of electron self energy. For the phonon counterpart, we measure the momentum-dependent phonon spectra of an optimal doped cuprate Bi2212 with high-resolution electron energy loss spectroscopy. The apical oxygen vibration mode at 80 meV exhibits distinct anisotropic anomaly due to EPC. By analyzing the phonon lifetime, the momentum-dependent EPC strength is determined with the knowledge of electron band structure. It is emphasized that the combination of analyses of phonon and electron structures leads to an unambiguous and comprehensive description of EPC.

Guo, Jiandong; Qin, Huajun; Shi, Junren; Cao, Yanwei; Wu, Kehui; Zhang, Jiandi; Plummer, E. W.; Wen, J.; Gu, G. D.

2010-03-01

371

Phonon confinement effect on electrophonon resonance in one dimensional structure

The electrophonon resonance in cylindrical quantum wires is investigated in the presence of optical phonon confinement effects. A macroscopic dielectric continuum model is used to describe confined and interface phonon modes, and the results are compared with the bulk phonon model. It is found that different selection rules apply to bulk phonon and confined/interface phonon treatments, which suggests a possibility that electron transport experiments may detect the evidence for optical phonon confinement. This work was supported, in part, by the U. S. Army Research Office and the Office of Naval Research.

Yu, Segi; Pevzner, V. B.; Jeon, Junbeom; Kim, K. W.; Stroscio, Michael A.

1998-03-01

372

Electron and phonon interactions a novel semiclassical approach

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

Rose, A

1989-01-01

373

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

374

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.

375

Phonon Anharmonicities in Graphite and Graphene.

Energy Technology Data Exchange (ETDEWEB)

The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. We determine from first principles the finite-temperature properties—linewidths, line shifts, and lifetimes—of the key vibrational modes that dominate inelastic losses in graphitic materials. In graphite, the phonon linewidth of the Raman-active E2g mode is found to decrease with temperature; such anomalous behavior is driven entirely by electron-phonon interactions, and does not appear in the nearly degenerate infrared-active E1u mode. In graphene, the phonon anharmonic lifetimes and decay channels of the A01 mode at K dominate over E2g at T and couple strongly with acoustic phonons, highlighting how ballistic transport in carbon-based interconnects requires careful engineering of phonon decays and thermalization.

Bonini, Nicola; Lazzeri, Michele; Marzari, Nicola N.; Mauri, Francesco

2007-10-24

376

Modified Sharma-Joshi model and phonon dispersion in ?-zirconium

International Nuclear Information System (INIS)

A new model is proposed. This model assumes the ion-ion interaction to be purely central and expresses the ion-ion coupling through the first and second derivatives of the potential. An equilibrium criterion, considering the volume dependent energies of ions and electrons, makes the model quite sound in its applicability. The volume-term due to Sharma-Joshi is modified to include the factors like G2 and Ksub(c)sup(2) ? (q). The latter factor accounts for the exchange and correlation effects of conduction electrons in their screening-action and the former factor includes the Umklapp processes, which essentially control the symmetry of the lattice. The model thus developed reproduces the phonon-dispersion in bcc zirconium quite successfully. (author)

377

Advances in semiconductor lasers and applications to optoelectronics

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

Dutta, Mitra

2000-01-01

378

Subwavelength waveguiding of surface phonons in pillars-based phononic crystal

In this study, we theoretically analyze the guiding of surface phonons through locally resonant defects in pillars-based phononic crystal. Using finite element method, we simulate the propagation of surface phonons through a periodic array of cylindrical pillars deposited on a semi-infinite substrate. This structure displays several band gaps, some of which are due to local resonances of the pillar. By introducing pillar defects inside the phononic structure, we show the possibility to perform a waveguiding of surface phonons based on two mechanisms that spatially confine the elastic energy in very small waveguide apertures. A careful choice of the height of the defect pillars, allows to shift the frequency position of the defect modes inside or outside the locally resonant band gaps and create two subwavelenght waveguiding mechanisms. The first is a classical mechanism that corresponds to the presence of the defect modes inside the locally resonant band gap. The seconde is due to the hybridation between the phonon resonances of defect modes and the surface phonons of the semi-infinite homogenous medium. We discuss the nature and the difference between both waveguiding phenomena.

Addouche, Mahmoud; Al-Lethawe, Mohammed A.; Elayouch, Aliyasin; Khelif, Abdelkrim

2014-12-01

379

Subwavelength waveguiding of surface phonons in pillars-based phononic crystal

Directory of Open Access Journals (Sweden)

Full Text Available In this study, we theoretically analyze the guiding of surface phonons through locally resonant defects in pillars-based phononic crystal. Using finite element method, we simulate the propagation of surface phonons through a periodic array of cylindrical pillars deposited on a semi-infinite substrate. This structure displays several band gaps, some of which are due to local resonances of the pillar. By introducing pillar defects inside the phononic structure, we show the possibility to perform a waveguiding of surface phonons based on two mechanisms that spatially confine the elastic energy in very small waveguide apertures. A careful choice of the height of the defect pillars, allows to shift the frequency position of the defect modes inside or outside the locally resonant band gaps and create two subwavelenght waveguiding mechanisms. The first is a classical mechanism that corresponds to the presence of the defect modes inside the locally resonant band gap. The seconde is due to the hybridation between the phonon resonances of defect modes and the surface phonons of the semi-infinite homogenous medium. We discuss the nature and the difference between both waveguiding phenomena.

Mahmoud Addouche

2014-12-01

380

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

381

Phonons and Lattice Dielectric Properties of Zirconia

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...

Zhao, X; Zhao, Xinyuan; Vanderbilt, David

2001-01-01

382

A Correlation Function for Phonon Eigenvectors

International Nuclear Information System (INIS)

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

383

Phonon multiplexing through 1D chains

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english 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.

A., Avila; D., Reyes.

2008-12-01

384

Electrons and Phonons in Semiconductor Multilayers

This book provides a detailed description of the quantum confinement of electrons and phonons in semiconductor wells, superlattices and quantum wires, and shows how this affects their mutual interactions. It discusses the transition from microscopic to continuum models, emphasizing the use of quasi-continuum theory to describe the confinement of optical phonons and electrons. The hybridization of optical phonons and their interactions with electrons are treated, as are other electron scattering mechanisms. The book concludes with an account of the electron distribution function in three-, two- and one-dimensional systems, in the presence of electrical or optical excitation. This text will be of great use to graduate students and researchers investigating low-dimensional semiconductor structures, as well as to those developing new devices based on these systems.

Ridley, B. K.

1996-11-01

385

Coherent phonon heat conduction in superlattices.

The control of heat conduction through the manipulation of phonons as coherent waves in solids is of fundamental interest and could also be exploited in applications, but coherent heat conduction has not been experimentally confirmed. We report the experimental observation of coherent heat conduction through the use of finite-thickness superlattices with varying numbers of periods. The measured thermal conductivity increased linearly with increasing total superlattice thickness over a temperature range from 30 to 150 kelvin, which is consistent with a coherent phonon heat conduction process. First-principles and Green's function-based simulations further support this coherent transport model. Accessing the coherent heat conduction regime opens a new venue for phonon engineering for an array of applications. PMID:23161996

Luckyanova, Maria N; Garg, Jivtesh; Esfarjani, Keivan; Jandl, Adam; Bulsara, Mayank T; Schmidt, Aaron J; Minnich, Austin J; Chen, Shuo; Dresselhaus, Mildred S; Ren, Zhifeng; Fitzgerald, Eugene A; Chen, Gang

2012-11-16

386

Lattice-Boltzmann modeling of phonon hydrodynamics.

