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1

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

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

CERN Multimedia

The phonon analog of an optical laser has long been a subject of interest. We demonstrate a compound microcavity system, coupled to a radio-frequency mechanical mode, that operates in close analogy to a two-level laser system. An inversion produces gain, causing phonon laser action above a pump power threshold of around 50 $\\mu$W. The device features a continuously tunable, gain spectrum to selectively amplify mechanical modes from radio frequency to microwave rates. Viewed as a Brillouin process, the system accesses a regime in which the phonon plays what has traditionally been the role of the Stokes wave. For this reason, it should also be possible to controllably switch between phonon and photon laser regimes. Cooling of the mechanical mode is also possible.

Grudinin, Ivan S; Vahala, Kerry J

2009-01-01

3

Low energy electron-phonon effective action from symmetry analysis  

CERN Document Server

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

4

Phonon confinement in silicon nanowires synthesized by laser ablation  

International Nuclear Information System (INIS)

The phonon confinement effect was investigated by Raman measurements for Si nanowires (SiNWs) synthesized by laser ablation of a Si target with nickel (Ni) catalyst and for SiNWs thermally oxidized at 700-1000 oC. The Si optical phonon peak for SiNWs, unlike that for bulk Si, showed a downshift and an asymmetric broadening. Thermal oxidation caused a further downshift and broadening. These phenomena can be explained by the phonon confinement effect due to the decrease in the diameter of the Si core of the SiNWs. It was additionally found that excess oxidation caused an upshift of the optical phonon peak due to compressive stress

2006-04-01

5

Phonon-Assisted Stimulated Emission and Ultra - Active Layers in Cleaved Cavity and Vertical Cavity Surface Emitting Lasers.  

Science.gov (United States)

Unique lasing processes in III-V semiconductor lasers are examined. The dynamics of stimulated photon emission in thin AlGaAs/GaAs single quantum well lasers are observed experimentally and modeled by rate equations describing the electron and photon densities. Agreement between experiment and theory are achieved when the transition probability matrix, calculated with the spreading out of electron and hole wave functions taken into account, is used. The phonon assisted stimulated photon emission observed in this work is delayed with respect to the unassisted emission. This observation is modeled by using a weaker matrix element for the unassisted process which is expected from theory and thus supports our claim that this emission is phonon assisted. Rate equations developed to simulate doubly stimulated emission of photons and phonons do not describe the experimental data so the possibility of stimulated phonon emission is ruled out for the samples studied in this work. Vertical Cavity Surface Emitting Lasers are also studied since they can be designed to support unique lasing processes. The design and growth of vertical cavity surface emitting lasers are discussed and these concepts are applied to the realization of a vertical cavity surface emitting laser with the thinnest active layer of any laser yet reported. Stimulated emission supported across the sub-monolayer thick InAs single quantum well active region can be understood by considering the spreading of the electron and hole wavefunctions beyond the confines of the quantum well to increase the length of the effective gain region. The dynamics of laser action in vertical cavity surface emitting lasers are also studied and reveal that low threshold lasers may not be suitable for high speed operation due to their relatively long photon lifetimes. Finally a structure is proposed to implement a multi-wavelength vertical cavity surface emitting laser using an active region that encourages phonon assisted stimulated emission.

Benjamin, Seldon David

6

Phonon temperature overshoot in GaAs excited by subpicosecond laser pulses  

International Nuclear Information System (INIS)

Hot electrons and phonons excited in GaAs by subpicosecond laser pulses have been studied by inelastic light scattering for photoexcited electron densities varying between 1017 and 1019 cm-3. Transient overshoot of longitudinal-optical (LO) phonon temperature above the electron temperature has been observed. This is explained by the fast production of zone-center LO phonons by hot electrons combined with slower reabsorption of the emitted phonons due to rapid cooling of ? valley electrons by intervalley scattering

1990-02-19

7

Dynamics of a vertical cavity quantum cascade phonon laser structure  

Science.gov (United States)

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

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

2013-01-01

8

Dynamics of a vertical cavity quantum cascade phonon laser structure.  

Science.gov (United States)

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

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

2013-01-01

9

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

CERN Document Server

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

10

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

Science.gov (United States)

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

11

Electron-phonon coupling effects on Yb3+ spectra in several laser crystals  

International Nuclear Information System (INIS)

The complex absorption spectra of Yb3+ in YAG, LiNbO3 and YLF, three important laser crystals, are analysed in terms of electron-phonon coupling effects. The local symmetry for Yb3+ in these crystals is noncentrosymmetric allowing the coexistence of several electron-phonon coupling mechanisms in the formation of vibronic spectra. The shape of several Yb3+ absorption lines is interpreted in terms of the near resonant electron-phonon coupling theory. The computer modelling, by taking into account more phonons in the resonance region enables the assignment of crystal-field levels of the Yb3+ 2F5/2 multiplet and an estimation of electron-phonon coupling strengths. The phonons involved in the near resonance processes were observed in Raman spectra too. For YAG the modelling with a phonon density with four peaks in the near resonant region is made and it gives a good description of the complex experimental pattern. In the case of Yb3+ in LiNbO3 and YLF the use of polarization data evidences also the symmetry characteristics of the electron-phonon coupling. (author)

1999-05-10

12

Observation of Zone-Folded Acoustic Phonons in Terahertz Quantum Cascade Lasers using Picosecond Ultrasonics  

CERN Document Server

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

13

Self-Organization in Multimode Microwave Phonon Laser (Phaser) Experimental Observation of Spin-Phonon Cooperative Motions  

CERN Document Server

An unusual nonlinear resonance was experimentally observed in a ruby phonon laser (phaser) operating at 9 GHz with an electromagnetic pumping at 23 GHz. The resonance is manifested by very slow cooperative self-detunings in the microwave spectra of stimulated phonon emission when pumping is modulated at a superlow frequency (less than 10 Hz). During the self-detuning cycle new and new narrow phonon modes are sequentially ``fired'' on one side of the spectrum and approximately the same number of modes are ``extinguished'' on the other side, up to a complete generation breakdown in a certain final portion of the frequency axis. This is usually followed by a short-time refractority, after which the generation is fired again in the opposite (starting) portion of the frequency axis. The entire process of such cooperative spectral motions is repeated with high degree of regularity. The self-detuning period strongly depends on difference between the modulation frequency and the resonance frequency. This period is in...

Makovetskii, D N

2001-01-01

14

Laser heating versus phonon confinement effect in the Raman spectra of diamond nanoparticles  

Energy Technology Data Exchange (ETDEWEB)

Nanodiamond particles with typical diameters of 20 and 6 nm produced by high pressure high temperature or detonation processes have been studied by micro-Raman spectroscopy. We show that the frequency downshift and broadening of the first-order diamond phonon band is not uniquely related to phonon confinement, as commonly assumed. Local heating caused by the focused laser light must be also taken in account, since it may affect the Raman spectrum in a similar fashion, even at relatively low laser power levels. A combined theoretical model considering both effects (quantum confinement and local heating) on the excited phonon modes is presented and adopted for the simulation of the experimental data. We observe different heating behaviours upon laser illumination depending on the particles origin, thus underscoring the importance to compensate for this effect before retrieving structural parameters.

Chaigneau, Marc; Picardi, Gennaro, E-mail: gennaro.picardi@poly.polytechnique.fr [LPICM, Ecole Polytechnique, CNRS (France); Girard, Hugues A.; Arnault, Jean-Charles [LIST, Diamond Sensors Laboratory, CEA (France); Ossikovski, Razvigor [LPICM, Ecole Polytechnique, CNRS (France)

2012-06-15

15

Photopumping of quantum well heterostructures at high or low Q: phonon-assisted laser operation  

Energy Technology Data Exchange (ETDEWEB)

Data are presented showing the basic difference in the stimulated emission spectrum of a photopumped Al{sub x}Ga{sub 1-x}As-GaAs or Al{sub y}Ga{sub 1-y}As-GaAs-In{sub x}Ga{sub 1-x} As quantum well heterostructure (QWH) heat sunk in a high-Q versus a low-Q cavity configuration. In the high-Q case a 1-2 {mu}m thick narrow (25-50 {mu}m) cleaved rectangle, with the (100) GaAs substrate removed, is heat sunk compressed in In under a sapphire, giving a high cavity photon lifetime because of metal reflectors folded up along the four samples edges. In the latter case (low Q) the (100) QWH rectangle is clamped under a sapphire into simple contact with Au, leaving the four cleaved (110) sample edges lossy and yielding, compared to carrier thermalization times, a short resonator photon lifetime across the sample. For photopumping (77 K, Ar{sup +} laser, 5145 {angstrom}) of a low-Q QWH sample, only lower energy recombination radiation is observed, including phonon-assisted laser operation (provided that the QWH is designed with good carrier, phonon, and photon confinement and with low alloy composition Al{sub x}Ga{sub 1-x}As thermalization layers generating GaAs, like phonons near the QW). For photopumping of an otherwise similar QWH heat sunk in the high-Q configuration (long photon lifetime across the sample), recombination at higher energy can compete with carrier thermalization, and laser operation is observed on the confined-particle transitions, thus making unambiguous the identification of phonon sideband laser operation. Comparison of various QWHs heat sunk in the form of low-Q or high-Q resonators reveals the heterostructure layer configurations appropriate for phonon-assisted laser operation.

Holonyak, N. Jr.; Nam, D.W.; Plano, W.E.; Hsieh, K.C. (Univ. of Illinois, Urbana-Champaign (USA)); Dupuis, R.D. (AT and T Labs., Murray Hill, NJ (USA))

1990-02-08

16

Coupled carrier–phonon nonequilibrium dynamics in terahertz quantum cascade lasers: a Monte Carlo analysis  

International Nuclear Information System (INIS)

The operation of state-of-the-art optoelectronic quantum devices may be significantly affected by the presence of a nonequilibrium quasiparticle population to which the carrier subsystem is unavoidably coupled. This situation is particularly evident in new-generation semiconductor-heterostructure-based quantum emitters, operating both in the mid-infrared as well as in the terahertz (THz) region of the electromagnetic spectrum. In this paper, we present a Monte Carlo-based global kinetic approach, suitable for the investigation of a combined carrier–phonon nonequilibrium dynamics in realistic devices, and discuss its application with a prototypical resonant-phonon THz emitting quantum cascade laser design. (paper)

2013-07-01

17

On the amplification of sound (acoustic phonons) by absorption of laser radiation in cylindrical quantum wires  

CERN Document Server

Based on the quantum transport equation for the electron-phonon system, the absorption coefficient of sound (acoustic phonons) by absorption of laser radiation in cylindrical quantum wires is calculated for the case of monophoton absorption process and the case of multiphoton absorption process. Analytical expressions and conditions for the absorption of sound are obtained. Differences between the two cases of monophoton absorption and of multiphoton absorption are discussed; numerical computations and plots are carried out for a GaAs/GaAsAl quantum wire. The results are compared with bulk semiconductors and quantum wells.

Hung, N Q; Bau, N Q; Hung, Nguyen Quoc; Nhan, Nguyen Vu; Bau, Nguyen Quang

2002-01-01

18

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

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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

19

Electron- and phonon-coupling in femtosecond laser-induced desorption of CO from Ru(0001)  

Science.gov (United States)

We studied femtosecond laser-induced desorption of CO from Ru(0001) using intense near-infrared and visible femtosecond laser pulses. We find a pronounced wavelength dependence with a factor 3-4 higher desorption yield at comparable fluence when desorption is induced via 400 nm light, compared to 800 nm and attribute this difference to the difference in penetration depth of the incident light. All our data can be described using empirical friction-modeling to determine the desorption mechanism with the same mechanism for both wavelengths. We find that both hot electrons and phonons contribute to the desorption process. We measured laser-induced desorption yield using 800 and 400 nm femtosecond pulses. We model the data using an empirical friction and two-temperature model approach. We find that both hot electrons and hot phonons contribute to the desorption.

Gladh, J.; Hansson, T.; Öström, H.

2013-09-01

20

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

CERN Document Server

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

 
 
 
 
21

Controlling of exciton condensate by external fields and phonon laser  

CERN Document Server

The novel method of observation and controlling of Bose-Einstein condensation in the system of spatially and momentum-space indirect excitons in coupled quantum wells using in-plane magnetic and normal electric fields is proposed. Fields are used for exciton dispersion engeneering. In the presence of in-plane magnetic field ground state of spatially indirect exciton becomes also indirect in the momentum space. Manipulation of electric field magnitude is used for tuning to resonance of transition of "dark" long-life spatially and momentum-space indirect exciton in condensate into spatially and momentum-space direct exciton in radiative zone, with phonon creation, and with subsequent recombination of the direct exciton in radiative zone. Recombination rate of indirect excitons in condensate according to proposed scheme sharply rises at resonance. As a result besides enhanced spectral narrow photoluminescence connected with recombination of direct exciton in radiative zone with specific angular dependence, almos...

Lozovik, Yu E; Lozovik, Yu.E.

2000-01-01

22

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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, indicatin...

Hu Jianbo; Misochko Oleg V.; Nakamura Kazutaka G.

2013-01-01

23

Laser driven currents in solids: dynamical Bloch oscillations and phonon scattering  

International Nuclear Information System (INIS)

We investigate the dynamics of conduction band electrons interacting with strong laser pulses. Time evolution of the reciprocal space electron distribution is described using an appropriate version of the Boltzmann equation. Although state of the art laser sources can be powerful enough to drive wave packets through the boundaries of the first Brillouin zone—i.e. they can induce dynamical Bloch oscillations—relaxation mechanisms can inhibit the appearance of this fundamental effect. The main source of relaxation in our model is the scattering interaction with longitudinal optical phonons. We find that signatures of dynamical Bloch oscillations are still visible even in the presence of realistically strong scattering. (paper)

2013-03-01

24

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.)

2002-10-01

25

Measurement of frequency gaps and waveguiding in phononic plates with periodic stepped cylinders using pulsed laser generated ultrasound  

Science.gov (United States)

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

26

Random laser action in bovine semen  

Science.gov (United States)

Experiments using bovine semen reveal that the addition of a high-gain water soluble dye results in random laser action when excited by a Q-switched, frequency doubled, Nd:Yag laser. The data shows that the linewidth collapse of the emission is correlated to the sperm count of the individual samples, potentially making this a rapid, low sample volume approach to count determination.

Smuk, Andrei; Lazaro, Edgar; Olson, Leif P.; Lawandy, N. M.

2011-03-01

27

Breaking the low phonon energy barrier for laser cooling in rare-earth doped hosts  

Science.gov (United States)

A new approach to cool rare earth doped solids with optical super-radiance (SR) is presented. SR is the coherent, sharply directed spontaneous emission of photons by a system excited with a pulsed laser. We consider an Yb3+ doped ZBLAN sample pumped at the wavelength 1015nm with a rectangular pulsed source with a power of ~700W and duration of 20ns. The intensity of the SR is proportional to the square of the number of excited ions. This unique feature of SR permits an increase in the rate of the cooling process in comparison with the traditional laser cooling of the rare earth doped solids with anti-Stokes spontaneous incoherent radiation (fluorescence). This scheme overcomes the limitation of using only low phonon energy glasses for laser cooling.

Nemova, Galina; Kashyap, Raman

2011-02-01

28

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

Science.gov (United States)

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

29

Phonon Assisted Laser Transitions and Energy Transfer in Rare Earth Laser Crystals.  

Science.gov (United States)

An extensive study of energy transfer and phonon interaction in rare earth doped LiYF4 has been conducted. The trivalent rare earth ions Pr, Nd, Dy, Ho, Er, Tm and Yb were used as the optically active ions. Y2Ti2O7, also doped with rare earth ions, was ex...

H. P. Jenssen

1971-01-01

30

Breathing coherent phonons and caps fragmentation in carbon nanotubes following ultrafast laser pulses  

International Nuclear Information System (INIS)

The response of carbon nanotubes to femtosecond laser pulses is studied with a nonadiabatic simulation technique, which accounts for the evolution of electronic and ionic degrees of freedom, and for the coupling with the external electromagnetic field. As a direct result of electronic excitation, three coherent breathing phonon modes are excited: two radial vibrations localized in the caps and cylindrical body, and one longitudinal vibration coupled to the nanotube length. Under high absorbed energies (but below 2.9 eV/atom, the graphite's ultrafast fragmentation threshold), the resulting oscillatory motion leads to the opening of nanotube caps. Following the cap photofragmentation the nanotube body remains intact for the rest of the 2 ps simulation time

2006-11-15

31

Theory of amplification of sound (acoustic phonons) by absorption of laser radiation in quantum wires with parabolic potential  

CERN Document Server

Based on the quantum transport equation for the electron-phonon system, the absorption coefficient of sound (acoustic phonons) by absorption of a laser radiation in quantum wires with parabolic potential is calculated for the case of monophoton absorption and the case of multiphoton absorption. Analytical expressions and conditions for the absorption coefficient of sound are obtained. Differences between the two cases of monophoton absorption and of multiphoton absorption are discussed; numerical computations and plots are carried out for a GaAs/GaAsAl quantum wire. The results are compared with bulk semiconductors and quantum wells.

Hung, N Q; Bau, N Q; Hung, Nguyen Quoc; Vuong, Dinh Quoc; Bau, Nguyen Quang

2002-01-01

32

Resonant-phonon depopulation terahertz quantum cascade lasers and their application in spectroscopic imaging  

International Nuclear Information System (INIS)

The terahertz (THz) frequency quantum cascade laser (QCL) is a semiconductor heterostructure laser that has attracted much research interest over the past decade. We report on the high performance of THz QCLs based on a three-well resonant-phonon (RP) depopulation active region (AR) and operating in the frequency range 2.7 THz to 4.0 THz. Devices, processed into surface-plasmon waveguides, lased up to 116 K in pulsed mode with threshold current densities as low as 840 Acm?2. The effects of the design frequency and laser cavity length on performance are discussed. We also report on the operation of QCLs with reduced AR thicknesses, and show, for the first time, that the AR thickness of RP QCLs processed in a surface plasmon waveguide can be reduced to as little as 5 µm. Finally, we demonstrate the use of an electrically tuneable THz QCL, based on a heterogeneous AR, for spectroscopic imaging of the high-explosive pentaerythritol tetranitrate. (paper)

2012-09-01

33

The impact of hot-phonons on the performance of 1.3?m dilute nitride edge-emitting quantum well lasers  

International Nuclear Information System (INIS)

A robust opto-electronic device simulation tool is extended to model the phonon bottleneck in edge-emitting 1.3?m InGaAsN double quantum well (QW) laser diodes. Both the steady state operation and the transient response of the phonon bottleneck are examined as a function of injection current and heatsink temperature. It is found that the hot phonon population can raise the electron and hole temperatures in the QW active region by up to 7K above the equilibrium lattice temperature at moderate injection currents. At high injection currents, it is found that the phonon bottleneck can significantly decrease the optical power

2007-12-01

34

Room-temperature laser action at 4.3--4.4 {micro}m in CaGa{sub 2}S{sub 4}:Dy{sup 3+}  

Energy Technology Data Exchange (ETDEWEB)

The authors report room-temperature mid-IR laser operation in a new low-phonon-frequency, non-hygroscopic host crystal CaGa{sub 2}S{sub 4} (calcium thiogallate). Laser action at 4.31 {micro}m on the {sup 6}H{sub 11/2} {r_arrow}{sup 6}H{sub 13/2} transition of trivalent dysprosium was achieved with a slope efficiency of 1.6%.

Nostrand, M; Page, R H; Payne, S A; Krupke, W F; Schunemann

1999-04-22

35

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

2013-10-28

36

Surface scattering velocities in III-nitride quantum well laser structures via the emission of hybrid phonons  

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

2011-12-01

37

Ab initio theory of electron-phonon mediated ultrafast spin relaxation of laser-excited hot electrons in transition-metal ferromagnets  

Science.gov (United States)

We report a computational theoretical investigation of electron spin-flip scattering induced by the electron-phonon interaction in the transition-metal ferromagnets bcc Fe, fcc Co, and fcc Ni. The Elliott-Yafet electron-phonon spin-flip scattering is computed from first principles, employing a generalized spin-flip Eliashberg function as well as ab initio computed phonon dispersions. Aiming at investigating the amount of electron-phonon mediated demagnetization in femtosecond laser-excited ferromagnets, the formalism is extended to treat laser-created thermalized as well as nonequilibrium, nonthermal hot electron distributions. Using the developed formalism we compute the phonon-induced spin lifetimes of hot electrons in Fe, Co, and Ni. The electron-phonon mediated demagnetization rate is evaluated for laser-created thermalized and nonequilibrium electron distributions. Nonthermal distributions are found to lead to a stronger demagnetization rate than hot, thermalized distributions, yet their demagnetizing effect is not enough to explain the experimentally observed demagnetization occurring in the subpicosecond regime.

Carva, K.; Battiato, M.; Legut, D.; Oppeneer, P. M.

2013-05-01

38

Coherent phonon generation in semiconducting single-walled carbon nanotubes using a few-cycle pulse laser  

Energy Technology Data Exchange (ETDEWEB)

Coherent phonon dynamics in single-walled carbon nanotubes with several chiralities is investigated by 7.1-fs pump-probe experiments. Vibrational wave-packets corresponding to the radial breathing mode (RBM) and G mode can be detected for four chiral systems, (6,4), (6,5), (7,5) and (8,3). Coherent phonon generation of RBMs is in-depth studied by analyzing the probe photon energy dependent amplitude profiles, which indicates that the real and imaginary parts of the third-order susceptibility can both contribute to the modulation of the probed difference absorbance. - Highlights: Black-Right-Pointing-Pointer We investigated coherent phonon dynamics in single-walled carbon nanotubes by 7.1-fs laser. Black-Right-Pointing-Pointer Vibrational wave-packets corresponding to the RBM and G mode can be detected. Black-Right-Pointing-Pointer Resonance conditions and mode frequencies lead to exact chirality assignments. Black-Right-Pointing-Pointer Both real and imaginary parts of the third order susceptibility contribute to the result.

Kobayashi, Takayoshi, E-mail: kobayashi@ils.uec.ac.jp [Advanced Ultrafast Laser Research Center, University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585 (Japan); JST, CREST, K' s Gobancho, 7, Gobancho, Chiyoda-ku, Tokyo, 102-0076 (Japan); Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan); Department of Electrophysics, National Chiao-Tung University, Hsinchu 30010, Taiwan (China); Institute of Laser Engineering, Osaka University, 2-6 Yamada-oka, Suita, Osaka 565-0871 (Japan); Nie, Zhaogang [Advanced Ultrafast Laser Research Center, University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585 (Japan); JST, CREST, K' s Gobancho, 7, Gobancho, Chiyoda-ku, Tokyo, 102-0076 (Japan); Du, Juan [Advanced Ultrafast Laser Research Center, University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585 (Japan); JST, CREST, K' s Gobancho, 7, Gobancho, Chiyoda-ku, Tokyo, 102-0076 (Japan); Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan); Kataura, Hiromichi [Nanosystem Research Institute, AIST, Higashi 1-1-1, Tsukuba, Ibaraki 305-8562 (Japan); Sakakibara, Youichi [Photonics Research Institute, AIST, Higashi 1-1-1, Tsukuba, Ibaraki 305-8562 (Japan); Miyata, Yasumitsu [Department of Chemistry, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8601 (Japan)

2013-01-15

39

An excimer laser radiation action on DNA and chromatin  

Energy Technology Data Exchange (ETDEWEB)

The fluorimetric method for DNA strand breaks determination, the establishment of the lifetimes of the complexes ligand-DNA and ligand-chromatin and the Turbo Pascal program for the calculation of the number of molecules of the reaction product formed during a pulse are useful tools in the study of the laser radiation action on DNA and chromatin. DNA is protected by bound proteins against laser action. (authors)

Radu, S. [Department of electrical Engineering, Polytechnic University, Bucharest (Romania)]|[Department of Molecular Genetic, Victor Babes Institute, Bucharest (Romania); Mihailescu, I. [Department of lasers, IFTAR, Bacharest (Romania); Radulescu, I. [Department of Biophysics, Physics Faculty, Bucharest University (Romania)

1997-03-01

40

Theory of electron-optical phonon interactions in quantum wells and quantum well laser structures  

International Nuclear Information System (INIS)

This thesis is concerned with the study of the quantum processes, including carder transitions and carrier capture, mediated by optical phonons in heterostructure quantum wells based on II-VI and III-V semiconductors and their alloys. The optical phonons are described by three different models namely, a model based on the bulk phonon approximation, the dielectric continuum (DC) model and the hybrid (HB) model. In order to create a discrete energy spectrum for the electrons with energies greater than the barrier energy and in order to reduce electron-phonon scattering rates, we concentrate on the situation in which the heterostructure is confined between metallic barriers. The essential features describing optical phonons are first discussed for the three models. In particular, in the case of the hybrid model we show that the hybridons form an orthogonal set of modes and are characterised by the property of non-locality, which is identified as the source of the mechanical boundary conditions. Calculations are then presented for the intersubband and intrasubband transition rates in the lowest electron subbands by the emission of DC and hybrid phonons in the case of the GaAs/AlAs heterostructure between two metal barriers. The dependence of the transition rates on the distance between the metallic barriers suggests that such, structures could be engineered so as to result in reduced scattering rates. A comparison of the predictions of total scattering rates via the hybrid model with those via the DC model shows that the DC and the hybrid models are very close in this case. This near-agreement between the two models prompts an investigation on the existence of a sum-rule for the total scattering rates which we discuss in conjunction with a derivation of the rates in terms of Green functions. A sizeable part of this thesis is concerned with the evaluation of electron capture rates for electrons with energies at the bottom of the first and second subbands above the barrier energy which make transitions into the quantum well. We emphasise these calculations for the AlN/GaN quantum well system and for the alloy system GaAs/AlxGa1-xAs. The capture rate within the context of a given model is defined as the transition rate into all available subbands within the quantum well by the emission of either (a) bulk phonons of the well material or (b) the confined and interface phonons of the DC model or (c) the hybridons of the hybrid model (HB). The predictions of the three models are displayed and compared. We find that sharp peaks emerge at regular intervals of increasing well width corresponding to resonances in the electron states as a subband from above the barrier drops into the well. Other peaks arise when the electrons can begin to make transitions into the highest subband in the well. These peaks correspond to optical phonon emission thresholds and so depend on the model used to describe the optical phonon modes. The comparison between the DC model and hybrid model in the case of electron capture shows that the two models are in good agreement with regard to the magnitudes of the electron and phonon resonances and the regular intervals that occur. A different approach is required when the barrier thickness is much larger than the well width. In order to deal with this situation for the process of capture we consider an electron flux injected electrically with energy within the continuum above the barrier. This is subsequently captured into the AlN/GaN and II-VI quantum wells by the emission of bulk and DC phonons. The situation requires the identification of new capture parameters and we show that capture velocity is the appropriate parameter in this case. Calculations of capture velocities against the well width are presented for the DC and bulk phonons. (author)

1999-01-01

 
 
 
 
41

Random laser action from flexible biocellulose-based device  

Science.gov (United States)

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

Atomic Laser Action in Rare Gas-SF6 Mixtures.  

Science.gov (United States)

Pulsed laser action was observed on a total of seven laser transitions in Ar, one of which has not been previously reported. In pure Ar, only one transition was observed; however, the other six transitions were observed to lase simultaneously upon the add...

D. G. Sutton L. Galvan P. R. Valenzuela S. N. Suchard

1975-01-01

43

Two-phonon laser operation (4. 2--77 K) of photopumped Al sub x Ga sub 1 minus x As-GaAs quantum well heterostructures  

Energy Technology Data Exchange (ETDEWEB)

Data are presented showing that photopumped Al{sub {ital x}}Ga{sub 1{minus}{ital x}}As-GaAs quantum well heterostructures (QWHs) are capable of stimulated emission (because of the large confined phonon population) one {ital and} {ital two} longitudinal optical (LO) phonons below the lowest confined-particle electron-to-heavy hole transition ({ital e}1{r arrow}{ital h}1). The phonon-assisted laser operation two phonons below the {ital e}1{r arrow}{ital h}1 transition ({Delta}{ital E}=2{h bar}{omega}{sub LO}=2{times}36 meV) is identified unambiguously using (on a single sample) two types of heat sink configurations, high {ital Q} to turn on and low {ital Q} to turn off the stimulated emission on the {ital e}1{r arrow}{ital h}1 (reference) transition. Because the one- and the two-phonon laser operations (4.2 K) are spectrally very narrow, narrower than that on QW confined-particle transitions, their separation affords an accurate measurement of QW phonon energy ({h bar}{omega}{sub LO}=36.1 meV).

Nam, D.W.; Holonyak, N. Jr.; Vesely, E.J. (Electrical Engineering Research Laboratory, Center for Compound Semiconductor Microelectronics, University of Illinois at Urbana-Champaign, Urbana, IL (USA) Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (USA)); Dupuis, R.D. (The University of Texas at Austin, Austin, TX (USA))

1990-07-02

44

Impulsive excitation of coherent magnons and phonons by subpicosecond laser pulses in the weak ferromagnet FeBO3  

Science.gov (United States)

Coherent magnons and phonons are excited by subpicosecond laser pulses in the weak ferromagnet FeBO3 . Impulsive stimulated Raman scattering (ISRS) is proven to be the microscopic mechanism of the excitation. It is shown that coherent magnons can be excited by both linearly and circularly polarized laser pulses where the efficiency of the process depends on the mutual orientation of the magnetic and crystallographic axes and the light propagation direction. The strong ellipticity of the ferromagnetic magnon mode is demonstrated, both experimentally and theoretically, to be essential for the excitation and observation of such coherent magnons. Because of this ellipticity, the amplitude of the coherent magnons excited by linearly polarized light may exceed by 2 orders of magnitude the amplitude of those excited by circularly polarized light. The primary difference between the excitation of coherent magnons by linearly polarized pulses via ISRS and via the earlier reported process of photoinduced magnetic anisotropy is discussed. Furthermore, the ISRS process is found to be responsible for the excitation of two optical phonon branches (8.4 and 12.1 THz) observed in our experiments. A coherent excitation, with a temperature-independent frequency of 0.7 THz, has also been observed in the magnetically ordered phase but could not be assigned to any optical phonon modes known in FeBO3 . The well-pronounced dependence of the amplitude of this mode on temperature suggests that this mode of nonmagnetic origin becomes Raman active only in the magnetically ordered phase and, therefore, can be excited and observed only below the Néel temperature.

Kalashnikova, A. M.; Kimel, A. V.; Pisarev, R. V.; Gridnev, V. N.; Usachev, P. A.; Kirilyuk, A.; Rasing, Th.

2008-09-01

45

Efficient generation of coherent THz phonons with a strong change in frequency excited by femtosecond laser plasma formed in a bulk of quartz  

Science.gov (United States)

We observed a strong change in the frequency of coherent THz phonons from 1.4 to 4.6 THz under tight focusing (NA ~ 0.4) of intense femtosecond laser radiation (~ 1013 W/cm2) ignited the plasma within a bulk of quartz. Strong frequency shifts are caused by local heating of a microvolume (4 × 4 × 60 ?m3) up to the temperature close to the ?- ? phase transition (846 K) of quartz. The effective target heating and coherent phonon excitation are provided via a laser-induced plasma.

Potemkin, F. V.; Mikheev, P. M.

2012-09-01

46

Phoenix's Laser Beam in Action on Mars  

Science.gov (United States)

[figure removed for brevity, see original site] Click on image to view the animation The Surface Stereo Imager camera aboard NASA's Phoenix Mars Lander acquired a series of images of the laser beam in the Martian night sky. Bright spots in the beam are reflections from ice crystals in the low level ice-fog. The brighter area at the top of the beam is due to enhanced scattering of the laser light in a cloud. The Canadian-built lidar instrument emits pulses of laser light and records what is scattered back. The Phoenix Mission is led by the University of Arizona, Tucson, on behalf of NASA. Project management of the mission is by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Spacecraft development is by Lockheed Martin Space Systems, Denver.

2008-01-01

47

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

48

Laser action in bulk Cr:ZnSe crystals  

Science.gov (United States)

Cr:ZnSe laser active material is one of the favourite possibility how to generate broadly tunable mid-infrared laser radiation at room-temperature. The aim of this study was to demonstrate and analyze pulsed as well as continuous-wave laser action in bulk Cr:ZnSe crystals grown by the floating-zone method or by the Bridgman method. The absorption spectra of Cr:ZnSe were measured to be from 1500 to 2000 nm, therefore various lasers were utilized for coherent longitudinal pumping of Cr:ZnSe laser, namely flashlamp-pumped Er:YAP laser (generated wavelength 1658 nm), diode-pumped Tm:YLF laser (generated wavelength 1912 nm), and diodepumped Tm:YAP laser (generated wavelength 1980 nm). In the first case, the Cr:ZnSe crystal grown by the Bridgman method was investigated. In the second case, the Cr:ZnSe crystal grown by the floating zone method was studied. In both cases, the homogeneity of the active Cr:ZnSe crystals was found reasonable good. The emission spectrum was from 2000 up to 2800 nm. The Cr:ZnSe laser generated radiation was broadly continuously tunable in the range from 2050 nm up to 2750 nm. The generated radiation beam spatial structure was close to TEM 00.

Koranda, Petr; Jelínková, Helena; Nemec, Michal; Šulc, Jan; Doroshenko, Maxim E.; Basiev, Tasoltan T.; Komar, Vitaly K.; Gerasimenko, Andriy S.; Puzikov, Vyacheslav M.; Badikov, V. V.; Badikov, D. V.

2008-05-01

49

Red-edge laser action from borondipyrromethene dyes  

Science.gov (United States)

Long-wavelength fluorescent dyes with improved efficiency and stability are required to realize new photoelectronic and biophotonic applications. We have designed and synthesized novel 2,6- or 3,5-substituted BODIPY (BDP) dyes by a simple protocol to reach wavelength-finely tunable laser action from 600 to 725 nm. The influence of the nature and position of substituents on the laser behavior of the new BDP dyes have been systematically characterized as a function of dye concentration and chemical character of the medium. Regarding efficiency and photostability, the new chromophores outperform the laser action of dyes presently commercialized and considered as benchmarks over this spectral region when pumped under identical conditions. The results obtained provide insight into the always complicated composition-structure-properties relationship of dyes, and suggest possible synthesis routes for new BDP derivatives with properties optimized for specific applications.

García-Moreno, Inmaculada; Zhang, Dakui; Costela, Ángel; Martín, Virginia; Sastre, Roberto; Xiao, Yi

2010-04-01

50

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2011-09-01

51

Femtosecond laser-induced crystallization of amorphous Sb2Te3 film and coherent phonon spectroscopy characterization and optical injection of electron spins  

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.

2011-09-01

52

Triboluminescence of tungsten initiated by termodeformations under laser action  

Science.gov (United States)

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

53

Observation of phonon-assisted laser operation of Al/sub x/Ga/sub 1-//sub x/As-GaAs quantum well heterostructures  

Energy Technology Data Exchange (ETDEWEB)

Data are presented showing that the key to observing the phonon-assisted photopumped laser operation of narrow rectangular samples of Al/sub x/Ga/sub 1-//sub x/As-GaAs quantum well heterostructures (QWHs) is the control of the edge-to-edge resonator Q across the sample. If the sample is heat sunk in metal, with metal reflectors folded upward along the edges, the resonator Q across the sample is high, and laser operation across the sample on confined-particle states (a reference) and along the sample a phonon lower in energy (..delta..Eapprox. =(h/2..pi..)..omega../sub LO/) is observed. If the sample edges across the sample are left uncoated (weakly reflecting, low Q), laser operation is observed only along the sample (longitudinal modes) but shifted (..delta..Eapprox. =(h/2..pi..)..omega../sub LO/) below the confined-particle states and absorption. A QWH rectangle, with proper heat sinking and control of its edge-to-edge resonator Q, can act as a hot-phonon ''spectrometer'' if it is fully photopumped across its width and is only partially pumped along its length.

