Holographic Methods for Investigating Molecular Processes and Dynamics of Condensed Media

In this review devoted to analysis of the mechanisms and characteristics of recording and relaxation of elementary spatial structures in polymer films and solutions colored by organic dyes, the basic principles of holographic analysis, the experimental technique and measuring methods, and some applications are considered consistently. The results of investigation of the dynamics of laser recording and subsequent relaxation of spatially inhomogeneous concentration and thermal structures in polymer films and solutions under their initiation by axisymmetric or sinusoidally modulated light field are reported. The probing beam diffraction on a nonstationary axisymmetric structure and the kinetics of the angular dependence of the diffracted probing beam during its transmission through and amplitude concentration or phase thermal grating is considered and a theoretical model that successfully describes the experimental results is proposed. For diffusive relaxation of holographic gratings recorded in biopolymer solutions under laser-induced fragmentation of molecular chains, the dispersion of macromolecule fragment lengths is taken into account. The problems of recording of stationary phase gratings and anthracene-containing polymer media in accordance with the oxidation mechanism are considered; for this mechanism, the effect of concentrations and mutual distribution of reagents on the grating recording process is assessed, and the mechanisms of the grating profile distortions are determined. The features of formation of the relief–phase gratings in polymer media with the laser-induced swelling are considered and the corresponding theoretical models ensuring good agreement with experiment are proposed. Holographic methods are employed for studying the kinetics of some molecular reactions; it is shown, for example, that during static annihilation of triplet centers, the grating profile is deformed, which is manifested in the kinetics of diffraction maxima. In recording of a grating in a disperse medium on triplet centers, in the case of their active annihilation, fluctuations of occupation numbers of microcavities are suppressed, while in the case of a diffusion-accelerated reaction, this effect becomes even more significant.