Stabilization of class-B broad-area lasers emission by external optical injection

We theoretically examine the effect of external optical injection on the spatio-temporal dynamics of class-B broad-area lasers. We demonstrate that optical injection can efficiently stabilize the intrinsic transverse instabilities in such lasers associated with both the boundaries of the pumping area and with the bulk nonlinearities of the active medium. Stabilizing action of optical injection is shown to be closely related to the suppression of inherent relaxation oscillations behavior.Comment: 8 pages, 7 figure

Dynamics of fast and slow magnetoacoustic waves in plasma slabs with thermal misbalance

Non-uniformity of the solar atmosphere along with the presence of non-adiabatic processes such as radiation cooling and unspecified heating can significantly affect the dynamics and properties of magnetoacoustic (MA) waves. To address the co-influence of these factors on the dispersion properties of MA waves, we considered a single magnetic slab composed of the thermally active plasma. Using the perturbation theory, we obtained a differential equation that determines the dynamics of the two-dimensional perturbations. Applying the assumption of strong magnetic structuring, we derived the dispersion relations for the sausage and kink MA modes. The numerical solution of the dispersion relations for the coronal conditions was performed to investigate the interplay between the non-uniformity and the thermal misbalance. For the heating scenario considered, it was obtained that the phase speed of both the sausage and kink slow MA waves is highly affected by the thermal misbalance in the long wavelength limit. The obtained characteristic timescales of the slow waves dissipation coincide with the periods of waves observed in the corona. Simultaneously, the phase speed of the fast waves is not affected by the thermal misbalance. The geometry of the magnetic structure still remains the main dispersion mechanism for the fast waves. Our estimation reveals that dissipation of the fast waves is weaker than dissipation of the slow waves in the coronal conditions. The obtained results are of importance for using the magnetoacoustic waves not only as a tool for estimating plasma parameters, but also as a tool for estimating the non-adiabatic processes

Spiral waves in large aperture laser model

Abstract -In this paper spontaneous formation of spiral waves in large aperture laser model has been reported. As a mathematical model the system of Maxwell-Bloch equations has been used. Linear stability and Floquet analyses were done. This analysis allows us to plot a bifurcation diagram and predict a characteristic size of exited spiral waves. Numerical simulations are in good according with theoretical analysis

The Study of Acoustic Perturbations Growth Time in the Orion Bar PDR

В областях фотодиссоциации (ОФД) межзвездного газа могут выполняться условия для появления изоэнтропической неустойчивости. Неустойчивость может привести к формированию ударноволновых структур, параметры которых не зависят от вида начального возмущения, а зависят лишь от свойств самой среды. Данное исследование направленно на численное моделирование распространения структур данного вида в среде с параметрами, характерными для ОФД Барьер Ориона и исследование времени их формирования.Conditions of isentropic instability are able to appear in photodissociation regions (PDR) in the interstellar gas medium. Instability can cause the shock wave forming, the parameters of which do not depend on the initial perturbation type, but depend only on medium properties. This study aims to numerically simulate the propagation of those structures in the medium with parameters, which are common for the Orion Bar PDR and to investigate their formation time.Работа выполнена при частичной поддержке Министерства науки и высшего образования Российской Федерации по государственному заданию для образовательных и исследовательских учреждений № FSSS-2023-0009 и № 0023-2019-0003

Formation of quasi-periodic slow magnetoacoustic wave trains by the heating/cooling misbalance

Slow magnetoacoustic waves are omnipresent in both natural and laboratory plasma systems. The wave-induced misbalance between plasma cooling and heating processes causes the amplification or attenuation, and also dispersion, of slow magnetoacoustic waves. The wave dispersion could be attributed to the presence of characteristic time scales in the system, connected with the plasma heating or cooling due to the competition of the heating and cooling processes in the vicinity of the thermal equilibrium. We analysed linear slow magnetoacoustic waves in a plasma in a thermal equilibrium formed by a balance of optically thin radiative losses, field-align thermal conduction, and an unspecified heating. The dispersion is manifested by the dependence of the effective adiabatic index of the wave on the wave frequency, making the phase and group speeds frequency-dependent. The mutual effect of the wave amplification and dispersion is shown to result into the occurrence of an oscillatory pattern in an initially broadband slow wave, with the characteristic period determined by the thermal misbalance time scales, i.e. by the derivatives of the combined radiation loss and heating function with respect to the density and temperature, evaluated at the equilibrium. This effect is illustrated by estimating the characteristic period of the oscillatory pattern, appearing because of thermal misbalance in the plasma of the solar corona. It is found that by an order of magnitude the period is about the typical periods of slow magnetoacoustic oscillations detected in the corona

New acoustical properties of the non-equilibrium gas with the reversible chemical reactions and the external injection of reagents

Paper presented at the 7th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Turkey, 19-21 July, 2010.The perturbation propagation in the chemically active non­-equilibrium gas mixture with the external volume pumping of the pure reagent is investigated. The external pumping of the pure reagent leads to the displacement of the chemical balance: the stationary values of the reagent concentrations are unequal to its equilibrium values. The stationary non-equilibrium mixture becomes acoustically unstable under certain conditions. The mixture behaviour and its perturbations structure depend on the external pumping of the reagent intensity, the chemical heat effect and rates of the direct and reverse chemical reactions. In the present work, we consider acoustics of such mixtures, mechanisms of the stabilization of the small perturbation growth and construct the shock wave adiabatic curves. A model of Arrhenius chemical reaction rate is used in the numerical results.ej201