Index-of-refraction change in optically pumped solid-state laser materials

Degenerate four-wave mixing measurements were made on several Nd(3+)-doped laser materials by resonantly pumping the Nd(3+) ions. The dominant contribution to the signal under these conditions is associated with the difference in polarizabilities of the Nd(3+) ions in the metastable state versus the ground state. Absolute measurements of the signal strengths imply a laser-induced polarizability change of the order of 0.01-0.05 A(3). The results indicate that, for the case of a single-shot laser amplifier system, the beam distortion induced by this population induced change in the refractive index is comparable with the distortion arising from thermal effects.