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 dispersion relation is obtained for a system of four-level atoms with an equidistant energy spectrum, which interact with resonant laser radiation, with account for three sequential one-photon optically allowed transitions, two-photon transitions, as well as a direct three-photon transition. It is shown that the dispersion relation consists of four polariton branches. The divergence and convergence of the dispersion relation branches, their intersection, and a self-consistent change in the binding force of photons with atoms are predicted using the fixed photon concentration approximation.

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.

Characteristic features of polariton dispersion laws are studied for four-level atoms interacting with three pulses of coherent laser radiation with frequencies that are in resonance with optically allowed one-photon transitions 1 $$\leftrightarrows$$ 2, 2 $$\leftrightarrows$$ 3, and 3 $$\leftrightarrows$$ 4 with regard to two-photon transitions 1 $$\leftrightarrows$$ 3 and 2 $$\leftrightarrows$$ 4, as well as a direct three-photon transition 1 $$\leftrightarrows$$ 4. The approximation of a given photon density of three pulses is used. It is shown that the dispersion law consists of four branches the position and shape of which are specified by the Rabi frequencies of the above transitions and the photon densities of the three pulses. The direct consideration of all six optical transitions leads to the dependence of the dispersion law of atomic polaritons on quantum parameters—the phase differences between the Rabi frequencies of the transitions under consideration. Parameter values are found for which the branches of the dispersion law may intersect.

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.

A dispersion law for the system of three-level atoms with an equidistant energy spectrum interacting with resonant laser radiation has been obtained taking into account two successive optically allowed one-photon transitions and an optically allowed two-photon transition between the lower and upper levels. It has been shown that the dispersion law consists of three polariton branches. The effects of repulsion and attraction of branches of the dispersion law and their intersection, as well as the self-consistent variation of the photon–atom coupling constant, have been predicted.

The theory of nonlinear s -polarized surface waves, which propagate in a symmetric planar threelayered structure with a metamaterial core and nonlinear coverings, has been constructed. It has been shown that the occurrence of only nonlinear quasi-surface waves is possible in such a structure. Dispersion laws and energy fluxes of symmetric, even, and odd modes at different parameters have been found and investigated. The qualitative behavior of dispersion laws substantially depends on the core thickness.

A theory of nonlinear polarized symmetric quasi-surface waves in a symmetric planar structure with a nonlinear core and linear coatings has been proposed. The nonlinearity of the core is caused by exciton-photon interaction and optical exciton-biexciton conversion. The dispersion laws for propagating waves have been obtained and studied.

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.

We obtained the system of nonlinear differential equations for the areas of the envelopes the propagating supershort pulses in two guides of the coupler, which are the area theorems. We predicted the self-switching phenomenon for the energy transfer from one guide to the other. We investigated the phase portraits and predicted a number of new mechanisms of the pulse transmitting.

A theory of asymmetric TE -polarized quasi-surface waves propagating inside a symmetrical planar three-layer structure with a linear core and nonlinear plates is developed. The nonlinearity of the plates is associated with the inclusion of the optical exciton-biexciton conversion. The dispersion laws of the propagating waves are derived and investigated.