The aim of this communication is to present in a concentrated from the main ideas of a method, developed by the author, for treating strongly nonequilibrium collective phenomena typical of the interaction of radiation with matter, as well as to give a survey of several applications of the method. The latter is called the Scale Separation Approach since its basic techniques rely on the possibility of separating different space-time scales in nonequilibrium statistical systems. This approach is rather general and can be applied to diverse physical problems, several of which are discussed here. These problems are: superradiance of nuclear spins, filamentation in resonant media, semiconfinement of neutral atoms, negative electric current,and collective liberation of light.

When pumping produces atomic coherence on working levels or atomic polarization two-level atom can generate the light without inversion. In such systems one- and two-photon generation of the light is considered for the laser and micromaser operation. Using Lamb-Scully model generalized for coherent pumping statistics of the light is considered. Two-photon laser operation is found to be phase squeezed and perfect noise reduction can be achieved. In maser a set of steady state of subpoissian photon statistics is found. For these states the noise reduction up to 60 percent can be obtained if inversion is zero. Phase squeezing in micromaser is found.

The difficulties, associated with UV divergences, of a consistent QED theory in describing the natural broadening of spectral line profiles of atoms are discussed. The way of the solution this problem by using nonlocal QED interaction is studied. Experimental consequences of such a nonlocality are discussed.

The general expression of the output-light Mandel parameter(xi) _out is obtained in case of purely absorptive bistability, for arbitrary value of (xi) _in of incident light. Calculations are based on stochastic rate equations. No adiabatic elimination of atomic variables is made; the coherent nature of 'incoming' of incident photon is into a cavity is correctly taken into account. On condition of bistability, although the strongly sub-Poisson input-photon statistics generally reduces the output noise as compared to the case of coherent input, the inequality (xi) _out > 0 still near the switching points.

We propose a new method of constructing a Bose-Einstein distribution in which one takes into account discreteness of the energy levels of the boson system. It permits the calculation of not only the average number of bosons in any state but also the probability distribution of particles in that state.

The paper considers some peculiarities of NaK-type diatomic molecule dynamics at multipulsed excitation by femtosecond laser fields. It is studied how intensity of the laser pulses may affect the form of the electronic-vibrational wave packet. Based on numerical calculations of the luminescence signal it has been found that there are domains of excitation parameters with stable and unstable vibrational dynamics.

This paper discusses an experimental scheme of quantum teleportation with two atomic beams in terms of the interaction between atoms of different bema via the field of virtual photon field with the emission or absorption of a real photon is interpreted as a third-order QED effect. Quantum teleportation of an unknown broadband electromagnetic field is investigated. Two types of field may be formate between tow beams, which we are considering. At first, the field of real photons exhibits with a time lag equal to L/c, where L is the distance between beams, c is the speed of light in vacuum. The second type of field is the polarizing field as the field of virtual photons. The polarizing field has formatted in the location of atoms of other beam instantaneously. The field is connected with the effect of quantum teleportation. We also consider other types of atom interaction, in which exhibit the effect of quantum teleportation, e.g., cooperation annihilation parapositronium atoms. Recently, it was realized that use of the properties of quantum electrodynamics might speed up certain computations and communication processes dramatically. Interest has since ben growing in the area of quantum teleportation. Quantum teleportation will be used for the construction of quantum computation networks.

The problem of the interaction of a positronium atom with the field of optical and annihilation photons is considered. The solution obtained for the occupation numbers is used to study kinetics of the annihilation decay of para-positronium atom from two states participating in stimulated optical transitions excited by a laser. It is shown that a non- exponential time dependence of the occupation numbers is observed under the conditions of a nonlinear coherent interaction of a positronium atom with the field of optical and annihilation photons, and in some cases there is a possibility of appearance of a long-lived state of a positronium atom with a lifetime hundreds of times longer than the lifetime of a positronium atom in the 1S state.

Some quantum optical models possessing a transition from regular to chaotic dynamics and influence of 'quantum chaos' to squeezing are investigated. Exploring coherent states method and 1/N-expansion technique we have derived an appropriate system of nonlinear equations and demonstrate in computer simulations a change of squeezing degree time dependence.

A conception of virtual quantum information bit - virtual qubit - is introduced. It is shown by means of virtual qubit representation that four states of a single quantum particle is enough for implementation of full set of the gates, which is necessary for creation an arbitrary algorithm for a quantum computer. The physical nature and mutual disposition of four working states is of no significance provided the existence of the suitable selection rules for the particle interaction with the external electromagnetic field pulses.

