Unstable resonator with high magnification and low output coupling

Abstract

The application of standard unstable resonators does not allow for an independent adjustment of the resonator magnification and the output coupling. Either you get a high magnification together with a high output coupling, or vice versa. Certain laser types, like e.g. thin-disc lasers or chemical oxygen iodine lasers, permit only quite low optimum output couplings. The corresponding low resonator magnification is equal to a poor beam quality. In order to apply unstable resonators with a high magnification also to low gain media an additional mirror surface retroreflects a part of the out coupled radiation back into the cavity. The output coupling is reduced efficiently, whereas the resonator magnification stays high. Accordingly low gain media can be operated with high power extraction in combination with a good beam quality. Numerical and experimental investigations are shown. The experiments are performed with a chemical oxygen iodine laser operating at a wavelength of 1.315 µm and demonstrate the feasibility of this resonator design.