bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of Hot Exciton Interaction in ZnTe Crystals
Authors: Baltramiejūnas R. , Stepankevičius V. , Tamulaitis G. , Žukauskas A.
Published: July 2007

Recombination‐induced heating of a gas of interacting excitons is investigated in ZnTe single crystals at a bath temperature of 80 K. The energy transfer in the system of self‐heated excitons and of nonequilibrium optical and acoustic phonons is considered. The density, the constant of bimolecular recombination, and the instantaneous lifetime of excitons in highly excited ZnTe crystal are found using the obtained experimental evidence of the effective temperature of excitons and the heat effect of the inelastic exciton–exciton collisions.
Optical Absorption and Stability of the Bipolaron Lattice
Authors: Puff H. , Streitwolf H. W.
Published: July 2007

The polaron lattice solution of the Brazovskii‐Kirova model is derived in the continuum approximation. The stability of the bipolaron lattice phase of this solution as well as the nature of the transition to the dimerized C‐phase are discussed. The optical conductivity is calculated for different excess electron densities and the optical sum rule is verified in each case. Finally a comparison with experimental results for polypyrrole, polythiophene, and its alkyl‐derivatives is made.
Sm3+ in ZnS on Lattice Sites and Wurtzite — Type Interstitial Sites?
Authors: Löbe K. , Boyn R.
Published: July 2007

The dye‐laser site‐selective excitation technique is used to investigate 4f–4f optical spectra of three Sm3+ centers in mixed‐polytype ZnS bulk crystals at 4.2 K. Measurements are made on crystals grown by the Bridgman method and by iodine transport, the latter containing Li as a codopant. One center (C), which obviously has cubic (Td) symmetry, is assigned, on the basis of a crystal‐field analysis, to Sm on (AN‐type) Zn sites. For the other two species (A and D), each of which is the dominant center in one of the two types of crystals, polarisation data indicate trigonal (C3V) symmetry, with symmetry axes parallel to [111]w. For these centers models are suggested involving “wurtzite‐type” interstitial site occupation, with local charge compensation by intrinsic defects and Li impurities, respectively.
Interplay between Superconductivity and Antiferromagnetism in the Triplet Local‐Electron‐Pair System
Authors: Li Yan‐Min , Zhang Li‐Yuan
Published: July 2007

The interplay between superconductivity and antiferromagnetism in the homogeneous triplet local‐electron‐pair system is investigated by using the self‐consistent broken‐symmetry Hartree approximation. A phase diagram of the antiferromagnetic, the superconducting, the mixed, and the nonordered phases is obtained from the calculation of free energies of these phases. It is found that there exists rather complicated competition and coexistence between superconductivity and antiferromagnetism in this system.
Magnetoresistance and Hall Effect in Bi2Te3〈Sn〉 in Ultrahigh Magnetic Fields and under Pressure
Authors: Kulbachinskii V. A. , Brandt N. B. , Cheremnykh P. A. , Azou S. A. , Horak J. , Lošták P.
Published: July 2007

The resistance and Hall effect are investigated in p‐Bi2Te3 and Bi2Te3〈Sn〉 with tin content x = 0.1 and 0.25 at% and hole concentrations p = (2 to 4) × 1018 cm−‐3 in the temperature range 0.5 K ≦ T ≦ 300 K, at stationary magnetic fields 0 ≦ B ≦ 22 T and under hydrostatic pressure 0 ≦ P ≦ 5.3 × 108 Pa. In the samples containing Sn the oscillations of resistance (Shubnikov‐de Haas effect (SdH)) show an anomalously high amplitude and the oscillations of Hall voltage show plateaus. In the ultrahigh region of magnetic fields the magnetoresistance and Hall resistance are practically constant. Under hydrostatic pressures P > 3 × 108 Pa all peculiarities of oscillations disappear. It is proposed that tin doping of Bi2Te3 leads to the appearance of an impurity band with high density of states not far from the maximum of the heavy hole band which stabilizes the Fermi level. Under hydrostatic pressure the light hole band rises relatively to the heavy hole band and carriers flow from the impurity band into the light hole band, which leads to the disappearance of peculiarities of oscillations in tin doped samples.
An Improved Mean Field Approximation
Authors: Ferreira J. R. Faleiro
Published: July 2007

An upper bound for the free energy may generate an approximation which preserves short order range effects even when a sum of single spins is used as the auxiliary Hamiltonian. Unlike the usual mean field approximation it may distinguish the cubic lattice from the planar triangular lattice. Its application to the Ising chain recovers some exact results.
Colour Centres in Alkali Metal Doped SrF2
Authors: Hamaïdia A.
Published: July 2007

Colour centres in SrF2:Na+ and SrF2:K+ are studied by optical spectroscopy, magnetic circular dichroism (MCD) and by EPR. It is shown that, in each of these two materials, there exist two kinds of FA centres, the weakly perturbed F and the more strongly perturbed F. The improperly named F2A centre is paramagnetic and its MCD has no similarity at all with the one of the F2 centre in SrF2. In SrF2:A+, non paramagnetic colour centres of the “F“ type are observed, as in CaF2:A+, but no defect corresponding to the f centre of CaF2:Na+. On the other hand, in SrF2:Na+ can be produced a centre which is called c', comparable to “F“, but with a spectral shift toward shorter wavelengths.
Optical Nonlinearity and Phase Coherence in CdSe and CdSexS1−x
Authors: Hvam J. M. , Dörnfeld C. , Schwab H.
Published: July 2007

