The parametric doppler effect upon oblique radiation incidence in quartz glass

Frequency and reflection angle of probe radiation from a refractive-index inhomogeneity induced by an intense pumping pulse in quartz glass and moving with a relativistic velocity are calculated. Conditions under which the normal component of the wave vector of the reflected wave is directed to the opposite or to the same direction as the same component for the incident wave are determined. Comparison with the case of radiation reflection from a relativistic mirror in vacuum is performed. Conditions of the appearance of the Vavilov-Cherenkov radiation from a relativistic refractive-index inhomogeneity induced in the medium by an intense laser pulse are discussed.     

Transformation of electromagnetic radiation by rapidly moving inhomogeneities of a transparent medium

A theory of reflection and transmission of electromagnetic radiation by inhomogeneities of the parameters of a static transparent medium moving at the velocity of light is developed. Expressions are obtained for the Doppler frequency shift of radiation; it turns out that, under the condition of pronounced frequency dispersion, the frequency of incident radiation corresponds to two frequencies of reflected radiation (complementary waves). It is found that, as the velocity of an inhomogeneity tends to the phase velocity of radiation in the medium, the reflection and transmission coefficients of radiation by the inhomogeneity indefinitely increase. It is shown that the electromagnetic radiation frequency may increase severalfold, with a transformation coefficient of about unity, due to the Doppler shift by the inhomogeneities of a nonlinear medium that are induced by pulses (solitons) of intense counterpropagating radiation.     

Pulse measurement of the I–V characteristics in Bi-2212 intrinsic junctions

Current-voltage (I–V) characteristics are studied in the intrinsic Josephson junctions of Bi₂Sr₂CaCu₂O_y single crystals. In order to examine the influence of self-heating, a current pulse (∼0.2 μsec) is applied to the mesas of 40 μmϕx0.15 μm patterned on the crystal. As a consequence, in contrast to small characteristic voltageV _c in the continuous-current measurement, theV _c data is found comparable to the BCS value. Moreover, theI–V curve is nearly ohmic forl>l _c , implying that the nonlinearity under the continuous current is due to heating. The quasiparticle resistance forT<T _c is also presented by an estimate from the characteristic voltage.     

Focal switch of cosine-Gaussian beams

The focal switch of cosine-Gaussian (CsG) beams passing through a system with the aperture and lens separated is studied analytically and numerically. It is shown that the focal switch of CsG beams can appear not only for the apertured case, but also for the unapertured case. The necessary condition for the focal switch is that truncation parameter α > α_c and the beam parameter β > β_c, α_c, β_c being the corresponding critical values. There exists a maximum of the relative transition height Δz _sw as α varies, and Δz _sw increases with increasing β and decreasing N _w. The normalized axial intensity minimum I _min / I _max decreases with an increase of α and β, and I _min / I _max remains unchanged as N _w varies.     

Nature of contact resistance in high-T c YBa2Cu3O7−δ Superconductors

The contacts between various metals and the high-T_c superconductor YBa₂Cu₃O_7– are characterized by contact resistance,R _c, andI–V measurements from 300 K to 90 K. The contacts with bulk superconductor were made by vacuum deposition. Four metals, Au, Ag, Al, and Bi were investigated. The current transport across the contact is by carrier tunneling. All contacts were ohmic as theirI–V characteristics were symmetrical with respect to current direction.R _c values range between 10^–2 to 10¹ cm² and increase linearly as the temperature is lowered. The contact resistance originates from two distinct physical processes. One is the modification of the carrier concentration at the interface by the contact metal. The second is the nature of carrier injection at the free surface of the superconductor. TheR _c values depend on the contact metal-oxygen interaction parameter signifying the need for oxygen passivation for obtaining low contact resistances.     

The reflectivity of relativistic ultra-thin electron layers

The coherent reflectivity of a dense, relativistic, ultra-thin electron layer is derived analytically for an obliquely incident probe beam. Results are obtained by two-fold Lorentz transformation. For the analytical treatment, a plane uniform electron layer is considered. All electrons move with uniform velocity under an angle to the normal direction of the plane; such electron motion corresponds to laser acceleration by direct action of the laser fields, as it is described in a companion paper [Eur. Phys. J. D 55, 433 (2009)]. Electron density is chosen high enough to ensure that many electrons reside in a volume λ_R ³, where λ_R is the wavelength of the reflected light in the rest frame of the layer. Under these conditions, the probe light is back-scattered coherently and is directed close to the layer normal rather than the direction of electron velocity. An important consequence is that the Doppler shift is governed by γ_x=(1-(V_x/c)²)^-1/2 derived from the electron velocity component V_x in normal direction rather than the full γ-factor of the layer electrons.     

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.     

