A method of non-coherent video-reflectometry based on acquisition and analysis of image sequences in the backreflection mode under white light illumination is examined to characterize the nucleation stage in a plasticized biodegradable polymer (polylactide). Nucleation in the foamed system “polylactide – supercritical/subcritical carbon dioxide” is provoked by a pressure quenching in the quasi-isothermal mode. The features of image formation are discussed for the cases of birth and growth of the surface and bulk pores in the plasticized polymer.
The dynamics of radiation of a two-frequency laser with a vertical cavity is studied by numerical methods. The dependence of the amplitude of the electric field in the stationary regime of laser radiation on the gain is shown.
We theoretically demonstrate a capability of injection-locked semiconductor laser to serve as a nonlinear device for suppression of the amplitude disturbances in a phase-modulated optical signal and significant BER improvement in DPSK optical communications.
Numerical model for calculations of spatio-temporal variations of amplitudes of counter-propagating pulses in a standing-wave laser cavity is proposed. Proposed model is based on the transport-type equations for the envelopes of oppositely running pulses, spatial discretization along the cavity axis, and calculation of temporal variations both electric field amplitude and active media polarization/inversion at these points.
Nucleation in plasticized polymers as the first stage of temperature- or pressure-mediated synthesis of highly porous polymeric matrices is the key factor affecting the structural properties of synthesized matrices. Accordingly, quantification of growth/collapse processes in the ensembles of pore germs during their evolution is of importance for the characterization and control of the morphological and functional properties of matrices. Additionally, analysis of the growth/collapse kinetics for single pore germs allows for evaluation of the physical-chemical properties (the surface tension, the mass fraction of plasticizing agent in the polymer) depending on the external conditions. In this work, the robust image analysis procedures for quantitative description of the pore evolution on the base of video-reflectometry data are discussed. Experimental results obtained in the case of supercritical/subcritical foaming of polylactides are presented.
The results on the low-frequency photo-conductivity of the thin randomly inhomogeneous WO3 layers are presented. The layers were formed using deposition of water-suspended WO3 micro-particles onto the glass substrates with flat interdigital electrode systems. The wavelength-dependent photo-conductivity was analyzed in the spectral interval covering the edge of the fundamental absorption band (from 440 nm to 520 nm). The estimated Urbach energy of the examined system occurred equal to ≈ 0.13 eV at 308 K.
The interpretation of OCT signals from layered strongly scattering media in the form of the sum of a diffuse and lowstep- scattered components is discussed. It is shown that when the latter component dominates over the diffuse contribution, the depth distribution of the backscattering efficiency can be recovered using the detrending of exponential attenuation of the OCT signal. The feasibility conditions for such detrending are discussed. Examples of experimental verification of this approach are presented.
The DC conductivity of thin random layers of anatase nanospheroids deposited onto the insulating substrates with interdigital electrode systems was experimentally studied using pulse-periodic laser irradiation near the edge of the fundamental absorption band of anatase. Evaluation of the conductivity slew rate at the beginning of laser irradiation depending on the laser wavelength was used for estimation of the Urbach energy of the examined system at various temperatures. Obtained results are compared with the previously reported data relating the Urbach energy of the densely packed ensembles of anatase nanotubes at room temperature.
KEYWORDS: Optical coherence tomography, Skin, Backscatter, Reflectometry, Pathology, Signal attenuation, Signal processing, Data processing, Signal detection, In vivo imaging
The main objective of our study was to identify and recover the depth distributions of the backscattering efficiency in macroscopically heterogeneous stratified media. The recovery technique is based on analysis and processing of the backscattering response of an examined medium in the case of its low-coherence reflectometric probing. In our case, the commercially available swept-source OCT system was applied as the instrument for low-coherence reflectometry. The discussed technique was applied to characterization of in-vivo human skin in the normal state and after optical clearing.
We consider the practical realization of a new optical probe method of the random media which is defined as the reference-free path length interferometry with the intensity moments analysis. A peculiarity in the statistics of the spectrally selected fluorescence radiation in laser-pumped dye-doped random medium is discussed. Previously established correlations between the second- and the third-order moments of the intensity fluctuations in the random interference patterns, the coherence function of the probe radiation, and the path difference probability density for the interfering partial waves in the medium are confirmed. The correlations were verified using the statistical analysis of the spectrally selected fluorescence radiation emitted by a laser-pumped dye-doped random medium. Water solution of Rhodamine 6G was applied as the doping fluorescent agent for the ensembles of the densely packed silica grains, which were pumped by the 532 nm radiation of a solid state laser. The spectrum of the mean path length for a random medium was reconstructed.
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