Four atomic optical energy levels is proposed to use as a two qubit quantum register. A single Pr³⁺ atom in a monocrystal LaF₃ subjected to resonant laser irradiation is used as an example to illustrate the implementation of the universal set of quantum gates. This physical system equilibrium state is a desirable input state for quantum computation and therefore there is no need for its special preparation procedure.

The work is devoted to the problem of presentation of informative parameters of photon echo signal in different hypercomplex spaces. Particular attention is directed to the polarization and time properties of photon echo, which can be useful for compression information in one optic channel. The experimental result of separating information by the polarization character are shown. The new effective scheme of coding information in technique of photon echo are discussed in detail. The considering of collection of informative parameters of photon echo signal is offered to consider in one of the isomorphic hypercomplex algebra.

A brief review of theoretical predictions for photon echo polarization properties is presented from the viewpoint of their dependence eon the are of exciting pulses and on the contribution of depolarizing collisions. The choice of intercombination transition in ytterbium vapor as subject of investigation is explained. First experimental results on kinetics of resonant fluorescence at the transition of Yb (6s^{2$0 (superscript 1}S₀-(6s6p) ³P₁ are presented for pure ytterbium vapor and its mixtures with Xe.

Long-lived quantum states in gases are analyzed from the view point of their nature, their formation under action of laser radiation, their detection and decay. The long lifetime of molecular vibro-rotational levels was detected by photon echo technique for slowly moving particles. Polarization moments of degenerated molecular states, created by resonant polarized radiation of CO₂ laser, were investigated by using stimulated photon echo technique. Long lifetime of polarization moments was detected in experiments on collisional decay in a gas SF₆ and its mixtures with He and Xe. Non-elastic depolarizing collisions contribute within experimental errors. Long-lived stats applications in high resolution spectroscopy and spectral references design are analyzed.

The primary photon echo signal excited by two non-collinear pulses in optically dense media with extreme inhomogeneous broadening is investigated theoretically and numerically. Non-linear evolution of both echo exciting pulses and echo response during propagation is taken into account. Red frequency shift of the primary photon echo is predicted. The influence of pulse transformation on the echo time delay is analyzed.

Visual method of identification of the branch type of resonant transition is suggested in this paper. the method is based on the measurement of ratio of primary photon echo amplitude to stimulated photon echo amplitude in the magnetic field, when the effect of non-Faraday rotation of the photon echo polarization vector is occurred. The experimental results of identification of the resonant transitions in the vapor of molecular iodine are demonstrated. The results were checked by the measurement of the maximum rotation angle range of primary photon polarization vector. This parameter is similarly characterized the resonant transition. For the first time fact of registration of the non-Faraday rotation polarization vector of stimulated echo, formed on the different resonant transitions, is reported.

Photon-echo (PE) measurements has been performed in (gamma) - irradiated ruby and in external constant electric field.There are considered the factors which determine the echo envelope decay of primary and backward PE echo for large samples of ruby. The data of PE for ruby of transitions with nucleus spin I equals 3/2 are presented. This sample is a perspective object for searching long-lived PE.

The possibility of advance and delay effects for the light induction, one-pulse, locked, two-humped and nutation photon echo (PE) signals is shown. The primary and stimulated backward echo-signals are considered also. A possible scheme of experimental realization for the case of nutation PE is discussed.

The possibility of observation of backward optical nutation, backward one-pulse Photon Echo (PE), backward locked PE, backward two-humped PE, backward nutation PE and backward color echo-hologram is shown from the analysis of experimental and theoretical investigations of backward optical free induction decay, backward primary and stimulated PEs.

Experimental results, obtained by the authors in molecular gases, are applied to the comparative analysis of Doppler- free spectroscopy in frequency domain and coherent transient effect in time domain from the view point of investigations of different sorts of collisions. Depending on the problem and the samples, define kinds of technique may be advantageous. However, both types of Doppler-free techniques reveal reasonable agreement in comparable experimental conditions, which allows to consider them as adequate and complementary approaches in collisions investigations.

The master equation for impurity atom in photonic band gap crystal is derived with account for two-atom and two-photon relaxation processes. An important role of these relaxation processes is clarified.

