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1.
K. V. Poletkin G. G. Gurzadyan J. Shang V. Kulish 《Applied physics. B, Lasers and optics》2012,107(1):137-143
Heat transfer processes, induced by ultrashort laser pulses in thin gold films, were studied with a time resolution of 50
fs. It is demonstrated that in thin gold films heat is transmitted by means of electron–phonon and phonon–phonon interactions,
and dissipated on nanoscale within 800 fs. Measurements show that the electron–phonon relaxation time varies versus the probe
wavelength from 1.6 to 0.8 ps for λ=560–630 nm. The applied mathematical model is a result of transforming the two-temperature model to the hyperbolic heat equation,
based on assumptions that the electron gas is heated up instantaneously and applying Cattaneo’s law to the phonon subsystem,
agrees well with the experimental results. This model allows us to define time of electron–phonon scattering as the ratio
of the heat penetration depth to the speed of sound in the bulk material that, in turn, provides an explanation of experimental
results that show the dependence of the electron–phonon relaxation time on the wavelength. 相似文献
2.
Ultra-fast optical measurements of few-layer suspended graphene films grown by chemical vapor deposition were performed with
femtosecond pump–probe spectroscopy. The relaxation processes were monitored in transient differential transmission (ΔT/T) after excitation at two different wavelengths of 350 and 680 nm. Intraband electron–electron scattering, electron–phonon
scattering, interband Auger recombination and impact ionization were considered to contribute to ΔT/T. All these processes may play important roles in spreading the quasiparticle distribution in time scales up to 100 fs. Optical
phonon emission and absorption by highly excited non-equilibrium electrons were identified from ΔT/T peaks in the wide spectral range. When the probe energy region was far from the pump energy, the energy dependence of the
quasiparticle decay rate was found to be linear. Longer lifetimes were observed when the quasiparticle population was localized
due to optical phonon emission or absorption. 相似文献
3.
A. S. Kirakosyan M. Tong T. V. Shahbazyan Z. V. Vardeny 《Applied physics. B, Lasers and optics》2008,93(1):131-138
We study the ultrafast dynamics of surface electromagnetic waves photogenerated on aluminum film perforated with subwavelength
holes array by means of transient photomodulation with ∼100 fs time resolution. We observed a pronounced blueshift of the resonant transmission band that reveals the important role of plasma attenuation in the dynamics and that is inconsistent
with plasmon–polariton mechanism of extraordinary transmission. The transient photomodulation spectra were successfully modeled
within the Boltzmann equation approach for the electron–phonon relaxation dynamics, involving non-equilibrium hot electrons
and quasi-equilibrium phonons. 相似文献
4.
Shihua Huang 《Applied physics. B, Lasers and optics》2006,84(1-2):323-326
Nanocrystal ZnSe material was prepared in a triethylamine solvent using the modified solvothermal method in which potassium
borohydride, a reducing reagent, is employed. Compared with the bulk ZnSe, the steady absorption edge and photoluminescence
peak of nanocrystal ZnSe shift toward high energy. With the decrease of nanoparticle size, the probability of inelastic collision
between electron and nanoparticle surface increases, which results in the enhancement of the intensity of electron–phonon
coupling and the decrease of electron–phonon scattering time. In the lower temperature range (13–100 K), the transition probability
between singlet state and triple state rapidly increases with the increase in temperature. With the further increase in temperature
(100–292 K), the radiative recombination between singlet state and ground state is dominant. The competitive non-radiative
recombination between singlet state and triple state is suppressed, therefore, the radiation decay time of singlet state changes
slightly.
PACS 78.55.Et; 73.61.Tm; 78.47.+p; 78.90.+t 相似文献
5.
E. Majkova S. Luby R. Senderak Y. Chushkin M. Jergel I. Zergioti D. Papazoglou A. Manousaki C. Fotakis 《Applied Physics A: Materials Science & Processing》2003,76(5):763-766
The sub-picosecond laser microstructuring of multilayer gratings is presented in this paper. A micromachining system operating
with a 0.5 ps KrF laser at 248 nm was used to etch grating structures with a groove width of 1–2 μm in Mo/Si and Si/Mo multilayers.
