Chaotization and decay instability of a diffraction-catastrophe field in the presence of focusing of high-power laser radiation in a nonlinear medium

Focusing of a high-power laser beam, whose initial wave front is deformed by spherical aberration and astigmatism, in a medium with refractive-index nonlinearity is investigated by the computer experiment method. It was found that the extended formations which arise near the focus are no longer diffraction catastrophes, since they are structurally unstable. It is shown that weak disturbances of the shape of the initial wave front produce extremely strong distortions of the optical field in the focusing region. As the wave propagates in the z direction, spatial chaos in the distribution of the optical field develops in the region of focusing (from 137 to 142 mm). Optical turbulence arises in the focusing region as a result of self-diffraction of light by self-induced nonuniformities of the refractive index of the medium. After the region with the smallest cross section of the formation near the focus, the three-dimensional optical field has the form of chaotically dispersing “splashes” and extended “filamentary ejecta.” Zh. Tekh. Fiz. 68, 74–83 (September 1998)     

Ultranarrow beams of electromagnetic radiation in media with a Kerr nonlinearity

The vector structure of a self-channeling electromagnetic field is determined by solving the complete system of Maxwell’s equations in a transparent medium with a Kerr nonlinearity. Self-channelling with an asymmetric angular distribution of the field occurs at powers several times the critical self-focusing power. As the power is increased, a universal (self-similar) field structure develops in which only the scales change as the power is varied. Self-channelling with a channel width much smaller than the (linear) wavelength of the light, i.e., a “needle of light” with an extreme concentration of radiant power, is found to occur. Zh. éksp. Teor. Fiz. 116, 458–468 (August 1999)     

Formation mechanisms and structure of the luminescence spectra of a dense resonant medium

The purely thermal visible and infrared radiation emitted by a dense resonant medium (sodium vapor) heated nonuniformly to temperatures of 600–1200 K was investigated experimentally for the first time under conditions where the photon mean free path is comparable with the emission wavelength. The profile of the recorded spectra and the absolute luminescence intensities in the different spectral ranges show good agreement with the results of a numerical simulation using a previously developed theory of resonance radiation transport which assumes a Boltzmann spectral distribution of the resonant level population proportional to exp(−ℏω/T). The self-reversed resonant sodium line exhibited strong asymmetry and it was shown that under certain conditions, the luminescence spectrum of the medium may exhibit an additional broad peak on the far “red” limb of the resonance line. Calculations and measurements demonstrated that the intensity of the thermal emission of sodium vapor at this red peak is several orders of magnitude higher than that obtained from the standard theory of resonance radiation transport. This effect is arbitrarily termed an infrared “ catastrophe.” It is noted that in a solar corona plasma and in gas-discharge lamps, the far red limbs of the resonant lines may make a substantial contribution to the total luminescence intensity and in some cases, considerably exceed the intensity of the photorecombination and bremsstrahlung continuum. Zh. éksp. Teor. Fiz. 114, 135–154 (July 1998)     

Optical vortices in the scattering field of magnetic domain holograms

Experimental investigations and theoretical-model analyses have been made of the magnetooptic diffraction of light at ferrite garnet magnetic films with a banded domain structure which includes isolated magnetic grating defects in the form of “forks” and “breaks.” An analysis of the magnetic grating structure and the light diffraction field shows that in terms of its action on laser radiation, a banded domain grating is similar to a computer-synthesized phase hologram of an isolated pure screw-wavefront dislocation. It is shown that as a result of magnetooptic diffraction at a magnetic hologram, optical vortices may be reconstructed with a helicoidal wavefront carrying the topological charge l=±1,±2. Zh. Tekh. Fiz. 68, 54–58 (December 1998)     

Effect of external noise on the optical thermal breakdown of semiconductor wafers

The optical thermal breakdown of a semiconductor wafer with a small Biot number under conditions of fluctuating incident light intensity is discussed. It is shown that external noise shifts the breakdown region toward somewhat higher values of the control parameter, and as the fluctuations grow this process leads to suppression of the critical point. Light intensities below the threshold noise can induce a nonequilibrium phase transition. Numerical estimates are given for germanium illuminated by a CO₂ laser. Zh. Tekh. Fiz. 67, 117–119 (September 1997)     

Nonuniform distribution of absorbed energy in high-resistance materials excited by an electron beam

Experimental results are presented on the changes in the optical characteristics of lithium fluoride induced by an electron beam with time-varying density and pulse energies close to the threshold for destruction of the material. The spatial distribution of color centers is investigated, especially near breakdown channels. Mechanisms for nonuniform accumulation of defects are discussed, along with the fundamental causes of the inhomogeneous energy distributions induced by the high-current electron beam. Concrete results of calculations of the field intensity distribution in LiF crystals during irradiation are presented, based on models of “uniform” and nonuniform charging of the sample. An abrupt increase in the electric field intensity is predicted near the breakdown channel. Zh. Tekh. Fiz. 68, 53–59 (April 1998)     

