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1.
We show that layers of acousto-optic gyrotropic paratellurite crystals perturbed by ultrasound can be used as efficient light
modulators in transmission and reflection mode. We have established that the relative intensities of the diffracted waves
are determined by the ratio of the refractive indices of the bounding media, the intensity of the ultrasound, and the thickness
of the modulated layer. We show that for an asymmetric diffraction structure, efficient acousto-optic conversion is possible
in reflection mode, and the weak effect of the gyrotropy is due to its suppression by Fresnel reflection at the boundaries
of the layer.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 6, pp. 819–823, November–December, 2006. 相似文献
2.
Yoav Linzon Boris A. Malomed Michael Zaezjev Roberto Morandotti Maite Volatier Vincent Aimez Richard Ares Shimshon Bar-Ad 《Central European Journal of Physics》2008,6(3):555-562
We study nonlinear interactions between discrete optical solitons that propagate in different regimes of diffraction, and
the nonlinear scattering of dispersive waves by local optical potentials. It is well known in optics that when linear coherent
waves meet, they interfere without interactions. Linear waves also scatter through local optical structures not exchanging
any power with the guided modes of these structures. As a focusing Kerr nonlinearity is present, such linearly-inhibited phenomena
can exist. Our studies are performed in silica and AlGaAs nonlinear waveguides, excited by ultra-short pulses in the near
infrared.
Presented at 9-th International Workshop on Nonlinear Optics Applications, NOA 2007, May 17–20, 2007, Świnoujście, Poland 相似文献
3.
A theoretical study is made of the trajectories and of the changes in magnitude and direction of the wave vectors of magnetostatic
backward surface waves with different frequencies propagating in ferrite-insulator-metal structures with different insulating
layer thicknesses and magnetized by a linearly nonuniform static field. It is shown that both forward and backward magnetostatic
surface waves (MSSWs) propagate in a waveguide channel, on one side of which MSSWs undergo mirror reflection and on the other
side of which their propagation direction is rotated, independently of the thickness of the insulator in the structure. It
is shown that when MSSWs propagate in a nonuniform field, the forward wave is converted into a backward wave and, under certain
conditions, the backward wave is converted into a forward wave. Some features of the propagation characteristics of magnetostatic
backward surface waves are determined.
Zh. Tekh. Fiz. 69, 70–77 (February 1999) 相似文献
4.
O. M. Barkhatova N. A. Barkhatov G. I. Grigoriev 《Radiophysics and Quantum Electronics》2009,52(10):683-698
The existence of magneto-gravity waves stipulated by the substorm activity can lead to the occurrence of traveling ionospheric
disturbances, whose velocity exceeds the sound speed. For detection of magneto-gravity waves, we used experimental data on
propagation of decameter radio waves on the midlatitude and subauroral oblique sounding paths Inskip–Rostov-on-Don, Cyprus–Rostovon-Don,
Irkutsk–Rostov-on-Don, and Norilsk–Rostov-on-Don in December 2006 and March 2007 under conditions of weak geomagnetic disturbance.
Time delays between the AE indices of polar electrojets and the maximum observable frequencies for the considered paths were
established by calculation of linear correlations. These delays correspond to the times required for transport of gravity
disturbances from the auroral region to the reflection points of radio waves on respective paths. Among the obtained time
shifts, we mention the 5–10-min ones which correspond to increased velocity of the disturbances compared with the usual velocities
of acoustic-gravity waves for the paths under study. Such cases can be related to the transport of magneto-gravity waves.
Study of the spectral composition of the AE-index disturbances and recorded maximum observable frequencies shows consistency
of their spectral features in the cases of increased correlation for small time delays. It is also found that the spectral
features of the AE-index disturbances coincide with the spectral features of the disturbances of the horizontal component
of the geomagnetic field on ground-based magnetic stations. According to calculated dispersion curves, the frequencies of
magneto-gravity waves were estimated, and they turned out to be equal to ω ≈ (1–2) ・ 10−4 Hz. 相似文献
5.
G. V. Kulak 《Optics and Spectroscopy》2005,98(6):866-870
The features of the Bragg diffraction of light by ultrasound under the conditions of Fresnel reflection from the boundaries of a perturbed layer have been investigated. It has been shown that layers based on acousto-optical gyrotropic crystals perturbed by ultrasound can be used as efficient light modulators. The relative intensities of diffracted waves have been found to be determined by the relation of the refractive indices of adjacent media and by the ultrasound intensity. With an increase in the thickness of the modulated layer, the reflection and transmission coefficients of the first-order diffracted waves achieve their maxima at a lower ultrasound intensity. 相似文献
6.
7.
This paper uses the two-dimensional Brusselator model to
study reflection and refraction of chemical waves. It presents some
boundary conditions of chemical waves, with which occurence of
observed phenomena at interface as refraction and reflection of
chemical waves can be interpreted. Moreover, the angle of reflection
may be calculated by using the boundary conditions. It finds that
reflection and refraction of chemical waves can occur simultaneously
even if plane wave goes from a medium with higher speed to a medium
with lower speed, provided the incident angle is larger than the
critical angle. 相似文献
8.
