A device and corresponding method for optical phase conjugation using a stimulated Brillouin scattering (SBS) medium and resulting in a reduction in the (SBS) threshold level. An incident light beam is brought to a first focus in the SBS medium, and light transmitted through the first focus is brought to a second focus in the SBS medium. Light transmitted through the second focus is brought to a third focus, and so forth through N foci in the medium. The effective SBS threshold level is inversely proportional to the number of foci N, which may be located in separate SBS cells, or may be in a single cell through which multiple passes are made by means of appropriate reflective optics. Laser sources operating in multiple longitudinal modes are handled by spacing the foci at an intergral multiple of the laser resonant cavity length.