Microwave breakdown initiated in a high-temperature superconducting film by thermal disturbances and defects

The effect of thermal disturbances and nonsuperconducting defects on the microwave breakdown of a high-temperature superconducting film is investigated theoretically. The dependence of the critical energy of thermal disturbances on the surface microwave field is obtained. It is shown that in a wide range of values of the surface microwave field the critical energy of local disturbances is less than the critical energy of spatially extended disturbances. It is established that microwave breakdown on defects may be preceded by a stage of formation of a finite-size normal-phase region localized at the defect. The effect of the form and absorption coefficient of the defect on scenarios leading to the destruction of superconductivity and on the microwave breakdown field of a film at a defect are investigated. Zh. Tekh. Fiz. 69, 52–59 (May 1999)     

Medium effects in the production and π0γ decay of ω-mesons in pA collisions in the GeV region

The ω resonance production and its π⁰γ decay in pA reactions close to threshold is considered within the Intranuclear Cascade (INC) model. The π⁰γ invariant-mass distribution shows two components which correspond to the ω decay “inside” and “outside” the nucleus, respectively. The “inside” component is distorted by medium effects, which introduce a mass shift as well as collisional broadening for the ω-meson and its decaying pion. The relative contribution of the “inside” component is analyzed in detail for different kinematical conditions and nuclear targets. It is demonstrated that a measurement of the correlation in azimuthal angle between the π⁰ and γ momenta allows to separate events related to the “inside”ω decay from different sources of background when uncorrelated π⁰'s and γ's are produced. Received: 2 April 2001 / Accepted: 5 June 2001     

Theory of scanning near-field magnetooptical microscopy

An analytical theory of scanning near-field magnetooptical microscopy is developed. The theory is based on the elastic scattering of light by small, resonantly polarizable particles, which are used to scan the plane surface of a nonuniformly magnetized medium. The effective polarizability of the particles is calculated with the effect of dynamic “image forces” taken into account in all orders of perturbation theory with respect to the interaction of the particle with a demagnetized ferromagnet, and the magnetooptical perturbation is calculated to first order in the magnetization. The major contributions to the magnetooptical light scattering for a ferromagnetic structure magnetized perpendicular to the surface are found, including a quasistatic approximation for the near-field particle-magnet interaction. The optical size resolution of a magnetic (dielectric) inhomogeneity is estimated. Zh. Tekh. Fiz. 68, 86–91 (July 1998)     

Theory of one-dimensional and quasi-one-dimensional heat conduction

It is shown that the heat conduction process in a one-dimensional flow of a fluid moving with a velocity V in a constant temperature field follows a law that is considerably more complicated than an “ordinary” exponential law. It is demonstrated that in the quasi-one-dimensional case the heat conduction process in an abstract space of dimension 1+ɛ, where ɛ varies from zero to unity, is described by a modified Fourier equation. Its solution for an infinite space is found. Zh. Tekh. Fiz. 67, 8–12 (July 1997)     

The formation of positronium in molecular substances

The theories regarding the formation of positronium in molecular substances are discussed. A modified theory based upon the “spur” theory is described. Theoretical derivation and experimental results suggest that the fraction of the long lifetime component due too-positronium annihilation has a complex origin. Initially, the electron of the positron-electron pair is likely to be separated from the positron by medium molecules even when the total kinetic energy of the pair is less than the potential energy between them. The formation of positronium depends on the mobilities of the positron and electron, the slowing down process and the potential energy between them. Positronium is formed in less than 10 ps. Then the positronium produced may react with the radicals created in the “spur” due to the positron. Only the fraction ofo-positronium able to escape the “spur” will have a long lifetime. Therefore, positronium formation is highly related to the fast reactions in the “spur” during the first 100 ps.     

Optical and Thermal Simulator for Laser-assisted Magnetic Recording

“Laser-assisted magnetic recording”, in which a recording media is heated by a laser beam while writing data, is attracting attention as a technology that enables a recording density of 1 Tb/in.². There exists another technology for media in which the recording layer is constructed with many small projections that enable high magnetic coercivity. This is called “patterned media”. For developing hard disk drives using these methods, we developed a simulator that analyzes the optical intensity distribution from the optical head for laser-assisted recording and the temperature profile on the patterned media. The simulator calculates the optical model using the finite-difference time-domain (FDTD) method. The thermal analysis of the three-dimensional model allows fast calculations using the alternating direction implicit (ADI) method. The heat source distribution data for thermal analysis is calculated in order to use the results of optical analysis. The optical and thermal analyses of the laser-assisted recording model were investigated with the simulator.     

