The effect of the triexciton state on the absorption of exciton-polaritons is studied under conditions when two high-power laser radiation pulses interacting with biexcitons and triexcitons and a probe pulse at the frequency of the exciton transition are incident on the medium. It is shown that even at low triexciton binding energies under the action of two high-power pulses, the exciton state splits into three quasi-levels, and the Autler--Townes effect (optical Stark effect) is observed. It turned out that the position of the quasi-levels depends on the detuning of the resonance of the pump pulses and their intensities, which makes it possible to identify them. These circumstances make it possible to diagnose the triexciton state in semiconductors with a higher degree of probability not by studying the absorption spectral line of the biexciton--triexciton transition, but by the effect of the triexciton state on absorption in the region of the exciton transition. Keywords: excitons, biexcitons, triexcitons, Autler--Townes effect.

The effect of the triexciton state on the absorption of exciton-polaritons is studied under conditions when two high-power laser radiation pulses interacting with biexcitons and triexcitons and a probe pulse at the frequency of the exciton transition are incident on the medium. It is shown that even at low triexciton binding energies under the action of two high-power pulses, the exciton state splits into three quasi-levels, and the Outler-Towns effect (optical Stark effect) is observed. It turned out that the position of the quasi-levels depends on the detuning of the resonance of the pump pulses and their intensities, which makes it possible to identify them. These circumstances make it possible to diagnose the triexciton state in semiconductors with a higher degree of probability not by studying the absorption spectral line of the biexciton-triexciton transition, but by the effect of the triexciton state on absorption in the region of the exciton transition.

Изучено влияние двухфотонных процессов на поглощение в системе экситонов и биэкситонов при двухимпульсном взаимодействии. Показано, что учет двухфотонных процессов приводит к возможности наблюдения несимметричного эффекта Аутлера--Таунса. При определенных величинах падающих полей возможно исчезновение эффекта Аутлера--Таунса, связанное с квантовой интерференцией всех механизмов взаимодействия. Предсказана возможность управления спектром поглощения с помощью изменения интенсивностей полей и расстроек резонанса падающего излучения. Ключевые слова: экситоны, биэкситоны, расщепление Аутлера--Таунса.

The influence of two-photon processes on absorption in a system of excitons and biexcitons in the case of two-pulse interaction is studied. It is shown that taking into account two-photon processes leads to the possibility of observing the asymmetric Autler–Townes effect. At certain values of incident fields, the Autler–Townes effect can vanish, which is associated with the quantum interference of all interaction mechanisms. The possibility of controlling the absorption spectrum by varying the field intensities and resonance detunings of the incident radiation is predicted.

The effects of laser beam propagation in a coupler composed of two parallel optical-fibre arrays are studied by the coupled-mode method taking into account the interaction of a given fibre with the nearest neighbours and the linear dependence of the propagation constant on the fibre number. It is shown that, due to the complex structure of each subsystem, the structure of light intensity spatial distribution becomes significantly complicated in the system under study. The occurrence of space limited transverse light diffraction is predicted.

Using the coupled-mode method, the effects of propagation of laser radiation in a coupler of two parallel waveguide arrays are studied. It is shown that due to the composite spatial structures of each of the subsystems, the structure of the spatial distribution of radiation intensity in the subsystems is substantially complicated in the investigating system.

AbstractThe double-pulse interaction with excitons and biexcitons in semiconductors is studied theoretically. It is shown that the dispersion law of carrier wave has three branches under the action of a powerful pumping in the region of the M -band of luminescence. Values of parameters at which the dispersion law branches can intersect due to the degeneration of the exciton level energy have been found. The effect of a significant change in the force of coupling between the exciton and photon of a weak pulse with a change in the pumping intensity is predicted.

The double-pulse interaction with excitons and biexcitons in semiconductors is studied theoretically. It is shown that the dispersion law of carrier wave has three branches under the action of a powerful pumping in the region of the M-band of luminescence. Values of parameters at which the dispersion law branches can intersect due to the degeneration of the exciton level energy have been found. The effect of a significant change in the force of coupling between the exciton and photon of a weak pulse with a change in the pumping intensity is predicted.