Holonyak N. Jr.; Nam, D.W.; Plano, W.E.; Vesely, E.J.; Hsieh, K.C.

1989-03-13

54

Ultrafast demagnetization after laser irradiation in transition metals: Ab initio calculations of the spin-flip electron-phonon scattering with reduced exchange splitting  

Science.gov (United States)

Despite intensive research, the underlying mechanisms for ultrafast demagnetization after laser irradiation in transition metals are still not understood. We discuss the possible processes which have been suggested in order to explain the ultrafast demagnetization within several hundreds of femtoseconds and argue that the spin angular momentum has to go to the lattice in the end. Based on this argument, we consider spin-flip electron-phonon scatterings. The demagnetization time ?M and the demagnetization rate dM/dt due to spin-flip electron-phonon scattering is calculated for fcc Ni and bcc Fe. Thereby, the electronic states and phononic states are calculated ab initio. We find that the demagnetization rates for fcc Ni and bcc Fe are too small to explain experimental demagnetization rates, which is in agreement with earlier publications. In addition, the demagnetization rates for band structures with reduced exchange splitting are calculated, however, also these demagnetization rates are too small. Finally, the phase space for scattering processes which is related to the maximum possible demagnetization is estimated for band structures with ground-state exchange splitting and with reduced exchange splitting. The maximum possible demagnetization is too small for bcc Fe and fcc Co but not necessarily for fcc Ni. We suggest to include magnons and to consider independent combinations of spin-flip electron-phonon and spin-flip electron-magnon scattering processes as a possible explanation for the ultrafast demagnetization.

Illg, Christian; Haag, Michael; Fähnle, Manfred

2013-12-01

55

Phonon confinement and electron capture time in quantum well  

International Nuclear Information System (INIS)

The electron capture time via an electron-polar optical phonon interaction is calculated considering the confinement of a phonon in GaAs quantum well laser structure. The effect of phonon confinement decreases the electron capture time about twice comparing the electron capture time obtained from the interaction of an electron with bulk phonon. (author)

1996-06-06

56

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

1999-10-01

57

Comparison of resonant-phonon-assisted terahertz quantum-cascade lasers with one-well injector and three-well module  

Science.gov (United States)

The authors compare resonant-phonon-assisted terahertz quantum-cascade lasers with different active region designs, i.e., one-well injector and three-well module, using an ensemble Monte Carlo method. Carrier transport under injection anticrossing, parasitic anticrossing, and collection anticrossing couplings are investigated for both structures. The results show that the main parasitic current channel is the resonance of the injector 1' with the lower lasing level 3 and one-well injector design benefits a high injection selectivity because of a better ?1'4/?1'3 ratio. Due to the diagonal radiative transition, the one-well injector design sacrifices the oscillator strength and modal gain to reduce the parasitic coupling. Temperature evaluation shows that longitudinal-optical phonon emission is the dominant scattering mechanism contributing to lasing and the calculated modal gain in the one-well design shows a slower decreasing rate with temperature.

Li, H.; Cao, J. C.; Tan, Z. Y.; Feng, S. L.

2008-11-01

58

Nonadiabatic generation of coherent phonons  

CERN Multimedia

The time-dependent density functional theory (TDDFT) is the leading computationally feasible theory to treat excitations by strong electromagnetic fields. Here the theory is applied to coherent optical phonon generation produced by intense laser pulses. We examine the process in the crystalline semimetal antimony (Sb), where nonadiabatic coupling is very important. This material is of particular interest because it exhibits strong phonon coupling and optical phonons of different symmetries can be observed. The TDDFT is able to account for a number of qualitative features of the observed coherent phonons, despite its unsatisfactory performance on reproducing the observed dielectric functions of Sb. A simple dielectric model for nonadiabatic coherent phonon generation is also examined and compared with the TDDFT calculations.

Shinohara, Y; Yabana, K; Iwata, J -I; Otobe, T; Bertsch, G F

2012-01-01

59

Laser characteristics of KCL:O2(-)  

Science.gov (United States)

Amplified spontaneous emission and laser action have been observed at 77 K in KCl crystals containing the superoxide ion (O2/-/). The laser operates in two bands of width approximately 50 A centered at 6350 A and 5984 A. These bands are the (lattice) phonon sidebands of vibronic transitions of the superoxide ion. At lower temperatures (approximately 6 K) amplified spontaneous emission is observed in the zero phonon line at 6294 A.

Wilk, S. R.; Boyd, R. W.; Teegarden, K. J.

1983-10-01

60

Stimulated emission of phonons in an acoustic cavity  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This thesis will present experiments on stimulated emission of phonons in dilute ruby following complete population inversion of the Zeeman-split E(2E) Kramers doublet by selective pulsed optical pumping into its upper component. The resulting phonon avalanches are detected by use of the R1 luminescence emanating from the inverted zone, located near the end face where the laser beam enters the crystal. The phonons appear to team up into a highly directional phonon beam. The phonon frequency i...

Tilstra, Lieuwe Gijsbert

2001-01-01

 
 
 
 
61

Laser action on "Scar"-modes and KAM-transition to chaos in semiconductor diode lasers with deformed resonators  

Science.gov (United States)

Measurements of the optical spectra of semiconductor injection lasers with deformed cylinder resonators show direct and unique signatures of laser action on scar-modes and of the Kolmogorov-Arnold-Moser (KAM) transition from integrability to chaos. The diode lasers studied in the present work operate with transverse electric (TE) polarization resulting in laser action on (partially) chaotic whispering gallery modes for all deformations. This observation is in contrast to the stable and quasi-stable, bouncing-ball type bow-tie modes of unipolar semiconductor lasers having the same resonator geometry but emitting with transverse magnetic (TM) polarization.

Narimanov, Evgenii E.; Gmachl, Claire F.; Capasso, Federico; Baillargeon, James N.; Cho, Alfred Y.

2002-06-01

62

KAM-Laser action on ``scar"-modes and KAM transition to chaos in semiconductor diode lasers with deformed resonators  

Science.gov (United States)

Measurements of the optical spectra of semiconductor injection lasers with deformed cylinder resonators show a direct and unique signature of the classical Komolgorov-Arnold-Moser (KAM) transition from integrability to chaos for devices with small deformation. At larger deformation, strong evidence for laser action on scar-modes is obtained. The diode lasers operate with transverse electric (TE) polarization resulting in laser action on (partially) chaotic whispering gallery modes for all deformations. This observation is in contrast to the stable and quasi-stable, bouncing-ball type "bow-tie" modes of unipolar semiconductor lasers having the same resonator geometry but emitting with transverse magnetic (TM) polarization.

Narimanov, Evgenii; Gmachl, Claire; Capasso, Federico

2002-05-01

63

Free-electron properties of metals under ultrafast laser-induced electron-phonon nonequilibrium: A first-principles study  

Science.gov (United States)

The electronic behavior of various solid metals (Al, Ni, Cu, Au, Ti, and W) under ultrashort laser irradiation is investigated by means of density functional theory. Successive stages of extreme nonequilibrium on picosecond time scale impact the excited material properties in terms of optical coupling and transport characteristics. As these are generally modelled based on the free-electron classical theory, the free-electron number is a key parameter. However, this parameter remains unclearly defined and dependencies on the electronic temperature are not considered. Here, from first-principles calculations, density of states are obtained with respect to electronic temperatures varying from 10-2 to 105 K within a cold lattice. Based on the concept of localized or delocalized electronic states, temperature dependent free-electron numbers are evaluated for a series of metals covering a large range of electronic configurations. With the increase of the electronic temperature we observe strong adjustments of the electronic structures of transition metals. These are related to variations of electronic occupation in localized d bands, via change in electronic screening and electron-ion effective potential. The electronic temperature dependence of nonequilibrium density of states has consequences on electronic chemical potentials, free-electron numbers, electronic heat capacities, and electronic pressures. Thus electronic thermodynamic properties are computed and discussed, serving as a base to derive energetic and transport properties allowing the description of excitation and relaxation phenomena caused by rapid laser action.

Bévillon, E.; Colombier, J. P.; Recoules, V.; Stoian, R.

2014-03-01

64

Excitons, polarons, and laser action in poly(p-phenylene vinylene) films  

Science.gov (United States)

We have used a multitude of linear and nonlinear cw optical spectroscopies to study the optical properties of water precursor poly(p-phenylene vinylene) (PPV) thin films. These spectroscopies include absorption, photoluminescence, photoinduced absorption and their respective optically detected magnetic resonance, and electroabsorption spectroscopy. We have studied singlet and triplet excitons, polarons, and laser action in PPV films. We found that the lowest-lying absorption band is excitonic in origin. It consists of two absorption components due to a bimodal distribution of the polymer chain conjugation lengths. Electroabsorption spectroscopy unambiguously shows the positions of the lowest-lying odd parity exciton 1Bu at 2.59 eV and two of the higher-lying even-parity excitons, namely, mAg at 3.4 eV and kAg at 3.7 eV. From these exciton energies we obtained a lower bound for the exciton binding energy in PPV, Eb(min)=E(mAg)-E(1Bu)=0.8 eV. The quantum efficiency spectrum for triplet exciton photogeneration consists of two contributions; the intersystem crossing and, at higher energies, singlet fission. From the onset of the singlet fission process at ESF=2ET, we could estimate the energy of the lowest-lying triplet exciton, 1 3Bu, at 1.55 eV, with a singlet-triplet splitting as large as 0.9 eV. From photoinduced absorption spectroscopy we measured the triplet-triplet transition, T-->T*, to be 1.45 eV. The quantum efficiency spectrum for polaron photogeneration also consists of two contributions: one extrinsic and the other intrinsic. The latter shows a monotonically increasing function of energy with an energy onset at 3.3 eV. The intrinsic photogeneration process is analyzed with a model of free-electron-hole pair photogeneration, which separate more effectively at higher energy. The carrier generation quantum yield at 3.65 eV is estimated to be 0.5%. The quantum efficiency for photoluminescence, on the other hand, shows one single step-function process, with an onset at 2.4 eV. The photoluminescence spectrum is well structured, showing five phonon side bands with 190 meV separation. We have also studied laser action in PPV thin films and microcavities such as microrings and microdisks. The effective gain spectrum is calculated and the estimated threshold excitation intensity for laser action for the 0-1 transition is found to be in good agreement with the data, with an estimated exciton density of 2×1018 cm-3. Lasing from microring devices shows several narrow waveguide modes, with intermode spacing of 0.45 nm that corresponds to an effective mode refractive index, neff=1.45. The spectral width of the laser modes is resolution limited and gives a lower estimate of the cavity quality factor, Q. For microrings we found Q>5000, which is limited by self-absorption in the polymer film.

Österbacka, R.; Wohlgenannt, M.; Shkunov, M.; Chinn, D.; Vardeny, Z. V.

2003-05-01

65

Phonon dynamics.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

An atomic lattice in its ground state is excited by the rapid displacement and release of an atomic constituent. The time dependence of the energy transfer to other constituents is studied by using a phonon dispersion relation that is linear in frequency and propagation vector components.

1990-01-01

66

The beat noise which arises from magnetic field action in an He-Ne laser  

Energy Technology Data Exchange (ETDEWEB)

Experimental research is run on the noise which arises from the earth magnetic field action in an He-Ne laser. The noise generation mechanism is explained within the scope of Zeeman laser theory and the dispersion properties of a laser medium. Methods are proposed for suppressing this noise.

Lu, K.; Ba, E.; Zhang, J.

1983-01-01

67

Phonons with orbital angular momentum  

Energy Technology Data Exchange (ETDEWEB)

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

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

2011-10-15

68

Phonons with orbital angular momentum  

International Nuclear Information System (INIS)

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

2011-10-01

69

Galaxy formation and phonons  

International Nuclear Information System (INIS)

The possibility that the spectrum of pregalactic inhomogeneities results from quantum density fluctuations in the early Universe is investigated. A hydrodynamical description of matter is used, which is reasonable for galactic scales. The excitations of the physical degrees of freedom for longitudinal matter displacements, and the corresponding perturbations of the metric, called phonons for brevity, are shown to be treatable in terms of a scalar field. We derive the quadratic Lagrangian for this field directly from the Einstein-Fock action. Using the method of canonical quantization, we calculate the spectrum of inhomogeneities in the long-wave limit and find that its form is a model-independent power law, while its amplitude is defined by the evolution of the equation of state of the background matter. As an example we present a model in which the conditions needed for galaxy formation may be realized by the creation of phonons. (author)

1982-01-01

70

Phonon manipulation with phononic crystals.  

Energy Technology Data Exchange (ETDEWEB)

In this work, we demonstrated engineered modification of propagation of thermal phonons, i.e. at THz frequencies, using phononic crystals. This work combined theoretical work at Sandia National Laboratories, the University of New Mexico, the University of Colorado Boulder, and Carnegie Mellon University; the MESA fabrication facilities at Sandia; and the microfabrication facilities at UNM to produce world-leading control of phonon propagation in silicon at frequencies up to 3 THz. These efforts culminated in a dramatic reduction in the thermal conductivity of silicon using phononic crystals by a factor of almost 30 as compared with the bulk value, and about 6 as compared with an unpatterned slab of the same thickness. This work represents a revolutionary advance in the engineering of thermoelectric materials for optimal, high-ZT performance. We have demonstrated the significant reduction of the thermal conductivity of silicon using phononic crystal structuring using MEMS-compatible fabrication techniques and in a planar platform that is amenable to integration with typical microelectronic systems. The measured reduction in thermal conductivity as compared to bulk silicon was about a factor of 20 in the cross-plane direction [26], and a factor of 6 in the in-plane direction. Since the electrical conductivity was only reduced by a corresponding factor of about 3 due to the removal of conductive material (i.e., porosity), and the Seebeck coefficient should remain constant as an intrinsic material property, this corresponds to an effective enhancement in ZT by a factor of 2. Given the number of papers in literature devoted to only a small, incremental change in ZT, the ability to boost the ZT of a material by a factor of 2 simply by reducing thermal conductivity is groundbreaking. The results in this work were obtained using silicon, a material that has benefitted from enormous interest in the microelectronics industry and that has a fairly large thermoelectric power factor. In addition, the techniques and scientific understanding developed in the research can be applied to a wide range of materials, with the caveat that the thermal conductivity of such a material be dominated by phonon, rather than electron, transport. In particular, this includes several thermoelectric materials with attractive properties at elevated temperatures (i.e., greater than room temperature), such as silicon germanium and silicon carbide. It is reasonable that phononic crystal patterning could be used for high-temperature thermoelectric devices using such materials, with applications in energy scavenging via waste-heat recovery and thermoelectric cooling for high-performance microelectronic circuits. The only part of the ZT picture missing in this work was the experimental measurement of the Seebeck coefficient of our phononic crystal devices. While a first-order approximation indicates that the Seebeck coefficient should not change significantly from that of bulk silicon, we were not able to actually verify this assumption within the timeframe of the project. Additionally, with regards to future high-temperature applications of this technology, we plan to measure the thermal conductivity reduction factor of our phononic crystals as elevated temperatures to confirm that it does not diminish, given that the nominal thermal conductivity of most semiconductors, including silicon, decreases with temperature above room temperature. We hope to have the opportunity to address these concerns and further advance the state-of-the-art of thermoelectric materials in future projects.

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

2012-01-01

71

Multiwavelength laser action of Nd 3+:YAlO 3 single crystals grown by the laser heated pedestal growth method  

Science.gov (United States)

We describe the growth of high quality transparent fibers of pure and Nd-doped YAlO 3 from unreacted pedestals (green rods) by the laser heated pedestal growth technique. The X-ray diffraction analysis shows that the fibers are monocrystalline, with a distorted Pnma perovskite structure and grow along direction ( b axis). In this work, multi-wavelength laser action is demonstrated for these fibers in the two main laser channels of Nd 3+ ions. In the 4F 3/2 ? 4I 11/2 laser transition, low threshold multi-wavelength laser emission is obtained at wavelengths of 1065, 1073 and 1081 nm. Additionally, for the first time in LHPG grown YAlO 3 fibers, laser action in the 4F 3/2 ? 4I 13/2 transition is demonstrated at a wavelength of 1341 nm.

Romero, J. J.; Montoya, E.; Bausá, L. E.; Agulló-Rueda, F.; Andreeta, M. R. B.; Hernandes, A. C.

2004-01-01

72

Induced phonon-sideband laser operation of large-quantum-well Al/sub x/Ga/sub 1-x/As-GaAs heterostructures (L/sub z/ approx. 200--500 A)  

Energy Technology Data Exchange (ETDEWEB)

Data are presented on photopumped metallorganic chemically vapor-deposited Al/sub x/Ga/sub 1-x/As-GaAs quantum-well heterostructures with active regions consisting of a large GaAs quantum well (L/sub z/1approx.200, 500 A) coupled to a phonon generating array of seven small GaAs wells (L/sub z/2approx.50 A). Phonon-sideband laser operation below the confined-carrier transitions of the large GaAs quantum well(s) is induced by the large number of phonons generated in the smaller GaAs wells. The induced phonon-sideband laser operation (of a larger quantum well by an array of smaller wells) leads to a measurement of the energy difference between the first-state light- and heavy-hole energies of a 200-A GaAs quantum well (4.9 meV) and directly to the GaAs L0-phonon energy h..omega../sub L/0approx. =41.0-4.9=36.1 meV.

Coleman, J.J.; Dapkus, P.D.; Vojak, B.A.; Laidig, W.D.; Holonyak, N. Jr.; Hess, K.

1980-07-01

73

Absorption and emission spectroscopy in the analysis of laser radiation and fast neutron action on chromatin  

Science.gov (United States)

The actions of a 248 mm excimer laser radiation (0.5 - 3 MJ/m2) and of fast neutrons (d(13 MeV) + Be thick target, 5 - 100 Gy) on chromatin (the complex of DNA and proteins of eukaryotic cells) were analyzed. The parameters estimated were: the thermal transition, the fluorescence of chromatin-ethidium bromide complexes, the chromatin intrinsic fluorescence and the energy transfer efficiency between specific fluorescent ligands coupled at chromatin. The mechanism of UV excimer laser action is similar to the fast neutrons action on chromatin. The complex action includes the production of chromatin DNA strand breaks, the protein structure lesion and the chromatin conformation modification.

Radu, Liliana; Mihailescu, Ion N.; Constantinescu, B.; Gostian, O.

1995-03-01

74

Researching of thin-plate mechanoluminescence initiated by thermal deformations resulting from laser pulse action  

Science.gov (United States)

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

75

Spectroscopy and laser action of rhodamine 6G doped aluminosilicate xerogels  

Energy Technology Data Exchange (ETDEWEB)

Rhodamine 6G (R6G) doped aluminosilicate glass synthesized by the sol-gel method exhibits laser action. Transparent 5 mm {times} 5 mm {times} 10 mm monoliths were used as cast in a simple laser cavity. This new material was pumped at rates of up to 25 Hz and was still active after as many as 40,000 pump pulses. Luminescence and free-running laser spectra are measured. The dependence of the R6G doped aluminosilicate dye laser output on the number of pump pulses and the pump pulse energy is discussed.

McKiernan, J.M.; Yamanaka, S.A.; Dunn, B.; Zink, J.I. (Univ. of California, Los Angeles (USA))

1990-07-26

76

Generation of electromagnetic radiation in laser action with solids  

Energy Technology Data Exchange (ETDEWEB)

A new effect of electromagnetic pulse generation in solids, exposed to laser irradiation was revealed experimentally. The ruby laser with 694.36 nm wave length was used in the experiments. Monocrystals of Si, GaAs, KCl, LiF, polycrystals of Cu, Al, metals, the rocks-calcite, marble, natural quartz, feldspar - were used as samples. The effect of electromagnetic pulse generation, which is characterized by sharp threshold dependence on the density of laser radiation power, as well as on the type of material and its characteristics was observed for each material. The possibility of using the method of electromagnetic pulse detection during laser irradiation for evaluation of defectiveness degree and strength characteristics of investigated materials was shown.

Aref' ev, K.P.; Vorob' ev, S.A.; Kuznetsov, M.F.; Mastov, Sh.R.; Pogrebnyak, A.D. (AN SSSR, Leningrad. Fiziko-Tekhnicheskij Inst.)

1984-04-01

77

Generation of electromagnetic radiation in laser action with solids  

International Nuclear Information System (INIS)

A new effect of electromagnetic pulse generation in solids, exposed to laser irradiation was revealed experimentally. The ruby laser with 694.36 nm wave length was used in the experiments. Monocrystals of Si, GaAs, KCl, LiF, polycrystals of Cu, Al, metals, the rocks-calcite, marble, natural quartz, feldspar - were used as samples. The effect of electromagnetic pulse generation, which is characterized by sharp threshold dependence on the density of laser radiation power, as well as on the type of material and its characteristics was observed for each material. The possibility of using the method of electromagnetic pulse detection during laser irradiation for evaluation of defectiveness degree and strength characteristics of investigated materials was shown

1984-04-01

78

Controlling phonon entanglement and squeezing via one- and two-phonon interference  

CERN Document Server

When ultrafast laser pulse strikes the crystal with a van Hove singularity in the phonon density of states, it creates a pair of anti-correlated in wave vector acoustic 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 create a two-phonon bound state in which the constituent phonons are entangled. The description of phonon squeezing and/or entanglement requires the quantization since the phenomena come entirely due to the grainy nature of the lattice field. Here we show that via the interplay between one- and two-phonon interference the bound and squeezed two-phonon state in ZnTe can be manipulated. We demonstrate that when two paired-phonon ensembles are overlapped, the strength of phonon squeezing and entanglement can be controlled. However, due to the complementarity of one- and two-phonon interference a larger entanglement comes at expense of a reduced squeezing.

Misochko, Oleg V; Takahashi, Hiroshi; Ohmori, Kenji; Takei, Nobuyuki; Nakamura, Kazutaka G

2010-01-01

79

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

International Nuclear Information System (INIS)

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

2009-11-15

80

Ground State ESR Measurements of Ruby During Laser Action.  

Science.gov (United States)

The use of electron spin resonance for measurement of the ground state population (GSP) of Cr(3+) in a ruby rod during optical pumping is described. For a 7.7 cm long rod at 90K and a mirror reflectance product R1R2 > 0.08, the GSP at laser threshold was ...

T. Igarashi A. Szabo

1966-01-01

 
 
 
 
81

Laser action in a lead Hollow cathode discharge and its excitation mechanism  

International Nuclear Information System (INIS)

CW or afterglow laser action in a lead hollow cathode discharge was obtained. It was found that the metastable states 6p23P1 and 6p23P2 of the Pb atom play an important role in the excitation process. The wavelengths of the laser lines were measured with higher accuracy than before and the discrepancies in the transition assignment could be eliminated. (orig.)

1981-03-01

82

Whispering-gallery mode resonators for highly unidirectional laser action  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Optical microcavities can be designed to take advantage of total internal reflection, which results in resonators supporting whispering-gallery modes (WGMs) with a high-quality factor (Q factor). One of the crucial problems of these devices for practical applications such as designing microcavity lasers, however, is that their emission is nondirectional due to their radial symmetry, in addition to their inefficient power output coupling. Here we report the design of elliptical resonators with...

Wang, Qi Jie; Yan, Changling; Yu, Nanfang; Unterhinninghofen, Julia; Wiersig, Jan; Pflu?gl, Christian; Diehl, Laurent; Edamura, Tadataka; Yamanishi, Masamichi; Kan, Hirofumi; Capasso, Federico

2010-01-01

83

Free-electron properties of metals under ultrafast laser-induced electron-phonon nonequilibrium: A first-principles study  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The electronic behavior of various solid metals (Al, Ni, Cu, Au, Ti, and W) under ultrashort laser irradiation is investigated by means of density functional theory. Successive stages of extreme nonequilibrium on picosecond time scale impact the excited material properties in terms of optical coupling and transport characteristics. As these are generally modelled based on the free-electron classical theory, the free-electron number is a key parameter. However, this parameter remains unclearly...

Be?villon, Emile; Colombier, Jean-philippe; Recoules, Vanina; Stoian, Razvan

2014-01-01

84

Diode-pumped efficient laser action of Yb3+:LYSO crystal  

Science.gov (United States)

Effective diode-pumped continuous wave (CW) tunable laser action of a new alloyed crystal Yb:LYSO is demonstrated. The alloyed LYSO crystal possesses the desirable physical and laser performance of La2SiO5 (LSO), as well as the favorable growth properties and costs of Y2SiO5 (YSO) in the same time. With a 5 at.-% Yb:LYSO sample, the output power of 2.84 W at 1085 nm and an optical-to-optical conversion efficiency of 54.5% are achieved. Its laser wavelength can be tuned over a broad range of 81 nm, from 1030 to 1111 nm.

Du, Juan; Liang, Xiaoyan; Xu, Yi; Li, Ruxin; Zhao, Guangjun; Yan, Chengfeng; Su, Liangbi; Xu, Jun; Xu, Zhizhan

2007-03-01

85

Laser radiation action on the biomedium as nonadiabatic excitation of macromolecules  

Science.gov (United States)

The extended sphere of the laser successful use at large vagueness of the gear of radiation interaction with biological and biosimilar objects is a main modern paradox in the application of low-intensity coherent radiation in biology and medicine. There are rather regularly, for example, the reasons of immateriality of such parameters as laser radiation coherency degree for biostimulation, but the replacement of semi-conductor lasers by the light diodes isn't observed in medical practice until now. there are also no convincing results on comparative analysis of biostimulated effect under coherent and noncoherent radiation. Action of coherent electromagnetic radiation of the visible and infrared spectral range causes, as appear, the same type structure-optical changes in various objects biological liquids, cells suspensions, model biomolecular solutions, cells of plan, insects and animals. The medicobiologic consequences of laser effect are extremely variable because of the complexity of biological object and sophistication of research techniques and analyses. The energy doze of radiation acting onto a bio-object, as a rule, is extremely small, and hence like the case of extremely high frequency radiation one can to name this action by the 'informative' one, i.e., initiating only biosystem reactions is produced due to its own energy. In connection with the relatively slow biosystem response to the laser radiation action, the nonlocality of this reaction at the local action and large variety of biochemical reactions caused with laser radiation one can assume the existence of uniform physical mechanism realizing the biostimulation effect of laser radiation for various biosystems.

Kompanets, Igor N.; Krasnov, A. E.; Malov, A. N.

1996-11-01

86

INTERACTION OF LASER RADIATION WITH MATTER. LASER PLASMA: Damage to the surface of silicon in the solid phase by the action of Nd:YAG laser pulses  

Science.gov (United States)

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

87

INTERACTION OF LASER RADIATION WITH MATTER. LASER PLASMA: Surface damage of silicon and copper by pulsed and pulse-periodic action of an Nd : YAG laser  

Science.gov (United States)

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

88

q-DEFORMED Phonons  

Science.gov (United States)

We make use of a recently identified distribution function for the q-deformed oscillators and apply it to the q-analog of phonons. The thermodynamic properties of such q-phonons and q-photons are derived and compared with the case of ordinary phonons.

Swamy, P. Narayana

89

Laser Action by Electron Beam Pumping: State of the Art, Technical Considerations, and Guide for Experiments.  

Science.gov (United States)

This report relates to laser action by electron beam pumping. Results of a literature survey conducted on the state of the art up to August, 1964, are presented. The papers chosen for review were selected to show the type of work being performed with elec...

M. Stimler

1964-01-01

90

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)

2009-09-01

91

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

1984-09-07

92

Length-scale dependent phonon interactions  

CERN Document Server

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

93

Control of generation regimes of ring chip laser under the action of the stationary magnetic field  

International Nuclear Information System (INIS)

We consider realisation of different generation regimes in an autonomous ring chip laser, which is a rather complicated problem. We offer and demonstrate a simple and effective method for controlling the radiation dynamics of a ring Nd:YAG chip laser when it is subjected to a stationary magnetic field producing both frequency and substantial amplitude nonreciprocities. The amplitude and frequency nonreciprocities of a ring cavity, arising under the action of this magnetic field, change when the magnet is moved with respect to the active element of the chip laser. Some self-modulation and stationary generation regimes as well as the regime of beatings and dynamic chaos regime are experimentally realised. Temporal and spectral characteristics of radiation are studied and conditions for the appearance of the generation regime are found. (control of laser radiation parameters)

2013-05-31

94

Laser phase noise effects on the dynamics of optomechanical resonators  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We investigate theoretically the influence of laser phase noise on the cooling and heating of a generic cavity optomechanical system. We derive the back-action damping and heating rates and the mechanical frequency shift of the radiation pressure-driven oscillating mirror, and derive the minimum phonon occupation number for small laser linewidths. We find that in practice laser phase noise does not pose serious limitations to ground state cooling. We then consider the effect...

Phelps, Gregory A.; Meystre, Pierre

2010-01-01

95

Phase control of oscillator excitation under the action of ultrashort laser pulses  

Science.gov (United States)

The phase control of the oscillator excitation under the action of an ultrashort laser pulse with a controllable carrier-envelope phase (CEP) is investigated theoretically. Analytical expressions for the phase modulation coefficient and excitation spectral line shape are obtained in the case of a harmonic oscillator. The main features of the phase control of an inharmonic oscillator in the linear and nonlinear regimes are analyzed in the framework of the Morse model. The approach developed for an oscillator is used for the description of the phase effects during the laser excitation of a quantum system in an one-photon approximation.

Arustamyan, M. G.; Astapenko, V. A.

2008-09-01

96

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

CERN Multimedia

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

97

Simulation of the thermal processes induced by action of laser radiation on organic media  

Science.gov (United States)

A mathematical model is proposed for calculation of the hyperthymia of a multilayer biological structure under the action of laser radiation. For the in vivo case, the dependences of the temperature field on the refractive index and absorption coefficient of the biological tissue under study (epidermis, the upper derma layer, the lower derma layer, blood and its corpuscles) are determined. The obtained quantitative estimates can be used to predict the changes in the optical properties of the biological structure that are caused by the biophysical, biochemical, and physiological processes during the action of a nonpolarized monochromatic radiation flow on the structure surface.

Kulikov, K. G.

2009-02-01

98

Coherent phonon-induced optical modulation in semiconductors at terahertz frequencies  

Science.gov (United States)

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

99

Phonon-phonon interactions in transition metals  

Science.gov (United States)

In this paper the phonon self-energy produced by anharmonicity is calculated using second-order many-body perturbation theory for all bcc, fcc, and hcp transition metals. The symmetry properties of the phonon interactions are used to obtain an expression for the self-energy as a sum over irreducible triplets, very similar to integration in the irreducible part of the Brillouin zone for one-particle properties. The results obtained for transition metals shows that the lifetime is on the order of 10-10 s. Moreover, the Peierls approximation for the imaginary part of the self-energy is shown to be reasonable for bcc and fcc metals. For hcp metals we show that the Raman-active mode decays into a pair of acoustic phonons, their wave vector being located on a surface defined by conservation laws.

Chaput, Laurent; Togo, Atsushi; Tanaka, Isao; Hug, Gilles

2011-09-01

100

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

Science.gov (United States)

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

 
 
 
 
101

ELECTRON-PHONON INTERACTIONS IN SEMICONDUCTORS : PHONON TRANSPORT AND DECAY  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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.

1981-01-01

102

Microscopic model of a phononic refrigerator  

CERN Multimedia

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

103

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

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)

1979-01-01

104

Chirality dependence of coherent phonon amplitudes in single-wall carbon nanotubes  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We simulate the ultrafast dynamics of laser-induced coherent phonons in single-wall carbon nanotubes (SWNTs). In particular, we examine the coherent phonon amplitude of the radial breathing mode (RBM) as a function of excitation energy and chirality. We find that the RBM coherent phonon amplitudes are very sensitive to changes in excitation energy and are strongly chirality dependent. We discuss how the SWNT diameter changes in response to femtosecond laser excitation and under what condition...

Dresselhaus, Mildred; Nugraha, A. R. T.; Sanders, G. D.; Sato, K.; Stanton, C. J.

2011-01-01

105

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)

2012-05-01

106

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)

1998-10-31

107

Phonon Assisted Ballistic Resistance.  

Science.gov (United States)

We investigate the influence of phonons on the ballistic transport in idealized semiconductor structures. We examine the onset of the collision controlled transport and estimate the critical temperature interval that separates ballistic and fully collisio...

V. L. Gurevich V. B. Pevzner K. Hess

1994-01-01

108

Phonons in fcc strontium  

International Nuclear Information System (INIS)

A more realistic model, requiring a few parameters to explain the interactions among distant neighbours and valid to various crystallographic structures, is developed to study the phonon dispersion in fcc metals. The model, free from usual fitting procedure, is employed to obtain phonon dispersion in fcc strontium, which has attracted scant attention so far. The computed results showing good agreement with the recent experimental findings lend reliability and credibility to the theory. (author). 21 refs., 1 figs., 2 tabs

1993-03-01

109

Phonon decay in silicon nanocrystals: Fast phonon recycling  

Science.gov (United States)

We present a theory of electron-phonon interaction and phonon decay in Si nanocrystals based on sp3d5s* empirical tight-binding model and anharmonic Keating model. We demonstrate that the time of optical phonon emission by hot carriers in Si nanocrystal lies in the subpicosecond time range. However, due to the fast phonon recycling, the energy relaxation rate is determined not by the phonon emission but by the phonon decay rate. The decay rate of the optical phonon into two phonons of smaller energy is found to be in the 1-10 ps range. It is this anharmonic phonon decay process that may control the energy relaxation rate of excited carriers in Si nanocrystals.

Prokofiev, A. A.; Poddubny, A. N.; Yassievich, I. N.

2014-03-01

110

NO release photosensitized by ryboflavin under action of laser irradiation on S-nitrosoglutathione and buthylnitrite  

Science.gov (United States)

Nitric oxide (NO) is one of the universal regulators of cell and tissue metabolism. Besides, it plays the role of one of the main cytotoxic effectors in cell immunity system. High reactivity of NO determines its short lifetime (several seconds) in organism. Low-molecular-weight S-nitrosothiols, S-nitrosocompounds of proteins, dinitrosyl compounds, along with nitrosohemoglobin, nitrosomyoglobin are more stable compounds than NO and probably create physiological depot of NO in organism. In this work it is shown that semiquinone and leuko forms of riboflavin (RF) interacted with S-nitrosoglutathione and buthylnitrite to release NO. Leuko form of RF was obtained under action of laser irradiation (? = 337 nm, nitrogen laser) in the presence of electron donors (NADH, pyruvate). After mixing of reduced, uncolored leuko form of RF with nitrosoglutathione or buthylnitrite absorption spectrum underwent transformation which testified about RF oxidized form production. Simultaneously with RF oxidized form production growth of fluorescence with maximum at 533 nm occurred. Production of RF oxidized form due to interaction of S-nitrosoglutathione with leuko or semiqiuinone forms of RF was accompanied by formation of glutathione and release of NO. In the case of buthylnitrite butanol and NO were formed. Semiquinone form of RF was obtained under action of laser irradiation in anaerobic conditions on oxidized RF in the presence of bivalent metal ions [Zn (II), Mg (II)]. Semiquinone form of RF as well as leuko form transfer electrons to nitrosoglutathione molecules. This process is also accompanied by formation of glutathione, NO, oxidized RF. Obtained results testify that RF plays important role in NO metabolism due to interactions of its redox forms with S-nitrosocompounds and alkylnitrites which possibly can serve as components of NO physiological depot in organism.

Stepuro, Ivan I.; Adamchuk, Raisa I.; Stepuro, Vitali I.

