EXCITATION OF HIGHER SPATIAL HARMONICS BY A MOVING LIGHT PATTERN IN SILLENITES

We investigate numerically the dependence of higher harmonics of the s pace-charge field on the detuning frequency between the pump waves, wh ich form a running interference pattern. Bistability and hysteresis of harmonics are predicted for a contrast of the interference pattern m greater than or similar to (0.25-0.3). For contrasts m similar or equa l to 1 and small detuning frequencies we show the existence of a narro w resonance, connected with the nonlinear excitation of a slowly decre asing sequence of spatial harmonics, For experiments we use a BSO crys tal in the optical configuration which avoids nonlinear optical distor tions. The experimental data show good qualitative agreement with theo ry.