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The problem of heating of optical components during the formation of the high-power continuous-wave fiber laser radiation is considered. The results of experimental measurements of heating of optical components made of the domestic quartz glass of the KU-1 brand and yttrium aluminum garnet crystal are presented. The time dependence of the heating temperature of the optical components and their stationary temperature are investigated as functions of the laser radiation power.

Structural–dimensional synthesis of laser variosystems (LVSs) for the formation of output Gaussian beam waist with smooth changes in its position and size according to a given law is considered. Synthesized variosystems can be used in setups and technological complexes with extended functionality: processing of materials, manufacturing of complex spatial configuration parts, moving micro-objects, etc. The method of automated dimensional synthesis of two-component LVSs on different operation principles with constraints on their parameters has been developed using the theory of laser optics. The method allows determining the best dimensional parameters of LVS, and in their absence, options of changing the initial data to obtain the solution of dimensional problem. Application of the method is demonstrated by examples of dimensional synthesis of LVSs of different types and extended functionality.

This paper investigated the diffraction of a Gaussian laser beam on a binary mask and a refractive axicon. The principles of the formation of a zero-order Bessel beam with sharp drops of the axial field intensity edges were discussed. A laser optical system based on an axicon for the formation of a Bessel beam with quasi-uniform distribution of axial field intensity was proposed. In the laser optical system, the influence of the axicon apex did not affect the output beam. The results of theoretical and experimental studies are presented. It is expected that the research results will have practical application in optical tweezers, imaging systems, as well as laser technologies using high-power radiation.

We address the design and mathematical modeling of acousto-optical (AO) system for laser trapping of microscopic particles. We present an approach to theoretical calculation of the shape, intensity and trajectory of the light trap formed by AO deflection system. Theoretical calculation are confirmed by modeling and experiments.

Optical variosystems that form the required diameter of the Gaussian beam waist and perform its smooth longitudinal movement with a constant diameter for laser technologies, processing materials, moving microobjects, etc., are considered. A combined method based on a movable tunable-focus lens for changing the optical characteristics of laser variosystems is proposed. The features and fundamental differences between the laws of transformation of Gaussian beams by optical systems of different structures for the dimensional synthesis of laser variosystems are discussed. Based on these laws and the theory of laser optics, a method for the dimensional synthesis of one- and two-component laser variosystems is developed, an algorithm for their automated synthesis, and an example of calculation are given.

Key theoretical concepts advanced by the Bauman MSTU scientific school 'Zoom lens design' are discussed. These include methods for design of both classical and laser zoom lenses, systems with linear and nonlinear relations between the displacements of components, basics of professor I. I. Pakhomov's theory of generalized parameters, a method of paraxial synthesis of multicomponent zoom systems, a method of aberration synthesis of zoom systems in the approximation of the third- and fifth-order aberrations. The effectiveness of the described methods is illustrated by examples of designing zoom systems with superior optical characteristics.

Optical tweezers use a special class of light beams – the so-called Bessel beams. The field amplitude of these beams is described by the Bessel function of the first kind of a zero order. The traditional method of forming zero-order Bessel beams involves the use of a classical optical element – a conical axicon lens. We designed and assembled an experimental test bench to study the parameters of the Bessel beam formed by the axicon. In the course of experimental studies, it was confirmed that Bessel beam is a diffraction-free beam. In addition, an influence of a divergence of the Gaussian beam at the axicon input on the parameters of the Bessel beam was investigated. The transformation of such a beam by an optical system was considered. It is shown that when the Bessel beam is transformed by an optical system, the principle of similarity of optical fields in the optical conjugate planes is fulfilled. The results of modeling the formation of the Bessel beam by the axicon obtained in this work are consistent with the experimental studies.

Quartz glass KU-1 optical elements heating experimental research results (KU-1 – Russian-made brand) under the influence of radiation of CW powerful fiber laser are presented. The dependences of optical elements maximum temperature from laser radiation power are determined.

On the basis of the scalar diffraction theory, the problem of calculating the characteristics of a laser beam in linear cavities of arbitrary configuration, taking into account the aberrations of the mirrors, is solved. The configurations of cavities in which the aberrations of the mirror surfaces have a significant influence on the characteristics of the formed laser radiation are determined.

This paper presents a modeling approach of a laser varifocal system for longitudinal Gaussian beam waist shifting. The developed approach is based on laser optics theory, which is considered to be classical optics generalized for coherent radiation. A basic optical system, consisting of two components, was developed using this theory. Components have fixed focal lengths and specific movements. An automated modeling algorithm was proposed, and an example was provided in text. Various systems shown in this paper form a Gaussian beam with required waist parameters and provide its longitudinal shifts, which exceed the length of the near-zone of a focused Gaussian beam. Such systems can be used in laser technologies, including micro- and nano-sized objects manipulation.