Atomic force microscopy, scanning electron microscopy and X-ray reflectivity were used to characterize the microetched patterns.
The ω-scans around the 1st Bragg maximum show symmetric satellites up to 3rd order, with positions corresponding to the grating
period. The use of sub-picosecond laser pulses minimizes the thermally affected zone and enhances the quality of the etched
features. Short pulse laser processing is advantageous for the fabrication of high spatial resolution microstructures required
in X-ray optics.
Received: 21 May 2002 / Accepted: 19 August 2002 / Published online: 15 January 2003
RID="*"
ID="*"Corresponding author. Email: dpapa@iesl.forth.gr 相似文献
6.
Time-resolved two-photon photoelectron spectroscopy is used to study the dynamics of non-equilibrium electron and hole distributions at bare and D2O-covered Ru(001) following optical excitation (55-fs, 800-nm pulses) with variable fluence (0.04–0.6 mJcm-2). Within the first 0.5 ps we observe an ultra-fast transient of the excited-carrier population and energy density at the surface which is accompanied by pronounced deviations of the electron-energy distribution from a (thermalized) Fermi–Dirac distribution. Comparison of the transient energy density of the photoexcited electrons at the surface with predictions of the two-temperature model provides fair agreement up to 400 fs, but exhibits a systematically lower energy density at later times, where electrons and phonons are equilibrated. We propose that this reduced energy density at the surface originates from ultra-fast energy transport of non-thermal electrons into the bulk in competition to electron–phonon coupling at the surface. This is corroborated by extending the two-temperature model to account for non-thermal, photoexcited electrons, whereby quantitative agreement with experiment can only be achieved if ballistic transport and reduced electron–phonon coupling is incorporated for non-thermal electrons. Implications for surface femtochemistry are discussed. PACS 78.47.+p; 71.38.-k; 73.40.-c 相似文献
7.
The lifetimes of quantum excitations are directly related to the electron and phonon energy linewidths of a particular scattering
event. Using the versatile double time thermodynamic Green’s function approach based on many-body theory, an ab-initio formulation of relaxation times of various contributing processes has been investigated with newer understanding in terms
of the linewidths of electrons and phonons. The energy linewidth is found to be an extremely sensitive quantity in the transport
phenomena of crystalline solids as a collection of large number of scattering processes, namely, boundary scattering, impurity
scattering, multiphonon scattering, interference scattering, electron–phonon processes and resonance scattering. The lattice
thermal conductivities of three samples of GaAs have been analysed on the basis of modified Callaway model and a fairly good
agreement between theory and experimental observations has been reported. 相似文献
8.
Short-laser-pulse-driven emission of energetic ions into a solid target from a surface layer spalled by a laser prepulse 总被引:1,自引:0,他引:1
A.G. Zhidkov L.V. Zhigilei A. Sasaki T. Tajima 《Applied Physics A: Materials Science & Processing》2001,73(6):741-747
An efficient emission of picosecond bunches of energetic protons and carbon ions from a thin layer spalled from a organic
solid by a laser prepulse is demonstrated numerically. We combine the molecular dynamics technique and multi-component collisional
particle-in-cell method with plasma ionization to simulate the laser spallation and ejection of a thin (∼20–30 nm) solid layer
from an organic target and its further interaction with an intense femtosecond laser pulse. In spite of its small thickness,
a layer produced by laser spallation efficiently absorbs ultrashort laser pulses with the generation of hot electrons that
convert their energy to ion energy. The efficiency of the conversion of the laser energy to ions can be as high as 20%, and
10% to MeV ions. A transient electrostatic field created between the layer and surface of the target is up to 10 GV/cm.
Received: 13 March 2001 / Accepted: 20 March 2001 / Published online: 20 June 2001 相似文献
9.
