Amplification Spectra Under the Conditions of Narrow-Band Pumping and in Probing by a Trial Field

The processes of parametric interaction in different techniques of organization of the effect of laser radiation on the resonant transitions of the vapors of alkali metal atoms have been investigated experimentally and theoretically. The results obtained show that, provided there are processes of four-wave mixing under the resonance conditions, it is necessary to consider the structure of the quasi-levels that are formed on exposure to the pumping-field narrow-band radiation. Based on the two-level model, a nonlinear theory of resonant frequency-nondegenerate mixing of arbitrary-intensity waves has been developed that describes the spectral regular and energy characteristics of parametric scattering. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 5, pp. 598–603, September–October, 2005.     

Optical pumping in a L-system by parametric luminescence light

We examine the optical pumping effect in an ensemble of three-level atoms with a Λ configuration of the energy sublevels excited by parametric luminescence light in the squeezed state. We derive quantum kinetic equations that describe the evolution of the density matrix of atoms irradiated by low-intensity squeezed light with a finite-width spectrum. In particular, we show that because of the quantum statistical properties of the squeezed light there can be a redistribution of atoms among the lower energy sublevels, despite the equality of the intensities of the spectral components of the light that resonantly excites optical transitions in the Λ-system. The relation of the optical pumping effect to the correlation and spatial-temporal spectral properties of squeezed light is discussed in detail. Finally, we show that the effects are closely linked to the finiteness of the width of the squeezed-light spectrum. Zh. éksp. Teor. Fiz. 112, 137–162 (July 1997)     

Multiple frequency radiofrequency-optical resonance in a four-level model of rubidium atoms with optical pumping

We consider a four-level model for alkali metal atoms with optical pumping by nonresonant light under conditions when magnetic dipole transitions are induced between energy sublevels of the hyperfine structure in the ground state. We present the dependences of the observed signal as a function of the frequency detuning of the applied rf fields relative to the resonant value, calculated in the density matrix formalism. We note the absence of a light shift in the radiofrequency-optical resonance signal, independent of the amplitude of the rf field and the optical and thermal relaxation rates. We show that when using a modulation technique for phase detection of the signal, its maximum discrimination ability is observed under conditions for simultaneous modulation of the pump light intensity and the frequency of the rf field, which in principle does not occur in the classical two-level model for optically oriented atoms in magnetic resonance. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 3, pp. 326–329, May–June, 2006.     

Interband resonant tunneling in superconductor heterostructures in a quantizing magnetic field

The resonant tunneling of electrons through quasistationary levels in the valence band of a quantum well in double-barrier structures based on III–V materials with type-II heterojunctions is considered in a quantizing magnetic field directed perpendicularly to the interfaces. The transmission coefficients of the tunnel structure for transitions from states corresponding to different Landau levels are calculated using the Kane model. It is shown that transitions with a unit change in the Landau level index n as a result of mixing of the wave functions of states with opposite spin orientations are possible on the interfaces due to spin-orbit coupling. The probability of such transitions can be comparable to the probability of transitions without a change in the Landau level index for InAs/AlGaSb/GaSb resonant-tunneling structures. Fiz. Tverd. Tela (St. Petersburg) 40, 2121–2126 (November 1998)     

Resonant scattering of three-level Rydberg atoms in a microwave field

We examine the theory of potential scattering of Rydberg atoms in a microwave field. The model of a three-level atom is employed to calculate the radiative force emerging in the resonant coherent interaction with the microwave field for the case of a two-photon resonance and high intensities, using the method of quasienergies of the system consisting of the atom and the field. We determine the probabilities of Landau-Zener transitions in the spatial regions where under two-photon resonance conditions the quasienergies of the atoms approach one another by a small quantity. We also study the dynamics of the variation of the spatial profile of a beam of Rydberg atoms caused by resonant scattering. Finally, we give the results of the first experimental observation of the variation of the transverse beam profile when Rydberg atoms pass through a nonuniform microwave field formed in a rectangular waveguide and in resonance with the two-photon 36P–37P transition. Zh. éksp. Teor. Fiz. 111, 796–815 (March 1997)     

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)     

Coherent repopulation of hyperfine structure levels in the field of a bichromatic resonant radio-frequency wave

We consider the resonant interaction between atoms with hyperfine energy levels and a bichromatic radio-frequency field. Nuclear Zeeman levels of an impurity center in a magnetic host form a structure of this kind. Using the spin-density-matrix formalism, we solve the problem of coherent repopulation of a system of three of these levels under the action of a bichromatic resonant radio-frequency wave, taking into account transverse relaxation, and note the connection between this effect and the well-known phenomenon of coherent population capture when a laser bichromatic field interacts resonantly with a three-level system. We discuss various possibilities for observation of this effect experimentally. Zh. éksp. Teor. Fiz. 111, 1236–1244 (April 1997)     

Interference phenomena in Doppler broadened quantum transitions: Amplification of intense radiation without population inversion