Based on the phonon Boltzmann equation, a lattice-Boltzmann model for phonon hydrodynamics is developed. Both transverse and longitudinal polarized phonons that interact through normal and umklapp processes are considered in the model. The collision term is approximated by the relaxation time model where normal and umklapp processes tend to relax distributions of phonons to their corresponding equilibrium distribution functions-the displaced Planck distribution and the Planck distribution, respectively. A macroscopic phonon thermal wave equation (PTWE), valid for the second-sound mode, is derived through the technique of Chapman-Enskog expansion. Compared to the dual-phase-lag (DPL) -based thermal wave equation, the PTWE has an additional fourth-ordered spatial derivative term. The fundamental difference between the two models is discussed through examining a propagating thermal pulse in a single-phased medium and the transient and steady-state transport phenomena on a two-layered structure subjected to different temperatures at boundaries. Results show that transport phenomena are significantly different between the two models. The behavior exhibited by the DPL model, as thermal wave behavior goes over to diffusive behavior, tau_{T}-->tau_{q} is incompatible with any microscopic phonon propagating mode. Unlike the DPL model, in which tau_{T} only has an effect on the transient phenomena, in the PTWE model tau_{T} shows effects on phenomena at both transient and steady state. With the intrinsic compatibility to the microscopic state, discontinuous quantities, such as a jump of temperature at a boundary or at an interface, can be calculated naturally and straightforwardly with the present lattice-Boltzmann method. PMID:18643400

Jiaung, Wen-Shu; Ho, Jeng-Rong

2008-06-01

387

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

388

Phonon emission in a degenerate semiconductor at low lattice temperatures

The characteristics of phonon growth in a degenerate semiconductor at low lattice temperatures have been studied for inelastic interaction of non-equilibrium electrons with the intravalley acoustic phonons. The energy of the phonon and the full form of the phonon distribution are taken into account. The results reveal significant changes in the growth characteristics compared to the same for a non-degenerate material.

Midday, S.; Nag, S.; Bhattacharya, D. P.

2015-02-01

389

Ultrafast dynamics of coherent phonon vibration in thermoelectric materials

Dynamics of phonons and excited carriers are key parameters for the performance of technologically important devices. The excited carriers (electrons and holes), which are either pumped optically or electrically, will relax back to the ground states by scattering with phonons, boundaries, impurities, and so on. Time-resolved optical measurement is a unique way to study specific optical phonon mode as ultrafast pulses generate predominantly the A 1g coherent phonon vibration. Compared with the...

Wu, Qihong

2008-01-01

390

Tuning correlation effects with electron-phonon interactions

We investigate the effect of tuning the phonon energy on the correlation effects in models of electron-phonon interactions using DMFT. In the regime where itinerant electrons, instantaneous electron-phonon driven correlations and static distortions compete on similar energy scales, we find several interesting results including (1) A crossover from band to Mott behavior in the spectral function, leading to hybrid band/Mott features in the spectral function for phonon frequenc...

Hague, J. P.; D Ambrumenil, N.

2007-01-01

391

Neutron-Phonon Interaction in Neutron Star Crusts

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...

Sedrakian, Armen

1998-01-01

392

Phonon absorption-spectroscopy in the presence of strong elastic phonon scattering

In this work we show that in the presence of a strong phonon scattering background absorption structures can only be well resolved by reducing sample thickness to the phonon mean free path. This mean free path can be determined by analyzing the pulse shape of 285 GHz phonons. By reducing sample thickness to the appropriate value of 0,3mm the 21,2 cm -1 crystalline field transition in CaF 2:Er 3+ could be evaluated with the very high resolution of 5 GHz. In experiments performed on a 1mm thick...

Mebert, Joachim; Koblinger, Otto; Do?ttinger, Siegfried; Eisenmenger, Wolfgang

1986-01-01

393

Electron-Phonon Coupling and the Soft Phonon Mode in TiSe$_2$

We report high-resolution inelastic x-ray measurements of the soft phonon mode in the charge-density-wave compound TiSe$_2$. We observe a complete softening of a transverse optic phonon at the L point, i.e. q = (0.5, 0, 0.5), at T ~ T_{CDW}. Renormalized phonon energies are observed over a large wavevector range $(0.3, 0, 0.5) \\le \\mathbf{q} \\le (0.5, 0, 0.5)$. Detailed ab-initio calculations for the electronic and lattice dynamical properties of TiSe2 are in quantitative ag...

Weber, F.; Rosenkranz, S.; Castellan, J. -p; Osborn, R.; Karapetrov, G.; Hott, R.; Heid, R.; Bohnen, K. -p; Alatas, A.

2011-01-01

394

Electron-phonon interaction and composition-dependent phonon anomaly in CeHsub(x)

International Nuclear Information System (INIS)

The Raman active phonon in CeHsub(approximately 3) is anomalously soft as compared with that in in CeHsub(approximately 2). It is shown that this can be attributed to enhanced electron-phonon interactions arising from changes in the electronic structure with composition: when going from CeH2 to CeH3 a new s-like valence band is formed, and the valence electrons screen the Raman active mode via virtual transitions into Ce d states. Frequency renormalisation due to the electron-phonon interaction has been calculated from the electronic energy bands. (author)

395

Electron-Phonon Interactions for Optical Phonon Modes in Few-Layer Graphene

We present a first-principles study of the electron-phonon (e-ph) interactions and their contributions to the linewidths for the optical phonon modes at $\\Gamma$ and K in one to three-layer graphene. It is found that due to the interlayer coupling and the stacking geometry, the high-frequency optical phonon modes in few-layer graphene couple with different valence and conduction bands, giving rise to different e-ph interaction strengths for these modes. Some of the multilaye...

Yan, Jia-an; Ruan, W. Y.; Chou, M. Y.

2009-01-01

396

Electronic structure, phonon spectra and electron-phonon interaction in ScB2

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.

Sichkar, S. M.; Antonov, V. N.

2013-07-01

397

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

398

It is demonstrated how the exciton and the biexciton state of a quantum dot can be prepared with high fidelity on a picosecond time scale by driving the dot with a strong laser pulse that is tuned above the exciton resonance for exciton preparation and in resonance with the exciton transition for biexciton preparation. The proposed protocols make use of the phonon-induced relaxation towards photon dressed states in optically driven quantum dots and combine the simplicity of traditional Rabi oscillation schemes with the robustness of adiabatic rapid passage schemes. Our protocols allow for an on-demand, fast, and almost perfect state preparation even at strong carrier-phonon interaction where other schemes fail. In fact, the performance of the presented protocols is shown to be better the stronger the carrier-phonon interaction is.

Glässl, M.; Barth, A. M.; Axt, V. M.

2013-04-01

399

Electron-phonon interaction in transition metals

International Nuclear Information System (INIS)

The Hopfield parameter eta of the electron-phonon coupling is calculated for twelve transition metals (Rh, Pd, Ag, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au) in the rigid muffin-tin approximation. Using relativistic APW band structure data and a generalized Gaspari-Gyorffy formula the influence of relativistic effects is completely taken into account. It is found that eta may be calculated in remarkably good approximation using spin-weighted averages of phase shifts and density matrix coefficients. The theoretical results for the electron-phonon parameter lambda and the electronic specific heat are compared with the experimental data. (author)

400

Site Symmetry and Band Representations for Phonons

Site symmetry centers and band representations are considered for phonon spectra in crystals. For the case of Bravais lattices (crystals with one atom in a unit cell) it is shown that the acoustic phonon-frequency band is described by a band representation that is induced from a vectorial representation of the local symmetry group for the Wyckoff position coinciding with the location of the atom. Band representations from local groups for all other Wyckoff positions are forbidden. A consequence of this is that the topological phase for the acoustic band is zero.

Walker, M. B.; Zak, J.

1995-05-01

401

Monochromatic phonon generation by superconducting tunnel junctions

International Nuclear Information System (INIS)

Superconducting tunneling junctions are metal-oxide-metal structures where the insulating oxide is thin enough so that electrons can tunnel quantum mechanically from one side to the other. The devices are used for fast switching computer elements, low noise microwave mixers, ultra sensitive magnetic flux detectors, and highly reproducible voltage standards. The junctions are also well suited for the generation and the detection of phonons. Two different ways of tunable monochromatic phonon generation by superconducting tunnel junctions are discussed. Examples of each method are presented

402

Phonon dispersion curves for CsCN

International Nuclear Information System (INIS)

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

403

Phonon interference effects in molecular junctions

DEFF Research Database (Denmark)

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.