Atomic mixing of Ni2O3/SiO2, NiO/SiO2, and Ni/SiO2 interfaces induced by swift heavy ion irradiation
B. Schattat W. Bolse S. Klaumünzer F. Harbsmeier A. Jasenek 《Applied Physics A: Materials Science & Processing》2003,76(2):165-169
We have investigated the interface mixing of Ni2O3/SiO2, NiO/SiO2, and Ni/SiO2 induced by the irradiation with Ar, Kr and Xe ions of energies ranging from 90 MeV to 260 MeV. Since these energies are in
the electronic stopping regime, atomic transport processes will not be directly initiated by elastic ion–target collisions,
but need to be excited by secondary processes like electron–phonon coupling or Coulomb explosion. Nevertheless, we have observed
a strong mixing effect in the ceramic systems if the electronic energy loss exceeds a certain threshold value. Estimation
of an effective diffusion constant indicates that diffusion takes place in the molten ion track. In contrast to the ceramics,
the metallic Ni layer is still insensitive even for the highest electronic stopping power used (Se=28 keV/nm) and does not exhibit mixing with its SiO2 substrate.
In addition, NiO/SiO2 and Ni/SiO2 were irradiated in the nuclear stopping regime with 600 keV Kr and 900 keV Xe–ions. Here the intermixing effect is in good
agreement with the assumption of ballistic atomic transport.
Received: 5 February 2002 / Accepted: 11 February 2002 / Published online: 3 May 2002
RID="*"
ID="*"Corresponding author. Fax: +49-711/685-3866, E-mail: bolse@ifs.physik.uni-stuttgart.de 相似文献
10.
U. Bovensiepen 《Applied Physics A: Materials Science & Processing》2006,82(3):395-402
The Gd(0001) surface is investigated by pump–probe experiments using femtosecond laser pulses at 740–860 nm wavelength. Employing
optical second-harmonic generation, spin and lattice dynamics are separated through the symmetry of optical field contributions
that are even and odd with respect to magnetization reversal. A coherent phonon–magnon mode at a frequency of 3 THz that is
excited through the exchange-split surface state is observed in the time domain. A magneto-elastic phonon–magnon interaction
based on spin–orbit coupling is weak for Gd and a modulation of the exchange interaction mediated by the lattice vibration
is proposed as a microscopic interaction mechanism of this coupled mode. In parallel, electron–electron and electron–phonon
interactions and their magnetic counterparts lead to incoherent dynamics of the electron, lattice, and spin subsystems. Variation
of the optical wavelength shows that for longer wavelengths up to 860 nm the coherent mode dominates, while for shorter ones
(≥740 nm) incoherent contributions prevail. This dependence indicates that selective depopulation of the occupied surface
state component drives the coherent excitation. However, temperature-dependent studies show that the oscillation amplitude
of even and odd contributions scales with the spin polarization of the surface state, suggesting that the spin dependence
of the ion potentials contributes as well. Furthermore, the frequency of the coherent mode presents a blue shift with a delay
of 0.17 THz/ps that saturates at the static frequency of the respective bulk phonon. This behavior is a consequence of equilibration
of the screened ion potential at the surface subsequent to the intense laser excitation.
PACS 78.47.+p; 63.22.+m; 63.20.Ls; 75.30.Ds 相似文献
11.
J. Sjakste V. Tyuterev N. Vast 《Applied Physics A: Materials Science & Processing》2007,86(3):301-307
Interactions between excited electrons and short-wavelength (intervalley) phonons in GaAs are studied using density functional
theory for the conduction bands, and density functional perturbation theory for phonon frequencies and matrix elements of
the electron–phonon interaction. We have calculated the deformation potentials (DPs) and the average intervalley scattering
time 〈τ〉. The integration of the scattering probabilities over all possible final states in the Brillouin zone has been performed
without any ad hoc assumption about the behavior of the electron–phonon matrix elements nor the topology of the conduction
band. For transitions from the L point to Γ valley (within the first conduction band), we find 〈τ〉L to be 1.5 ps at 300 K, in good agreement with time-resolved photoluminescence experiment. We discuss the difference between
our calculated DPs, and effective parameters used in Monte Carlo simulations of optical and transport properties of semiconductors.
