Аннотация:Two laser-induced instabilities (deformation-concentration and deformation-thermal) are discussed which make it possible to explain certain experimental results on the interaction of high-power laser radiation with semiconductors and metals: the formation of spatially periodic surface structures with different lattice morphologies in the form of concentric rings; strong nonlinear-optic absorption in semiconductors; and ultrafast (of the order of 10 to the -13th sec) laser melting of semiconductor surfaces. Numerical estimates are given, and a comparison is made with experimental data.