Speaker
Description
AlGaAs/GaAs crystalline coatings are promising for future gravitational-wave detectors due to their low mechanical loss and superior optical properties. However, their high optical absorption at 532 nm precludes the use of conventional arm-length stabilization schemes based on 532 nm auxiliary lasers.
We present an alternative arm-length stabilization scheme employing an auxiliary laser at 1596nm, where the absorption of AlGaAs/GaAs coatings is sufficiently low. The 1596 nm light is converted to 532 nm via single-pass third-harmonic generation, enabling phase locking to the second harmonic of the main 1064 nm interferometer laser. The resulting phase-locked loop stabilizes the frequency difference between the two systems.
We demonstrate sub-Hz linewidth in the beat signal between the two 532 nm fields. Furthermore, arm-length stabilization is experimentally realised using a rigid tabletop cavity, confirming the viability of this scheme for future gravitational-wave detectors incorporating crystalline coatings.