The latter are based on Conwell’s model, in which electron–phonon interaction is described by one single constant and a parabolic
model is used for conduction bands. We deduce the effective DP from our 〈τ〉, and compare it to our calculated DPs. We conclude
that only effective DPs obtained from a full calculation of 〈τ〉 are relevant parameters for Monte Carlo simulations.
PACS 71.10-w; 72.10.Di; 71.55.Eq 相似文献
12.
Rapid melting and resolidification of a free-standing gold film subject to nano- to femtosecond laser pulses are investigated
using the two-temperature model in conjunction with an interfacial tracking method. The interfacial velocity, as well as elevated
melting temperature and depressed solidification temperature, in the ultra-fast phase-change process are obtained by considering
the interfacial energy balance and nucleation dynamics. A nonlinear electron heat capacity and a temperature-dependent electron–lattice
coupling factor for the rapid phase change are taken into account. Effects of laser pulse width and fluence on melting and
resolidification are also studied.
PACS 42.62.Eh; 63.20.Kr; 64.70.Dv 相似文献
13.
A. etin 《Physica B: Condensed Matter》2009,404(21):3982-3985
We have studied the effect of electron–phonon interaction for small electron–phonon coupling on the electronic energy spectrum of an electron confined by a parabolic potential and a repulsive antidot potential in the presence of a uniform strong magnetic field and an Aharonov–Bohm flux field by using a variational procedure. We have shown that the presence of the antidot potential removes degeneracy of the Landau levels and electron–phonon interaction has nonnegligible effects on these levels. 相似文献
14.
15.
J. Kröger 《Applied Physics A: Materials Science & Processing》2007,87(3):345-350
Some aspects of the coupling between phonons and electrons and the interaction between electrons at metal surfaces are reviewed.
Surface science techniques as diverse as electron energy loss spectroscopy, angle-resolved photoelectron spectroscopy, and
scanning tunnelling microscopy are employed to study these interactions. Electron–phonon and electron–electron coupling are
discussed in terms of renormalized phonon dispersion relations, and increased decay rates of electronic excitations.
PACS 63.20.Kr; 68.35.Ja; 68.37.Ef; 68.43.Pq; 72.10.Fk; 72.15.Qm; 73.20.At 相似文献
16.
A. I. Bezuglyi V. A. Shklovskii 《Journal of Experimental and Theoretical Physics》1997,84(6):1149-1163
The theoretical analysis of experiments on pulsed laser irradiation of metallic films sputtered on insulating supports is
usually based on semiphenomenological dynamical equations for the electron and phonon temperatures, an approach that ignores
the nonuniformity and the nonthermal nature of the phonon distribution function. In this paper we discuss a microscopic model
that describes the dynamics of the electron-phonon system in terms of kinetic equations for the electron and phonon distribution
functions. Such a model provides a microscopic picture of the nonlinear energy relaxation of the electron-phonon system of
a rapidly heated film. We find that in a relatively thick film the energy relaxation of electrons consists of three stages:
the emission of nonequilibrium phonons by “hot” electrons, the thermalization of electrons and phonons due to phonon reabsorption,
and finally the cooling of the thermalized electron-phonon system as a result of phonon exchange between film and substrate.
In thin films, where there is no reabsorption of nonequilibrium phonons, the energy relaxation consists of only one stage,
the first. The relaxation dynamics of an experimentally observable quantity, the phonon contribution to the electrical conductivity
of the cooling film, is directly related to the dynamics of the electron temperature, which makes it possible to use the data
of experiments on the relaxation of voltage across films to establish the electron-phonon and phonon-electron collision times
and the average time of phonon escape from film to substrate.
