Internal waves of free charge carriers in semiconductors

We show that internal waves that are similar to internal gravity waves in the ocean can propagate in semiconductors with a gradient of free charge carrier concentration. Unlike internal gravity waves in the ocean, which are observed at infrasonic frequencies, the waves under consideration are excited in the microwave range, which opens up interesting possibilities for creating new types of electron devices. In the nonlinear rigime such waves assume the form of solitons described by the KdV equation. State Technical University, Ul’yanovsk, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 3, pp. 370–377, March, 1997.     

Propagation of optical pulses in periodic nonlinear fibers

We study the conditions of formation and propagation of soliton pulses in a periodic two-mode nonlinear fiber with allowance for dispersion of the fiber material and intermode dispersion of interacting modes under the condition of their phase synchronism. State University, Ul’yanovsk, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 8, pp. 1032–1042, August, 1998.     

Investigation of thin-film electroluminescent structures on rough subsrates

Results of experimental investigations of the volt-brightness characteristics, frequency dependences of brightness, and the directional radiation pattern of electroluminescent MSDM, MSCM, and MSDCM emitters, where M stands for the first transparent and second nontransparent electrodes, S is a semiconductor, D is a thin-film dielectric, and C is a silicone-based composite liquid dielectric with a powdered segnetoelectric filler, developed on conventional “smooth” and rough glass substrates are presented. It is shown that electroluminescent structures on rough surfaces have a brightness approximately two times higher than that of similar structures developed on a “smooth” substrate. Ul’yanovsk State University, 42, L. Tolstoi St., Ul’yanovsk, 432700, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 4, pp. 507–512, July–August, 1997.     

Propagation and transformation of a frequency-modulated pulse in a periodically nonuniform fiber

The specific features of transformation of the time envelopes of mode components of a pulse with allowance for the material and intermode dispersion and different types of fiber excitation are studied for a Gaussian frequency-modulated pulse propagating in a two-mode periodic fiber. State University, Ul’yanovsk, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 6, pp. 792–802, June, 1998.     

Thin-film electroluminescent structures on substrates with rough surfaces

It is shown that the use of substrates with inner rough and outer diffusely scattering surfaces in film electroluminescent structures makes it possible to substantially increase the coefficient of radiation extraction (by a factor of 1.3–2.5) and the brightness of luminescence (by a factor of 1.2–3.5) as compared to the structure on a smooth surface, which can be employed to enhance the brightness of individual colors of the luminescence of electroluminescent emitters. The results of the investigations indicate a substantial decrease in the constant of the time of brightness buildup (by a factor of 6–8 for MDSDM structures and by a factor of ∼3.8 for MDSCM structures) and the appearance of two segments of brightness decay for MDSMD structures with different constant decay times in going from the structure on a smooth substrate to the structures built on substrates with an inner rough surface. Unlike this, MDSCM structures have two segments of brightness decay on both a smooth substrate and a rough substrate. Ul’yanovsk State University, 42, L. Tolstoi St., Ul’yanovsk, Russia, 432700. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 5, pp. 787–793, September–October, 1998.     

Conversion of waveguide modes in a periodic optical fiber

We investigate the distinctive features of the propagation and interaction of linearly polarized modes of an unperturbed step-index fiber, perturbed by a periodic distribution of the dielectric constant along the axis of the optical fiber. An analysis is made for unidirectional and opposite modes and two-mode excitation of the optical fiber. Ul’yanovsk Branch, Moscow State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, p. 40–46, March, 1998.     

Optical resonant processes in thin excited films

It is shown that coherent processes of elastic scattering of resonant radiation form a “buffer” electromagnetic field near the boundary of excited media. This part of radiation is not governed by the standard refractive index, but precisely this part of radiation forms the beams reflected and refracted by the excited medium. The presence of the “buffer” field causes the suppression of stimulated emission near the boundary and leads to the appearance of a frequency angular broadening of the beam transmitted through a thin film of excited atoms at an oblique angle.     