2004-08-01

111

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/m"2 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)

1992-09-21

112

Emission of submillimeter electromagnetic waves by coherent phonons  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report on the first observation of the emission of electromagnetic radiation from coherent lattice vibrations in a semiconductor. Coherent optical phonons are excited by ultrashort laser pulses in single-crystal tellurium. THz frequency radiation emitted by the Dember-field-driven phonons is detected by time-resolved THz-emission spectroscopy. The measurements are complemented by optical pump-probe experiments with a polarization-sensitive detection scheme utilizing the symmetry of the Ram...

Dekorsy, Thomas; Auer, Holger; Waschke, Christian; Bakker, Huib J.; Roskos, Hartmut G.; Kurz, Heinrich; Wagner, Veit; Grosse, Peter

1995-01-01

113

Deformation dynamics and spallation strength of aluminium under a single-pulse action of a femtosecond laser  

Energy Technology Data Exchange (ETDEWEB)

An interferometric method is developed and realised using a frequency-modulated pulse for diagnosing a dynamics of fast deformations with a spatial and temporal resolution under the action of a single laser pulse. The dynamics of a free surface of a submicron-thick aluminium film is studied under an action of the ultrashort compression pulse with the amplitude of up to 14 GPa, excited by a femtosecond laser heating of the target surface layer. The spallation strength of aluminium was determined at a record high deformation rate of 3 Multiplication-Sign 10{sup 9} s{sup -1}. (extreme light fields and their applications)

Ashitkov, Sergei I; Komarov, P S; Ovchinnikov, A V; Struleva, E V; Agranat, Mikhail B [Joint Institute for High Temperatures, Russian Academy of Sciences, Moscow (Russian Federation)

2013-03-31

114

Phonons in semiconductor nanostructures  

Energy Technology Data Exchange (ETDEWEB)

Phonons in semiconductor nanostructures like quantum dots affect the dephasing of optical excitations decisively. In our presented work, the inhomogeneous, atomistic nature of the problem is simulated by employing a valence-force field description. The parameters are taken either directly from experiment or are calculated by density functional theory. The investigated structures include quantum dots of different shapes and alloy compositions. They consist of compounds with either zincblende or wurtzite crystal structure, therefore capturing the equilibrium structures of III-V and group III-nitrides. The phonon density of states is determined by calculating the velocity correlation function in a molecular dynamics simulation. We present also a comparison to continuum elasticity solutions of the wave equation for acoustical phonons.

Knittel, Andreas; Grosse, Frank [Institut fuer Physik der Humboldt- Universitaet zu Berlin, Newtonstr. 15, 12489 Berlin (Germany)

2007-07-01

115

Strength properties of an aluminum melt at extremely high tension rates under the action of femtosecond laser pulses  

Science.gov (United States)

The dynamics of the melting of a surface nanolayer and the formation of thermal and shock waves in metals irradiated by femtosecond laser pulses has been investigated both experimentally and theoretically. A new experimental-computational method has been implemented to determine the parameters of laser-induced shock waves in metallic films. Data on the strength properties of the condensed phase in aluminum films at an extremely high strain rate ( dot V / V ˜ 109 s-1)under the action of a laser-induced shock wave have been obtained.

Agranat, M. B.; Anisimov, S. I.; Ashitkov, S. I.; Zhakhovskii, V. V.; Inogamov, N. A.; Komarov, P. S.; Ovchinnikov, A. V.; Fortov, V. E.; Khokhlov, V. A.; Shepelev, V. V.

2010-05-01

116

The heat-pipe resembling action of boiling bubbles in endovenous laser ablation.  

Science.gov (United States)

Endovenous laser ablation (EVLA) produces boiling bubbles emerging from pores within the hot fiber tip and traveling over a distal length of about 20 mm before condensing. This evaporation-condensation mechanism makes the vein act like a heat pipe, where very efficient heat transport maintains a constant temperature, the saturation temperature of 100 degrees C, over the volume where these non-condensing bubbles exist. During EVLA the above-mentioned observations indicate that a venous cylindrical volume with a length of about 20 mm is kept at 100 degrees C. Pullback velocities of a few mm/s then cause at least the upper part of the treated vein wall to remain close to 100 degrees C for a time sufficient to cause irreversible injury. In conclusion, we propose that the mechanism of action of boiling bubbles during EVLA is an efficient heat-pipe resembling way of heating of the vein wall. PMID:20644976

van der Geld, Cees W M; van den Bos, Renate R; van Ruijven, Peter W M; Nijsten, Tamar; Neumann, H A Martino; van Gemert, Martin J C

2010-11-01

117

Structure of the phonon vacuum state  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The action of the long-range residual force on the expectation value of observables in the nuclear ground states is evaluated by finding optimal values for the coefficients of the canonical transformation which connects the phonon vacuum state with the (quasi-)particle ground-state. After estimating the improvements over the predictions of the independent-particle approximation we compare the ground-state wave functions, obtained using the presented approach, with those, obt...

Mishev, S.

2012-01-01

118

Action of the 216-nm fifth harmonic of a Nd:YAP laser on photosensitive germanosilicate glass films  

International Nuclear Information System (INIS)

The absorption spectrum, refractive index, and relief of the surface of a germanosilicate glass film are studied upon the non-destructive action of the 216-nm (5.75-eV) fifth harmonic of a repetitively pulsed Nd:YAP laser. It is shown that laser irradiation of films induces a strong photorefractive effect despite the relatively low absorption coefficient. For the 100-mJ cm-2 energy density and above, two-photon process make a noticeable contribution to the absorption of laser radiation at 216 nm. The diffraction efficiency of photoinduced phase gratings achieved ?7x10-3 for the exposure dose ?6 kJ cm-2, which corresponds to the induced refractive index 1.5x10-3. At higher exposure doses, a relief appears on a film surface and the diffraction efficiency of a phase grating is reduced. (interaction of laser radiation with matter. laser plasma)

2003-11-30

119

Abnormal increase of time of oxygen diffusion with oxidation of silicon surface under action of powerful laser pulses  

Science.gov (United States)

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

120

Continuous mode cooling and phonon routers for phononic quantum networks  

International Nuclear Information System (INIS)

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

2012-11-01

 
 
 
 
121

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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...

1981-01-01

122

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

123

Spectrum and entanglement of phonons in quantum fluids of light  

CERN Document Server

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

124

Spectrum and entanglement of phonons in quantum fluids of light  

Science.gov (United States)

We study the quantum state of phonons propagating on top of a fluid of light coherently generated in a planar microcavity device by a quasiresonant 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 of 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 the nonseparability of the phonon state from measurements of the correlation functions of the emitted light are discussed.

Busch, Xavier; Carusotto, Iacopo; Parentani, Renaud

2014-04-01

125

Superconductivity without phonons.  

Science.gov (United States)

The idea of superconductivity without the mediating role of lattice vibrations (phonons) has a long history. It was realized soon after the publication of the Bardeen-Cooper-Schrieffer (BCS) theory of superconductivity 50 years ago that a full treatment of both the charge and spin degrees of freedom of the electron predicts the existence of attractive components of the effective interaction between electrons even in the absence of lattice vibrations--a particular example is the effective interaction that depends on the relative spins of the electrons. Such attraction without phonons can lead to electronic pairing and to unconventional forms of superconductivity that can be much more sensitive than traditional (BCS) superconductivity to the precise details of the crystal structure and to the electronic and magnetic properties of a material. PMID:18097398

Monthoux, P; Pines, D; Lonzarich, G G

2007-12-20

126

LATTICE PHONON LIFETIME CALCULATIONS  

Digital Repository Infrastructure Vision for European Research (DRIVER)

It is shown that phonon lifetimes can be calculated using finite periodicities and discrete frequencies without going completely to the limit of infinite periodicities or quasi-continuous frequency distributions. In applying the Golden Rule equation in time-dependent perturbation theory there is a time interval over which the transition rate is very nearly independent of time and energy level differences (or periodicity). As the periodicity of the lattice increases the time interval over whic...

Henkel, J.

1981-01-01

127

Phonon-phonon interactions and modified specific heat equation  

International Nuclear Information System (INIS)

The anharmonicity due to phonon-phonon interactions which changes the phonon self-energy of the crystal under isochoric condition, is considered to derive a modified specific heat equation. The main assumption introduced is that the isochoric self-energy Gruneisen parameter, two of its first order derivatives and the isobaric Gruneisen parameter are the same for all the phonon frequencies. In the low temperature range, the Debye temperature calculated in the case of aluminium, by using the modified specific heat equation shows a shift towards the value calculated using elastic data obtained by using Houstan's six-direction approximation method. The thermodynamic theory introduced in this study suggests a simple method of including the effect of phonon-phonon interactions on the thermal properties of crystalline solids. (author)

1975-08-01

128

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

2012-10-10

129

Heralded single phonon preparation, storage and readout in cavity optomechanics  

CERN Document Server

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 downconversion. Subsequent detection of a single scattered Stokes photon projects the macroscopic oscillator into a single-phonon Fock state. The non-classical 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; Piro, Nicolas; Gisin, Nicolas; Kippenberg, Tobias J

2013-01-01

130

Phonons in strained semiconductor nanostructures  

Energy Technology Data Exchange (ETDEWEB)

Semiconductor nanostructures contain significant strain contributions, which in turn influence phonon properties. Model calculations for spherically shaped nanodots embedded in a host crystal are presented using the Keating model as interaction potential. It is shown that the local dot phonon density of states is to a good approximation given by the phonon density of the bulk material under identical strain. We present calculations of effective elastic constants for various strain situations employing ab initio density functional theory.

Grosse, F; Knittel, A; Zimmermann, R [Institut fuer Physik der Humboldt-Universitaet zu Berlin Newtonstr. 15, 12489 Berlin (Germany)

2007-12-15

131

Phonons in strained semiconductor nanostructures  

International Nuclear Information System (INIS)

Semiconductor nanostructures contain significant strain contributions, which in turn influence phonon properties. Model calculations for spherically shaped nanodots embedded in a host crystal are presented using the Keating model as interaction potential. It is shown that the local dot phonon density of states is to a good approximation given by the phonon density of the bulk material under identical strain. We present calculations of effective elastic constants for various strain situations employing ab initio density functional theory

2007-12-01

132

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

1984-09-07

133

Dissection of the frustules of the diatom Synedra acus under the action of picosecond impulses of submillimeter laser irradiation.  

Science.gov (United States)

Diatom algae realize highly intriguing processes of biosynthesis of siliceous structures in living cells under moderate conditions. Investigation of diatom physiology is complicated by frustule (siliceous exoskeleton). Frustules consist of valves and girdle bands which are adhered to each other by means of organic substances. Removal of the frustule from the lipid membrane of diatom cells would open new possibilities for study of silicon metabolism in diatoms. We found that submillimeter laser irradiation produced by a free-electron laser causes splitting of diatom frustules without destruction of cell content. This finding opens the way to direct study of diatom cell membrane and to isolation of cell organelles, including silica deposition vesicles. We suppose that the dissection action of the submillimeter irradiation results from unusual ultrasonic waves produced by the short (30-100 ps) but high-power (1 MW) terahertz laser impulses at 5.6 MHz frequency. PMID:23709009

Annenkov, Vadim V; Kozlov, Alexander S; Danilovtseva, Elena N; Basharina, Tatjana N; Petrov, Alexander K

2013-07-01

134

A magnetically field-controllable phononic crystal  

Science.gov (United States)

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

135

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)

2005-01-01

136

Acoustic Metamaterials and Phononic Crystals  

CERN Document Server

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

137

Phononic crystal with adaptive connectivity.  

Science.gov (United States)

The band structure of a phononic crystal can be controlled by tuning the mechanical stiffness of the links connecting its constituting elements. The first implementation of a phononic crystal with adaptive connectivity is obtained by using piezoelectric resonators as variable stiffness elements, and its wave-propagation properties are experimentally characterized. PMID:24734298

Bergamini, Andrea; Delpero, Tommaso; De Simoni, Luca; Di Lillo, Luigi; Ruzzene, Massimo; Ermanni, Paolo

2014-03-01

138

Tooth bleaching using three laser systems, halogen-light unit, and chemical action agents  

Science.gov (United States)

?The study describes the preclinical experience with laser-activated bleaching agent for discolored teeth. Extracted human upper central incisors were selected, and in the bleaching experiment 35% hydrogen peroxide was used. Three various laser systems and halogen-light unit for activation of the bleaching agent were applied. They were Alexandrite laser (wavelength 750 nm and 375 nm - SHG), Nd:YAG laser (wavelength 1.064 m), and Er:YAG laser (wavelength 2.94 ?m). The halogen-light unit was used in a standard regime. The enamel surface was analyzed in the scanning electron microscope. The method of chemical oxidation results in a 2-3 shade change in one treatment. The halogen-light units produced the same effect with shorter time of bleaching process (from 630 s to 300 s). The Alexandrite laser (750 nm) and bleaching agent helped to reach the desired color shade after a shorter time (400 s). Alexandrite laser (375 nm) and Nd:YAG laser had no effect on the longevity of the process of bleaching. Overheating of the chemical bleaching agent was visible after Er:YAG laser activation (195 s). Slight surface modification after bleaching process was detected in SEM.

Dostalova, Tatjana; Jelinkova, Helena; Housova, Devana; Sulc, Jan; Nemec, Michal; Koranda, Petr; Miyagi, Mitsunobu; Shi, Yi-Wei; Matsuura, Yuji

2004-09-01

139

Microstructural changes of Nimonic-263 superalloy caused by laser beam action  

International Nuclear Information System (INIS)

Pulsed laser treatments induce changes in the microstructure of materials. We have exposed the Nimonic-263 superalloy to pulsed laser beams of various repetition rates and wavelengths and investigated the changes in microstructure and microhardness. Two types of laser treatment of the material surface occurred: mechanical and thermomechanical. The microstructure changes have been comparatively analyzed by scanning electron microscopy and energo-dispersive spectrometry. The grain size was measured before and after the treatment and microhardness tests were performed. These investigations aim to contribute to the study of the level of improvement of microstructure and mechanical properties because of the interaction with laser beams.

2012-05-01

140

Homoclinic dynamics of the vibronic laser  

Energy Technology Data Exchange (ETDEWEB)

Herewith we report on the nonlinear dynamics of the vibronic laser, it means the laser, in which the laser action is possible only due to phonons of the host crystal lattice. We have described such a system using five level model, in which the number of the coherently excited lattice phonons is included as one of the dynamical variables. We have shown that at certain values of control parameters, such as pump wavelengths and pump intensities, the system follows the homoclinic trajectory in the phase space and eventually passes to the chaotic state. It keeps traveling between two or more unstable fixed points. We have investigated the evolution of the homoclinic orbits with the change of the control parameters. The theoretical predictions have been proved by us experimentally in the short-cavity alexandrite laser. We demonstrate the homoclinic character of the laser output, occurring for different pump wavelengths and pump powers. Instead there are the regions of parameters for which we usually observe the stable CW action and pulsations can hardly be achieved.

Gadomski, W.; Ratajska-Gadomska, B.; Meucci, R

2003-07-01

 
 
 
 
141

Homoclinic dynamics of the vibronic laser  

International Nuclear Information System (INIS)

Herewith we report on the nonlinear dynamics of the vibronic laser, it means the laser, in which the laser action is possible only due to phonons of the host crystal lattice. We have described such a system using five level model, in which the number of the coherently excited lattice phonons is included as one of the dynamical variables. We have shown that at certain values of control parameters, such as pump wavelengths and pump intensities, the system follows the homoclinic trajectory in the phase space and eventually passes to the chaotic state. It keeps traveling between two or more unstable fixed points. We have investigated the evolution of the homoclinic orbits with the change of the control parameters. The theoretical predictions have been proved by us experimentally in the short-cavity alexandrite laser. We demonstrate the homoclinic character of the laser output, occurring for different pump wavelengths and pump powers. Instead there are the regions of parameters for which we usually observe the stable CW action and pulsations can hardly be achieved

2003-07-01

142

Phonon Linewidths and Electron Phonon Coupling in Nanotubes  

CERN Document Server

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

143

Laser action in Rhodamine 6G doped titania-containing ormosils  

Science.gov (United States)

A new titania-containing ormosil xerogel derived from 80 mol% glycidoxypropyltrimethoxysilane (GPTMS) and 20 mol% titanum alkoxide (Ti(OBu) 4) modified by methyl methacrylate (MMA) was synthesized via the sol-gel method as dye laser host. Two kinds of matrices, one without initiator for the polymerization of MMA and another with benzoyl peroxide initiator, were prepared. Their optical properties, microstructure characteristics and surface laser damage thresholds are reported. Laser oscillation was easily achieved in all hand-polished Rhodamine 6G doped titania-containing ormosil xerogels. The effects of dye concentration and dye-matrix combination on the fluorescent emission, slope efficiency, photostability and tunable bandwidth were examined. Benzoyl peroxide is confirmed to be effective in improving the matrix density, but it is harmful to the laser behavior of Rhodamine 6G dye. A laser efficiency of 13% and photostability of 12 GJ/mol were obtained in a 2×10 -4 M Rhodamine 6G doped dye laser. A brief comparison of laser performance and matrix properties of Rhodamine 6G doped dye lasers based on the present matrix and PMMA, ormosil and sol-gel silica glass is made.

Hu, Lili; Jiang, Zhonghong

1998-03-01

144

Electron-phonon coupling and electron heat capacity of metals under conditions of strong electron-phonon nonequilibrium  

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 metals

2008-02-15

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

1980-10-01

146

Optical Investigations of Powerful Laser Actions on Massive and Flyer Targets  

International Nuclear Information System (INIS)

In this paper we present experimental, theoretical, and computer simulation studies of craters formation produced by high power lasers in single and double layer targets. The experimental investigation was carried out using the PALS (Prague Asterix Laser System) facility working with two different laser beam wavelengths: ?1 = 1.315 ?m and ?3 0.438 ?m. Two types of targets made of Al were used: single massive targets, and double targets consisting of a foil or disk (6 ?m thick for both cases) placed in front of the massive target part at a distance of 200-500 ?m. Experiments with single massive targets were performed at laser intensities in the range of 1013-1015 W/cm2 by varying the laser beam diameters on the target surface from 70 ?m up to 1200 ?m (i.e. moving the target away from the focus). The double targets were illuminated by laser energies EL = 100-500 J focused always on a diameter of 250 ?m. In all experiments performed the laser pulse duration was equal to 400 ps. 3-frame interferometry was employed to investigate the plasma dynamics through measurements of the electron density distribution time development as well as of the disks and foil fragments velocities. The dimensions and shapes of craters were obtained by crater replica technology and microscopy measurement. The experiments were complemented by a 2-D analytical theory and computer simulations, which helped at interpretation of the results. This way the values of laser energy absorption coefficient, ablation loading efficiency and efficiency of energy transfer, as well as two-dimensional shock wave generation at the laser-driven macroparticle impact were obtained from the measured crater parameters for both the wavelengths of laser radiation

2006-01-15

147

Optical investigations of powerful laser actions on massive and flyer targets  

International Nuclear Information System (INIS)

In this paper we present experimental, theoretical, and computer simulation studies of craters formation produced by high power lasers in single and double layer targets. The experimental investigation was carried out using the PALS (Prague Asterix Laser System) facility working with two different laser beam wavelengths: ?1 = 1.315 ?m and ?3 0.438 ?m. Two types of targets made of Al were used: single massive targets and double targets consisting of a foil or disk (6 ?m and 11 ?m thick for both cases) placed in front of the massive target at the distance of 200-500 ?m. Experiments with single massive targets were performed at laser intensities in the range of 1013-1015 W/cm2 by varying the laser beam diameter on the target surface from 70 ?m up to 1200 ?m (moving the target away from the focus). The double targets were illuminated by laser energies EL = 100-500 J always focused on diameter of 250 ?m. In all experiments performed the laser pulse duration was equal to 400 ps. The 3-frame interferometry was employed to investigate the plasma dynamics by means of the electron density distribution time development as well as the disks and foil fragments velocity measurements. Dimensions and shapes of craters were obtained by crater replica technology and microscopy measurement. Experimental results were complemented by two-dimensional analytical theory and computer simulations to help their interpretation. This way the values of laser energy absorption coefficient, ablation loading efficiency and efficiency of energy transfer as well as two-dimensional shock wave generation at the laser-driven macro-particle impact were obtained from measured craters' parameters for both wavelengths of laser radiation. (author)

2005-09-06

148

Phonon properties of plutonium pnictides  

International Nuclear Information System (INIS)

The phonon properties of plutonium pnictides (PuX; X= As, Sb ) have been studied by using rigid ion (RIM) and breathing shell models (BSM) which includes breathing motion of electron of the Pu-atoms due to f-d hybridization. We discuss the significance of these two approaches in predicting the phonon dispersion curves of PuX compounds and examine the role of f-electron. Dominant ionic nature of bonding has been predicted for PuX compounds from the large LO-TO phonon splitting at zone center. We also report, for the first time specific heat for these compounds. (author)

2008-12-16

149

Piezoelectric surface acoustical phonon amplification in graphene on a GaAs substrate  

Science.gov (United States)

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/RDAproperties of graphene and to the application of graphene as an acoustical phonon amplifier and a frequency-tunable acoustical phonon device.

Nunes, O. A. C.

2014-06-01

150

Generation of radicals in hard biological tissues under the action of laser radiation  

Science.gov (United States)

The formation of radicals upon UV and IR laser irradiation of some biological tissues and their components was studied by the EPR technique. The radical decay kinetics in body tissue specimens after their irradiation with UV light were described by various models. By the spin trapping technique, it was shown that radicals were not produced during IR laser irradiation of cartilaginous tissue. A change in optical absorption spectra and the dynamics of optical density of cartilaginous tissue, fish scale, and a collagen film under exposure to laser radiation in an air, oxygen, and nitrogen atmosphere was studied.

Sviridov, Alexander P.; Bagratashvili, Victor N.; Sobol, Emil N.; Omelchenko, Alexander I.; Lunina, Elena V.; Zhitnev, Yurii N.; Markaryan, Galina L.; Lunin, Valerii V.

2002-07-01

151

Photonic and phononic quasicrystals  

International Nuclear Information System (INIS)

This review focuses on the peculiarities of quasiperiodic order for the properties of photonic and phononic (sonic) heterostructures. The most beneficial feature of quasiperiodicity is that it can combine perfectly ordered structures with purely point-diffractive spectra of arbitrarily high rotational symmetry. Both are prerequisites for the construction of isotropic band gap composites, in particular from materials with low index contrast, which are required for numerous applications. Another interesting property of quasiperiodic structures is their scaling symmetry, which may be exploited to create spectral gaps in the sub-wavelength regime. This review covers structure/property relationships of heterostructures based on one-dimensional (1D) substitutional sequences such as the Fibonacci, Thue-Morse, period-doubling, Rudin-Shapiro and Cantor sequence as well as on 1D modulated structures, further on 2D tilings with 8-, 10-, 12- and 14-fold symmetry as well as on the pinwheel tiling, the Sierpinski gasket and on curvilinear tilings and, finally, on the 3D icosahedral Penrose tiling. (topical review)

2007-07-07

152

The evolution of large clusters under the action of ultrashort superintense laser pulses  

International Nuclear Information System (INIS)

The evolution of large clusters exposed to a superintense ultrashort laser pulse is considered. Cluster excitation results from the interaction of its electron subsystem with the laser field. Multiple ionization and X-ray emission followed by explosion in clusters irradiated by a laser field are investigated. The increase of the electron temperature in this process and of the charge of the cluster ion are discussed. The reabsorption of photons in such a plasma is found to be relatively small. The optimal conditions are analyzed for efficient absorption of laser radiation by large clusters. This absorption occurs on the surface of the cluster only. The review is done of the works devoted to X-ray emission and generation of high harmonics of the incident radiation from a hot cluster ion. The optical density of the cluster plasma is found to be relatively small for resonance photons of multiply charged atomic ions produced inside the cluster. Expansion and decay of the cluster during and after the laser pulse are discussed. (reviews of topical problems)

2000-09-30

153

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

Science.gov (United States)

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

154

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

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)

2006-09-01

155

Frequency tuning of PbTe injection lasers by combined action of pressure and temperature  

Energy Technology Data Exchange (ETDEWEB)

The radiation emitted from a PbTe injection laser was tuned in the wavelength range 5--9.6 ..mu.. using an independent optical high-pressure chamber and a cryostat with a consinuously flowing cooling agent. The wide-range (within 600 cm/sup -1/) pressure tuning was combined with continuous temperature tuning (within 400 cm/sup -1/). The pressure was varied from 0 to 12 kbar and the temperature from 4 to 120/sup 0/K. The system was used in a laser spectrometer.

Anzin, V.B.; Britov, A.D.; Glushkov, M.V.; Itskevich, E.S.; Kalyuzhnaya, G.A.; Kosichkin, Y.V.; Shirokov, A.M.

1977-06-01

156

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.)

1982-06-30

157

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

Science.gov (United States)

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

Yuzhakov, A. V.; Sviridov, A. P.; Shcherbakov, E. M.; Baum, O. I.; Sobol, E. N.

2014-01-01

158

Red-edge-wavelength finely-tunable laser action from new BODIPY dyes.  

Science.gov (United States)

New BODIPY dyes with two 4-formylphenyl, 4-(2,2-dimethoxycarbonylvinyl)phenyl and 4-(2,2-dicyanovinyl)phenyl groups at the 3- and 5-positions have been successfully designed and synthesized via palladium-catalyzed coupling reaction or Knoevenagel-type condensations. Structural modification of the BODIPY core via conjugation-extending residues significantly affects the spectroscopy and photophysical properties of the BODIPY fluorophore. These substituents cause the largest bathochromic shift in both absorption and emission spectra, which are shifted toward the red compared to its 4-phenylsubstituted analogue. Additionally, the fluorescence quantum yields and the Stokes shifts are also significantly higher than the corresponding phenyl-substituted dye. New BODIPY dyes have a high laser photostability, superior to that of commercial dyes with laser emission in the same spectral region, such as Perylene Red and Rhodamine 640. The substitution introduced in these derivatives allows to obtain tunable laser emission with a bandwidth of 0.15 cm(-1) and a tuning range of up to 50 nm. So with these three dyes it is possible to cover the spectral range 590-680 nm in a continuous way and with stable laser emission and small linewidth. PMID:20502810

Ortiz, M J; Garcia-Moreno, I; Agarrabeitia, A R; Duran-Sampedro, G; Costela, A; Sastre, R; López Arbeloa, F; Bañuelos Prieto, J; López Arbeloa, I

2010-07-28

159

Optical phonons and electron-phonon interaction in quantum wires  

Science.gov (United States)

A unified macroscopic continuum theory for the treatment of optical-phonon modes in quantum-wire structures is established. The theory is based on a Lagrangian formalism from which the equations of motion are rigorously derived. They consist of four coupled second-order differential equations for the vibrational amplitude and electrostatic potential. The matching boundary conditions are obtained from the fundamental equations. It is shown that no incompatibility exists between mechanical and electrostatic matching boundary conditions when a correct mathematical treatment of the problem is given. The particular case of a GaAs quantum wire buried in AlAs, where the phonons can be considered completely confined, is analyzed and the vector displacement and electron-phonon interaction potential are illustrated for several modes.

Comas, F.; Trallero-Giner, C.; Cantarero, A.

1993-03-01

160

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. = 10"9 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

1979-01-01

 
 
 
 
161

PHONONS IN RESONANT SECONDARY EMISSION OF IMPURITY MOLECULES IN CRYSTALS  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Resonant Raman scattering (RS), hot luminescence (HL) and ordinary luminescence (OL) were studied in the spectra of S2 and Se2 impurity molecules in KI at various frequencies of laser excitation and temperatures. Characteristic times of phase relaxation in the excited electronic state caused by phonon scattexing were estimated. In contradiction with the simple version of the RSE theory no resonance in the Raman scattering cross section was observed when the excitation frequency was close or i...

Rebane, L.; Rebane, K.

1981-01-01

162

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

CERN Multimedia

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

163

Phonon-induced topological insulation  

Science.gov (United States)

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

164

Phonons from neutron powder diffraction  

CERN Document Server

The spherically averaged structure function $\\soq$ obtained from pulsed neutron powder diffraction contains both elastic and inelastic scattering via an integral over energy. The Fourier transformation of $\\soq$ to real space, as is done in the pair density function (PDF) analysis, regularizes the data, i.e. it accentuates the diffuse scattering. We present a technique which enables the extraction of off--center phonon information from powder diffraction experiments by comparing the experimental PDF with theoretical calculations based on standard interatomic potentials and the crystal symmetry. This procedure (dynamics from powder diffraction(DPD)) has been successfully implemented for two systems, a simple metal, fcc Ni, and an ionic crystal, CaF$_{2}$. Although computationally intensive, this data analysis allows for a phonon based modeling of the PDF, and additionally provides off-center phonon information from powder neutron diffraction.

Dimitrov, D A; Röder, H

1998-01-01

165

Structure of the phonon vacuum state  

CERN Document Server

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

Mishev, S

2012-01-01

166

Introduction to phonons and electrons  

CERN Document Server

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

167

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

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[â??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 QDâ??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

168

Phonons in UCoGa5  

International Nuclear Information System (INIS)

We have studied phonons in UCoGa5, an isostructural compound of the heavy fermion superconductor PuCoGa5. Our neutron inelastic scattering experiment revealed very clear longitudinal and transverse acoustic phonons and low energy optical phonons along the high symmetry directions. The phonon frequencies measured at room temperature are in good agreement with ab initio calculation assuming a Coulomb repulsion U=0

2006-05-01

169

Change of vanadium pentoxide optical properties under action of CO2-laser radiation  

International Nuclear Information System (INIS)

It is experimentally shown and theoretically based from the point of view of modern representations about solid-state physics that semiconductor oxide capabilities for interaction with reducers (carbon and hydrogen) are shown during heating to such a temperature when they manifest their intrinsic conductivity, i.e. concentration of free electrons in a crystal lattice increases sharply. CO2-laser radiation exciting greatly Me-O lattice vibrations has thermochemical effect, as a result of which partial oxide dissociation takes photochemical process includes vacancy and another crystal defect formation taking place at medium temperatures of a smple, not exceeding 180 K

1987-01-01

170

Unprecedented solid-state laser action from BODIPY dyes under UV-pumping radiation  

Science.gov (United States)

Highly efficient and stable laser emission is demonstrated under drastic UV pumping conditions from recently synthesized BODIPY dye incorporated into polymer host. Under transversal pumping at 355 nm, lasing efficiencies of up to 29%, similar to those obtained in liquid phase, were obtained, with useful lifetimes (drop of the emission by 50%) of 70,000 pulses at 5 Hz repetition rate. The obtained efficiency and photostability are much higher than those obtained with usual commercial dyes emitting in the same spectral region, such as Coumarin 540A, under the same experimental conditions.

Pérez-Ojeda, M. E.; Martín, V.; Costela, A.; García-Moreno, I.; Arroyo Córdoba, I. J.; Peña-Cabrera, E.

2012-03-01

171

Effect of ion formation following resonance action of intense infrared laser radiation on polyatomic molecules  

International Nuclear Information System (INIS)

Effect of ion formation in the field of intensive infra-red laser emission in the conditions excluding gas-kinetic collisions is experimentally discovered. Gas-like BCl3 is studied. The charged particles are recorded by the conduction current. Conduction currents have been found in a wide range of pressures. The observed phynomenon has a sharply defined threshold character depending on the intensity of the laser emission. The pressure dependence of the threshold intensity is given. Characteristic times of conduction pulses in collisionless conditions bear evidence of the fact that formed charged particles are ions. High concentration of ions indicates high effectivity of the process of the collisionless resonance infra-red photoionization of multiatomic molecules. This process has low thresholds ( 2) and proceeds effectively at intensities (approximately 50 MW/cm2)which are essentially less than in the case of non-resonance photoionization. At high pressures (from 1 mm Hg and higher) the conductivity of the BCl3 gas observed on irradiation is due to radiative-collisional processes and is characterized by low thresholds of origin. The processes of radiative-collisional infra-red photoionization are followed by visible luminescence

1976-01-11

172

Heating of two-dimensional electron gas and LO-phonons in delta-doped GaAs by far-infrared radiation  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A change in the conductivity of the two-dimensional electron gas in ?-doped GaAs samples due to pulsed far-infrared laser irradiation has been detected. It is shown that the observed positive photoconductivity is caused by heating of 2D electrons. The energy loss of hot electrons is accomplished by scattering with nonequilibrium longitudinal optical (LO) phonons. An expression for the effective emission frequency of LO phonons coupled with electrons and the thermal bath of acoustic phonons i...

1996-01-01

173

Phononic Frequency Combs through Nonlinear Resonances  

Science.gov (United States)

We explore an analogue of optical frequency combs in driven nonlinear phononic systems, and present a mechanism for generating phononic frequency combs through nonlinear resonances. In the underlying process, a set of phonon modes is simultaneously excited by the external driving which yields frequency combs with an array of discrete and equidistant spectral lines of each nonlinearly excited phonon mode. Frequency combs through nonlinear resonance of different orders are investigated, and in particular the possibility of correlation tailoring in higher-order cases is revealed. We suggest that our results can be applied in various nonlinear acoustic processes, such as phonon harvesting, and can also be generalized to other nonlinear systems.

Cao, L. S.; Qi, D. X.; Peng, R. W.; Wang, Mu; Schmelcher, P.

2014-02-01

174

Topological Nature of the Phonon Hall Effect  

CERN Document Server

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

Zhang, Lifa; Wang, Jian-Sheng; Li, Baowen; 10.1103/PhysRevLett.105.225901

2011-01-01

175

Sound and heat revolutions in phononics  

Science.gov (United States)

The phonon is the physical particle representing mechanical vibration and is responsible for the transmission of everyday sound and heat. Understanding and controlling the phononic properties of materials provides opportunities to thermally insulate buildings, reduce environmental noise, transform waste heat into electricity and develop earthquake protection. Here I review recent progress and the development of new ideas and devices that make use of phononic properties to control both sound and heat. Advances in sonic and thermal diodes, optomechanical crystals, acoustic and thermal cloaking, hypersonic phononic crystals, thermoelectrics, and thermocrystals herald the next technological revolution in phononics.

Maldovan, Martin

2013-11-01

176

Sound and heat revolutions in phononics.  

Science.gov (United States)

The phonon is the physical particle representing mechanical vibration and is responsible for the transmission of everyday sound and heat. Understanding and controlling the phononic properties of materials provides opportunities to thermally insulate buildings, reduce environmental noise, transform waste heat into electricity and develop earthquake protection. Here I review recent progress and the development of new ideas and devices that make use of phononic properties to control both sound and heat. Advances in sonic and thermal diodes, optomechanical crystals, acoustic and thermal cloaking, hypersonic phononic crystals, thermoelectrics, and thermocrystals herald the next technological revolution in phononics. PMID:24226887

Maldovan, Martin

2013-11-14

177

Polar phonons in SO 2 single crystal  

Science.gov (United States)

The Raman spectrum of a single SO 2 crystal in various polarization geometries has been measured at 20 K and discussed in terms of LO and TO components of polar crystal modes. Lattice phonons have been assigned on the basis of their behaviour with polarization. Lattice dynamical calculations on both the internal and lattice phonons are in good agreement with experimental data. Using gas-phase transition dipole moments and a dipole—dipole intermolecular potential the angular dispersion of fundamental vibrons has been calculated. For lattice phonons, a combination of atom—atom and electrostatic potential reproduces not only the phonon frequencies but, for polar phonons, also their LO—TO splitting.

Tafi, A.; Procacci, P.; Castellucci, E.; Salvi, P. R.