Zh. éksp. Teor. Fiz. 111, 2106–2133 (June 1997) 相似文献
17.
Temporal evolution of absorption induced by single femtosecond pulse (13Ors, 800nm) with high intensity in LiNbO3 is obtained using the probe shadow imaging technique in order to investigate light-induced electron relaxation processes. By saturating the polaron density with a high intensity laser pulse, ultra-fast decay process on picosecond time scale is observed. The decay time constant is about 141 ps and it is attributed to the direct interband electron-hole recombination process. 相似文献
18.
Correlated electron current and temperature dependence of the conductance of a quantum point contact
C. Sloggett A. I. Milstein O. P. Sushkov 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(4):427-432
We investigate finite temperature corrections to the Landauer formula
due to electron–electron interaction within the quantum point contact.
When the Fermi level is close to the barrier height, the conducting
wavefunctions become peaked on the barrier, enhancing the
electron–electron interaction. At the same time, away from the contact
the interaction is strongly suppressed by screening. To describe
electron transport we formulate and solve a kinetic equation for the
density matrix of electrons. The correction to the conductance G is
negative and strongly enhanced in the region 0.5 × 2e2/h ≤ G
≤ 1.0 × 2e2/h. Our results for conductance agree with the
so-called “0.7 structure” observed in experiments. 相似文献
19.
W. Holzer A. Penzkofer T. Pertsch N. Danz A. Bräuer E.B. Kley H. Tillmann C. Bader H.-H. Hörhold 《Applied physics. B, Lasers and optics》2002,74(4-5):333-342
Wave-guided thin-film distributed-feedback (DFB) polymer lasers are fabricated by spin coating a PPV-derived semiconducting
polymer, thianthrene-DOO-PPV, onto oxidised silicon wafers with corrugated second-order periodic gratings. The gratings are
written by reactive ion beam etching. Laser action is achieved by transverse pumping with picosecond laser pulses (wavelength
347.15 nm, duration 35 ps). The DFB-laser surface emission and edge emission are analysed. Outside the grating region the
polymer film is used for comparative wave-guided travelling wave laser (amplified spontaneous emission (ASE)) studies. The
pump pulse threshold energy density for wave-guided DFB-laser action (4–9 μJ cm-2) is found to be approximately a factor of two lower than the threshold for wave-guided travelling wave laser action. The
spectral width of the DFB laser (down to ΔλDFB≈0.07 nm) is considerably narrower than that of the travelling wave laser (ΔλTWL≈14 nm). The DFB-laser emission is highly linearly polarised transverse to the grating axis (TE mode). Only at high pump pulse
energy densities does an additional weak TM mode build up. The surface-emitted DFB-laser radiation has a low divergence along
the grating direction. For both the DFB lasers and the travelling wave lasers, gain saturation occurs at high excitation energy
densities.
Received: 7 January 2002 / Revised version: 15 February 2002 / Published online: 14 March 2002 相似文献
20.
The optical and non-linear optical properties of peripheral-substituted vanadium oxide phthalocyanine (VOPc) film and substituted
VOPc/polymer composite film were investigated using stationary and transient spectroscopy techniques. The absorption Q band
of the VOPc/polymer composite film shows a red shift relative to that of the peripheral-substituted VOPc film, revealing the
monomeric characteristics of VOPc molecules. Effective quenching of PL emission was observed for the VOPc/polymer composite
film and could be assigned to the efficient VOPc–polymer interaction. From pump-probe and optical Kerr effect (OKE) measurements,
two decay components were obtained by fitting the transients for both VOPc films. The fast component, in a femtosecond time
domain, originates from the electron–phonon interaction, and the difference in their slow decay is an indication of an efficient
ISC process in the VOPc/polymer composite film. The third-order non-linear optical susceptibilities of these films were determined
to be in the order of 10-11 esu.
Received: 25 October 2001 / Revised version: 8 January 2002 / Published online: 7 February 2002 相似文献