Twistability of the path of radiation propagating in an absorbing medium

The effect of rotation of the speckle pattern accompanying the propagation of radiation in an absorbing multimode optical fiber is predicted in the geometrical optics approximation. The direction of the angle of rotation of the speckle pattern at the fiber exit is determined by the photon helicity. The absolute value of the angle of rotation is proportional to the square of the fiber length.     

Mechanism for optical parametric generation in an absorbing medium

A theory that makes it possible to determine the parameter regions where amplification is observed in an absorbing medium and absorption is observed in an amplifying medium is constructed. In these regions stationary generation of a pair of symmetric modes can be established in an absorbing medium. Polychromatic pumping to other modes is the energy source. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 1, 19–24 (10 January 1996)     

Observation of non-phase-matched parametric amplification in resonant nonlinear optics

The coupling between a resonant excitation and a nonresonant parametric process in a nonlinear system is studied experimentally under non-phase-matched conditions. Our study performed in the context of anti-Stokes stimulated Raman scattering provides a clear observation of the self-induced phase matching of a parametric process. A close agreement with theoretical predictions is observed.     

Point source of resonant radiation in an excited dispersive medium

Neglecting the Doppler effect at r , the decay of a single-photon state constantly generated by a foreign atom in a thermally excited medium of two-level molecules is determined by a sum of two exponentials. The asymptotic behavior is determined by the splitting of the energy spectrum of a single-photon state in excited media. This quantum electrodynamic effect has no classical counterpart.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 5–9, October, 1988.     

具有腔内光放大的单共振光参量振荡器

推导了描述稳态运行，具有腔内光放大的环形腔单共振光参量振荡器(ICOASRO)的功率特性的高斯光束理论.在这种结构的单共振光参量振荡器(SRO)中，适当地选择光放大器的参数，可以很大程度地降低单共振光参量振荡器的抽运阈值.在平均场近似下无二阶非线性交叉耦合作用的具有腔内光放大的环形腔单共振光参量振荡器的工作范围分成四个工作区域，且存在最小的单共振光参量振荡器的抽运阈值.文中的分析考虑了作为光放大器的激光增益介质的端面抽运特性，考虑了一般化单共振光参量振荡器的特性. 关键词： 单共振光参量振荡器 光放大 阈值     

Passage of monochromatic radiation through a resonance radiation absorbing medium

The problem of passage of monochromatic radiation pulses through a one-dimensional medium containing several types of nonuniformly distributed absorption centers with coincident energy levels are considered. The physical picture associated with the effect of a brightening wave arising in an optically dense absorbing medium is analyzed. The investigated relations represent a generalization of Bouguer's law for the case of powerful fluxes of monochromatic radiation with allowance for absorption saturation.     

Ablation of an optically homogeneous absorbing medium by scattered pulsed laser radiation

We have studied the ablation of an aqueous CuCl₂ solution in a pulsed Nd:YAG laser field featuring a speckle-patterned structure characterized by spatial radiation energy fluence fluctuations. This leads to a nonuniform distribution of the energy absorbed in the bulk of the sample being irradiated and causes local overheating centers to form, wherein ablation is observed to take place at laser energy fluences below the threshold value found in experiments with a homogeneous laser beam. This effect should be manifest in the laser irradiation of biotissues which, as a rule, scatter light strongly.     

Observation of parametric amplification of propagating dipole-exchange spin waves in yttrium iron garnet films

Amplification of a weak-signal spin wave by a strong pump spin wave propagating in an yttrium iron garnet film is observed for the first time. A theoretical explanation of the amplification phenomenon is suggested on the basis of the four-wave parametric processes. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 3, 160–165 (10 August 1996) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Parametric collective phenomena during the propagation of polychromatic laser pulses in an optically dense resonant medium without population inversion

We experimentally and theoretically study the interaction of broadband polychromatic laser pulses with an optically dense resonant extended medium without population inversion. Experimental (probe field-pumping beam) measurements of the transmission and amplification spectra were carried out in the plasma of a positive neon glow-discharge column containing a large number of metastable atoms. The strong coupling in the field-matter system and the collective behavior of the atomic system in a resonant field were attributable to a high (～10¹² cm^?3) density of atoms at the lower (metastable) level of the optical transitions under consideration and to a relatively low intensity of the interacting laser beams. We observed a broadband weakening of the probe field in the absence of pumping and its strengthening in the line wings in the presence of a strong field. We develop a theoretical model for the parametric amplification of collective interactions in dense extended media based on the solution of the semiclassical Maxwell-Bloch equations for conditions under which the pumping field does not destroy the dipole interaction between atoms through probe-field photons.     

