Wavelength-selective grating mirrors for high-power thin-disk lasers

In this paper a two novel optical elements based on sub-wavelength resonant reflective gratings is presented. The elements were used as the rear mirror of the high-power thin-disk laser cavity. The element is composed of a HR mirror, a thin-film waveguide and a high-contrast grating on top. By a proper design of the structure parameters, the 0^th order reflection can be cancelled. Thus, if the grating period is set in such a way that only the -1st order can propagate, the light is diffracted with high efficiency. In the second setup a partial reflector is used in association with a resonant waveguide grating to reach a specular reflectivity of about 99.9 % with a narrow spectral bandwidth under normal incidence.