Markussen, Troels

2013-01-01

404

Quantized phonon-enhanced spin fluctuations

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

Koo, Je Huan

2015-01-01

405

Phonon interference effects in molecular junctions

International Nuclear Information System (INIS)

We study coherent phonon transport through organic, ?-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

406

Phonon Overlaps: Polyacetylene, Polarons, and Molecular Size

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.

Chang, C T; Chang, Connie Te-ching; Sethna, James P.

2006-01-01

407

International Nuclear Information System (INIS)

X-ray diffraction analysis was used to investigate the influence of bulk isothermal and surface laser annealings on crystallization of Fe61Co20Si5B14 metallic glass. It is shown that crystallization proceeds in different ways on isothermal and laser annealings. Low-energy laser treatment makes it possible to produce complex phase composition in a surface layer which may be controlled by irradiation dose rate

408

Phonon heat capacity of single-walled carbon nanotubes

International Nuclear Information System (INIS)

The research of phonon spectra of carbon nanotubes is presented. The behavior of heat capacity at low temperatures allows to define phonon dispersion and to understand mechanisms of transformations of phonon spectra by rolling up of single graphite sheet to form carbon nanotube

409

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 ...

Dolgov, O. V.; Andersen, O. K.; Mazin, I. I.

2007-01-01

410

Barium strontium titanate ferroelectric tunable photonic and phononic crystals

This thesis presents the results of theoretical simulations and experimental investigations on developing electro-optically tunable photonic crystals and thermally tunable phononic crystals based on the ferroelectric materials, Barium Strontium Titanate (Ba0.7Sr0.3TiO3, BST). One-dimensional photonic crystal (PC), consists of alternating Ba 0.7Sr0.3TiO3 and MgO layers, was fabricated using pulsed laser deposition. A photonic bandgap has been observed in the transmission measurement which is consistent with simulation using the plane wave expansion (PWE) method and the transfer matrix method. A 2-nm shift towards the longer wavelength is observed when a dc voltage of 240 V (corresponding to an electric field of about 12 MV/m) has been applied across the coplanar electrodes on the film surface. The experimental result suggests that the electric field induced change in the refractive index of Ba0.7Sr0.3TiO 3 is about 0.5%. Photonic bandstructures and photonic bandgap maps of two-dimensional (2D) Ba0.7Sr0.3TiO3-based photonic crystals with different cavity geometries (square or circular air rods) in square lattice were calculated using the PWE method. Bandgap features along different symmetry directions have also been compared. The appropriate geometry of a single-mode rib waveguide based on Ba 0.7Sr0.3TiO3 thin film was determined by applying the effective index method. A photonic crystal cavity embedded Ba0.7 Sr0.3TiO3 rib waveguide which functions as a tunable filter for lambda = 1550 nm was designed with the help of the finite-difference time-domain (FDTD) simulation. A 6-nm shift in the resonant peak for a 0.5% change in the refractive index of Ba0.7Sr0.3TiO 3 was illustrated in the simulation. Photonic crystal cavities were fabricated on a Ba0.7Sr0.3TiO3 rib waveguide by focused ion beam etching with satisfactory results. A drastic variation in the sound velocities was observed across the Curie temperature of Ba0.7Sr0.3TiO3 via the ultrasonic through-transmission technique. Phononic crystal composed of Ba0.7Sr 0.3TiO3 square rods in a matrix of epoxy were fabricated using the dice-and-fill method. The temperature dependence of the phononic bandgaps was characterized by the reflection spectra obtained using the ultrasonic pulse-echo technique. Thermal tuning of the phononic bandgap was observed and the results were in good agreement with the phononic bandstructure calculation by the PWE method.

Jim, Kwok Lung

2009-12-01

411

Ultrashort shear acoustic pulse excitation via laser-induced electrostrictive effect (abstract)

In principle there are several opportunities to achieve excitation of ultrashort shear pulses by laser radiation. One of them is to use the anisotropy of material properties such as elasticity and thermal expansion (in the case of the thermoelastic mechanism of the optoacoustic transformation) or the electron-phonon deformation potential (in the case of sound excitation via electron-hole plasma photogeneration). Another is related to application of the laser-induced inverse (converse) piezoelectric effect. Laser-generated electron-hole plasma creates an electric field due to the electron-hole spatial separation (Dember field) or can screen an electric field (built-in or induced externally) pre-exsisting near the crystal surface. In piezoelectric materials the induced ultrafast transients in electric field distribution in the proximity of the crystal surface should cause excitation of ultrashort acoustic pulses of various modes. Experimentally achieved excitation of plane TA pulses in piezoelectric crystals by nanosecond laser pulses, and also excitation of both optical phonons and ultrashort electromagnetic pulses (THz radiation) by femtosecond laser pulses all support the possibility of exciting ultrashort TA, as well as LA, pulses. The idea of using the inverse piezoelectric effect is also supported by recent observations of extremely high efficiency of quasi-monochromatic LA coherent oscillations generation by laser-induced screening of built-in electric fields in strained multiple quantum wells of piezoelectric semiconductors. We analyze one more opportunity for ultrashort TA pulse excitation in optoacoustic transformation via the action of laser-induced electrostrictive stress on surface of optically transparent crystals. A simple theory is developed and numerical estimates are presented to demonstrate the possibility of exciting ultrashort acoustic pulses in optically transparent materials by laser-induced electrostrictive surface mechanical stresses. Both longitudinal and shear coherent acoustic pulses can be excited. The conditions for which the polarization of ultrashort shear pulses is controlled by the polarization of an incident laser pulse are established. The profiles and duration of longitudinal and shear acoustic strain pulses are shown to coincide with laser pulse intensity envelope. Picosecond shear pulses might be very useful in diverse applications related to measurements of shear rigidity or shear viscosity, including ultrafast solid-liquid phase transitions, ultrafast tribology, and diagnostics of liquids in confined geometry.

Gusev, V.; Picart, P.; Mounier, D.; Breteau, J. M.

2003-01-01

412

Coherent acoustic phonons in phonon cavities investigated by asynchronous optical sampling

International Nuclear Information System (INIS)

Using a recently introduced measurement technique, called asynchronous optical sampling (ASOPS), we have investigated the dynamics of coherent acoustic phonons in a semiconductor heterostructure composed of a GaAs film between two GaAs/AlAs superlattices, serving as a cavity for acoustic phonons. Measurements were performed at liquid helium temperatures. The possibility to perform two-color pump-probe spectroscopy allowed us to tune the probe pulse energy to the cavity band gap, while sweeping the pump pulse energy over the superlattice resonance. The large measurement window of 1 ns in combination with a resolution of about 150 fs made a detailed analysis of the observed phonon dynamics possible. We observed a long lived oscillation in the gap of the phonon dispersion at 466 GHz, which we attribute to a cavity mode

413

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

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''

2014-11-01

414

Using time resolved ultrafast spectroscopy, we have demonstrated that the far infrared (FIR) excitations in ferroelectric crystals may be modified through an arsenal of control techniques from the fields of guided waves, geometrical and Fourier optics, and optical pulse shaping. We show that LiNbO3 and LiTaO3 crystals of 10-250 micron thickness behave as slab waveguides for phonon-polaritons, which are admixtures of electromagnetic waves and lattice vibrations, when the polariton wavelength is on the order of or greater than the crystal thickness. Furthermore, we show that ferroelectric crystals are amenable to processing by ultrafast laser ablation, allowing for milling of user-defined patterns designed for guidance and control of phonon-polariton propagation. We have fabricated several functional structures including THz rectangular waveguides, resonators, splitters/couplers, interferometers, focusing reflectors, and diffractive elements. Electric field enhancement has been obtained with the reflective stru...

Ward, D W; Feurer, T; Nelson, K A; Osgood, R M; Roth, R M; Statz, E R; Stoyanov, N; Beers, Jaime D.; Feurer, Thomas; Nelson, Keith A.; Osgood, Richard M.; Roth, Ryan M.; Statz, Eric; Stoyanov, Nikolay; Ward, David W.

