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1.
The spectral dependence of the electron-phonon relaxation rate γe−ph(ℏω) in metals is studied in pump-supercontinuum-probe (PSCP) experiments with femtosecond time resolution. Investigation
of this spectral dependence, which exhibits a substantial slowing of the relaxation rate γe−ph(ℏω) near the Fermi level E
F
, using the parametrization γe−ph(ℏω)∝λ〈Ω2〉 (ℏω−E
F
)2 makes it possible to determine directly the electron-phonon interaction parameter λ〈Ω2〉. The parameter λ〈Ω2〉 for YBa2Cu3O7−δ is analyzed using this method.
Pis’ma Zh. éksp. Teor. Fiz. 70, No. 5, 329–332 (10 September 1999) 相似文献
2.
A strong resonant interaction of a two-level atom with a dielectric microsphere is studied on the basis of quantum electrodynamics.
The initial condition considered is one in which the atom is initially excited and the resonant mode of the microsphere has
been excited by a single photon. The spectrum of two emitted photons depends strongly on the method used to excite the microsphere,
i.e., on the spatial distribution of the photon energy. The most characteristic feature of the two-photon fluorescence spectrum
is a strong energy correlation of the emitted photons. This correlation is expressed in the fact that the energies of the
emitted photons are related by the equation of an ellipse (ω+ω
2−2ω
vA
)2+3(ω
1−ω
2)2= 4Ω
Rabi
2
. The relation between the results obtained and the predictions of the theory of dressed states is discussed.
Pis’ma Zh. éksp. Teor. Fiz. 70, No. 3, 192–197 (10 August 1999) 相似文献
3.
A new effect—light backscattering from exciton Bose-condensate—is considered. This effect is connected with the photoinduced coherent recombination of two excitons in the condensate with the production of two photons with opposite momenta. The effect of two-exciton coherent recombination leads also to the appearance of the second-order coherence in exciton luminescence connected with squeezing between photon states with opposite momenta. The estimations given for Cu2O and GaAs excitons show that the effect of stimulated light backscattering can be detected experimentally. Moreover, in the system of 2D excitons in coupled quantum wells, the effect of stimulated anomalous light transmission must also take place. Anologous effects can also take place in systems of Bose-condensed atoms in excited (but metastable) states. 相似文献
4.
We examine the absorption and amplification bands of a weak probe signal in the presence of Bose-Einstein condensation of
excitons that emerges in nonequilibrium conditions in the field of coherent laser radiation with a wave vector k
0. We assume that the detuning
from resonance between the energy ħω
ex
(k
0)+L
0 of the exciton level, which is shifted because of exciton-exciton interaction, and the laser photon energy ħω
L
, is generally nonzero. The elementary excitation spectrum consisting of the quasiexcitonic and quasienergy branches determines
the optical properties of the system. When there is real induced Bose-Einstein condensation, at
the two branches touch, as they do in spontaneous Bose-Einstein condensation. In virtual induced Bose-Einstein condensation,
when
, instabilities emerge in the spectrum in certain regions of the k-space. These instabilities are caused by a real transformation of two laser photons into two extracondensate particles. Nonequilibrium
extracondensate excitons strongly affect the absorption and amplification of the probe light signal. We show that light absorption
is due to the quantum transition from the ground state of the crystal to the quasiexcitonic branch of the spectrum. On the
other hand, amplification of the signal is caused by the transition from the quasienergy branch to the ground state of the
crystal. The same transition can be explained by a real transformation of two laser photons into a vacuum photon of frequency
ħcq and a crystal exciton with a wave vector 2k
0−q. Finally, we show that the excitonic absorption and light-amplification bands are essentially anisotropic at
and depend on the orientation of the vectors q and k
0.
Zh. éksp. Teor. Fiz. 112, 167–179 (July 1997) 相似文献
5.
