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1.
S. A. Baruzdin 《Physics of the Solid State》2005,47(12):2207-2212
Different regimes of excitation of a stimulated spin echo by pseudorandom pulses and short coherent delta-shaped pulses are considered. Radio pulses phase-shifted by a 127-element M sequence are used as pseudorandom signals. The shape of the complex envelope of the stimulated echo is simulated in linear and nonlinear regimes with respect to the phase-shifted pulses. It is demonstrated that the excitation pulses can be described by correlation functions. Appropriate conditions are determined under which the amplitude of the stimulated echo can be greater than the amplitude corresponding to the classical algorithm used for exciting a stimulated echo by three delta-shaped pulses. The results obtained can be used for analyzing the formation of a stimulated photon echo. 相似文献
2.
Primary acoustic echo during excitation of a paramagnetic crystal by picosecond elastic video pulses
The primary acoustic echo formed during excitation of a paramagnetic crystal with effective spin S=1 by two transverse picosecond elastic video pulses is investigated theoretically. Both exciting video pulses are applied
perpendicular to the external magnetic field. It is shown that the primary acoustic echo in the general case consists of six
longitudinal and transverse signals at the frequencies of the transitions within a Zeeman triplet. The optimal parameters
of the exciting video pulses for the appearance of different echo signals are determined.
Fiz. Tverd. Tela (St. Petersburg) 41, 623–628 (April 1999) 相似文献
3.
The mechanism governing the shaping of the echo response in a monodomain order-disorder ferroelectric crystal to excitation
by two pulses of a microwave electric field at the frequencies ω and 2ω [(ω, 2ω) echo] and at the frequency ω [(ω, ω) echo] is described in the framework of the pseudospin formalism (S=1/2). The parameters of the echo response are calculated, and the results obtained are in good qualitative agreement with
experiment.
Fiz. Tverd. Tela (St. Petersburg) 39, 697–703 (April 1997) 相似文献
4.
S. A. Baruzdin 《Optics and Spectroscopy》2016,121(4):607-613
The excitation of photon echo by noise pulses that are formed by modulation of the carrying frequency with Gauss noise is modeled. The modeling is based on optical Bloch equations the solution of which for noise pulse realizations is constructed by their stepwise approximation. In terms of the formalism of state transfer matrices, the two- and three-pulse excitation modes are analyzed. The complex envelopes of the primary and stimulated echo responses are determined. In the linear (low-level-signal) mode, the shape of the two-pulse echo corresponds to that of the time delayed and inverted noise pulse. The boundary of the linear mode, upon exceeding of which distortions of the shape of the noise pulse become noticeable, is determined. The shape of the stimulated (three-pulse) echo in the linear mode corresponds to that of the autocorrelation function of the noise pulse realization. Upon passage beyond the boundary of the linear mode, the shape of the three-pulse echo corresponds either to the cross-correlation function of distorted noise pulses (with different intensities) or to the autocorrelation function of distorted pulses (with the same intensities). The modeled photon echo excitation modes can be used in photon echo processors to process signals in the light range. 相似文献
5.
6.
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
7.
S. A. Baruzdin 《Optics and Spectroscopy》2001,91(2):255-261
Excitation of stimulated photon echo by two incoherent pulses obtained from one source and one coherent pulse is considered. The dependence of the average amplitude of stimulated echo on the parameters of noise pulses is determined. The results can be used for analysis of the corresponding algorithm of excitation of stimulated spin echo, as well as in calculations of characteristics of the signal processors based on the phenomena of photon and spin echoes. 相似文献
8.
N. N. Rubtsova L. S. Vasilenko E. B. Khvorostov 《Journal of Experimental and Theoretical Physics》1999,89(1):24-29
Collisional relaxation in SF6 gas and its mixtures with He and Xe is studied by photon echo and stimulated photon echo methods from the standpoint of the
possibility of identifying the contributions of different types of collisions. The nonexponential nature of the kinetic curve
of the photon echo is clearly observed for pure SF6, it is weaker in the mixture SF6+Xe, and it is virtually completely absent for high degrees of dilution of SF6 with helium. These features can be explained on the basis of estimates, made from experimental data, of the critical delay
between the exciting pulses (for which the nonexponential behavior should be most strongly manifested). In pure SF6 it is possible to distinguish the contribution of the inelastic channel (rotational relaxation) and the contribution of weak
collisions. To distinguish successfully the relaxation channels in mixtures with buffer gases a heavier buffer gas and a much
better time resolution must be used. It is shown that data obtained on the orientation and alignment relaxation rates by the
stimulated photon echo method can serve as an upper limit for the rates of inelastic processes which cannot be measured by
the photon echo method. The combined use of photon echo and stimulated photon echo methods made it possible to obtain data
on the cross sections for elastic and inelastic scattering of the collisional pairs SF6–SF6, SF6–Xe, and SF6–He.
Zh. éksp. Teor. Fiz. 116, 47–56 (July 1999) 相似文献
9.