2004-01-01

415

Theory of coherent acoustic phonons in InGaN/GaN multi-quantum wells

A microscopic theory for the generation and propagation of coherent LA phonons in pseudomorphically strained wurzite (0001) InGaN/GaN multi-quantum well (MQW) p-i-n diodes is presented. The generation of coherent LA phonons is driven by photoexcitation of electron-hole pairs by an ultrafast Gaussian pump laser and is treated theoretically using the density matrix formalism. We use realistic wurzite bandstructures taking valence-band mixing and strain-induced piezo- electric fields into account. In addition, the many-body Coulomb ineraction is treated in the screened time-dependent Hartree-Fock approximation. We find that under typical experimental conditions, our microscopic theory can be simplified and mapped onto a loaded string problem which can be easily solved.

Sanders, G D; Kim, C S; Kim, Chang-Sub

2001-01-01

416

High-speed asynchronous optical sampling for high-sensitivity detection of coherent phonons

International Nuclear Information System (INIS)

A new optical pump-probe technique is implemented for the investigation of coherent acoustic phonon dynamics in the GHz to THz frequency range which is based on two asynchronously linked femtosecond lasers. Asynchronous optical sampling (ASOPS) provides the performance of on all-optical oscilloscope and allows us to record optically induced lattice dynamics over nanosecond times with femtosecond resolution at scan rates of 10 kHz without any moving part in the set-up. Within 1 minute of data acquisition time signal-to-noise ratios better than 107 are achieved. We present examples of the high-sensitivity detection of coherent phonons in superlattices and of the coherent acoustic vibration of metallic nanoparticles

417

Unified theory of electron-phonon renormalization and phonon-assisted optical absorption.

We present a theory of electronic excitation energies and optical absorption spectra which incorporates energy-level renormalization and phonon-assisted optical absorption within a unified framework. Using time-independent perturbation theory we show how the standard approaches for studying vibronic effects in molecules and those for addressing electron-phonon interactions in solids correspond to slightly different choices for the non-interacting Hamiltonian. Our present approach naturally le...

Patrick, Ce; Giustino, F.

2014-01-01

418

Illustrative numerical comparisons between phonon mean free paths and phonon thermal conductivity

International Nuclear Information System (INIS)

Measurements of thermal conductivity are often used as an interrogative technique to learn about phonon scattering processes in solids. In general the relationship between thermal conductivity lambda and a phonon mean free path l is complex and it is therefore necessary to make some simplifying assumptions in order to make this relationship tractable. These assumptions may lead to erroneous conclusions, many of which have appeared in the published literature. An intuitive insight is provided to the relationship between lambda and l

419

Optimized phonon approach for the diagonalization of electron-phonon problems

We propose a new optimized phonon approach for the numerical diagonalization of interacting electron-phonon systems combining density-matrix and Lanczos algorithms. We demonstrate the reliablity of this approach by calculating the phase diagram for bi-polaron formation in the one-dimensional Holstein-Hubbard model, and the Luttinger parameters for the metallic phase of the half-filled one-dimensional Holstein model of spinless fermions.

Weisse, A.; Fehske, H.; Wellein, G.; Bishop, A. R.

2000-01-01

420

Hydrodynamic states of phonons in insulators

Directory of Open Access Journals (Sweden)

Full Text Available The Chapman-Enskog method is generalized for accounting the effect of kinetic modes on hydrodynamic evolution. Hydrodynamic states of phonon system of insulators have been studied in a small drift velocity approximation. For simplicity, the investigation was carried out for crystals of the cubic class symmetry. It has been found that in phonon hydrodynamics, local equilibrium is violated even in the approximation linear in velocity. This is due to the absence of phonon momentum conservation law that leads to a drift velocity relaxation. Phonon hydrodynamic equations which take dissipative processes into account have been obtained. The results were compared with the standard theory based on the local equilibrium validity. Integral equations have been obtained for calculating the objects of the theory (including viscosity and heat conductivity. It has been shown that in low temperature limit, these equations are solvable by iterations. Steady states of the system have been considered and an expression for steady state heat conductivity has been obtained. It coincides with the famous result by Akhiezer in the leading low temperature approximation. It has been established that temperature distribution in the steady state of insulator satisfies a condition of heat source absence.

S.A. Sokolovsky

2012-12-01

421

Phonon dispersion curves of fcc La

International Nuclear Information System (INIS)

Large single crystals of fcc La were grown in situ and were used to study the lattice dynamics of this phase of La by coherent inelastic neutron scattering. The phonon dispersion curves have been measured along the [xi00], [xixi0], [xixixi], and [0xi1] symmetry directions at 660 and 1100 K. The T[xixixi] branch exhibits anomalous dispersion for xi>0.25 and, in addition, close to the zone boundary, the phonon frequencies of this branch decrease with decreasing temperature. This soft-mode behavior may be related to the #betta??# transformation in La, an assumption supported by recent band-theoretical calculations of the generalized susceptibility of fcc La. At X the frequencies of the L[xi00] branch are considerably lower than those of the corresponding branch of #betta#-Ce; a similar but not as pronounced effect is observed for the frequencies of the L[xixixi] branch close to the point L. Since the calculated generalized susceptibility of fcc La exhibits strong peaks at X and L, these anomalies may be due to the renormalization of the phonon frequencies by virtual fbold-arrow-left-rightd transitions to the unoccupied 4f level in La. The data were used to evaluate the elastic constants, the phonon density of states, and the lattice specific heat at constant pressure C/sub P//sup

422

Phonon echo in hydrogen-containing metals

The phonon echo due to the tunneling of the hydrogen atom between two equilibrium positions in hydrogen-containing niobium NbOxHy is investigated. The time dependence of the intensity and shape of the two-pulse echo signal is obtained.

Chotorlishvili, L. L.; Tutberidze, I. A.; Kakabadze, G. R.

2001-06-01

423

Tuning phonon properties in thermoelectric materials

This review article presents a discussion of theoretical progress made over the past several decades towards our understanding of thermoelectric properties of materials. Particular emphasis is placed upon describing recent progress in ‘tuning’ phonon properties of nanocomposite materials for gaining enhancement of the thermoelectric figure of merit.

Srivastava, G. P.

2015-02-01

424

Synthetic thermoelectric materials comprising phononic crystals

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.

El-Kady, Ihab F; Olsson, Roy H; Hopkins, Patrick; Reinke, Charles; Kim, Bongsang

2013-08-13

425

Phononic band gap structures as optimal designs

DEFF Research Database (Denmark)

In this paper we use topology optimization to design phononic band gap structures. We consider 2D structures subjected to periodic loading and obtain the distribution of two materials with high contrast in material properties that gives the minimal vibrational response of the structure. Both in-plane and out-of-plane vibrations are considered.

Jensen, Jakob SØndergaard; Sigmund, Ole

2003-01-01

426

Phononic fluidics: acoustically activated droplet manipulations

Microfluidic systems have faced challenges in handling real samples and the chip interconnection to other instruments. Here we present a simple interface, where surface acoustic waves (SAWs) from a piezoelectric device are coupled into a disposable acoustically responsive microfluidic chip. By manipulating droplets, SAW technologies have already shown their potential in microfluidics, but it has been limited by the need to rely upon mixed signal generation at multiple interdigitated electrode transducers (IDTs) and the problematic resulting reflections, to allow complex fluid operations. Here, a silicon chip was patterned with phononic structures, engineering the acoustic field by using a full band-gap. It was simply coupled to a piezoelectric LiNbO3 wafer, propagating the SAW, via a thin film of water. Contrary to the use of unstructured superstrates, phononic metamaterials allowed precise spatial control of the acoustic energy and hence its interaction with the liquids placed on the surface of the chip, as demonstrated by simulations. We further show that the acoustic frequency influences the interaction between the SAW and the phononic lattice, providing a route to programme complex fluidic manipulation onto the disposable chip. The centrifugation of cells from a blood sample is presented as a more practical demonstration of the potential of phononic crystals to realize diagnostic systems.

Reboud, Julien; Wilson, Rab; Bourquin, Yannyk; Zhang, Yi; Neale, Steven L.; Cooper, Jonathan M.

