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Experiments on testing long-term stability of metrological parameters of the CLWS-300 model laser pattern generator used in the technological process of production of goniometric equipment have been carried out. It is shown that the CLWS-300 model laser pattern generator retained the ability to reproduce its indicators practically unchanged over an interval of 18 years.

A coherent fiber optic transmission system for OFDM signals is considered. The channels are formed using spectrally efficient modulation formats - QPSK and M-QAM. It is shown that the nonlinear phase noise arising in the optical path is converted into the amplitude noise and, after mixing with the noise of optical amplifiers, leads to a decrease in the signal quality index. Evaluation formulas are given for determining the noise immunity of channel signals using the Q-factor.

The Fraunhofer diffraction phenomena in coherent light on an extended object of constant thickness in the form of a volumetric asymmetric edge with a bevel and a flat reflecting (gray) inner surface of the object, characterized by the modulus of the amplitude coefficient of light reflection and the phase shift in the reflected wave, are investigated using the model of equivalent transparencies. It is shown that the field in the far zone can be represented in the form of two components: transmitted and reflected, the former corresponding to diffraction of light at an absolutely absorbing asymmetric edge, and the latter describes diffraction phenomena at a volume structure in the form of a biplanar slit illuminated by a plane light wave. On the basis of a constructive approximation of the Fresnel integral function, an expression for the spectrum of the object is obtained in analytical form, which allows studying the behavior of fields in the far-field zone. It is shown that, in the case of a large object obliqueness, the main contribution to the field is given by the reflected component. Methods of determining the geometric parameters of the object by measuring the position of the central maximum of the reflected component and its effective width are proposed.

The paper presents experimental data on phonon and optical properties of (111)-oriented GaAs nanowires on a gold substrate studied by means of Raman scattering and photoluminescence (PL). The structural parameters of the nanowires are determined by atomic force and scanning electron microscopy (AFM and SEM, respectively). In the micro-Raman and micro-PL spectra of a single GaAs nanowire, phonon modes of GaAs and their overtones up to the third order and an exciton photoluminescence band are observed. In the micro-PL spectra, anisotropy of the PL intensity in nanowires is revealed, and the maximum/minimum signal is observed when the polarization vector is directed along/across the wire. Nano-PL maps of a single GaAs nanowire with a spatial resolution of 20 nm are obtained, which is significantly smaller than the diffraction limit. Plasmon enhancement of the near-field exciton nano-PL in the vicinity of the metallized tip of the AFM microscope is detected.

Under ultra-high vacuum conditions, epitaxial and polycrystalline films of iron (Fe), chromium (Cr), and calcium (Ca) silicides of various thicknesses (from 3.2 nm to 380 nm) are grown on silicon and sapphire substrates by three methods (solid phase epitaxy (SPE), reactive epitaxy (RE), and molecular beam epitaxy (MBE)). The crystal structure and matching with the silicon lattice are determined for them using the X-ray diffraction (XRD) method. A comparative analysis of Raman spectra (RS) and far-IR spectroscopy spectra shows that films of semiconductor silicides have the maximum intensity of Raman peaks, and the detected shifts in their positions are caused by distortions in the silicide lattices. It has been established that the intensity of Raman peaks in films of iron and chromium monosilicides at a fixed laser excitation wavelength (λ = 628.3 nm) and a power of 3.4 mW decreases with decreasing film thickness, which leads to their complete disappearance at a thickness below 10 nm. Chromium trisilicide films are grown on single-crystal sapphire, which makes it possible for the first time to detect Raman-active phonons at 214.3 cm^-1 and 273.1 cm^-1 at λ = 488 nm and a power of 0.42 mW. The studied films of transition metal monosilicides are of significant interest from the viewpoint of the prospects for their use as materials for thermoelectronics and spintronics, and systematic information on Raman-active and IR-active phonons will allow rapid determination the phase type formed immediately after film growth.

The spectral characteristics of optically detectable magnetic resonance (ODMR) are investigated for negatively charged nitrogen-vacancy (NV^-) centers in synthetic diamonds and nanopillars on their surface formed by a Ga⁺ focused ion beam (FIB), when lower spin sublevels are populated with the microwave radiation in 0-20 G magnetic fields. Both a significant decrease in the gyromagnetic ratio and the quenching of luminescence from the NV^- centers inclined to the nanopillar axis are revealed due to residual defects and stresses created by them.

Here we propose the use of photopolymer stereolithography to create millifluidic devices for spectroscopic studies. The efficiency of the approach is demonstrated by an example of the development of a millifluid cuvette for studying single mouse oocytes using Raman scattering under conditions of a varying composition of the surrounding solution. It is shown that using the “sandwich” cuvette designallows Raman measurements from samples inside the cuvette, despite the intense signal from the material from which the cuvette is made.

A method is proposed for determining the orientation of the pore direction in metal-organic frameworks from the spectra of polarized Raman scattering. The method uses the sensitivity of the intensity of the Raman lines to the geometry of light propagation in the crystal. The efficiency of the method is demonstrated on DUT-8 (Ni, Co) crystals. The interpretation results are interpreted by analyzing the symmetry and direction of vibrations within the framework of periodic calculations of the electron density functional theory. The joint approach makes it possible to describe the vibrations and find the main orientation of the crystal, which is collinear to the direction of the pores. The knowledge of the pore orientation is necessary for solving adsorption problems and creating complex multicomponent materials based on metal-organic framework compounds.

A new method for generating laser radiation without population inversion in the «red» wing of the D₁ line of alkali metal atoms under resonant absorption of broadband radiation from pump laser diodes at the D₁ transition has been theoretically investigated. The reason for the occurrence of laser generation is the fact that the probability of stimulated emission in the red wing of the spectral line exceeds the probability of absorption if the uniform broadening due to the interaction of active particles with the buffer gas significantly exceeds the natural one (at high pressures of the buffer gas). Analytical formulas that describe the operation of an alkali metal vapor laser under transverse diode pumping are derived. It has been found that the most promising objects for observing laser lasing without population inversion in the red wing of the D₁ line of alkali metal atoms are cesium atoms. In a sufficiently long active medium (the length of the medium is 50 times greater than its width), the conversion efficiency of pump radiation into laser radiation can reach 57% at a buffer gas pressure of 5 atm, a pump diode radiation intensity of 5 kW/cm², and a half-width of its spectrum of 1 cm^-1. The frequency of laser radiation can be tuned by several tens of cm^-1.

Narrow spectral modes comprising the generation spectrum of a random fiber laser near the threshold are of a great interest in both fundamental aspect and possible applications. The narrow bandwidth, stochastic generation nature, and relatively short lifetime lodge significant issues on the experimental equipment and utilized investigation methods. Possible attitudes for experimental registration and characterization of these modes are discussed in the present paper.