bluuebunny/crossref_metadata_2025_split huggingface dataset:
Transverse Effects in Optical Bistability for Transportation of Light Information Signals
Authors: Apanasevich S. P. , Lyakhnovich A. V. 
Published: July 2007

AbstractThe transformation kinetics is studied experimentally of wide light beam profiles at optical switching of the states of bistable thin‐film interferometers with nonlinearity of their thermal nature. The evolution of switch‐wave type autowave processes and inhomogeneous stationary structures at the stages of their stable existence and decay are traced. The possibility is shown of optical control of the direction and speed of switch wave front motion.
Optical Nonlinearities of Semiconductor Microcrystallites
Authors: Woggon U. , Henneberger F. , Müller M. 
Published: July 2007

AbstractAn investigation is made of both, the linear and nonlinear optical properties of semiconductor microcrystallites embedded in glass. The specific situation when the radius of the microcrystallites is 5 to 10 times larger than the bulk exciton radius is studied using CuBr microcrystallites. In this case the observed blue‐shift of the exciton peak is explained in terms of exciton–exciton interaction in the presence of quantum confinement. Effective optical switching at cryo‐ and room temperature is achieved with very large contrast and Lorentzian saturation intensities in the 100 kW/cm2 range. Also the change of transmission with rising excitation intensities of CdS microcrystallites is analyzed with respect to its physical origin. Here a strong broadening due to a large size distribution results in a more complex situation.
Room‐Temperature Optical Nonlinearity in Semiconductor‐Doped Glasses
Authors: Zimin L. G. , Gaponenko S. V. , Lebed V. Yu. 
Published: July 2007

AbstractThe bleaching effect in commercial samples of glasses is investigated at the fundamental absorption edge of semiconductor microcrystals responsible for the colour of the glass. At room temperature under an optical excitation intensity up to 107 W/cm2 an increase of the optical transmission by five orders and more is observed. The spectral band width in which nonlinear optical response occurs reaches 0.5 eV. The results are compared with the results obtained for nonlinear absorption of semiconductor monocrystals.
Carrier Diffusion and Trapping by Quantum Wells
Authors: Uchiki H. , Kobayashi T. , Tokunaga E. 
Published: July 2007

AbstractA picosecond time‐of‐flight experiment is performed for GaAs/AlGaAs quantum well structures at 77 K in order to obtain diffusion constants and trapping rates of carriers by quantum wells. Analysis of the data by a diffusion model gives an ambipolar diffusion constant of AlxGa1−xAs (x ≈ 0.35) of 16 cm2/s and a capture efficiency of carriers by a single quantum well with 5 nm width of 0.75.
Many‐Body Effects in the Electron–Hole Plasma Confined in GaAs–(GaAl) As Quantum Wells
Authors: Bongiovanni G. , Staehli J. L. , Martin D. 
Published: July 2007

AbstractTwo‐beam transmission and photoluminescence spectra of GaAs–(GaAl)As multiple quantum wells are presented. The spectra are studied as a function of the electron–hole (c–h) pair density. At low and with increasing density a blue‐shift of the lowest exciton line is found. At densities above the Mott value, the band gap reduction depends on the width of the well and is much smaller than in a strictly two‐dimensional e–h plasma. Further, even in a relatively dense plasma the excitonic enhancement factor differs strongly from unity, though it depends only weakly on the energy.
Reflectivity and Dynamic Gratings in Implanted Si Induced by Picosecond Laser Pulses
Authors: Galeckas A. , Netiksis V. , Petrauskas M. , Vaitkus J. 
Published: July 2007

AbstractThe relaxation processes are investigated in high‐excited ion‐implanted silicon using transient‐reflectivity and dynamic grating methods in the picosecond time domain. The dependences of the optical parameters of ion‐implanted Si versus implantation dose are presented. The temporal behaviour of the non‐equilibrium charge carriers obtained from the induced‐reflectivity change and grating decay measurements is analysed. The reflectivity decay process is found to be always faster than the corresponding grating decay process. By the numerical calculations the surface recombination velocity is estimated to S = 4 × 104 cm/s. The influence of the implantation process on the effective carrier lifetime is discussed.
Nonlinear Optical Properties of the System CdS1−xSex
Authors: Swoboda H.‐E. , Majumder F. A. , Renner R. , Weber C. , Sence M. , Jie Lu , Noll G. , Göbel E. O. , Vaitkus J. , Klingshirn C. 
Published: July 2007

