Interaction of light waves on a reflecting holographic grating in cubic photorefractive crystals

The interaction of two antiparallel light waves on a reflecting grating is analyzed theoretically in arbitrarily oriented optically active cubic crystals of point group 23. The effect of nonunidirectional energy transfer on the interaction efficiency is investigated in the undepleted-pump-power approximation in (100)-, (111)-, and $(11\bar 2)$ -cut Bi₁₂TiO₂₀ crystals.     

Multiphoton effects in laser-assisted ionization of a helium atom by electron impact

The dynamics of the electron impact multiphoton ionization of a He atom in the presence of an intense laser field (n $\gamma _e$ , 2e) is studied theoretically for laser polarization ( $\vert\vert^l$ ) and perpendicular ( $\bot^r$ ) to the incident momentum. The triple differential (TDCS) as well as the double differential (DDCS) cross sections are studied for the coplanar asymmetric geometry. The results are compared with the only available kinematically complete experiment at high incident energy (1000 eV). Significant laser modification (enhancement) is noted due to multiphoton effects in the present binary and recoil peak intensities of the TDCS for both the geometries, in qualitative agreement with the experiment. In the single photon case, the net effect of the laser field is to suppress the field free (FF) TDCS as well as the DDCS in the zeroth order approximation of the ejected electron wave function (CV), while in the first order (MCV), the cross sections are found to be enhanced. The CV multiphoton cross sections obey the famous Kroll Watson (KW) sum rule while the latter does not hold good in the corresponding MCV approximation.     

Steady-state vectorial self-diffraction on a non-local photorefractive grating in a crystal of symmetry \overline{4}3m at symmetrical transmitting geometry

The steady-state two-wave interaction in a cubic crystal of the symmetry group 3m with the non-local photorefractive response in the absence of an external electric field is considered for the case of arbitrary interaction orientation with respect to the crystallographic coordinate system and for arbitrary intensities and polarization states of incident light waves. The self-diffraction problem is described on the basis of four coupled-wave equations in terms of the complex scalar amplitudes of components of the light waves with orthogonal linear polarization. The derived conservation laws are valid for the non-linear dependency of the photorefractive-grating amplitude on the modulation coefficient of the interference light pattern. It follows from these laws that the two non-unidirectional energy fluxes can form the total energy exchange between the two interacting light waves. A set of independent conservation laws allows us to decouple the coupled-wave equations and to obtain their analytical solution, at least, in the form of quadrature formulae. For example, such a solution is derived for the case of linearly polarized incident light waves and for the linearized dependency of the photorefractive-grating amplitude on the modulation coefficient. The explicit analytical expressions for the scalar amplitudes are obtained for the transversal electro-optic configuration of interaction. The possibility of polarization-state transformation of light waves without energy exchange between them is shown. Received: 30 July 2002 / Published online: 11 December 2002 RID="*" ID="*"Corresponding author. Fax: +7-3822/414321, E-mail: litvinov@ed.rk.tusur.ru     

Electrical properties and Pockels effect in BaTiO_{3}/SrTiO_{3} superlattices

The electrical and linear electro-optical properties of BaTiO $_{3}$ (BT)/SrTiO $_{3}$ (ST) superlattices epitaxially grown on ST substrate are theoretically investigated using a microscopic quantum mechanical model based on the orbital approximation in correlation with the dipole–dipole interaction. Both the first-, second-, and third-order electronic polarizabilities were considered in this calculation in order to obtain accurate results for both the spontaneous local electric field, spontaneous polarization, relative dielectric constant, and linear electro-optic coefficients (Pockels constants) of BT/ST superlattices. The calculations show that the spontaneous local electric field, spontaneous polarization and linear electro-optic coefficients of BT/ST superlattices increase with their content in BT while the relative dielectric constant increases with their content in ST. Moreover, we have shown that significant enhancement of the linear electro-optic coefficients can be achieved in BT/ST superlattices. This enhancement, which concerns the ST as well as the BT layers, arises from the combined effects of strain, induced in the BT layers by the epitaxial growth, and internal polarizing electric field originating in the BT layers and acting on the electronic clouds of the polarizable constituent ions of the system.     

Production of the bottom analogs and the spin partner of the X(3872) at hadron colliders

The propagation of gravitational waves on the background of a nonperturbative vacuum of a spinor field is considered. It is shown that there are several distinctive features in comparison with the propagation of plane gravitational waves through empty space: there exists a fixed phase difference between the \(h_{yy,zz}\) and \(h_{yz}\) components of the wave; the phase and group velocities of gravitational waves are not equal to the velocity of light; the group velocity is always less than the velocity of light; under some conditions the gravitational waves are either damped or absent; for given frequency, there exist two waves with different wave vectors. We also discuss the possibility of an experimental verification of the obtained effects as a tool to investigate nonperturbative quantum field theories.     