1991-03-01

178

A study of non-equilibrium phonons in GaAs/AlAs quantum wells  

Energy Technology Data Exchange (ETDEWEB)

In this thesis we have studied the non-equilibrium phonons in GaAs/AlAs quantum wells via Raman scattering. We have demonstrated experimentally that by taking into account the time-reversal symmetry relation between the Stokes and anti-Stokes Raman cross sections, one can successfully measure the non-equilibrium phonon occupancy in quantum wells. Using this technique, we have studied the subject of resonant intersubband scattering of optical phonons. We find that interface roughness plays an important role in resonant Raman scattering in quantum wells. The lateral size of the smooth regions in such interface is estimated to be of the order of 100 {Angstrom}. Through a study of photoluminescence of GaAs/AlAs quantum wells under high intensity laser excitation, we have found that band nonparabolicity has very little effect on the electron subband energies even for subbands as high as a few hundred meV above the lowest one. This finding may require additional theoretical study to understand its origin. We have also studied phonon confinement and propagation in quantum wells. We show that Raman scattering of non-equilibrium phonons in quantum wells can be a sensitive measure of the spatial extent of the longitudinal optical (LO) phonons. We deduce the coherence length of LO phonons in GaAs/Al{sub x}Ga{sub 1-x}As quantum wells as a function of the Al concentration x.

Su, Zhenpeng

1996-11-01

179

Lasers  

Energy Technology Data Exchange (ETDEWEB)

Rapid advances in laser technology have created an abundance of new product offerings. This reference allows one to make product evaluations of a wide range of laser equipment. Product descriptions and specifications from over 100 manufacturers are organized into eight convenient sections covering laser components, laser accessories, helium/neon lasers, CO/sub 2/ lasers, Nd:Yag, general purpose laser workstations, special lasers, and applications.

1986-01-01

180

Quasiparticle-phonon nuclear model  

International Nuclear Information System (INIS)

Basic assumption of the quasiparticle-phonon nuclear model (QPNM) and its two applications are presened. The introduction of tensor forces in the QPNM is described and the results of studying the fragmentation of charge-exchange resonances in spherical nuclei are given. The low-lying Ksup(?)=0sup(+), 2+, 3+ and 4+ states in doubly even deformed nuclei are described. The results calculated in the QPNM are compared with those obtained in the interacting boson model

1985-01-01

 
 
 
 
181

Phonon anomalies and dynamic stripes  

Science.gov (United States)

Stripe order where electrons self-organize into alternating periodic charge-rich and magnetically-ordered charge-poor parallel lines was proposed as a way of optimizing the kinetic energy of holes in a doped Mott insulator. Static stripes detected as extra peaks in diffraction patterns, appear in a number of oxide perovskites as well as some other systems. The more controversial dynamic stripes, which are not detectable by diffraction, may be universally present in copper oxide superconductors. Thus it is important to learn how to detect dynamic stripes as well as to understand their influence on electronic properties. This review article focuses on lattice vibrations (phonons) that might show signatures of the charge component of dynamic stripes. The first part of the article describes recent progress in learning about how the phonon signatures of different types of electronic charge fluctuations including stripes can be distinguished from purely structural instabilities and from each other. Then I will focus on the evidence for dynamic stripes in the phonon spectra of copper oxide superconductors.

Reznik, D.

2012-11-01

182

Heralded single-phonon preparation, storage, and readout in cavity optomechanics.  

Science.gov (United States)

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. PMID:24765960

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

2014-04-11

183

Phononic Frequency Combs via Nonlinear Resonances  

CERN Document Server

We study the analogue of optical frequency combs in driven nonlinear phononic systems, and present a new generation mechanism for phononic frequency combs via nonlinear resonances. The nonlinear resonance refers to the simultaneous excitation of a set of phonon modes by the external driving, and thereby generated frequency combs are characterized by an array of equidistant spectral lines in the spectrum of each nonlinearly excited phonon mode. Frequency combs via nonlinear resonance of different orders are investigated, and particularly we reveal the possibility for correlation tailoring in higher order cases. The investigation contributes to potential applications in various nonlinear acoustic processes, such as harvesting phonons and generating phonon entanglements, and can also be generalized to other nonlinear systems.

Cao, Lushuai; Peng, Ruwen; Wang, Mu; Schmelcher, Peter

2013-01-01

184

Towards Microscopic Understanding of the Phonon Bottleneck  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The problem of the phonon bottleneck in the relaxation of two-level systems (spins) to a narrow group of resonant phonons via emission-absorption processes is investigated from the first principles. It is shown that the kinetic approach based on the Pauli master equation is invalid because of the narrow distribution of the phonons exchanging their energy with the spins. This results in a long-memory effect that can be best taken into account by introducing an additional dyna...

Garanin, D. A.

2006-01-01

185

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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, A.; Serrano, J.; Bosak, A.; Lazzeri, M.; Molodtsov, S. L.; Wirtz, L.; Attaccalite, C.; Krisch, M.; Rubio, A.; Mauri, F.; Pichler, T.

2009-01-01

186

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

The two-dimensional mapping of the phonon dispersions around the K point of graphite by inelastic x-ray scattering is provided. The present work resolves the longstanding issue related to the correct assignment of transverse and longitudinal phonon branches at K. We observe an almost degeneracy of the three TO-, LA-, and LO-derived phonon branches and a strong phonon trigonal warping. Correlation effects renormalize the Kohn anomaly of the TO mode, which exhibits a trigonal warping effect opp...

Grueneis, A.; Serrano, J.; Bosak, A.; Lazzeri, M.; Molodtsov, S. L.; Wirtz, Ludger; Attaccalite, C.; Krisch, M.; Rubio, A.; Mauri, F.; Pichler, T.

2009-01-01

187

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].

Jauho, Antti-Pekka

1999-01-01

188

Ultrafast electron-phonon decoupling in graphite  

Science.gov (United States)

We report the ultrafast dynamics of the 47.4THz coherent phonons of graphite interacting with a photoinduced nonequilibrium electron-hole plasma. Unlike conventional materials, upon photoexcitation the phonon frequency of graphite upshifts, and within a few picoseconds relaxes to the stationary value. Our first-principles density functional calculations demonstrate that the phonon stiffening stems from the light-induced decoupling of the nonadiabatic electron-phonon interaction by creating a nonequilibrium electron-hole plasma. Time-resolved vibrational spectroscopy provides a window on the ultrafast nonquilibrium electron dynamics.

Ishioka, Kunie; Hase, Muneaki; Kitajima, Masahiro; Wirtz, Ludger; Rubio, Angel; Petek, Hrvoje

2008-03-01

189

Phonon engineering in nanoscale layered structures  

Science.gov (United States)

Thermal conductivity in GaN/AlGaN heterostructures is investigated by solving the steady-state phonon Boltzman equation in the relaxation-time approximation using phonon density of state, average group velocity and phonon relaxation time. In this paper dispersion curves, group velocity, density of states of energy, relaxation time of phonon and finally thermal conduction of several types of symmetric and asymmetric nanostructures are simulated. It has been concluded that proper selection of layer widths yields minimum thermal conduction in the considered structure. Also, making the structure asymmetric, affects the thermal conduction.

Rostami, A.; Alizade, A.; Bagban, H.; Alizade, T.; Balazadeh Bahar, H.

2010-12-01

190

Tailoring electron–phonon interaction in nanostructures  

Science.gov (United States)

Efficient design of optoelectronic devices based on electron intersubband transitions depends critically on the knowledge of the intersubband relaxation times which in turn, depends on electron scattering with LO and acoustic phonons. In this article the intersubband scattering time associated with electron–acoustic-phonon interaction has been discussed in terms of phonon mode quantization and phonon confinement with describing the acoustic phonon dispersion relation in detail by introducing the cut-off frequency for each mode. It has been shown that the quantization of acoustic phonon modes lead to an enhancement in electron–phonon scattering time in AlGaAs quantum well structures. Based on the presented model, a new tailoring method has presented to adjust the electron–phonon scattering time in intersubband-transition-based structures while keeping the electronic properties unaltered. Also, we illustrated that for a quantum well with subband energy separation of ˜30 meV, the intersubband scattering time with acoustic-phonon-assisted transitions could be tailored from ˜120 ps to increased value of ˜400 ps or reduced value of ˜45 ps by inserting a 1 nm-thickacoustically soft or hard layers, respectively, while keeping the same the initial energy separation.

Alizadeh, A.; Rostami, A.; Baghban, H.; Bahar, H. B.

2014-04-01

191

From color centers to coherent phonon states  

International Nuclear Information System (INIS)

The author traces the progression of scientific steps which start with color centers in alkali halides and ends with his current research on the coherent generation and dephasing of vibrations in solids. Among the observed phenomena are crystal field splitting of atomic states in ionic materials; localized and extended phonon states in alkaline-earth halides, and other insulators; spectral, spatial and temporally resolved phonon transport in various materials, the generation of coherent phonon and polariton states in semiconductors, and the dephasing of the coherent states and the observations of a long sought after long-lived phonon state. (author)

1994-01-01

192

Polaronic signatures in phonon isotopic shifts  

International Nuclear Information System (INIS)

The effect of O(16) by O(18) isotopic substitution in the excitation spectrum of a model electron-phonon Hamiltonian, previously used to describe the dynamics of the O(4)-Cu(1)-O(4) cluster in YBa2Cu3O7, is presented. This model includes electronic correlations and electron-phonon interactions, exhibiting the presence of polaron tunneling. The calculated isotopic shifts of phonon excitations differ from those found using harmonic or anharmonic potentials, and are consistent results of optical measurements of c-axis phonons. The isotopic substitution changes the dynamics of polaron tunneling and produces a change in the local structure

1998-06-02

193

Polaronic Signatures in Phonon Isotopic Shifts  

International Nuclear Information System (INIS)

The effect of O(16) by O(18) isotopic substitution in the excitation spectrum of a model electron-phonon Hamiltonian, previously used to describe the dynamics of the O(4)-Cu(1)-O(4) cluster in YBa2Cu3O7, is presented. This model includes electronic correlations and electron-phonon interactions, exhibiting the presence of polaron tunneling. The calculated isotopic shifts of phonon excitations differ from those found using harmonic or anharmonic potentials, and are consistent results of optical measurements of c-axis phonons. The isotopic substitution changes the dynamics of polaron tunneling and produces a change in the local structure

1998-06-01

194

The phonons of Nb3Sn  

International Nuclear Information System (INIS)

Calculations of the phonon dispersion curves and the electron-phonon coupling in Nb3Sn are presented, using the non-orthogonal tight-binding method without any adjustable parameter in the theory. The calculations are based on realistic energy bands. The results are in good agreement with the available experimental data. Various anomalous features in the phonon dispersion curves are predicted, especially along the ? direction of the Brillouin zone. The importance of the chain structure for the large electron-phonon coupling is stressed. (orig.)

1982-06-30

195

Design and operation of a microfabricated phonon spectrometer utilizing superconducting tunnel junctions as phonon transducers  

International Nuclear Information System (INIS)

In order to fully understand nanoscale heat transport it is necessary to spectrally characterize phonon transmission in nanostructures. Toward this goal we have developed a microfabricated phonon spectrometer. We utilize microfabricated superconducting tunnel junction (STJ)-based phonon transducers for the emission and detection of tunable, non-thermal and spectrally resolved acoustic phonons, with frequencies ranging from ?100 to ?870 GHz, in silicon microstructures. We show that phonon spectroscopy with STJs offers a spectral resolution of ?15–20 GHz, which is ?20 times better than thermal conductance measurements, for probing nanoscale phonon transport. The STJs are Al–AlxOy–Al tunnel junctions and phonon emission and detection occurs via quasiparticle excitation and decay transitions that occur in the superconducting films. We elaborate on the design geometry and constraints of the spectrometer, the fabrication techniques and the low-noise instrumentation that are essential for successful application of this technique for nanoscale phonon studies. We discuss the spectral distribution of phonons emitted by an STJ emitter and the efficiency of their detection by an STJ detector. We demonstrate that the phonons propagate ballistically through a silicon microstructure, and that submicron spatial resolution is realizable in a design such as ours. Spectrally resolved measurements of phonon transport in nanoscale structures and nanomaterials will further the engineering and exploitation of phonons, and thus have important ramifications for nanoscale thermal transport as well as the burgeoning field of nanophononics. (paper)

2013-04-01

196

Design and operation of a microfabricated phonon spectrometer utilizing superconducting tunnel junctions as phonon transducers  

Science.gov (United States)

In order to fully understand nanoscale heat transport it is necessary to spectrally characterize phonon transmission in nanostructures. Toward this goal we have developed a microfabricated phonon spectrometer. We utilize microfabricated superconducting tunnel junction (STJ)-based phonon transducers for the emission and detection of tunable, non-thermal and spectrally resolved acoustic phonons, with frequencies ranging from ˜100 to ˜870 GHz, in silicon microstructures. We show that phonon spectroscopy with STJs offers a spectral resolution of ˜15-20 GHz, which is ˜20 times better than thermal conductance measurements, for probing nanoscale phonon transport. The STJs are Al-AlxOy-Al tunnel junctions and phonon emission and detection occurs via quasiparticle excitation and decay transitions that occur in the superconducting films. We elaborate on the design geometry and constraints of the spectrometer, the fabrication techniques and the low-noise instrumentation that are essential for successful application of this technique for nanoscale phonon studies. We discuss the spectral distribution of phonons emitted by an STJ emitter and the efficiency of their detection by an STJ detector. We demonstrate that the phonons propagate ballistically through a silicon microstructure, and that submicron spatial resolution is realizable in a design such as ours. Spectrally resolved measurements of phonon transport in nanoscale structures and nanomaterials will further the engineering and exploitation of phonons, and thus have important ramifications for nanoscale thermal transport as well as the burgeoning field of nanophononics.

Otelaja, O. O.; Hertzberg, J. B.; Aksit, M.; Robinson, R. D.

2013-04-01

197

Laser phase noise effects on the dynamics of optomechanical resonators  

International Nuclear Information System (INIS)

We investigate theoretically the influence of laser phase noise on the cooling and heating of a generic cavity optomechanical system. We derive the back-action damping and heating rates and the mechanical frequency shift of the radiation-pressure-driven oscillating mirror, and derive the minimum phonon occupation number for small laser linewidths. We find that, in practice, laser phase noise does not pose serious limitations to ground-state cooling. Additionally, we explore the regime of parametric amplification where coherent oscillations of the mirror are realizable. It is found that heating from laser phase noise is of significance and can cause the onset of instabilities. We then consider the effects of laser phase noise in a parametric cavity driving scheme that minimizes the back-action heating of one of the quadratures of the mechanical oscillator motion. Laser linewidths, narrow compared to the decay rate of the cavity field, do not pose any significant problems in an experimental setting, but broader linewidths limit the practicality of this back-action evasion method.

2011-06-01

198

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

CERN Document Server

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

Englund, Dirk; Vuckovic, Jelena

2008-01-01

199

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

Directory of Open Access Journals (Sweden)

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

Yanagi K.

2013-03-01

200

The effect of Landau-Zener dynamics on phonon lasing  

Science.gov (United States)

Optomechanical systems couple light to the motion of nanomechanical objects. Intriguing new effects are observed in recent experiments that involve the dynamics of more than one optical mode. There, mechanical motion can stimulate strongly driven multi-mode photon dynamics that acts back on the mechanics via radiation forces. We show that even for two optical modes Landau-Zener-Stueckelberg oscillations of the light field drastically change the nonlinear attractor diagram of the resulting phonon lasing oscillations. Our findings illustrate the generic effects of Landau-Zener physics on back-action induced self-oscillations.

Wu, Huaizhi; Heinrich, Georg; Marquardt, Florian

2013-12-01

 
 
 
 
201

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

202

Double-? phonon excitation in the Os nuclei  

International Nuclear Information System (INIS)

We investigate double-? phonon excitation in the Os nuclei within the framework of the proton-neutron Interacting Boson Model (IBM-2). We decompose the IBM-2 wave-functions into multiphonon states, and see the contributions of zero, one and two phonon components in the low lying levels of the Os nuclei. (orig.)

1993-05-31

203

Double-? phonon excitation in the Os nuclei  

Science.gov (United States)

We investigate double-? phonon excitation in the Os nuclei within the framework of the proton-neutron Interacting Boson Model (IBM-2). We decompose the IBM-2 wave-functions into multiphonon states, and see the contributions of zero, one and two phonon components in the low lying levels of the Os nuclei.

Sugita, M.; Otsuka, T.

1993-05-01

204

EFFECT OF PHONONS ON THE SPIN SUSCEPTIBILITY  

Digital Repository Infrastructure Vision for European Research (DRIVER)

That phonons do not affect the Pauli spin susceptibility seems to be a standard, well-accepted result. Since the recent suggestion by Enz and Matthias that phonons might play a decisive role in the ferromagnetism of ZrZn2, this question has been "reopened". We review both the old and new work on this problem and try to clarify the present situation.

Fay, D.; Appel, J.

1981-01-01

205

Phonon spectrum and electron-phonon coupling in zigzag graphene nanoribbons  

Science.gov (United States)

In this paper, we report a first-principles study of the lattice dynamics of small graphene nanoribbon with zigzag edges. Our investigation is based on spin polarized density functional calculations (DFT). Nesting properties in the electronic band structure are very different for nanoribbons with unpolarized, ferromagnetic, and antiferromagnetic configurations. As a result, the phonon spectrum and nesting related softening in phonon frequencies differ in these cases. The unpolarized and ferromagnetic structures show nesting related phonon softening and considerable electron phonon linewidth, while for the antiferromagnetic structure, a band gap at the Fermi energy eliminates these effects. Saturating the nanoribbon edge with hydrogen has negligible effect on the phonon spectra for the magnetic structures while for the unpolarized configuration all structures without hydrogen are unstable due to soft phonon modes. The electron-phonon coupling coefficients have also been calculated and implications for Peierls transition and superconductivity are discussed.

Zhang, Ting; Heid, Rolf; Bohnen, Klaus-Peter; Sheng, Ping; Chan, C. T.

2014-05-01

206

Phonon Drag Dislocations at High Pressures  

Energy Technology Data Exchange (ETDEWEB)

Phonon drag on dislocations is the dominant process which determines the flow stress of metals at elevated temperatures and at very high plastic deformation rates. The dependence of the phonon drag on pressure or density is derived using a Mie-Grueneisen equation of state. The phonon drag is shown to increase nearly linearly with temperature but to decrease with density or pressure. Numerical results are presented for its variation for shock-loaded copper and aluminum. In these cases, density and temperature increase simultaneously, resulting in a more modest net increase in the dislocation drag coefficient. Nevertheless, phonon drag increases by more than an order of magnitude during shock deformations which approach melting. Since the dependencies of elastic moduli and of the phonon drag coefficient on pressure and temperature are fundamentally different, the effect of pressure on the constitutive law for plastic deformation can not simply be accounted for by its effect on the elastic shear modulus.

Wolfer, W.G.

1999-10-19

207

Phonon dynamics of plutonium chalcogenides and pnictides  

Energy Technology Data Exchange (ETDEWEB)

We have investigated the phonon dynamics of the plutonium compounds (PuX; X = S, Se, Te, As, and Sb) by using rigid ion (RIM) and breathing shell models (BSM), later includes breathing motion of the electrons of the Pu-atoms due to f-d hybridization. We discuss the significance of these two approaches in predicting the phonon dispersion curves of PuX compounds and examine the role of electron-phonon interactions. Dominant ionic nature of bonding has been predicted for PuX compounds from the large LO-TO phonon splitting at zone center. We also report the one phonon density of states and first time calculated the lattice specific heat for these compounds.

Arya, Balwant S., E-mail: bsarya13@yahoo.co [Department of Physics, Govt. Narmada College, Hoshangabad 461001 (India); Department of Physics, University of Bhopal, Bhopal 462026 (India); Aynyas, Mahendra [Department of Physics, S.V. College, Bhopal 462030 (India); Sanyal, S.P. [Department of Physics, University of Bhopal, Bhopal 462026 (India)

2009-09-15

208

Detection of Random Laser Action from Silica Xerogel Matrices Containing Rhodamine 610 Dye and Titanium Dioxide Nanoparticles  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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...

2012-01-01

209

Phonon line emission revealed by self-assembly of colloidal nanoplatelets.  

Science.gov (United States)

We show that colloidal nanoplatelets can self-assemble to form a 1D superlattice. When self-assembled, an additional emission line appears in the photoluminescence spectrum at low temperatures. This emission line is a collective effect, greatly enhanced when the NPLs are self-assembled. It is attributed to the longitudinal optical (LO) phonon replica of the band-edge exciton, and its presence in self-assembled nanoplatelets is explained using a model based on an efficient photons reabsorption between neighboring nanoplatelets. The presence of phonon replica at low temperatures in ensemble measurements suggests the possibility to design a laser, based on self-assembled nanoplatelets. PMID:23458277

Tessier, Mickaël D; Biadala, Louis; Bouet, Cécile; Ithurria, Sandrine; Abecassis, Benjamin; Dubertret, Benoit

2013-04-23

210

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.

Souza, Fabrício M.; Egues, J. Carlos.

211

Far-infrared laser action in vinyl chloride, vinyl bromide, and vinyl fluoride optically pumped by a CW N2O laser  

Science.gov (United States)

This paper reports the first use of a N2O laser for optically pumping vinyl halides, to obtain new cw submillimeter laser lines. Eighteen far-infrared (FIR) emissions have been observed in vinyl chloride, twenty five in vinyl bromide and thirty eight in vinyl flouride.

Gastaud, C.; Redon, M.; Belland, P.; Fourrier, M.

1984-06-01

212

Optical properties and surface structure comparison of tooth whitening using four laser systems and chemical action agents  

Science.gov (United States)

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

213

Lasers  

Energy Technology Data Exchange (ETDEWEB)

This book contains the following chapters: 1. An Introduction to Lasers; 2. Atomic Transitions: The Classical Electron Oscillator Model; 3. Electric Dipole Transitions in Real Atoms; 4. Atomic Rate Equations; 5. Large Signal Atomic Responses: The Rabi Frequency; 6. Laser Pumping and Population Inversion; 7. Laser Amplification; 8. More on Laser Amplification; 9. Linear Optical Pulse Propagation; 10. Nonlinear Optical Pulse Propagation; 11. Laser Mirrors, Cavities and Regenerative Feedback; 12. Fundamentals of Laser Oscillation; 13. More on Laser Oscillation; 14. Optical Beams and Resonators: An Introduction; 15. Ray Optics and Ray Matrices; 16. Wave Optics and Gaussian Beams; 17. Physical Properties of Gaussian Beams; 18. Beam Perturbation and Diffraction Effects; 19. Stable Two-Mirror Gaussian Resonators; 20. Complex Paraxial Wave Optics; 21. Generalized Paraxial Resonator Theory; 22. Unstable Optical Resonators; 23. More on Unstable Resonators; 24. Laser Dynamics: The Laser Cavity Equations; 25. Laser Spiking, Modulation, and Mode Competition; 26. Laser Q-Switching; 27. Active Laser Mode Coupling and Mode Locking; 28. Passive Locking; 29. Laser Interjection Locking; 30. Hole Burning and Saturation Spectroscopy; 31. Magnetic Dipole Transitions; Appendix A - Thermal Radiation Sources.

Siegmann, A.E.

1986-01-01

214

Lasers  

Energy Technology Data Exchange (ETDEWEB)

This book explains the operating principles and applications of lasers, including central background material. It incorporates many intuitive explanations and practical examples. Introduces basic principles, including the necessary classical and quantum physics, and provides discussions of specific lasers, laser resonators, and applications, including nonlinear optics.

Eberly, J.H.; Milonni, P.W.

1988-01-01

215

Cooperative two-phonon phenomena in superconductivity  

Energy Technology Data Exchange (ETDEWEB)

The problem of the two-photon coherent generation of entanglement photon pairs in quantum optics has been intensively studied over the passing years. It is important to note that the two-quanta cooperative effects also play a main role in other fields of physics. One example is superconductivity, where the Cooper pairs are created due to the simultaneous two-phonon exchange between electrons. It occurs when the one-phonon exchange integral between the band electrons is smaller than that of the two-phonon exchange. This is possible in many-band superconducting materials, in which the two-phonon exchange integral arises through the virtual bands of the material. Some estimates of the two-phonon superconductivity have already been given. A more realistic model which takes into account the specificities of the many-band aspects of superconductor materials will be proposed. In two-phonon processes, a more complicated temperature dependence on the order parameter is expected. A rigorous study of this anomalous temperature dependence on the order parameter of superconductors is presented. One expects that the two-phonon exchange effects can amplify the superconductivity in a way similar to the way the thermal field amplifies the two-photon super-radiance in a microcavity.

Enaki, N A [Institute of Applied Physics, Academy of Sciences of Moldova, Academiei str. 5, Chisinau (Moldova, Republic of); Eremeev, V V [Institute of Applied Physics, Academy of Sciences of Moldova, Academiei str. 5, Chisinau (Moldova, Republic of)

2002-10-01

216

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

International Nuclear Information System (INIS)

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

1996-10-07

217

Electron and phonon coupling dynamics in low-gap semiconductor: quantum versus classical scale.  

Science.gov (United States)

We have studied the characteristics of longitudinal-optical-phonon-plasmon coupled (LOPC) mode by using the ultrashort pulsed laser with 45 THz bandwidth as a function of thickness in InAs epilayers, ranging from 10 to 900 nm. We have observed the LOPC modes split into the upper (L(+) mode) and the lower (L(-) mode) branches only in the classical scale, but the longitudinal-optical (LO) phonon peak was persistently observed. The shorter decay time of the plasmon-like L(+) modes rather than the phonon-like L(-) modes should be associated with carrier-carrier scattering which is further considered with diffusion properties in the low-gap semiconductors. This result leads to that the absence of the LOPC modes in a scale less than exciton Bohr radius manifests the role of electron diffusion rather than the carrier screening via drift motion in surface depletion region. PMID:24757998

Min, Kyung-Gu; Yee, Ki-Ju; Stanton, Christopher J; Song, Jin-Dong; Jho, Young-Dahl

2014-07-01

218

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

219

Positron scattering by phonons in a metal  

International Nuclear Information System (INIS)

In the paper one estimated parameters of positron scattering by phonons on the basis of available theoretical models for positron-phonon interaction and of the experimental data on positron energy in a metal. One studied the processes governing positron interaction with a substance. For scattering by phonons dominating at energy values in the neighbourhood of 1 eV one derived formulae for braking ability, length of free run. For tungsten one estimated braking ability, length of free run and run total length for 0,025-10 eV positron energy values

2000-07-01

220

Temperature dependent phonon confinement in silicon nanostructures  

International Nuclear Information System (INIS)

Temperature dependent variation in Raman line-shape from silicon (Si) nanostructures (NSs) is studied here. Asymmetry and red-shift in room temperature Raman spectrum is attributed to phonon confinement effect. Raman spectra recorded at higher temperatures show increase in FWHM and decrease in asymmetry ratio with respect to its room temperature counterpart. Theoretical Raman line-shape analyses of temperature dependence of phonon confinement is done by incorporating the temperature dependence of phonon dispersion relation. Experimental and theoretical temperature dependent Raman spectra are in good agreement

2008-12-22

 
 
 
 
221

The Phonon Drag Effect in Single-Walled Carbon Nanotubes  

CERN Document Server

A variational solution of the coupled electron-phonon Boltzmann equations is used to calculate the phonon drag contribution to the thermopower in a 1-D system. A simple formula is derived for the temperature dependence of the phonon drag in metallic, single-walled carbon nanotubes. Scattering between different electronic bands yields nonzero values for the phonon drag as the Fermi level varies.

Scarola, V W

2002-01-01

222

Phonon Spectrum of SrFe2As2 determined by multizone phonon refinement  

Energy Technology Data Exchange (ETDEWEB)

The ferropnictidesuperconductors exhibit a sensitive interplay between the lattice and magnetic degrees of freedom, including a number of phonon modes that are much softer than predicted by nonmagnetic calculations using density functional theory (DFT). However, it is not known what effect, if any, the long-range magnetic order has on phonon frequencies above 23 meV, where several phonon branches are very closely spaced in energy and it is challenging to isolate them from each other. We measured these phonons using inelastic time-of-flight neutron scattering in 40 Brillouin zones, and developed a technique to determine their frequencies. We find this method capable of determining phonon energies to 0.1 meV accuracy, and that the DFT calculations using the experimental structure yield qualitatively correct energies and eigenvectors. We do not find any effect of the magnetic transition on these phonons.

Parshall, D [University of Tennessee, Knoxville (UTK); Heid, R [Kernforschungszentrum Karlsruhe, Germany; Niedziela, Jennifer L [ORNL; Wolf, Th. [Kernforschungszentrum Karlsruhe, Germany; Stone, Matthew B [ORNL; Abernathy, Douglas L [ORNL; Reznik, Dmitry [University of Colorado, Boulder

2014-01-01

223

Electron and phonon thermal waves in semiconductors: the effect of carrier diffusion and recombination on the photoacoustic signal  

Energy Technology Data Exchange (ETDEWEB)

The electron and phonon temperature distributions are calculated in bipolar semiconductors by taking into account generation and heating of carriers on the surface due to the incident modulated laser beam as well as the finite carrier diffusion and recombination in the solid. We solve the coupled one-dimensional heat and carrier diffusion equations in the linear approximation using appropriate boundary conditions according to the photoacoustic experimental conditions. In addition, special emphasis is laid on the dependence of the electron system heat flux on the electron and phonon temperature. We also consider the influence of both temperatures on the recombination of the electron-hole pairs. The dependence of the amplitude of the electron and phonon temperatures on the modulation frequency are analyzed for different values of characteristic parameters of the problem: electron-phonon energy exchange and carrier thermal generation rate.

Villegas-Lelovsky, L.; Gonzalez de la Cruz, G.; Gurevich, Yu.G

2003-06-02

224

Energy resolved phonon scattering in thin film amorphous solids  

International Nuclear Information System (INIS)

Energy resolved phonon scattering measurements were performed using a novel heat pulse technique. Two thin film phonon generators were deposited on one face of a sapphire crystal substrate and two phonon detectors were deposited on the opposite face, under one of which a thin film amorphous material was deposited. The phonon detectors were superconducting tunnel heterojunctions. A comparison of the number of phonons detected at each junction gave information on the fraction of phonons transmitted through the amorphous film as a function of energy from which the phonon mean free path as a function of energy could be deduced. Materials investigated were silicon monoxide and germanium. (author)

1980-01-01

225

Effects of phonon-phonon coupling on properties of pygmy resonance in $^{124-132}$Sn  

CERN Document Server

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

Arsenyev, N N; Voronov, V V; Van Giai, Nguyen

2012-01-01

226

The optical phonon distribution function in a quntum well  

Science.gov (United States)

We have used Monte Carlo technique to solve coupled nonlinear kinetic equations for electrons and optical phonons in a double barrier heterostructure to study the electron transport and the optical phonon distribution function. Nonequilibrium optical phonons do not escape from nanostructures, due to confinement. Their decay on two short wavelength acoustic phonons is the only mechanism which control their concentration. The average time of optical phonon emission by electrons (0.15 ps) is approximately fifty times shorter than the average time of optical phonon decay into acoustic phonons (7 - 8 ps for GaAs). We have investigated the electron transport and the optical phonon distribution function in a wide range of the lattice temperatures and the applied electric fields. We have obtained that when the optical phonon accumulation is significant, it is accompanied by the narrowing of the optical phonon distribution and substantially affect the electron transport.

Mitin, V. V.; Paulavicius, G.; Bannov, N. A.

1996-03-01

227

Room temperature laser action and Q-switching of F-aggregate color centers in LiF  

International Nuclear Information System (INIS)

The authors have verified room temperature operation of F/sub 2/ and F/sub 2//sup +/ color center lasers in LiF heavily irradiated with gamma rays. The F/sub 2//sup -/ centers in their samples exhibit exceptional stability and can be used as solid state passive Q-switches for Nd:YAG lasers. The authors have presented a preliminary picture which helps to explain the origin of unusual behavior in the F/sub 2/ and F/sub 2//sup +/ lasers. Larger doses of gamma radiation, antireflection coatings, and a longitudinal pumping geometry should provide higher efficiencies for the remarkably simple, tunable F/sub 2//sup +/ solid state laser

1985-01-01

228

Inclusion of neutron-proton phonons into the quasiparticle-phonon nuclear model  

International Nuclear Information System (INIS)

The problem of inclusion of neutron-proton phonon operators into the quasiparticle-phonon nuclear model is considered. The model Hamiltonian is transformed allowing for the solutions of secular equations for the one-phonon states. The system of basic equations is derived in the general form, and the transition to the system of approximate equations is realized. They are used to describe the fragmentation of neutron-proton phonons and thereby to calculate the charge-exchange giant resonance in spherical nuclei

1983-01-01

229

Phonon-Drag Thermopower at High Temperatures  

CERN Document Server

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

230

Pressure-enabled phonon engineering in metals.  

Science.gov (United States)

We present a combined first-principles and experimental study of the electrical resistivity in aluminum and copper samples under pressures up to 2 GPa. The calculations are based on first-principles density functional perturbation theory, whereas the experimental setup uses a solid media piston-cylinder apparatus at room temperature. We find that upon pressurizing each metal, the phonon spectra are blue-shifted and the net electron-phonon interaction is suppressed relative to the unstrained crystal. This reduction in electron-phonon scattering results in a decrease in the electrical resistivity under pressure, which is more pronounced for aluminum than for copper. We show that density functional perturbation theory can be used to accurately predict the pressure response of the electrical resistivity in these metals. This work demonstrates how the phonon spectra in metals can be engineered through pressure to achieve more attractive electrical properties. PMID:24889627

Lanzillo, Nicholas A; Thomas, Jay B; Watson, Bruce; Washington, Morris; Nayak, Saroj K

2014-06-17

231

Phonon-mediated electron pairing in graphene  

International Nuclear Information System (INIS)

The possibility of superconducting pairing of electrons in doped graphene due to in-plane and out-of-plane phonons is studied. Quadratic coupling of electrons with out-of-plane phonons is considered in details, taking into account both deformation potential and bond-stretch contributions. The order parameter of electron-electron pairing can have different structures due to four-component spinor character of electrons wave function. We consider s-wave pairing, diagonal on conduction and valence bands, but having arbitrary structure with respect to valley degree of freedom. The sign and magnitude of contribution of each phonon mode to effective electron-electron interaction turns out to depend on both the symmetry of phonon mode and the structure of the order parameter. Unconventional orbital-spin symmetry of the order parameter is found.

2010-06-14

232

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

233

Design of phonon detectors for neutrinos  

International Nuclear Information System (INIS)

Several alternative neutrino detection schemes are described briefly and compared. It is suggested that a ballistic-phonon experiment might be promising. In such an experiment the amplitude received at a bolometer would depend on the distance it is from the neutrino event, and also on the direction because of phonon focusing, so several bolometers suggested to locate the event position from the difference in arrival times. The design of such an experiment is discussed assuming the phonons are detected by conventional superconducting bolometers. Determination of the direction of neutrino flux would be obtained from a study of the distribution of direction of the tracks of recoiling electrons or nuclei. The problem of smearing out the effective source over a distance of approximately a mean free path is addressed, and the need for high-resolution phonon focusing studies is expressed

1986-06-02

234

Phonon assisted site-to-site electronic energy transfer between Eu3+ ions in an amorphous solid  

International Nuclear Information System (INIS)

The dynamics of phonon assisted electronic energy transfer between Eu3+ ions, experiencing different crystal fields in an amorphous Ca(PO3)2 matrix, have been investigated using the technique of time-resolved fluorescence line-narrowing (TRFLN). From the concentration and temporal dependence of the transfer rate, the mechanism of the ion-ion electronic coupling has been identified as electric dipole-dipole. Both the excitation wavelength independence and the power law temperature dependence of the transfer rate identify the mechanism of the phonon participation in the transfer process as one involving a two-phonon process, with one-phonon action at each of two coupled ion sites. (Auth.)

