Resonances in BSO with frequency shifted input beams

In this publication we report experiments with a frequency modulated offset frequency, which illustrate in which situations the problem may be considered linear, and in which it may not. Surprisingly we find, that even in the region of subharmonic generation, the space-charge field of the primary grating is basically a harmonic function with only a small content of higher harmonics, i.e., the space-charge field is basically a linear function of the incident optical intensity. The strongest nonlinearity occurs at or near the fundamental resonance in the space-charge field and at very low offset frequencies. We also report how resonances, forced by even a weak modulation of the frequency detuning may cause the suppression of the subharmonic generation.