A theory of the shift current induced by direct two-photon and indirect one-photon absorption is developed for noncentrosymmetric
crystals. A formula is derived for the microscopic shifts of Bloch electrons induced by two-quantum processes. It is shown
that the ratio of the two-photon photocurrent at the photon frequency ω to the photocurrent induced by direct one-photon transitions
at the photon frequency 2ω, as compared to the corresponding absorption-rate ratio, contains a large factor {ie152-1}ω/(2{ie152-2}ω
− E
g), where E
g is the bandgap; i.e., these photocurrent can be comparable in order of magnitude. For crystals of T
d
symmetry, the photocurrents induced by one- and two-photon absorption are compared in terms of polarization dependence. 相似文献
6.
L. V. Butov A. V. Mintsev A. I. Filin K. Eberl 《Journal of Experimental and Theoretical Physics》1999,88(5):1036-1044
The kinetics of indirect photoluminescence of GaAs/AlxGa1−x
As double quantum wells, characterized by a random potential with a large amplitude (the linewidth of the indirect photoluminescence
is comparable to the binding energy of an indirect exciton) in magnetic fields B≤12 T at low temperatures T≥1.3 K is investigated. It is found that the indirect-recombination time increases with the magnetic field and decreases with
increasing temperature. It is shown that the kinetics of indirect photoluminescence corresponds to single-exciton recombination
in the presence of a random potential in the plane of the double quantum wells. The variation of the nonradiative recombination
time is discussed in terms of the variation of the transport of indirect excitons to nonradiative recombination centers, and
the variation of the radiative recombination time is discussed in terms of the variation of the population of optically active
excitonic states and the localization radius of indirect excitons. The photoluminescence kinetics of indirect excitons, which
is observed in the studied GaAs/AlxGa1−x
As double quantum wells for which the random potential has a large amplitude, is qualitatively different from the photoluminescence
kinetics of indirect excitons in AlAs/GaAs wells and GaAs/AlxGa1−x
As double quantum wells with a random potential having a small amplitude. The temporal evolution of the photoluminescence
spectra in the direct and indirect regimes is studied. It is shown that the evolution of the photoluminescence spectra corresponds
to excitonic recombination in a random potential.
Zh. éksp. Teor. Fiz. 115, 1890–1905 (May 1999) 相似文献
7.
X. M. Song Z. G. Huang H. Q. Lu Q. Q. Sun 《International Journal of Theoretical Physics》2008,47(4):865-872
In dilatonic cosmology model, we study the behavior of attractor solution in ω–ω′ plane, which is defined by the equation of state parameter for the dark energy and its derivative with respect to N (the logarithm of the scale factor a). This is a good method which is useful to the study of classifying the dynamical dark energy models including “freezing”
and “thawing” model. We find that our model belongs to “freezing” type model classified in ω–ω′ plane. We show mathematically the property of attractor solutions which correspond to ω
σ
=−1, Ω
σ
=1. The present values of energy density parameter
,
and
are 0.715001, 0.284972 and 0.00002706 respectively, which meet the current observations well. Finally, we can obtain that
the coupling between dilaton and matter affects the evolutive process of the Universe, but not the fate of the Universe. 相似文献
8.
X.-H. Guo Gang Lü Z.-H. Zhang 《The European Physical Journal C - Particles and Fields》2008,58(2):223-244
In the framework of factorization we study direct CP violation in the decays of bottom hadrons containing a strange quark or a charm quark, H
b
→f
ρ
0(ω)→f
π
+
π
− (H
b
is the bottom hadron and f is the product hadron) including the effect of ρ–ω mixing. We find that the CP violating asymmetry can be enhanced greatly via the ρ–ω mixing mechanism when the invariant mass of the π
+
π
− pair is in the vicinity of the ω resonance. For the processes associated with b→d transitions, e.g.
