Performance of a Modified Negative Branch Unstable Resonator

Abstract

Far field deployment of high power chemical oxygen iodine laser (COIL) affords optimally adapted resonator architectures. Such resonators shall enable high brightness operation. The different resonator concepts suffer from the low gain medium and the rectangular geometry typical of COIL. Even full exploitation of the laser active medium yields small outcoupling fractions and in consequence small magnifications for unstable resonator design. Additionally, the realization of suitable aspect ratios for the output aperture is difficult. An off-axis modified confocal negative branch unstable resonator (MNBUR) is recommended for high power COIL. For first verification tests, such a resonator is especially designed and coupled to a medium-sized COIL. Near field and far field characteristics are measured and compared to the theoretical predictions. The results and experiences gathered at the 10 kW-class DLR-COIL are encouraging to recommend MNBUR as a well suitable resonator for tactical COIL systems.