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1.
Diffraction effects, taking place during nonlinear transformations in inhomogeneous acoustic fields, are experimentally investigated.
The case of a convergent spherical wave front propagating in a uniform nonlinear medium, detection of an acoustic field in
a focus, and receiving of the detected signal in the region of the initial wave front aperture are considered. A spherical
piezoceramic transducer is used in the experiments as a focusing device. Broad-angle “nonlinear scattering” signals have been
recorded at the experimental facility where a pulsed mode of focused transducer operation in water is implemented. The dependence
of the amplitude of the signal, detected in the focal area, and its shape on the scattering direction, as well as on the distance
between the focus and the receiving point, are studied. 相似文献
2.
Transient processes accompanying the conversion of a video pulse into a radio pulse in a nonlinear transmission line having
hysteretic properties are studied. It is established that the transition process leading to the establishment of “steady-state”
(close in amplitude) oscillations has a minimum when the electromagnetic shock wave front is phase-matched with the wave excited
by it at a frequency near the minimum local dispersion of the group velocity.
Zh. Tekh. Fiz. 68, 89–95 (January 1998) 相似文献
3.
I. R. Smirnovskii 《Technical Physics》1999,44(12):1444-1448
It is shown that multiple ion reflection, arising as a result of collisional dissipation, from a shock front can produce an
ion-sound shock wave with an arbitrarily large Mach number. For an exponentially small number of reflected ions, the ion-sound
shock wave “degenerates” into a collisionless quasishock wave. The comparative role of viscosity and sound dispersion with
different initial nonisothermality of the plasma is discussed.
Zh. Tekh. Fiz. 69, 52–56 (December 1999) 相似文献
4.
V. A. Maisheev 《Journal of Experimental and Theoretical Physics》1997,85(6):1102-1109
The head-on propagation of a beam of γ grays through the field of a laser wave is investigated. The optical properties of the laser wave (as a medium) are described
by the dielectric tensor. The refractive indices are determined, and the polarization characteristics of electromagnetic normal
modes capable of propagating in such a medium are investigated. Relations are derived to describe the variation of the initial
polarization and intensity of a γ-ray beam as it propagates in a laser field. The influence of laser intensity on the investigated process is discussed.
Zh. éksp. Teor. Fiz. 112, 2016–2029 (December 1997) 相似文献
5.
S. V. Tarasenko 《Physics of the Solid State》1998,40(2):272-276
It is shown that first-principles inclusion of nonuniform exchange interaction leads to the creation of a new type of generalized
shear acoustic wave propagating near the mechanically free surface of a magnet. Criteria are formulated that can be used to
specify conditions under which an “exchange” type of surface acoustic wave can exist at the boundary between a magnetic and
a nonmagnetic medium once the spectrum of magnetoelastic oscillations of the unbounded magnetic crystal is known.
Fiz. Tverd. Tela (St. Petersburg) 40, 299–304 (February 1998) 相似文献
6.
A. P. Bogatov 《Journal of Russian Laser Research》1994,15(5):417-453
The electromagnetic field inside a nonlinear active medium of a laser is considered as a system of counterpropagating waves.
Such an approach changes radically an earlier studied behavior of the lateral field instability due to self-deformaion (or
self-focusing). In our calculations we used an expression for a laser field in the form of two “strong” counterpropagating
waves whose complex amplitudes have weak perturbations. Amplitude perturbations of each of the “strong” waves can be presented
by two spatial harmonics corresponding to two weak perturbation waves with wave vectors making some tilted angle ±φ with the
cavity axis. Thus six waves would participate in the interaction: two counterpropagating strong waves and two pairs of weak
waves. Using this approach, we have developed a theory for the propagation of four “weak” perturbation waves in a nonlinear
amplifying medium in the presence of two counterpropagating “strong” waves. It is shown that perturbation waves with tilted
angle φ⋍0.5–1.2° inside the active region, and respecively, with the side lobes of the far-field pattern at ∼1.7–4°, have
the greatest growth increment. These perturbation waves produce lateral intensity modulation with period 10–30 μm for the
0.85 μm lasing wavelength. The appearance of such waves corresponds to the instability threshold of a homogeneous lateral
distribution of optical power in a diode laser.