The magnitude of the optical nonlinearity and its phase coherence are investigated at low temperatures in single crystals of CdSe and CdSexS1−x, using picosecond time resolved degenerate four‐wave mixing. In the pure compound semiconductors, the optical nonlinearity as well as the dephasing is governed by free exciton and biexciton interactions. In the mixed crystals, excitons localized by the alloy disorder play the dominant role, giving rise to larger nonlinearities and longer dephasing times than in the pure compounds.
Periodic and Stochastic Self‐Pulsations in the System of Coherent Excitons, Photons, and Biexcitons
Authors: Moskalenko S. A. , Rotaru A. H. , Zaloi V. A.
Published: July 2007

Possible appearance of quasiperiodic and chaotic self‐pulsations in a system of coherent excitons and photons as well as in the processes of one‐ and two‐photon exciton–biexciton conversions are established for the first time. In the last two cases the generalized Lorenz equations are obtained. Lyapunov analysis of the stationary state stability and computer experiments are made. The main bifurcations in the three considered systems of quasiparticles are found.
Femtosecond Studies of Room Temperature Optical Nonlinearities in Wide‐Gap II–VI Compounds
Authors: Puls J. , Rudolph W. , Henneberger F. , Lab D.
Published: July 2007

Fs‐excite‐and‐probe measurements are made on wide‐gap II–VI compounds at room temperature. A variety of nonlinear processes are observed and their ultrafast transients are studied. The results emphasize the use of these materials for fs optical switching.
Optical Stark Effect in an Exciton–Phonon System
Authors: Higashimura T. , Iida T. , Komatsu T.
Published: July 2007

A theoretical study is made of the optical Stark effect in an exciton‐phonon system in which the Fano effect takes place due to the interference between two exciton bands through the exciton‐LO‐phonon interaction. Formal expressions of spectra are derived for the absorption and the time‐resolved resonant secondary emission of probe light, using the resolvent method. The spectral change of absorption induced by the optical Stark effect corresponds to Im (χ(3)). Carrying out numerical computations for a model system, it is demonstrated what spectral structures and temporal behaviors are expected to be observed when there coexist the optical Stark effect and the Fano effect.
The Exciton Reflection Shifting and Modification in Presence of Intensive Polariton Wave Interacting with LO‐Phonons in Polar Semiconductors
Authors: Ivanov A. L. , Vygovskii G. S.
Published: July 2007

A set of macroscopic phonoriton equations describing exciton, photon, and LO‐phonon spectra renormalization in presence of intensive polariton wave is analyzed. New specific additional boundary conditions are introduced and corresponding exciton reflection spectra are calculated for the problem of probe wave reflection at the crystal boundary. The appearance of the new phonoriton spike and the exciton line shifting in reflection spectra are determined by the intensity of the pumping wave.
Remarks on Optical Nonlinearity and Bistability in Composite Media
Authors: Jungk G.
Published: July 2007

Necessary conditions for intrinsic (without external feedback) bistability are discussed for the field‐intensity dependent dielectric function within the most simple homogeneous model. Some of the restrictions imposed in this way can be relaxed in composite media by local‐field corrections. The results are illustrated with stationary bistable reflectivities and transmissivities as function of the impinging light intensity.
Resonatorless Dissipative Optical Bistability of Electronic Origin in Direct‐Gap Semiconductors
Authors: Kochelap V. A. , Kuznetsov A. V. , Sokolov V. N.
Published: July 2007

The results of numerical calculations of the band edge absorption dependence on photoexcitation density for hexagonal CdS, CdSe, and cubic ZnSe are presented. The calculations are based on the recent plasma screening theory of Banyai and Koch modified to take into account the band structure and anisotropy of these materials. At low temperatures the resonatorless optical bistability is predicted for all three materials provided their quality is high enough. It is shown that the proper material and parameter choice apparently may lower the corresponding intensities down to kW/cm2 range.
Spatial Resolution of Dynamic Thermo‐Optical Hysteresis in CdS
Authors: Nguyen H. X. , Egorov V. D.
Published: July 2007

Transverse effects in the thermo‐optical switching processes in CdS crystals a t room and liquid N2 temperature are investigated experimentally by recording the time–space distribution of the transmitted laser beam. Numerical solving the nonstationary two‐dimensional heat transport equation confirms the formation of a ring structure in the transmitted beam profile due to the induced absorption mechanism of the switching at room temperature. For the interpretation of the experimental findings at 77 K, probably dispersive effects must be taken into account as well.
New Mechanism of Intrinsic Bistability of Nonlinear Slugged Structures under the Action of Repetitive Pulse Excitation
Authors: Gainer A. V. , Surdutovich G. I.
Published: July 2007

A new type of the cavityless bistability is proposed where the nonlinear medium does not show intrinsic bistability under action of a continuous input signal but shows bistability under action of a time‐dependent input signal. A strict criterion for the observation of such a bistability is given. It depends on the shape of the temporal response of the nonlinear medium under action of the isolated rectangular input pulse.
Effects of Spatial Distributivity in Semiconductor Optical Bistable Systems
Authors: Rosanov N. N. , Fedorov A. V. , Khodova G. V.
Published: July 2007

Results are presented of a theoretical analysis of transverse and longitudinal distributivity effects in semiconductor optical bistable systems. For a resonatorless increasing absorption bistable system the kinetics of autopulsations (resulting from the formation of moving absorption domains) are described. For wideaperture nonlinear interferometers new types of field spatial structures are shown: immovable and moving autosolitons, waves of automodulation and autostochasticity, and pulsing distributions.
Exciton–Phonon Mechanism of Optical Bistability
Authors: Nitsovich B. M. , Krechivskii O. V. , Pestryakov G. M.
Published: July 2007