,
, B
c
−→D
−
π
+
π
−, B
c
−→D
*−
π
+
π
−, Ξ
b
0→Λ
π
+
π
−, and Ω
b
−→Ξ
−
π
+
π
−, the maximum CP violating asymmetries can reach about −84%, while for the processes associated with b→s transitions, e.g.
,
, B
c
−→D
s
−
π
+
π
−, B
c
−→D
s
*−
π
+
π
−, Ξ
b
−→Ξ
−
π
+
π
−, and Ω
b
−→Ω
−
π
+
π
−, the CP violating asymmetries can be enhanced to about 95%. Furthermore, taking ρ–ω mixing into account we calculate the b-hadron decay branching ratios. We also discuss the possibility to observe the predicted CP violating asymmetries at the LHC. 相似文献
9.
A. N. Starukhin B. S. Razbirin A. V. Chugreev M. Happ F. Henneberger 《Physics of the Solid State》1999,41(8):1271-1274
The Zeeman effect in the emission spectra of localized excitons in semiconductor solid solutions has been studied by selective
laser spectroscopy. It was shown that the fine structure appearing in the emission spectra of GaSe1−x
Tex crystals under resonant monochromatic excitation in a magnetic field originates from spin relaxation of the light-induced
localized excitons between their Zeeman sublevels. The localized-exciton g factor and its dependence on the energy of localized-exciton formation and solid-solution composition has been measured.
Fiz. Tverd. Tela (St. Petersburg) 41, 1389–1393 (August 1999) 相似文献
10.
Optical nutation at the Raman-active transition 6P
1/2−6P
3/2 of thallium atoms (ω
R
/2πc=7793 cm −1) under resonant Raman excitation by a biharmonic picosecond pulsed field, giving rise to substantial motion of the population,
is detected. Optical nutation appears as an oscillatory behavior of the energy of the anti-Stokes scattering of probe pulses,
which follow with a fixed delay, as a function of the product of the energies of the excitation pulses. As a result of the
dynamic Stark effect, which decreases the frequency of the transition under study, resonance excitation conditions are satisfied
for negative initial detunings of the Raman excitation frequency from resonance. The Raman scattering cross section for the
transition under study is estimated by comparing the experimental data with the calculations.
Pis’ma Zh. éksp. Teor. Fiz. 70, No. 1, 7–12 (10 July 1999) 相似文献
11.
A. A. Kaminskii H. Rhee H. J. Eichler K. Ueda K. Oka H. Shibata 《Applied physics. B, Lasers and optics》2008,93(4):865-872
We report the experimental investigations of nonlinear-laser effects in LuVO4 vanadate under one-micron picosecond Nd3+:Y3Al5O12 pumping. In this tetragonal host-crystal for Ln3+ lasants for the first time we excited ultra-broad, more than one and half octave (13500 cm−1) Raman induced Stokes and anti-Stokes generation combs and observed multi-step cascaded parametric χ
(3)-lasing in UV spectral region. All generation lines were identified and attributed to SRS-promoting modes of the crystal (ω
SRS1≈900 cm−1 and ω
SRS2≈113 cm−1). We classified this vanadate as a promising material for self-Raman laser converters. 相似文献
12.
13.
Molin Liu Jianbo Lu Yuanxing Gui 《The European Physical Journal C - Particles and Fields》2009,59(1):107-116
On the basis of the 4D momentum, the influence of quintessence on the gravitational frequency shift and the deflection of
light are examined in modified Schwarzschild space. We find that the frequency of a photon depends on the state parameter
of the quintessence w
q: the frequency increases for −1<w
q<−1/3 and decreases for −1/3<w
q<0. Meanwhile, we adopt an integral power number a (a=3ω
q+2) to solve the orbital equation of photon. The photon’s potentials become higher with the decrease of ω
q. The behavior of the bending light sensitively depends on the state parameter ω
q. In particular, for the case of ω
q=−1, there is no influence on the deflection of light by quintessence. Furthermore, according to the H-masers of the GP-A
redshift experiment and long-baseline interferometry, the constraints on the quintessence field in the solar system are presented
here. 相似文献
14.
