For laser media with large cross-section and low small signal gain neither the stable nor the unstable conventional resonator is an applicable choice. Either the large Fresnel number leads to a multimode operation or the low output coupling ring results in large diffraction effects and therefore in a heavily structured far field. In order to reduce these diffraction effects a modified negative-branch unstable resonator (MNBUR) was introduced. In rotational symmetry the off-axis setup provides an output coupling in the shape of a half ring and is accomplished with the help of a scraper. The shape of this scraper can also be modified to adapt the MNBUR to a rectangular symmetry, whereas the spherical resonator mirrors are kept unchanged. The scraper either takes the shape of a rectangular bracket "[" or of the letter "L". The performance of both scrapers is tested using a chemical oxygen iodine laser (COIL) of the 10 kW class. The results are compared to numerical calculations.

Date Published: 15 November 2010
PDF: 6 pages
Proc. SPIE 7751, XVIII International Symposium on Gas Flow, Chemical Lasers, and High-Power Lasers, 775115 (15 November 2010); doi: 10.1117/12.880946

Published in SPIE Proceedings Vol. 7751:
XVIII International Symposium on Gas Flow, Chemical Lasers, and High-Power Lasers
Tanja Dreischuh; Petar A. Atanasov; Nikola V. Sabotinov, Editor(s)