Narrow-bandwidth unstable resonator laser cavity

An unstable resonator laser cavity providing high power radiation with diffraction limited divergence and narrow bandwidth comprises a gain medium for generating and amplifying laser radiation optically coupled to a reflector via a frequency narrowing element for providing feedback and bandwidth narrowing of the laser radiation traveling between the gain medium and the reflector. A telescopic ring is optically coupled to the gain medium opposing the reflector. The telescopic ring comprises a polarized beam splitter, which transmits a first polarization polarized laser radiation into the telescopic ring traveling in a first direction and reflects a second polarization polarized laser radiation into the telescopic ring in a second direction; first and second rotators for rotating the first polarization polarized laser radiation to provide second polarization polarized laser radiation traveling in the first direction; and lenses for magnifying the second polarization polarized laser radiation traveling in the first direction onto the polarized beam splitter, which reflects the second polarization polarized laser radiation produced by the first and second rotators back into the gain medium. A scraper mirror, located between the gain medium and the reflector, provides the output beam.