Studying the possibility of recovering np and nn helicity amplitudes on the basis of \vec p + \vec d and \vec n + \vec d scattering data at intermediate energies

In this work, we study the possibility of direct recovery of np helicity amplitudes, which are unknown at incident neutron energies T _n > 1.1 GeV, and nn helicity amplitudes, which are unknown at any energy, from data on $\vec p + \vec d$ and $\vec n + \vec d$ scattering. For the inversion of $\vec N + \vec d$ data, we use formulas that relate N _d- and NN amplitudes derived in terms of a refined Glauber model. It is found that the critical factors for solving the inverse problem under study are the accuracy and completeness of the set of input $\vec N + \vec d$ observables.     

Characterization of blade Bragg grating modeling with different incident angle profiles for strain sensor applications

This paper presents the design, realization and measurement of a thin lightweight absorbing material for space applications. Absorber design is based on high impedance surfaces loaded with resistors and known as a resistive high impedance surface (RHIS). The behavior of RHIS is analyzed at normal and oblique incidences for TE and TM polarizations. Prototypes have been realized and measured. Final design has a reflection coefficient less than $-$ 15 dB in S-Band (2–2.3 GHz) at normal incidence and till an angular dispersion of 40 $^\circ $ for waves in TE polarization, and 35 $^\circ $ for waves in TM polarization. Simulation results are validated by measurement.     

Scattering of a few-cycle laser pulse by a single relativistic electron

The scattering of a single relativistic electron with few-cycle plane wave laser pulse with intensity of about $I=1.38\times 10^{14}\,\text{ W/cm }^{2}$ is theoretically and numerically analyzed in the linear regime, and the radiated energy spectra of electron shows that zeptosecond X-ray pulses can be supported. The influences of the initial carrier-envelope phase offset $\varphi _0$ of the incident few-cycle laser pulses are studied, and the results demonstrate that a single zeptosecond pulse can be produced from scattering by using a single-cycle laser pulse with fixed initial carrier-envelope phase offset $\varphi _0 =\pi /2$ . It is discovered that the influence of the initial carrier-envelope phase $\varphi _0$ on the spectrum of the radiation is apparent for low and high frequency of the spectrum, but there is no influence of the central part of the spectrum.     

Growth specifics of GaAs nanowires in mesa

The possibility of epitaxial growth of nanowire arrays on tilted faces of linear mesa has been demonstrated. The structural properties of GaAs nanowires grown on ( $33\bar 1$ ), ( $11\bar 7$ ), and (113) faces of samples with the (100) crystallographic orientation of the substrate have been studied. It has been found that there is a relation between the structural parameters of nanowires and the geometric orientation of the growth surface relative to the 〈111〉 directions and the surface of the substrate.     

Anisotropic photoionization as a mechanism of axial iron center alignment in KTaO3

An EPR study has revealed light-induced recharging and optical alignment of the Fe _Ta ⁴⁺ -V _O tetragonal complexes in KTaO₃. The data on the optical creation and destruction of this center by light of different polarizations and wavelengths are discussed together with similar results obtained for the Fe _K ³⁺ -O_i center. These two centers were established to undergo mutual charge transfer, in which the electron released in the photoionization of the Fe _K ²⁺ -O_i center is trapped by the Fe _Ta ⁵⁺ -V _O center. Irradiation by light with a photon energy below 2.05 eV, which is the ionization threshold of Fe _K ²⁺ -O_i, reverses this process. In both cases, the absorption cross section depends on the orientation of the center axis relative to the light polarization vector. As a result, the Fe _Ta ⁴⁺ -V _O and Fe _K ³⁺ -O_i tetragonal centers in KTaO₃ acted upon by polarized light undergo orientation-sensitive light-induced recharging and the defects with the given charge state are no longer characterized by an equally probable distribution of the orientations of their axes over the three 〈100〉 directions. This mechanism, which does not involve real reorientations of the Fe_Ta-V _O and Fe_K-O_i complexes, gives rise, nevertheless, to the alignment of the centers along (or at right angles to) the light polarization vector.     

Effects of modified Chaplygin gas on structure formation in the universe

In this paper, the structure formation theories for the modified Chaplygin gas (MCG) model are established in the linear and non-linear regimes. Concretely, for the linear regime, the evolutions of the growth index $f$ and the growth variable $T$ are illustrated for the interacting MCG (IMCG) model and MCG model without interaction between dark energy and dark matter, which can give reasonable predictions for structure formation. While for the non-linear regime, by supposing the homogeneity and conservation of dark energy when the system reaches virialization, we can point out that MCG reaches the state of turn around later than GCG, the value of the collapse factor in MCG model is bigger than the fiducial value 0.5 in Einstein-de Sitter universe, namely $\eta >0.5$ , because of the effective repulsive force of dark energy, and the density contrast of the virialization tends to the Einstein-de Sitter value $18\pi ^{2}$ . Furthermore, the evolutions of the cluster number counts in LCDM, GCG and MCG models without and with interaction between dark energy and dark matter are illustrated by extending the Press-Schechter framework, which can exhibit the differences among the three models.     

