Injection-locked unstable laser

Abstract

A laser system for producing a laser beam in an unstable resonator whose spatial and temporal characteristics conform with those of a laser beam from a stable resonator. The laser system includes three reflectors, an optical switch and a laser gain medium positioned within an optical propagation path extending between the optical switch and the third reflector. The optical switch selectably exposes either the first or the second reflector to the aforesaid propagation path, the first and second reflectors being designed to form, in combination with the third reflector, a stable and an unstable resonator, respectively. In operation, the optical switch initially is set so as to include the first reflector in the laser resonator, thereby forming a stable resonator which produces a beam of laser light. A short time thereafter, the optical switch changes states so as to substitute the second reflector for the first, thereby forming an unstable resonator. The light from the stable resonator serves as 'seed radiation' for the unstable resonator, so that the unstable resonator produces a light beam having the same spatial and temporal characteristics as the light from the stable resonator. The system permits the use of a single laser gain medium for both resonators, and it overcomes the need for holes or other surface discontinuities in the resonator reflectors which can degrade the quality of the laser's output beam.