B. A. Kalinikos N. G. Kovshikov M. P. Kostylev P. Kabos C. E. Patton 《JETP Letters》1997,66(5):371-375
The propagation of envelope solitons of microwave-frequency spin waves in a spatially periodic field oriented parallel to
the magnetic pump has been investigated experimentally. In a pulsed pumping regime with amplitude much greater than the threshold
for parametric excitation of spin systems, amplification of spin-wave envelope solitons exceeding their natural damping was
obtained.
Pis’ma Zh. éksp. Teor. Fiz. 66, No. 5, 346–350 (10 September 1997) 相似文献
10.
11.
S. A. Baruzdin 《Journal of Experimental and Theoretical Physics》1997,85(1):34-41
The third-order cross-correlations between a free induction signal of an inhomogeneously broadened two-level system and white
Gaussian noise exciting this system are studied. The temporal properties of the third-order cross-correlation functions are
found to correspond to the characteristics of ordinary two-and three-pulse spin and light (photon) echoes excited by determinate
radio pulses. The nonlinear properties of correlation echoes are studied as functions of the noise pulse parameters. It is
established that the correlation echo amplitude is determined not only by the noise pulse parameters but also by the position
on the time axis of the noise counts that form the given type of echo. Finally, the behavior of the spin and light correlation
echoes in the appropriate ranges is discussed.
Zh. éksp. Teor. Fiz. 112, 63–77 (July 1997) 相似文献
12.
A microscopic theory of the electro-acoustic echo (EAE) is proposed for the case in which two pulses of a variable electric
field act on an antiferroelectric. This theory augments the phenomenological theory proposed for the purpose of interpreting
experiments on the main regularities of the electro-acoustic echo in order-disorder antiferroelectrics. The deuterization
effect and “pre-polarization” effect are explained. The shape of the echo signal is derived analytically and it is shown that
this shape depends on the time interval between pump pulses.
Fiz. Tverd. Tela (St. Petersburg) 40, 118–121 (January 1998) 相似文献
13.
14.
The dependence of the ablation rate of aluminium on the fluence of nanosecond laser pulses with wavelengths of 532 nm and
respectively 1064 nm is investigated in atmospheric air. The fluence of the pulses is varied by changing the diameter of the
irradiated area at the target surface, and the wavelength is varied by using the fundamental and the second harmonic of a
Q-switched Nd-YAG laser system. The results indicate an approximately logarithmic increase of the ablation rate with the fluence
for ablation rates smaller than ∼6 μm/pulse at 532 nm, and 0.3 μm/pulse at 1064 nm wavelength. The significantly smaller ablation rate at 1064 nm is due to the small optical absorptivity,
the strong oxidation of the aluminium target, and to the strong attenuation of the pulses into the plasma plume at this wavelength.
A jump of the ablation rate is observed at the fluence threshold value, which is ∼50 J/cm2 for the second harmonic, and ∼15 J/cm2 for the fundamental pulses. Further increasing the fluence leads to a steep increase of the ablation rate at both wavelengths,
the increase of the ablation rate being approximately exponential in the case of visible pulses. The jump of the ablation
rate at the threshold fluence value is due to the transition from a normal vaporization regime to a phase explosion regime,
and to the change of the dimensionality of the hydrodynamics of the plasma-plume.
相似文献
15.
L. S. Vasilenko N. N. Rubtsova E. B. Khvorostov 《Journal of Experimental and Theoretical Physics》1998,86(3):450-454
A stimulated photon echo technique with specially selected linear polarizations of the coherent resonant driver pulses is
used to study depolarizing collisions in the molecular gas SF6 and in mixtures of it with buffer He and Xe. The collisional decay rates of the population, orientation, and alignment in
an ensemble of gas particles are determined for the first time in a single experiment. These relaxation rates are measured
as a function of the longitudinal translational velocities of the resonant particles. To within the experimental accuracy,
no significant dependence of the collisional decay rates on the translational velocities of the particles was observed. This
result confirms the conventional theoretical approach to depolarizing collisions. In pure SF6 the decay rates for the orientation and alignment were lower than the relaxation constant for collisions involving a change
in the longitudinal velocity (elastic collisions) that is known from experimental observations of the ordinary photon echo.
This means that only some of the elastic collisions participate in destroying the multipole moments of the levels. Evidence
is found that the relaxation of the multipole moments created by polarized radiation in a resonant medium of molecular SF6 gas depends on j, the total angular momentum of the level.
Zh. éksp. Teor. Fiz. 113, 826–833 (March 1998) 相似文献
16.
