Phase conjugate mirrors

Phase conjugate mirrors are attractive devices to improve the beam quality of lasers. At first, the fundamental properties of phase conjugate mirrors (PCMs) are summarized and a basic mathematical description is given. Degenerate four-wave mixing (DFWM) facilitates phase conjugation of weak signals and their amplification at the same time, but requires additional pumping beams. In contrast, self pumped phase conjugation is achieved by stimulated Brillouin scattering (SBS) in appropriate media. Liquids and gases of high purity as well as solid materials like silica fibers can be used with high efficiency. Solid-state laser systems with average output powers up to 500 W have been equipped with SBS phase conjugate mirrors to compensate for phase distortions in active media.