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1.
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
2.
An investigation is reported of stimulated two-photon emission by Bose-condensed excitons accompanied by a coherent two-exciton
recombination, i.e., by simultaneous recombination of two excitons with opposite momenta leaving unchanged the occupation
numbers of exciton states with momenta p≠0. Raman light scattering (RLS) accompanied by a similar two-exciton recombination (or production of two excitons) is also
analyzed. The processes under consideration can occur only if a system contains Bose condensate, so their detection can be
used as a new method to reveal Bose condensation of excitons. The recoil momentum, which corresponds to a change in the momentum
of the electromagnetic field in the processes, is transferred to phonons or impurities. If the recoil momentum is transmitted
to optical phonons with frequency ω
0
s
, whose occupation numbers are negligible, and the incident light frequency satisfies ω<2Ω, where Ω_=Ω−ω
0
s
is the difference frequency and Ω is the light frequency corresponding to the recombination of an exciton with zero momentum,
stimulated two-photon emission and RLS with coherent two-exciton recombination give rise to a line at 2Ω_ −ω and an anti-Stokes component at ω+2Ω_, respectively. For ω2Ω_ the RLS spectrum contains Stokes and anti-Stokes components at frequencies ω±2Ω_, whereas stimulated two-photon emission is impossible. Formulas for the cross sections at finite temperatures are obtained
for the processes under consideration. Our estimates indicate that a spectral line at 2Ω_−ω, corresponding to the stimulated two-photon emission accompanied by coherent optical phonon-assisted two-exciton recombination
can be experimentally detected in Cu2O.
Zh. éksp. Teor. Fiz. 115, 1353–1376 (April 1999) 相似文献
3.
We report the calculation of matrix element effects in the frequency dependent dielectric function,ε
2
ω, for insulatingd-band perovskites. Analytical expressions are obtained forε
2
ω which yield results that are in good agreement with data for SrTiO3. These results also provide a direct comparison betweenε
2
ω and the joint density-of-states. The joint density-of-state approximation is found to be particularly poor due to unusually
large transition matrix element effects.
On leave from Middle East Technical University, Ankara, Turkey 相似文献
4.
5.
T. Mercouris C.A. Nicolaides 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(2):241-248
By implementing a time-independent, nonperturbative many-electron, many-photon theory (MEMPT), cycle-averaged complex eigenvalues
were obtained for the He atom, whose real part gives the field-induced energy shift, Δ(ω
1, F
1;ω
2, F
2,ϕ), and the imaginary part is the multiphoton ionization rate, Γ(ω
1, F
1;ω
2, F
2,ϕ), where ω is the frequency, F is the field strength and ϕ is the phase difference. Through analysis and computation we show that, provided the intensities
are weak, the dependence of Γ(ω
1, F
1;ω
2, F
2,ϕ) on ϕ is simple. Specifically, for odd harmonics, Γ varies linearly with cos(ϕ) whilst for even harmonics it varies linearly
with cos(2ϕ). In addition, this dependence on ϕ holds for Δ(ω
1, F
1;ω
2, F
2,ϕ) as well. These relations may turn out to be applicable to other atomic systems as well, and to provide a definition of
the weak field regime in the dichromatic case. When the combination of (ω
1, F
1) and (ω
2, F
2) is such that higher powers of cos(ϕ) and cos(2ϕ) become important, these rules break down and we reach the strong field
regime. The herein reported results refer to Γ(ω
1, F
1;ω
2, F
2,ϕ) and Δ(ω
1, F
1;ω
2, F
2,ϕ) for He irradiated by a dichromatic ac-field consisting of the fundamental wavelength λ = 248 nm and its 2nd, 3rd and 4th
higher harmonics. The intensities are in the range 1.0×1012-3.5×1014 W/cm2, with the intensity of the harmonics being 1-2 orders of magnitude smaller. The calculations incorporated systematically
electronic structure and electron correlation effects in the discrete and in the continuous spectrum, for 1S, 1P, 1D, 1F, 1G, and 1H two-electron states of even and odd parity.
Received 9 July 2000 and Received in final form 2 November 2000 相似文献
6.
G. G. Fedoruk 《Journal of Experimental and Theoretical Physics》1997,84(4):665-668
This paper reports the results of an experimental study of the decay of transient NMR nutations in a two-level spin system
with homogeneous line broadening. The NMR nutation signals in glycerin were studied for 10⩽ω
1
T
2⩽150, where ω
1=γH
1, with γ the gyromagnetic ratio and H
1 the amplitude of the magnetic component of the radio-frequency field, and T
2 is the transverse relaxation time. It is found that in a high-power field (ω
1
T
2≫1) the nutation decay rate is independent of ω
1 and is quantitatively described by Bloch’s model. The data is compared with the data on non-Bloch (ω
1-dependent) EPR-nutation decay in quartz (R. Boscaino, F. M. Gelardi, and J. P. Corb, Phys. Rev. B 48, 7077 (1993)).