AbstractThe influence of localization on the nonlinear optical properties of CdS1−xSex is investigated for 0 ≦ x ≦ 1 in the temperature range from 5 to 300 K. Results from time‐integrated and time‐resolved luminescence, from pump‐ and probebeam experiments, and from measurements using laser‐induced gratings are given. From all investigations likewise free and “localized” excitons are found in the mixed crystals at temperatures below 60 K, with a spectrally rather broad transition region. The mobility of the “localized” excitons is non‐zero but is decreased by more than a factor three with respect to free excitons. Above 60 K, the optical properties approach those of the pure compounds and are dominated by the formation of an electron–hole plasma at high excitation intensities. This process reflects a delocalization of the excited electron–hole pairs due to thermal re‐excitation from “localized” into extended states.
Quantum‐Statistical Investigation on the Nonlinear Optical Oscillation in Amorphous Semiconductor GeSe2 Films
Authors: Xu Lun‐Biao , Cai Shou‐Fu , Xie Guo‐Xin 
Published: July 2007

AbstractWith the quantum‐statistical three‐level cascade Jaynes‐Cummings model, the relationship between the nonlinear optical oscillation phenomena in amorphous vacuum evaporated GeSe2 films and the dynamical correlation of the high‐dense defects are investigated. The collective behaviour of the system shows that the interaction between the incident photon fields and the three defect levels really causes the transmittance oscillating, which was reported recently by Hajto. The calculated results concide with the experiments very well. Also some experimental phenomena are analysed to show the origin in physical mechanism and some interesting possibilities for practices are discussed.
Optical Nonlinearity and Bistability in the Bound Exciton Energy Range of CdS
Authors: Hönig T. , Gutowski J. 
Published: July 2007

AbstractUnder high excitation conditions thick CdS samples show pronounced broad‐band nonlinear transmission in the bound exciton region and up to a wavelength of about 515 nm at cryo‐temperatures. This behavior is only explainable in a model based on impurity neutralization and bound exciton creation. The suitability of these nonlinearities to yield optical bistability will be shown. Bistable operation is investigated in dependence of crystal thickness, impurity concentration, excitation density, wavelength, and temperature. A strong correlation to acceptor‐bound exciton generation is obtained, and the explanation of this bistable operation fits well with that of the above mentioned transmission behavior.
Analysis of Stress Relaxation and Creep Curves for a Log‐Normal Distribution of Relaxation Times
Authors: Povolo F. , Hermida Elida B. 
Published: July 2007

AbstractA procedure to determine the characteristic parameters of a log‐normal distribution of relaxation times, both for stress relaxation and creep tests, is presented. The method is based on the use of either the normalized stress relaxation or creep functions and their first derivatives. Furthermore, the limiting stress or strain can be obtained directly from the experimental data. Finally, the procedure developed is applied to actual stress relaxation curves reported for aluminum and polysulphide rubber and the results are compared with those obtained by approximate methods, based on the use of the error function.
Optical Theorem in Ultra‐Thin Film Electrodynamics
Authors: Khudik B. I. , Lozovskii V. Z. , Zhuravlev A. F. 
Published: July 2007

AbstractThe optical theorem in the ultra‐thin film electrodynamics is formulated. The coefficients of reflection are calculated in different cases of the incident electromagnetic wave polarization. The generalized response function of the film which is calculated in previous works, satisfies the optical theorem for the ultra‐thin films.
Binding Energy of Two‐Dimensional Excitons in Strong Magnetic Fields
Authors: Marasas R. , Spector H. N. 
Published: July 2007

AbstractBecause of current interest in the behavior of excitons in semiconducting quantum well systems in the presence of strong magnetic fields, variational calculations are performed of the exciton binding energy as a function of the magnetic field using two types of variational wave functions, a hydrogenic wave function which corresponds to the exact wave function in the limit of low magnetic fields and a Gaussian wave function which corresponds to the exact wave function in the limit of high magnetic fields. In the low and high field limits, the results correspond to those obtained by others using perturbation and WKB approximations. However, the variational results enable us to bridge the region of intermediate magnetic fields for which the previous approximation methods are not valid and to determine the region of validity of these approximation methods. Also calculated are the oscillator strength for 2D excitons as a function of magnetic field to determine the intensity of the exciton peak as a function of the field.
Band Corepresentations of Magnetic Space Groups
Authors: Evarestov R. A. , Smirnov V. P. , Egorov S. A. 
Published: July 2007