1977-08-15

235

Phonon spectrum in a plasma crystal  

International Nuclear Information System (INIS)

The Fourier spectra of longitudinal and transverse waves corresponding to random particle motion were measured in a two-dimensional plasma crystal. The crystal was composed of negatively charged microspheres immersed in a plasma at a low gas pressure. The phonons were found to obey a dispersion relation that assumes a Yukawa interparticle potential. The crystal was in a nonthermal equilibrium, nevertheless phonon energies were almost equally distributed with respect to wave number over the entire first Brillouin zone

2002-07-15

236

Lasers  

Energy Technology Data Exchange (ETDEWEB)

An improved design for a laser discharge tube cooling system is proposed. The laser tube is housed in a large unit made from a metal with a high thermal conductivity (Al, Cu). Heat removal tubes whose ends hold plastic heat sinks pass through this unit in a direction perpendicular to the laser beam axis. Fans are used to provide an air flow over the system of heat sinks.

Mitikhiro, K.

1984-02-09

237

Strong optical-mechanical coupling in a vertical GaAs/AlAs microcavity for subterahertz phonons and near-infrared light.  

Science.gov (United States)

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

238

Lasers  

CERN Document Server

A comprehensive introduction to the operating principles and applications of lasers. Explains basic principles, including the necessary elements of classical and quantum physics. Provides concise discussions of various laser types including gas, solid state, semiconductor, and free electron lasers, as well as of laser resonators, diffraction, optical coherence, and many applications including holography, phase conjugation, wave mixing, and nonlinear optics. Incorporates many intuitive explanations and practical examples. Discussions are self-contained in a consistent notation and in a style that should appeal to physicists, chemists, optical scientists and engineers.

Milonni, Peter W

1988-01-01

239

Waveguiding in supported phononic crystal plates  

Energy Technology Data Exchange (ETDEWEB)

We investigate, with the help of the finite element method, the existence of absolute band gaps in the band structure of a free-standing phononic crystal plate and of a phononic crystal slab deposited on a substrate. The two-dimensional phononic crystal is constituted by a square array of holes drilled in an active piezoelectric (PZT5A or AlN) matrix. For both matrix materials, an absolute band gap occurs in the band structure of the free-standing plate provided the thickness of the plate is on the order of magnitude of the lattice parameter. When the plate is deposited on a Si substrate, the absolute band gap still remains when the matrix of the phononic crystal is made of PZT5A. The AlN phononic crystal plate losses its gap when supported by the Si substrate. In the case of the PZT5A matrix, we also study the possibility of localized modes associated with a linear defect created by removing one row of air holes in the deposited phononic crystal plate.

Vasseur, J [Institut d' Electronique, de Microelectronique et de Nanotechnologies, Cite Scientifique, 59652 Villeneuve d' Ascq Cedex (France); Hladky-Hennion, A-C [Institut d' Electronique, de Microelectronique et de Nanotechnologies, Cite Scientifique, 59652 Villeneuve d' Ascq Cedex (France); Deymier, P [Department of Materials Science end Engineering, University of Arizona, Tucson, Arizona, 85721 (United States); Djafari-Rouhani, B [Institut d' Electronique, de Microelectronique et de Nanotechnologies, Cite Scientifique, 59652 Villeneuve d' Ascq Cedex (France); Duval, F [Institut d' Electronique, de Microelectronique et de Nanotechnologies, Cite Scientifique, 59652 Villeneuve d' Ascq Cedex (France); Dubus, B [Institut d' Electronique, de Microelectronique et de Nanotechnologies, Cite Scientifique, 59652 Villeneuve d' Ascq Cedex (France); Pennec, Y [Institut d' Electronique, de Microelectronique et de Nanotechnologies, Cite Scientifique, 59652 Villeneuve d' Ascq Cedex (France)

2007-12-15

240

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. (a

1965-04-01

 
 
 
 
241

Detection of Random Laser Action from Silica Xerogel Matrices Containing Rhodamine 610 Dye and Titanium Dioxide Nanoparticles  

Directory of Open Access Journals (Sweden)

Full Text Available 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 the optimum concentrations, the results show that the values of bandwidth at full width half-maximum (FWHM and the threshold energy are about 11 nm and 3 mJ respectively. The scattered and amplified probe light has been collected on a PC-interfaced CCD camera system.

Firas J. Al-Maliki

2012-09-01

242

Theory of the Influence of Phonon-Phonon and Electron-Phonon Interactions on the Scattering of Neutrons by Crystals  

International Nuclear Information System (INIS)

As predicted by harmonic theory the coherent inelastic spectrums of neutrons, scattered by a single, non-conducting crystal, for a particular angle of scattering consists of a number of delta-function peaks superposed on a continuous background. The peaks correspond to one-phonon processes in which one phonon is absorbed or emitted by the neutron; the background arises from multi-phonon processes. When anharmonic forces (phonon-phonon interactions) are present, the delta-function peaks are broadened into finite peaks, while their central frequencies are shifted with respect to the harmonic values. In the case of a metal there is in addition to phonon-phonon interactions an interaction between phonons and conduction electrons, which also gives a contribution to the displacement and broadening oftheone-phononpeaks. Continuing earlier work of Van Hove (sho considered the relatively simple case of a non-conductin crystal in its ground state (T = 0oK) ), we have studied the shifts and widths of the scattering peaks as a 'result of the above-mentioned interactions by means of many particle perturbation theory, making extensive use of diagram techniques. Prerequisite to the entire discussion is the assumption that, independent of the strength of the interactions, the width of each peak is small compared to the value of the frequency at its centre; only then the peaks can be considered as being well defined with respect to the background to higher order in the interactions. This condition is expected to be fulfilled for temperatures which are not too high and values of the phonon wave vector which are not too large. Our procedure yields closed formulae for the partial scattering function describing the peaks, which can be evaluated to arbitrarily high accuracy. In particular an expansion for calculating the line shift and line width in powers of u/d and in terms of simple connected diagrams is obtained (u is an average atomic or ionic displacement, d is the smallest interatomic or interionic distance in the crystal). Approximate calculations are performed to give some insight into the orders of magnitude of the effects under study. (author)

1963-01-01

243

Anisotropic phonon anomaly in Bi2212 manifested by electron-phonon coupling  

Science.gov (United States)

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

244

Electron-Phonon Coupling and the Soft Phonon Mode in TiSe2  

Science.gov (United States)

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

245

Ação do laser terapêutico e do ultrassom na regeneração nervosa periférica Action of therapeutic laser and ultrasound in peripheral nerve regeneration  

Directory of Open Access Journals (Sweden)

Full Text Available OBJETIVO: Avaliar a ação precoce do laser terapêutico e do ultrassom no processo de regeneração de uma lesão experimental em ratos. MÉTODO: Utilizou-se 24 ratos. Dezoito foram submetidos ao procedimento cirúrgico de lesão do nervo ciático por compressão, através de uma pinça hemostática acima da fossa poplítea. Os animais foram divididos em três grupos com seis animais em cada. Grupo controle normal. GI: controle lesado sem intervenção terapêutica. GII: intervenção terapêutica do laser ArGaAl. GIII: intervenção terapêutica do ultrassom Pulsado. Iniciamos as intervenções terapêuticas 24 horas após a lesão, com aplicações diárias, por um período de quatorze dias consecutivos. RESULTADOS: Ao avaliar a perimetria dos músculos da coxa direita obteve-se os seguintes valores médios de diminuição (mm, para cada grupo GI: 0,45; GII: 0,42; GIII: 0,40. Quanto ao tempo de deslocamento tanto o GII e GIII apresentaram diferença significativa, quando comparados ao GI. Na avaliação final do IFC o GII sobressaiu ao GIII. Quanto a cicatrização observou-se grande melhora no GII e GIII. CONCLUSÃO: Os resultados evidenciaram que a recuperação nervosa foi maior com a aplicação do laser. Nível de evidência II, Estudos terapêuticos - Investigação dos resultados do tratamentoOBJECTIVE: To assess the efficacy of early therapeutic laser and ultrasound in the regeneration process of an injury in rats. METHODS: We used 24 rats. Eighteen underwent surgery for sciatic nerve compression by a hemostat above the popliteal fossa. The animals were divided into three groups of six animals each. Normal control group. GI: Injured control without therapeutic intervention. GII: laser ArGaAl therapeutic intervention. GIII: therapeutic intervention of Pulsed Ultrasound. We begin therapeutic interventions 24 hours after injury, with daily applications for a period of fourteen consecutive days. RESULTS: In assessing the girth of the muscles of the right they, the following average decrease (in mm for each GI: 0.45, GII: 0.42, GIII: 0.40 In relation to travel time, both GII and GIII presented significant difference when compared to GI. In the final evaluation of the IFC, GII excelled in the GIII. As for the healing observed, a major great improvement was observed in GII and GIII. CONCLUSION: The results showed that nerve recovery was higher with the laser application. Level of evidence II, Therapeutic Studies - Investigation of the results of treatment.

Fabrício Borges Oliveira

2012-01-01

246

Further observation on He-Ne laser action versus staphylococcus aureus--2nd during different moon and perigee presentations  

Science.gov (United States)

The authors describe the results of a series of experiences made to evaluate the interaction in vitro between He-Ne laser light and Staphylococcus aureus. The results confirm the interaction in decreasing energy necessary in relaction with black-white moon and perigee for inducing sensitivity at some antibiotics by Staphylococcus aureus.

Codazza, Danilo; Cassinerio, Mauro; Fava, Giannino

1994-09-01

247

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

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

1995-01-01

248

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

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)

2001-01-01

249

Evidence of the influence of phonon density on Tm3+ upconversion luminescence in tellurite and germanate glasses  

Science.gov (United States)

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

250

FY05 LDRD Final Report Mapping Phonons at High-pressure  

Energy Technology Data Exchange (ETDEWEB)

In order to shed light on the intriguing, and not yet fully understood fcc-isostructural {gamma} {yields} {alpha} transition in cerium, we have begun an experimental program aimed at the determination of the pressure evolution of the transverse acoustic (TA) and longitudinal acoustic (LA) phonon dispersions up to and above the transition. {gamma}-Ce Crystals of 60-80 mm diameter and 20 mm thickness were prepared from a large ingot, obtained from Ames Lab, using laser cutting, micro-mechanical and chemical polishing techniques. Three samples with a surface normal approximately oriented along the [110] direction were loaded into diamond anvil cells (DAC), using neon as a pressure transmitting medium. The crystalline quality was checked by rocking curve scans and typical values obtained ranged between one and two degrees. Only a slight degradation in the sample quality was observed when the pressure was increased to reach the {alpha}-phase, and data could be therefore recorded in this phase as well. The spectrometer was operated at 17794 eV in Kirkpatrick-Baez focusing geometry, providing an energy resolution of 3 meV and a focal spot size at the sample position of 30 x 60 mm{sup 2} (horizontal x vertical, FWHM). Eight to ten IXS spectra were typically recorded per phonon branch. Figure 1 reports the pressure dependence of the LA[100] branch in the {gamma}-phase for pressures of 1, 4 and 6 kbar, together with previous inelastic neutron scattering (INS) results [1] at ambient pressure. A clear decrease of the phonon energies with increasing pressure is observed for 1 and 4 kbar, whereas the phonon energies increase again at 6 kbar, still well within the stability field of the {gamma}-phase. Figure 2 reports the LA dispersion along all three main symmetry directions at 6 kbar ({gamma}-phase) and 8 kbar ({alpha}-phase), together with the INS results at ambient conditions. Besides the already discussed unusual behavior along the [100] direction, the pressure evolution of the two other longitudinal branches in the {gamma}-phase is quite different. The LA [110] branch displays a downward bending near the zone boundary (ZB), whereas the phonon energies at low reduced momentum transfer remain close to the ones at room pressure. In contrast to this, the LA [111] branch does not display any pressure dependence. The LA phonon energies in the {alpha}-phase at 8 kbar are systematically higher than the corresponding lower pressure phonon energies, consistent with the higher density of the {alpha}-phase and the expected larger elastic constants. We note, however, substantial changes in the lattice dynamics along the [110] direction. While the phonons between {zeta} = 0.4 and 0.6 show a large energy increase with pressure, the phonon energy decreases at the zone boundary, thus leading to a pronounced overbending of the branch. The shape of the LA phonon branches in the {alpha}-phase are close to those measured in thorium at ambient conditions [2] while the {gamma}-phase phonon dispersion resembles fcc metastable lanthanum [3]. This behavior might be a signature of substantial changes in the Fermi surface topology, leading to significant changes in the electron-phonon coupling mechanism. A Born-von Karman fit to the phonon dispersion is currently being performed in order to quantify the changes in the force constant matrix.

Farber, D L; Antonangelli, D; Beraud, A; Krisch, M; Aracne, C

2006-02-10

251

FY05 LDRD Final Report Mapping Phonons at High-pressure  

International Nuclear Information System (INIS)

In order to shed light on the intriguing, and not yet fully understood fcc-isostructural ? ? ? transition in cerium, we have begun an experimental program aimed at the determination of the pressure evolution of the transverse acoustic (TA) and longitudinal acoustic (LA) phonon dispersions up to and above the transition. ?-Ce Crystals of 60-80 mm diameter and 20 mm thickness were prepared from a large ingot, obtained from Ames Lab, using laser cutting, micro-mechanical and chemical polishing techniques. Three samples with a surface normal approximately oriented along the [110] direction were loaded into diamond anvil cells (DAC), using neon as a pressure transmitting medium. The crystalline quality was checked by rocking curve scans and typical values obtained ranged between one and two degrees. Only a slight degradation in the sample quality was observed when the pressure was increased to reach the ?-phase, and data could be therefore recorded in this phase as well. The spectrometer was operated at 17794 eV in Kirkpatrick-Baez focusing geometry, providing an energy resolution of 3 meV and a focal spot size at the sample position of 30 x 60 mm2 (horizontal x vertical, FWHM). Eight to ten IXS spectra were typically recorded per phonon branch. Figure 1 reports the pressure dependence of the LA[100] branch in the ?-phase for pressures of 1, 4 and 6 kbar, together with previous inelastic neutron scattering (INS) results [1] at ambient pressure. A clear decrease of the phonon energies with increasing pressure is observed for 1 and 4 kbar, whereas the phonon energies increase again at 6 kbar, still well within the stability field of the ?-phase. Figure 2 reports the LA dispersion along all three main symmetry directions at 6 kbar (?-phase) and 8 kbar (?-phase), together with the INS results at ambient conditions. Besides the already discussed unusual behavior along the [100] direction, the pressure evolution of the two other longitudinal branches in the ?-phase is quite different. The LA [110] branch displays a downward bending near the zone boundary (ZB), whereas the phonon energies at low reduced momentum transfer remain close to the ones at room pressure. In contrast to this, the LA [111] branch does not display any pressure dependence. The LA phonon energies in the ?-phase at 8 kbar are systematically higher than the corresponding lower pressure phonon energies, consistent with the higher density of the ?-phase and the expected larger elastic constants. We note, however, substantial changes in the lattice dynamics along the [110] direction. While the phonons between ? = 0.4 and 0.6 show a large energy increase with pressure, the phonon energy decreases at the zone boundary, thus leading to a pronounced overbending of the branch. The shape of the LA phonon branches in the ?-phase are close to those measured in thorium at ambient conditions [2] while the ?-phase phonon dispersion resembles fcc metastable lanthanum [3]. This behavior might be a signature of substantial changes in the Fermi surface topology, leading to significant changes in the electron-phonon coupling mechanism. A Born-von Karman fit to the phonon dispersion is currently being performed in order to quantify the changes in the force constant matrix

2006-01-01

252

Phonons and electron-phonon coupling in the phonon-mediated superconductor YNi2B2C  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present a combined density-functional-perturbation-theory and inelastic neutron scattering study of the lattice dynamical properties of YNi2B2C. In general, very good agreement was found between theory and experiment for both phonon energies and line widths. Our analysis reveals that the strong coupling of certain low energy modes is linked to the presence of large displacements of the light atoms, i.e. B and C, which is unusual in view of the rather low phonon energies. ...

Weber, F.; Pintschovius, L.; Reichardt, W.; Heid, R.; Bohnen, K. -p; Kreyssig, A.; Reznik, D.; Hradil, K.

2014-01-01

253

Phonon dispersion in quasiperiodic semiconductor superlattices  

International Nuclear Information System (INIS)

The phonon spectra of unstrained and strained quasiperiodic semiconductor superlattices (QSSL) have been calculated using one-dimensional linear chain model. Two types of quasiperiodic systems, namely cantor triadic bar (CTB) and Fibonacci sequences (FS), constituting of AlAs, GaAs and GaSb of which the latter two have a lattice mismatch of about 7% is considered. The calculations have been made using transfer matrix method and also with and without the inclusion of strain. The results on phonon spectra of two component CTB and two as well as three component FS semiconductor superlattices (SSL), thickness and order dependence on LO mode of GaAs, effect of strain on LO frequency of GaAs are presented. The calculated results show that the strain generated due to lattice mismatch reduces significantly the magnitudes of the confined optical phonon frequency of GaAs. (author). 27 refs., 5 figs

1995-07-01

254

Tunable laser action in a dye-doped nematic liquid-crystal waveguide under holographic excitation based on electric-field-induced TM guided-mode modulation  

Science.gov (United States)

Electrically tunable laser action has been demonstrated in a dye-doped nematic liquid-crystal (NLC) waveguide by holographic excitation. The optical feedback was provided by the distributed feedback induced by two-beam interference by use of the Lloyd mirror configuration. Electrical tuning of the lasing wavelength was realized owing to the change of the effective refractive index of the NLC core layer caused by the reorientation of NLC molecules. On the basis of a waveguiding mode theory, numerical analysis of a TM guided mode in the presence of an applied electric field was performed, and field-induced tuning of the lasing wavelength was investigated in detail. Prospects for the realization of a single-mode operation and tuning of the lasing wavelength were also shown.

Matsui, Tatsunosuke; Ozaki, Masanori; Yoshino, Katsumi

2004-09-01

255

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)

2004-08-01

256

Phonon Excitations of Composite Fermion Landau Levels  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Phonon excitations of fractional quantum Hall states at filling factors nu = 1/3, 2/5, 4/7, 3/5, 4/3, and 5/3 are experimentally shown to be based on Landau level transitions of Composite Fermions. At filling factor nu = 2/3, however, a linear field dependence of the excitation energy in the high-field regime rather hints towards a spin transition excited by the phonons. We propose to explain this surprising observation by an only partially polarized 2/3-ground-state making ...

Schulze-wischeler, F.; Hohls, F.; Zeitler, U.; Reuter, D.; Wieck, A. D.; Haug, R. J.

2004-01-01

257

Electron-Phonon Coupling in Charged Buckminsterfullerene  

CERN Multimedia

A simple, yet accurate solution of the electron-phonon coupling problem in C_{60} is presented. The basic idea behind it is to be found in the parametrization of the ground state electronic density of the system calculated making use of ab-initio methods, in term of sp$^{2+x}$ hybridized orbitals. This parametrization allows for an economic determination of the deformation potential associated with the fullerene's normal modes. The resulting electron-phonon coupling constants are used to calculate Jahn-Teller effects in C_{60}^-, and multiple satellite peaks in the corresponding photoemission reaction. Theory provides an accurate account of the experimental findings.

Breda, N; Colò, G; Román, H E; Alasia, F; Onida, G; Ponomarev, V; Vigezzi, E

1998-01-01

258

Phonon interference effects in molecular junctions.  

Science.gov (United States)

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. PMID:24387351

Markussen, Troels

2013-12-28

259

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

260

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

 
 
 
 
261

Measurements of phonons generated by optical excitation of GaAs, using a superlattice phonon spectrometer  

Energy Technology Data Exchange (ETDEWEB)

Previously we have demonstrated that a weakly coupled AlAs/GaAs superlattice (SL) works as a tuneable phonon spectrometer. In this paper we describe measurements made using the SL spectrometer of the phonons generated by relaxation of optically excited carriers in bulk GaAs. We find that, sub-THz acoustic phonons ({approx}420 GHz) are generated by direct optical excitation of bulk GaAs. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Kini, R.N.; Stanton, N.M.; Kent, A.J.; Henini, M. [School of Physics and Astronomy, University of Nottingham, Nottingham, NG72RD (United Kingdom)

2004-11-01

262

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

263

Optical phonons in Ge quantum dots obtained on Si(111)  

CERN Multimedia

The light combination scattering on the optical phonons in the Ge quantum dots, obtained on the Si surface of the (111) orientation through the molecular-beam epitaxy, is studied. The series of lines, connected with the phonon spectrum quantization, was observed. It is shown, that the phonon modes frequencies are well described by the elastic properties and dispersion of the voluminous Ge optical phonons. The value of the Ge quantum dots deformation is determined

Talochkin, A B

2002-01-01

264

Neutron-Phonon Interaction in Neutron Star Crusts  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

265

Proposal for an Optomechanical Traveling Wave Phonon-Photon Translator  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this article we describe a general optomechanical system for converting photons to phonons in an efficient, and reversible manner. We analyze classically and quantum mechanically the conversion process and proceed to a more concrete description of a phonon-photon translator formed from coupled photonic and phononic crystal planar circuits. Applications of the phonon-photon translator to RF-microwave photonics and circuit QED, including proposals utilizing this system for ...

Safavi-naeini, Amir H.; Painter, Oskar

2010-01-01

266

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

2013-03-01

267

Electron-phonon interaction in mixed valence systems  

International Nuclear Information System (INIS)

One considers an Hamiltonian describing mixed valence compounds and including d and f electron-phonon coupling. One shows that the renormalization of the electronic energy parameters induced by the electron-phonon interaction depends strongly on the nature (static or adiabatic) of the approximation used. One discusses the importance of the d-electron-phonon coupling on the narrowing of the f-level and the softening of the phonon modes. (author)

1980-01-01

268

On the conformational changes in human serum albumin under the action of electric current and low-level laser irradiation  

International Nuclear Information System (INIS)

An electric current decreases the diameter of monomeric globules and increases the number of large-size globules of human serum albumin. Low-level laser therapy leads to a photochemical process in the protein with a modification of its conformation. The physiotherapeutic curative effect of the electric current and low-level therapy is realized in the immediate change of the conformation takes place in the system 'water-protein' of living organism. The experimental data indicate the dependence of the properties of water and human serum albumin on the dose of electromagnetic fields

2006-06-01

269

Nonlinear stochastic effects during the action of noise on relaxation oscillations in a ring solid-state laser  

International Nuclear Information System (INIS)

The influence of the pump noise intensity on the characteristics of the fundamental relaxation frequency of the emission spectrum of a ring chip laser operating in the self-modulation regime of the first kind is studied theoretically and experimentally. It is shown that the noise effects give rise to such nonlinear stochastic phenomena as a change in the relaxation oscillation frequency, a noticeable broadening of the relaxation peak in the emission spectrum, and the resonance dependence of the amplitude of this peak on the noise intensity (the peak becomes maximal at a particular noise intensity). (nonlinear optical phenomena)

2009-01-31

270

Instabilities of a short-cavity standing-wave vibronic laser  

Science.gov (United States)

Self pulsing and chaotic dynamics of the short cavity vibronic alexandrite laser is reported. This phenomenon is explained by the process of energy pulling between the laser photons and the host crystal phonons.

Gadomski, W.; Ratajska-Gadomska, B.

1998-08-01

271

Lasers  

Energy Technology Data Exchange (ETDEWEB)

The scope of our research in laser and related technologies has grown over the years and has attracted a broad user base for applications within DOE, DOD, and private industry. Within the next few years, we expect to begin constructing the National Ignition Facility, to make substantial progress in deploying AVLIS technology for uranium and gadolinium enrichment, and to develop new radar sensing techniques to detect underwater objects. Further, we expect to translate LLNL patent ideas in microlithography into useful industrial products and to successfully apply high-power, diode-based laser technology to industrial and government applications.

NONE

1995-01-01

272

Synthetic thermoelectric materials comprising phononic crystals  

Energy Technology Data Exchange (ETDEWEB)

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

273

Tunnel spectroscopy of phonons in indium arsenide  

International Nuclear Information System (INIS)

Tunnel spectra of InAs-hyperfine oxide-Au structures in the energy area of 0-40 MeV are measured. Peculiarities of volt-ampere characteristics, which may be connected with the semiconductor acoustic and optical phonon disturbance are revealed in spectra

1985-12-01

274

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

275

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

276

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

Science.gov (United States)

Based on a generalized Fröhlich 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

2010-06-01

277

Sub-Poissonian phononic population in a nanoelectromechanical system  

Energy Technology Data Exchange (ETDEWEB)

The properties of the phononic distribution of a mechanical oscillator coupled to a single-electron transistor are investigated in the sequential tunnelling regime. It is shown that for not too strong electron-phonon interaction the electrical current may induce a distribution of phonons with sub-Poissonian statistics, which is characterized by a selective population of few phonon states. Depending on the choice of parameters, such a sub-Poissonian phonon distribution can be accompanied either by a super- or a sub-Poissonian electronic Fano factor.

Merlo, M; Haupt, F; Cavaliere, F; Sassetti, M [Dipartimento di Fisica, Universita di Genova and LAMIA INFM-CNR, Via Dodecaneso 33, 16146 Genova (Italy)], E-mail: merlo@fisica.unige.it

2008-02-15

278

Interfacial and Confined Optical Phonons in Wurtzite Nanocrystals  

CERN Multimedia

We derive within the dielectric-continuum model an integral equation that defines interface and confined polar optical-phonon modes in nanocrystals with wurtzite crystal structure. It is demonstrated theoretically, that while the frequency of confined polar optical phonons in zincblende nanocrystals is equal to that of the bulk crystal phonons, the confined polar optical phonons in wurtzite nanocrystals have a discrete spectrum of frequencies different from those of the bulk crystal. The calculated frequencies of confined polar optical phonons in wurtzite ZnO nanocrystals are found to be in an excellent agreement with the experimental resonant Raman scattering spectra of spherical ZnO quantum dots.

Fonoberov, V A; Fonoberov, Vladimir A.; Balandin, Alexander A.

2004-01-01

279

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

280

Theory of Interfacial Plasmon-Phonon Scattering in Supported Graphene  

Digital Repository Infrastructure Vision for European Research (DRIVER)

One of the factors limiting electron mobility in supported graphene is remote phonon scattering. We formulate the theory of the coupling between graphene plasmon and substrate surface polar phonon (SPP) modes, and find that it leads to the formation of interfacial plasmon-phonon (IPP) modes, from which the phenomena of dynamic anti-screening and screening of remote phonons emerge. The remote phonon-limited mobilities for SiO$_{2}$, HfO$_{2}$, h-BN and Al$_{2}$O$_{3}$ substra...

Ong, Zhun-yong; Fischetti, Massimo V.

2012-01-01

 
 
 
 
281

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

2012-09-01

282

Molecular dynamics study of phonon screening in graphene  

Science.gov (United States)

Phonon interaction with electrons or phonons or with structural defects result in a phonon mode conversion. The mode conversion is governed by the frequency wave-vector dispersion relation. The control over phonon mode or the screening of phonon in graphene is studied using the propagation of amplitude modulated phonon wave-packet. Control over phonon properties like frequency and velocity opens up several wave guiding, energy transport and thermo-electric applications of graphene. One way to achieve this control is with the introduction of nano-structured scattering in the phonon path. Atomistic model of thermal energy transport is developed which is applicable to devices consisting of source, channel and drain parts. Longitudinal acoustic phononmode is excited fromone end of the device. Molecular dynamics based time integration is adopted for the propagation of excited phonon to the other end of the device. The amount of energy transfer is estimated from the relative change of kinetic energy. Increase in the phonon frequency decreases the kinetic energy transmission linearly in the frequency band of interest. Further reduction in transmission is observed with the tuning of channel height of the device by increasing the boundary scattering. Phonon mode selective transmission control have potential application in thermal insulation or thermo-electric application or photo-thermal amplification.

Javvaji, Brahmanandam; Roy Mahapatra, D.; Raha, S.

2014-04-01

283

Towards a microscopic understanding of the phonon bottleneck  

International Nuclear Information System (INIS)

The problem of the phonon bottleneck in the relaxation of two-level systems (spins) to a narrow group of resonant phonons via emission-absorption processes is investigated from first principles. It is shown that the kinetic approach based on the Pauli master equation is invalid because of the narrow distribution of the phonons exchanging their energy with the spins. This results in a long-memory effect that can be best taken into account by introducing an additional dynamical variable corresponding to the nondiagonal matrix elements responsible for spin-phonon correlation. The resulting system of dynamical equations describes the phonon-bottleneck plateau in the spin excitation, as well as a gap in the spin-phonon spectrum, for any finite concentration of spins. On the other hand, it does not accurately render the line shape of emitted phonons and still needs improving

2007-03-01

284

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; Jauho, Antti-Pekka

2012-01-01

285

Observation of the Full Exciton and Phonon Fine Structure in CdSe/CdS Dot-in-Rod Heteronanocrystals.  

Science.gov (United States)

Light emission of semiconductor nanocrystals is a complex process, depending on many factors, among which are the quantum mechanical size confinement of excitons (coupled electron-hole pairs) and the influence of confined phonon modes and the nanocrystal surface. Despite years of research, the nature of nanocrystal emission at low temperatures is still under debate. Here we unravel the different optical recombination pathways of CdSe/CdS dot-in-rod systems that show an unprecedented number of narrow emission lines upon resonant laser excitation. By using self-assembled, vertically aligned rods and application of crystallographically oriented high magnetic fields, the origin of all these peaks is established. We observe a clear signature of an acoustic-phonon assisted transition, separated from the zero-phonon emission and optical-phonon replica, proving that nanocrystal light emission results from an intricate interplay between bright (optically allowed) and dark (optically forbidden) exciton states, coupled to both acoustic and optical phonon modes. PMID:24861569

Granados Del Águila, Andrés; Jha, Bhawana; Pietra, Francesca; Groeneveld, Esther; de Mello Donegá, Celso; Maan, Jan C; Vanmaekelbergh, Daniël; Christianen, Peter C M

2014-06-24

286

An investigation of electron-phonon coupling via phonon dispersion measurements in graphite using angle-resolved photoelectron spectroscopy  

Science.gov (United States)

Electron-phonon coupling (EPC) plays an important role in solid state physics. Here, we demonstrate an experimental method that enables investigation of the elemental processes of the indirect transition, in which EPC participates in photoexcitation in solids, by resolving the energy and momentum of phonons and electrons simultaneously. For graphite, we used angle-resolved photoelectron spectroscopy to observe electron emission at the ?-point being scattered from the K-point by a phonon. Energy conservation during phonon emission implies that the step-like structure in the spectrum is near the Fermi level, and angle-resolved measurements revealed phonon dispersions that contribute to EPC because of parallel momentum conservation. The observed phonon branch depends on the photon energy, i.e., the final photoexcitation state; this dependency is partly explained by the selection rule, which is determined by the electron state symmetry for the initial, intermediate, and final states and the phonon.

Tanaka, Shin-Ichiro; Matsunami, Masaharu; Kimura, Shin-Ichi

2013-10-01

287

Spatiotemporal Stability of a Femtosecond Hard-X-Ray Undulator Source Studied by Control of Coherent Optical Phonons  

International Nuclear Information System (INIS)

We report on the temporal and spatial stability of the first tunable femtosecond undulator hard-x-ray source for ultrafast diffraction and absorption experiments. The 2.5-1 A output radiation is driven by an initial 50 fs laser pulse employing the laser-electron slicing technique. By using x-ray diffraction to probe laser-induced coherent optical phonons in bulk bismuth, we estimate an x-ray pulse duration of 140±30 fs FWHM with timing drifts below 30 fs rms measured over 5 days. Optical control of coherent lattice motion is demonstrated

2007-10-26

288

Spatiotemporal stability of a femtosecond hard-x-ray undulator source studied by control of coherent optical phonons.  

Science.gov (United States)

We report on the temporal and spatial stability of the first tunable femtosecond undulator hard-x-ray source for ultrafast diffraction and absorption experiments. The 2.5-1 Angstrom output radiation is driven by an initial 50 fs laser pulse employing the laser-electron slicing technique. By using x-ray diffraction to probe laser-induced coherent optical phonons in bulk bismuth, we estimate an x-ray pulse duration of 140+/-30 fs FWHM with timing drifts below 30 fs rms measured over 5 days. Optical control of coherent lattice motion is demonstrated. PMID:17995338

Beaud, P; Johnson, S L; Streun, A; Abela, R; Abramsohn, D; Grolimund, D; Krasniqi, F; Schmidt, T; Schlott, V; Ingold, G

2007-10-26

289

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

1980-01-01

290

Electron-phonon superconductivity beyond Migdal's theorem  

International Nuclear Information System (INIS)

One of the common elements between the various high Tc superconductors, cuprates and C60 compounds, is the very small value of the Fermi energy, comparable with the Debye phonon frequencies. This situation implies a breakdown of Migdal's theorem for the electron-phonon many body problem and leads to important nonadiabatic effects. We have generalized Eliashberg equations to include vertex corrections and other nonadiabatic effects in a perturbative scheme. This leads to a rather complex situation in which the critical temperature for superconductivity can be strongly enhanced if the el-ph scattering involves mainly small momenta. Recent studies show that this situation can be naturally realized in view of electronic correlations. ((orig.))

1995-01-01

291

Electron-Phonon Interaction in Tetrahedral Semiconductors  

CERN Document Server

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 atoms, the effect of the vibration of each separate atom can thus be investigated by isotopic substitution. Because of the zero-point vibrations, such effects are present even at zero temperature (T = 0). In this paper we discuss state-of-the-art calculations of the dielectric function spectra and compare them with experimental results, with emphasis on the differences introduced by the electron-phonon interaction. The temperature dependence of various optical parameters will be described by means of one or two (in a few cases three) Einstein...

Cardona, M

2004-01-01

292

Scattering of phonons by cluster defects  

International Nuclear Information System (INIS)

The scattering of phonons in crystals containing defect aggregates of spherical shape has been studied. An expression is obtained for the phonon mean free path in the form of a series in ascending powers of the wave vector q. The wave vector dependence of the scattering can be satisfactorily represented by qsup(4)(qsup(3) + (qsub(o)sup(3))/qsup(3)+qsub(o)sup(3)), where C and qsub(o) are constants depending on the defect diameter (C>> 1). It is observed that the scattering is of the qsup(4) type for wavelengths small compared with the defect size. For wave-lengths comparable to and smaller than the defect size, the mean free path exhibits a weak dependence on the wave vector. The result is at variance with the wave-vector-independent geometrical scattering often assumed for small wave-lengths. Thermal conductivity measurements on irradiated crystals can be consistently explained by the present results. (auth.)

1978-12-31

293

First tests on phonon threshold spectroscopy  

International Nuclear Information System (INIS)

Using the proximity effect of iridium and gold we fabricate sensitive phase transition thermometers. In spite of problems with other material combinations iridium/gold thermometers show an excellent long-term stability. Up to now we reached transition temperatures in the range from 20 to 100 mK on different absorber materials for example silicon, germanium and sapphire. A study of detectors consisting of a dielectric sapphire absorber, an Ir/Au thermometer and an additional superconducting film is presented. In this case some phonons produced by an interaction in the absorber can break up Cooper-Pairs in the superconducting film. Some energy is stored in the quasiparticle system and reemitted into the absorber with a delay. The recombination phonons are again detected with the thermometer. From the pulse shape of the temperature signal the lifetime of the quasiparticles can be extracted. The results for aluminum and tantalum are presented

2000-04-07

294

The anharmonic electron-phonon problem  

CERN Document Server

The anharmonic electron-phonon problem is solved in the infinite-dimensional limit using quantum Monte Carlo simulation. Charge-density-wave order is seen to remain at half filling even though the anharmonicity removes the particle-hole symmetry (and hence the nesting instability) of the model. Superconductivity is strongly favored away from half filling (relative to the charge-density-wave order) but the anharmonicity does not enhance transition temperatures over the maximal values found in the harmonic limit.

