<title>Line-selective resonators with variable reflectivity gratings (VRG) for slab-laser geometry</title>

Abstract

A diffusion cooled lineselective CO2 laser with a variable reflectivity grating is presented in this paper. The line-selective CO2 laser acts as a pump source for far infrared lasers. We use an rf-excited slab laser geometry to achieve a compact laser design due to the area power scaling in contrast to the conventional longitudinal DC excited lasers with length power scaling. The huge Fresnel number of a slab system normally leads to a higher order mode operation of the laser and uncontrolled transversal mode-hops. In order to reduce this effect, so called Variable Reflectivity Mirrors (VRM) were investigated for stable and unstable resonators in the past. Instead of a VRM we use a modified binary Littrow grating to achieve the same effect in a lineselective resonator setup. The reflectivity of a binary Littrow grating with constant depth and grating period depends on the width of the grating bars. The grating splits the incident power into the -1st and 0th diffraction order. The splitting radio depends on the duty cycle of the grating. The -1st diffraction order is reflected back into the resonator whereas the 0th diffraction order is used to couple out the laser beam. Therefore the grating acts as lineselective, outcoupling and, due to the nature of VRM resonators, as a modeselective element as well. The gratings are realized by a microgalvanic process on copper substrates. Results of different resonator concepts (stable and unstable) with planar and convex gratings are presented.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.