Influence of thermal defocusing on the quality of phase conjugation of Gaussian beams by stimulated Brillouin scattering

A numerical investigation is reported of the influence of the thermal self-interaction of a Gaussian pump beam on the quality of phase conjugation by stimulated Brillouin scattering (SBS). A laser pulse is assumed to be sufficiently long to apply the equalised pressure approximation in calculating the acoustic field. All the calculations are carried out in a three-dimensional formulation for focused beams making use of an approximation linear in respect of the pump intensity. It is confirmed that the growth of thermal perturbations increases the SBS threshold and lowers the phase conjugation quality. A comparison of the calculated and published experimental results shows that they are in satisfactory quantitative agreement.