Exact calculation of O(α) QED corrections for f_1 \overline {f_1 } \uparrow f_2 \overline {f_2 } processes induced by polarized incident particles

For $f_1 \overline {f_1 } \uparrow f_2 \overline {f_2 }$ (γ) processes induced by polarized incident particles, exact covariant expressions for the energy spectrum of one of the emitted fermions, for the total cross section, and for the polarization asymmetry are obtained in theα³ order of QED.     

An interacting dark energy model in a non-flat universe

In this paper, an interacting dark energy model in a non-flat universe is studied, with taking interaction form $C=\alpha H\rho _{de}$ C = α H ρ d e . And in this study a property for the mysterious dark energy is aforehand assumed, i.e. its equation of state $w_{\Lambda }=-1$ w Λ = - 1 . After several derivations, a power-law form of dark energy density is obtained $\rho _{\Lambda } \propto a^{-\alpha }$ ρ Λ ∝ a - α , here $a$ a is the cosmic scale factor, $\alpha $ α is a constant parameter introducing to describe the interaction strength and the evolution of dark energy. By comparing with the current cosmic observations, the combined constraints on the parameter $\alpha $ α is investigated in a non-flat universe. For the used data they include: the Union2 data of type Ia supernova, the Hubble data at different redshifts including several new published datapoints, the baryon acoustic oscillation data, the cosmic microwave background data, and the observational data from cluster X-ray gas mass fraction. The constraint results on model parameters are $\Omega _{K}=0.0024\,(\pm 0.0053)^{+0.0052+0.0105}_{-0.0052-0.0103}, \alpha =-0.030\,(\pm 0.042)^{+0.041+0.079}_{-0.042-0.085}$ Ω K = 0.0024 ( ± 0.0053 ) - 0.0052 - 0.0103 + 0.0052 + 0.0105 , α = - 0.030 ( ± 0.042 ) - 0.042 - 0.085 + 0.041 + 0.079 and $\Omega _{0m}=0.282\,(\pm 0.011)^{+0.011+0.023}_{-0.011-0.022}$ Ω 0 m = 0.282 ( ± 0.011 ) - 0.011 - 0.022 + 0.011 + 0.023 . According to the constraint results, it is shown that small constraint values of $\alpha $ α indicate that the strength of interaction is weak, and at $1\sigma $ 1 σ confidence level the non-interacting cosmological constant model can not be excluded.     

On the Boyd-Kadomstev System for a Three-Wave Coupling Problem and its Asymptotic Limit

We consider the Boyd-Kadomstev system which is in particular a model for the Brillouin backscattering in laser-plasma interaction. It couples the propagation of two laser beams, the incoming and the backscattered waves, with an ion acoustic wave which propagates at a much slower speed. The ratio ${\varepsilon}$ between the plasma sound velocity and the (group) velocity of light is small, with typical value of order 10^?3. In this paper, we make a rigorous analysis of the behavior of solutions as ${\varepsilon \to 0}$ . This problem can be cast in the general framework of fast singular limits for hyperbolic systems. The main new point which is addressed in our analysis is that the singular relaxation term present in the equation is a nonlinear first order system.     

Inverse model of the piezoelectric ceramic polarization under wide bandwidth mechanical excitations with fractional derivative consideration

This paper presents an inverse piezoelectric ceramic polarization model, $T(P)$ , working in wide bandwidth under various mechanical excitations. The model was derived from the polarization model under electric field, $P(E)$ , by use of the correlation ( $E =\alpha \cdot T\cdot P$ ) between the external mechanical excitation and piezoelectric ceramic electric field. Using the model, $T(P)$ , a given polarization could be obtained by calculating the mechanical stress waveform applied to the ceramic. The piezoelectric ceramic P188 was investigated in the experiment; measurement bench and procedures have been developed to evaluate the accuracy of the model. By means of modeling dynamic counterpart (a fractional derivative part), large range of frequency ( $10^{-3} \text{ Hz } < f < 10 \text{ Hz }$ ) imposed polarization have been examined and experimental results turned out to be good both with sinusoidal and triangular waveforms. The same fractional derivative operator is universal both in mechanical and electrical excitations.     