We show that the electric activity of superfluid helium (HeII) observed in the experiments [3] during the excitation of standing
second sound waves in an acoustic resonator can be described in terms of the phenomenological mechanism of the inertial polarization
of atoms in a dielectric, in particular, in HeII, when the polarization field induced in the medium is proportional to the
mechanical acceleration, by analogy with the Stewart-Tolman effect. The variable relative velocity w = v
n
− v
s
of the normal and superfluid HeII components that emerges in the second sound wave determines the mean group velocity of
rotons, V
g
≈ w, with the density of the normal component related to their equilibrium number density in the temperature range 1.3 K ≤ T ≤ 2 K. Therefore, the acceleration of the 4He atoms involved in the formation of a roton excitation is proportional to the
time derivative of the relative velocity.w. In this case, the linear local relations between the variable values of the electric
induction, electric field strength, and polarization vector should be taken into account. As a result, the variable displacement
current induced in the bulk of HeII and the corresponding potential difference do not depend on the anomalously low polarizability
of liquid helium. This allows the ratio of the amplitudes of the temperature and potential oscillations in the second sound
wave, which is almost independent of T in the above temperature range, consistent with experimental data to be obtained. At the same time, the absence of an electric
response during the excitation of first sound waves in the linear regime is related to an insufficient power of the sound
oscillations. Based on the experimental data on the excitation of first and second sounds, we have obtained estimates for
the phenomenological coefficient of proportionality between the polarization vector and acceleration and for the drag coefficient
of helium atoms by rotons in the second sound wave. We also show that the presence of a steady heat flow in HeII with nonzero
longitudinal velocity and temperature gradients due to finite viscosity and thermal conductivity of the normal component leads
to a change in the phase velocities of the first and second sound waves and to an exponential growth of their amplitudes with
time, which should cause the amplitudes of the electric signals at the first and second sound frequencies to grow. This instability
is analogous to the growth of the amplitude of long gravity waves on a shallow-water surface that propagate in the direction
of decreasing basin depth. 相似文献
17.
Two-pulse and three-pulse echoes in powdered yttrium and bismuth high-T
c superconductors are investigated to determine the dependence of the signal amplitude on the magnetic field, the temperature,
and the gas pressure. The temperature is measured as a function of the relaxation time of the echo signal. The properties
of the long-lived rf echo are studied in detail; it exhibits a persistent (lasting more than several hours) memory of a time
series of write pulses and a cumulative storage effect. The experimental results can be explained qualitatively within the
framework of the theory proposed by Asadullin [Sverkhprovodimost’ 6, 545 (1993)] to account for the nonlinear motion of vortices associated with sample defects.
Zh. éksp. Teor. Fiz. 111, 1032–1046 (March 1997) 相似文献
18.
F.P. Alberti 《Journal of sound and vibration》1983,86(2):227-233
Numerous problems of current concern involve the designs of aerodynamic systems which either travel at high speeds or contain structural elements which are excited by moving pressure fluctuations. In a number of recent papers responses of dynamic systems to random excitation have been considered. The appropriate theory for calculating the mean square response of linear systems to both stationary and non-stationary random excitation is well known [1–7]. In this paper, the mean square response of a finite cable to non-stationary random excitation is considered. The non-stationary random excitation is of the form s(t) = e(t)α(t), where e(t) is a well defined envelope function and α (t) is the Guassian, narrow band, stationary part of the excitation which has zero mean. Both the unit step and rectangular step functions are used for the envelope function, and both white noise and noise with an exponentially decaying harmonic correlation function are used to prescribe the statistical property of the excitation. The results obtained are shown to be a complete expression for the mean square response when checked for accuracy by reduction to expressions previously obtained by Lyon [4]. It is felt that these results will aid the design of both linear and two-dimensional aerodynamic systems excited by random pressure fluctuations. 相似文献
19.
S. V. Meriakri 《Technical Physics》1999,44(12):1472-1476
The propagation of a microwave pulse in a ferrite thin film-substrate structure in a regime of rereflections (“ringing”) of
the acoustic component of the substrate is studied theoretically. It is shown that as a result of the interaction of microwave
pulses with the boundaries of the substrate, propagation of a microwave excitation in this system can be regarded as a propagation
of a wave packet in a periodic nonuniform medium. The basic characteristics of a propagating wave packet are obtained.
Zh. Tekh. Fiz. 69, 82–86 (December 1999) 相似文献
20.
We study the statistics of the reflectance (the ratio of reflected and incident intensities) of an N-mode disordered waveguide with weak absorption g per mean free path. Two distinct regimes are identified. The regime γ N
2≫1 shows universal fluctuations. With increasing length L of the waveguide, the variance of the reflectance changes from the value 2/15N
2, characteristic for universal conductance fluctuations in disordered wires, to another value 1/8N
2, characteristic for chaotic cavities. The weak-localization correction to the average reflectance performs a similar crossover
from the value 1/3N to 1/4N. In the regime γ N
2≫1, the large-L distribution of the reflectance R becomes very wide and asymmetric, P(R)∝(1−R)−2 for R≪1−γN.
Pis’ma Zh. éksp. Teor. Fiz. 64, No. 4, 289–293 (25 August 1996)
Published in English in the original Russian journal. Edited by J. R. Anderson. 相似文献