Speaker
Description
From the 10 cm optical cavities used to reference ultra-stable lasers to the 3 km arm cavities of interferometric gravitational-wave detectors, precision optical experiments have reached a fundamental performance limit: mirror thermal-noise. In the context of gravitational-wave detection, planned observatory upgrades aim for a decrease in mirror coating thermal-noise, where in particular, the Virgo Coating R&D group is in the midst of an extensive survey of coating materials for Virgo_nEXT. This project benefits from support through metrology of coating candidates for research and validation.
At the Institut Fresnel, we are currently developing GraviTerm, a testbed for the direct measurement of thermal noise. While previous experiments have measured thermal noise by comparing test and reference samples separated spatially, GraviTerm will explore a new technique, separating the signals temporally. This will be accomplished via measurement of mirror surface position noise as strain noise in a resonant fiber-optic sensor, an experimental design that is a comparatively compact and optically simpler system. Key to this design is the high degree of common-mode noise rejection between the reference and sample signals, which share an optical path counterpropagating in a cyclical interferometer. Here we present details of this design and early steps in its realization.