# Optics and spectroscopy. Laser physics

## A Hybrid Approach in Modeling of Statistical Characteristics of Multiple Scattered Light

**Background and Objectives:** A hybrid approach to modeling of the statistical characteristics of multiple scattered light in application to optical probes of random media is considered. The approach is based on recovery of the probability density of path lengths for partial components of a scattered light field in a probed medium using approximate analytical methods or the numerical simulation.

## Methods of Autodyne Interferometry of the Distance by Injected Current Modulation of a Semiconductor Laser

**Background and Objectives: **Two methods of distance interferometry for two types of wave modulation of laser radiation have been presented. The methods of triangular and harmonic wave modulation of a signal have been described. The advantages of the triangular wave modulation method in combination with the use of the frequency of the self-mixing signal spectrum, as well as the advantages of the harmonic wave modulation method in combination with the use of the amplitudes of the self-mixing signal spectrum have been shown.

## Intermolecular Interaction in Two-component Compounds of Nanodiamonds and Doxorubicin

**Background and Objectives:** Detonation nanodiamond (ND) is one of the most promising materials for targeted drug delivery – one of rapidly developing areas of modern chemistry, pharmacology and medicine. Wide possibilities of surface modification and advantageous dimensions make nanodiamonds very attractive objects for using in the drug delivery process. A number of studies have shown that therapeutic efficacy of drugs is enhanced and their toxicities may be attenuated with immobilization on the enriched ND. There are a lot of drug immobilization methods on ND surfacy.

## Optical Absorption and Raman Scattering in Doped Crystals TlGaSe2 and TlInS2

Background and Objectives. The TlGaSe2 and TlInS2 monocrystals are the А3В3С6 2 type ternary semiconductor compounds. Studies of TlGaSe2 and TlInS2 materials are carried out quite intensively due to the uniqueness of their optical and electrophysical properties and significant prospects for their practical use. At the same time, information about the effect of specific doping impurities on the properties of such materials is insufficient and often contradictory.

## Discrete-Eigenvalue Multiplexing for Soliton Fiber-Optic Communication Links

Background and Objectives: The nonlinear Fourier transform gives a powerful tool to analyze fiber-optics solitons. The solitons are described by a discrete set of eigenvalues of two coupled differential equations, which gives the nonlinear Fourier transform. Using the discrete eigenvalues for optical signal coding can increase the signal-to-noise ratio and reduce the effect of fiber nonlinearity. In the present paper an all-fiber-optics method is proposed to modulate the discrete eigenvalues.

## Mathematical Modeling of Lihgt Transfer in Low-Coherence Reflectometry of Random Media

Background and Objectives: The mathematical model of stochastic interference of spectrally selected fluorescence radiation in multiple scattering random media is considered. The expressions for the normalized second- and third-order moments of spatial intensity fluctuations of detected probe light are derived. The developed model establishes the relationships between the normalized second- and third-order statistical moments of the intensity fluctuations of detected probe light and the probability density function of the pathlength differences of fluorescence radiation in probed media.

## Application of Dynamic Light Scattering and Absorption Spectroscopy to Studies of Systems with Colloidal Gold Nanoparticles + DNA

Background and Objectives: The dynamic light scattering (DLS) method is widely used to evaluate the particle size distributions. However, DLS is not free of serious drawbacks. For a fast approximate estimation of the average size of colloidal gold nanoparticles (AuNPs) within the range of 15–100 nm reasonable results can be obtained with using the absorption spectroscopy. We discuss the advantages and drawbacks of DLS, transmission electron microscope (TEM), and absorption spectroscopy in gold nanoparticle sizing.

## Dynamic Light Scattering Method in Studies of Silica and Gold Nanoparticles

Background and Objectives: It is well known, that uncritical use of the dynamic light scattering (DLS) method may give unacceptable results for the volume or number distributions of particles as compared with transmission electron microscopy (TEM) data. The purpose of this study is to investigate application of the DLS method for determining the size of colloidal silica and gold nanoparticles and to compare results of three methods: DLS, TEM, and absorption spectroscopy (see next paper).

## Optical Soliton Inelastic Interacitons in Nonlinear Schrödinger Equation with Variable Coefficients Model

It is shown that in systems described by nonlinear Schrödinger equation with variable coefficients, interaction of two solitons can carry an inelastic character. Inelastic collision solitons can lead to changes in their group velocities, amplitudes and durations. We consider some particular cases related to the separation of the soliton pair and formation of a bound state of two solitons. In the applied aspect these phenomena can be used to control the soliton interaction in optical fiber communications.

## Methods of Digital Holography in Interference Microscopy of Reflective Object in Partially Coherent Light

The theoretical foundation of the possibility of using the interference microscopes with extended and frequency broadband light source for recording digital holograms of microscopic objects, reconstruction and visualization of phase images is presented. Numerical procedure for processing of spatially localized digital holograms of the focused image in a partially coherent light are considered. Results of experiments on digital holographic microscopy of biological objects in a partially coherent light with Linnik interference microscope are shown.