A joint effect of exciton–phonon and exciton–exciton interactions on optical properties of semiconductors is studied. In these substances the exciton density is shown to be a multivalued function of incident light intensity and the frequency and temperature conditions under which the optical bistability arises are specified. Investigation of nonlinear optical properties of semiconductors with account for the indirect phototransitions exhibits that both multistable optical states and the bistable ones distinguished by a complicated dynamics of the switching may be observed in such systems.
Analysis of Absorptive Bistability in a Two‐Section Semiconductor Injection Laser
Authors: Šrobár F.
Published: July 2007

The phenomenon of absorptive bistability in a two‐section injection laser is analysed employing the method of causal diagrams. Steady‐state rate equations for electrons in the gain (n1) and in the saturable absorber (n2) sections and for photons (np) can be represented by diagrams containing feedback loop attached to vertex np and encompassing vertex n2. Numerical analysis of typical cases confirms the crucial role played by the feedback relationships in producing the bistable regime.
Optoelectronic Bistability with Internal Feedback in Cadmium Sulfide
Authors: Bogdanov S. V. , Lyssenko V. G.
Published: July 2007

Optoelectronic bistability with internal feedback in CdS is studied in the presence of an electric field. Feedback results from heating of the crystal by exciton impact ionization current and absorption induced by an electric field.
On the Possibility of the Optical Connection between SEED'S within One Array
Authors: Butusov D. M. , Gotsadze G. G. , Larionov V. R. , Ryvkin B. S.
Published: July 2007

The principle of optical waveguide connection among the semiconductor switching elements SEED integrated within two‐dimensional array is proposed. The first preliminary experimental results are given that confirm the realisation possibility of such a connection.
Quasisoliton Mechanism of Generation of Bistable Injection Laser with External Cavity
Authors: Velichanskii V. L. , Gainer A. V. , Saptsov V. I. , Sautenkov V. A. , Seregin V. F. , Solodkov V. F. , Surdutovich G. I.
Published: July 2007

In an arbitrary distributed bistable system – passive or active – the existence of quasirectangular pulse (dip) with a duration less than the by‐pass time of the resonator is predicted. Such a quasisoliton regime is realized experimentally in the system with bicompound injection laser and external cavity.
Photoinduced Charge Dynamics in Photorefractive Semiconductors
Authors: Astratov V. N. , Ilinskii A. V. , Furman A. S.
Published: July 2007

Photoinduced charge dynamics in photorefractive semiconductors is studied from both, theoretical and experimental points of view in the case of an external field screening. This dynamics shows two different regimes depending on the parameter τM/τi where τM is the Maxwellian time and τi is the impurity ionization time. For τM ≪τi, the stratification effect arises and numerous space charge layers of alternating sign occur in the crystal. Another regime occurs for τi ≪ τM, the broadening of the single layer leads to the screening. In BSO, the first regime takes place for room crystal temperatures T, and the second one for 130 K < T < 200 K. Such charge dynamics determines optical nonlinearity of photorefractive semiconductors.
Coherent Second‐Order Photoinduced Effects in Noncentrosymmetric Semiconductors
Authors: Pishchev A. , Kristoffel N.
Published: July 2007

Within the frames of a modified version of the Kubo scheme a consistent calculation of the coherent stationary second‐order optical responses along current, polarization, and orbital magnetization is carried out.
The Optical Bistability in the Active and Absorptive Tandem Semiconductor Lasers
Authors: Zhang Xiaobo , Flint I.
Published: July 2007

Experimental results and a theoretical analysis are given of the active and absorptive ridge waveguide tandem semiconductor lasers. It is found that the relative hysteresis width in the optical output of the laser depends on the parameters of the laser structure such as the relative length of the two regions and also the pumping levels. Especially, a small extraction current from the passive part causes the enhancement of the bistability. Both, the experimental and theoretical results suggest that there is an optimum selection of the relative length of the two regions and of the current level applied on the passive region, if a maximum hysteresis is required.
Nonlinear Optics of Semiconductor‐Doped Glasses
Authors: Ekimov A. I. , Efros A. L.
Published: July 2007

Nonlinear optical properties of semiconductor‐doped glasses are reviewed. A growth technique enabling to obtain semiconductor microcrystals with controlled sizes grown in a glassy matrix is described. It is shown that the optical properties of such systems are determined by the energy spectrum of the electron–hole pairs confined in the small‐size microcrystals. The dependences of these spectra on the microcrystal size are analysed. The effect of the blue‐shift of the spectra occurring at high excitation levels is discussed. At excitation with light of photon energy below the energy gap of the glass photoionization is discovered. In this process the electron is ejected from the microcrystal to the glass where it is captured by the long‐lived centers. The latter process is likely to explain the effect of the glass darkening and the formation of permanent volume grating.
Large Optical Nonlinearity of the Two‐Dimensional Exciton States at a Stacking Fault Interface in BiI3
Authors: Iakai I. , Karasawa T. , Komatsu T. , Kaifu Y.
Published: July 2007

The optical Stark effect of an exciton system localized at a stacking fault (stacking fault excitons, SFE) in BiI3 crystals is presented. The SFE states show three very sharp absorption lines called R, S, and T. The excitation laser frequency dependence of the peak shift of the absorption line T is observed in a wide frequency range covering the three SFE states. The peak shift can be seen even for far off‐resonance excitation, and shows drastic change for the on‐resonance excitation of R, S, and T states. This behaviour can be explained by a “dressed exciton” model. The excitation intensity dependence of the peak shift manifests a very large nonlinear optical polarizability of the SFE system.
Optical Nonlinearity of Semiconductor Microcrystals CdSxSe1−x under the Action of Picosecond and Nanosecond Laser Pulses
Authors: Gribkovskii V. P. , Zyulkov V. A. , Kazachenko A. E. , Tikhomirov S. A.
Published: July 2007

