High-order optical nonlinearities in saturable absorbers

Transient self-diffraction in Nd:YAG saturable amplifiers

We investigate self-diffraction and multiwave scattering by a nonsinusoidal gain grating induced in a thick laser medium with pulses of duration much less than the population relaxation time. The energies of the transmitted and of the two first-order self-diffracted beams are calculated. Experimental measurements performed in a flash-lamp-pumped Nd:YAG amplifier at lambda = 1.064 microm show good agreement with the theoretical results. A total energy in the two first-order scattered waves of 1.1 mJ is obtained for a total incident energy of 14 mJ.

Nondegenerate two-wave mixing in GdAIO(3):Cr(3+)

We have measured the nearly degenerate two-wave mixing in GdAlO(3):Cr(3+) crystals. In contrast to that in other chromium-doped materials, the signal in this sample arises from a mixed phase absorption grating where the absorption contribution is intensity dependent. The real (n(2)') and the imaginary (n(2)'') parts of the nonlinear index of refraction, the saturation intensity, and the excited-state lifetime are determined. The ratio r = n(2)''/n(2)' changes linearly with the intensity. Owing to saturation, the grating presents anharmonicities that give rise to self-diffracted beams (forward four-wave mixing). For comparison, results are also presented for ruby and alexandrite.