Dynamic magnetic permeability of a thin, high-T c superconducting wafer

The field dependence of the vibrational contribution to the dynamic magnetic permeability μ _V(H) is calculated for a thin (of thickness d∼λ) high-T _c superconducting wafer in a magnetic field parallel to the surface. The resulting curves are plotted on the basis of an exact numerical analysis of the vortex structures both for the thermodynamic-equilibrium vortex lattice and in the presence of pinning forces and the Bean-Livingston surface barrier. It is shown that the μ _V(H) curves are highly sensitive to the size factor (d/λ) and exhibit abrupt changes corresponding to a change in the number of vortex rows. The equilibrium μ _V(H) curve is found to be similar in its general behavior and absolute value (obtained with allowance for the distribution of grain sizes and with appropriate values of λ and ϰ) to the experimental μ _V(H) curve plotted at nitrogen temperature for fine-grained YBa₂Cu₃O_x with grain diameters 〈D〉∼λ in an increasing magnetic field. It is established that the main cause of the experimentally observed irreversible behavior of the μ _V(H) curves during cyclic variation of the applied magnetic field is the existence of a surface barrier to the exit of vortices from the superconductor. The lower limit H _min(B) of stability of the mixed state in the presence of an ideal surface barrier in a thin, high-T _c superconducting wafer (d∼λ) is determined, along with the range of the vortex state (H _max-H _min) for a fixed number of vortices in micrometer-size grains of the investigated YBaCuO samples. Fiz. Tverd. Tela (St. Petersburg) 39, 1943–1947 (November 1997)     

Fluctuation power spectrum of a Josephson junction

The fluctuation power spectrum of the Josephson junction has been evaluated in the limit of large energy barriers [(U _n ^max−U _n ^min)γ]≫1 and small currents [x≪x _e]. The result is valid for finite capacitance of the junction. The effect of the fluctuating Josephson current on the voltageV(t) across the junction has also been taken into account.     

Escape into vacuum of fast electrons generated by oblique incidence of an ultrashort, high-power laser pulse on a solid target

The possibility that fast electrons can escape in a direction close to the trajectory of a reflected ultrashort laser pulse at extremely high laser radiation fluxes is examined analytically and numerically. Analytic estimates are made of the feasibility of forming electron bursts in the plasma and of their subsequent motion. The self-consistent, collisionless motion of a plasma acted on by specified incident and reflected ultrashort laser pulses is modeled in two dimensions by the particle-in-cell method. It is shown that a substantial number of electrons located in the subcritical region are gathered into bunches by the resultant forces and escape to the vacuum in a direction different from the normal to the target surface within a narrow range of solid angles. This demonstrates the feasibility of laser acceleration of an electron burst during reflection of an ultrashort laser pulse from a solid target. Zh. éksp. Teor. Fiz. 116, 1184–1197 (October 1999)     

Polarization stokes polarimetry of the amplitude and phase characteristics of surface plasmon polariton resonance

The amplitude and phase characteristics of internal reflection of gold nanofilms have been investigated using polarization modulation of electromagnetic radiation in the Kretschmann geometry. The component Q (the difference between the reflection coefficients R _s ² and R _p ² for the s and p polarizations, respectively) and the component V of the Stokes vector (the difference between the phases of the orthogonal components of linearly polarized radiation) of light reflected from a half-cylinder of the total internal reflection with gold films of different thicknesses on its flat surface have been measured as a function of the angle of incidence of light in the wavelength range 500–1000 nm. It has been demonstrated that, in the range of parameters corresponding to the manifestation of the plasmon polariton resonance (the angle of incidence of light, the wavelength, the metal film thickness), the dispersions of the amplitude and phase characteristics are in quantitative and qualitative agreement with the model concepts of a classical oscillator.     

Canonical Ensemble with Temperature Limitation

Ideal Bose and Fermi systems are studied on the basis of a canonical ensemble, subject to the condition that their temperature is less than a given temperature T_max. A single new parameter (the tau-parameter, τ) is needed to keep account of the new constraint. The parameter τ is shown to be the exponential of a pseudo-chemical potential that is linearly dependent on temperature. The inclusion of the τ- parameter leads to generalizations of usual thermodynamic quantities (internal energy, heat capacity and entropy) and various particular cases are discussed. The heat capacity of a Bose system can exhibit a maximum at a temperature less than the maximum temperature T_max. The number of micro-states in the canonical ensemble is found to increase with τ. The heat capacity c_V of a Fermi system of non-interacting spins exhibits a Schottky anomaly. The peak depends on τ, and for some cases c_V/k can significantly exceed unity. The influence of τ on the entropy of the Fermi system and on the number of micro-states in the canonical ensemble is significant but not spectacular.     

Formation of the 255-keV annihilation line near the magnetic poles of pulsars

The possibility of existance is discussed for pulsars emitting soft γ radiation near their magnetic poles upon the annihilation of ultrarelativistic positrons from the magnetosphere and electrons from the surface of a star. With an increase in the energy of incident positrons, the photon energy of this backward radiation tends to a constant value m _e c ²/2=255 keV. This radiation is shown to be directed opposite to the positron flux direction.