2011-02-01

427

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

428

Kohn anomaly in phonon driven superconductors

Anomalies often occur in the physical world. Sometimes quite unexpectedly anomalies may give rise to new insight to an unrecognized phenomenon. In this paper we shall discuss about Kohn anomaly in a conventional phonon-driven superconductor by using a microscopic approach. Recently Aynajian et al.'s experiment showed a striking feature; the energy of phonon at a particular wave-vector is almost exactly equal to twice the energy of the superconducting gap. Although the phonon mechanism of superconductivity is well known for many conventional superconductors, as has been noted by Scalapino, the new experimental results reveal a genuine puzzle. In our recent work we have presented a detailed theoretical analysis with the help of microscopic calculations to unravel this mystery. We probe this aspect of phonon behaviour from the properties of electronic polarizability function in the superconducting phase of a Fermi liquid metal, leading to the appearance of a Kohn singularity. We show the crossover to the standard Kohn anomaly of the normal phase for temperatures above the transition temperature. Our analysis provides a nearly complete explanation of this new experimentally discovered phenomenon. This report is a shorter version of our recent work in JPCM.

Das, M. P.; Chaudhury, R.

2014-08-01

429

Fractional Carbon Dioxide Laser Resurfacing

Currently available ablative fractional CO2 lasers provide excellent results and diminish down time with fewer complications than previous generation CO2 lasers. Mechanisms of action, treatment parameters, as well as pre- and postoperative care will be discussed.

Ramsdell, William M.

2012-01-01

430

Phonon bottleneck in the low-excitation limit

The phonon-bottleneck problem in the relaxation of two-level systems (spins) via direct phonon processes is considered numerically in the weak-excitation limit where the Schroedinger equation for the spin-phonon system simplifies. The solution for the relaxing spin excitation p(t), emitted phonons n_k(t), etc. is obtained in terms of the exact many-body eigenstates. In the absence of phonon damping Gamma_{ph} and inhomogeneous broadening, p(t) approaches the bottleneck plate...

Garanin, D. A.

2007-01-01

431

The phonon and thermal properties of a ladder nanostructure

Directory of Open Access Journals (Sweden)

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.

M Mardaani

2011-12-01

432

Calculation of anharmonic phonon couplings in C, Si, and Ge

International Nuclear Information System (INIS)

Frozen-phonon total-energy calculations are used to extract anharmonic phonon couplings for the tetrahedral elements C, Si, and Ge. The local-density approximation is employed, with a localized-orbital basis used for C and a plane-wave expansion used for Si and Ge. The bare interactions between optical phonons are completely determined through fourth order at the Brillouin-zone center. These are used to compute renormalized couplings, in which a vertex is screened by virtual phonons. The renormalized couplings are found to have the wrong sign to allow formation of a proposed two-phonon bound state in diamond

433

Magnetic-Field-Assisted Terahertz Quantum Cascade Laser Operating up to 225 K

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.

Wade, A.; Fedorov, G.; Smirnov, D.; Kumar, S.; Williams, B. S.; Hu, Q.; Reno, J. L.

2008-01-01

434

Phonon anharmonicity-induced decoherence slowing down in exciton-phonon systems

Energy Technology Data Exchange (ETDEWEB)

Based on a generalized Froehlich model, a time-convolutionless master equation is established for studying the dynamics of an exciton coupled with anharmonic phonons. Special attention is paid to describing the influence of the phonon anharmonicity on specific elements of the exciton reduced density matrix. These elements, called coherences, characterize the ability of the exciton to develop quantum states that are superimpositions involving the vacuum and the local one-exciton states. Whether the phonons are harmonic or not, it is shown that dephasing limited-coherent motion takes place. The coherences irreversibly decrease with time, the decay rate being the so-called dephasing rate, so that they experience a localization phenomenon and propagate over a finite length scale. However, it is shown that the phonon anharmonicity softens the influence of the phonon bath and reduces the dephasing rate. A slowdown in the decoherence process appears so that the coherences are able to explore a larger region along the lattice. Moreover, the phonon anharmonicity modifies the way the dephasing rate depends on both the adiabaticity and the temperature. In particular, the dephasing rate increases linearly with the temperature in the weak anharmonicity limit whereas it becomes almost temperature-independent in the strong anharmonicity limit. Note that the present formalism is applied to describe amide-I excitons (vibrons) in a lattice of H-bonded peptide units.

Pouthier, Vincent, E-mail: vincent.pouthier@univ-fcomte.f [Institut UTINAM, Universite de Franche-Comte, UMR CNRS 6213, F-25030 Besancon Cedex (France)

2010-06-30

435

International Nuclear Information System (INIS)

A generalization of the quasiparticle-phonon nuclear model (QPNM) for describing the interaction with (2p-2h) configurations at finite temperature is presented. By taking exactly into account the occupation numbers of one-phonon energy levels a closed system of approximate equations for Green functions with one- to two-phonon transition, phonon-ground state correlation and phonon scattering propagators in even-even spherical nuclei is explicitly derived. A one-to-one correspondence between this system and the system of QPNM equations of the coefficients of the excited state wave function is established. It is shown that in the zero temperature limit one obtains the standard basic equations employed so far within the QPNM. The numerical evaluation of the phonon scattering effects has shown that for temperatures T<1 MeV the zero temperature limit of the QPNM is a quite good approximation. The equivalence between the QPNM diagrams and the diagrams of the nuclear field theory and the theory of finite Fermi-systems is discussed

436

Unified theory of electron-phonon renormalization and phonon-assisted optical absorption

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.

Patrick, Christopher E.; Giustino, Feliciano

2014-09-01

437

Establishment of correlated states in a quantum dot interacting with an acoustic-phonon reservoir

We investigate the effects of a low-frequency (acoustic) phonon bath on the dynamics of a quantum dot modeled as a cascade three-level system. We show that the phonon bath appears to the upper transition of the cascade system as a broadband reservoir of inverted rather than conventional harmonic oscillators. The action of the annihilation and creation operators of the inverted oscillator are interchanges relative to those of the usual harmonic oscillator that it serves as a linear amplifier to the system, and thereby gives rise to unusual features in the dynamics of the quantum dot. We find that the phonon bath, although being in a thermal state, affects the quantum dot as a correlated-type reservoir which results in the decay of the system to a correlated two-photon state with the population distribution no longer obeying a Boltzmann distribution. It is particularly interesting that even for a zero-temperature phonon reservoir, the steady state is a correlated state which, under appropriate conditions on the Rabi frequencies and the damping rates, can reduce to a strongly correlated pure state. It is shown that the two-photon correlations result in a significant squeezing and strong two-photon correlations in the radiation field emitted by the quantum dot. The presence of the correlations in the system is manifest in the presence of quantum beats in the time evolution of the populations and the radiation intensity. The effect of the ordinary spontaneous emission on the features induced by the phonon bath is also discussed.

Huang, Hui; Li, Gao-xiang; Gu, Wen-ju; Ficek, Zbigniew

2014-08-01

438

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)

439

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

440

Single-photon indistinguishability: influence of phonons

DEFF Research Database (Denmark)

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.

Nielsen, Per Kær; Lodahl, Peter

2012-01-01

441

Microscopic theory of phonons in the semiconductor microcavity luminescence

Energy Technology Data Exchange (ETDEWEB)

The strong interaction between electrons and longitudinal optical (LO) phonons in ZnO gives rise to pronounced phonon sidebands in the photoluminescence (PL) spectrum as strikingly shown in recent experiments and theoretical investigations. To develop a consistent microscopic theory of the sideband emission, we have generalized the semiconductor luminescence equations (SLE) by including phonon-assisted processes. This approach allows us to compute both spontaneous and stimulated emission at the excitonic resonance and its first phonon sideband. In addition, we have developed an analytic model to describe phonon-assisted luminescence in a cavity. Because phonon-assisted emission and absorption take place on different sides of the excitonic resonance, we found that no normal-mode splitting occurs for the phonon sideband. This is in pronounced contrast to the usual case where the cavity mode coincides with the zero phonon line leading to strong qualitative changes in the spectra due to the normal-mode coupling. Our numerical and analytical results confirm that the sideband intensity is strongly enhanced when the reflectivity of the mirrors reaches a critical value. We show that also ZnO-based systems can reach normal-mode coupling for the zero-phonon line and strongly enhanced emission for the first phonon sideband.

