RESONANT 2-WAVE MIXING OF OPTICAL BEAMS BY REFRACTIVE-INDEX AND GAIN GRATINGS IN INVERTED ND-YAG

It is shown experimentally that a weak optical signal in a Nd:YAG ampl ifier can have an extraordinarily large gain that is due to transient coherent nonlinear interaction with a strong laser beam. The effect is explained by the diffraction of the strong beam on the dynamic refrac tive-index grating induced in the interference field of the interactin g optical waves and caused by the difference of polarizability of the excited and the unexcited Nd3+ ions. The numerical calculation confirm ed the energy transfer from the strong beam to the weak one owing to t he predominance of diffraction efficiency of the refractive-index grat ing over the gain grating in an inverted laser crystal. The investigat ions give the estimation of the ratio of the real and the imaginary pa rts of the resonant susceptibility of Nd:YAG at 1064 nn in the range 2 -3. (C) 1998 Optical Society of America [S0740-3224(98)00408-1] OCIS c odes: 190.7070, 140.3530.