The spin-lattice relaxation kinetics of radical cation C₆₀⁺ in polycrystalline C₆₀ has been studied at room temperature by two-pulse delayed nutation and nutational echo methods. It has been found that the kinetics is well described by a function exp(-a(root)t), as expected when the distribution of relaxation time of paramagnetic centers takes place. Our results suggest that oxygen molecules cause the observed kinetics. These molecules play role of fast-relaxing impurities and accelerate spin-lattice molecules cause the observed kinetics. These molecules play role of fast-relaxing impurities and accelerate spin-lattice relaxation of C₆₀⁺ radicals. The earlier obtained peculiarities of C₆₀⁺ radical relaxation in fullerites are discussed.

IR absorption spectra of several small molecules in liquid phase and CCl₄ solutions have been investigated. Band profile analysis of the spectra in the 3300-2700 cm^-1 region was performed, using Cauchy-Gauss functions as individual components. For nonpolar molecules all the individual components can be unambiguously assigned to fundamental and combination vibrations, while for the polar molecules and additional, very broad component was observed. Basing on the molecular structure and taking into account the temperature and solvent effects on the spectra, the broader components were assigned to interactions of the C-H stretching vibrations with single particle and collective reorientations of molecular dipoles.

The influence of speed-changing self-similar collisions on the spectral lien shape is considered in terms of the classical Fourier integral theory. The self-similar mechanism of interference of scalar perturbations for phase shifts of an atomic oscillator is developed. The motion of a radiating dipole in a perturbed gas is examined in the framework of the self-similar diffusion model. A general formula for the correlation function, which allows for a combined effect of speed-dependent Doppler and pressure broadening, is derived. In the Doppler regime this formula yield the self-similar Galatry profile and in the case when speed-changing collisions are neglected it leads to the self-similar Voigt profile. In the limiting case when the self-similar character of collisions is omitted these profiles become identical to the Galatry profile and Voigt profile respectively. It is shown that self-similar collisions are of important in a low and high pressure region for far IR and radio lines. In general case spectral profiles broadened by the self-similar collision mechanism are asymmetric, the line shape depends on a type of the interference of scalar perturbations. In the Doppler regime self-similar collisions give rise to the additional spectral line Dicke-narrowing.

In this paper the classical notion of resistance is considered with a geometrical view. First order processes are considered through the scope of their state trajectory. By applying a geometrical procedure, the resistance can be seen as the deviation between two points on border of an hyperbolic space. The same procedure is then applied to the Cole-Cole expressions, typical of fractal media phenomena. In spite of the abandon of transformation group structure, the notion of resistance takes a wide sense, linked not only to a deviation of the border, but also coming from the thickness of this border.

Without using the slowly varying amplitude approximation a nonlinear propagation of supremely short pulses in the three-level quantum medium have been investigated. At this by the pulse spectral wide is exceeding only one of quantum transitions. The nonlinear wave equations of 'sin-Gordon + Korteweg-de Vries'-type and 'sin-Gordon + Korteweg- de Vries'-type, which describe pulse dynamics, was obtained. On the basis of approximate solution we come to a conclusion about minimum temporal duration of propagating pulse.

The phenomenon of rotation of optical solitons propagated in a nonlinear medium is investigated theoretically. The orbiting state with formation of a space structure, similar double helix, can arise, when the solitons are directed noncoplanarly. Numerical solution of the variational equations for the beams, interacting in Kerr medium, reveals that if the powers of beams are less than critical power of a self-focusing, it is possible to select parameters of beams, when the diffraction bleed is the slower process on a comparison with shaping of a helix. In the cubic-quintic media the multidimensional solitons are stable and analysis of angular momentum conservation and interaction potential of a soliton pair show, that stable orbiting state can be used for all-optical over-fast switches in a bulk media.

Propagation of the ultrashort pulses of the electromagnetic wave was considered in framework of the anharmonic oscillator model. For the quasi-harmonic waves, the model leads to the description of quadratic parametric processes, e.g., sum-frequency and difference-frequency mixings. Unipolar steady state pulse was obtained by analytical method. In numerical simulations it was shown that these steady state pulses are stable under collisions and small harmonic perturbations. However, these pulses are not solitons in the strict sense. Multipolar pulses demonstrate the stable regime of propagation too if these pulses exhibit a few oscillation of the electric field and the energy of these impulse is fairly high.

