Use of a multilayer dielectric diffraction grating as the resonator mirror of a neodymium-doped yttrium aluminium garnet laser

摘要

The use of metal gratings inside laser resonators is limited to medium power because of a low damage threshold. High-reflectivity (HR) dielectric layer systems commonly used as laser mirrors offer a damage threshold 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 wavelength 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 binary diffraction grating on a dielectric layer system is based on a new finite-element method. Also for the more difficult configuration, a diffraction 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 material combinations, HR gratings are fabricated. The limiting factors in realizing 100% efficiency, are the material parameters and fabrication tolerances. First examples of gratings offer fairly good agreement with the theoretical values. [References: 8]