Stimulated Brillouin Scattering in the Off-axis Resonator

It has been shown recently that stimulated Raman radiation can be built up in the off-axis direction using a resonator the axis of which is rotated from the axis of the ruby laser resonator.'S3 The stimulated Brillouin scattering which has been found by Chiao, Townes, and Stoicheff4 shows a characteristic which is different from that of the stimulated Raman scatterings: the stimulated Brillouin scattering was observed even in the direction perpendicular to the incident laser beam when the active medium was placed outside the ruby laser resonator. Thus it is interesting to investigate the possibility of building up the stimulated Brillouin radiation in the off-axis resonator. The spectrum of the output of the off-axis resonator was studied with the experimental arrangement shown in Fig. 1. The lens, iris, and FabryPerot interferometer were removed in order to investigate the far field pattern of each component. Benzene and carbon disulfide were chosen as typical and exceptional liquid samples, respectively. The results are shown in Fig. 2. When the carbon disulfide cell was inserted in the off-axis resonator, the coherent radiation at approximately the same wave length as the incident laser beam was found to be built up at an exciting power slightly higher than the threshold exciting power of the first stimulated Raman Stokes line. The angular divergence was measured to be a few milliradians, which was the