The return current induced in a plasma by a relativisitc electron beam generates a new electron-ion two-stream instability
(return current instability). Although the effect of these currents on the beam-plasma e-e instability is negligible, there
exists a range of wave numbers which is unstable only to return current (RC) instability and not to e-e instability. The electromagnetic
waves propagating along the direction of the external magnetic field, in which the plasma is immersed, are stabilized by these
currents but the e.m. waves with frequencies,ω
2≪Ω
e
2
≪ω
pe
2
(Ω
e andω
pe being cyclotron and plasma frequency for the electrons of the plasma respectively) propagating transverse to the magnetic
field get destabilized. Heuristic estimates of plasma heating, due to RC instability and due to decay of ion-acoustic turbulence
generated by the return current, are made. The fastest time scale on which the return current delivers energy to the plasma
due to the scattering of ion-sound waves by the electrons can be ∼ω
pi
−1
(ω
pi being the plasma frequency for the ions). 相似文献
15.
The nonadiabatic corrections to the self-energy part Σs(q, ω) of the phonon Green’s function are studied for various values of the phonon vectors q resulting from electron-phonon interactions. It is shown that the long-range electron-electron Coulomb interaction has no
direct influence on these effects, aside from a possible renormalization of the corresponding constants. The electronic response
functions and Σs(q, ω) are calculated for arbitrary vectors qand energy ω in the BCS approximation. The results obtained for q=0 agree with previously obtained results. It is shown that for large wave numbers q, vertex corrections are negligible and Σs(q, ω) possesses a logarithmic singularity at ω=2Δ, where Δ is the superconducting gap. It is also shown that in systems with nesting, Σs(Q, ω) (where Q is the nesting vector) possesses a square-root singularity at ω=2Δ, i.e., exactly of the same type as at q=0. The results are used to explain the recently published experimental data on phonon anomalies, observed in nickel borocarbides
in the superconducting state, at large q. It is shown, specifically, that in these systems nesting must be taken into account in order to account for the emergence
of a narrow additional line in the phonon spectral function S(q, ω)≈−π
−1 Im D
s
(q, ω), where D
s
(q, ω) is the phonon Green’s function, at temperatures T<T
c
.
Zh. éksp. Teor. Fiz. 115, 1799–1817 (May 1999) 相似文献
16.
A series of 2,6-bis(p-dihexylaminostyryl)anthracence derivatives having phenyl, styryl, and phenylethynyl groups at 9,10-positions (1−4) have been synthesized and their two-photon cross-sections were determined. Overall, the wavelengths of the longest wavelength
absorption band and emission spectra increase with increase in the conjugation length and the electron withdrawing ability
of the 9,10-substituents. All compounds show two-photon cross sections in the range of 740−3940 GM at 780−960 nm, which increase
significantly by the donor and acceptor groups at 9,10-positions. In addition, Ph and phenylethynyl groups are better when
compared to the styryl group at the 9,10-positions in terms of the two-photon action cross section. From a practical perspective,
1a, 2a–c, and 4b showed significant two-photon action cross-section and are most useful for applications that use two-photon excited fluorescence. 相似文献
17.
V. I. Ritus 《Journal of Experimental and Theoretical Physics》1998,87(1):25-34
This paper discusses the symmetry of the wave field that lies to the right and left of a two-sided accelerated mirror in 1+1
space and satisfies a single condition on it. The symmetry is embodied in the Bogolyubov matrix coefficients α and β that connect the two complete sets of solutions of the wave equations. The amplitudes of the quantum processes in the right
and left half-spaces are expressed in terms of α and β and are related to each other by the transformation (12). The coefficient β
ω′ω
*
plays the role of the source amplitude of a pair of oppositely directed particles with frequencies ω and ω′ of which one is in the left half-space and the other is in the right half-space because one of them has undergone reflection.