AbstractThe band corepresentations of the magnetic space groups are introduced; the procedure of their generation is considered. The band corepresentations are essential for the symmetry analysis of phonons and magnons in magnetic crystals and for the study of the magnon‐phonon hybridization. The magnetic structures of CuFeS2 and La2CuO4 crystals are analyzed. In the antiferromagnetic phase these crystals are described by Shubnikov space groups of different types. The band corepresentations for each of these groups are tabulated.
EPR Study of the Antiferromagnetic Phase Transition in (Cd, Mn)S
Authors: Goede O. , Backs D. , Heimbrodt W. , Kanis M. 
Published: July 2007

AbstractThe antiferromagnetic phase transition of octahedrally coordinated (Cd. Mn)S single crystals with Mn concentrations 0.8 ≦ xMn ≦ 1 is studied by EPR measurements in the temperature range 80 to 550 K. The width of the Mn2+ EPR line is found to increase with decreasing temperature nearly proportional to (T ‐ TN)s−1 due to a corresponding decrease of the spin‐spin relaxation time. The Néel temperature TN for the transition from the paramagnetic into the (disordered) antiferromagnetic phase being determined from the linewidth divergence decreases strongly with decreasing xMn. The results are discussed in connection with actual EPR investigations of (Cd, Mn) and (Zn, Mn) chalcogenide mixed crystals with zincblende/wurtzite structure for lower Mn concentrations. The EPR signal below TN being observed in the case of polycrystalline thin films or powder samples is ascribed to surface near regions of the microcrystals.
Effect of a Random Potential on the Resonant One‐LO‐Phonon Raman Process
Authors: Klochikhin A. A. , Ogloblin S. G. 
Published: July 2007

AbstractThe effect is considered of Gaussian white noise potential on the one‐longitudinal‐optical (LO)‐phonon assisted Raman or photoluminescence process following the resonant excitation. The theory is based on the multiple scattering description of the excitonic state in a random potential. The Lipatov‐Brezin‐Parisi approach is extended into the multistep probability evaluation. It is shown that the joint analysis of the LO‐phonon assisted processes and the excitonic spectral density data gives new information on the exciton lifetime in the region of its localized states as well as at the positive energies where the exciton is almost free.
Monovacancy Formation Energies in Cubic Crystals
Authors: Krause U. , Kuska J. P. , Wedell R. 
Published: July 2007

AbstractUsing the conception of an extended object (Umezawa et al.) based on the continuum theory of elasticity, monovacancy formation energies are calculated. Anisotropy is included for cubic symmetry by means of a first order approximation to the Green's function tensor and some tensor algebraic calculations. The last considerations contribute to a better understanding of the meaning of “Voigt's average isotropic elastic constants”. Further lattice structure effects are taken into account by a common parameter for every type of structure. A comparison with experimental data or results from other theories shows either satisfactory agreement or the inconsistency of the first order approximation to the anisotropy for some materials with common properties.
The Correction Term and Core Dislocations in the Frame of the Generalized Callaway Integral
Authors: Awad A. H. , Saif J. S. 
Published: July 2007

AbstractConsidering four types of scattering mechanisms, viz. boundary scattering, core dislocation scattering, point defect scattering, and three phonon scattering, analytical expressions for the correction term are obtained in the low temperature approximation on the basis of the generalized Callaway integral. The expressions show that the correction term is proportional to the product of the three phonon normal process scattering strength and the square of the boundary scattering relaxation time.
Higher‐Order Terms in the Homogenized Stress‐Strain Relation of Periodic Elastic Media
Authors: Gambin B. , Kröner E. 
Published: July 2007

AbstractApplying the method of two‐scale asymptotic expansions to the displacement field in periodic elastic structures the completed macroscopic stress‐strain relation of such media is derived. This relation contains beside the usually considered local part also weakly nonlocal contributions in the form of strain gradients up to infinite order. Formulae for the determination of the pertaining homogenized material tensors are derived.
Atomic and Solid State Effects in X‐Ray Absorption Spectra of Ionic Crystals
Authors: Gegsin I. I. , Datsyuk V. N. , Yumatoff A. D. , Vedrinskii R. V. 
Published: July 2007