Single decay-lepton angular distributions in polarizede + e − →\overline {tt} and simple angular asymmetries as a measure of CP-violating top dipole couplingsand simple angular asymmetries as a measure of CP-violating top dipole couplings

In the presence of an electric dipole coupling of $\overline {tt} $ to a photon, and an analogous ‘weak’ dipole coupling to the Z, CP violation in the process e⁺e^? → $\overline {tt} $ results in modified polarization of the top and the anti-top. This polarization can be analyzed by studying the angular distributions of decay charged leptons when the top or anti-top decays leptonically. Analytic expressions are presented for these distributions when eithert or $\overline t $ decays leptonically, including $\mathcal{O}$ (α_s) QCD corrections in the soft-gluon approximation. The angular distributions are insensitive to anomalous interactions in top decay. Two types of simple CP-violating polar-angle asymmetries and two azimuthal asymmetries, which do not need the full reconstruction of thet or $\overline t $ , are studied. Independent 90% CL limits that may be obtained on the real and imaginary parts of the electric and weak dipole couplings at a linear collider operating at √ s = 500 GeV with integrated luminosity 500 fb^? and also at √s = 1000 GeV with integrated luminosity 1000 fb^? have been evaluated. The effect of longitudinal electron and/or positron beam polarizations has been included.     

Dynamic generation of beating signals in an atomic system with a static magnetic field

In an \(F_{e}=0\,\leftrightarrow \,F_{g}=1\) transition, which interacting with a weak \(\pi \) -polarized probe field and a strong \(\sigma \) -polarized coupling field, we obtain the controlled beating signals depending on the applied magnetic field. In this configuration, we devise a procedure of light storage and retrieval where the magnetic field is switched off in the storage stage, but the magnetic field is switched on in the retrieval stage. Therefore, the beating signals is generated in the retrieval stage, which exhibits a series of maxima and minima in intensity. In addition, we can obtain two fast optical precursors and slow beating singals when the incident probe field is a squared pulse.     

Photon Asymmetries in {nd\rightarrow} 3 Hγ Using EFT({/\!\!\!\pi}) Approach

The parity-violating Lagrangian of the weak nucleon-nucleon (NN) interaction in the pionless effective field theory (EFT( \({/\!\!\!\pi}\) )) approach contains five independent unknown low-energy coupling constants (LECs). The photon asymmetry with respect to neutron polarization in \({np\rightarrow d\gamma A_\gamma^{np}}\) , the circular polarization of outgoing photon in \({np\rightarrow d\gamma P_\gamma^{np}}\) , the neutron spin rotation in hydrogen \({\frac{1}{\rho}\frac{d\phi^{np}}{dl}}\) , the neutron spin rotation in deuterium \({\frac{1}{\rho}\frac{d\phi^{nd}}{dl}}\) and the circular polarization of γ-emission in \({nd\rightarrow}\) ³ Hγ \({P^{nd}_\gamma}\) are the parity-violating observables which have been recently calculated in terms of parity-violating LECs in the EFT( \({/\!\!\!\pi}\) ) framework. We obtain the LECs by matching the parity-violating observables to the Desplanques, Donoghue, and Holstein (DDH) best value estimates. Then, we evaluate photon asymmetry with respect to the neutron polarization \({a^{nd}_\gamma}\) and the photon asymmetry in relation to deuteron polarization \({A^{nd}_\gamma}\) in \({nd\rightarrow}\) ³ Hγ process. We finally compare our EFT( \({/\!\!\!\pi}\) ) photon asymmetries results with the experimental values and the previous calculations based on the DDH model.     

Time reversal test in the nuclear muon capture

Possible effects of breaking CP-symmetry are looked for in the muon capture by a linearly polarized target nucleus. With this aim the recoil polarization in the partial transitions \(0\xrightarrow{{\mu ^ - }}I,1/2\xrightarrow{{\mu ^ - }}J\) and \(1\xrightarrow{{\mu ^ - }}I\) is investigated in a nuclear model independent way. It is shown that the hyperfine structure of the muonic atom significantly influences theT-odd correlations in the recoil polarization formula, and the expectation for theT- odd signal in case of the linearly polarized target is higher by one order of magnitude. We obtain the complete set of theT-odd observables which could enter the polarization formula. As an example, within the impulse approximation for the weak interaction hamiltonian, we analyse the nonstandard, CP-breaking extension of the Fermi theory using complex Fujii-Primakoff form factorG _V e^iφ .     

Static Magnetic Susceptibility of the Systems with Anisotropic Kondo Interaction

We theoretically investigated the static magnetic susceptibility in the heavy fermion compounds YbRh \(_2\) Si \(_2\) and YbIr \(_2\) Si \(_2\) . The molecular field approximation together with the renormalization of the Kondo interaction by the high-energy conduction electron excitations results in the Curie–Weiss law and Van Vleck susceptibility with temperature-dependent Curie and Weiss parameters.