When designing high-quality optical systems, it is necessary to calculate the real field distribution of the output beam. In this work, the solution of this problem by the method of the scalar theory of diffraction is considered. For calculate the diffraction integral and visualize the results, the software package Mathematica (Wolfram Mathematica) is used. Aberration analysis of laser optical systems and simulation in the program Mathematica of the output field distribution showed a significant distortion of the field distribution and deviation of the spatial beam parameters from the ideal one, described by analytic expressions.

A practical method is proposed and developed for calculating characteristics of the laser beam formed by stable and unstable cavities of an arbitrary configuration.

De-noising of terahertz (THz) pulsed spectroscopy (TPS) data is an essential problem, since a noise in the TPS system data prevents correct reconstruction of the sample spectral dielectric properties and to perform the sample internal structure studying. There are certain regions in TPS signal Fourier spectrum, where Fourier-domain signal-to-noise ratio is relatively small. Effective de-noising might potentially expand the range of spectrometer spectral sensitivity and reduce the time of waveform registration, which is an essential problem for biomedical applications of TPS. In this work, it is shown how the recent progress in signal processing in wavelet-domain could be used for TPS waveforms de-noising. It demonstrates the ability to perform effective de-noising of TPS data using the algorithm of the Fast Wavelet Transform (FWT). The results of the optimal wavelet basis selection and wavelet-domain thresholding technique selection are reported. Developed technique is implemented for reconstruction of in vivo healthy and deseased skin samplesspectral characteristics at THz frequency range.

The present paper is dedicated to studying the accuracy of sample material parameter reconstruction using terahertz (THz) pulsed spectroscopy. The technique for characterizing the material parameters of thin flat samples allowing to take into account multiple wave reflections in a flat have been considered. While transmitting through the resonant sample, THz pulse undergoes multiple reflections, which result in satellite pulses in THz waveform. The accuracy of material parameter reconstruction strongly depends on the number of satellite pulses. We have analytically estimated an impact of satellite pulses on material parameter reconstruction by considering the local linearization of theoretical sample transfer function based on the model of quasi-Fabry-Perot-resonator.

Analysis of experimental results and theoretical studies has confirmed that the free- space propagation and the transformation of a high-power fibre laser beam by an optical system can be described by the theory of laser optics. The need to use the theory of laser optics to develop modern high-performance optical systems of laser processing heads, which form the beam of the high-power fibre laser, is discussed.

This paper presents new experimental and theoretical results for the material parameter reconstruction utilizing the terahertz (THz) pulsed spectroscopy (TPS). The material parameter reconstruction algorithm was realized and experimentally implemented to study the test sample. The algorithm takes into account multiple reflections of THz pulse within the flat sample during the transmission mode measurements. Therefore the samples with small thickness or low refractive index could be studied utilizing the proposed method. In order to estimate the reconstruction accuracy, test sample material parameters, obtained with the TPS, were compared with the results of the same sample studying by the use of the backward-wave oscillator (BWO) spectroscopy. Thus, high reconstruction accuracy was demonstrated.

New experimental and theoretical results for the material parameter reconstruction using terahertz (THz) pulsed spectroscopy (TPS) are presented. The material parameter reconstruction algorithm was realized and experimentally implemented to study the test sample. In order to both verify the algorithm and to estimate the reconstruction accuracy, test sample material parameters obtained with the TPS were compared with the results of the same sample studying by the use of the backward-wave oscillator (BWO) spectroscopy. Thus, high reconstruction accuracy was demonstrated for the spectral range, corresponding to the BWO sensitivity and located between 0.2 and 1.2 THz. The numerical simulations were applied for determining the material parameter reconstruction stability in the presence of white Gaussian noise in TPS waveforms as well as fluctuations in the femtosecond (FS) optical pulse duration. We report a strong dependence of the inverse problem solution stability on these factors. We found that the instabi...

This paper presents a technique of aberrational synthesis of laser optical systems with small wave aberrations for maintaining similarity of the fields when multimode laser beams are being transformed. The minimization of the wave aberrations of laser optical systems is based on the detected connection of its design parameters with the expansion coefficients of the wave aberration. Examples are given of the automatic synthesis of laser optical systems to illustrate the effectiveness and high response rate of the proposed algorithm.