D. A. Zimnyakov

Effects of laser-induced quenching and restoration of photoluminescence in hybrid Si/SiOx nanoparticles

We studied the processes of pulsed and continuous-wave (CW) laser excitation of photoluminescence (PL) in nc-Si/SiOx nanoparticles. CW laser irradiation of the nc-Si/SiOx sol in dimethylsulfoxide (DMSO) and in a thin film was found to quench PL with an essentially nonexponential dynamics. The laser-induced variation of the Rayleigh scattering signal from the nc-Si/SiOx sol in DMSO was found to replicate that of the PL quenching. The IR and Raman spectra of the laser-exposed nc-Si/SiOx exhibited no new bands that could be evidence of their chemical transformations. There were also no perceptible effects pointing to laser-induced aggregation of the nc-Si/SiOx particles in the sol. 355xa0nm pulse-periodic laser irradiation of the nc-Si/SiOx particles preliminarily exposed to a 405xa0nm CW laser (which causes a strong PL quenching effect) was found to result in a rapid restoration of the original PL signal, which means that the effect of laser quenching of PL can be entirely reversible. We considered a mechanism of the reversible photosensitivity of nc-Si/SiOx, based on the processes of ionization of the photoluminescent oxygen-deficient centers in their suboxide shell and electron capture by traps, followed by their laser-assisted photorecombination.

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.

Optical clearing and laser light dynamic scattering near the critical point of fluid in mesoporous materials

The effects of dynamic scattering of laser light and optical clearing of a mesoporous system impregnated by near-critical fluid (carbon dioxide) were studied for the case of quasi-equilibrium isothermal transitions between the phase states of the fluid (CO2) in the vicinity of the critical point. The rate of optical clearing with increasing pressure near the saturation vapor point of the filling subcritical substance was found to be controlled by the co-existence of the liquid and gaseous phases in mesopores and decayed with an increase in detuning from the critical temperature. It was shown that the decorrelation of speckle-modulated scattered light during slow variations of the pressure can be described in terms of the Fourier transform of the pathlength probability density of the scattered light. The transform parameter is defined by the pressure derivative of the effective refractive index of the system. The results obtained can be used as a physical basis for laser probing of near-critical disperse systems.

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.

Nonlinear optical properties of open-ended amichair single-wall carbon nanotubes (SW-CNT)

Summary form only given: Optical properties of carboxylic acid functionalized open-ended armchair single-wall carbon nanotubes (SW-CNT) are studied by numerical simulations and in experiments. The polarizability, extinction, saturated absorbance and non-linear refraction are analyzed in various conditions for different types of SW-CNT and compared with experimental data.

Emerging correlation optics.

This feature issue of Applied Optics contains a series of selected papers reflecting the state-of-the-art of correlation optics and showing synergetics between the theoretical background and experimental techniques.

Spatially resolved speckle-correlometry of sol-gel transition

Sol-gel transition was studied using the speckle correlometry method with a localized light source and spatial filtering of backscattered radiation. Water solutions of technical or food gelatin with added TiO2 nanoparticles were used as studied objects. Structural transformation of sol-gel system was studied at various temperatures from 25°C to 50°C using analysis of the correlation and structure functions of speckle intensity fluctuations. The characteristic temperatures of “sol – gel” transition were evaluated for studied systems. Obtained results can be used for various applications in biomedicine and food industry.

Evolution of the scattering anisotropy of aged foams in the wet-to-dry transition

Empirical data on the diffuse and collimated transmittance of aged liquid foams are discussed in terms of influence of mutual correlations in the scatter positions. This influence can be described introducing the static structure factor of a scattering system and occurs remarkable in the case of wet foams with gas bubbles as the basic scattering units. On the contrary, mutual correlations of basic scattering units (Plateau-Gibbs channels and vertices) in dry foams are negligible due to low values of their volume fraction. This causes dramatic changes of the scattering anisotropy of foam layers in the vicinity of the wet-to-dry transition. Some analogies can be drawn between this effect and a previously reported optical inversion of densely packed random media.