“Nanoscale physics”
Temperature dependence of the loss coefficients in the formation of laser-stimulated nanostructures
L.V. Shmeleva, A.D. Suprun, S.M. Yezhov, V.V. Datsyuk
Department of Theoretical Physics, Faculty of Physics, Taras Shevchenko National University of Kyiv. Volodymyrska Street, 64/13, Kyiv-01601, Ukraine. 
E-mail: lshmel@univ.kiev.ua 

A numerical simulation of the formation of a nano-crater on a solid surface during powerful laser processing was performed. The theoretically derived earlier [1] system of two interconnected differential equations for the dynamics of the crater form and surface pressure underlies the problem under consideration. This system describes a process of high precision laser processing without a melt formation. It contains the phenomenological parameters  and , which are the optical and thermal loss coefficients for the initial flow when it reaches the interface. In numerical modeling, these coefficients were considered constant and took values in the range from 0 to 1. The performed calculations determine the pressure changes in the process of crater formation, depending on the parameters of the irradiated material and radiation parameters.
Also, a theoretical improvement of the model was carried out. The possibility of a more accurate determination of the parameters  and  is shown. Based on studies on heating the irradiated surface [2], the dependence of the parameter  on the temperature of this surface was established. It is proved that the coefficient L with a high degree of accuracy is determined by the equality: . It was found that during the pulse, with increasing temperature, the parameter  decreases in time. That is, heating the irradiated surface weakens the optical loss of flow and increases thermal one. A comparative numerical analysis of the improved model with previous calculations is carried out.

1.	L.V. Shmeleva, A.D. Suprun, S. M. Yezhov. Simulation of the Formation of a Surface Nano-Crater Under the Action of High-Power Pulsed Radiation. // Springer Proceedings in Physics book series (SPPHY, volume). 2019. -221 chap. 34. -P 505-515. 
2.	L.V. Shmeleva, A.D. Suprun, M.A.Razumova The influence of bulk absorption of substance on the threshold of destruction by the intensive pulse of electromagnetic radiation. // Functional materials. -2011. -18, N2. –P 237-243.