Size effects in microcrystal luminescence relaxation are observed. A change in the character of bleaching in glasses at excitation of carriers with energy higher by 0.2 to 0.5 eV than the absorption edge is detected. Transient bleaching spectra are measured and mechanisms of nonlinearity are elucidated.
Optical Investigation of Exciton Screening in GaAs/GaAlAs MQW Structures
Authors: Lach E. , Walther M. , Träkle G. , Forchel A. , Weimann G.
Published: July 2007

In transmission experiments performed under quasi‐equilibrium conditions the bleaching of the quasi‐2D excitons in GaAs/GaAlAs MQW structures is studied with special emphasis on the behavior of the excitons at different subband edges. The 11h‐excitons are found to be much more sensitive to bleaching than the higher excitons. This is attributed to phase space filling effects which reduce the oscillator strength of the 11h‐excitons additionally to the usual screening due to longrange Coulomb interaction.
Dynamics of Incoherent Excitonic Optical Nonlinearities in GaAs–GaAlAs MQWS's
Authors: Henneberger K. , Manzke G.
Published: July 2007

The dynamics of optical nonlinearities connected with the blue‐shift of the exciton line in resonantly excited GaAs–GaAlAs MQWS's is investigated theoretically simulating a two‐beam experiment. Jumps in the optical spectra of a weak test pulse (optical switching), which follows the intense pump pulse at different time delays, are observed, basing on a strong increase of the absorption. A similar mechanism of the bistability is observed in connection with the electro‐absorptive effect.
Time‐Resolved Photoluminescence of a GaAs/GaAlAs Superlattice
Authors: Weinert H. , Latinis V. , Juršenas S. , Baltramiejunas R.
Published: July 2007

The photoluminescence of a GaAs/GaAlAs superlattice at TL = 4.2 K is investigated at different excitation intensities with ps time resolution. The observed complicated time behaviour of the excitonic luminescence depends sensitively on excitation intensity. For a qualitative explanation of the experimental results different screening mechanisms and a time‐delayed capture of carriers into the quantum wells should be taken into account.
Optical Nonlinearity and Fast Switching in PbSnTe Fabry‐Perot Etalon
Authors: Paskov P. P. , Pavlov L. I. , Atanasov P. A. , Kushev D. B. , Zheleva N. N.
Published: July 2007

Optical bistability is observed in a PbSnTe etalon at room temperature by two‐photon exitation with tunable TEA CO2 laser. The experimental results are compared with a numerical model which also takes into account the heating of the sample.
Mechanism of Optical Nonlinearity in CdS Due to Increasing Absorption at Room Temperature
Authors: Yang F. , Xiong G. , Xu X.
Published: July 2007

Transmission and luminescence properties of CdS around the fundamental absorption edge at room temperature are investigated. Experimental results suggest that increasing absorption non‐linearity is related to two mechanisms. One is ascribed to the absorption red shift of exciton–electron (ex–el) scattering with increasing input laser intensity. A qualitative analysis and discussion about the nonlinearity due to ex–el scattering are given. The other is lattice heating of samples with cw laser illumination. The optical bistability due to thermal effect is observed.
Nonlinear Effects in the Emission Spectra of High Density Excitons in CdS Crystals
Authors: Nelson D. K. , Klochikhin A. A. , Mikhailov G. V. , Panfilov A. G. , Razbirin B. S.
Published: July 2007

Investigations of exciton ground state fine structure and exciton–phonon emission of CdS are carried out at e–h concentrations below or close to the Mott threshold. A considerable (about 0.5 meV) shift of the longitudinal exciton emission line AL towards the low energy is discovered when the excitation intensity increases up to 100 kW/cm2. This shift is accounted for by the reduction of the excitonic oscillator strength produced by screening effect. An enormous growth of the integral intensity of A‐LO luminescence band is observed with increasing excitation power. Possible reasons of the A‐LO band enhancement are considered.
Nonlinear Optical Effects in Amorphous Semiconductors
Authors: Jánossy I.
Published: July 2007

In amorphous semiconductors electronic optical nonlinearities are used as a spectroscopic tool rather than a non‐linear effect. On the other hand light‐induced rearrangement of certain atomic positions, a unique process occuring only in the amorphous state, has a strong effect on the optical properties. Such “photostructural changes” are reversible in bulk samples or well‐annealed films. This fact makes possible to switch the irradiated spot between two states by using light signals of different amplitudes, wavelengths or polarizations. The possibility of using these effects as a part of optical circuits is pointed out.
Optical Response of Nonlinear Absorbing and Saturable Multilayer Systems
Authors: Trutschel U. , Lederer F. , Langbein U.
Published: July 2007

Oblique‐incidence transmissivity and reflectivity of a multilayer system consisting of N unit cells is investigated. Each unit cell is formed of two absorbing, saturable nonlinear films. In detail the optical response of a multilayer system in investigated, illuminated by a plane wave close to the edge of the stop gap, in dependence on the input flux. It is shown that the combined effects of linear/nonlinear absorption and saturation will considerably affect bistable switching from the low‐transmission to the high‐transmission state. Eventually just this switching can disappear.
Nonlinear Optical Behaviour of Absorbing CdSxSe1−x Interference Filters
Authors: Ferencz K. , Szipöcs R.
Published: July 2007