Interaction of a three-level atom with an elliptically polarized wave

The interaction of elliptically polarized radiation with a resonant medium consisting of atoms with an excited state split into a doublet was studied theoretically. Interference terms associated with the coherent interaction of the field with the excited sublevels of the doublet were found to appear in the refractive index. The dispersion dependence of the refractive index was studied. It was shown that the decay constants for the multipole moments of the current of a dipole-forbidden atomic transition can be determined by the choice of the wave polarization.     

Diffraction of the wave packet of a three-level Λ atom in the field of a multifrequency standing light wave

The diffraction of the wave packet of a three-level atom in a multifrequency optical radiation field is studied. A new type of coherent beam splitter for atoms that employs the scattering of a wave packet in the field of four standing light waves with different spatial shifts is proposed on this basis. It is shown that this interaction scheme makes it possible to obtain large splittings (>100ℏk) of the wave packet of a three-level Λ atom in momentum space into only two coherent components. In addition, the atoms in these coherent components are in long-lived atomic states, which substantially simplifies the experimental implementation of such a splitter. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 6, 386–391 (25 September 1997)     

Laser-induced quantum adsorption of neutral atoms in dielectric surfaces

We propose an optical technique to load neutral atoms in quantum adsorption states of a dielectric surface. Considering a realistic atom–surface potential well, we show that free cold lithium atoms approaching a LiF surface may be transferred to a surface bound state of the first excited atomic state. We also discuss schemes to populate adsorption energy levels of the atomic electronic ground state, and we find that spontaneous mechanisms transfer more than 90% of the excited adsorbed atoms into vibrational levels of the fundamental adsorption potential. The lifetime of the resulting two-dimensional waveguide is calculated, considering the adatoms’ interaction with the crystal phonons. PACS 34.50.Dy; 68.43.-h; 68.35.Ja; 32.80.Pj     

The wave flow effect on a plane boundary between vacuum and an optical medium with a quasi-zero refractive index

A boundary problem in which a plane electromagnetic wave is reflected and refracted at a plane boundary of a semi-infinite optical medium with a quasi-zero refractive index has been solved. Such a medium has a random refractive index taking values in an interval from zero to some finite value less than unity. It means that the concept of a sharp interface between two media loses its meaning, the boundary of the medium becomes inhomogeneous, and laws of reflection and refraction of light become non-Fresnelian. Formulas for non-Fresnelian amplitudes of reflection and refraction have been derived. It is shown that a surface wave arises near the boundary of a medium with a quasi-zero refractive index. The wave propagates both on the inside and outside of the boundary.     

Gain without inversion in a medium of 1/2→1/2 atoms

Amplification of a probe field without inversion in a medium of non-degenerate two-level atoms pumped by a circularly polarized optical field in resonance with a 1/2→1/2 atomic transition in the presence of a dc magnetic field orthogonal to the wave vector of the pump field is demonstrated. It is shown that gain without inversion is possible in strong optical and magnetic fields in the case of a pump with a finite spectral width which can be much greater than the natural width of the excited level. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 5, 364–369 (10 September 1998)     

Circular electrodichroism of light in isotropic optically active media

Circular electrodichroism is predicted in liquids and gases containing unequal concentrations of mirror stereoisomers of chiral molecules. A longitudinal (quasi)static electric field increases absorption for a light wave circularly polarized in one direction and decreases the absorption for a wave circularly polarized in the opposite direction. The corresponding nonlinear susceptibility is proportional to the decay constants of the excited states and is absent in a nondissipative medium. Estimates of the magnitude of the effect are presented and show that it may well be observable experimentally. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 8, 515–520 (25 October 1997)     

Stimulated resonance scattering of light waves in laser crystals with a population inversion

