Thermal noise of silicon based grating reflectors for high-precision metrology

The sensitivity of many experiments in the field of high-precision optical metrology is severely limited by coating thermal noise of the optical components, for example cavity mirrors. These components are commonly based on alternating layer pairs of amorphous materials. Particularly, for cryogenic applications highly reflective silicon gratings can be a promising low-noise alternative to these layer stacks. In this contribution we present a method to evaluate thermal noise of such micro-structured surfaces. For the example of the Einstein Telescope low-frequency detector it is found that coating thermal noise can be reduced up to one order of magnitude by using monolithic silicon gratings instead of conventional multilayer mirrors.