We derive the threshold conditions for the instability of counterpropagating waves in a nonlinear medium with local photorefractive
response against the excitation of transverse small-angle structures. These conditions allow for all the important types of
diffraction from refractive-index reflection gratings and are not limited to the case of strict frequency degeneracy of the
waves. We study the dependence of the crystal-thickness threshold and the secondary wave emission angle on the crystal parameters
and the pump conditions. We show that when the pump wave intensities differ considerably, excitation of standing light structures
is replaced by excitation of traveling structures. Finally, we discuss the applications of the theory to experiments with
the photorefractive crystals LiNbO3 and LiTaO3.
Zh. éksp. Teor. Fiz. 111, 1611–1623 (May 1977) 相似文献
9.
10.
The dependence of the nonlinear reflection coefficient R of a mirror with a wavefront reversing surface on the intensity I
of the reference wave is analyzed in terms of a phenomenological model of a medium having a nonlinear Fresnel reflection amplitude
coefficient φ. Substantial differences are revealed for media having different signs of the nonlinearity coefficient β=(dφ/dI).
It is shown that R is related to the magnitude D of the dynamic range of the wavefront reversing mirror by the expression
RD=Qs' where Qs is a parameter which defines the “quality” of the nonlinear medium.
Far-Eastern State Academy of Communications. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 68–70,
August, 1997. 相似文献
11.
Chan-Wei Hsu Yang-Chun Lee Hsuen-Li Chen Yung-Fang Chou 《Photonics and Nanostructures》2012,10(4):523-533
The external quantum efficiency of a light-emitting diode (LED) is strictly limited by total internal reflection and Fresnel reflection effects. In this study, we sought to optimize light extraction by monitoring the shape effects of four kinds of periodic textured structures (nanorod, inverted rod, pyramid, inverted pyramid) on the surface of gallium nitride (GaN)-based LEDs. We employed the three-dimensional rigorous coupled waves approach to calculate the direct emissions at different incident angles on the various textured structures, and then determined an optimized structure that would improve the extraction efficiency of LEDs. The optical gradient of the inverted pyramid structure could decrease not only the Fresnel reflection at incident angles less than the critical angle but also the total internal reflection at incident angles greater than the critical angle. Many inverted pyramid structures at the GaN–air interface, with various sizes and periods, provided enhancement factors of greater than 150%. 相似文献
12.
V. P. Uryadov G. G. Vertogradov V. G. Vertogradov S. V. Kubatko A. A. Ponyatov Yu. N. Cherkashin I. V. Krasheninnikov V. A. Valov G. P. Komrakov A. V. Makarov D. V. Bredikhin 《Radiophysics and Quantum Electronics》2009,52(4):241-251
We describe the operation of an ionosonde/position finder with chirp modulation of the signal. The first results of measuring
the characteristics of short-wave radio signals scattered by artificial small-scale inhomogeneities, which were obtained by
means of an ionosonde/position finder on the IZMIRAN—“SURA”—Rostov-on-Don path are presented. It was found that under certain
ionospheric conditions, the angular and frequency selection of the scattered signals take place, in which case the signals
are observed simultaneously in several frequency intervals (mainly, in three, namely, 6–9.5 MHz, 10–12 MHz, and 15–18 MHz)
with different angles of incidence of radio waves in the vertical plane. In this case, the incidence angles were 20◦–35◦,
18◦–32◦, and 10◦–20◦ from the horizon for the first, second, and third frequency interval, respectively. Ionograms of oblique
sounding were modeled allowing for the scattering of radio waves by artificial small-scale inhomogeneities. It is shown that
at frequencies from 10 to 12 MHz, aspect conditions are fulfilled for the signals ducting along the high-angle beam (Pedersen
mode). At frequencies 15–18 MHz (higher than the maximum observable frequency of the forward signal on the path IZMIRAN—Rostov-on-Don),
aspect scattering conditions are fulfilled for the signals incident on a scattering area in the ascending part of the trajectory.
At low frequencies 6–9.5 MHz (below the maximum observed frequency of the forward signal on the IZMIRAN—Rostov-on-Don path),
the observable additional signals are caused by the scattering of radio waves by artificial inhomogeneities with subsequent
relfection of the scattered signal from the Earth on the “SURA”—Rostov-on-Don path.
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 52, No. 4, pp. 267–278, April 2009. 相似文献
13.
The boundary problem of nonlinear optics was investigated for a trial wave reflected (refracted) by an excited region of a
nonlinear medium considered as a system of multilevel atoms in the spectrum of which there are two closely-spaced energy levels
excited by a powerful quasi-resonant radiation. It is shown that under interference conditions of the atomic states in the
field of the trial and resonance waves there exist three types of waves: an inverse wave and two polarization waves. By way
of extension of the Ewald-Oseen procedure to this case a formula for the complex refractive index of a nonlinear medium for
the three types of waves as well as a generalized extinction theorem have been obtained. It is shown that the trial wave can
be amplified without inversion of the interfering atomic states and that the refractive index can be markedly changed at certain
concentrations of atoms in the medium. General formulas for the amplitudes of the reflected and refracted waves have been
obtained.