Freericks, J K; Mahan, G D; Jarrell, Mark

1996-01-01

295

The anharmonic electron-phonon problem  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The anharmonic electron-phonon problem is solved in the infinite-dimensional limit using quantum Monte Carlo simulation. Charge-density-wave order is seen to remain at half filling even though the anharmonicity removes the particle-hole symmetry (and hence the nesting instability) of the model. Superconductivity is strongly favored away from half filling (relative to the charge-density-wave order) but the anharmonicity does not enhance transition temperatures over the maxima...

Freericks, J. K.; Jarrell, Mark; Mahan, G. D.

1996-01-01

296

Phononic crystal waveguides for electromechanical circuits  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Nanoelectromechanical systems (NEMS), utilising localised mechanical vibrations, were pioneered for sensors, signal processors and to study macroscopic quantum mechanics. Increasingly the concept of integrating multiple mechanical elements via electrical/optical means has emerged as a challenge towards NEMS circuits. Here we develop phononic crystal waveguides (PnC WGs), using a 1-dimensional array of suspended membranes, that offer purely mechanical means to integrate isola...

Hatanaka, Daiki; Mahboob, Imran; Onomitsu, Koji; Yamaguchi, Hiroshi

2014-01-01

297

Defect energetics and phonons in UO2  

International Nuclear Information System (INIS)

We have studied the formation energies of interstitial Frenkel pair involving oxygen and uranium vacancies and Schottky trio defect energies in UO2. Classical molecular dynamics simulations have been used to carry out these calculations. We find that oxygen Frenkel defect is energetically the most favorable as it has the lowest energy. There are significant changes in the phonon spectrum due to formation of Frenkel and Schottky defects, which would significantly alter their high temperature thermodynamic properties. (author)

2007-12-27

298

Sub-wavelength phononic crystal liquid sensor  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We introduce an acoustic liquid sensor based on phononic crystals consisting of steel plate with an array of holes filled with liquid. We both theoretically and experimentally demonstrate sensor properties considering the mechanism of the extraordinary acoustic transmission as underlying phenomenon. The frequency of this resonant transmission peak is shown to rely on the speed of sound of the liquid, and the resonant frequency can be used as a measure of speed of sound and rela...

Ke, Manzhu; Zubtsov, Mikhail; Lucklum, Ralf

2011-01-01

299

Phonons of the anomalous element cerium  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Many physical and chemical properties of the light rare-earths and actinides are governed by the active role of f electrons, and despite intensive efforts the details of the mechanisms of phase stability and transformation are not fully understood. A prominent example which has attracted a lot of interest, both experimentally and theoretically over the years is the isostructural ? - ? transition in cerium. We have determined by inelastic X-ray scattering, the complete phonon dispersion sc...

Krisch, Michael; Farber, D. L.; Xu, R.; Antonangeli, Daniele; Aracne, C. M.; Beraud, Alexandre; Chiang, Tai-chang; Zarestky, J.; Kim, Duck Young; Isaev, Eyvaz I.; Ahuja, Rajeev; Johansson, Bo?rje

2011-01-01

300

Phononic crystal slabs: fundamentals and applications  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present in this paper theoretical and experimental studies of guided acoustic wave propagating in phononic crystal slabs. By the insertion of scatters or the deposition of pillars on slabs, we are able to built up these artificial crystals. With appropriate choice of the geometrical parameters, we show that these structures can display complete band gaps in silicone membrane based on a Bragg or a local resonance mechanism. Additionally, the introduction of defects inside the perfect crysta...

Khelif, Abdelkrim

2012-01-01

 
 
 
 
301

Electron-Phonon Interaction in Tetrahedral Semiconductors  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

302

Design and characterization of bubble phononic crystals  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report the practical realization of phononic crystals with gas inclusions, using soft lithography techniques. Ultrasonic experiments from 0.3 to 5 MHz confirm the existence of deep and wide minima of transmission through the crystal. We show that the first gap is due to the combined effects of Bragg reflections and bubble resonances. We propose a simple layered model that gives a reasonable prediction of the ultrasonic transmission. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3...

Leroy, Valentin; Bretagne, Alice; Fink, Mathias; Willaime, Herve; Tabeling, Patrick; Tourin, Arnaud

2009-01-01

303

Phonon dynamics in parent and superconducting FeAs compounds  

International Nuclear Information System (INIS)

We have carried out extensive measurements of the phonon dispersion relation and phonon density of states for the newly discovered parent and superconducting FeAs compounds using inelastic neutron as well as xray scattering techniques. The phonon spectra are analyzed using ab-initio and empirical model calculations giving density of states and dispersion relation. We found strong temperature dependence of some phonons in CaFe2As2 near the structural phase transition around 172 K, which may indicate strong electron phonon coupling and/or anharmonicity. The measurement of pressure dependence of phonon modes across the tetragonal to collapsed tetragonal phases of CaFe2As2 shows that variation of frequency with pressure is closely associated with the structural change, rather than with the phase transition itself. Furthermore, measurement of temperature dependence of phonon density of states across the magnetic/structural phase transition temperature indicates that softening of low energy phonon modes in the paramagnetic state of these compounds may be due to the interaction of phonons with electron or short-range spin fluctuations in the normal state of the superconducting compound as well as in the parent compound. Our work shows that electron-phonon coupling is present in these compounds but it can not be solely responsible for the superconductivity. (author)

2009-12-14

304

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

305

Theory of coherent phonons in carbon nanotubes and graphene nanoribbons  

International Nuclear Information System (INIS)

We survey our recent theoretical studies on the generation and detection of coherent radial breathing mode (RBM) phonons in single-walled carbon nanotubes and coherent radial breathing like mode (RBLM) phonons in graphene nanoribbons. We present a microscopic theory for the electronic states, phonon modes, optical matrix elements and electron–phonon interaction matrix elements that allows us to calculate the coherent phonon spectrum. An extended tight-binding (ETB) model has been used for the electronic structure and a valence force field (VFF) model has been used for the phonon modes. The coherent phonon amplitudes satisfy a driven oscillator equation with the driving term depending on the photoexcited carrier density. We discuss the dependence of the coherent phonon spectrum on the nanotube chirality and type, and also on the graphene nanoribbon mod number and class (armchair versus zigzag). We compare these results with a simpler effective mass theory where reasonable agreement with the main features of the coherent phonon spectrum is found. In particular, the effective mass theory helps us to understand the initial phase of the coherent phonon oscillations for a given nanotube chirality and type. We compare these results to two different experiments for nanotubes: (i) micelle suspended tubes and (ii) aligned nanotube films. In the case of graphene nanoribbons, there are no experimental observations to date. We also discuss, based on the evaluation of the electron–phonon interaction matrix elements, the initial phase of the coherent phonon amplitude and its dependence on the chirality and type. Finally, we discuss previously unpublished results for coherent phonon amplitudes in zigzag nanoribbons obtained using an effective mass theory. (topical review)

2013-04-10

306

INTERACTION OF LASER RADIATION WITH MATTER. LASER PLASMA: Dynamics of the development of a microrelief on the surface of silicon under the action of high-power laser pulses  

Science.gov (United States)

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

307

Universal exchange-driven phonon splitting  

Science.gov (United States)

We report on a linear dependence of the phonon splitting on the non-dominant exchange coupling Jnd in the antiferromagnetic monoxides MnO, Fe0.92O, CoO and NiO, and in the highly frustrated antiferromagnetic spinels CdCr2O4, MgCr2O4 and ZnCr2O4. For the monoxides our results directly confirm the theoretical prediction of a predominantly exchange induced splitting of the zone-centre optical phonon [1,2]. We find the linear relation ??= ?JndS^2 with slope ? = 3.7. This relation also holds for a very different class of systems, namely the highly frustrated chromium spinels. Our finding suggests a universal dependence of the exchange-induced phonon splitting at the antiferromagnetic transition on the non-dominant exchange coupling [3].[4pt] [1] S. Massidda et al., Phys. Rev. Lett. 82, 430 (1999).[0pt] [2] W. Luo et al., Solid State Commun. 142, 504 (2007).[0pt] [3] Ch. Kant et al., arxiv:1109.4809.

Deisenhofer, Joachim; Kant, Christian; Schmidt, Michael; Wang, Zhe; Mayr, Franz; Tsurkan, Vladimir; Loidl, Alois

2012-02-01

308

Phonons and Thermal Properties of Carbon Nanotubes  

Science.gov (United States)

The thermal properties of carbon nanotubes display a wide range of behaviors which are related both to their graphitic nature and their unique structure and size. The specific heat of individual nanotubes should be similar to that of two-dimensional graphene at high temperatures, with the effects of phonon quantization becoming apparent at lower temperatures. Inter-tube coupling in SWNT ropes, and interlayer coupling in MWNTs, should cause their low-temperature specific heat to resemble that of three-dimensional graphite. Experimental data on SWNTs show relatively weak inter-tube coupling, and are in good agreement with theoretical models. The specific heat of MWNTs has not been examined theoretically in detail. Experimental results on MWNTs show a temperature dependent specific heat which is consistent with weak inter-layer coupling, although different measurements show slightly different temperature dependences. The thermal conductivity of both SWNTs and MWNTs should reflect the on-tube phonon structure, regardless of tube-tube coupling. Measurements of the thermal conductivity of bulk samples show graphite-like behavior for MWNTs but quite different behavior for SWNTs, specifically a linear temperature dependence at low T which is consistent with one-dimensional phonons. The room-temperature thermal conductivity of highly aligned SWNT samples is over 200W/mK, and the thermal conductivity of individual nanotubes is likely to be higher still.

Hone, James

309

Phonon-Mediated Tunneling into Graphene  

Science.gov (United States)

Recent scanning tunneling spectroscopy experiments on graphene reported an unexpected gap of about ±60meV around the Fermi level [V. W. Brar , Appl. Phys. Lett.APPLAB0003-6951 91, 122102 (2007); 10.1063/1.2771084Y. Zhang , Nature Phys.NPAHAX1745-2481 4, 627 (2008)10.1038/nphys1022]. Here we give a theoretical investigation explaining the experimentally observed spectra and confirming the phonon-mediated tunneling as the reason for the gap: We study the real space properties of the wave functions involved in the tunneling process by means of ab initio theory and present a model for the electron-phonon interaction, which couples the graphene’s Dirac electrons with quasifree-electron states at the Brillouin zone center. The self-energy associated with this electron-phonon interaction is calculated, and its effects on tunneling into graphene are discussed. Good agreement of the tunneling density of states within our model and the experimental dI/dU spectra is found.

Wehling, T. O.; Grigorenko, I.; Lichtenstein, A. I.; Balatsky, A. V.

2008-11-01

310

Phonon effects in molecular conduction junctions  

Science.gov (United States)

This talk will give an overview of our work on effects of electron-phonon coupling on molecular conduction, including dephasing, dissipation and heating, then describe some recent observations, interpretations and predictions on three phenomena involving phonons in molecular junctions: (a) Heat conduction and its rectification by molecular wires^1,2; (b) inelastic electron tunneling spectroscopy^3-5 and (c) phonon-induced multi-stability, hysteresis and negative differential resistance in molecular conduction.^6 ^1 D. Segal, A. Nitzan and P. Hä'nggi, J. Chem. Phys. 119, 6840-6855 (2003) ^2 D. Segal and A. Nitzan, cond-mat/0405472 ^3 M. Galperin, M. Ratner and A. Nitzan, J. Chem. Phys. 121, 11965-11979 (2004) ^4 M. Galperin, M. Ratner and A. Nitzan, Nano Lett., 4, 1605-1611 (2004) ^5 M. Galperin, A. Nitzan, M. A. Ratner and D. R. Stewart, to be published http://atto.tau.ac.il/˜nitzan/253.pdf ^6 M. Galperin, M. A.Ratner and A. Nitzan, Nano Letters, in press http://atto.tau.ac.il/˜nitzan/254.pdf

Nitzan, Abraham

2005-03-01

311

Semiconductor laser  

Energy Technology Data Exchange (ETDEWEB)

A semiconductor laser of the rib guide type having the thickness of an active layer within a stripe-shaped region thicker than that of the outside, and thus the stripe-shaped region is made to have a waveguide action and, thereby, fundamental mode laser may be achieved.

Sakuma, I.; Furuse, T.; Kawano, H.; Matsumoto, S.; Matsumoto, Y.; Nishida, K.; Ueno, M.

1984-02-28

312

Phase-space properties of two-dimensional elastic phononic crystals and anharmonic effects in nano-phononic crystals  

Science.gov (United States)

This dissertation contains research directed at investigating the behavior and properties of a class of composite materials known as phononic crystals. Two categories of phononic crystals are explicitly investigated: (I) elastic phononic crystals and (II) nano-scale phononic crystals. For elastic phononic crystals, attention is directed at two-dimensional structures. Two specific structures are evaluated (1) a two-dimensional configuration consisting of a square array of cylindrical Polyvinylchloride inclusions in air and (2) a two-dimensional configuration consisting of a square array of steel cylindrical inclusions in epoxy. For the first configuration, a theoretical model is developed to ascertain the necessary band structure and equi-frequency contour features for the realization of phase control between propagating acoustic waves. In contrasting this phononic crystal with a reference system, it is shown that phononic crystals with equifrequency contours showing non-collinear wave and group velocity vectors are ideal systems for controlling the phase between propagating acoustic waves. For the second configuration, it is demonstrated that multiple functions can be realized of a solid/solid phononic crystal. The epoxy/steel phononic crystal is shown to behave as (1) an acoustic wave collimator, (2) a defect-less wave guide, (3) a directional source for elastic waves, (4) an acoustic beam splitter, (5) a phase-control device and (6) a k-space multiplexer. To transition between macro-scale systems (elastic phononic crystals) and nano-scale systems (nano-phononic crystals), a toy model of a one-dimensional chain of masses connected with non-linear, anharmonic springs is utilized. The implementation of this model introduces critical ideas unique to nano-scale systems, particularly the concept of phonon mode lifetime. The nano-scale phononic crystal of interest is a graphene sheet with periodically spaced holes in a triangular array. It is found through equilibrium molecular dynamics simulation techniques, that phonon-boundary collision effects and coherent phononic effects (band-folding) are two competing scattering mechanisms responsible for the reduction of acoustic and optical phonon lifetimes. Conclusions drawn about the lifetime of thermal phonons in phononic crystal patterned graphene are linked with the anharmonic, one-dimensional crystal model.

Swinteck, Nichlas Z.

313

Electron-Phonon Interaction and Phonon Softening in Systems with Magnetovolume Instabilities  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The interrelation of Invar and martensitic behaviour in transition metal alloys like Fe65Ni35 is discussed on the basis of ab initio calculations for stoichiometric systems like Fe3Ni. We also examined face centered cubic iron as a model system for Antiinvar which like Invar shows a pronounced phonon softening. Neutron scattering experiments on Invar systems have shown that the TA1 phonon mode softens for small wavevectors (vector q) along the [110] direction in the fcc lattice. To day there ...

Herper, H.; Entel, P.; Weber, W.

1995-01-01

314

Plasma pumped laser  

International Nuclear Information System (INIS)

This invention relates to a laser and in particular to a laser utilizing a plasma to create a population inversion in the laser active medium. The laser can be pumped by the output plasma from a fusion reactor, for example, or by plasma from other sources. Either the plasma ions or electrons or both can be used to pump the laser. Also the plasma ions can be used to provide energy to achieve a chemical laser action. (U.S.)

1975-01-01

315

Entanglement production under electron phonon interaction in a quantum dot  

Directory of Open Access Journals (Sweden)

Full Text Available We consider the quantum dot entangler device introduced by Oliver et al. [1] coupled to a single phonon mode. While we take the phonon interaction to all orders, we perform a fourth order calculation in electron-dot coupling. Using the Von Neumann entropy we measure the degree of entanglement. We find that the phonon mechanism habilitates single electron processes which manifest themselves as decoherent processes.

A.Lopez

2006-01-01

316

Phonon Decoherence of a Double Quantum Dot Charge Qubit  

CERN Multimedia

We study decoherence of a quantum dot charge qubit due to coupling to piezoelectric acoustic phonons in the Born-Markov approximation. After including appropriate form factors, we find that phonon decoherence rates are one to two orders of magnitude weaker than was previously predicted. We calculate the dependence of the Q-factor on lattice temperature, quantum dot size, and interdot coupling. Our results suggest that mechanisms other than phonon decoherence play a more significant role in current experimental setups.

Vorojtsov, S B; Baranger, H U; Vorojtsov, Serguei; Mucciolo, Eduardo R.; Baranger, Harold U.

2004-01-01

317

Anharmonicity due to Electron-Phonon Coupling in Magnetite  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present the results of inelastic x-ray scattering for magnetite and analyze the energies and spectral widths of the phonon modes with different symmetries in a broad range of temperature 125phonon modes with X_4 and Delta_5 symmetries broaden in a nonlinear way with decreasing temperature when the Verwey transition is approached. It is found that the maxima of phonon widths occur away from high-symmetry points which indicates the incommensurate character of ...

Hoesch, Moritz; Piekarz, Przemyslaw; Bosak, Alexey; Tacon, Mathieu Le; Krisch, Michael; Kozlowski, Andrzej; Oles, Andrzej M.; Parlinski, Krzysztof

2013-01-01

318

Selective heating of the ferroelectric film soft mode phonons  

CERN Document Server

Results of the experimental study of the electromagnetic pumping of frequency 0.3 THz upon the soft mode phonons in the (Ba, Sr)TiO3 film are presented. Some features of the phonon state are revealed using the capacitor thermometer and the thermocouple. The soft mode phonon overheating estimated comparing changes of the planar capacitor capacitance was observed to be quite significant

Prudan, A M; Ktitorov, S A

2007-01-01

319

Phononics: Manipulating heat flow with electronic analogs and beyond  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The form of energy termed heat that typically derives from lattice vibrations, i.e. the phonons, is usually considered as waste energy and, moreover, deleterious to information processing. However, with this colloquium, we attempt to rebut this common view: By use of tailored models we demonstrate that phonons can be manipulated like electrons and photons can, thus enabling controlled heat transport. Moreover, we explain that phonons can be put to beneficial use to carry and...

Li, Nianbei; Ren, Jie; Wang, Lei; Zhang, Gang; Ha?nggi, Peter; Li, Baowen

2011-01-01

320

Phonon transmission through solid-liquid helium interfaces  

International Nuclear Information System (INIS)

The previously reported technique for measuring phonon emission at a solid/"4He boundary as a function of angle has been extended. A new technique is described whereby such angular measurements can be performed using superconducting tunnel junctions as frequency selective phonon detectors. Measurements of the angular emission from an atomically flat NaF sample into liquid "4He have been carried out using both bolometers and tunnel junctions as phonon detectors. (author)

1980-01-01

 
 
 
 
321

Sub-Poissonian phonon distributions in suspended carbon nanotubes  

Energy Technology Data Exchange (ETDEWEB)

We study a quantum dot embedded into a vibrating suspended carbon nanotube. The out-of-equilibrium dynamics of the vibrational degrees of freedom is analyzed introducing the phonon Fano factor F to characterize different phonon distributions. Sub-Poissonian distributions with F < 1 are found in selected transport regimes and are explained in terms of a selective population of phonon states due to a peculiar transport mechanism.

Piovano, G; Cavaliere, F; Sassetti, M, E-mail: giulia.piovano@gmail.co [Dipartimento di Fisica and CNR-SPIN, Universita di Genova, Via Dodecaneso 33, 16146 Genova (Italy)

2010-11-01

322

Isotopic effects on the phonon modes in boron carbide  

International Nuclear Information System (INIS)

The effect of isotopes (10B-11B; 12C-13C) on the infrared- and Raman-active phonons of boron carbide has been investigated. For B isotopes, the contributions of the virtual crystal approximation, polarization vector and isotopical disorder are separated. Boron and carbon isotope effects are largely opposite to one another and indicate the share of the particular atoms in the atomic assemblies vibrating in specific phonon modes. Some infrared-active phonons behave as expected for monatomic boron crystals.

2010-10-06

323

SU(6) limit of the quasiparticle-phonon nuclear model  

International Nuclear Information System (INIS)

Quasiparticle-phonon nuclear model is considered. It is shown that the Hamiltonian of the quasiparticle-phonon nuclear model has the SU(6) limit. Under some conditions this Hamiltonian can be represented as a rotational invariant which is constructed of the generators of the SU(6) algebra. The collective quadrupole random phase approximation phonon operators and their commutators form a closed algebra. The microscopic expressions for the parameters of the quadrupole phonon model are derived. The calculation of maximal numbers of bosons and the test of the conditions giving the SU(6) limit for some Zn isotopes have been performed

1985-01-01

324

Frictional drag between quantum wells mediated by phonon exchange  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We use the Kubo formalism to evaluate the contribution of acoustic-phonon exchange to the frictional drag between nearby two-dimensional electron systems. In the case of free phonons, we find a divergent drag rate (tau(D)(-l)). However, tau(D)(-l) becomes finite when phonon scattering from either lattice imperfections or electronic excitations is accounted for. In the case of GaAs quantum wells, we find that for a phonon mean free path l(ph) smaller than a critical value, imperfection scatter...

Bønsager, M. C.; Flensberg, Karsten; Hu, Ben Yu-kuang; Macdonald, A. H.

2006-01-01

325

Proposal for an Optomechanical Traveling Wave Phonon-Photon Translator  

CERN Document Server

In this article we describe a general optomechanical system for converting photons to phonons in an efficient, and reversible manner. We analyze classically and quantum mechanically the conversion process and proceed to a more concrete description of a phonon-photon translator formed from coupled photonic and phononic crystal planar circuits. Applications of the phonon-photon translator to RF-microwave photonics and circuit QED, including proposals utilizing this system for optical wavelength conversion, long-lived quantum memory and state transfer from optical to superconducting qubits are considered.

Safavi-Naeini, Amir H

2010-01-01

326

Trans-phonon effects in ultra-fast nanodevices  

International Nuclear Information System (INIS)

We report a novel phenomenon in carbon nanotube based ultra-fast mechanical devices, the trans-phonon effect, which resembles the transonic effects in aerodynamics. It is caused by dissipative resonance of nanotube phonons similar to the radial breathing mode, and subsequent drastic surge of the dragging force on the sliding tube, and multiple phonon barriers are encountered as the intertube sliding velocity reaches critical values. It is found that the trans-phonon effects can be tuned by applying geometric constraints or varying chirality combinations of the nanotubes

2008-06-25

327

Phonon bandgap engineering of strained monolayer MoS2.  

Science.gov (United States)

The phonon band structure of monolayer MoS2 is characteristic of a large energy gap between acoustic and optical branches, which protects the vibration of acoustic modes from being scattered by optical phonon modes. Therefore, the phonon bandgap engineering is of practical significance for the manipulation of phonon-related mechanical or thermal properties in monolayer MoS2. We perform both phonon analysis and molecular dynamics simulations to investigate the tension effect on the phonon bandgap and the compression induced instability of the monolayer MoS2. Our key finding is that the phonon bandgap can be narrowed by the uniaxial tension, and is completely closed at ? = 0.145; while the biaxial tension only has a limited effect on the phonon bandgap. We also demonstrate the compression induced buckling for the monolayer MoS2. The critical strain for buckling is extracted from the band structure analysis of the flexure mode in the monolayer MoS2 and is further verified by molecular dynamics simulations and the Euler buckling theory. Our study illustrates the uniaxial tension as an efficient method for manipulating the phonon bandgap of the monolayer MoS2, while the biaxial compression as a powerful tool to intrigue buckling in the monolayer MoS2. PMID:24932612

Jiang, Jin-Wu

2014-06-26

328

Zero-phonon linewidth and phonon satellites in the optical absorption of nanowire-based quantum dots  

CERN Multimedia

The optical properties of quantum dots embedded in a catalytically grown semiconductor nanowire are studied theoretically. In comparison to dots in a bulk environment, the excitonic absorption is strongly modified by the one-dimensional character of the nanowire phonon spectrum. Besides pronounced satellite peaks due to phonon-assisted absorption, we find a finite width of the zero-phonon line already in the lowest-order calculation.

Lindwall, G; Weber, C; Knorr, A; Lindwall, Greta; Wacker, Andreas; Weber, Carsten; Knorr, Andreas

2007-01-01

329

Phonon lineshapes in the vortex state of the phonon-mediated superconductor YNi$_2$B$_2$C  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present an inelastic neutron scattering study of phonon lineshapes in the vortex state of the type-II superconductor YNi$_2$B$_2$C. In a previous study [Phys. Rev. Lett. \\textbf{101}, 237002 (2008)] it was shown that certain phonons exhibit a clear signature of the superconducting gap $2\\Delta$ on entering the superconducting state. Our interest was to find out whether or not the lineshape of such phonons reflects the inhomogeneous nature of the vortex state induced by a ...

Weber, F.; Pintschovius, L.; Hradil, K.; Petitgrand, D.

2012-01-01

330

Non-equilibrium acoustic phonons in nanocrystalline ceramics based on C-modification of Y2O3 sesquioxide  

International Nuclear Information System (INIS)

The transport processes in highly transparent nanocrystalline laser-host ceramics based on C-modification of Y2O3 sesquioxide were investigated by the heat-pulse technique. The propagation kinetics of acoustic phonons was studied in the range of liquid helium temperature (1.7-3.8 K). A structural model for the grain boundary layers is suggested and their thickness is estimated. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

2005-08-01

331

Phonons in ZnTe/CdSe superlattices with interchange of cation layers across interfaces  

Energy Technology Data Exchange (ETDEWEB)

The ZnTe/CdSe superlattice is one of the wide-gap semiconductor superlattices grown successfully in recent years which have potential applications in blue-green diode lasers. There exists experimental evidence of interchange of entire atom layers across the interfaces of ZnTe/CdSe superlattices in spite of the resulting interface strain. First-principles pseudopotential calculations of the total energy of such systems confirmed the possibility of such interchanges. By using the combination of a first-principles pseudopotential method and an empirical method with parameters extracted from the available experimental data and pseudopotential calculations, we studied phonons in ZnTe/CdSe superlattices with interchange of atom layers across the interface. The results are compared with phonons in ZnTe/CdSe superlattices with ideal interfaces. Several unique features of phonon modes in superlattices with interchange of atomic layers across interfaces are identified and discussed. These results provide more information about interface structures in such heterostructures, and we hope that they will stimulate more experimental measurements in these materials. (author)

Xu Zhizhong; Dowd, H.; Ren Shangfen [Department of Physics, Illinois State University, Normal, IL (United States); Gu Zong Quan [State Key Laboratory for Surface Physics, Institute of Physics and Center for Condensed Matter Physics, Academia Sinica, Beijing (China)

1998-02-23

332

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

Science.gov (United States)

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

333

Waveguiding inside the complete band gap of a phononic crystal slab.  

Science.gov (United States)

The propagation of acoustic waves in a square-lattice phononic crystal slab consisting of a single layer of spherical steel beads in a solid epoxy matrix is studied experimentally. Waves are excited by an ultrasonic transducer and fully characterized on the slab surface by laser interferometry. A complete band gap is found to extend around 300 kHz, in good agreement with theoretical predictions. The transmission attenuation caused by absorption and band gap effects is obtained as a function of frequency and propagation distance. Well confined acoustic wave propagation inside a line-defect waveguide is further observed experimentally. PMID:18233776

Hsiao, Fu-Li; Khelif, Abdelkrim; Moubchir, Hanane; Choujaa, Abdelkrim; Chen, Chii-Chang; Laude, Vincent

2007-11-01

334

Optical gain by simultaneous photon and phonon confinement in indirect bandgap semiconductor acousto-optical cavities  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Optical gain that could ultimately lead to light emission from silicon is a goal that has been pursued for a long time by the scientific community. The reason is that a silicon laser would allow for the development of low-cost, high-volume monolithic photonic integrated circuits created using conventional CMOS technologies. However, the silicon indirect bandgap-requiring the participation of a proper phonon in the process of light emission-is a roadblock that has not been overcome so far. A h...

Escalante, Jose M.; Martinez, Alejandro

2013-01-01

335

Measurement of the Absolute Raman Cross Section of the Optical Phonons in Type Ia Natural Diamond  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The absolute Raman cross section \\(\\sigma_{RS}\\)of the first-order \\(1332-cm^{?1}\\) optical phonons in type Ia natural diamond was measured using 785- and 1064-nm pump lasers for the excitation of Raman scattering. A small temperature-controlled blackbody was used for the signal calibration of the 785- and 1064-nm Raman systems. Measurements were made with a 0.9-mm thick (111) natural diamond sample. Values of \\(2.7\\pm0.6×10^{?29}\\) and \\(0.95\\pm0.2×10^{?29} cm^2\\) per carbon atom wer...

2012-01-01

336

Probing LO phonons of graphene under tension via the 2D ' Raman mode  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We use ab initio simulations and perturbation theory to study the 2D' Raman mode of graphene subject to biaxial and uniaxial strains up to 2%. We demonstrate that 2D' Raman measurements, as a function of polarization and laser energy E-L, can probe the LO phonons of graphene with arbitrary radial and angular extent around Gamma. The 2D' profile is highly sensitive to uniaxial strain and depends on both polarization and strain orientation. The Gruneisen parameter gamma(2D') approximate to 1.71...

2013-01-01

337

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

338

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

2007-12-01

339

Quantum statistical properties of photon and phonon fields in degenerate hyper-Raman scattering  

International Nuclear Information System (INIS)

In this paper the complete normal quantum characteristic function is calculated in the short-time approximation for degenerate hyper-Raman scattering from which fluctuations in separate modes and correlations among these are deduced. The results are discussed from the view-point of anticorrelation or antibunching assuming that (i) the phonon mode is initially chaotic whereas all photon modes are initially coherent, and (ii) the laser mode is initially coherent and all other modes are initially chaotic. A comparison with non-degenerate hyper-Raman scattering and Raman scattering is made. (author)

1979-01-01

340

Phonon frequency spectrum in random binary alloys  

International Nuclear Information System (INIS)

Starting from the augmented space formalism (Mookerjee 1973 a,b), a cluster CPA calculation for the phonon density of states is presented for linear chains as well as three-dimensional lattices. Off-diagonal disorder has been taken into account, and a self-consistent medium has been generated. Unlike earlier work, the Green function does not suffer from analytical difficulties in any concentration range. At the same time, the self-consistent medium gives a superior estimate of the band edges and the structures near them. (author)

1979-01-01

 
 
 
 
341

Purely electronic zero phonon lines. Recent developments  

International Nuclear Information System (INIS)

The usefulness of zero-phonon lines (ZPL) in science and applications is pointed out. Two recent developments are considered: (1) Interference of a single photon emitted by a single impurity in solid host with (a) the excitation light; (b) itself. (2) The exciting consequences for ZPLs in science and applications, following from the discovery of very low lying (about 3.5 eV) excited ?-level in isomer of 229Th. Quite possible that transition from it may produce luminescence ('nuclear light') in blue. The possibility to create broad-band absorption-emission by means of Doppler shift and also burning of spectral holes is shown

2004-05-01

342

Light scattering by surface phonons in crystals  

International Nuclear Information System (INIS)

Theory of inelastic light scattering by surface acoustic phonons homogeneous crystals is presented. The Green functions are determined by the use of a classical linear response method and used to evaluate the Brillouin cross section. The acoustic modes are found from solutions to the acoustical-wave equation and boundary conditions appropriated. Two light-scattering mechanisms, amely the surface corrugation and bulk elasto-optic effect are analyzed by deriving optical fields which satisfy both the acousto-optically driven wave equation and the electromagnetic boundary conditions. No restrictions are imposed concerning the angle of incidence of the light. Some representative computed Brillouin ineshapes are also presented and their features discussed. (author)

1980-12-01

343

Spectroscopy of nonequilibrium electrons and phonons  

CERN Document Server

The physics of nonequilibrium electrons and phonons in semiconductors is an important branch of fundamental physics that has many practical applications, especially in the development of ultrafast and ultrasmall semiconductor devices. This volume is devoted to different trends in the field which are presently at the forefront of research. Special attention is paid to the ultrafast relaxation processes in bulk semiconductors and two-dimensional semiconductor structures, and to their study by different spectroscopic methods, both pulsed and steady-state. The evolution of energy and space distrib

Shank, CV

1992-01-01

344

Quantum Measurement of Phonon Shot Noise  

CERN Multimedia

We provide a full quantum mechanical analysis of a weak energy measurement of a driven mechanical resonator. We demonstrate that measurements too weak to resolve individual mechanical Fock states can nonetheless be used to unambiguously detect the non-classical energy fluctuations of the driven mechanical resonator, i.e. "phonon shot noise". We also show that the third moment of the oscillator's energy fluctuations provides a far more sensitive probe of quantum effects than the second moment, and that measuring the third moment via the phase shift of light in an optomechanical setup directly yields the type of operator ordering postulated in the theory of full-counting statistics.

Clerk, Aashish; Harris, Jack

2010-01-01

345

Phonons, electronic charge response and electron-phonon interaction in the high-temperature superconductors  

International Nuclear Information System (INIS)

We investigate the complete phonon dispersion, the phonon induced electronic charge response and the corresponding self-consistent change of the crystal potential an electron feels as a direct measure of the electron-phonon interaction in the high-temperature superconductors within a microscopic model in the framework of linear response theory. Moreover, dielectric and infrared properties are calculated. The experimentally observed strong renormalization of the in-plane oxygen bond-stretching modes which appears upon doping in the high-temperature superconductors is discussed. It is shown that the characteristic softening, indicating a strong nonlocal electron-phonon interaction, is most likely a generic effect of the CuO plane and is driven by a nonlocal coupling of the displaced ions to the localized charge-fluctuations at the Cu and the Oxy ions. At hand of the oxygen bond-stretching modes it is illustrated how lattice-, charge- and spin-degrees of freedom may act synergetically for anisotropic pairing in the high-temperature superconductors. The different behaviour of these modes during the insulator-metal transition via the underdoped phase is calculated and from a comparison of these generic modes in the different phases conclusions about the electronic state are drawn. For the non-cuprate potassium doped high-temperature superconductor Ba-Bi-O also a very strong and anisotropic renormalization of the oxygen bond-stretching modes is predicted. In another investigation c-axis polarized infrared- and Raman-active modes of the HTSC's are calculated in terms of charge fluctuations and anisotropic dipole-fluctuations. Mode assignments discussed controversially in the literature are proposed. Finally, interlayer phonons propagating along the c-axis and their accompanying charge response are investigated. Depending on the strength of the interlayer coupling calculations are performed ranging from the static, adiabatic response regime to the non-adiabatic regime where dynamical screening of the bare Coulomb interaction and phonon-plasmon coupling becomes relevant within a certain region around the direction of the c-axis. A comparison with the experimental situation is given. Both, the oxygen bond-stretching modes calculated in adiabatic approximation and the non-adiabatic coupled c-axis phonon-plasmon modes are found to be important for pairing via lattice- and charge-degrees of freedom. Favouring aspects to achieve high-temperature superconductivity are also discussed. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

2005-01-01

346

Reflector switched lasers  

Energy Technology Data Exchange (ETDEWEB)

This patent describes an improvement in a laser of the type including a continuous lasing medium, an adjustable mirror which, when properly aligned with the optical axis of the lasing medium, enables laser action and means for continuously exciting the lasing medium. The improvement comprises: means for switching the laser between on and off states including: electromagnetic means for changing the angle of the mirror between an aligned condition in which laser action takes place and a misaligned condition in which laser action is suppressed.

