Nonlinear absorption of a molecular crystal in an external magnetic field is considered. The exciton absorption shape functions under polarized laser radiation and a weak magnetic field, as well as the mechanisms responsible for the formation of a hysteresis loop in the dependence of the output light intensity on the applied magnetic field, were studied for the particular case of benzene. It was established that, for the magnetooptical response of the molecular crystal under study, the formation of bistable loops is inverse in character, which makes it possible to monitor and control the behavior of bistable elements in optical logics systems with an external magnetic field at a fixed illumination frequency.

A theory of exciton light absorption in inorganic semiconductors with an arbitrary number of hydrogen-like exciton series levels has been suggested. The specific character of the behavior of the exciton-phonon interaction function for different levels of the series in the whole region of the phonon quasimomentum variation has been analyzed in detail. The influence of the weak magnetic field on the energy position of the exciton excitation levels has been investigated. It is shown that there is a full correlation between the bands of magneto-optical and exciton absorption.

The investigation is concerned with layer crystals of the GaSe, InSe, GaTe, MoS2 - type and other inorganic semiconductors, whose phonon spectrum has a great number of peculiarities, among them the availability of low-energy optical phonons. In this case the dispersion of these phonons can be essential and vary in character. The mass operator of the exciton-phonon system and the light absorption coefficient for different dispersion laws of optical phonons have been calculated The influence of the sign of the phonon "effective mass" on the exciton absorption band of layer crystals, which causes the opposite in sign dynamics of the absorption maximum shift, and the change of the absorption curve asymmetry have been determined.

The influence of an external magnetic field on the optical characteristics of the exciton spectra of a semiconductor is studied. It is shown that the diamagnetic shift of the exciton level essentially changes the dynamics of the exciton absorption. The combination of the excitonic and magnetic properties of a crystal in the range of excitonic frequencies gives new opportunities to control the bistable behavior of the crystal. It is revealed that the magnetooptical response of the semiconductor to the laser field gives rise to bistable loops with respect to both the intensity of the incident light and the magnitude of the magnetic field.

The influence of an external magnetic field on optical features of semiconductor exciton spectra is researched in this work. It is shown that the magnetic field brings about the shift of the exciton level in the high-energy spectrum area. This causes the arising of a unique effect-- brightening-- of the crystal on the fixed external excitement frequency with the growth of the magnetic intensity value. The combination of electronic and magnetic characteristics of a crystal in an exciton frequency region opens new possibilities of giving control over the bistable behavior of the crystal. It is shown that the magnetic- optical response of a semiconductor on laser excitation generates bistable loops, both on the intensities of falling light (tau) (T) and in the size of the magnetic field-- (tau) (Hyields).

The electronic structure of the layer compound PbI2 is calculated by use of the pseudopotential method. The norm-conserving nonlocal form factors of pseudopotential were constructed according to Bachelet-Hamann-Schluter scheme. From the pseudowavefunctions the imaginary part of dielectric function were computed in order to obtain the absorption spectra of PbI2 in fundamental region. On these way the integration over (k) over right arrow space within the irreducible part of Brillouin zone was performed in framework of special points method.

This paper proposes for consideration an additional mechanism for influencing the exciton absorption spectra and observing temperature redistribution peculiarities of the crystal absorptive power. They are caused by nonlinear phonon-exciton interactions, which are due to anharmonic effects in the exciton-phonon system. The arising of the borderline frequency, which possesses the smallest region of optical bistability (OB) realization, is caused by a break in the direction of the absorption curve. At low temperatures the basic role is played by the exciton-exciton interaction, and at high temperatures nonlinear exciton-exciton-phonon processes play the most important role. The value of the borderline frequency is defined by the size and sign of the nonlinear exciton-exciton-phonon function as well as by the crystal temperature and the exciton density, which is created by the external powerful laser wave.