Zh. éksp. Teor. Fiz. 111, 1207–1213 (April 1997) 相似文献
7.
Studying the ω<Emphasis Type="Italic">N</Emphasis> elastic and inelastic cross section with nucleons
Ye.S. Golubeva W. Cassing L.A. Kondratyuk A. Sibirtsev M. Büscher 《The European Physical Journal A - Hadrons and Nuclei》2000,7(2):271-277
We explore the possibility to measure the elastic and inelastic ωN cross section in p+d→d+ω+p
sp and p+A reactions. Our studies indicate that the elastic scattering cross sections can be determined for ω momenta above 1 GeV/c
in p+d reactions by gating on high proton spectator momenta whereas the ωN absorption cross section down to low relative ω momenta is most effectively studied in p+A reactions at beam energies 2.0–2.7 GeV.
Received: 15 October 1999 相似文献
8.
Hydrostatic pressure has been used to tune in resonance Raman scattering (RRS) in bulk GaAs. Using a diamond anvil cell, both
the photoluminescence peak (PL) and the 2 LO and LO-phonon Raman scattered intensities have been monitored, to establish RRS
conditions. When theE
0 gap of GaAs matchesħω
S orħω
L, the 2 LO and LO-phonon intensity, respectively, exhibit resonance Raman scattering maxima, at pressures determined byħω
L. With 647.1 nm radiation (ħω
L = 1.916 eV), a sharp and narrow resonance peak at 3.75 GPa is observed for the 2 LO-phonon. At this pressure the 2 LO-phonon
goes through its maximum intensity, and falls right on top of the PL peak, revealing thatħω
S(2 LO) =E
0. This is the condition for “outgoing” resonance. Experiments with other excitation energies (ħω
L) show, that the 2 LO resonance peak-pressure moves to higher pressure with increasingħω
L, and the shift follows precisely theE
0 gap. Thus, the 2 LO RRS is an excellent probe to follow theE
0 gap, far beyond the Γ-X cross-over point. A brief discussion of the theoretical expression for resonance Raman cross section is given, and from this
the possibility of a double resonance condition for the observed 2 LO resonance is suggested. The LO-phonon resonance occurs
at a pressure whenħω
L ≈E
0, but the pressure-induced transparency of the GaAs masks the true resonance profile. 相似文献
9.
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
10.
Vl.A. Margulis S.V. Makarov T.V. Piterimova E.A. Gaiduk 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(2):153-164
Using a mean-field approximation, we have developed a systematic treatment of collective electronic modes in a semiconductor
superlattice (SL) in the presence of strong electric and magnetic fields parallel to the SL axis. The spectrum of collective
modes with zero wavevector along the SL axis is shown to consist of a principle magnetoplasmon mode and an infinite set of
Bernstein-like modes. For non-zero wavevector along the SL axis, in addition to the cyclotron modes, extra collective modes
are found at the frequencies |Nω
c±Mω
s|, which we call cyclotron-Stark modes (ω
c and ω
s are respectively the cyclotron and Stark frequencies, N and M are integer numbers). The frequencies of the modes propagating in “oblique” direction with respect to the SL axis show oscillatory
behavior as a function of electric field strength. All the modes considered have very weak spatial dispersion and they are
not Landau damped. The specific predictions made for the dispersion relations of the collective excitations should be observable
in resonant Raman scattering experiments.
Received 29 August 2002 / Received in final form 25 February 2003 Published online 4 June 2003
RID="a"
ID="a"e-mail: 612033@inbox.ru 相似文献
11.
12.
A new method is proposed for setting a lower or upper limit a α
n
* on the neutron electric polarizability α
an
. It is based on the fact that the real part of the s-wave scattering amplitude changes sign near the s-wave neutron resonance at E=E*. The methods consist of the observation of the energy behavior of the forward-backward scattering asymmetry ω
1 which experiences a jump at E=E*. If the jump is such that dω
1/dE>0, then α
n
>α
n
*, while if dω
1/dE<0, then α
n
<α
n
*, and if dω
1/dE∼0, then α
n
∼α
n
*. Seven even-even nuclei are found with α
n
* from 0.5 to 3.1 in 10−3 fm3. Some details of a possible experiment with 182W are described.
Pis’ma Zh. éksp. Teor. Fiz. 70, No. 3, 171–174 (10 August 1999)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
13.