First experimental results of nonlinear, thin film interference filter wedges with mixed CdSxSe1−x as spacer material at the 633 nm wavelength of He–Ne laser are reported. Optical bistability is observed with less than 7.5 mW of optical power in single‐cavity structures. The change in refractive index is found to be positive which is in accordance with the thermal mechanism of nonlinearity. Producing a double‐cavity structure a device is obtained which works as an optical astable multivibrator having periodical change of transmission as the function of time.
Nonlinear Optical Properties of CdS and Optical Bistability
Authors: Dneprovskii V. S. , Furtichev A. I. , Klimov V. I. , Li Shen , Nazvanova E. V. , Okorokov D. K. , Vandishev U. V.
Published: July 2007

Fast and slow types of nonlinear absorption and resonatorless optical bistability of electronic and thermal origin is observed.
Exciton Nonequilibrium Steady States in Laser‐Excited Molecular Crystals
Authors: An Nguyen Ba
Published: July 2007

Nonequilibrium steady states of excitons in laser‐excited three‐dimensional molecular crystals are investigated not resorting to the usual boson description but using the exact trilinear commutation relations for exciton operators. The nonequilibrium property, non‐bosonity, and optical nonlinearity of the many‐exciton system under the action of an external classical laser field are considered on the same footing. Eigenfrequencies and dampings of the giant polariton are found to be dependent on the excitation degree. Conditions are determined for two types of bistability: density–light and light–light bistability.
Nonlinear Phenomena in Single‐Mode Optical Fibers
Authors: Tomlinson W. J.
Published: July 2007

The low losses of optical fibers made of silica glasses make it possible to study, and use, nonlinear optical phenomena at lower optical power levels than are required for most other materials, despite their very small nonlinearities. Some of the more important and/or interesting nonlinear phenomena observed in single‐mode optical fibers are reviewed, including pulse compression, bright soliton propagation, ultrafast all‐optical switching, and new results on dark soliton propagation.
Optical Bistability in Two‐Dimensional Waveguide Structures
Authors: Trutschel U. , Golz M. , Abraham M.
Published: July 2007

A device with optical bistability is proposed well adapted to planar technology in the framework of integrated optics. The device is composed by a dielectric layer of Al2O3 deposited onto an InSb waveguide with defocussing Kerr‐nonlinearity and a metal substrate. It works at the wavelength of 10.6 μm, where the refractive index of Al2O3 is lower than in air and coupling into a waveguide‐mode without prism is possible. The reflectivity in dependence on the input power density is investigated. The shape of the resonance curve can be tuned by the angle of incidence. This should permit the implementation of a modulator, latching switch, logic gate, and power limiter within a fixed configuration.
Experimental Investigations of Optical Nonlinearities in Semiconductor‐Doped Glass Waveguides
Authors: Dannberg P. , Possner T. , Bräuer A. , Bartuch U.
Published: July 2007

Both, thermal and electronic optical nonlinearities are studied in semiconductor‐doped glass (SDG) waveguides which are fabricated in commercially available sharp‐cut filters by Cs+–K+ ion exchange. The relaxation time in photodarkened substrates is measured to be 30 ps. By means of a prism coupling set‐up the saturation value of the nonlinear index change is determined. Furthermore, a high stability dual‐beam interferometer is presented for the measurement of both, thermal and electronic nonlinear refractive index n2 in planar waveguides. Conclusions about the application of SDG to opto‐optical switching are given.
Investigation of the Field‐Dependent Carrier Mobility in GaAs by Picosecond Photoconductivity Measurements
Authors: Bergner H. , Brückner V. , Lenzner M. , Strobel R.
Published: July 2007

The carrier velocity is measured in Cr‐compensated GaAs in dependence on the applied field strength by picosecond photoconductivity measurements. Two different behaviours are obtained in dependence on the excitation energy. In the case of low excitation a region of negative differential conductivity due to the electron transfer from L‐valley into the L‐valley exists. In the case of high excitation the formation of charge domains lowers the mobility.
Picosecond Holographic Diagnostic of Light Pulse Absorption in Semiconductors
Authors: Bugaev A. A. , Zakharchenya B. P.
Published: July 2007

The results of using picosecond holographic interferometry in traditional excite‐and‐probe technique for the study of light pulse absorption in semiconductors are presented. The method allows to record the two‐dimensional distribution of transient light‐induced refractive index in a volume of the semiconductors which corresponds to the known time‐delay between exciting and probing pulses. The distribution obtained is compared with calculations based on Drude's relation and the solution of the system of equations describes the process of single (Si)‐ or two‐photon (GaAs) light pulse absorption. As a result it is possible to determine either some nonlinear parameters of semiconductor or parameters of the exciting pulse.
Picosecond Optical Nonlinearities and Stimulated Emission in Indirect AlxGa1−xAs
Authors: Kalt H. , Smirl A. L. , Boggess T. F.
Published: July 2007

The nonlinear optical properties of indirect‐gap AlxGa1−xAs in the presence of a dense electron‐hole plasma are studied by picosecond luminescence and transient transmission spectroscopy. The fundamental X‐band gap is found to be renormalized by exchange and correlation effects within the plasma. Higher‐lying band gaps in the same sample are also renormalized but here the electron‐exchange contribution to the narrowing is negligible. Strong plasma‐induced nonlinearities like persistent bleaching of absorption, enhanced absorption, and large changes of the refractive index are observed at the direct absorption edge for lattice temperatures of 15 as well as 293 K. Stimulated emission from the indirect X‐band is made possible by alloy‐disorder induced band mixing.
Light‐Induced Thermal Gratings in Natural Diamond
Authors: Gorbachev V. V. , Durasov V. M. , Zezin R. B. , Ivakin E. V. , Rubanov A. S. , Tatyanina N. A.
Published: July 2007