In this paper one of the methods of polarimeter investigation of exciton spectra is proposed. The analysis is based on the peculiarities of semiconductor layer crystals, the dipole moment of the exciton transition and one of the main properties of the laser wave, its polarization. As a result, libration oscillations of the exciton dipole become quite actual in anisotpopic semiconductors. This leads to the change of the mechanism of light absorption on the exciton frequencies and to the actualization of the indirect vertical phototransition (IVP) with the change of the polarization angle. These processes result in the depolarization of the absorption spectrum, its structurization, and redistribution of the power along the frequency scale. Finally, the dying away of purely exciton absorption and the increase of oscillatory components take place.

The results of theoretical investigations of the role of the dipole moment of excitons during the formation of optical spectra of exciton absorption are presented in this work. Using the model of the indirect phototransition, we calculated the frequency distribution of the coefficient of exciton absorption for different temperatures. It is shown that libration oscillations lead to temperature dependences of the integral absorption; stipulate the anomalous temperature changes of the height of the exciton absorption peak, and make the exciton absorption band structural.

The nonlinear light transmission of semiconductors, in which the indirect exciton phototransition is realized, is studied. It is shown that the presence of two channels of dissipation of light wave energy of the indirect phototransition (the excitation of libration phonons) and exciton relaxation (the excitation of lattice phonons) -- leads to arising of optical multistable states in crystals. Investigations of polarization peculiarities of the dynamics of nonlinear processes with changing intensity of the input signal have been carried out.

The effect of the phonon subsystem of a crystal on laser absorption is considered. The exciton- phonon interaction is shown to result in a nonlinear behavior of absorption as a function of exciton gas density. The output light intensity is calculated as a function of temperature and the temperature range in which optical bistability occurs is established.

Effect of the phonon subsystem on absorption of laser irradiation is considered. It is shown that the exciton-phonon interaction results in a nonlinearity of absorption of incident radiation arising with an increase of exciton density. Temperature dependence of the output intensity has been calculated and an optical bistability has been shown to take place in this temperature region under certain conditions.

The exciton energy renormalized as a result of interaction between excitons and phonons of different effective mass has been calculated, Existence of the energy gap (in the vicinity of the integral energy of exciton and phonon) in which the deformation exciton is realized is confirmed. The dispersional dependence of such a slowly attenuating excitation is completely governed by the phonon effective mass.

physica status solidi (b)Volume 148, Issue 1 p. K29-K32 Short Note Phonon-Induced Splitting of Polariton States in Crystals B. M. Nitsovich, B. M. Nitsovich Institute of Physics, Academy of Sciences of the Ukrainian SSR, Kiev Search for more papers by this authorO. V. Krekhivskii, O. V. Krekhivskii Institute of Physics, Academy of Sciences of the Ukrainian SSR, Kiev Search for more papers by this authorG. M. Pestryakov, G. M. Pestryakov Institute of Physics, Academy of Sciences of the Ukrainian SSR, Kiev Search for more papers by this authorG. T. Avanesyan, G. T. Avanesyan Institute of Physics, Academy of Sciences of the Ukrainian SSR, Kiev Search for more papers by this author B. M. Nitsovich, B. M. Nitsovich Institute of Physics, Academy of Sciences of the Ukrainian SSR, Kiev Search for more papers by this authorO. V. Krekhivskii, O. V. Krekhivskii Institute of Physics, Academy of Sciences of the Ukrainian SSR, Kiev Search for more papers by this authorG. M. Pestryakov, G. M. Pestryakov Institute of Physics, Academy of Sciences of the Ukrainian SSR, Kiev Search for more papers by this authorG. T. Avanesyan, G. T. Avanesyan Institute of Physics, Academy of Sciences of the Ukrainian SSR, Kiev Search for more papers by this author First published: 1 July 1988 https://doi.org/10.1002/pssb.2221480147 Prospekt Nauki 144, SU-252028 Kiev, USSR. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Volume148, Issue11 July 1988Pages K29-K32 RelatedInformation

AbstractA 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.