Phase conjugation offers a practical, realistic approach for scaling solid-state lasers to high energies and high peak powers with a minimum increase in complexity. The specific approach reviewed in this article involves coherently combining the outputs of multiple parallel amplifiers in a single phase-conjugate oscillator-amplifier configuration. In this configuration, the use of phase conjugation eliminates the phase distortions that would otherwise result from individual amplifiers having different optical lengths. Using this approach, the laser output energy can be scaled well beyond the limits imposed by traditional volume constraints of crystalline laser media. Since an increase in output energy also implies an increase in the energy incident on the phase-conjugate mirror (PCM), the energy scalability of PCMs based on stimulated Brillouin scattering has been actively investigated over the past decade. Practical single-cell PCMS offer somewhat limited energy scaling potential. However, the investigations reviewed in this article show that a series combination of two Brillouin cells can accommodate energies of several tens of joules. Finally, we suggest how future development efforts involving diode-pumped solid-state lasers will also benefit from application of phase conjugation when medium energies or high pulse repetition frequencies are required.
