Interaction length for optical phase conjugation by stimulated Brillouin scattering: an experimental investigation.

We have investigated experimentally the parameters which govern the effective interaction length at threshold for phase conjugation due to stimulated Brillouin scattering. We found the length to be the shorter of the following parameters: the cell length, 3 times the coherence length or 5 times the Rayleigh range of the input laser radiation. We have also found that the fidelity of the return depends strongly on the coherence length when this parameter is much shorter than the cell length. Results are also presented on fluctuations in fidelity at high power and long pulse lengths.