Free-radical-mediated processes are involved in a variety of physiological events, while oxidative stress and related redox deregulation are implicated in various pathological events. Tripeptide glutathione plays an important role in the antioxidant defense of the brain, particularly in the maintenance of the optimal redox state in neurons and glial cells. We studied the combined effects of pantothenic acid derivatives, pantothenol and calcium pantothenate, and memantine, which is a glutamate receptor antagonist that is widely used for the treatment of dementia, on amnesia induced by scopolamine in rats. Scopolamine induced amnesia in rats; however, unexpectedly, this effect was even more expressed in the memantine-pretreated animals. Memory impairments were less manifested in the rats that were pretreated with memantine in combination with panthenol or calcium pantothenate. The detrimental scopolamine effect on memory was accompanied by significant depletions of glutathione and coenzyme A in the brain. While memantine recovered the glutathione status to some extent, it nevertheless further aggravated the scopolamine influence on coenzyme A levels. An alleviation of scopolamine-induced memory impairments that was observed after combined pretreatment with memantine and panthenol or calcium pantothenate was accompanied by a normalization of coenzyme A levels, while the effects on glutathione redox did not correlate with the behavioral data.

A new mechanism of the generation (amplification) of terahertz radiation in semiconductors is proposed, which is based on the quantum transitions between two-exciton and biexciton under conditions of single-photon excitation from the ground state of a crystal.

A new lasing mechanism for semiconductors like CuCl, CuBr is proposed based on the two-photon pumping of biexcitons from the ground state of the crystal and generation or amplification of light in the region of M-band of luminescence due to the optical exciton-biexciton conversion. It was shown that the net gain essentially depends on the level of two-photon pumping and rapidly decreases deep into the crystal due to the spatial depletion of pump radiation. Estimations for CuCl give the values of lasing photons with the energy about 3,2 eV and the maximum small signal gain about the value of the exciton absorption coefficient.

A theoretical and numerical analysis of the transmission of phase-modulated laser pulses through a thin film with excitonic nonlinearity is performed. It is shown that, by choosing the modulation law, one can efficiently control the optical nonlinearity of the film down to the inversion of the sign of nonlinearity.

Taking into account the exciton-photon and elastic exciton-exciton interactions we investigated peculiarities of transmission of supershort light pulses by thin semiconductor films. We predict the appearance of time dependent phase modulation and dynamical red and blue shifts of transmitted pulse.

The transmission and reflection of an ultrashort laser pulse by a thin semiconductor film under the conditions of resonance excitation of biexcitons by two photons are theoretically investigated. The numerical solutions of the macroscopic equations are found for various values of the film thickness, the detuning from the two-photon resonance, the laser pulse duration, and the intensity. These equations have been obtained in the framework of the generalized bipolariton model. In this model a biexciton is formed from virtual excitons of four kinds and only some of them interact with the light. It is shown that the thin film substantially transforms the incident pulse. For specific conditions, high and narrow transmission and reflection peaks can appear, or even trains of such peaks. In some cases their height can considerably exceed the amplitude of the incident pulse. The results are compared with similar results obtained on the basis of other models.

Taking into account the exciton-photon and elastic exciton-exciton interactions we investigated peculiarities of transmission of supershort light pulses by thin semiconductor films. We predict the appearance of time dependent phase modulation and dynamical red and blue shifts of transmitted pulse.

The peculiarities of nonlinear transmission (reflection) of the supershort pulses of laser radiation by a thin semiconductor film due to the two-photon biexciton excitation from the ground state of the crystal. It is shown that the transmission is sufficiently determined by the amplitude, halfwidth and resonance detuning of the incident pulse and by the film thickness. The bifurcation region of the existence of the stable and unstable solutions is found.

Multistability of the reflection coefficient as a function of incident amplitude is theoretically demonstrated to be possible for a semiinfinite optically homogeneous medium with the Kerr nonlinearity. The multistability arises at certain relations between the system parameters. The treatment is essentially free from the assumption that field envelopes vary slowly in space. Underlying physical processes are described.