Electric oxygen-iodine laser performance enhancement using larger discharge and resonator mode volumes

The authors observed 95% enhancement in continuous-wave laser power on the 1315 nm transition of atomic iodine for only a 50% increase in gain length (5.1 cm to 7.6 cm), flow rates, and discharge input power, making use of a large volume 16-mm gap transverse discharge. A gain of 0.26% cm^-1 was obtained and the laser output power was 55 W in a stable resonator with two 5 cm (2-in.) diameter, 0.9970 reflective mirrors. A longer gain length cavity permits use of lower reflectivity resonator mirrors that reduce diffractive spill losses, and thereby extract power from the gain medium more efficiently. The outcoupled power was increased to 92 W by increasing the mirror diameter to 10 cm (4-in.), demonstrating that significantly higher power was available in the electric oxygen-iodine laser gas flow which could be extracted by tailoring the cavity design. Two 4-mirror folded resonator configurations using 5 cm optics were also demonstrated, a stable "Z-resonator" with a z-shaped optical path having six roundtrip passes through the gain medium, and a stable "X-resonator" having four roundtrip passes through the gain medium. The best measured outcoupled powers for these folded designs were 102 W and 109 W for the Z-resonator and X-resonator, respectively. Continued expansion of the operating envelope to higher flow conditions, pressures, and gain length of the laser cavity, plus the addition of an iodine pre-dissociator discharge are expected to provide significant increases to the gain and laser power. The results presented herein represent more than two orders of magnitude improvement in gain and laser power since the initial demonstration in 2005.