Stabilized laser system at 1550 nm wavelength for future gravitational-wave detectors

Abstract

Proposed future gravitational wave detectors place high demands on their prestabilized laser system. We present a prototype for such a prestabilized laser system at 1550 nm wavelength with frequency and power stabilizations optimized for the needs of gravitational wave detectors. A power stabilization with shot noise limited operation below a relative power noise of 1×10-8 Hz-1/2 between 100 Hz to 100 kHz and an active frequency stabilization with a unity-gain bandwidth above 2 MHz were operated simultaneously. Out-of-loop measurements are performed to characterize the achieved stability and to analyze sensor noise limits. We find that nonlinear noise couplings at the spatial mode-filter cavity are of high relevance and lead to increased frequency stability requirements above 100 kHz. This prestabilized laser system can serve as the baseline for the Einstein Telescope gravitational wave detector [ET steering committee, Design report Update 2020 for the Einstein Telescope, Technical Report, Einstein gravitational wave Telescope, 2020.] and demonstrates stabilization concepts generally applicable to optical precision experiments.