Large thermal nonlinearities and spatial self-phase modulation in SrxBa_1−xNb_2O_6 and BaTiO_3 crystals

We find strong optical nonlinearities in Sr(x)Ba(1-x)Nb(2)O(6) (x = 0.61 and x = 0.75) and in BaTiO(3) crystals caused by thermally induced changes of the refractive indices. This gives strong spatial self-phase modulation and self-focusing of Gaussian light beams and light-induced birefringence. The light intensities are of the order of 10(2)-10(3)m W/mm(2), and the time response of the effect is of the order of milliseconds.