The present theory makes it possible to investigate the stability of the homogeneous lateral optical intensity distribution
in a diode laser of any design. This allows one to choose a suitable design of a laser with a homogeneous lateral distribution
at high radiation power.
Translated from Preprint No. 43 (1992) of the Lebedev Physics Institute, Russian Academy of Sciences. 相似文献
7.
V. A. Gusev 《Acoustical Physics》2011,57(5):598-605
An asymptotic “extended characteristics method” is developed for solving nonlinear Riemann-type wave equations as applied
to calculating the ray pattern of intense spatially modulated waves in weakly inhomogeneous media. The method makes it possible
to avoid the singularity related to the foci of the initial wavefront, calculate the displacement in foci caused by the inhomogeneity
of the medium, and thus calculate the ray pattern and intensity of the acoustic field. The beauty of the method is an exact
nonlinear transfer equation for the field along the ray and the construction of its general solution for an arbitrary form
of inhomogeneity. It is shown that the method is applicable to calculating the spatial structure of intense focused waves
and wave beams outside the focal region in a nonlinear geometric acoustics approximation. 相似文献
8.
The scattering of a plane electromagnetic wave by a solitary scatterer randomly positioned near a perfectly reflecting surface
is investigated in the dipole approximation taking into account infinite multiplicity of scattering. It is shown that the
presence of multiply reflected waves increases the “effective” polarizability of the particle and adds another component of
the dipole moment along the normal to the surface. As a result, the backscattering enhancement effect becomes stronger, and
the angle of incidence at which amplification of the p-polarized wave vanishes becomes smaller. The influence of multiply scattered waves increases as the particle approaches the
boundary in this case.
Zh. Tekh. Fiz. 67, 72–75 (September 1997) 相似文献
9.
A. E. Bernardini 《International Journal of Theoretical Physics》2007,46(6):1562-1569
We shall proceed with the construction of normalizable Dirac wave packets for fermionic particles (neutrinos) with dynamics governed by a “modified” Dirac equation with a non-minimal coupling with an external
magnetic field. We are not only interested on the analytic solutions of the “modified” Dirac wave equation but also on the
construction of Dirac wave packets which can be used for describing the dynamics of some observable physical quantities which
are relevant in the context of the quantum oscillation phenomena. To conclude, we discuss qualitatively the applicability
of this formal construction in the treatment of chiral (and flavor) oscillations in the theoretical context of neutrino physics.
PACS numbers: 02.30.Cj, 03.65.Pm 相似文献
10.
Spectral lines of Yb lasing in 1.03–1.05 μm region structured by 50–200 μm spots were found at focusing a pulsed LiF:F2+ color center laser of 0.5–5.0 GW/cm2 intensity on highly doped Yb:YAG or Yb:glass plates in a resonator. Small spots at the spectrograph located ≈ 1 m apart from
the resonator indicated a “sub-diffraction” directivity of Yb generation, 1–2 orders better than the diffraction limit 10−3–10−2 rad determined by the pumped volume dimensions. Observed features of Yb emission are explained assuming off-axis oscillations
in Yb laser on phase-synchronized photons due to a strong spatial-angular selection of radiation in the resonator. Propagation
of near diffraction free beams at angles to the axis built at the spectrograph slit for every 10–15 ns pulse of Yb generation
a magnified “image” of a structure of generating channels in the active medium. This image projection brought a corresponding
structure of spots in Yb spectra. It was found that channels may be formed due to a high-frequency spatial modulation (micrometers
scale) of the refractive index profile in samples caused by the oscillating amplitude of thermoelastic stresses in the pumped
medium. Obtained data demonstrate a possibility to study (with high spatial and temporal resolution) non-equilibrium stales
of materials in small volumes using laser radiation emerging from these objects. This study results evidence for the novel
concept of the spatial distribution of electromagnetic field of a photon: not in the form of a “travelling” wave but in the
form of a wave with maxima and nodes located at fixed positions along the photon propagation direction. 相似文献
11.
