USE OF A MULTILAYER DIELECTRIC DIFFRACTION GRATING AS THE RESONATOR MIRROR OF A NEODYMIUM-DOPED YTTRIUM-ALUMINUM-GARNET LASER

The use of metal gratings inside laser resonators is limited to medium power because of a low damage threshold. High-reflectivity (HR) diele ctric layer systems commonly used as laser mirrors offer a damage thre shold significantly above that of metals. A diffraction grating on top of a HR system combines high reflectivity with spectral properties.We describe a special HR grating used in a Littrow mounting as a wavelen gth selective resonator mirror in a 1.41 mu m neodymium-doped yttrium aluminium garnet laser. The necessary restrictions lead to conditions with four transmission orders, making it more difficult to reach high efficiency, than found by Ferry and co-workers. The design of the bina ry diffraction grating on a dielectric layer system is based on a new finite-element method. Also for the more difficult configuration, a di ffraction efficiency of nearly 100% is theoretically possible. Because of the new conditions in contrast with these in the work of Ferry and co-workers, other materials have to be used. For two different materi al combinations, HR gratings are fabricated. The limiting factors in r ealizing 100% efficiency, are the material parameters and fabrication tolerances. First examples of gratings offer fairly good agreement wit h the theoretical values.