Boettge, Christoph N.; Feldtmann, Thomas; Kira, Mackillo; Koch, S.W. [Department of Physics and Material Sciences Center, Philipps-University, Marburg (Germany)

2011-07-01

442

A quantum formalism for a terahertz acoustic laser

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english 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.

Ihosvany, Camps Rodríguez; Sergio Saul, Makler; Enrique Victoriano, Anda.

1999-12-01

443

Spectroscopy of the two Lowest Exciton Zero-Phonon Lines in Single CdSe/ZnS Nanocrystals

Energy Technology Data Exchange (ETDEWEB)

We study the optical properties of the lowest-energy exciton states in highly photostable individual CdSe/ZnS nanocrystals at low temperatures. We observe two sharp zero-phonon lines which we attribute to the radiative recombination from the two lowest-energy levels of the band-edge exciton fine structure. By using resonant laser excitation on these two lines we measure a spectral broadening of 10 {mu}eV over integration times of 100 ms.

Louyer, Y; Biadala, L; Tamarat, Ph; Lounis, B, E-mail: y.louyer@cpmoh.u-bordeaux1.f [Centre de Physique Moleculaire Optique et Hertzienne, University of Bordeaux and CNRS, 351 cours de la Liberation, Talence, F-33405 (France)

2010-09-01

444

It is demonstrated how the exciton and the biexciton state of a quantum dot can be prepared with high fidelity on a picosecond time-scale by driving the dot with a strong laser pulse that is tuned above the exciton resonance for exciton preparation and in resonance with the exciton transition for biexciton preparation. The proposed schemes make use of the phonon-induced relaxation towards photon dressed states in optically driven quantum dots and combine the simplicity of Ra...

Gla?ssl, M.; Barth, A. M.; Axt, V. M.

2013-01-01

445

Ultrafast generation of optical and acoustic phonons in nanocrystallites (Invited Paper)

We report on the impulsive generation of optical and acoustic phonons in CdTe0.68Se0.32 nanocrystallites embedded in glass, at room temperature. Using ultrafast laser pulses in a pump-probe configuration, we were able to generate coherent vibrations. The energy of our laser was tuned to the absorption edge of the nanocrystals so as to resonantly excite the quantum dots. We identified two longitudinal optical phonons, an optical mode of mixed longitudinal-transverse nature and a longitudinal-like acoustic mode. The frequency, amplitude, decay and phase as a function of excitation energy were determined for the optical modes. These results clearly identify impulsive stimulated Raman scattering as the underlying mechanism of the coherent field generation. The acoustic oscillations are associated with the lowest confined acoustic mode with pseudo angular momentum l=0. We find that the frequency of this mode increases as the laser central energy increases. Since the energy of the exciton at the fundamental gap depends strongly on the particle size, such a behavior is attributed to resonant size-selective excitation of the nanocrystallites. In contrast, spontaneous Raman measurements obtained from the same sample do not show size selectivity and, in addition, the resonant spectra show l=1 and l=2 modes, which are not seen in the pump-probe data. Possible explanations and comparison with other reports are discussed.

Bragas, Andrea V.; Aku-Leh, Cynthia; Merlin, Roberto

2005-04-01

446

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

447

Interaction of Thermal Phonons with Interfaces

Energy Technology Data Exchange (ETDEWEB)

In this chapter we will first explore the connection between interface scattering and thermal transport using the Boltzmann transport equation (BTE). It will be shown that Boltzmann transport provides a convenient method for considering boundary scattering in nanochannel structures. For internal interfaces such as grain boundaries found in polycrystals, it is more natural to consider transmission and reflection across a single boundary. In this regard we will discuss theories related to interface thermal resistance. Our qualitative discussion of the theories of phonon transport will be followed by a discussion of experimental techniques for measuring thermal transport. We end this chapter by giving a detailed description of two complimentary experimental techniques for measuring the influence of interfaces on thermal phonon transport.

David H. Hurley; Subhash Shinde; Edward Piekos

2013-11-01

448

Phonon affected transport through molecular quantum dots.

To describe the interaction of molecular vibrations with electrons at a quantum dot contacted to metallic leads, we extend an analytical approach that we previously developed for the many-polaron problem. Our scheme is based on an incomplete variational Lang-Firsov transformation, combined with a perturbative calculation of the electron-phonon self-energy in the framework of generalized Matsubara functions. This allows us to describe the system at weak-to-strong coupling and intermediate-to-large phonon frequencies. We present results for the quantum dot spectral function and for the kinetic coefficient that characterizes the electron transport through the dot. With these results we critically examine the strengths and limitations of our approach, and discuss the properties of the molecular quantum dot in the context of polaron physics. We place particular emphasis on the importance of corrections to the concept of an anti-adiabatic dot polaron suggested by the complete Lang-Firsov transformation. PMID:21832393

Loos, J; Koch, T; Alvermann, A; Bishop, A R; Fehske, H

2009-09-30

449

Structural Properties and Phonon dispertion of NACl

Directory of Open Access Journals (Sweden)

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.

R. Khoda-Bakhsh

2001-06-01

450

Raman study of the coupling of crystal-field excitations to phonons in NdBa2Cu3O7-?

International Nuclear Information System (INIS)

A double peak observed near 300 cm-1 in the Raman and inelastic-neutron-scattering spectra of the high-Tc superconductor NdBa2Cu3O7-? is due to a strong coupling and mixing of the B1g-symmetry Raman phonon and crystal-field (CF) excitations of the Nd3+ 4f electrons of the same symmetry. In this paper, we describe in detail a model based on the coupling of extended phonons and localized CF excitations. Higher phonon quantum numbers have to be taken into account at room temperature. We show that this interpretation is compatible with measurements of the dependence on temperature, oxygen isotopic substitution, laser wavelength, and oxygen content. We obtain from our model the CF-phonon coupling constant as well as the frequencies of the unperturbed phonon and CF excitation. We also discuss the breaking of the polarization selection rules for the highest phonon based on the substitution of Ba by Nd ions

451

Sputtering of ceramic matrix and phonon spectra

International Nuclear Information System (INIS)

This paper reports on the model that is formed based on the continual deformation of mass distribution by sputtering of thin films. It was shown that due to mass deformation acoustical phonons are eliminated. This can cause a higher critical superconductive temperatures. The agreement of theory and experimental data of ceramic oxides is satisfactory. It is expected that presented theory is at service for synthesis of new superconductive materials

452

Phononic properties of hexagonal chiral lattices

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...

Spadoni, Alessandro; Ruzzene, Massimo; Gonella, Stefano; Scarpa, Fabrizio

2009-01-01

453

Phonon Knudsen flow in nanostructured semiconductor systems

We determine the size effect on the lattice thermal conductivity of nanoscale wire and multilayer structures formed in and by some typical semiconductor materials, using the Boltzmann transport equation and focusing on the Knudsen flow effect. For both types of nanostructured systems we find that the phonon transport is reduced significantly below the bulk value by boundary scattering off interface defects and/or interface modes. The Knudsen flow effects are important for al...

Ziambaras, Eleni; Hyldgaard, Per

2005-01-01

454

Phonon spectral function of the Holstein polaron

The phonon spectral function of the one-dimensional Holstein model is obtained within weak and strong-coupling approximations based on analytical self-energy calculations. The characteristic excitations found in the limit of small charge-carrier density are related to the known (electronic) spectral properties of Holstein polarons such as the polaron band dispersion. Particular emphasis is laid on the different physics occurring in the adiabatic and anti-adiabatic regimes, r...

Loos, J.; Hohenadler, M.; Alvermann, A.; Fehske, H.

2006-01-01

455

Soft phonon anomalies in relaxor ferroelectrics

International Nuclear Information System (INIS)

A review is given of the phonon anomalies, which have been termed waterfalls', that were recently discovered through a series of neutron inelastic scattering measurements on the lead-oxide relaxor systems PZN-xPT, PMN, and PZN. We discuss a simple coupled-mode model that has been used successfully to describe the basic features of the waterfall, and which relates this unusual feature to the presence of polar micro-regions. (author)

456

Soft Phonon Anomalies in Relaxor Ferroelectrics

A review is given of the phonon anomalies, which have been termed ``waterfalls,'' that were recently discovered through a series of neutron inelastic scattering measurements on the lead-oxide relaxor systems PZN-xPT, PMN, and PZN. We discuss a simple coupled-mode model that has been used successfully to describe the basic features of the waterfall, and which relates this unusual feature to the presence of polar micro-regions.

