Grating fabrication for gravitational-wave interferometers and LISA GRS

Future LISA and LIGO projects may require gratings for interferometry and angular sensing to accurately monitor test mass positions. This paper summarizes some techniques used to create gratings on materials that will make up the test masses of next generation gravitational-wave detectors. As grating tip/tilt sensing will require two-dimensional grating structures with duty cycles and unit cell shapes that are as of yet undetermined, we concentrate on approaches that allow us to readily generate complex patterns. This paper discusses e-beam lithography for dielectric surfaces, and mechanical trans-imprinting and focused ion-beam writing for gold. These methods are more flexible than traditional techniques, such as the holographic exposure of photoresist with multiple laser beams. Grating patterns suitable for optical sensing have been successfully demonstrated on the surfaces of dielectric materials and gold. Their diffraction efficiencies have been measured to be sufficiently high for tip/tilt sensing.