V. L. Komolov 《Technical Physics》1997,42(5):499-503
An investigation is made of the conditions for the nucleation of optical breakdown in transparent material when recombination-stimulated
defect-formation reactions occur in it. It is shown that a positive feedback between the conduction electron concentration
and point defects activates defect formation even if the medium is not heated. Under real conditions, where heating of the
medium by the light is important, lowering of the activation barrier by thermal defect generation aided by conduction electrons
results in optical breakdown of the medium at light intensities much lower than predicted in the classical “semiconductor”
or “thermochemical” models of thermal breakdown. The analysis confirms that optical breakdown of transparent condensed media
is due to electron-aided defect formation reactions over a broad range of illumination conditions.
Zh. Tekh. Fiz. 67, 48–53 (May 1997) 相似文献
12.
The general expression for the static permittivity ε(q, 0) of the Coulomb system in the region of small wave vectors was derived based on exact limit relations. The relation obtained
describes the function ε(q, 0) in both “metal” and “dielectric” states of the Coulomb system. On this basis, the concept of the “true” dielectric is
introduced and the definition of the “true” screening length was discussed. Exact relations were derived for the function
ε(q, 0) in the region of small wave vectors q within the random phase approximation at an arbitrary degeneracy. 相似文献
13.
14.
This paper investigates stimulated emission and absorption near resonance for a driven system of interacting two-level atoms.
Microscopic kinetic equations for the density matrix elements of N-atom states including atomic motion are built, taking into account atom-field and atom-atom interactions. Analytical solutions
are given for the resulting macroscopic equations in different limits, for a system composed of a strong coherent “pump” field
and a weak counter-propagating “probe” field. It was shown that the existence of a dipole-dipole (long-range) interaction
between atoms separated by distance less than the pump wave-length can cause the formation of periodic polarization and population
structures (gratings in time and space) in the pumped medium without a probe field. The magnitude of pump induced population
grating can have a strong dependence on the relation between the pump field detuning and the polarization decay rate. The
“interaction” between pump and probe induced polarization/population gratings through a dipole-dipole interaction mechanism
causes the absorption line shape asymmetry. Under certain conditions, this asymmetry is revealed in increasing probe gain
for the “red”-shifted (relative to pump) probe and suppressing the gain for the “blue”-shifted probe field when pump is “red”-shifted
relative to the ensemble averaged resonant frequency. The theoretical results are consistent with experimental data for the
probe gain or absorption as the function of frequency and the dependance of the gain on atomic density for sodium vapor when
the pump laser is tuned near the D
2 line. Here the dependance of gain on particle density was explained in the terms of the long-range interaction between the
atoms. 相似文献
15.
S. M. Aulchenko V. P. Zamuraev I. A. Znamenskaya A. P. Kalinina D. M. Orlov N. N. Sysoev 《Technical Physics》2009,54(3):343-353
A way of effectively affecting the gasdynamic structures of a transonic flow over a surface by means of instantaneous local
directed energy deposition into a near-surface layer is proposed. Experimental investigations into the influence of a pulsed
high-current nanosecond surface discharge of the “plasma sheet” type on gas fast flow with a shock wave near the surface are
carried out. The self-localization of energy deposition into a low-pressure region in front of the shock wave is described.