AbstractA new method for XANES calculations is offered. It allows to take into account simultaneously band structure effects as well as the core‐hole potential. The predicted K‐spectra of various ionic crystals agree well with the experimental ones. It is argued that the observed spectra correspond as a rule to the local partial densities of states of the nonperturbed crystal potential. Some of the new narrow peaks in the near‐edge region are due to electron transitions to resonance or bound‐electron states. These states are formed as a consequence of the hole potential, but exhibit essentially multicenter properties.
Two‐Photon Absorption via Deep Local Levels as Virtual Intermediate States in Semiconductors
Authors: Baltramiejūnas R. , Gavryushin V. , Račiukaitis G. , Kubertavičus V. , Kazlauskas A. 
Published: July 2007

AbstractThe enhancement of the coherent nonlinear losses are observed in ZnO and ZnSe crystals within the whole range of the interband two‐photon absorption (TPA) spectra. The effect is explained theoretically in terms of nonresonant participation of the deep local levels (DL) of impurities and native defects in the forbidden gap as additional intermediate virtual states of TPA. Calculations of interband TPA via DL including the influence of the momentum indeterminacy in local states are presented. The role of spatial interference of virtual contributions of the localized intermediate states in the momentum conservation is revealed. The possibility of the technological control of the additional nonlinearities is shown experimentally. The place of these phenomena among the widely investigated processes of coherent TPA via band states and the incoherent two‐step absorption through DL are discussed.
Stimulated Brillouin Scattering in Doped Centrosymmetric Semiconductors
Authors: Aghamkar P. , Sen P. K. 
Published: July 2007

AbstractBased upon the electromagnetic treatment, stimulated Brillouin scattering (SBS) in nearly centrosymmetric doped semiconductors is investigated analytically. The origin of the nonlinear interaction is considered to be in the third‐order optical susceptibility arising due to the nonlinearly induced current density and finite electrostriction of the medium. The threshold conditions are obtained for the onset of SBS as well as the effective Brillouin susceptibility and the resulting gain constant for both, lightly and heavily doped semiconductors. The numerical estimations are made for n‐type InSb crystals at 77 K duly shined by a pulsed 10.6 μm CO2 laser. In highly doped n‐InSb, the gain constant is significantly enhanced under high power pulsed excitation below the damage threshold. The analysis establishes the possibility of occurrence of optical phase conjugation via SBS in doped semiconductors.
Theoretical study of the Raman spectrum in a‐Si1−xNx: H Films
Authors: Yu Gong , Chen Guanghua , Zhang Fangqing 
Published: July 2007

AbstractThe vibrational excitations in a‐Si1−xNx: H films are calculated in terms of a simplified amorphous cluster. The main vibrational modes as well as correlative frequencies and intensities are obtained. By means of a random substitution of nitrogen atoms for silicon atoms the phonon density of states at different x values are deduced. It can be found that the results are in accord with the experimental Raman spectra.
Study of electron distribution in rhodium by compton scattering technique
Authors: Mohammad F. M. , Sharma B. K. , Singh H. , Ahuja B. L. 
Published: July 2007

AbstractThe results of a Compton scattering study on polycrystalline rhodium are presented. The measurements are carried out using 59.54 keV γ‐rays on a sample of 0.13 mm thickness. The renormalised‐free‐atom approach is applied to calculate the spherically averaged Compton profile for Rh for various 4d‐5s electronic configurations. Best agreement between measured and calculated values is found for the 4d85s1 electron configuration. These results are also compared with the recent band structure calculation for electron momentum distribution in Rh.
Ising ferromagnet with biquadratic exchange interaction of negative sign
Authors: Iwashita T. , Uryû N. 
Published: July 2007

