Development ultrashort laser pulse technology has had significant influence on laser applications in material processing and modification, medicine, communication and information technologies, and fundamental research. Almost 40 years of experience in research and development in lasers has proven that its effective application is closely related to the progress in development of the physical basis and deeper understanding of the principles of laser–matter interaction. During the past 15 years the focus of these investigations has moved primarily toward subpicosecond pulses and ultrashort laser action. The main results of such action are an extremely short laser pulse duration tp, which is much smaller than the characteristic time of any transformation of absorbed light energy into heat τ, and which elapses before effective expansion of the matter begins. Actually, this means that during a laser pulse only the processes of photoexcitation and fast electron processes, including electron emission, take place.
In spite of the short duration time of ultrashort laser pulse action, a number of instabilities and self-organization processes can be initiated that substantially influence the action dynamics and results. This chapter considers several phenomena of fast-laser-induced instability that are important both for understanding and describing its main features and practical applications. Laser-induced instabilities include fast thermal instability in the electron subsystem of metal under heating by ultrashort laser pulses; formation of periodic surface structures; and electrodynamic instability of field distributions in a transparent dielectric around and inside transparent inhomogenities of refractive index variations. Accordingly, for the mentioned peculiarities of ultrashort laser pulse action, the main consideration is premised by an analysis of nonequilibrium processes of the electrons and the lattice heating during and after action of an ultrashort laser pulse.
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