E. A. Isaeva

Laser speckle probes of relaxation dynamics in soft porous media saturated by near-critical fluids

Speckle correlation analysis was applied to study the relaxation dynamics in soft porous media saturated by near-critical carbon dioxide. The relaxation of soft matrix deformation was caused by a stepwise change in the fluid pressure. It was found that the deformation rate in the course of relaxation and the relaxation time strongly depend on the temperature of the system. The values of relaxation time reach their maximal values in the vicinity of the critical point of saturating fluid. The contributions of hydrodynamic relaxation of the fluid density and viscoelastic relaxation of the porous matrix to its creeping are analyzed.

Resonant scattering and absorption in the titanate-based nanoplatelet dispersions in near ultraviolet region.

Extinction enhancement and nonlinear near-resonant absorption of potassium polytitanate nanoplatelets were experimentally studied in the near-UV region. Phenomenological models such as the one-oscillator Lorentz model for dielectric function and the two-level model with the depleted ground state were used to interpret the experimental data. The introduced model parameters demonstrate the adequately high sensitivity to variations in nanoplatelet morphology and chemical environment.

Speckle correlometry method for evaluating the transport scattering coefficient of a randomly inhomogeneous medium

We propose a method for evaluating the transport scattering coefficient of a randomly inhomogeneous medium, which is based on a correlation analysis of the intensity of laser radiation backscattered from the moving medium. The method employs a localized source of radiation (laser beam focused on the surface of medium) and makes use of the spatial filtration of detected scattered radiation in the image plane of the optical system with the aid of a programmed ring filter.

Analysis of the scatter growth in dispersive media with the use of dynamic light scattering

Analysis of the structure functions of intensity fluctuations of scattered laser light was applied to monitor the phase separation in probed disperse media. UV-cured mixtures of a liquid crystal and prepolymer were studied during the formation of the structure of dispersive polymer-liquid crystal (DPLC) composites. The experimentally observed features of light beating induced by dynamic light scattering in DPLC systems (the scaling properties of the structure functions, the narrowing of the beating spectrum for certain weight fractions of the liquid-crystalline component) were interpreted in terms of the discrete scattering model using the results of statistical modeling.

Full-field speckle correlometry of non-stationary systems with temperature-dependent scatter dynamics

The experimental results of speckle-correlometric analysis of such temperature-governed processes as the sol-gel transition and the foam aging are presented. Analysis of the temperature dependencies of speckle correlation time for solgel systems with embedded scatterers allows the estimation of gelation activation energy. The effect of increase in the speckle correlation time at later stages of the foam structure evolution is presumably caused by the increasing role of local avalanche-like processes in the structure formation.

Spatially resolved speckle correlometry in application to media structure characterization

We propose an original speckle-correlometry method for the structural analysis through a random multiple scattering media with complex dynamics and structure. The use of a localized radiation source and spatial ring filtration of scattered field give the opportunity to select the partial components of scattered field. In this work, the dynamic process of gel formation beginning from the stage of sol to the stage of gelling are investigated and the experimental data are presented. The object under study consist of 0.28 %weight fraction of gelatin dissolved in water and 1 gram per liter (gL-1) and 100 mg per liter (gL-1) of TiO2 for optical scattering.

Diffusing low-coherence interferometry of turbid media: an approach to transport parameters evaluation

The features of formation of interferometer output in the case of a broadband light source and random medium as a retro-reflector in the interferometer object arm are considered. It is shown for the large values of the pathlength difference the interferometer output decays exponentially with the decay rate dependent on the transport parameters of a probed random medium. This allows us to determine the transport mean free path of light propagation in the medium. This approach can e applied not only for the strongly scattering media, but also for scattering samples characterized by non-diffusive regime of light propagation.