A refraction of short pulses by a thin film of atoms at two- photon resonance is numerically considered with the process of third harmonic generation involved in analysis. It is shown that a light pulse, being refracted by a tin film of resonance atoms, decays into subpulses, which number is determined by the energy penetrated in the film. The process depends on the angle of incidence. The variation of the resonance detuning allows compensating Stark effect and creating the preferable conditions for light pulse transmission. The effect of local field is similar in its action to the Stark effect, but its contribution to the frequency shift could be significant only in the media with greater concentration of the resonance atoms.

The superradiance of a thin layer of inverted two-level active medium has been investigated on the basis of numerical solution of semiclassical Maxwell-Bloch equations with stochastic initial conditions. The correlation of counter-propagation pulses delay times was analyzed with the account of diffraction divergence of radiation.

We analyze the superradiant emission with and without inversion from a thin film comprised of three-level atoms with the A-scheme of operating transitions. Since the thickness of the system is assumed to be smaller than the emission wavelength, the local-field correction to the acting field becomes of great importance and affects the three-level superradiance to a large extent. Due to this correction, a competition between the operating transitions occurs, resulting under suitable conditions in the suppression of one of them.

We investigate the different regimes of an optically dense extended two-level system. Taking into account the atomic concentration profile we compute both the transmitted and reflected outputs as a function of the length of a system. We show that the boundary structure essentially influence on the ratio of the transmitted and the reflected wave intensities.

We investigate the influence of the local field on the competition between the operating transitions in the superradiant emission from a thin film comprised of the three-level atoms with the initial coherence of lower doublet. Due tot this influence a coherent Raman transition between the sublevels of a doublet may occur.

It is shown that the magnetic field local inhomogeneous, caused by the stochastic spin distribution over the volume, effects significantly on the nuclear superradiance process.

We develop a theory of extreme spontaneous pulsations in open class D lasers corresponding to the bad-cavity limit when the medium relaxation rates are much less than the field relaxation rate T_E^-1. In this case it is mode superfluorescence (SF), not unidirectional one, which is responsible for the formation of an individual pulse, the latter being almost independent on pumping if it is strong enough. For the simple Fabry-Perot model of a short cylindrical sample, we investigate generation of 'hot' inhomogeneous polariton modes formed either by weak reflections from mirrors or by 'resonance' reflections from sharp boundaries of inverted medium. We pay particular attention to the cavity-free situation and describe one-mode and two-mode SF regimes, both giving rise to correlations between delay times of the counterpropagating pulses. We write down the solution of the initial value problem and analyze dynamics of forward-backward symmetrization of coherent transient emission initiated asymmetrically. We calculate analytically the reflection factors and growth rate of unstable discrete modes and continuous waves and indicate conditions which are necessary for mode SF to be much more efficient than unidirectional one.

Triggering optical superradiance, which allows a control of spontaneous emission with the use of an injection optical pulse, is considered. The multipulse regime of excitation of optical superradiance and the long-lived optical superradiance are analyzed as the generalizations of the triggering regime of superradiance excitation.

The results of theoretical and experimental superradiance studies in a pyrene-doped biphenyl crystal are presented. The superradiance nature of photon emission under certain conditions is experimentally proved for this crystal system. Experimental data fit the theory. The influence of induced radiation and of electron-phonon coupling on optical superradiance is theoretically investigated using the nonequilibrium statistical operator method. Possible superradiance applications are discussed, including coherent nonlinear spectroscopy, coherent electromagnetic pulse generation, and superradiant echo.

The chain of kinetic equations for a three-level extended macroscopic system interacting with an electromagnetic field is obtained on the basis of the method of elimination of the boson variables taking into account the coherent pumping processes. On its basis the conventional superradiance of the system is examined in the markovian limit. The relations between the parameters of the superradiant pulse and those of the pumping pulse of arbitrary duration are obtained. The possibility of description of the triggering superradiance is discussed.

Experimental results on cascade superradiance are observed. Kinetic equations of cascade superradiance are derived in the framework of nonequilibrium statistical operator method of Zubarev-Peletminsky. Their approximate solutions are obtained for the initial and final stages of process.

The anti-Stokes regime of the laser cooling of solids is theoretically investigated with the method of nonequilibrium statistical Zubarev-Peletminsky operator. The possibility of laser cooling of crystals doped with non-Kramers rare-earth ions is predicted.