     

Atomistic simulation of the interaction of slow protons with an iron surface

Summary We have studied the dynamical behaviour of low-energy protons (1.0 eV≤E _in≤50 eV) interacting with a Fe {100} surface atT=300 K, by means of molecular-dynamics simulations. The inelastic energy losses have been taken into account by means of a friction term proportional to the projectile velocity and depending on the instantaneous local electronic density experienced by the projectile. For a given incident energy and irradiation geometry, we have estimated the particle and energy reflection coefficients and obtained a detailed evaluation of the different contributions (elastic and inelastic) to the energy loss of the reflected particles.     

Insulating phases of the one-dimensional t-J model with nearest-neighbor repulsive interaction

Using the deformed Hubbard operator approach, we analytically study weak-coupling phase diagram of the one-dimensional t-J-V model at half filling. In the case of small deformed parameter ζ(≪1), the interactions induced by the no double occupancy constraint are softened, accessible by the bosonization field theory and the renormalization group technique. The ground state exhibits insulating behavior of density-wave correlations. The bond-spin-density-wave (BSDW) and bond-charge-density-wave (BCDW) phases are realized in the whole weak-coupling regime while the charge-density-wave (CDW) and spin-density-wave (SDW) phases depend on V/J > (V/J) _c or V/J < (V/J) _c , where (V/J) _c = 1/4. Furthermore, our results are expected to adiabatically continue back to ζ = 1.     

Field and temperature dependence of intergranular hysteresis in YBa2Cu3O7

We have studied the variation of low field magnetization hysteresis in YBa₂Cu₃O₇ as a function of the maximum magnetic field applied during a hysteresis cycle (1 G<H _max<7.3 G) and also as a function of temperature (77 K<T<95 K). The remnant magnetization is studied as a function ofH _max andT and the measured dependences are explained using the extended critical state model. The potential of this technique as a contactless method of probing the temperature dependence ofJ _c is discussed.     

Bragg reflection waveguide: Anti-mirror reflection and light slowdown

The effect of the light group velocity reduction in dielectric Bragg reflection waveguide structures (SiO₂/TiO₂) in the vicinity of the cutoff frequency is studied experimentally. The effect of anti-mirror reflection specific to Bragg reflection waveguides is described and employed to detect slow light. Experiments were performed using Ti:sapphire laser pulses ∼100 fs in length. The group index n _g ∼ 30 with a fractional pulse delay (normalized to the pulse width) of ∼10 is demonstrated. The problems and prospects of the implementation of slow-light devices based on Bragg reflection waveguide structures are discussed.     

Displacement damage analysis and modified electrical equivalent circuit for electron and photon-irradiated silicon solar cells

Solar modules and arrays are the conventional energy resources of space satellites. Outside the earth's atmosphere, solar panels experience abnormal radiation environments and because of incident particles, photovoltaic (PV) parameters degrade. This article tries to analyze the electrical performance of electron and photon-irradiated mono-crystalline silicon (mono-Si) solar cells. PV cells are irradiated by mono-energetic electrons and poly-energetic photons and immediately characterized after the irradiation. The mean degradation of the maximum power (P_max) of silicon solar cells is presented and correlated using the displacement damage dose (D_d) methodology. This method simplifies evaluation of cell performance in space radiation environments and produces a single characteristic curve for P_max degradation. Furthermore, complete analysis of the results revealed that the open-circuit voltage (V_oc) and the filling factor of mono-Si cells did not significantly change during the irradiation and were independent of the radiation type and fluence. Moreover, a new technique is developed that adapts the irradiation-induced effects in a single-cell equivalent electrical circuit and adjusts its elements. The “modified circuit” is capable of modeling the “radiation damage” in the electrical behavior of mono-Si solar cells and simplifies the designing of the compensation circuits.     

Reflection measurements in CO2 laser solid deuterium target interaction

Using a 60 nsec, 300 MW CO₂ TEA laser reflection measurements from solid deuterium targets have been investigated. Energy, reflected and scattered pulse shape are recorded at various angles: 0°, 45°, 90°, 135°. Reflection, X-ray measurements and ion mean kinetic energy are correlated at the focussing lens position with respect to the target position. The maximum plasma temperature varies from 20 to 35 eV for incident laser fluxes ranging from 5 × 10¹⁰ up to 5 × 10¹¹ W/cm². The cut-off density inside the deuterium ice has been observed and located. In each case reflection has been found to be weak less than 5% for each direction. For the maximum fluxes X-ray energies greater than 0.5 keV have been observed.     

On the connectivity index for lattices of nonintegral dimensionality

We define the connectivity indexc for an infinite graph by the requirement that to disconnect a subset of at leastV points from the rest of the graph requires the deletion of a minimum ofS(V) bonds whereS(V) ∼V ^(c−1)/c for largeV. For ad-dimensional hypercubical lattice withd integral,c=d. We construct explicit examples of lattices with nonintegral connectivity indexc, 1<c<∞. It is argued that the connectivity index is an important parameter determining the critical behaviour of Hamiltonians on these lattices.