AbstractFor Ising ferromagnets with S = 1, S = 3/2, and S = 2, the magnetization 〈Sz〉 is calculated using the pair model approximation. Assuming bilinear exchange interaction J and biquadratic exchange interaction J′ of negative sign between nearest‐neighbour pair of spins, the behaviour of 〈Sz〉 as a function of these exchange parameters are investigated for the Ising spin systems. At low temperatures, an anomalous behaviour of the temperature dependence of 〈Sz〉 is obtained. With regard to these anomalous behaviours, the ground state spin structure is discussed for the Ising ferromagnet with J′ of negative sign.
Free‐carrier absorption for intervalley phonon scattering
Authors: Gashimzade F. M. , Tagirov E. V. 
Published: July 2007

AbstractThe frequency dependence of the free‐carrier absorption coefficient in multivalley semiconductors is calculated for intervalley deformation potential scattering between parabolic M0 and saddle M1 points. The methods of group theory are used to summarize the contributions of all the equivalent valleys to the absorption coefficient for crystals of arbitrary symmetry.
Colour centres in barium hexaaluminate (Phase I). Study by electron paramagnetic resonance, optical absorption, and thermally stimulated luminescence
Authors: Gourier D. , Gbehi T. , Visocekas R. , Thery J. , Vivien D. 
Published: July 2007

AbstractColour centres produced by X‐ray irradiation of barium hexaaluminate (phase I) with β‐alumina structure are studied by electron paramagnetic resonance, optical absorption, and thermally stimulated luminescence. It is shown that in addition to the F+ centres characteristic of β‐alumina phases, this compound presents other colour centres such as F, O−, and possibly V‐type centres. The stability of these defects is investigated by means of thermal bleaching experiments and thermally stimulated luminescence. An alternative model to the generally accepted one is proposed, for the F+ centres, together with a mechanism of defect formation.
Weak localization effects in n‐type inversion layers of InSb grain boundaries under high hydrostatie pressure
Authors: Kraak W. , Trott S. , Herrmann R. 
Published: July 2007

AbstractMeasurements of the low‐field magnetoresistance are reported for an n‐type inversion layer adjacent to the grain boundary in InSb bierystals. At high pressures (ρ > 4 × 102 MPa), under the conditions that only one electric subband is populated, a strong negative magnetoresistance appears. From the observed experimental data it is concluded that weak localization effects play an important role in the electronic transport properties of the grain boundary interface. Some characteristic scattering parameters of this two‐dimensional disordered system are determined.
Atomic forces in the self‐consistent tight‐binding model
Authors: Kohyama M. , Yamamoto R. , Ebata Y. , Kinoshita M. 
Published: July 2007

AbstractThe self‐consistent tight‐binding (SCTB) model for structural and electronic properties of solids, which can treat both ionicity and covalency on an equal footing, is re‐formulated so as to be applicable to general and disordered systems and is analyzed in comparison with the tight‐binding bond (TBB) model. It is shown that atomic forces in the SCTB model are given very simply as well as in other tight‐binding type theories. Atomic forces consist of three types of contributions, which are those from the interatomic Coulomb interaction, from the covalent energy, and from the overlap repulsion. By using the present formulation, it is possible to calculate quantum‐mechanically the structural and electronic properties of extended defects or disordered systems of sp‐bondod materials with both the properties, ionicity and covalency, which have not yet been treated enough theoretically or quantitatively.
New off‐centre system. Jahn‐Teller mercury‐like impurities in alkali halides
Authors: Liidja G. , Nagirnyi V. , Soovik T. , Zazubovich S. 
Published: July 2007

AbstractTwo slow decay components are found in the low‐temperature decay kinetics of the AT emission of Ga+ and In+ centres in alkali halides. The emission, excitation, and polarization spectra of these components as well as the temperature dependences of their decay times and light sums and the influence of the electric and magnetic fields on the decay kinetics of the polarized AT emission are carefully investigated. It is shown that the observed effects are caused by an off‐centre position of Ga+ and In+ ions in the triplet relaxed excited state (RES). The off‐centre displacement occurs most probably in one of the 〈100〉 directions perpendicular to the tetragonal Jahn‐Teller distortion axis. Rapid tunnelling transitions between various energetically equivalent off‐centre positions of the impurity ion lead to the tunnel splitting of each metastable tetragonal (T) minimum of the triplet RES. Both the observed slow decay components of the AT emission are connected with the radiative decay of the two lower states. The orthorhombic structure of the AT RES, found by the technique of optical detection of electron spin resonance (OD ESR) several years ago for Ga+ centres in some alkali halides, is explained here as another evidence of the same phenomenon.