Wojnarowski, R.J.; Eichelberger, C.W.

1991-05-21

347

YCOB lasers  

Energy Technology Data Exchange (ETDEWEB)

We review new developments with a new laser host material, YCa{sub 4}O(BO{sub 3}){sub 3} or YCOB. Lasers based on this host material will open new opportunities for the development of compact, high-power, frequency-agile visible and near IR laser sources, as well as sources for ultrashort pulses. Efficient diode-pumped laser action with both Nd-doped and Yb-doped YCOB has already been demonstrated. Moreover, since these materials are biaxial, and have high nonlinear optical coefficients, they have become the first laser materials available as efficient self-frequency-doubled lasers, capable of providing tunable laser emission in several regions of the visible spectrum. Self-frequency doubling eliminates the need for inclusion of a nonlinear optical element within or external to the laser resonator. These laser materials possess excellent thermal and optical properties, have high laser-damage thresholds, and can be grown to large sizes. In addition they are non-hygroscopic. They therefore possess all the characteristics necessary for laser materials required in rugged, compact systems. Here we summarize the rapid progress made in the development of this new class of lasers, and review their potential for a number of applications. (author)

Richardson, Martin; Hammons, Dennis; Eichenholz, Jason [Laser Energetics inc., Oviedo (United States); Chai, Bruce [Crystal Photonics Inc., Sandford (United States); Ye, Qing [Corning Research Laboratories, Corning (United States); Jang, Won [Hanseo University, Seosan (Korea, Republic of); Shah, Lawrence [University of Central Florida, Orlando (United States)

1999-07-01

348

Cooling carbon nanotubes to the phononic ground state with constant electron current  

CERN Multimedia

We present a quantum theory of cooling of a mechanical resonator using back-action with constant electron current. The resonator device is based on a doubly clamped nanotube, which mechanically vibrates and acts as a double quantum dot for electron transport. Mechanical vibrations and electrons are coupled electrostatically using an external gate. The fundamental eigenmode is cooled by absorbing phonons when electrons tunnel through the double quantum dot. We identify the regimes in which ground state cooling can be achieved for realistic experimental parameters.

Zippilli, Stefano; Bachtold, Adrian

2008-01-01

349

Variational Monte Carlo method for electron-phonon coupled systems  

Science.gov (United States)

We develop a variational Monte Carlo (VMC) method for electron-phonon coupled systems. The VMC method has been extensively used for investigating strongly correlated electrons over the last decades. However, its applications to electron-phonon coupled systems have been severely restricted because of its large Hilbert space. Here, we propose a variational wave function with a large number of variational parameters, which is suitable and tractable for systems with electron-phonon coupling. In the proposed wave function, we implement an unexplored electron-phonon correlation factor, which takes into account the effect of the entanglement between electrons and phonons. The method is applied to systems with diagonal electron-phonon interactions, i.e., interactions between charge densities and lattice displacements (phonons). As benchmarks, we compare VMC results with previous results obtained by the exact diagonalization, the Green function Monte Carlo method and the density matrix renormalization group for the Holstein and Holstein-Hubbard model. From these benchmarks, we show that the present method offers an efficient way to treat strongly coupled electron-phonon systems.

Ohgoe, Takahiro; Imada, Masatoshi

2014-05-01

350

Emission of Phonons from a Rotating Sonic Black Hole  

Science.gov (United States)

We investigate the Hawking radiation from a rotating acoustic black hole. The phonon emission is calculated by using two methods and the same results are obtained. The contribution of the time coordinate to the phonon radiation is also discussed, which cannot be ignored for the coordinate systems that are not well-behaved at the horizon.

Fang, Heng-Zhong; Zhou, Kai-Hu

2014-01-01

351

Double-[gamma] phonon excitation in the Os nuclei  

Energy Technology Data Exchange (ETDEWEB)

We investigate double-[gamma] phonon excitation in the Os nuclei within the framework of the proton-neutron Interacting Boson Model (IBM-2). We decompose the IBM-2 wave-functions into multiphonon states, and see the contributions of zero, one and two phonon components in the low lying levels of the Os nuclei. (orig.)

Sugita, M. (Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan)); Otsuka, T. (Dept. of Physics, Univ. of Tokyo (Japan))

1993-05-31

352

PHONON MECHANISM OF THE MAGNETOVOLUME EFFECT IN ITINERAN ELECTRON FERROMAGNETS  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We show the possibility of having a negative phonon Grüneisen constant in the ferromagnetic state of a metal. With such behavior of Grüneisen constant, we propose phonons can be playing an important role in causing zero or negative thermal volume expansion often observed in ferromagnetic metals.

Kim, D.

1988-01-01

353

Multiple interruption of optically generated acoustic phonons in ruby  

International Nuclear Information System (INIS)

This thesis clarifies the rate-determining processes which tend to equilibrate the bottlenecked 29 cm"-"1 phonons with the temperature bath in stationary experiments. In addition, the direct relaxation between the Zeeman components of E is measured, revealing at high pumping, both continuous and time-resolved, a strong phonon bottleneck. (Auth.)

1979-01-01

354

Phonons and charge-transfer excitations in HTS superconductors  

International Nuclear Information System (INIS)

Some of the experimental and theoretical evidence implicating phonons and charge-transfer excitations in HTS superconductors is reviewed. It is suggested that superconductivity may be driven by a synergistic interplay of (anharmonic) phonons and electronic degrees of freedom (e.g., charge fluctuations, excitons). 47 refs., 5 figs

1989-07-04

355

Raman-Active Phonons in Aluminum, Gallium, and Iron Garnets.  

Science.gov (United States)

The Raman-active phonons in eight different aluminum, gallium, and iron garnet crystals have been investigated. The energies and symmetries of phonons in YbAlG, YbGaG, LuAlG, and LuGaG, as well as DyIG, ErIg, YbIG, and YIG, have been determined. Owing to ...

J. J. Song M. Selders P. B. Klein R. L. Wadsack S. Mroczkowski

1973-01-01

356

Quasiparticle-phonon coupling in inelastic proton scattering  

International Nuclear Information System (INIS)

Multistep-processes in inelastic proton scattering from "8"9Y are analyzed by using CCBA and DWBA on a quasiparticle phonon nuclear structure model. Indirect excitations caused by quasiparticle phonon coupling effects are found to be very important for the transition strengths and the shape of angular distributions. Core excitations are dominant for the higher order steps of the reaction. (author)

1980-01-01

357

Phonon-pumped nonequilibrium states in superfluid 3He  

International Nuclear Information System (INIS)

The authors consider stationary nonequilibrium states induced in the superfluid phases of 3He by phonon pumping at frequencies lower than the average pair-binding energy and far from the resonances of the collective triplet-condensate modes. The kinematic exclusion of the phonon single-particle absorption channel in He-3 interferes with the simulation mechanism known from superconductivity physics. Superfluidity can nonetheless be stimulated by phonon-absorption events in which several Fermi excitations participate. The calculations are performed for both the B and A phases of He-3. For the latter, account is taken of competing production of excess excitations by phonons via direct condensate-pair breaking. The stimulation is found to predominate at low frequencies, so that phonon emission can induce an A-B phase transition

1989-04-01

358

One-phonon excitations in 92Zr from electron scattering  

International Nuclear Information System (INIS)

Low-lying collective vibrational excitations of 92Zr have been investigated with electron scattering at the S-DALINAC. The form factors of isospin polarized one-quadrupole phonon states of 92Zr at the Z = 40 proton subshell closure have been measured and the momentum-transfer dependence of the form factors for the one-quadrupole phonon states have been compared to the prediction of the Quasiparticle Phonon Model. The E2 transition strengths of the one-quadrupole phonon states and the E3 transition strength of the one-octupole phonon state have been extracted. A comparison to the data on 94Mo and previous spectroscopic information on mixed-symmetric states (MSSs) of 92Zr will be given.

2010-01-01

359

Surface anharmonicity: Temperature dependence of phonon energies on Cu(110)  

International Nuclear Information System (INIS)

The temperature dependence of surface phonons on Cu(110) has been determined with high resolution electron energy loss spectroscopy between 21 and 766 K. Phonons at bar ? and at bar Y, both with atomic motion perpendicular to the surface, have been examined to assess the importance of anharmonicity at the surface. As the temperature is increased the observed phonon energies decrease and the linewidths increase. The same percentage decrease is observed at bar ? and bar Y. A simple model using an anharmonic potential can reproduce the magnitude and shape of the temperature dependence of the phonon at bar ?. Direct comparison with bulk phonon studies shows that the anharmonicity at the surface is 4.1--4.8 times greater. 18 refs., 5 figs

1990-09-10

360

Phonon localization drives polar nanoregions in a relaxor ferroelectric.  

Science.gov (United States)

Relaxor ferroelectrics exemplify a class of functional materials where interplay between disorder and phase instability results in inhomogeneous nanoregions. Although known for about 30 years, there is no definitive explanation for polar nanoregions (PNRs). Here we show that ferroelectric phonon localization drives PNRs in relaxor ferroelectric PMN-30%PT using neutron scattering. At the frequency of a preexisting resonance mode, nanoregions of standing ferroelectric phonons develop with a coherence length equal to one wavelength and the PNR size. Anderson localization of ferroelectric phonons by resonance modes explains our observations and, with nonlinear slowing, the PNRs and relaxor properties. Phonon localization at additional resonances near the zone edges explains competing antiferroelectric distortions known to occur at the zone edges. Our results indicate the size and shape of PNRs that are not dictated by complex structural details, as commonly assumed, but by phonon resonance wave vectors. This discovery could guide the design of next generation relaxor ferroelectrics. PMID:24718289

Manley, M E; Lynn, J W; Abernathy, D L; Specht, E D; Delaire, O; Bishop, A R; Sahul, R; Budai, J D

2014-01-01

 
 
 
 
361

Carrier dynamics and coherent acoustic phonons in nitride heterostructures  

CERN Document Server

We model generation and propagation of coherent acoustic phonons in piezoelectric InGaN/GaN multi-quantum wells embedded in a \\textit{pin} diode structure and compute the time resolved reflectivity signal in simulated pump-probe experiments. Carriers are created in the InGaN wells by ultrafast pumping below the GaN band gap and the dynamics of the photoexcited carriers is treated in a Boltzmann equation framework. Coherent acoustic phonons are generated in the quantum well via both deformation potential electron-phonon and piezoelectric electron-phonon interaction with photogenerated carriers, with the latter mechanism being the dominant one. Coherent longitudinal acoustic phonons propagate into the structure at the sound speed modifying the optical properties and giving rise to a giant oscillatory differential reflectivity signal. We demonstrate that coherent optical control of the differential reflectivity can be achieved using a delayed control pulse.

Sanders, G D

2006-01-01

362

Phonon studies of energy loss in vertical tunnelling structures  

International Nuclear Information System (INIS)

The energy loss of hot electrons in double barrier resonant tunnelling structures has been studied using nanosecond phonon pulses. Two symmetric devices were studied, fabricated from GaAs/AlGaAs heterostructures, grown by M.B.E. on (100) semi-insulating GaAs substrates. The devices had heavily doped collector regions, AlGaAs barriers and undoped quantum wells. The phonon detectors used were thin film aluminium bolometers, operated on the edge of the superconducting transition. A new technique was developed to determine the temperature excursion of the bolometer from the measured phonon signals. The phonon data displays evidence of two energy loss mechanisms. At low electron energies, the phonon data confirms previous work and shows that the energy loss of hot electrons in heavily doped GaAs is primarily due to the excitation of plasmon-optic phonon coupled modes. The ballistic TA phonon signal arises from the decay of the coupled mode cascade and the LA phonon signal from the direct heating of the Fermi gas in the collector of the device. At higher electron energies, the phonon data shows evidence of ? to L and L to L intervalley scattering. New LA data is shown to be due purely to the intervalley transfer and onset energies for this process have been measured. Simple expressions for the rates of energy loss due to coupled mode emission and intervalley scattering have been used to estimate both the intervalley deformation potential coupling constant D?L and the lifetime of coupled modes at a particular incident electron energy. The consistency of the answers gives great confidence in the validity of the above interpretation of the phonon data. (author)

1998-01-01

363

Search for the 3-phonon state of 40Ca  

International Nuclear Information System (INIS)

We study collective vibrational states of the nucleus: giant resonances and multiphonon states. It has been shown that multiphonon states, which are built with several superimposed giant resonances, can be excited in inelastic heavy ion scattering near the grazing angle. No three photon states have been observed until now. An experiment has been performed at GANIL, aiming at the observation of the 3-phonon state built with the giant quadrupole resonance (GQR) in 40Ca, with the reaction 40Ca + 40Ca at 50 A.Me.V. The ejectile was identified in the SPEG spectrometer. Light charged particles were detected in 240 CsI scintillators of the INDRA 4? array. The analysis confirms the previous results about the GQR and the 2-phonon state in 40Ca. For the first time, we have measured an important direct decay branch of the GQR by alpha particles. Applying the so-called 'missing energy method' to events containing three protons measured in coincidence with the ejectile, we observe a direct decay branch revealing the presence of a 3-phonon state in the excitation energy region expected for the triple GQR. Dynamical processes are also studied in the inelastic channel, emphasizing a recently discovered mechanism named towing-mode. We observe for the first time the towing-mode of alpha particles. The energies of multiphonon states in 40Ca and 208Pb have been computed microscopically including some anharmonicities via boson mapping methods. The basis of the calculation has been extended to the 3-phonon states. Our results show large anharmonicities (several MeV), due to the coupling of 3-phonon states to 2-phonon states. The extension of the basis to 4-phonon states has been performed for the first time. The inclusion of the 4 phonon states in the calculation did not affect the previous observations concerning the 2-phonon states. Preliminary results on the anharmonicities of the 3-phonon states are presented. (author)

2002-01-01

364

On the problem of local tissue hyperthermia control: multiscale modelling of pulsed laser radiation action on a medium with embedded nanoparticles  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Methods for solving analytically and numerically the problem of multiscale modelling of the laser hyperthermia processes in a medium with nanoparticles are developed with regard to composite spherical nanoparticles (nanoshells). The features of the laser radiation field localisation on nanoscale inhomogeneities are investigated. Issues related to the control of the tissue hyperthermia processes by choosing the parameters of spatiotemporal localisation of the laser beam and of the absorbing na...

2010-01-01

365

Quasi-Bound Exiton-LO Phonon Intermediate State in Multi-Phonon Raman Scattering of Semiconductors.  

Science.gov (United States)

A new model is proposed to understand multi-phonon Raman spectrum (MRS) of II-VI semiconductors. A quasibound state of exciton-LO phonon complex (EPQBS) in the intermediate state is shown to be responsible for the observed overtone series. The observation...

K. P. Jain C. S. Jayanthi

1982-01-01

366

Ultraviolet photon absorption in single- and double-wall carbon nanotubes and peapods: Heating-induced phonon line broadening, wall coupling, and transformation  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Ultraviolet photon absorption has been used to heat single- and double-wall carbon nanotubes and peapods in vacuum. By increasing the laser intensity up to 500 mW, a downshift and a broadening of the optical phonons are observed corresponding to a temperature of 1000°C. The UV Raman measurements are free of blackbody radiation. We find that the linewidth changes for the G+ and G? bands differ considerably in single-wall carbon nanotubes. This gives evidence that the phonon decay process is...

Puech, Pascal; Puccianti, Frederic; Bacsa, Revathi; Arrondo, Ce?cile; Paillard, Vincent; Bassil, Ayman; Monthioux, Marc; Flahaut, Emmanuel; Barde?, Fanny; Bacsa, Wolfgang

2007-01-01

367

Phonon Absorption Experiments on Composite Fermions  

Science.gov (United States)

We present a time-resolved phonon absorption technique as an efficient tool to investigate the properties of the fractional quantum Hall effect (FQHE). We interpret our data within the Composite Fermion (CF) picture of the FQHE, were the CF quasiparticles are constructed by attaching two magnetic flux quanta ?0 to each electron. As a result, the CFs at filling factor ? and electron density n experience only an reduced magnetic field B^* = B - 2 ?0n, so that they behave in B^* in analogy to electrons in the magnetic field B and form Landau levels of CFs with effective filling factor p = ?1-2? in particular. In a first set of experiments, we measure phonon excitation gaps in the FQH regime for various filling factors and find that the measured gaps can be well described in the framework of Landau-level transitions of CFs involving no spin flip [1]. We are able to deduce the CF mass m^*(10 T) = 0,5m0 from these transitions. We apply the same model to energy gaps which we deduce from transport experiments. These gaps are transitions from one level to another reduced by disorder. Here, spin flip are allowed. From results near the crossing of two levels, we were able to deduce the g-factor of CFs [2]. A second set of phonon absorption experiments focuses on the specific heat C of the 2DES at various filling factors ? [3]. Here, we find an exponential dependence C (1/T)^2 exp(-?/T) on temperature T if the 2DES is in a state with an energy gap ?. At ?= 1/2, where the external magnetic field is fully cancelled by the gauge field, we find a linear temperature dependence as expected for a Fermi sea of CFs. *F. Schulze-Wischeler, F. Hohls, U. Zeitler, D. Reuter, A. D. Wieck, and R. J. Haug, Phys. Rev. Lett. 93, 026801 (2004). *F. Schulze-Wischeler, E. Mariani, F. Hohls, and R. J. Haug, Phys. Rev. Lett. 92, 156401 (2004). *F. Schulze-Wischeler et al., to be published in 2006.

Schulze-Wischeler, Fritz

2006-03-01

368

Transmission characteristics of the kinematics of the high power laser-plasma wave in solid under compton scattering  

International Nuclear Information System (INIS)

Using the model of inelastic scattering between electron and photon-groups, we have studied in the frame of quantum mechanics the transmission characteristics of the kinematics of the coupling laser-plasma wave, this is formed by the scattered light, the incident light, the electron vibration radiation wave and the high frequency branch of ILOTW (ion long optics transverse wave) in solid under nonlinear Compton scattering. The results show that the transmission velocity of the electromagnetism coupling phonon in the laser-plasma in the sold is raised along with the increase of the magnetic field intensity, the decrease of the electron screening action and the decrease of the plasma vibration frequency. But this increase of transmission velocity is resisted by the scattering light, and will be slowly reduced. (authors)

2008-12-01

369

Phonons and electron-phonon coupling in YNi2B2C  

Science.gov (United States)

We present a combined density functional perturbation theory and inelastic neutron scattering study of the lattice dynamical properties of YNi2B2C. In general, very good agreement was found between theory and experiment for both phonon energies and line widths. Our analysis reveals that the strong coupling of certain low energy modes is linked to the presence of large displacements of the light atoms, i.e., B and C, which is unusual in view of the rather low phonon energies. Specific modes exhibiting a strong coupling to the electronic quasiparticles were investigated as a function of temperature. Their energies and line widths showed marked changes on cooling from room temperature to just above the superconducting transition at Tc = 15.2 K. Calculations simulating the effects of temperature allow us to model the observed temperature dependence qualitatively.

Weber, F.; Pintschovius, L.; Reichardt, W.; Heid, R.; Bohnen, K.-P.; Kreyssig, A.; Reznik, D.; Hradil, K.

2014-03-01

370

Phonon-phonon interactions due to non-linear effects in a linear ion trap  

CERN Document Server

We examine in detail the theory of the intrinsic non-linearities in the dynamics of trapped ions due to the Coulomb interaction. In particular the possibility of mode-mode coupling, which can be a source of decoherence in trapped ion quantum computation, or, alternatively, can be exploited for parametric down-conversion of phonons, is discussed and conditions under which such coupling is possible are derived.

Marquet, C; James, D F V; Marquet, Cyrille; Schmidt-Kaler, Ferdinand; James, Daniel F. V.

2002-01-01

371

Application of MIR-FEL irradiation to selectively excite phonons in wide-gap semiconductors  

Energy Technology Data Exchange (ETDEWEB)

A mid-infrared free electron laser (MIR-FEL) (5 - 20 {mu}m) facility (KU-FEL: Kyoto University Free Electron Laser) was constructed to aid various energy science researchers at the Institute of Advanced Energy, Kyoto University. In May 2008, the first power saturation at 13.2 {mu}m was achieved. A pilot application to evaluate selective phonon excitation processes in solid materials by irradiating with MIR-FEL was implemented, and a preliminary experiment without FEL irradiation was conducted. N-doped silicon carbide (SiC) was selected as a sample material due to its unique electrical property where the lattice vibration and the electronic structure are coupled. Two peaks, 1.8 - 2.2 eV and 2.4 - 2.8 eV, which showed strong temperature dependences in both their intensities and peak energies, were observed. These tendencies could be explained by using a donor-acceptor pair luminescence (DAP) model with impurity and defects in the SiC sample. The results imply that we can verify selective phonon excitation by investigating the change in the PL spectrum introduced by MIR-FEL irradiation.

Yoshida, K.; Sonobe, T.; Bakr, M. A. [Kyoto University, Kyoto (Japan); and others

2011-11-15

372

The phonon theory of liquid thermodynamics  

CERN Multimedia

Heat capacity of matter is considered to be its most important property because it holds information about system's degrees of freedom as well as the regime in which the system operates, classical or quantum. Heat capacity is well understood in gases and solids but not in the third state of matter, liquids, and is not discussed in physics textbooks as a result. The perceived difficulty is that interactions in a liquid are both strong and system-specific, implying that the energy strongly depends on the liquid type and that, therefore, liquid energy can not be calculated in general form [1]. Here, we develop a phonon theory of liquids where this problem is avoided. We demonstrate good agreement of calculated heat capacity of important monatomic, molecular and hydrogen-bonded network liquids such as H2O in a wide range of pressure and temperature.

Bolmatov, Dima; Trachenko, Kostya

2012-01-01

373

Phonon assisted IR spectroscopy of quantum antiferromagnets  

Energy Technology Data Exchange (ETDEWEB)

The authors review resent theoretical results for multimagnon-phonon assisted infrared absorption in antiferromagnetic Heisenberg systems. They show spin wave theory line shapes for 2D spin 1/2 systems (like the parent insulating high-Tc cuprates) 1D spin 1/2 systems and 2D spin 1 systems (like the nickelates) and exact diagonalization results in two-dimensional spin 1/2 systems. The theoretical line shapes are compared with experiments. In the case of the cuprates they explain mid-infrared peaks observed in the insulator. In the case of the nickelates a predicted line shape is also shown to agree with the experiments. They discuss the possibility to observe this excitations in other experiments.

Lorenzana, J. [CE de Saclay, Gif-sur-Yvette (France). Lab. Leon Brillouin; Eder, R.; Sawatzky, G.A. [Univ. of Groningen (Netherlands). Lab. of Applied and Solid State Physics

1996-12-31

374

Phonon spectral function of the Holstein polaron  

International Nuclear Information System (INIS)

The phonon spectral function of the one-dimensional Holstein model is obtained within weak-coupling and strong-coupling approximations based on analytical self-energy calculations. The characteristic excitations found in the limit of small charge-carrier density are related to the known (electronic) spectral properties of Holstein polarons such as the polaron band dispersion. Particular emphasis is laid on the different physics occurring in the adiabatic and anti-adiabatic regimes, respectively. Comparison is made with a cluster approach exploiting exact numerical results on small systems to yield an approximation for the thermodynamic limit. This method, similar to cluster perturbation theory, confirms the analytical findings, and also yields accurate results in the intermediate-coupling regime

2006-08-09

375

Intermediate Exciton-Phonon Coupling in Tetracene  

Science.gov (United States)

Polarized absorption spectra of tetracene (naphthacene) single crystals have been investigated between 300 and 13 K, with particular emphasis on the b-polarized spectrum. The low energy tails of the a- and b-polarized first absorption bands are expressed by the Urbach rule with the steepness coefficients ?a'{=}1.37± 0.12, ?b'{=}1.58± 0.13, with which possibility of self-trapping of excitons is discussed along with the dimensionality of tetracene crystals. The exciton-phonon coupling constants are found to be ga{=}1.09± 0.1 and gb{=}0.95± 0.08, consistent with luminescence experiments which show that excitons in tetracene are self-trapped very shallowly. The line halfwidth, the oscillator strength of the first and the second absorption bands, refractive indices, and surface exciton structure are briefly discussed.

Mizuno, Kenichi; Matsui, Atsuo; Sloan, G. J.

1984-08-01

376

Cavity-type hypersonic phononic crystals  

International Nuclear Information System (INIS)

We report on the engineering of the phonon dispersion diagram in monodomain anodic porous alumina (APA) films through the porosity and physical state of the material residing in the nanopores. Lattice symmetry and inclusion materials are theoretically identified to be the main factors which control the hypersonic acoustic wave propagation. This involves the interaction between the longitudinal and the transverse modes in the effective medium and a flat band characteristic of the material residing in the cavities. Air and filled nanopores, therefore, display markedly different dispersion relations and the inclusion materials lead to a locally resonant structural behavior uniquely determining their properties under confinement. APA films emerge as a new platform to investigate the rich acoustic phenomena of structured composite matter. (paper)

2012-11-01

377

Point source in a phononic grating: stop bands give rise to phonon-focusing caustics  

International Nuclear Information System (INIS)

We use locally-excited gigahertz surface phonon wavepackets in microscopic line structures of different pitches to reveal profound anisotropy in the radiation pattern of a point source in a grating. Time-domain data obtained by an ultrafast optical imaging technique and by numerical simulations are Fourier transformed to obtain frequency-filtered real-space acoustic field patterns and k-space phononic band structure. The numerically-obtained k-space images are processed to reveal an intriguing double-horn structure in the lowest-order group-velocity surface, which explains the observed non-propagation sectors bounded by caustics, noted at frequencies above the bottom of the first stop band. We account for these phonon-focusing effects, analogous to collimation effects previously observed in two- and three-dimensional lattices, with a simple analytical model of the band structure based on a plane wave expansion. As the frequency is increased, a transition to dominant waveguiding effects along the lines is also documented. (paper)

2012-12-01

378

Thermal diffusivity of electrical insulators at high temperatures: Evidence for diffusion of bulk phonon-polaritons at infrared frequencies augmenting phonon heat conduction  

Science.gov (United States)

We show that laser-flash analysis measurements of the temperature (T) dependence of thermal diffusivity (D) for diverse non-metallic (e.g., silicates) single-crystals is consistently represented by D(T) = FT-G + HT above 298 K, with G ranging from 0.3 to 2, depending on structure, and H being ˜10-4 K-1 for 51 single-crystals, 3 polycrystals, and two glasses unaffected by disorder or reconstructive phase transitions. Materials exhibiting this behavior include complex silicates with variable amounts of cation disorder, perovskite structured materials, and graphite. The high-temperature term HT becomes important by ˜1300 K, above which temperature its contribution to D(T) exceeds that of the FT-G term. The combination of the FT-G and HT terms produces the nearly temperature independent high-temperature region of D previously interpreted as the minimal phonon mean free path being limited by the finite interatomic spacing. Based on the simplicity of the fit and large number of materials it represents, this finding has repercussions for high-temperature models of heat transport. One explanation is that the two terms describing D(T) are associated with two distinct microscopic mechanisms; here, we explore the possibility that the thermal diffusivity of an electrical insulator could include both a contribution of lattice phonons (the FT-G term) and a contribution of diffusive bulk phonon-polaritons (BPP) at infrared (IR) frequencies (the HT term). The proposed BPP diffusion exists over length scales smaller than the laboratory sample sizes, and transfers mixed light and vibrational energy at a speed significantly smaller than the speed of light. Our diffusive IR-BPP hypothesis is consistent with other experimental observations such as polarization behavior, dependence of D on the number of IR peaks, and H = 0 for Ge and Si, which lack IR fundamentals. A simple quasi-particle thermal diffusion model is presented to begin understanding the contribution from bulk phonon-polaritons to overall heat conduction.

Hofmeister, Anne M.; Dong, Jianjun; Branlund, Joy M.

2014-04-01

379

Deformation Electron-Phonon Coupling in Disordered Semiconductors and Nanostructures  

CERN Multimedia

We study the electron-phonon relaxation (dephasing) rate in disordered semiconductors and low-dimensional structures. The relaxation is determined by the interference of electron scattering via the deformation potential and elastic electron scattering from impurities and defects. We have found that in contrast to the destructive interference in metals, which results in the Pippard ineffectiveness condition for the electron-phonon interaction, the interference in semiconducting structures substantially enhances the effective electron-phonon coupling. The obtained results provide an explanation to energy relaxation in silicon structures.

Sergeev, A; Mitin, V

2005-01-01

380

Phonon Quasidiffusion in Cryogenic Dark Matter Search Large Germanium Detectors  

Energy Technology Data Exchange (ETDEWEB)

We present results on quasidiffusion studies in large, 3 inch diameter, 1 inch thick [100] high purity germanium crystals, cooled to 50 mK in the vacuum of a dilution refrigerator, and exposed with 59.5 keV gamma-rays from an Am-241 calibration source. We compare data obtained in two different detector types, with different phonon sensor area coverage, with results from a Monte Carlo. The Monte Carlo includes phonon quasidiffusion and the generation of phonons created by charge carriers as they are drifted across the detector by ionization readout channels.

Leman, S.W.; /MIT, MKI; Cabrera, B.; /Stanford U., Phys. Dept.; McCarthy, K.A.; /MIT, MKI; Pyle, M.; /Stanford U., Phys. Dept.; Resch, R.; /SLAC; Sadoulet, B.; Sundqvist, K.M.; /LBL, Berkeley; Brink, P.L.; Cherry, M.; /Stanford U., Phys. Dept.; Do Couto E Silva, E.; /SLAC; Figueroa-Feliciano, E.; /MIT, MKI; Mirabolfathi, N.; Serfass, B.; /UC, Berkeley; Tomada, A.; /Stanford U., Phys. Dept.

2012-06-04

 
 
 
 
381

Proposal for an optomechanical traveling wave phonon-photon translator  

Energy Technology Data Exchange (ETDEWEB)

In this paper, we describe a general optomechanical system for converting photons to phonons in an efficient and reversible manner. We analyze classically and quantum mechanically the conversion process and proceed to a more concrete description of a phonon-photon translator (PPT) formed from coupled photonic and phononic crystal planar circuits. The application of the PPT to RF-microwave photonics and circuit QED, including proposals utilizing this system for optical wavelength conversion, long-lived quantum memory and state transfer from optical to superconducting qubits, is considered.

Safavi-Naeini, Amir H; Painter, Oskar, E-mail: safavi@caltech.edu, E-mail: opainter@caltech.edu [Thomas J Watson, Sr., Laboratory of Applied Physics, California Institute of Technology, Pasadena, CA 91125 (United States)

2011-01-15

382

Proposal for an optomechanical traveling wave phonon-photon translator  

International Nuclear Information System (INIS)

In this paper, we describe a general optomechanical system for converting photons to phonons in an efficient and reversible manner. We analyze classically and quantum mechanically the conversion process and proceed to a more concrete description of a phonon-photon translator (PPT) formed from coupled photonic and phononic crystal planar circuits. The application of the PPT to RF-microwave photonics and circuit QED, including proposals utilizing this system for optical wavelength conversion, long-lived quantum memory and state transfer from optical to superconducting qubits, is considered.

2011-01-01

383

Bloch oscillations of THz acoustic phonons in coupled nanocavity structures.  

Science.gov (United States)

Nanophononic Bloch oscillations and Wannier-Stark ladders have been recently predicted to exist in specifically tailored structures formed by coupled nanocavities. Using pump-probe coherent phonon generation techniques we demonstrate that Bloch oscillations of terahertz acoustic phonons can be directly generated and probed in these complex nanostructures. In addition, by Fourier transforming the time traces we had access to the proper eigenmodes in the frequency domain, thus evidencing the related Wannier-Stark ladder. The observed Bloch oscillation dynamics are compared with simulations based on a model description of the coherent phonon generation and photoelastic detection processes. PMID:20866997

Lanzillotti-Kimura, N D; Fainstein, A; Perrin, B; Jusserand, B; Mauguin, O; Largeau, L; Lemaître, A

2010-05-14

384

Observation of phonons with resonant inelastic x-ray scattering  

International Nuclear Information System (INIS)

Phonons, the quantum mechanical representation of lattice vibrations, and their coupling to the electronic degrees of freedom are important for understanding thermal and electric properties of materials. For the first time, phonons have been measured using resonant inelastic x-ray scattering (RIXS) across the Cu K-edge in cupric oxide (CuO). Analyzing these spectra using an ultra-short core-hole lifetime approximation and exact diagonalization techniques, we can explain the essential inelastic features. The relative spectral intensities are related to the electron-phonon coupling strengths.

2010-12-08

385

Observation of phonons with resonant inelastic x-ray scattering.  

Science.gov (United States)

Phonons, the quantum mechanical representation of lattice vibrations, and their coupling to the electronic degrees of freedom are important for understanding thermal and electric properties of materials. For the first time, phonons have been measured using resonant inelastic x-ray scattering (RIXS) across the Cu K-edge in cupric oxide (CuO). Analyzing these spectra using an ultra-short core-hole lifetime approximation and exact diagonalization techniques, we can explain the essential inelastic features. The relative spectral intensities are related to the electron-phonon coupling strengths. PMID:21406750

Yava?, H; van Veenendaal, M; van den Brink, J; Ament, L J P; Alatas, A; Leu, B M; Apostu, M-O; Wizent, N; Behr, G; Sturhahn, W; Sinn, H; Alp, E E

2010-12-01

386

PHONON SOFTENING IN INTERMEDIATE VALENT SmB6  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We have measured the Raman spectrum of a SmB6 single crystal and compared it to LaB6 and EuB6. Beside the three high energy Raman active phonons we found additional excitations in these compounds. Most prominent is a peak at 172 cm-1 for SmB6, 214 cm-1 for LaB6 and 220 cm-1 for EuB6. The spectra are analysed in terms of defect induced phonon scattering. The softening of the line in intermediate valent (IV) SmB6 is explained in analogy with the phonon anomalies found in other IV compounds.

Mo?rke, I.; Wachter, P.

1981-01-01

387

Apparent electron-phonon interaction in strongly correlated systems  

CERN Multimedia

We study the interaction of electrons with phonons in strongly correlated solids, having high-T_c cuprates in mind. Using sum-rules, we show that the apparent strength of this interaction strongly depends on the property studied. If the solid has a small fraction (doping) delta of charge carriers, the influence of the interaction on the phonon self-energy is reduced by a factor delta, while there is no corresponding reduction of the coupling seen in the electron self-energy. This supports the interpretation of recent photoemission experiments, assuming a strong coupling to phonons.

Rösch, A

2004-01-01

388

Coupling of molecular vibrons with contact phonon reservoirs  

International Nuclear Information System (INIS)

In this paper we describe a computational method for coupling localized molecular vibrations with contact phonons using a Green's function formalism. The phonon Green's function is constructed from the dynamical matrix of the contact-molecule-contact coupled system. Within this formalism we identify the imaginary part of the self-energy as the vibron lifetime for decay into contact phonons. This first-principles calculation allows us to compute the microscopic energy dissipation and the heat transport from the molecule to the contacts. This is a fundamental step for the evaluation of the power dissipated in molecular devices and for studying the thermal stability of molecular devices

2007-05-30

389

Effect of Anharmonicity on the Phonon Spectrum near its Discontinuity  

International Nuclear Information System (INIS)

The method based on Green's function is used in investigating the effect of anharmonicity on the phonon spectrum near its discontinuity. In contrast to the usual case, the effect that phonon branches, which are independent in the harmonic approximation, have on one another requires the solution of the Dyson system of equations. The authors consider cases of significant and irregular discontinuity and show that for irregular discontinuity the excitations which arise can have a widely varying lifetime and frequency renormalization with respect to both value and temperature dependence. In particular, the one-phonon coherent neutron scattering cross section near the spectrum discontinuity is analysed. (author)

1965-04-01

390

Phonon Quasidiffusion in Cryogenic Dark Matter Search Large Germanium Detectors  

CERN Document Server

We present results on quasidiffusion studies in large, 3 inch diameter, 1 inch thick [100] high purity germanium crystals, cooled to 50 mK in the vacuum of a dilution refrigerator, and exposed with 59.5 keV gamma-rays from an Am-241 calibration source. We compare data obtained in two different detector types, with different phonon sensor area coverage, with results from a Monte Carlo. The Monte Carlo includes phonon quasidiffusion and the generation of phonons created by charge carriers as they are drifted across the detector by ionization readout channels.

