Improving the Cool-down times for Third Generation Gravitational Wave Observatories

Interferometric gravitational wave observatories recently launched a new field of gravitational wave astronomy with the first detections of gravitational waves in 2015. The number and quality of these detections is limited in part by thermally induced vibrations in the mirrors, which show up as noise in these interferometers. One way to reduce this thermally induced noise is to use low temperature mirrors made of high purity single-crystalline silicon. Although the operating temperature can be reached without compromising the isolation of the optic components by using a dual shield system and radiative cooling, the cool-down times are slow and unpractical for a full scale mirror like the ones planned for the next iteration of LIGO, LIGO Voyager. We experimentally demonstrate the cool-down time can be improved by injecting gaseous Nitrogen in the two shield array. It is also shown that this procedure does not compromise the temperature of the rest of the apparatus inside the vacuum chamber. Finally these results can be reliably scaled up to satisfy the requirements imposed by a future LIGO Voyager design.