Mufei Xiao 《Applied Physics A: Materials Science & Processing》1996,64(1):91-99
Within the framework of electric dipole approximation, the focused light spot produced by a tiny optical fiber tip in front
of a phase conjugate mirror is investigated numerically. The fiber tip is the probe of a reflection scanning near field optical
microscope and the incident light is guided through the fiber. Intensity distribution of local field is calculated in the
half space where the fiber tip locates. Both homogeneous (q
‖≤ω/c
0) and part of inhomogeneous (ω/c
0<q
‖≤ωn/c
0) fields are included in establishing a field propagator (Green’s function) which is employed to calculate the local field
distribution. The local field forms at the tip position a diffraction light spot with a finite central value and a finite
size, and when the tip-surface distance is sufficient small, the strength and the shape of the light spot become a function
of the distance, which is due to the contribution of evanescent field. Fairly good agreements are found with the existing
experimental reports.
Received: 30 April 1996/Accepted: 19 August 1996 相似文献
14.
V E Kravtsov 《Pramana》2002,58(2):183-193
It is shown that the variance of the linear dc conductance fluctuations in an open quantum dot under high-frequency ac pumping
depends significantly on the spectral content of the ac field. For a sufficiently strong ac field the dc conductance fluctuations
are much stronger for the periodic pumping than in the case of the noise ac field of the same intensity. The reduction factor
r in a static magnetic field takes the universal value of 2 only for the white-noise pumping. In general r may deviate from 2 thus signalling on the time-reversal breaking by the ac field. For the bi-harmonic ac field of the form
A(t) = A
0[cos(ω
1
t) − cos(ω
2
t)] we predict the enchancement of effects of T-symmetry breaking at commensurate frequencies ω
2/ω
1 = P/Q. In the high-temperature limit there is also the parity effect; the enchancement is only present if either P or Q is even. 相似文献
15.
R.K. Varma 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(2):211-218
It has been shown earlier [3,6] that matter waves which are known to lie typically in the range of a few angstrom, can also
manifest in the macrodomain with a wave length of a few centimeters, for electrons propagating along a magnetic field. This
followed from the predictions of a probability amplitude theory by the author [1,2] in the classical macrodomain of the dynamics
of charged particles in a magnetic field. It is shown in this paper that this case constitutes only a special case of a generic
situation whereby composite systems such as atoms and molecules in their highly excited internal states, can exhibit matter
wave manifestation in macro and mesodomains, in one-dimensional scattering. The wave length of these waves is determined,
not by the mass of the particle as in the case of the de Broglie wave, but by the frequency ω, of the classical orbital motion
of the internal state in the correspondence limit, and is given by a nonquantal expression, λ = 2πv/ω, v being the velocity of the particle. For the electrons in a magnetic field the frequency corresponds to the gyrofrequency,
Ω and the nonquantal wave length is given by λ = 2πv
|| /Ω; v
|| being the velocity of electrons along the magnetic field.
Received 29 September 2001 / Received in final form 23 May 2002 Published online 19 July 2002 相似文献
16.
A computational scheme based on the infinite order sudden approximation (IOS) is proposed for treating molecular and screening
effects in muonic atom scattering at low energies. With this scheme the differential (dσ/dΩ(ɛj← 0|θ) and the total σtot(ɛ) cross-sections of muonic atom scattering on molecules of hydrogen isotopes are calculated at energies ɛrot=ℏωI⩽ɛ⩽ɛvib= ℏω03BD;. The IOS permits a quantitative analysis of the dependence of the differential cross-sections on the scattering angle and
on the rotational excitations, particularly the rotational rainbow effects. An attractive feature of this approach is also
to include the energy and the angular dependencies in the “input” cross-sections describing the muonic atom scattering on
each bare nucleus of the molecule. The calculated total cross-sections ωtot(ɛ) are in agreement with the data obtained earlier with the pseudopotential approach.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
17.
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
18.
The dispersion relation of electromagnetic waves in the presence of magnetic monopoles of electron mass in a uniform magnetic
field is obtained. The waves of the frequencyω in the range ωϱi<Ωi<ω<Ω
e
<ωϱa are analysed. It is shown that the monopole charges lead to observable effects. Finally, the results are applied to a typical
pulsar. 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 present here an approximate scheme to obtain the complex frequency-dependent local field correction,G (q, ω). Using the equation of motion approach we develop here a methodology from which the results obtained by earlier workers,
for density-density response function of an electron gas, can be arrived at in a simple systematic manner. We study in detail
an approximation made along the similar lines as Singwi and coworkers, which leads to a compact expression for a complex frequency-dependent
local field correction. We give results for damping coefficient of long wavelength plasmons which depends on ImG(q, ω). The real and imaginary parts ofG(q, ω) as functions ofω for various values ofq are also calculated. The dynamic structure factorS(q, ω) is evaluated forq=1.6q
F and compared with earlier theoretical and experimental results.
An erratum to this article is available at . 相似文献