We study the effect of nonlinear interference processes on quantum transitions in intense resonant electromagnetic fields with allowance for changes in level populations, relaxation processes, incoherent excitation, and Doppler broadening of the transitions, on the absorption, amplification, and refraction of the interacting fields. The theory is generalized to the case of nonlinear interference interaction of two intense fields in open and closed three-level quantum systems. Using the density matrix, we derive general expressions in the case of stationary interaction that make it possible to analyze the optical characteristics for various configurations of the interfering transitions by a simple substitution of parameters. The possibility of amplifying light without saturated population inversion in a resonant transition is discussed. We formulate the conditions for such amplification and use examples to show that under appropriate changes in the initial level populations and the intensity of the auxiliary light, the inversionless amplification coefficient does not decrease with increasing intensity of the amplified radiation. We also show that allowance for these accompanying processes greatly affects the choice of optimal conditions for interference in optical transitions. As an illustration we list the results of a numerical analysis of possible experiments. Zh. éksp. Teor. Fiz. 113, 445–470 (February 1998)     

On the propagation and interaction of ultralow-frequency waves in a waveguide with gyrotropic plasma

The propagation of ultralow-frequency (ULF) electromagnetic waves in a waveguide filled with magnetoactive plasma is consieered on the basis of the monoaxial crystal approximation which is more general than the MHD approximation. The formulas for the phase and group velocities of the ordinary (magnetoacoustic) and extraordinary waves (similar to Alfvén waves in the MHD approximation) are derived. It is shown that analysis outside the scope of the MHD approximation results in a finite (nonzero) velocity of energy propagation of the extraordinary wave (Alfvén wave at the limit) along the waveguide. The possible waveguide mode triplets satisfying the conditions of synchronism are found. Three-wave resonant parametric and nonlinear interaction between waves with such characteristics leads to effective spectral transformation of the ULF radiation. Radiophysical Research Institute, Nizhny Novgorod; State Technical University of Nizhny Novgorod. Translated from lzvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, Nos. 1–2, pp. 111–122, January–February, 1997.     

Parametric interaction of magnetostatic waves with a nonstationary local pump

A solution is obtained for the general problem of the nonstationary interaction of backward volume magnetostatic waves in films of yttrium-iron garnet with local parametric pumping. In the case of a large pump region, l≫λ, where λ is the wavelength of the backward volume magnetostatic waves, the problem reduces to a system of truncated equations for two packets of counter propagating waves. In the opposite case, l<λ, the exact problem of parametric interactions of the eigenmodes of a ferrite film (both counterpropagating and in the same direction) is solved numerically. Both cases are studied experimentally and good qualitative and quantitative agreement is obtained with the theory. For the first time, the reversal of a wave front and the time reversal of the shape of backward volume magnetostatic wave pulses are observed and a change in the propagation time for the peak of the signal pulse and a reduction in its width owing to pumping are recorded. Two operating regimes are identified for a nonstationary parametric backward volume magnetostatic wave amplifier with local pumping, which differ in the ratio of the duration of the pump pulse to the transit time for the wave through the local pump region, and the effect of the parametric excitation of two-dimensional spin waves on the interaction of backward volume magnetostatic waves with a local nonstationary parametric pump is determined. Zh. éksp. Teor. Fiz. 116, 2192–2211 (December 1999)     

Effect of interaction of electromagnetic fields with a resonant medium in epr when the saturating field is small compared with the local field

We propose a system of Bloch equations, modified to take into account the presence of a dipole-dipole reservoir (DDR), for the case when the saturating magnetic field is small compared with the local field. We take into account the transverse and longitudinal magnetizations in the equation for the DDR, in contrast to our previous papers in which we took into account only the longitudinal magnetization. Using the system obtained, we solve the problem of the interaction of three fields, where one is the saturating field, the second is the probe field, and the third is a combination field that is the result of the interaction of the first two fields in a resonant medium. We have studied the imaginary and real parts of the susceptibility of the system at the probe field frequency, both when the interacting waves have different frequencies and when they have matching frequencies (the degenerate case). We have compared the results with those we obtained previously. For the degenerate case, we consider the frequency dependence of the parametric coupling coefficient of the waves. We show that weak waves can be enhanced as they pass through a layer of a resonant absorbing medium. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 4, pp. 462–466, July–August, 2006.     

Wave Generation in a Warm Magnetized Multi‐Component Plasma

The resonant interaction between three waves propagating perpendicularly to an external magnetic field in a plasma is considered. We present the explicit expressions for the three wave coupling coefficients of a warm multi‐component plasma. The results of previous work on the generation of THz radiation by laser plasma interaction are significantly improved. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Parametric amplification at low-frequency pumping and generation of four-mode entangled states

We show that parametric amplification at low-frequency pumping can be implemented in aperiodic nonlinear photonic crystals. In this process, the intensities of the waves with frequencies higher than the pumping frequency increase with increase in the interaction length as in the case of the standard process of parametric amplification at high-frequency pumping. The process under consideration includes a nondegenerate parametric down-conversion followed by two parametric up-conversions in the same pumping wave. As a result, generation at four new frequencies arises. Quantum analysis of the process demonstrates the presence of entanglement in the states of four modes. Talk presented at the oral issue of J. Russ. Laser Res. dedicated to the memory of Professor Vladimir A. Isakov, Professor Alexander S. Shumovsky, and Professor Andrei V. Vinogradov held in Moscow February 21–22, 2008.     