Experimental demonstration of phase control of dispersion effects for an ultrashort pulse train propagating in a resonant medium

We present an experiment in which an ultrashort pulse train propagates resonantly through anoptically dense vapor of atomic rubidium. The sequence obtained from a Fabry-Perot interferometer comprises nearly 10 regularly time-delayed and mode-locked pulses. We show that a sequence with phase shift phi = 0[2pi] between two successive pulses propagates with important temporal distortion, whereas a sequence with phi = pi[2pi] experiences few propagation effects, thus leading for the first time to our knowledge to the possibility of phase control of dispersion effects for an ultrashort pulse train.     

Coherence-controlled transparency and far-from-degenerate parametric gain in a strongly absorbing Doppler-broadened medium

An inversionless gain of anti-Stokes radiation above the oscillation threshold in an optically dense far-from-degenerate double- ? Doppler-broadened medium accompanied by Stokes gain is predicted. The outcomes are illustrated with numerical simulations applied to sodium dimer vapor. Optical switching from absorption to gain via transparency controlled by a small variation of the medium and of the driving radiation parameters, which are at a level of less than one photon per molecule, is shown.     

Large polarization squeezing in non-degenerate parametric amplification of coherent radiation

Polarization squeezing is shown to occur in non-degenerate parametric amplification of coherent light and the degree of squeezing at interaction time T can be as large as 1 ? e^-2T. This gives 86.4% polarization squeezing for T = 1 and 98.2% for T = 2. One simple case when this occurs is on taking initially plane polarized light having equal amplitudes in the two modes that finally has equal intensities of two circular polarizations. This suggest the experimental settings of parameters to achieve this extent of polarization squeezing in coherent light.     

Nonstationary heating of a plane-layered medium by pulsed electromagnetic radiation

Nonstationary heat exchange in a nontransparent plane-layered medium irradiated with a directional beam of pulsed radiation is investigated theoretically. The radiation is absorbed on the irradiated surface, which becomes a distributed source of heat. The propagation of the heat into the layers is described by the heat-conduction equation with nonlinear boundary conditions, which take into account convection and heat exchange with the radiation. Dimensionless parameters, on which the solution depends, are obtained, and their effect on the change of the surface temperatures of the layers with time for one- and two-layered media and also on the heat pulse transmitted through the medium is analyzed.M. V. Lomonosov Moscow State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 115–121, November, 1992.     

Transport of radiation incident obliquely on the boundary of an absorbing randomly inhomogeneous medium

Radiophysics and Quantum Electronics -     

Non-Fourier heat conduction with radiation in an absorbing, emitting, and isotropically scattering medium

This article numerically analyses the combined conductive and radiative heat transfer in an absorbing, emitting, and isotropically scattering medium. The non-Fourier heat conduction equation, which includes the time lag between heat flux and the temperature gradient, is used to model the conductive heat transfer in the medium. It predicts that a temperature disturbance will propagate as a wave at finite speed. The radiative heat transfer is solved using the P₃ approximation method. In addition, the MacCormack's explicit predictor-corrector scheme is used to solve the non-Fourier problem. The effects of radiation including single scattering albedo, conduction-to-radiation parameter, and optical thickness of the medium on the transient and steady state temperature distributions are investigated in detail. Analysis results indicate that the internal radiation in the medium significantly influences the wave nature. The thermal wave nature in the combined non-Fourier heat conduction with radiation is more obvious for large values of conduction-to-radiation parameter, small values of optical thickness and higher scattering medium. The results from non-Fourier-effect equation are also compared to those obtained from the Fourier equation. Non-Fourier effect becomes insignificant as either time increases or the effect of radiation increases.