Stimulated thermal scattering induced by two-photon absorption and experimental observation of genuine stimulated brillouin scattering in the near-ultraviolet region

Some of the experimental measurements of the frequency shift and phase-conjugation fidelity gained from previous studies of stimulated scattering (SS) of nanosecond (5 divided by 10 ns) near-ultraviolet (uv) (lambda = 193 divided by 351 nm) laser pulses in liquids (hexane, heptane, and others) are found to disagree with the theory of SS, which takes into account only the linear (single-photon) light absorption. To resolve the inconsistency, SS of XeCl excimer laser radiation (lambda = 308 nm) with the duration of 8 ns in liquid hexane is investigated experimentally. A theoretical analysis of the results obtained revealed three nonlinear optical phenomena induced by the heating due to two-photon absorption: stimulated thermal scattering (two-photon STS-2), phase mismatch for stimulated Brillouin scattering (SBS), and phase self-modulation. The experimental SS spectrum contains two additional lines - a two-photon STS-2 line and a genuine SBS line in the near-uv region.