Ring laser cavities

A ring laser, comprising:

• a cavity;
• a source laser emitting a wide diverging pattern of polarized radiation into the cavity of the ring laser, the source laser being a device that is effective to emit a wide pattern of polarized radiation with a wide-lobed far field distribution;
• routing means located in the cavity near the source laser for routing an angular portion of the wide pattern of polarized radiation in a predetermined direction;
• a Faraday rotator for rotating polarization direction of radiation;
• the Faraday rotator being located in the cavity of the ring laser;
• a half-wave plate for rotating polarization direction of radiation;
• the half-wave plate being located in the cavity of the ring laser;
• the routing means and the Faraday rotator and the half-wave plate being located in an optical ring path in the cavity so that radiation can propagate around the path and pass from the routing means to and through the Faraday rotator and to and through the half-wave plate;
• the routing means and the Faraday rotator and the half-wave plate in conjunction with the source laser allowing radiation to propagate in only one direction in the ring path in the cavity by causing the radiation polarization in that direction to be correct for maximum amplification by the source laser when the polarized radiation is routed from the routing means to the source laser via the Faraday rotator and the half-wave plate, while causing the radiation polarization to be such that it allows minimum gain for radiation propagating in the ring path in the cavity in the opposite direction to the one direction;
• optical means including a spatial filter and a power splitter located along the ring path to filter polarized radiation propagating along the ring path and to split radiation from the radiation propagating in the ring path;
• the Faraday rotator, the spatial filter, and the power splitter being located along the ring path being arranged in serial fashion so that radiation routed from the source laser by the routing means can return to the source laser after passing through the spatial filter, the power splitter, and the Faraday rotator;
• the Faraday rotator rotating the polarization of the radiation emitted by the laser source and assuring propagation of the radiation in the one direction around the ring path because the polarized radiation on passing through the Faraday rotator changes its polarization direction so that on returning to the source laser the polarized radiation returning to the source laser has a polarization matching the polarization of the radiation emitted by the source laser;
• the power splitter being located on the ring path where the power splitter serves as a radiation coupling means for coupling some of the radiation out of the ring path while passing some of the radiation along to the source laser;
• the radiation passing through the Faraday rotator and the spatial filter and the half-wave plate being injected into the source laser with a polarization that assures emission of radiation in a narrow far field lobe by the source laser as a result of suppressing broad lobed radiation of the polarized radiation emitted by the source laser through interaction of the injected radiation with the source laser.