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During several last decades much attention was paid to the processes that occur in solidstate optical media under the interaction with high-power focused laser radiation. A great number of studies were devoted to the phenomena of optical breakdown, structure changes, stimulated scatterings, generation of hypersonic waves in transparent dielectrics under the action of nanosecond (ns) and picosecond (ps) laser pulses (Manenkov & Prokhorov, 1986; Nelson et al., 1982; Ready, 1971; Robinson et al., 1984; Stuart et al., 1995). Recent interest in these studies was stimulated by the appearance of lasers with femtosecond (fs) pulses (Gordienko et al., 2010; Merlin, 1997; Sakakura et al., 2007). An experimental study of a small region with high pressure and temperature gradients formed in a medium at focusing high-power laser radiation had been performed, as a rule, outside the laser cavity. In our experiment (Basiev et al., 2004), a region with such properties happened to be formed directly in the 2-mirror laser cavity, when Yb:YAG samples were pumped by the focused wide-band (0,89-0,95 ┤m) radiation from a pulsed LiF: F2+ color center laser (ccl). Thus, in contrast to many studies on ytterbium lasers, conditions for generation in Yb-doped samples in this experiment had been distinguished by the very high intensity (over 1 GW/cm2) of the pump, which moreover had a low coherence. Experiments on pumping of Yb-doped and non-doped samples of different optical media (YAG, glass, LiF et al.) by powerful low-coherent radiation from LiF: F2+ ccl were continued in subsequent papers (Bykovsky, 2005, 2006; Bykovsky & Senatsky, 2008a,b, 2010). At intensities I ≥ 1 GW/cm2 interaction of ccl pump radiation with the medium in the focal region was essentially nonlinear. The interaction of ccl pulses with samples was accompanied by excitation of stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS) of pump radiation. The scattering generated hypersonic waves of high amplitude, which were converted into a periodic sequence of shock waves with sharp pressure jumps on their fronts propagating along the direction of pump. Pressure jumps were so large that they caused a phase transition in an optical medium, which was observed near the sample surface in the form of small domains with spatial modulation of the refractive index caused by the interference of hypersonic waves.

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Excitation of Periodical Shock Waves in Solid–State Optical Media (Yb:YAG, Glass) at SBS of Focused Low–Coherent Pump Radiation: Structure Changes, Features of Lasing