For the first time thermal dynamic gratings in Ia‐type diamond are recorded. Thermal diffusivity of eight samples is measured by diffraction of a cw laser beam from light‐induced spatially periodic temperature distributions. The connection between absorption of the 8.5 μm, wavelength and the thermal resistance of the crystals is demonstrated. No strict correlation is observed due to the influence of defects on the heat transfer in diamond which do not appear in the IR spectrum.
Possible Anomalies in Multicomponent Diffusion
Authors: Kvasnica J.
Published: July 2007

The evolution of concentrations in multicomponent diffusion depends on a characteristic parameter Δ constructed in terms of the diffusion coefficients Dik. For ternary diffusion Δ = (D22  D11)2 + + 4D12D21 where D12D21 can have both signs. In the case Δ > 0 one gets the normal monotonous evolution of concentrations, Δ < 0 leads to damped oscillations, at Δ = 0 there appear maxima and minima of concentrations for some values x2/t.
Suzuki Phase Precipitates in Doubly Doped KCI: Pb2+, Mn2+ Crystals
Authors: Cywiński R. , Mugeński E. , Nowy‐Wiechula W. , Wiechula J.
Published: July 2007

KCl crystals doubly doped with Pb2+ and Mn2+ ions are examined by EPR and optical (emission and absorption spectra) methods. The presence of a Pb2+ rich phase containing Mn2+ ions in a cubic crystal field is ascertained. According to the results obtained one should expect the existence of trace amounts of the Suzuki phase (6 KCl · PbCl2 doped with Mn2+ ions) distributed in a quasilinear form along dislocations or (and) grain boundaries present in the matrix.
Dynamic Structure Factor of a Slowly Moving Soliton in a Thermal Bath
Authors: Dzyub I. P. , Zerov Yu. E.
Published: July 2007

The quasielastic and inelastic scattering functions of neutrons which interact with local and extended vibrations around kink‐like lattice displacement are examined within the φ4‐theory. The polaronic renormalization of the kink mass and explicit expressions for the scattering functions are obtained.
On the Ideal Strength of Crystals
Authors: Pokluda J. , Šandera P.
Published: July 2007

A simplified model of f.c.c., b.c.c., and diamond crystalline structures is used to obtain a dependence of the ideal cohesive strength on some easily measurable quantities. The proposed conception is physically more justified as the well known Kelly‐Orowan approach. On the basis of the relationship between cohesive energy, bulk elasticity modulus, and atomic concentration, a very simple expression for the approximative determination of the ideal strength can be found.
Two‐Component Solitary Excitations in Molecular‐Bonded Chains
Authors: Ichinose S.
Published: July 2007

Two‐component solitary excitations are studied analytically in the continuum version of the Takeno model for molecular‐bonded chains. The vibronic structure of the model system is exactly calculated in the presence of the inhomogeneity in the distortion pattern of a chain. The small oscillations around a static soliton are considered as the eigenvalue problem for linear modes.
Coordination Symmetry and Energy Spectrum Analysis of Fe2+ in ZnS: Fe2+ Crystals
Authors: Zhao Sang‐Bo , Wang Hui‐Su , Xie Jun‐Kai
Published: July 2007

The Td symmetry complex model suggested by previous works is unable to give an unified theoretical analysis of the abundant absorption bands of Fe2+ ions mixed into ZnS. Many bands cannot be assigned by this model. As an improvement, a C2v model is used in the present paper by which, after considering the spin‐orbit coupling and the vibronic coupling, all of the bands (about 80) obtain a unified theoretical explanation; and also the shift direction of Fe2+ due to the crystal site distortion is determined. In the calculation a simplified strong field scheme including spin‐orbit coupling is applied to establish the complete C(d6) strong field matrices. All the related crystal field parameters are determined by the observed spin‐allowed bands. Thus the difficulty in low symmetry problems caused by the large number of parameters to be determined is removed and the prediction ability of the theory is well improved.
Plasma Excitation in Semiconductors Containing Extended Scattering Centers
Authors: Gerlach E. , Kistinger S.
Published: July 2007

Dynamical carrier scattering caused by extended crystal perturbations (models for clusters, doping inhomogeneities, precipitations etc.) is studied using the “energy‐loss method”. Based on Mermin's dielectric function multiple scattering is selfconsistently taken into account. Since extended perturbations are mainly described by small wavevectors, plasmon excitation by scattering strongly exceeds single particle excitation. It is conceivable to utilize the dominant plasma‐peak to characterize perturbations in semiconductor crystals.
Interpretation of 57Fe Mössbauer Measurements on Nd2Fe14B at 83 and 295 K
Authors: Shi Yan , Jin Hanmin , Jin Mingzhi
Published: July 2007

The 57Fe Mössbauer spectrum of the Nd2Fe14B compound at 83 K is analyzed with eighteen Zeeman sextuplets by taking into account of the splittings of the six Fe sites (Fec, Fec, Fej1, Fej2, Fek1, and Fek2) into 2, 2, 3, 3, 4, and 4 magnetically inequivalent sub‐sites. The spectrum at 295 K is analyzed with six Zeeman sextuplets. The electric quadrupole splittings at each Fe site are calculated on the basis of a point charge model with different electric charges for Fe and B. When the charges of Nd, Fe, and B are 3e, 2e and zero (e > 0), the calculated results coincide with those obtained by fitting the Mössbauer spectra measured at 83 and 295 K.
Magnetic and Mössbauer Studies of Anion‐Substituted Nickel Ferrites
Authors: Bayukov O. A. , Ikonnikov V. P. , Savitskii A. F.
Published: July 2007