Shirane, G.; Gehring, P. M.

2000-01-01

457

Particle Path Correlations in a Phonon Bath

The path integral formalism is applied to derive the full partition function of a generalized Su-Schrieffer-Heeger Hamiltonian describing a particle motion in a bath of oscillators. The electronic correlations are computed versus temperature for some choices of oscillators energies. We study the perturbing effect of a time averaged particle path on the phonon subsystem deriving the relevant temperature dependent cumulant corrections to the harmonic partition function and fre...

Zoli, Marco

2003-01-01

458

Phonons and Lattice Dielectric Properties of Zirconia

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...

Zhao, Xinyuan; Vanderbilt, David

2001-01-01

459

Electron-Phonon Interaction in Tetrahedral Semiconductors

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...

Cardona, Manuel

2004-01-01

460

Mechanism of phonon localized edge modes

The phonon localized edge modes are systematically studied, and two conditions are proposed for the existence of the localized edge modes: (I) coupling between different directions ($x$, $y$ or $z$) in the interaction; (II) different boundary conditions in three directions. The generality of these two conditions is illustrated by different lattice structures: one-dimensional (1D) chain, 2D square lattice, 2D graphene, 3D simple cubic lattice, 3D diamond structure, etc; and w...

Jiang, Jin-wu; Wang, Jian-sheng

2010-01-01

461

Phonon analogue of topological nodal semimetals

Recently, Kane and Lubensky proposed a mapping between bosonic phonon problems on isostatic lattices to chiral fermion systems based on factorization of the dynamical matrix [Nat. Phys. 10, 39 (2014)]. The existence of topologically protected zero modes in such mechanical problems is related to their presence in the fermionic system and is dictated by a local index theorem. Here we adopt the proposed mapping to construct a two-dimensional mechanical analogue of a fermionic t...

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

2014-01-01

462

Symmetry constraints on phonon dispersion in graphene

Taking into account the constraints imposed by the lattice symmetry, we calculate the phonon dispersion for graphene with interactions between the first, second, and third nearest neighbors in the framework of the Born--von Karman model. Analytical expressions obtained for the dispersion of the out-of-plane (bending) modes give the nonzero sound velocity. The dispersion of four in-plane modes is determined by coupled equations. Values of the force constants are found in fitt...

Falkovsky, L. A.

2008-01-01

463

Ab initio calculation of the thermodynamic properties of InSb under intense laser irradiation

Energy Technology Data Exchange (ETDEWEB)

In this paper, phonon spectra of InSb at different electronic temperatures are presented. Based on the phonon dispersion relationship, we further perform a theoretical investigation of the thermodynamic properties of InSb under intense laser irradiation. The phonon entropy, phonon heat capacity, and phonon contribution to Helmholtz free energy and internal energy of InSb are calculated as functions of temperature at different electronic temperatures. The abrupt change in the phonon entropy- temperature curve from T{sub e} = 0.75 to 1.0 eV provides an indication of InSb undergoing a phase transition from solid to liquid. It can be considered as a collateral evidence of non-thermal melting for InSb under intense electronic excitation effect.

Feng, ShiQuan; Cheng, XinLu [Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065 (China); Key Laboratory of High Energy Density Physics and Technology of Ministry of Education, Sichuan University, Chengdu, 610064 (China); Zhao, JianLing [Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065 (China); Zhang, Hong [College of Physical Science and Technology, Sichuan University, Chengdu 610065 (China)

2013-07-28

464

Nonharmonic phonons in ?-iron at high temperatures

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.

Mauger, L.; Lucas, M. S.; Muñoz, J. A.; Tracy, S. J.; Kresch, M.; Xiao, Yuming; Chow, Paul; Fultz, B.

2014-08-01

465

Heat capacity of suspended phonon cavities

We present a detailed analysis of the vibrational spectrum and heat capacity of suspended mesoscopic dielectric plates, for various thickness-to-side ratios at sub-Kelvin temperatures. The vibrational modes of the suspended cavity are accurately obtained from the three-dimensional (3D) elastic equations in the small strain limit and their frequencies assigned to the cavity phonon modes. The calculations demonstrate that the heat capacity of realistic quasi-2D phonon cavities approach the linear dependence on T at sub-Kelvin temperatures. The behavior is more pronounced for the thinnest cavities, but takes place also for moderately thick structures, with thickness-to-side ratios $\\gamma$=0.1 to 0.2. It is also demonstrated that the heat capacity of the suspended phonon cavities is invariant under the product of the temperature (T) with a characteristic lateral dimension (L) of the sample. The present results establish a lower bound for the heat capacity of suspended mesoscopic structures and indicate the emerg...

Gusso, A; Gusso, Andre; Rego, Luis G. C.

2006-01-01

466

Disruption of superlattice phonons by interfacial mixing

Molecular dynamics simulations and lattice dynamics calculations are used to study the vibrational modes and thermal transport in Lennard-Jones superlattices with perfect and mixed interfaces. The secondary periodicity of the superlattices leads to a vibrational spectrum (i.e., dispersion relation) that is distinct from the bulk spectra of the constituent materials. The mode eigenvectors of the perfect superlattices are found to be good representations of the majority of the modes in the mixed superlattices for up to 20% interfacial mixing, allowing for extraction of phonon frequencies and lifetimes. Using the frequencies and lifetimes, the in-plane and cross-plane thermal conductivities are predicted using a solution of the Boltzmann transport equation (BTE), with agreement found with predictions from the Green-Kubo method for the perfect superlattices. For the mixed superlattices, the Green-Kubo and BTE predictions agree for the cross-plane direction, where thermal conductivity is dominated by low-frequency modes whose eigenvectors are not affected by the mixing. For the in-plane direction, mid-frequency modes that contribute to thermal transport are disrupted by the mixing, leading to an underprediction of thermal conductivity by the BTE. The results highlight the importance of using a dispersion relation that includes the secondary periodicity when predicting phonon properties in perfect superlattices and emphasize the challenges of estimating the effects of disorder on phonon properties.

Huberman, Samuel C.; Larkin, Jason M.; McGaughey, Alan J. H.; Amon, Cristina H.

2013-10-01

467

Phonon Knudsen flow in nanostructured semiconductor systems

We determine the size effect on the lattice thermal conductivity of nanoscale wire and multilayer structures formed in and by some typical semiconductor materials, using the Boltzmann transport equation and focusing on the Knudsen flow effect. For both types of nanostructured systems we find that the phonon transport is reduced significantly below the bulk value by boundary scattering off interface defects and/or interface modes. The Knudsen flow effects are important for almost all types of semiconductor nanostructures but we find them most pronounced in Si and SiC systems due to the very large phonon mean-free paths. We apply and test our wire thermal-transport results to recent measurements on Si nanowires. We further investigate and predict size effects in typical multilayered SiC nanostructures, for example, a doped-SiC/SiC/SiO$_2$ layered structure that could define the transport channel in a nanosize transistor. Here the phonon-interface scattering produces a heterostructure thermal conductivity smalle...

Ziambaras, E; Ziambaras, Eleni; Hyldgaard, Per

2005-01-01

468

Phonon drag thermopower and weak localization

Previous experimental work on a two-dimensional (2D) electron gas in a Si-on-sapphire device led to the conclusion that both conductivity and phonon drag thermopower $S^g$ are affected to the same relative extent by weak localization. The present paper presents further experimental and theoretical results on these transport coefficients for two very low mobility 2D electron gases in $\\delta-$doped GaAs/Ga$_x$Al$_{1-x}$As quantum wells. The experiments were carried out in the temperature range 3-7K where phonon drag dominates the thermopower and, contrary to the previous work, the changes observed in the thermopower due to weak localization were found to be an order of magnitude less than those in the conductivity. A theoretical framework for phonon drag thermopower in 2D and 3D semiconductors is presented which accounts for this insensitivity of $S^g$ to weak localization. It also provides transparent physical explanations of many previous experimental and theoretical results.

