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AbstractThe angular distributions of various spectral components of terahertz radiation generated by filament plasma are measured in a wide range of numerical apertures NA of the laser beam from 0.003 to 0.1. It is shown that propagation angles of terahertz radiation are inversely proportional to the square root of the terahertz frequency. It is shown that an increase in the numerical aperture of the laser beam leads to an increase in propagation angles of terahertz radiation in the entire range of observed frequencies.

In this paper, we measure broadband terahertz spectra from a single 744-nm filament produced in tight, medium, and loose geometrical focusing conditions. Terahertz spectra are measured using interferometer coupled to a helium-cooled bolometer avoiding any cutoff frequencies. Based on THz spectrum maximum position and spectral width, we estimate electron-heavy particle (neutrals and ions) collision rate. Numerical simulations are performed using the state-of-the-art model of unidirectional femtosecond pulse propagation and convergence/divergence of optical radiation at large angles.

Directivity patterns of terahertz emission by femtosecond laser filament plasma in air after radiation propagation in hollow tubes with metal and dielectric (polypropylene) walls are experimentally studied. It is shown that narrow directed radiation can be obtained using quasi-waveguide propagation in a tube with dielectric walls, while the terahertz pulse duration is not affected significantly.

Propagation of a tightly focused high-power ultrashort laser pulse in an optical medium is usually substantially influenced by the medium optical nonlinearity that can noticeably affect the laser pulse parameters around the nonlinear focus and lead to unavoidable and often undesirable spatial distortions of the focal waist. We present the results of our experimental study and numerical simulations on a femtosecond Ti-Sapphire laser pulse propagation in air under different spatial focusing. We concentrated our study on spectral-angular and spatial pulse transformations under different focusing regimes, from linear to nonlinear one, when pulse filamentation occurs. For the first time to the best of our knowledge, we found the laser pulse numerical apertures range,namely, from NA=0.002 to 0.005 (for laser pulse energy of 1 mJ), where the laser pulse distortions both in frequency-angular spectrum and pulse spatial shape are minimal. By means of the numerical simulations, we found the threshold pulse energy and peak power in a wide range of focusing conditions, within which a transition between the linear and strongly nonlinear laser pulse focusing in air takes place. This energy limit is shown to decrease with pulse numerical aperture enhancement. Our findings identify the laser pulse numerical apertures and energy adequate for getting a maximum laser intensity with a good beam quality around the focal point suitable for various laser micropatterning and micromachining technologies.

The critical power of self-focusing in the air for ultrashort UV laser pulses stretched due to dispersion from 90 up to 730 fs was experimentally measured. It was shown that the pulse duration enhancement due to its propagation in condensed media within above mentioned time-range leads to almost linear decrease of self-focusing critical power. It was also observed that when the pulse peak power exceeds the critical one, the maximum of linear plasma distribution along the UV laser filament does not shifted in the direction opposite to the laser pulse propagation as in the case of IR laser filament, but remains at the geometrical focus.

We proposed remote spectroscopy approach consisted in luminescence light utilization. During interaction with different targets ultrashort UV laser pulse generates broadband spectrum light, which can be applied for remote spectroscopy purposes. We selected appropriate target materials to cover required spectral range from 300 to 600 nm and provided an example of spectrum reconstruction of known material. Obtained spectra are in a good correlation with calculated ones.

An influence of plasma channel created by a filament of focused UV or IR femtosecond laser pulse (=248 nm or 740 nm) on characteristics of other plasma channel formed by a femtosecond pulse at the same wavelength following the first one with varied nanosecond time delay was experimentally studied. A dependence of optical transparency of the first channel and plasma density of the second channel on the time delay was demonstrated to be quite different for such a double UV and IR femtosecond pulses.

Filamentation of linear polarized ultrashort laser pulses in non-axisymmetric optical schemes with preferential directions to the optical axis in dependence on the beam orientation was experimentally studied. Our experiments demonstrated strong influence of a laser beam orientation on self-focusing of the beam and plasma generation during filamentation. Maximum of linear plasma density generated by an astigmatic laser pulse was different in both meridional and sagittal foci and depended on the beam orientation. A difference of linear plasma density was observed in the case of superposition of two parts of the laser beam going through a two-hole diaphragm depending on the beam orientation and through a slit for collinear and normal slit orientation relative to the beam orientation. Laser pulses in IR and UV wavelength domains led to similar result.

AbstractThe biological properties of a new gene-activated osteoplastic material based on chitosan sponges impregnated with plasmids with the gene BMP-2 for bone morphogenetic protein-2 have been studied. The optimal conditions for the transfection of multipotent mesenchymal stromal cells with TurboFect reagent are selected. It is shown that the in vitro osteoinductive effect of the developed material is associated with an increase in the expression of osteogenic markers in mesenchymal stromal cells. The designed gene-activated material can be used to repair bone defects.

Objective: to assess the impact of coronavirus (COVID-19) on the youth labor market in the context of the spread of precarization processes in employment.Methods: qualitative methods were used to analyze labor market institutions, together with in-depth interviews and interpretative analysis of actors’ discourses.Results: the COVID-2019 pandemic posed new challenges to the economy and contributed to the active development of new employment formats and employer-employee interaction in the form of informal employment, freelance platforms, and precariat development. The article considers the features and risks of informal and non-standard employment. Based on the labor market analysis, we determined the impact of the pandemic on working conditions, inequality growth and the increasing role of the informal sector. The impact of the crisis on employment conditions for young people with higher education is particularly emphasized. To form the models of students’ behavior under the conditions of labor market instability, the authors conducted in-depth interviews with students and graduates of the Southern Federal University to assess the employment opportunities of university graduates. The characteristics of respondents’ perception of the processes associated with precarization in the context of the COVID-19 pandemic consequences are clarified and specified. Scientific novelty: it consists in the development of theoretical and methodological approaches to the analysis of precarization of youth employment in the context of the COVID-19 pandemic consequences. It is shown that the observed increase of employment precarization is associated with behavioral features caused by dominant behavioral models and distortions in the perception of unstable employment by university graduates in relation to the structural opportunities provided by the labor market.Practical significance: the identified features of employment of the Russian university graduates can be used to develop recommendations for improving the system for monitoring the employment precarization level in the regional labor markets.