We show experimentally that counterpropagating laser beams in a Brillouin-active medium are unstable to the growth of intensity fluctuations. The intensities of the transmitted beams are found to oscillate at the Brillouin frequency of the medium, which is equal to 7.7 GHz for our experimental conditions of excitation of carbon disulfide at a wavelength of 532 nm. The depth of modulation is found to be as large as 25%. The threshold for this instability depends on the ratio of the intensities of the counterpropagating beams. The threshold is lowest for the case of equal input intensities and is found to be as much as 33% lower than the threshold for single-beam stimulated Brillouin scattering.
© 1989 Optical Society of America
Alexander L. Gaeta, Mark D. Skeldon, Robert W. Boyd, and Paul Narum, "Observation of instabilities of laser beams counterpropagating through a Brillouin medium," J. Opt. Soc. Am. B 6, 1709-1713 (1989)