Theoretical models for interisomer transitions of complex molecules and their spectral manifestations

We have used computer simulation to compare theoretical models for describing interisomer transitions of complex molecules and their spectral manifestations. We have shown that the kinetics of the intramolecular processes and time-resolved spectra, taking into account quantum beats between resonant (bound) states of the isomers (or isolated level subsystems for one isomer form), can be described not only by using a general molecular model in which the resonant levels of the subsystems act as a single level of a mixed state, with a time-dependent wave function in the form of quantum beats, but also by using a model interpreting the beat effect as a nonradiative transition. These models are completely equivalent: the parameters describing them have the same values, and numerical differences in the results obtained are no greater than 1% and are due to numerical round-off errors in the calculations and not differences between the models. The second model is preferred because it is graphically clear and conventionally used for describing and interpreting intramolecular processes, but it does take somewhat longer (∼10%) to run the simulation. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 1, pp. 36–41, January–February, 2006.     

On the dominant role of two-photon relaxation in photonic crystals in external fields

It is shown that resonant interaction of a coherent wave with impurity atoms leads to filling of levels of an impurity atom that lie in the gap in the photon density of states and do not belong to resonant transitions, while the interaction of impurity atoms with a nonresonant coherent wave results in effective deactivation of the indicated levels. The main mechanism determining the pumping and decay of an impurity level in a gap are two-photon radiative relaxation processes previously investigated by the present author (Zh. éksp. Teor. Fiz. 102, 1126 (1992) [Sov. Phys. JETP 75, 611 (1992)]). Pis’ma Zh. éksp. Teor. Fiz. 70, No. 7, 434–438 (10 October 1999)     

Magnetostatic surface waves produced by an inhomogeneity of the anisotropy with a turning point of the spectral function on a ferromagnet surface

Magnetostatic surface waves with fixed frequency and wave vector are predicted to exist in a ferromagnet with an inhomogeneity of the magnetic anisotropy such that the spectral function has a turning point on the surface. This result is most important for the case when an external magnetic field magnetizes the ferromagnet perpendicular to its surface. The frequency of the surface wave is determined by the frequency of the magnetostatic volume wave at the surface of the ferromagnet, and the wave vector is determined by the surface values of the local magnetic anisotropy field and its derivative. Zh. Tekh. Fiz. 68, 118–123 (June 1998)     

Contribution of the tensor component to the light shift of the rf optical microwave resonance frequency in rubidium vapor

We have calculated the tensor component of the light shift for the frequency of the rf optical microwave resonance on the magnetically independen 0−0 and 1, −1 transitions in rubidium-87 atoms under conditions of isotope filtering of the resonant pump light. We have observed a difference between the temperatures of the filter cell at which a zero frequency shift is achieved for the rf optical resonance for these transitions. We have noted that selective optical pumping on theD ₁ lines is advisable when using a two-photon microwave transition in rubidium vapor in applications. St. Petersburg State Technical University, St. Petersburg. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 42, No. 2, pp. 86–90, February, 1999.     

Propagation of a localized wavepacket in a metamaterial with a negative index of refraction

Propagation properties of electromagnetic waves in a medium with a negative index of refraction are investigated. A model of a physical signal that combines simultaneously qualities of both a spatially-localized beam and a wavepacket was used as the incident wave. Such a choice was necessary because of the strong frequency dispersion of metamaterials in the spectral region with a negative index of refraction. An approximate analytical solution was derived that describes the propagation dynamics of such a signal through a slab made of material showing simultaneously a negative dielectric permittivity and magnetic permeability. Presented at the XIIIth International Conference “Physics of Pulse Discharges in Condensed Media,” August 21–25, 2007, Nikolaev, Ukraine. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 2, pp. 187–193, March–April, 2008.     

Susceptibility of a three-level V-type quantum system in a bichromatic field

A theory of interaction of a three-level V-type quantum system with a bichromatic field of two waves, one of which is weak, has been developed. It is suggested that the upper two levels of this system are closely spaced and, therefore, both waves interact simultaneously with both allowed transitions. An expression for nonlinear macroscopic polarization of the V-system has been obtained by the density-matrix method.__________Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 1, pp. 67–71, January–February, 2005.     

The SRS line-shaped nonlinear resonance in consideration of flight effects

We investigate the problem of nonlinear interaction of a gas of three-level atoms with the field of standing waves in the situation where the atomic free path length at the initial and final metastable levels is comparable with the transverse dimensions of the field. The standing waves are resonant to adjacent Doppler-broadened transitions. The case of fields of Gaussian profile is analysed. It has been shown that in the limiting case of large free path length the nonlinear resonance width is of the order of the inverse time of flight of an atom in the field. The first and second derivatives of resonance with respect to frequency are considered. It has been shown that in the situation of flight they contain narrow resonant structures with a width of the order of a homogeneous width of the forbidden transition between metastable levels.