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ACCOUNTING OF MANY-PARTICLE INTERACTIONS IN MOLECULAR J-AGGREGATES AND NONLINEAR OPTICAL EFFECTS IN THESE SYSTEMS

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The paper deals with generalization of investigation materials performed by the authors in recent years and analysis of obtained results. The subject of the paper is accounting of many-particle interactions in molecular J-aggregates at their resonance excitation by laser radiation. In this case, not only twin interactions are taken into considerations, but also the interactions of a given particle with three and more particles simultaneously. Three basic directions can be denoted among carried out investigations. The first direction is connected with derivation (from the first principles) of motion equations for molecular of J-aggregates in view of many-particle interactions, and also twin correlations between particles. The derivation of equations from the first principles leads in general to the system of coupled equations for the means of products of n operators relating to n different molecules. Since n increases in every following equation, the problems arise, connected with uncoupling of this system and also factorization of the means with the highest n. The most difficult and complicated problem in this process is correct calculation of relaxed terms, arising due to exciton-exciton annihilation. The first direction is connected concretely with solution of all above mentioned problems. Within the second direction the study of bistability has been carried out on the basis of obtained equations, in view of three-particle interactions. Meanwhile primary attention has been concentrated on analysis of homogeneous regimes in J-aggregates. It has been shown, in particular, that accounting of many-particle contributions leads to the shift of bistability boundary into region of smaller constants of exciton-exciton annihilation. And, at last, the third direction of investigations is connected with analysis of modulation instability for stationary states of J-aggregates considered earlier at bistability study. The study of stability region boundaries and their correlation with boundaries of bistability regions has been carried out. Obtained results give the possibility to determine more rigorously the parameters region, where nonlinear effects can be observed. They can be used for development of optical logic devices and, in particular, molecular memory circuits.

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