Wavefront reproduction by stimulated Brillouin and Raman scattering

Abstract

Experimental investigations were made of the wavefront reproduction process (WFR) by backward stimulated Brillouin scattering (SES) and backward stimulated Raman scattering (SRS) in CS2 with a linearly polarized ruby pump beam. The experimental studies were carried out as a function of the pump power into the cell, the diameter of the optical waveguide, the length of the optical waveguide, and the frequency shift, Delta vr,b, between the pump and backscattered beams for both CS2 and C7H6O. Photographic records comparing the pump beam with the backscattered SES and SRS beams were obtained over several orders of magnitude of exposure and quantitative measurements of the percentage of nonreproduced radiation in the backscattered beams were made. In all of the cases studied there was a high degree of replication observed between the SBS and pump beams using both non-Gaussian and near-Gaussian incident laser profiles. In all of the cases studied the efficiency of the WFR process by backward SBS was better than 85% and it improved as the pump intensity was increased and the frequency shift, Delta vb', was decreased. Neither the diameter nor the length of the optical waveguides utilized in these experiments appeared to significantly influence the efficiency of the WFR process by backward SBS. The results obtained for WFR by backward SRS were somewhat different than those obtained for SBS. In contrast to the SES results, a significant deterioration in the quality of the replicated SRS beam was observed as a function of the diameter and length of the optical waveguide used, and the efficiency of the WFR process by SRS decreased as the cross-sectional area and length of the waveguide were increased. It was also observed that the quality of the WFR process by backward SRS was influenced by the profile of the incident laser beam. As for the case of SES, the efficiency of the WFR process by SRS improved as the pump power into the cell was increased and the frequency shift, Delta vr, was decreased.