Ul’yanovsk State University, 42, Tolstoi Str., Ul’yanovsk, 432700, Russia. Translated from Zhurnal Prikladnoi Spektroskopii,
Vol. 65, No. 4, pp. 568–575, July–August, 1998. 相似文献
14.
S. G. Rautian 《Journal of Experimental and Theoretical Physics》2008,106(3):442-449
Eikonal approximation is used to derive equations describing propagation of monochromatic electromagnetic waves in a three-dimensionally inhomogeneous medium, including volume Fresnel reflection from inhomogeneities. The analysis is based on a locality principle. Separation into reflection and transmission effects is performed. The former effects are found to be isotropic, whereas the latter are anisotropic and depend on interference phenomena. Interference effects lead to violation of the Rytov law of polarization rotation. Brewster phenomena in layered and three-dimensionally inhomogeneous media are shown to occur under different conditions. 相似文献
15.
Generation of electromagnetic waves by an annular shell of plasma rotating in crossed radial electrostatic and axial magnetic
fields in a cylindrical resonator is investigated theoretically. Dispersion relations are obtained describing the interaction
of the waves with the plasma. It is shown that generation of waves by a narrow plasma shell is possible due to a cyclotron
resonance, Čerenkov resonance, or plasma resonance. Here we consider a Čerenkov resonance, where the velocities of the plasma
components and the phase velocities of the waves are perpendicular to the constant magnetic field. The frequencies and growth
rates of the waves are found under conditions of the above-mentioned resonances in a uniform and in a nonuniform plasma shell.
Advantages and disadvantages of wave generation under various conditions are noted.
Zh. Tekh. Fiz. 69, 16–21 (February 1999) 相似文献
16.
G. V. Kulak 《Journal of Applied Spectroscopy》1997,64(3):428-432
The intermediate regime of optoacoustic interaction, similar to the Bragg one, with Rayleigh surface ultrasonic waves in gyrotropic
planar waveguides is studied. A system of equations of bound waves is presented that describes planar optoacoustic interaction
in the intermediate, Raman-Natoh, and Bragg regimes of light diffraction by surface ultrasonic waves. It is shown that the
optical activity of a wavequide film favors the incident light energy pumping to diffracted light for a TE-polarization wave
and decelerates this process for an incident TM-polarization wave.
Mozyr' State Pedagogical Institute, 28, Studencheskaya St., Mozyr', 247760, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii,
Vol. 64, No. 3, pp. 412–416, May–June, 1997. 相似文献
17.
K. K. Mondal 《Pramana》2004,63(5):1021-1030
For an unmagnetized partially ionized dusty plasma containing electrons, singly charged positive ions, micron-sized massive
negatively charged dust grains and a fraction of neutral atoms, dispersion relations for both the dust-ion-acoustic and the
dustacoustic waves have been derived, incorporating dust charge fluctuation. The dispersion relations, under various conditions,
have been exhaustively analysed. The explicit expressions for the growth rates have also been derived.
International Conference on the Frontiers of Plasma Physics and Technology, 9–14 December 2002, Bangalore, India. 相似文献
18.
V. G. Lapin 《Radiophysics and Quantum Electronics》1997,40(10):827-834
It is shown that backscattering of electromagnetic waves is possible in a periodically inhomogeneous medium by random inhomogeneities
whose scale is greater than the wavelength. A small scattered field emerges in the case of appearance of the Bragg cavity
when the periodic layer is a matching system for the incident wave. Scattering is effective even for inhomogeneities whose
scale is much greater than the Fresnel radius of the inhomogeneous layer. The correlation radius of the scattered field can
also be that large.
Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika,
Vol. 40, No. 10, pp. 1230–1240, October, 1997. 相似文献
19.
G. B. Altshuller V. S. Ermolaev V. B. Karassev S. A. Kozlov K. I. Krylov L. I. Pavlov 《Applied physics. B, Lasers and optics》1983,32(2):97-100
Nonlinear reflection of elliptically polarized light waves from the interface of two isotropic transparent media, is investigated for the first time. Nonlinear Fresnel formulae are obtained. It is shown, that when linear refractive indices are equalized, selfdeformation of the polarization ellipse in nonlinear reflection depends only on incident light ellipticity, not upon its intensity and the angle of incidence. 相似文献
20.
A theoretical investigation is carried out for an intermediate regime of optoacoustic interaction, close to the Bragg one,
by ultasonic Rayleigh surface waves in gyrotropic planar waveguides in an external electric field. A system of equations of
associated waves is presented which describes the planar optoacoustic interaction in intermediate, Raman—Nath, and Bragg regimes
of diffraction by ultrasonic surface waves in gyrotropic crystals with electrically induced anisotropy. It is shown that the
intermediate (transition) regime of optoacoustic interaction, which is characterized by an angular selectivity and by the
presence of several diffraction maxima, is the basic regime of diffraction. In this case diffracted light is generally elliptically
polarized with an ellipticity and polarization azimuth that depend on the external electric field intensity.
Translated from Zhurrnal Prikladnoi Spektroskopii, Vol. 66, No. 1, pp. 30–35, January–February, 1999. 相似文献