The measurements of the sublattice magnetizations in the spinels NiFe2O4−xSx are reported. Using the superexchange model the 3d‐electron transfer parameters of ligand‐cation and the integrals of cation‐cation exchange interactions are determined.
Luminescence Properties of {(CH3)4N}2ZnCl4 Single Crystals
Authors: Martín A. , López F. J. , Arend H.
Published: July 2007

Results on the X‐ray induced luminescence (RL), after‐glow (AG), and thermoluminescence (TL) spectra in the range 10 to 300 K of {(CH3)4N}2ZnCl4 single crystals are presented and compared with previous results for Rb2ZnCl4 and K2ZnCl4. The emissions for the three cases are proposed to be associated to intrinsic electron‐hole recombination processes.
Raman Scattering in Ferroelectric TlGaSe2. Soft Mode and Order Parameter
Authors: Burlakov V. M. , Yakheev M. R.
Published: July 2007

The Raman scattering spectra of soft and rigid modes in TlGaSe2 are investigated over a wide temperature range. The interaction between soft and rigid modes is observed from the description of the experimental spectrum within a model of interacting harmonic oscillators. Temperature dependences of the soft mode frequency and halfwidth are confirmed. The splitting of the rigid Raman mode in the ferroelectric phase is also detected.
Resonant Raman Scattering near E1 + Δ1 in CdxHg1−xSe
Authors: Kumazaki K.
Published: July 2007

Raman scattering by phonons is measured in CdxHg1−xSe with x = 0 to 0.3 on (100), (110) and (111) surfaces near the E1 + Δ1 energy gap at room temperature. From these measurements, the composition dependence of the HgSe‐like TO and LO mode frequencies is obtained. The plasmon‐LO phonon coupled modes and a cluster mode are also observed. Effective high‐frequency dielectric constants calculated by the extended Lyddane‐Sachs‐Teller relation show a discontinuity near the semimetal‐semiconductor transition point. This discontinuity is attributed to the contribution of interband terms to the dielectric function. The results obtained from the Raman measurements are compared with those from far‐infrared measurements.
Generalized Transfer‐Matrix Description of the Optical Properties of Spatially Dispersive Periodic Metal Multilayers
Authors: Trutschel U. , Golz M. , Abraham M.
Published: July 2007

A transfer matrix formalism is used to treat in a general way the optical response of different kind of metal superlattices. The dispersion relation of infinite and semi‐infinite superlattices and the reflectivity of semiinfinite superlattices are calculated. Spatial dispersion is included via additional boundary conditions. Each unit cell of the superlattices can be built up by an arbitrary number of layers with local and/or nonlocal dielectric functions. In the case of a spatially dispersive double layer unit cell the explicit dispersion relation is derived. The limits when one of the layers is local as well as the complete local case are shown to be included.
Effect of Pressure on Lattice Parameters of Intercalation Compounds MxTiS2 (M = Fe and Ni)
Authors: Negishi H. , Ōhara S. , Inoue M.
Published: July 2007

Lattice parameters a and c of 1T‐CdI2 type layered TiS2 crystals and its intercalation compounds MxTiS2 (M = Fe and Ni; x = 0.05 and 1/4) are measured under hydrostatic pressures up to 1.2 GPa at room temperature. Both, a and c, of these crystals are decreased linearly with pressure, and their linear elastic moduli are strongly dependent on the guest concentration x. The effect of 3d metal intercalation on the structural properties is qualitatively discussed.
Laser‐Induced F‐F− Conversions in KCl Crystals
Authors: Subrahmanyam R. , Murti Y. V. G. S.
Published: July 2007

F centers in KCl crystals are converted to F− centers by bleaching with radiation from a low power HeNe laser. Growth curves of these centers are constructed by monitoring the optical absorption at 720 nm at several temperatures. The growth curves are analyzed and the thermal ionization energy of the F− center is deduced. The results are discussed in terms of the kinetics of the processes.
Dynamic Effects in a New Substitutional Center of Trivalent Iron in Quartz
Authors: Stegger P. , Lehmann G.
Published: July 2007

After exchange of Li against Na in a natural quartz of high quality by electrolysis at higher temperatures a new center of Fe3+ with monoclinic site symmetry at room temperature is detected by electron paramagnetic resonance (EPR). At temperatures below 200 K the linewidths of the EPR spectra increase considerably, and at about 60 K a signal of a triclinic center with a well‐resolved quartet hyperfine splitting appears instead. Thus the charge‐compensating Na ion evidently changes rapidly between two equivalent positions at higher temperatures. An estimate of the activation energy for this hopping process is obtained from the temperature dependence of the linewidths for the monoclinic spectrum.
Exciton‐Grating Induced Light Mixing at the Giant Two‐Photon Resonances of Excitonic Molecules in CuBr
Authors: Mizutani G. , Nagasawa N.
Published: July 2007

It is shown that in CuBr crystals a coherent scattering process where the exciton population grating and the excitonic molecule are involved is present, from the experiment of a three beam non‐degenerate optical mixing. This process cannot be described by the 3rd order optical nonlinearity but at least a 5th order non‐linearity is necessary.
Electronic Absorption Spectrum of Ni2+ Ions Doped in Zinc Thallium Sulphate Hexahydrate
Authors: Rao J. L. , Reddy M. R. , Lakshman S. V. J.
Published: July 2007

Optical absorption spectra of Ni2+ ions doped in zinc thallium sulphate hexahydrate (ZT1SH) are studied at room and liquid nitrogen temperatures. The spectrum shows characteristic features of Ni2+ ions in octahedral crystalline fields. At liquid nitrogen temperature, one of the bands exhibits splitting. The fine splitting is interpreted as due to spin‐orbit interaction. From a detailed analysis of the bands of the spectrum, the crystal field parameters B, C, Dq, and ξ are evaluated.
On the Binding Energies of D− States in Doped Germanium. Effects of Valley‐Orbit Corrections and Compressive Uniaxial Stress
Authors: Weber G. , Oliveira L. E.
Published: July 2007