Based on this effect, a facility for automated energy deposition into a dynamic region bounded by the moving shock front can
be designed. The limiting value of the specific energy deposition on the surface in front of the shock wave is found. With
the help of the direct-shadow method, an unsteady quasi-two-dimensional discontinuous flow arising when a plasma sheet is
initiated on the wall in a flow with a plane shock wave is studied. By numerically solving the two-dimensional nonstationary
equations of gas dynamics, the influence of the energy of a pulsed nanosecond discharge, which is applied in the frequency
regime, on the aerodynamic characteristics of a high-lift profile is investigated. It is ascertained that the energy delivered
to the gas before the closing shock wave in a local supersonic region that is located in the neighborhood of the profile contour
in zones extended along the profile considerably decreases the wave drag of the profile. 相似文献
16.
G. K. Ustinova 《Doklady Physics》2011,56(4):219-223
The effects of the shock wave diffusive acceleration of particles are considered in the case of formation of isotopic relations
of the anomalous Xe-HL component of xenon in relic grains of nanodiamonds in chondrites. It is shown that this component could be formed and captured
simultaneously with the nanodiamond synthesis in the conditions of the explosive shock wave propagation from supernova outbursts.
The specificity of isotopic composition of Xe-HL is due to the high hardness of the spectrum of nuclear-active particles at the shock wave front and its enrichment with heavy
isotopes. The spallogenic nature of both the anomalous and normal components of xenon is ascertained, and the role of the
subsequent evolutionary processes in the change of their isotopic systems is shown. Experimental evidence of the formation
of the power law spectrum of particles with the spectral index γ ∼ 1 by the supersonic turbulence during the carbon-detonation
supernova SnIa explosion is obtained; this perhaps opens new perspectives in studying the problem of the origin of cosmic
rays. It is shown that at the stage of free expansion of the explosive shock wave, the degree of compression of the matter
at the wave front was σ = 31 (the corresponding Mach number M ∼ 97); this led to a 31-fold increase of the magnetic field as well as of the maximum energy of accelerated particles, so
that even the energy of protons reached ∼ 3 × 1015 eV, i.e., the “knee” region. 相似文献
17.
Yu. Kh. Vekilov I. A. Gordeev É. I. Isaev 《Journal of Experimental and Theoretical Physics》1999,89(5):995-999
The electronic spectrum and wave functions of a new quasicrystal structure—a two-dimensional Fibonacci lattice—are investigated
in the tight-binding approximation using the method of the level statistics. This is a self-similar structure consisting of
three elementary structural units. The “central” and “nodal” decoration of this structure are examined. It is shown that the
electronic energy spectrum of a two-dimensional Fibonacci lattice contains a singular part, but in contrast to a one-dimensional
Fibonacci lattice the spectrum does not contain a hierarchical gap structure. The measure of allowed states (Lebesgue measure)
of the spectrum is different from zero, and for “central” decoration it is close to 1. The character of the localization of
the wave functions is investigated, and it is found that the wave functions are “critical.”
Zh. éksp. Teor. Fiz. 116, 1834–1842 (November 1999) 相似文献
18.
M. O. Sopin 《Technical Physics》1998,43(1):110-111
An analysis is made of the topological structure of an electromagnetic vector field near the point where the amplitude of
the field vanishes. Linear topological defects in the form of dislocations of the wave front and disclinations are studied.
It is shown that the polarization of the field near a zero of the amplitude differs from the initial value. The structural
stability of the amplitude zeros is studied.
Zh. Tekh. Fiz. 68, 122–124 (January 1998) 相似文献
19.
Experimental investigations and theoretical-model analyses have been made of the magnetooptic diffraction of light at ferrite
garnet magnetic films with a banded domain structure which includes isolated magnetic grating defects in the form of “forks”
and “breaks.” An analysis of the magnetic grating structure and the light diffraction field shows that in terms of its action
on laser radiation, a banded domain grating is similar to a computer-synthesized phase hologram of an isolated pure screw-wavefront
dislocation. It is shown that as a result of magnetooptic diffraction at a magnetic hologram, optical vortices may be reconstructed
with a helicoidal wavefront carrying the topological charge l=±1,±2.
Zh. Tekh. Fiz. 68, 54–58 (December 1998) 相似文献
20.
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