Such an interpretation makes β
ω′ω
*
observable and explains why, as shown by Eq. (1) and found earlier by Nikishov and Ritus [Zh. éksp. Teor. Fiz. 108, 1121 (1995); transl. JETP 81, 615 (1995)] and by Ritus [Zh. éksp. Teor. Fiz. 110, 526 (1996); transl. JETP 83, 282 (1996)], the emission spectra of a mirror in 1+1 space coincide with those of charges in 3+1 space. The reason is that
the angular momentum of the pair emitted by the mirror coincides with the angular momentum of the single particle emitted
by the charge.
Zh. éksp. Teor. Fiz. 114, 46–62 (July 1998) 相似文献
18.
Yasuo Oka 《Physics of the Solid State》1998,40(5):778-780
Excitonic properties and the dynamics are reported in quantum dots (QDs) and quantum wells (QW) of diluted magnetic semiconductors.
Transient spectroscopies of photoluminescence and nonlinear-optical absorption and emission have been made on these quantum
nanostructures. The Cd1−x
MnxSe QDs show the excitonic magnetic polaron effect with an increased binding energy. The quantum wells of the Cd1−x
MnxTe/ZnTe system display fast energy and dephasing relaxations of the free and localized excitons as well as the tunneling process
of carriers and excitons in the QWs depending on the barrier widths. The observed dynamics and the enhanced excitonic effects
are the inherent properties of the diluted magnetic nanostructures.
Fiz. Tverd. Tela (St. Petersburg) 40, 846–848 (May 1998)
Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor. 相似文献
19.
L. Bartosch P. Kopietz 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(1):29-36
We consider the effect of Coulomb interactions on the average density of states (DOS) of disordered low-dimensional metals
for temperatures T and frequencies ω smaller than the inverse elastic life-time 1/τ. Using the fact that long-range Coulomb interactions in two dimensions (2d) generate ln2-singularities in the DOS ν(ω) but only ln-singularities in the conductivity σ(ω), we can re-sum the most singular contributions
to the average DOS via a simple gauge-transformation. If σ(ω) > 0, then a metallic Coulomb gapν(ω) ∝ |ω|/e
4 appears in the DOS at T = 0 for frequencies below a certain crossover frequency Ω
2 which depends on the value of the DC conductivity σ(0). Here, - e is the charge of the electron. Naively adopting the same procedure to calculate the DOS in quasi 1d metals, we find ν(ω) ∝ (|ω|/Ω
1)1/2exp(- Ω
1/|ω|) at T = 0, where Ω
1 is some interaction-dependent frequency scale. However, we argue that in quasi 1d the above gauge-transformation method is on less firm grounds than in 2d. We also discuss the behavior of the DOS at finite temperatures and give numerical results for the expected tunneling conductance
that can be compared with experiments.
Received 28 August 2001 / Received in final form 28 January 2002 Published online 9 July 2002 相似文献
20.
We investigate the spectroscopic properties of the 1.5-μm emission from the 4I13/2 → 4I15/2 transition of Er3+ ions in PbO–Bi2O3–Ga2O3–GeO2 glasses for applications in broadband fiber amplifiers. The measured emission peak locates at 1,532 nm with a full width
at half-maximum of ∼45 nm. The glasses exhibit a large stimulated emission cross-section of 0.89 × 10−20 cm2 and a large product of 40.0. Infrared-to-green upconversion occurs simultaneously upon excitation of the 1.5-μm emission with a commercially
available 980 nm laser diode. The green-upconversion intensity has a quadratic dependence on incident pump laser power, indicating
a two-photon process. Energy transfer processes and nonradiative phonon-assisted decays could account for the population of
the 2H11/2 of Er3+. The results indicate the possibility towards the development of lead–bismuth–gallate–germanate based glasses as photonics
devices. 相似文献