Low phase noise squeezed vacuum for future generation gravitational wave detectors
Squeezed light has become a standard technique to enhance the sensitivity of gravitational wave detectors. Both optical losses and phase noise in the squeezed path can degrade the achievable improvements. Phase noise can be mitigated by having a high bandwidth servo to stabilize the squeezer phase to the light from the interferometer. In advanced LIGO, this control loop bandwidth is limited by the 4 km arm cavity free spectral range to about ~15 kHz. Future generation gravitational-wave detectors are designed to employ much longer arm cavities. For cosmic explorer , a 40 km arm length will limit the bandwidth to ~1.5 kHz. We propose an alternative controls scheme that will increase the overall phase noise suppression by using the in-vacuum filter cavity as a reference for stabilizing the laser frequency of the squeezed light source. This will allow for rms phase noise of less than a milliradian—a negligible level for all future generations of gravitational-wave detectors .
© 2020 IOP Publishing Ltd. Received 30 March 2020; Accepted 10 July 2020; Accepted Manuscript online 10 July 2020; Published 19 August 2020. LIGO was constructed by the California Institute of Technology and Massachusetts Institute of Technology with funding from the National Science Foundation, and operates under Cooperative Agreement No. PHY-0757058. Advanced LIGO was built under Grant No. PHY-0823459. The authors also gratefully acknowledge the support of the Australian Research Council under the ARC Center of Excellence for Gravitational Wave Discovery, Grant No. CE170100004 and Linkage Infrastructure, Equipment and Facilities Grant No. LE170100217; the National Science Foundation Graduate Research Fellowship under Grant No. 1122374; and the LIGO Scientific Collaboration Fellows program. This document has been assigned the LIGO Laboratory document number LIGO-P2000064.