The getting problems of UV and VUV laser action on the base of trivalent rare-earth ions activated crystals and the opportunities of upconversion pumping are discussed. The data of spectroscopical studies of stepwise multiphoton excitation of 4P'5d mixed configuration of Nd3, Pr3 and Ce3 ions in LiLuF4 and LiYF4 crystals are reported. The selection criterions of an intermediate 4f-state and a range of allowable pumping photon energies for the stepwise multiphoton excitation are proposed.

Kinetics of the decay of a dynamical grating formed by nonequilibrium charge carries in thin monocrystalline silicon films under femtosecond laser excitation are studied. A case of limiting concentration of charge carriers is analyzed. Contributions of ambipolar diffusion and Auger- recombination in the decay of a dynamical grating are estimated. At high intensities an effect of the long-lived dynamical grating is discovered.

It is shown that Michelson's experience on the determination of influence of Earth's motion on the light velocity admits twofold interpretation of obtained result. It is proposed to increase the experience purity by way of separate passage of direct and reverse light beams through both interferometer arms.

The physical and kinetic parameters were calculated for laser on copper vapors. The Boltzmann kinetic equation was solved by numeric methods with some approximations. There are isotropic distribution and stationarity of the physical parameters. The influence of the HBr admixtures on the physical parameters and electron energy distribution functions in gas discharges were investigated. Using cross sections of the electron impact excitation processes the velocity coefficients for reactions were calculated. It was confirmed, that excitation of the resonance level 3d⁹ 4s^{2 2}D with HBr admixtures is going more better.

In the development of three fundamental light sources, ultra high peak power laser, x-ray laser and superconducting linear accelerator based free electron laser, 100TW with 18.9 fs pulse width for ultra high peak power laser and 360W average power for free electron laser was obtained, and x- ray laser is ready for experiment using ultra thin film target. Basic technologies for optics and earlier stage of application studies are also introduced.

The importance of coherence in the interaction of (gamma) - radiation with nuclei is demonstrated for nuclear emission holography. Radiation, produced by a radioactive source nucleus, can go directly to a detector or can be resonantly scattered by neighboring nuclei before going to the detector. The interference between these two processes gives rise to the holographic image. The quantum mechanical theory of emission holography with (gamma) -radiation is sketched. An expression for the contrast function in the single scattering approximation is given and discussed. Simulations for a bcc-lattice of ⁵⁷Fe nuclei show the feasibility of nuclear emission holography. The technique will be very useful to study small clusters of resonant nuclei.

In recent years there became actual studies of quantum interference on gamma spectroscopic transitions induced by coherent perturbations.A special attention is paid to gamma transitions in compound systems. In this work it is shown that quantum interference effects (QIE) occur in gamma quantum spontaneous emission spectrum of an electron-nuclear paramagnetic system when electron spin resonance is induced. Occurrence of QIE is connected to preparation of the quantum system initial state. The role of electron relaxation is defined: increase of relaxation rate leads to extinguishing of QIE. The cases of stationary excitation of Mossbauer levels by wide and narrow spectra are considered.

Nuclear forward scattering of synchrotron radiation is theoretically modeled when a nuclear target is of either high-spin ferric protein or intermediate-spin one. It considers the spin fluctuations in the electron environment of Mossbauer ion are described by the stochastic non- adiabatic Clauser-Blume model. Of particular interest is the low-temperature case when spin-spin interaction are the main type of electron relaxation. It is shown how the pattern of quantum beats of the resonant response is changed if the interaction strength between the electron spin and dipole bath is increased.

The two possible schemes of inversionless amplification of resonant (gamma) -radiation with radiofrequency pumping have been analyzed by making use of the effective model of nuclear states.

The effects of electron fluctuations on nuclear forward scattering of synchrotron radiation (SR) are theoretically modeled when a nuclear target is a low-spin protein complex. Two possible cases of the states of Mossbauer ion are considered: 1) the subsystems of electron and nuclear states which are independent from each other in the effective magnetic field model: 2) the coupled electron-nuclear system of states under an external orient magnetic field. The influence of spin fluctuations on the patter of quantum beats of resonant response to SR pulse is analyzed in both general relaxation model and stochastic 'strong redistristribution' model of spectral diffusion.

The variant of the Schroedinger equation solution for the atom of hydrogen is submitted in view of the nucleus rotation, i.t. with the account received earlier by one of the authors potential energy for a rotating pointed charged particle. The received result allows by a quasi-classical way to take into account in the analytical decision of the Schroedinger equation for atom of hydrogen additional splitting of the atom energy levels because of rotation of the atomic nucleus.