Miele, A; Zaremba, E; Feng, Y; Foxon, C T; Harris, J J

1998-01-01

469

Phase seeding of a terahertz quantum cascade laser

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...

Oustinov, Dimitri; Jukam, Nathan; Rungsawang, Rakchanok; Made?o, Julien; Barbieri, Stefano; Filloux, Pascal; Sirtori, Carlo; Marcadet, Xavier; Tignon, Je?ro?me; Dhillon, Sukhdeep

2010-01-01

470

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.

Khan, M. Z. M.; Ng, Tien K.; Lee, C.-S.; Bhattacharya, P.; Ooi, Boon S.

2013-03-01

471

Rabi oscillations in a quantum dot-cavity system coupled to a nonzero temperature phonon bath

International Nuclear Information System (INIS)

We study a quantum dot strongly coupled to a single high-finesse optical microcavity mode. We use a rotating wave approximation (RWA) method, commonly used in ion-laser interactions, together with the Lamb-Dicke approximation to obtain an analytic solution of this problem. The decay of Rabi oscillations because of the electron-phonon coupling is studied at arbitrary temperature and analytical expressions for the collapse and revival times are presented. Analyses without the RWA are presented as means of investigating the energy spectrum

472

Hypersonic modulation of light in three-dimensional photonic and phononic band-gap materials.

The elastic coupling between the a-SiO2 spheres composing opal films brings forth three-dimensional periodic structures which besides a photonic stop band are predicted to also exhibit complete phononic band gaps. The influence of elastic crystal vibrations on the photonic band structure has been studied by injection of coherent hypersonic wave packets generated in a metal transducer by subpicosecond laser pulses. These studies show that light with energies close to the photonic band gap can be efficiently modulated by hypersonic waves. PMID:18764257

Akimov, A V; Tanaka, Y; Pevtsov, A B; Kaplan, S F; Golubev, V G; Tamura, S; Yakovlev, D R; Bayer, M

2008-07-18

473

Picosecond ultrasonic investigations of phonons in 2D nano-scaled lattices

International Nuclear Information System (INIS)

We time-resolved the acoustical response of lattices of aluminum nano-dots with a step of a few hundreds nanometers using tunable femtosecond laser pulses in a pump and probe scheme. We detected two kinds of modes, the first being the individual modes of the dots. The other modes are shown to be both dependent on the dot size and on the lattice and are thus interpreted as collective modes. Using several step sizes we show that we can plot the phonon dispersion relation. A simple analytical model very well reproduces the data from which we can describe completely the dependence of the lattice modes on the sample parameters

474

Picosecond ultrasonic investigations of phonons in 2D nano-scaled lattices

Energy Technology Data Exchange (ETDEWEB)

We time-resolved the acoustical response of lattices of aluminum nano-dots with a step of a few hundreds nanometers using tunable femtosecond laser pulses in a pump and probe scheme. We detected two kinds of modes, the first being the individual modes of the dots. The other modes are shown to be both dependent on the dot size and on the lattice and are thus interpreted as collective modes. Using several step sizes we show that we can plot the phonon dispersion relation. A simple analytical model very well reproduces the data from which we can describe completely the dependence of the lattice modes on the sample parameters.

Robillard, J-F; Devos, A; Roch-Jeune, I [Institut d' electronique, de Microelectronique et de Nanotechnologie, Unite Mixte de Recherche CNRS 8520, Avenue Poincare BP 69, F-59652 Villeneuve d' Ascq CEDEX (France)

2007-12-15

475

Evidence for a resonant behavior of the E$_{2g}$ phonon in MgB$_{2}$

Polarized and Resonant Raman scattering (PRS, RRS) have been carried out in microcrystals of MgB$_{2}$ at room temperature in order to study the symmetry of the broad E$_{2g}$ phonon and its coupling to electronic states. We observe a breakdown of the polarization selection rules when the medium is excited with the 2.41 eV laser line. The RRS experiments show that this breakdown is associated to the resonant behavior of the E$_{2g}$ mode. These results may be understood in terms of band structure calculations. These calculations predict a strong coupling between the E$_{2g}$ modes and the B-$% \\sigma $ bands. Unpolarized Raman scattering measurements between 10-300 K in polycrystalline MgB$_{2}$ using the resonant line of 2.41 eV show the expected anharmonic decay of the linewidth for the E$_{2g}$ mode and its energy remains the same below and above the superconducting critical temperature. These results indicate that the E$_{2g}$ phonon may not play an important role in the electron-phonon coupling mechanism...

Martinho, H; Rettori, C; De Lima, O F; Pagliuso, P G; Moreno, N O; Sarrao, J L

2001-01-01

476

Graphene-to-substrate energy transfer through out-of-plane longitudinal acoustic phonons.

Practically, graphene is often deposited on substrates. Given the major substrate-induced modification of properties and considerable energy transfer at the interface, the graphene-substrate interaction has been widely discussed. However, the proposed mechanisms were restricted to the two-dimensional (2D) plane and interface, while the energy conduction in the third dimension is hardly considered. Herein, we disclose the transfer of energy perpendicular to the interface of the combined system of the 2D graphene and the 3D base. More precisely, our observation of the energy dissipation of optically excited graphene via emitting out-of-plane longitudinal acoustic phonon into the substrate is presented. By applying nanoultrasonic spectroscopy with a piezoelectric nanolayer embedded in the substrate, we found that under photoexcitation by a femtosecond laser pulse graphene can emit longitudinal coherent acoustic phonons (CAPs) with frequencies over 1 THz into the substrate. In addition, the waveform of the CAP pulse infers that the photocarriers and sudden lattice heating in graphene caused modification of graphene-substrate bond and consequently generated longitudinal acoustic phonons in the substrate. The direct observation of this unexplored graphene-to-substrate vertical energy transfer channel can bring new insights into the understanding of the energy dissipation and limited transport properties of supported graphene. PMID:24559107

Chen, I-Ju; Mante, Pierre-Adrien; Chang, Cheng-Kai; Yang, Szu-Chi; Chen, Hui-Yuan; Huang, Yu-Ru; Chen, Li-Chyong; Chen, Kuei-Hsien; Gusev, Vitalyi; Sun, Chi-Kuang

2014-03-12

477

Studies on the complex behavior of optical phonon modes in wurtzite (ZnO)1-x (Cr2O3) x

This paper reports on the use of phonon spectra obtained with laser Raman spectroscopy for the uncertainty concerned to the optical phonon modes in pure and composite ZnO1-x (Cr2O3) x . Particularly, in previous literature, the two modes at 514 and 640 cm-1 have been assigned to ZnO are not found for pure ZnO in our present study. The systems investigated for the typical behavior of phonon modes with 442 nm as excitation wavelength are the representative semiconductor (ZnO)1-x (Cr2O3) x (x = 0, 5, 10 and 15 %). Room temperature Raman spectroscopy has been demonstrated polycrystalline wurtzite structure of ZnO with no structural transition from wurtzite to cubic with Cr2O3. The incorporation of Cr3+ at most likely on the Zn sub-lattice sites is confirmed. The uncertainty of complex phonon bands is explained by disorder-activated Raman scattering due to the relaxation of Raman selection rules produced by the breakdown of translational symmetry of the crystal lattice and dopant material. The energy of the E 2 (high) peak located at energy 53.90 meV (435 cm-1) due to phonon-phonon anharmonic interaction increases to 54.55 meV (441 cm-1). A clear picture of the dopant-induced phonon modes along with the B 1 silent mode of ZnO is presented and has been explained explicitly. Moreover, anharmonic line width and effect of dislocation density on these phonon modes have also been illustrated for the system. The study will have a significant impact on the application where thermal conductivity and electrical properties of the materials are more pronounced.

Khan, Taj Muhammad; Irfan, M.

2014-05-01

478

An impact of different doses (10-500 kGy) of ?-irradiation on electron-phonon coupling in Ge-doped CdTe (CdTe:Ge) si