“Nanoscale physics”
Influence of changes in the phase state of the surface and external factors of laser irradiation on the nanocraters formation
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 

Under the influence of powerful laser irradiation, a micro explosion occurs on the solid surface with the formation of a nanocrater and luminous plasma. From the start of the laser action process, the surface actively heated in the local area of the irradiated substance. When the light pressure on the surface and its temperature take critical values, a local phase transition occurs. Phase changes cause the substance ablation and are accompanied by a glow. The substance removed from the surface is a plasma with a complex structure. Later on the flying out from the surface solid and liquid particles (aerosol) affect the degree of laser exposure. To assess the consequences of such an influence, an analytical study of this process was carried out in the work. It was assumed that the aerosol formed near the surface has a complex drops-cluster structure. For this case, approximate piece-wise continuous solutions were obtained during the time of the pulse and after its termination. The obtained solutions include two dimensionless parameters Λ and , which are the characteristics of the interaction of radiation with ablative substance.
Based on these solutions, averaged expressions for pressure and crater function were obtained. Analysis of their behavior is carried out for various values of the parameters Λ and . The quantity Λ is directly proportional to the absorption coefficient of radiation. The parameter  depends exponentially on Λ. Both parameters affect the value of the maximum pressure near the surface at the time of active laser exposure.
Also Λ depends on the frequency of the radiation and the frequency characteristics of the irradiated physical system. In the paper, the influence of the frequency parameter  to the absorption coefficient is studied. The influence of this parameter to the maximum pressure in the process under consideration is analyzed. It is shown that in the case of resonance, aerosol can to put up significant resistance to the laser action and practically stops the nanostructures formation on the substance surface.