Leman, S W; McCarthy, K A; Pyle, M; Resch, R; Sadoulet, B; Sundqvist, K M; Brink, P L; Cherry, M; Silva, E Do Couto E; Figueroa-Feliciano, E; Mirabolfathi, N; Serfass, B; Tomada, A

2011-01-01

391

Phonon Quasidiffusion in Cryogenic Dark Matter Search Large Germanium Detectors  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present results on quasidiffusion studies in large, 3 inch diameter, 1 inch thick [100] high purity germanium crystals, cooled to 50 mK in the vacuum of a dilution refrigerator, and exposed with 59.5 keV gamma-rays from an Am-241 calibration source. We compare data obtained in two different detector types, with different phonon sensor area coverage, with results from a Monte Carlo. The Monte Carlo includes phonon quasidiffusion and the generation of phonons created by cha...

Leman, S. W.; Cabrera, B.; Mccarthy, K. A.; Pyle, M.; Resch, R.; Sadoulet, B.; Sundqvist, K. M.; Brink, P. L.; Cherry, M.; Silva, E. Do Couto E.; Figueroa-feliciano, E.; Mirabolfathi, N.; Serfass, B.; Tomada, A.

2011-01-01

392

Anharmonic phonon frequency shift in MgB2  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We compute the anharmonic shift of the phonon frequencies in MgB2, using density functional theory. We explicitly take into account the scattering between different phonon modes at different q-points in the Brillouin zone. The shift of the E2g mode at the Gamma point is +5 % of the harmonic frequency. This result comes from the cancellation between the contributions of the four- and three-phonon scattering, respectively +10 % and -5 %. A similar shift is predicted at the A p...

Lazzeri, Michele; Calandra, Matteo; Mauri, Francesco

2003-01-01

393

Interface phonon modes of dual-gate MOSFET system  

Science.gov (United States)

Herein, analytical expressions are derived for the interface phonon modes of the dual-gate MOSFET system. These analytical results are essential for studies of phonon scattering in MOSFET structures which will affect the performance of the device. We consider selected cubic systems within the framework of macroscopic dielectric continuum model. A principal finding of this paper is that the normally-dominant and unwanted carrier scattering caused by interface phonon interactions can be strongly suppressed through the appropriate placement of the two gates.

Zhang, Nanzhu; Dutta, Mitra; Stroscio, Michael A.

2014-04-01

394

Optomechanical photon detection and enhanced dispersive phonon readout  

CERN Multimedia

In cavity optomechanics, nanomechanical motion couples to a localized optical mode. The regime of single-photon strong coupling is reached when the optical shift induced by a single phonon becomes comparable to the cavity linewidth. We consider a setup in this regime comprising two optical modes and one mechanical mode. For mechanical frequencies nearly resonant to the optical level splitting, we find the photon-phonon and the photon-photon interactions to be significantly enhanced. In addition to dispersive phonon detection in a novel regime, this offers the prospect of optomechanical photon measurement. We study these QND detection processes using both analytical and numerical approaches.

Ludwig, Max; Painter, Oskar; Marquardt, Florian

2012-01-01

395

Isotopic effects on the phonon modes in boron carbide.  

Science.gov (United States)

The effect of isotopes ((10)B-(11)B; (12)C-(13)C) on the infrared- and Raman-active phonons of boron carbide has been investigated. For B isotopes, the contributions of the virtual crystal approximation, polarization vector and isotopical disorder are separated. Boron and carbon isotope effects are largely opposite to one another and indicate the share of the particular atoms in the atomic assemblies vibrating in specific phonon modes. Some infrared-active phonons behave as expected for monatomic boron crystals. PMID:21403227

Werheit, H; Kuhlmann, U; Rotter, H W; Shalamberidze, S O

2010-10-01

396

Coupling of molecular vibrons with contact phonon reservoirs  

Science.gov (United States)

In this paper we describe a computational method for coupling localized molecular vibrations with contact phonons using a Green's function formalism. The phonon Green's function is constructed from the dynamical matrix of the contact-molecule-contact coupled system. Within this formalism we identify the imaginary part of the self-energy as the vibron lifetime for decay into contact phonons. This first-principles calculation allows us to compute the microscopic energy dissipation and the heat transport from the molecule to the contacts. This is a fundamental step for the evaluation of the power dissipated in molecular devices and for studying the thermal stability of molecular devices.

Romano, G.; Pecchia, A.; Di Carlo, A.

2007-05-01

397

Comparative study of the action of two different types of bleaching agents activated by two different types of irradiation fonts: xenon plasma arc lamp and 960 nm diode laser  

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)

2001-01-01

398

New effects involving the influence of nonequilibrium acoustic phonons on the luminescence of semiconductors  

Energy Technology Data Exchange (ETDEWEB)

Experiments concerning the influence of nonequilibrium acoustic phonons on the luminescence spectra of semiconductors and semiconductor structures are described. Results are presented on a hot phonon spot in Cu/sub 2/O, the phonon entrainment of excitons in silicon, the metastable state of holes in n-GaAs, and electron-phonon interaction in structures with quantum wells. It is noted that the use of nonequilibrium phonons in luminescence studies can yield important information about acoustic phonons, electron states in semiconductors, and the interaction between phonon and electron subsystems. 12 references.

Akimov, A.V.; Kaplianskii, A.A.

1988-04-01

399

Theoretical study of the phonon spectra of multiferroic BiFeO{sub 3} nanoparticles  

Energy Technology Data Exchange (ETDEWEB)

The phonon properties of multiferroic BiFeO{sub 3} (BFO) nanoparticles are studied using a Green's function technique on the basis of the Heisenberg and the transverse Ising models, taking into account anharmonic spin-phonon and phonon-phonon interaction terms. The phonon spectrum is obtained for different exchange, magnetoelectric, and spin-phonon interaction constants. The influence of temperature, surface and size effects on the phonon energy and damping is discussed. The phonon energy and damping in BFO nanoparticles are greater in comparison to those in bulk BFO. The strong spin-phonon interactions lead to anomalies in the phonon spectrum around the magnetic and ferroelectric phase transitions. The influence of an applied magnetic field is studied, too. The predictions are consistent with experimental results.

Apostolova, I [Faculty of Forest Industry, University of Forestry, Boulevard Kliment Okhridsky 10, 1756 Sofia (Bulgaria); Apostolov, A T [Department of Applied Physics, Technical University, Boulevard Kliment Okhridsky 8, 1000 Sofia (Bulgaria); Wesselinowa, J M [Department of Physics, University of Sofia, Boulevard J. Bouchier 5, 1164 Sofia (Bulgaria)

2009-01-21

400

Ultrafast Quenching of the Antiferromagnetic Order in FeBO3: Direct Optical Probing of the Phonon-Magnon Coupling  

Science.gov (United States)

The dynamics of the optically induced phase transition from the antiferromagnetic to the paramagnetic state in FeBO3 is observed using a pump-probe magneto-optical Faraday technique employing 100fs laser pulses. At the pump energy of 1.55eV phonon-assisted transitions dominate in the absorption of light and ultrafast heating of the lattice occurs. The quenching of the magnetic order is caused by an increase of the magnon temperature due to energy transfer from the heated lattice. The heating time of the magnon system is around 700ps, which is a factor of 20 faster than previously reported phonon-magnon interaction times.

Kimel, A. V.; Pisarev, R. V.; Hohlfeld, J.; Rasing, Th.

2002-12-01

 
 
 
 
401

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.

402

Phononics and Micromechanics of Bio-Colloidal Wiseana Iridovirus.  

Science.gov (United States)

By using Brillouin Light Scattering (BLS), we have investigated phononic properties of Wiseana iridovirus (WIV) assemblies and dispersed individual viruses at hypersonic frequency window. Propagating modes in virus assemblies and localized vibrational eig...

A. Kisliuk H. Xiong J. Neiswinger R. D. Hartschuh S. P. Wargacki

2008-01-01

403

Phonon temperature and electron temperature in thermoelectric coupling  

Science.gov (United States)

We develop a mesoscopic model of thermoelectric coupling in nanosystems, allowing for different phonon and electron temperatures, and mutual energy exchange. Its compatibility with the second law of thermodynamics is proved. By comparisons with other theoretical proposals, the different coefficients involved in the model are identified. We consider two illustrations: (a) for systems where the electron mean-free path is considerably shorter than the phonon mean-free path, the non-equilibrium phonon temperature may be different with respect to the local-equilibrium temperature of electrons; (b) for systems with large electron mean-free path, one may have the so-called "hot electrons," namely, electrons having a higher temperature than that of the phonons.

Jou, David; Sellitto, Antonio; Cimmelli, Vito A.

2013-12-01

404

Exact numerical methods for electron-phonon problems  

CERN Document Server

We present the basic principles of exact diagonalization and (dynamical) density-matrix renormalization-group approaches to the calculation of ground state and dynamical properties in electron-phonon systems.

Jeckelmann, E; Jeckelmann, Eric; Fehske, Holger

2006-01-01

405

Charge tuning of nonresonant magnetoexciton phonon interactions in graphene.  

Science.gov (United States)

Far from resonance, the coupling of the G-band phonon to magnetoexcitons in single layer graphene displays kinks and splittings versus filling factor that are well described by Pauli blocking and unblocking of inter- and intra-Landau level transitions. We explore the nonresonant electron-phonon coupling by high-magnetic field Raman scattering while electrostatic tuning of the carrier density controls the filling factor. We show qualitative and quantitative agreement between spectra and a linearized model of electron-phonon interactions in magnetic fields. The splitting is caused by dichroism of left- and right-handed circular polarized light due to lifting of the G-band phonon degeneracy, and the piecewise linear slopes are caused by the linear occupancy of sequential Landau levels versus ?. PMID:24580621

Rémi, Sebastian; Goldberg, Bennett B; Swan, Anna K

2014-02-01

406

Interatomic potential for accurate phonons and defects in UO2  

Science.gov (United States)

We have developed an improved uranium dioxide interatomic potential by fitting to forces, energies, and stresses of first principles molecular dynamics calculations via a genetic algorithm approach called Iterative Potential Refinement (IPR). We compare the defect energetics and vibrational properties of the IPR-fit potential with other interatomic potentials, density functional theory calculations, and experimental phonon dispersions. We find that among previously published potentials examined, there is no potential that simultaneously yields accurate defect energetics and accurate vibrational properties. In contrast, our IPR-fit potential produces both accurate defects and the best agreement with the experimental phonon dispersion and phonon density of states. This combination of accurate properties makes this IPR-fit potential useful for simulating UO2 in high temperature, defect-rich environments typical for nuclear fuel. Additionally, we verify that density functional theory with a Hubbard U correction accurately reproduces the experimentally derived UO2 phonon density of states.

Thompson, Alexander E.; Meredig, Bryce; Stan, Marius; Wolverton, C.

2014-03-01

407

Phonon Cooling of Nanomechanical Beams with Tunnel Junctions  

Science.gov (United States)

We demonstrate electronic cooling of 1D phonon modes in suspended nanowires for the first time, using normal-metal-insulator-superconductor (N-I-S) tunnel junctions. Simultaneous cooling of both electrons and phonons to a common temperature was achieved. In comparison with nonsuspended devices, better cooling performance is achieved in the whole operating range of bath temperatures between 0.1-0.7 K. The observed low-temperature thermal transport characteristics are consistent with scattering of ballistic phonons at the nanowire-bulk contact as being the mechanism limiting thermal transport. At the lowest bath temperature of the experiment ˜100mK, both phonons and electrons in the beam were cooled down to 42 mK, which is below the refrigerator base temperature.

Koppinen, P. J.; Maasilta, I. J.

2009-04-01

408

Phonon Dynamics and Inelastic Neutron Scattering of Sodium Niobate  

CERN Multimedia

Sodium niobate (NaNbO3) exhibits most complex sequence of structural phase transitions in perovskite family and therefore provides as excellent model system for understanding the mechanism of structural phase transitions. We report temperature dependence of inelastic neutron scattering measurements of phonon densities of states in sodium niobate. The measurements are carried out in various crystallographic phases of this material at various temperatures from 300 K to 1048 K. The phonon spectra exhibit peaks centered around 19, 37, 51, 70 and 105 meV. Interestingly, the peak around 70 meV shifts significantly towards lower energy with increasing temperature, while the other peaks do not exhibit an appreciable change. The phonon spectra at 783 K show prominent change and become more diffusive as compared to those at 303 K. In order to better analyze these features, we have performed first principles lattice dynamics calculations based on the density functional theory. The computed phonon density of states is fo...

Mishra, S K; Mittal, R; Zbiri, M; Rols, S; Schober, H; Chaplot, S L

2013-01-01

409

First-order transverse phonon deformation potentials of tetragonal perovskites.  

Science.gov (United States)

A theoretical formalism is put forward with the aim of describing the softening of first-order transverse optical phonons in a strained tetragonal perovskitic lattice. On the basis of the dynamical equation for nondegenerate polar modes, the influence of oblique phonons could be first described by assuming a prevalence of short-range interatomic forces; then, the softening effect arising from external stress could be explicitly expressed as a function of orientation of the crystallographic texture. As a further step in the adopted formalism, the microstructure of a perovskitic polycrystal has been ideally modeled as an ensemble of mesocrystals, whose individual crystallographic directions corresponded to an average orientation over the unit volume of the probe. An experimental confirmation of the theoretical formalism is concurrently carried out, and phonon deformation potentials (PDP) have been directly measured for the first-order transverse phonon of a tetragonal PbZrTiO3 perovskite lattice. PMID:18841950

Deluca, Marco; Pezzotti, Giuseppe

2008-11-01

410

Improved model of optical phonon confinement in silicon nanocrystals  

Energy Technology Data Exchange (ETDEWEB)

We develop a model for calculating the Raman scattering spectra from phonons confined in for silicon nanocrystals, which is based on the familiar approach taking into account the uncertainty in the quasi-momentum of phonons localized in the nanocrystals. The model is considerably improved by taking into account dispersion of phonons not only in the magnitude of the quasi-momentum, but also in its direction. A significant refinement of the model is also due to the fact that phonon dispersion is calculated using the widely approved Keating model instead of being approximated by empirical expressions as was done in earlier approaches. The calculations based on this model make it possible to determine the sizes of silicon nanocrystals more precisely from analysis of the experimental Raman spectra.

Volodin, V. A., E-mail: volodin@isp.nsc.ru [Russian Academy of Sciences, Rzhanov Institute of Semiconductor Physics, Siberian Branch (Russian Federation); Sachkov, V. A. [Russian Academy of Sciences, Omsk Branch, Rzhanov Institute of Semiconductor Physics, Siberian Branch (Russian Federation)

2013-01-15

411

Improved model of optical phonon confinement in silicon nanocrystals  

International Nuclear Information System (INIS)

We develop a model for calculating the Raman scattering spectra from phonons confined in for silicon nanocrystals, which is based on the familiar approach taking into account the uncertainty in the quasi-momentum of phonons localized in the nanocrystals. The model is considerably improved by taking into account dispersion of phonons not only in the magnitude of the quasi-momentum, but also in its direction. A significant refinement of the model is also due to the fact that phonon dispersion is calculated using the widely approved Keating model instead of being approximated by empirical expressions as was done in earlier approaches. The calculations based on this model make it possible to determine the sizes of silicon nanocrystals more precisely from analysis of the experimental Raman spectra.

2013-01-01

412

Electron-phonon interaction in the Hubbard model  

International Nuclear Information System (INIS)

Superconductivity existence in the Hubbard model is studied, taking into account both electron-phonon and electron-electron interactions. Using Sarker's functional integral formalism a system of equations for the dynamical order parameters is derived. (author). 7 refs

1994-01-01

413

Electron-phonon interaction in the Hubbard model.  

Science.gov (United States)

Superconductivity existence in the Hubbard model is studied, taking into account both electron-phonon and electron-electron interactions. Using Sarker's functional integral formalism a system of equations for the dynamical order parameters is derived. (au...

Hoang Anh Tuan Nguyen Toan Thang Nguyen Ngoc Thuan

1994-01-01

414

Strong coupling theory of phonons in the Hubbard Model  

Science.gov (United States)

The role of phonons in strongly correlated electronic systems including the high Tc cuprates has not been completely well understood. Recent experimental results, notably those of Lanzara et. al reveal the existence of a kink in the quasiparticle dispersion data for various classes of cuprate superconductors including BiSCO , LSCO and NCCO at an energy scale of around 50 meV to 70 meV using ARPES techniques. Direct comparison of ARPES and neutron scattering data has also been done for LSCO. One of the possible explanations for this kink is believed to be coupling of electrons with phonon modes of the above energy scale. We obtain the electron spectral function as a function of electron- phonon coupling strength using Cluster Dynamic Mean Field Theory (CDMFT on the 2-D Hubbard Model with phonons and compare it with the experimental data.

Chakraborty, Shiladitya; Stanescu, Tudor; Phillips, Philip

2006-03-01

415

Phonon-assisted tunneling through a double quantum dot system  

International Nuclear Information System (INIS)

Electron transport through a double quantum dot system is studied, taking into account the electron-phonon interaction. The Keldysh nonequilibrium Green function formalism is used to compute the current and transmission coefficient of the system. The influence of the electron-phonon interaction, interdot tunneling and temperature on the density of states and current is analyzed. Results show that the transmission coefficient is a function of the bias in the presence of the electron-phonon interaction. We found that although the electron-phonon interaction results in the appearance of side peaks in the conductance at low temperatures, these disappear at high temperatures. In addition, the temperature influences the shape of the density of the states.

2012-09-01

416

Phonon spectra of cobaltite/manganites in strong magnetic fields  

Energy Technology Data Exchange (ETDEWEB)

Far-infrared spectroscopy has been employed to determine phonon modes in the cobaltite/manganites A(Co{sub 1/2}Mn{sub 1/2})O{sub 3}, where A is a lanthanide, in magnetic fields up to 17.5 T. The phonon energies in the compounds with A=La,Nd or Ho show little change with applied magnetic field. In contrast, with A=Yb, all the phonon modes exhibit a splitting when a magnetic field is applied. It is thought that this field dependence of the phonon energies is related to the metamagnetism of Yb(Co{sub 1/2}Mn{sub 1/2})O{sub 3}.

Lewis, R.A. E-mail: roger@uow.edu.au; Wang, Y.-J.; Gao, F.; Wang, X.L.; Dou, S.X

2004-05-01

417

Ferromagnetism, Phonons and Superconductivity in ZrZn_2  

Science.gov (United States)

We report density functional studies of the electronic structure, magnetism, zone center phonons and electron phonon coupling in the ferromagnetic superconductor, ZrZn_2. It has been long suspected that spin fluctuations in the weak itinerant ferromagnet ZrZn2 may lead to triplet superconductivity. However, our calculations suggest that this is not the only possibility. In particular, there is an alternate scenario consisting of an s-wave, FFLO state. This is based on our findings of significant Fermi surface nesting, non-uniform exchange splittings, and soft Zr rattling type phonons with high electron phonon coupling. Experiments to determine which of these two possible superconducting states is present in ZrZn2 are suggested.

Singh, David J.; Mazin, Igor I.

2002-03-01

418

Confinement of acoustical vibrations in a semiconductor planar phonon cavity  

CERN Multimedia

Extending the idea of optical microcavities to sound waves, we propose a {\\it phonon cavity} consisting of two semiconductor superlattices enclosing a spacer with thickness determined by the acoustic wavelength at the center of the first zone-center folded minigap. We show that acoustical phonons can be confined in these layered structures, and propose Raman experiments which are able to probe these novel excitations. The Raman experiments take profit of an optical microcavity scattering geometry that, through the forward-scattering contribution, gives access to the zone-center excitations. We report experimental results of Raman scattering in a structure based in GaAs/AlAs materials that demonstrate unambiguously the observation of phonon cavity confined acoustical vibrations. The experimental results compare precisely with photoelastic model calculations of the Raman spectra of the proposed phonon-cavity embedded optical microcavity.

Trigo, M; Fainstein, A; Jusserand, B; Thierry-Mieg, V

2002-01-01

419

Detection of dark matter particles with low temperature phonon sensors  

Energy Technology Data Exchange (ETDEWEB)

Taking as an example the development effort in Berkeley, the author discusses for nonspecialists (Astronomers and Particle Physicists) the promises of phonon sensing at low temperature for the detection of dark matter particles and the difficulties faced. 31 refs.

Sadoulet, B.

1988-03-01

420

Phonon-assisted decoherence and tunneling in quantum dot molecules  

DEFF Research Database (Denmark)

We study the influence of the phonon environment on the electron dynamics in a doped quantum dot molecule. A non-perturbative quantum kinetic theory based on correlation expansion is used in order to describe both diagonal and off-diagonal electron-phonon couplings representing real and virtual processes with relevant acoustic phonons. We show that the relaxation is dominated by phonon-assisted electron tunneling between constituent quantum dots and occurs on a picosecond time scale. The dependence of the time evolution of the quantum dot occupation probabilities on the energy mismatch between the quantum dots is studied in detail. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Grodecka-Grad, Anna; Foerstner, Jens

2011-01-01

 
 
 
 
421

Planck distribution of phonons in a Bose-Einstein condensate.  

Science.gov (United States)

The Planck distribution of photons emitted by a blackbody led to the development of quantum theory. An analogous distribution of phonons should exist in a Bose-Einstein condensate. We observe this Planck distribution of thermal phonons in a 3D condensate. This observation provides an important confirmation of the basic nature of the condensate's quantized excitations. In contrast to the bunching effect, the density fluctuations are seen to increase with increasing temperature. This is due to the nonconservation of the number of phonons. In the case of rapid cooling, the phonon temperature is out of equilibrium with the surrounding thermal cloud. In this case, a Bose-Einstein condensate is not as cold as previously thought. These measurements are enabled by our in situ k-space technique. PMID:23952415

Schley, R; Berkovitz, A; Rinott, S; Shammass, I; Blumkin, A; Steinhauer, J

2013-08-01

422

Phonon excitation and instabilities in biased graphene nanoconstrictions  

DEFF Research Database (Denmark)

We investigate how a high current density perturbs the phonons in a biased graphene nanoconstriction coupled to semi-infinite electrodes. The coupling to electrode phonons, electrode electrons under bias, Joule heating, and current-induced forces is evaluated using first principles density functional theory and nonequilibrium Green's function calculations. We observe a strongly nonlinear heating of the phonons with bias and breakdown of the harmonic approximation when the Fermi level is tuned close to a resonance in the electronic structure of the constriction. This behavior is traced back to the presence of negatively damped phonons driven by the current. The effects may limit the stability and capacity of graphene nanoconstrictions to carry high currents.

Gunst, Tue; Lu, Jing Tao

2013-01-01

423

Electron-phonon coupling as an order-one problem  

CERN Document Server

The coupling between electrons and phonons plays important roles in physics, chemistry and biology. However, the accurate calculation of the electron-phonon coupling constants is computationally expensive as it involves solving the Schrodinger equation for O(N) nuclear configurations, where N is the number of nuclei. Herein we show that by considering the forces on the nuclei caused by the addition or subtraction of an arbitrarily small electronic charge one may calculate the electron-phonon coupling constants from O(1) solutions of the Schrodinger equation. We show that Janak's theorem means that this procedure is exact within the density functional formalism. We demonstrate that the O(1) approach produces numerically accurate results by calculating the electron-phonon coupling constants for a series of molecules ranging in size from H_2 to C_60. We use our approach to introduce a computationally fast approximation for the adiabatic ionisation potentials and electron affinities which is shown to be accurate ...

Powell, B J; Baruah, T; Pederson, Mark R.; Baruah, Tunna

2005-01-01

424

Semiconductor phonon and charge transport Monte Carlo simulation using Geant4  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A phonon and charge transport simulation based on the Geant4 Monte Carlo toolkit is presented. The transport code is capable of propagating acoustic phonons, electrons and holes in cryogenic crystals. Anisotropic phonon propagation, oblique carrier propagation and phonon emission by accelerated carriers are all taken into account. The simulation successfully reproduces theoretical predictions and experimental observations such as phonon caustics, heat pulse propagation times...

Brandt, D.; Agnese, R.; Redl, P.; Schneck, K.; Asai, M.; Kelsey, M.; Faiez, D.; Bagli, E.; Cabrera, B.; Partridge, R.; Saab, T.; Sadoulet, B.

2014-01-01

425

Phonon-assisted tunneling in asymmetric resonant tunneling structures  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Based on the dielectric continuum model, we calculated the phonon assisted tunneling (PAT) current of general double barrier resonant tunneling structures (DBRTSs) including both symmetric and antisymmetric ones. The results indicate that the four higher frequency interface phonon modes (especially the one which peaks at either interface of the emitter barrier) dominate the PAT processes, which increase the valley current and decrease the PVR of the DBRTSs. We show that an a...

Shi, Jun-jie; Sanders, Barry C.; Pan, Shao-hua

1998-01-01

426

Inelastic x-ray scattering from phonons under multibeam conditions  

International Nuclear Information System (INIS)

We report on an experimental observation of a previously neglected multibeam contribution to the inelastic x-ray scattering cross section. Its manifestation is a substantial modification of the apparent phonon selection rules when two (or more) reciprocal lattice points are simultaneously intercepted by the Ewald sphere. The observed multibeam contributions can be treated semi-quantitatively in the frame of Renninger's 'simplest approach'. A few corollaries, relevant for experimental work on inelastic scattering from phonons, are presented

2007-03-01

427

Phonon Mediated Transresistivity in a Double Layer Composite Fermion System  

CERN Multimedia

We consider the fractional drag in a double layer system of two-dimensional electrons in the half-filled lowest Landau level. At sufficiently large inter-layer separations the drag is dominated by exchange of acoustic phonons and exhibits novel temperature and inter-layer distance dependences. At low temperatures the phonon mediated drag is strongly enhanced with respect to the case of zero magnetic field.

Khveshchenko, D V

1998-01-01

428

Electron-phonon interaction in thin copper and gold films  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We have studied the electron-phonon (e-p) interaction in thin Cu and Au films at sub-Kelvin temperatures with the help of the hot electron effect, using symmetric normal metal-insulator-superconductor tunnel junction pairs as thermometers. By Joule heating the electron gas and measuring the electron and the lattice temperatures simultaneously, we show that the electron-phonon scattering rate follows a $T^{4}$ temperature dependence in both metals. The result is in accordance...

Karvonen, J. T.; Taskinen, L. J.; Maasilta, I. J.

2004-01-01

429

Phonon cooling of nanomechanical beams with tunnel junctions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We demonstrate electronic cooling of 1D phonon modes in suspended nanowires for the first time, using normal metal--insulator--superconductor (NIS) tunnel junctions. Simultaneous cooling of both electrons and phonons to a common temperature was achieved. In comparison with non-suspended devices, better cooling performance is achieved in the whole operating range of bath temperatures between 0.1-0.7 K. The observed low-temperature thermal transport characteristics are consist...

Koppinen, P. J.; Maasilta, I. J.

2009-01-01

430

Properties of interface phonon spectra in complicated cylindrical nanosystem  

Directory of Open Access Journals (Sweden)

Full Text Available The spectra of two types of interface phonons (top and side optical are studied within the framework of dielectric continuum model for combined nanoheterosystems consisting of semiconductor cylindrical quantum dots inside the cylindrical quantum wire placed into dielectric or semiconductor medium. The dependencies of both types of interface phonon energies on the quasiwave numbers and geometric parameters of nanosystem are calculated and analysed.

O.M.Voitsekhivska

2007-01-01

431

Effect of phonons on the ac conductance of molecular junctions  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract We theoretically examine the effect of a single phonon mode on the structure of the frequency dependence of the ac conductance of molecular junctions, in the linear response regime. The conductance is enhanced (suppressed by the electron-phonon interaction when the chemical potential is below (above the energy of the electronic state on the molecule. PACS numbers: 71.38.-k, 73.21.La, 73.23.-b

Ueda Akiko

2011-01-01

432

Superconductivity-Induced Distortions of Phonon Lineshapes in Niobium  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Superconductivity-induced changes of phonon lineshapes in niobium have been re-investigated by high-resolution inelastic neutron scattering. We show that the changes go beyond a simple change in lifetime and frequency when the phonon frequency is close to the superconducting energy gap $2\\Delta$. The observed lineshapes in elemental niobium are qualitatively similar to those found previously in borocarbide superconductors and agree very well with those predicted by the theor...

Weber, F.; Pintschovius, L.

2010-01-01

433

Moments of the phonon spectra in alkali halides  

International Nuclear Information System (INIS)

The results of a systematic calculation of the moments of the phonon spectra for 20 alkali halides are reported. The relevant phonon spectra needed are taken from the Green's function compilations by Haridasan et al. The calculated moments show good agreement with the available experimental data for sodium, potasium and caesium halides. The moments deduced from Debye-Waller factor data and from specific heat data are mutually consistent. A critical inter-comparison of these moments in these crystals is made. (author)

1976-06-01

434

X-ray studies of phonon softening in tise2.  

Science.gov (United States)

The charge-density-wave transition in TiSe (2), which results in a commensurate (2x2x2) superlattice at temperatures below approximately 200 K, presumably involves softening of a zone-boundary phonon mode. For the first time, this phonon-softening behavior has been examined over a wide temperature range by synchrotron x-ray thermal diffuse scattering. PMID:11329327

Holt, M; Zschack, P; Hong, H; Chou, M Y; Chiang, T C

2001-04-23

435

Onset of nondiffusive phonon transport in transient thermal grating decay  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The relaxation of a spatially sinusoidal temperature perturbation in a dielectric crystal at a temperature comparable to or higher than the Debye temperature is investigated theoretically. We assume that most phonons contributing to the specific heat have a mean free path (MFP) much shorter than the thermal transport distance and can be described by the thermal diffusion model. Low-frequency phonons that may have MFP comparable to or longer than the grating period are described by the Boltzma...

Maznev, Alexei; Nelson, Keith Adam; Johnson, Jeremiah A.

2011-01-01

436

Experimental studies of electron-phonon interactions in gallium nitride  

CERN Multimedia

This thesis presents an experimental investigation of the electron-phonon interaction in GaN. Bulk epilayers, grown by MBE, and AIGaN/GaN heterostructure grown by MOCVD, have been studied. The energy relaxation rate for hot electrons has been measured over a wide range of temperatures, allowing both acoustic and optic phonon emission to be studied in GaN epilayers. Direct phonon measurements, both studying the emission and absorption processes, have been performed. Detection of phonons emitted when hot electrons relax their excess energy complements the measurements of relaxation rates. Absorption of acoustic phonons by the epilayers, using both fixed and extended metal film phonon sources, allowed investigation into the effectiveness of the 2k sub F cutoff in the low mobility layers. The experimental findings are compared with the predictions of theory. AIGaN/GaN heterostructures were characterised and measurements of the energy relaxation rate in the temperature range 4K-40K obtained. Excellent agreement wi...

Stanton, N M

2001-01-01

437

Electron-phonon coupling in the rare-earth metals  

DEFF Research Database (Denmark)

We have estimated the strength of the mass enhancement of the conduction electrons due to electron-phonon interaction in the rare metals Sc, Y, and Laâ??Lu. The underlying self-consistent energy bands were obtained by means of the scalar relativistic linear-muffin-tin-orbital method, and the electron-phonon parameters were calculated within the Gaspari-Gyorffy formulation. For the heavier rare earths Gdâ??Tm spin polarization was included both in the band-structure calculations and in the treatment of the electron-phonon coupling to take into account the spin splitting of the conduction electrons induced by the 4f states. The calculated electron-phonon mass enhancement λ exhibits a pronounced variation through the series with a maximum value of 1.07 in Pr and a minimum of 0.3 in Ho. We analyze the experimental data from specific heat and de Haasâ??van Alphen measurements in light of the calculated electron-phonon contribution to the mass enhancement. Finally, we present for the superconducting elements Sc, Y, La, and Lu a comparison with the empirical electron-phonon coupling constants derived from the transition temperatures.

Skriver, Hans Lomholt; Mertig, I.

1990-01-01

438

Frictional drag between quantum wells mediated by phonon exchange  

DEFF Research Database (Denmark)

We use the Kubo formalism to evaluate the contribution of acoustic-phonon exchange to the frictional drag between nearby two-dimensional electron systems. In the case of free phonons, we find a divergent drag rate (tau(D)(-l)). However, tau(D)(-l) becomes finite when phonon scattering from either lattice imperfections or electronic excitations is accounted for. In the case of GaAs quantum wells, we find that for a phonon mean free path l(ph) smaller than a critical value, imperfection scattering dominates and the drag rate varies as ln(l(ph)/d) over many orders of magnitude of the layer separation d. When l(ph) exceeds the critical value, the drag rate is dominated by coupling through an electron-phonon collective mode localized in the vicinity of the electron layers. We argue that the coupled electron-phonon mode may be observable for realistic parameters. Our theory is in good agreement with experimental results for the temperature, density, and d dependence of the drag rate.

Hu, Ben Yu-Kuang

1998-01-01

439

Phononic crystals of spherical particles: A tight binding approach  

International Nuclear Information System (INIS)

The vibrational dynamics of a fcc phononic crystal of spheres is studied and compared with that of a single free sphere, modelled either by a continuous homogeneous medium or by a finite cluster of atoms. For weak interaction among the spheres, the vibrational dynamics of the phononic crystal is described by shallow bands, with low degree of dispersion, corresponding to the acoustic spheroidal and torsional modes of the single sphere. The phonon displacements are therefore related to the vibrations of a sphere, as the electron wave functions in a crystal are related to the atomic wave functions in a tight binding model. Important dispersion is found for the two lowest phonon bands, which correspond to zero frequency free translation and rotation of a free sphere. Brillouin scattering spectra are calculated at some values of the exchanged wavevectors of the light, and compared with those of a single sphere. With weak interaction between particles, given the high acoustic impedance mismatch in dry systems, the density of phonon states consist of sharp bands separated by large gaps, which can be well accounted for by a single particle model. Based on the width of the frequency gaps, tunable with the particle size, and on the small number of dispersive acoustic phonons, such systems may provide excellent materials for application as sound or heat filters

2013-11-07

440

Theory of electron-phonon coupling in semiconductor quantum dots: non-diagonal coupling, phonon memory and initial correlations  

Energy Technology Data Exchange (ETDEWEB)

Memory effects play an important role in the theory of dephasing processes of semiconductor quantum dots. To describe strong electron-phonon coupling (e.g. in nitrid materials) beyond perturbation theory, typically methods such as generating functions, cumulant expansion, time convolution less theories (TCL) are used. These methods are usually restricted to a diagonal electron-phonon interaction, that does not include transitions between different electronic levels. Non-diagonal electron-phonon coupling is of dramatic importance, if coupled quantum dots or several levels contribute to the optical response. In order to address this problem, we present an extended TCL theory, which makes an inclusion of nondiagonal electron-phonon coupling to the calculation of the nonlinear optical response function possible.

Richter, Marten; Knorr, Andreas [Institut fuer Theoretische Physik, AG Nichtlineare Optik und Quantenelektron