A new type of stimulated scattering of light is discovered in a Nd:YAG laser crystal with a population inversion. The scattering occurs for light at the resonance frequency of the laser transition, with a small anti-Stokes shift. It is shown that the effect is due to the appearance of a wave of population of the metastable level and the associated traveling index grating in a laser medium with different polarizability of the excited and unexcited atoms. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 1, 13–18 (10 January 1996)     

Total reflection in a uniaxial crystal–uniaxial crystal interface

Considering an interface between two uniaxial birefringent crystals, four reflected and four refracted waves for each incidence direction are obtained. Along this direction can propagate an ordinary wave and an extraordinary wave. Here, we present the analytic expressions for the four critical angles, from which each refracted wave no more exists as propagating wave. We show the variation in these critical angles for different interfaces varying the orientation of the incidence plane with respect to the optical axes. When both principal refractive indices of the second medium are smaller than those of the first medium, then the four critical angles exist for each incidence plane and for any direction of the optical axes. But, when one of the indices has an intermediate value between the values of the indices of the other crystal, we can chose the optical axes directions in such a way that certain critical angles do not exist. Therefore, we can select the refracted wave that is eliminated by total reflection.     

Nonlinear refraction and absorption in hetero- thiometallic planar clusters

The nonlinear absorption and refraction of the clusters [MoS₄Cu₄Br₂(py)₆] and [Et₄N]₂[MoS₄Cu₄(SCN)₄(2-pic)₄] have been investigated using the z-scan technique with a ns laser at 532 nm wavelength. They have the same planar ‘open’ structures and the same skeleton metal atoms; the only difference is that the former has halogen ligands while the latter possesses pseudo-halogen groups – SCN – as ligands. Alteration of nonlinear refractive index and enhancement of nonlinear absorption were found in these two clusters. A steady state model of excited state nonlinear refraction was proposed to explain this phenomenon. Received: 12 June 2001 / Revised version: 4 September 2001 / Published online: 29 November 2001     

On the virtual source method for an earth-ionosphere waveguide with inhomogeneous upper wall

We consider the influence of a smooth, with respect to the wavelength, upper wall curvature of a plain Earth-ionosphere waveguide on the propagation of electromangetic waves excited by a dipole source. Since the height disturbance is one-dimensional, it is possible to construct a system of virtual sources in an infinite medium, which excite the same total field as the field of a dipole source in the waveguide. The effective inhomogeneous refractive index of such a system is obtained. We estimate the number of reflections for which Kirchhoff’s principle can be used. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 43, No. 4, pp. 296–303, April, 2000.     

Reflection–refraction of attenuated waves at the interface between a thermo-poroelastic medium and a thermoelastic medium

Phenomenon of reflection and refraction is considered at the plane interface between a thermoelastic medium and thermo-poroelastic medium. Both the media are isotropic and behave dissipative to wave propagation. Incident wave in thermo-poroelastic medium is considered inhomogeneous with deviation allowed between the directions of propagation and maximum attenuation. For this incidence, four attenuated waves reflect back in thermo-poroelastic medium and three waves refract to the continuing thermoelastic medium. Each of these reflected/refracted waves is inhomogeneous and propagates with a phase shift. The propagation characteristics (velocity, attenuation, inhomogeneity, phase shift, amplitude, energy) of reflected and refracted waves are calculated as functions of propagation direction and inhomogeneity of the incident wave. Variations in these propagation characteristics with the incident direction are illustrated through a numerical example.     

Excitation of surface and volume electromagnetic waves in left-handed media by an electron bunch

We study theoretically the Vavilov-Čerenkov radiation from a nonrelativistic electron bunch moving in free space over a left-handed medium. It is shown that in the frequency range in which the refractive index of the medium is negative, Vavilov-Čerenkov radiation leads to simultaneous excitation of volume and surface electromagnetic waves in the same frequency range. The wave vector of the surface wave in the plane of an interface of two media is greater in magnitude than the corresponding quantity for the volume wave. The energy fluxes of volume and surface waves in the left-handed medium are studied. The radiation pattern of the bunch is found. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 5, pp. 406–417, May 2007.