The effects of compressive uniaxial stress along the [111] direction and of valley‐orbit corrections on the binding energies of D− states in Sb‐ and P‐doped germanium are calculated. A variational procedure is used with a Chandrasekhar‐type of variational wave function. The model Hamiltonian takes into account electron‐electron interaction, valley‐orbit corrections, and stress effects. The results show similar behavior as in previous work on doped silicon and quantitatively agree with available long‐wavelength photoconductivity measurements for doped germanium.
The Local Electron‐Spin‐Density Fluctuation Mechanism of the Superconductivity in Narrow‐Band Metals
Authors: Grebennikov V. I. , Sokolov O. B.
Published: July 2007

A novel mechanism is proposed of electron pairing due to local electron‐spin‐density fluctuations in copper oxide superconductors. Self‐consistent equations are formulated. Their input data are the density of states curve and the intra‐atomic electron repulsion parameter. The pairing interaction has a peak at small energy transfers. The superconductivity region is limited both, from below and from above the initial‐repulsion values. The gap width to critical temperature Tc ratio is large; Tc is higher than its value in the phonon mechanism.
Nonthermal Spread of Quantum Levels in Solids Due to Defects
Authors: Dmitriev A. I. , Lashkarev G. V.
Published: July 2007

The quantum level spread is treated in terms of the Dingle temperature, TD. The universal nature of the nonthermal spreading of the Landau levels in solids is established and explained. The importance of the low‐angle scattering of current carriers for the quantum oscillation effects is shown. The effect of the random electrostatic potential fluctuations on the magnitude of the quantum level spread is studied in detail. Experimental data are compared with theory for a wide range of compositions, x, and carrier concentrations, N, in Pb1−xSnxTe alloys.
Mössbauer Radiation Transfer in a Plane Layer. Anisotropic Case
Authors: Gabrielyan R. G. , Kotandjian Kh. V.
Published: July 2007

Traditionally only single resonance scattering is taken into account in the Mössbauer spectroscopy for scattering. In the present paper as in previous papers a more precise theory is developed taking into account multiple scattering of the Mössbauer radiation transfer using the theory of the optical radiation transfer. The frequency‐modulated γ‐radiation scattering in a plane parallel layer is also considered.
A New Type of Bond‐Dilution Problem in a Ferromagnetic Insulator with a Fractional Random Coordination Number
Authors: Sarmento E. F. , da Cruz H. R. , Kaneyoshi T.
Published: July 2007

The ferromagnetic phase stability limits (or phase diagrams) of a quenched bond‐diluted spin‐ ½ transverse Ising ferromagnetic insulator with a fractional random coordination number are studied within the framework of the effective‐field theory with correlations. The changes of transition temperature and critical concentration with the topology of the network (or the averaged connectivity) are examined in the zero transverse field. The results obtained are compared with those available in the literature. The influences of transverse field on the critical frontiers are also obtained.
Approximate Solution for a Two‐Dimensional Anisotropic Ferromagnetic Spin Lattice with Bloch Wall and Bloch Line. I. Analytic Computation
Authors: Knoop U. , Heber G.
Published: July 2007

For a two‐dimensional spin lattice with exchange and local anisotropy nonlinear equations are deduced. Under the condition that the spin lattice contains a Bloch wall and a Bloch line, approximate solutions are derived in the classical continuum approximation.
Temperature Dependent Frequency Shifts in the Resonance Absorption and Resonance Fluorescence Scattering of Mössbauer γ‐Quanta
Authors: Follath R. , Jex H.
Published: July 2007

The relativistic Doppler effect in the resonance absorption and resonance fluorescence scattering of Mössbauer γ‐quanta of a 57Co source is investigated in the temperature range 295 K ≦ T ≦ ≦ 585 K. The temperature shift of the resonance is d(ln ω)/dT = − (2.38 ± 0.07) × 10−15 K−1 in absorption and − (2.67 ± 0.10) × 10−15 K−1 in backscattering. The data are compared with Bragg scattered Mössbauer γ‐quanta from the (200) reflection of NaCl in the same temperature range. A limit d(ln ω)/dT ≦ 7.5 × 10−17 K−1 is obtained.
Effect of High Pressure on the Optical Transmission Spectra of AIIIBIIIC Crystals
Authors: Prins A. D. , Allakhverdiev K. R. , Babaev S. S. , Guseinov S. S. , Mekhtiev E. I. , Shirinov M. M. , Tagyev M. M. , Dunstan D. J.
Published: July 2007

The influence of high pressure up to 13 GPa on the optical transmission spectra of layered AIIIBIIIC crystals was investigated. The value of the pressure coefficient of the transmission spectra at 30% transmission is reported. Results indicate that these materials undergo a series of phase transitions in the region investigated.
The conversion of electronic centres into U and OH‐ centres
Authors: Topa V. , Ioan A. , Iliescu B. , Mitroaica G.
Published: July 2007

A quantitative treatment is made of F → U conversion in H2 in very pure KC1 crystals and the conversion of electronic centres (like Ag−, Cu−, Tl−, Pb in U centres by the same treatment. This fact gives the possibility to elaborate a method for detecting negative metal ion centres. By thermal treatment in water vapour, electronic centres like Ag−, Cu−, Tl−, Pb are transformed mainly into OH− ions and colloids of heavy metal elements.