Ion milling-assisted study of defect structure of HgCdTe films grown by liquid phase epitaxy

Ion milling, as a tool for “stirring” defects in HgCdTe by injecting high concentration of interstitial mercury atoms, was used for studying films grown by liquid phase epitaxy (LPE) on CdZnTe substrates. The films appeared to have very low residual donor concentration (∼10¹⁴ cm⁻³), yet, similar to the material grown by molecular beam epitaxy, contained Te-related neutral defects, which the milling activated electrically. It is shown that ion milling has a stronger effect on HgCdTe defect structure than thermal treatment, and yet eventually brings the material to an “equilibrium” state with defect concentration lower than that after low-temperature annealing.     

Heat conductivity and the Lorentz number of the Sm1−x GdxS “black” phase

Measurement of the heat conductivity and electrical resistivity of two Sm_1−x Gd_xS compositions with x=0.1 and 0.14 is reported within the 80–300 K interval. An analysis of experimental data on the electronic component of heat conductivity permits a conclusion that the d subband of “heavy” carriers in the conduction band of these materials lies above the s “light”-carrier subband. Fiz. Tverd. Tela (St. Petersburg) 41, 26–29 (January 1999)     

Thermally induced defect photoluminescence in hydrogenated amorphous silicon

The intrinsic defect photoluminescence of hydrogenated amorphous silicon (a-Si:H) films has been investigated at high intensities of optical pumping that lead to heating of the film. It has been revealed that, for short heating times, the intensity of the defect photoluminescence increases exponentially with an increase in the temperature with an activation energy of 0.85 eV, which is considerably higher than the activation energy (∼0.2 eV) determined from experiments on classical annealing. This and other experimental results on the temperature dependence of the intensity and kinetics of the defect photoluminescence have been explained in terms of the “hydrogen glass” model by thermally induced generation of intrinsic defects in amorphous silicon. The results of the calculations are in good agreement with the experimental data on the defect photoluminescence that reflects the formation and annihilation of defects for short heating times under optical excitation.     

Optical and magneto-optical properties of Fe/Cu multilayered films: Influence of the modulation period and the bcc-fcc phase transition in iron

The optical and magneto-optical properties of multilayered film samples of the Fe/Cu system prepared by high-frequency sputtering on an Si(100) substrate are studied by ellipsometry and by measuring the equatorial Kerr effect (the δ _p effect) in the spectral range 0.25–7 μm. The optical characteristics, the plasma frequency ω _p and the relaxation frequency γ ₀ of the conduction electrons, and the δ _p effect are found as functions of the modulation period D=12.5–100 Å. Anomalous behavior of the optical and magneto-optical characteristics is discovered in short-period Fe/Cu structures. The results are discussed within a phenomenological theory of optical and magneto-optical properties for layered structures. Several factors, such as the indirect exchange interaction between the iron layers, the presence of a transition layer on the internal boundaries, the possible “magnetizing” of copper, and the formation of an fcc iron phase in the thin layers, are taken into account in the analysis of the experimental data. Zh. éksp. Teor. Fiz. 112, 1694–1709 (November 1997)     

Goldstone mode relaxation in a quantum hall ferromagnet due to hyperfine interaction with nuclei

Spin relaxation in quantum Hall ferromagnet regimes is studied. As the initial non-equilibrium state, a coherent deviation of the spin system from the B direction is considered and the breakdown of this Goldstone-mode state due to hyperfine coupling to nuclei is analyzed. The relaxation occurring non-exponentially with time is studied in terms of annihilation processes in the “Goldstone condensate” formed by “zero spin excitons”. The relaxation rate is calculated analytically even if the initial deviation is not small. This relaxation channel competes with the relaxation mechanisms due to spin-orbit coupling, and at strong magnetic fields it becomes dominating.     

Anomalous behavior of excitons at light holes in strained (In, Ga)As/GaAs heterostructures

Additional localization of holes due to Coulomb attraction to the electron located in a quantum well is important for light-hole excitons in the heterostructure (In, Ga)As/GaAs. The fine structure of the optical and magneto-optical spectra of these quantum wells is examined in detail with the formation of a “Coulomb well” and deformations taken into account. Fiz. Tverd. Tela (St. Petersburg) 40, 797–799 (May 1998)     

Correlated Knowledge: an Epistemic-Logic View on Quantum Entanglement

In this paper we give a logical analysis of both classical and quantum correlations. We propose a new logical system to reason about the information carried by a complex system composed of several parts. Our formalism is based on an extension of epistemic logic with operators for “group knowledge” (the logic GEL), further extended with atomic sentences describing the results of “joint observations” (the logic LCK). As models we introduce correlation models, as a generalization of the standard representation of epistemic models as vector models. We give sound and complete axiomatizations for our logics, and we use this setting to investigate the relationship between the information carried by each of the parts of a complex system and the information carried by the whole system. In particular we distinguish between the “distributed information”, obtainable by simply pooling together all the information that can be separately observed in any of the parts, and “correlated information”, obtainable only by doing joint observations of the parts (and pooling together the results). Our formalism throws a new light on the difference between classical and quantum information and gives rise to an informational-logical characterization of the notion of “quantum entanglement”.