Thickness uniformity measurements and damage threshold tests of large-area GaAs/AlGaAs crystalline coatings for precision interferometry

• DOI: 10.1364/oe.27.036731
• Publication Date: 2019-12-04T12:22:16Z
• Authors: P. Koch; G. D. Cole; C. Deutsch; D. Follman; P. Heu; M. Kinley-Hanlon; R. Kirchhoff; S. Leavey; J. Lehmann; P. Oppermann; A. K. Rai; Z. Tornasi; J. Wöhler; D. S. Wu; T. Zederbauer; H Lück
• Keywords: Optical coating

Precision interferometry is the leading method for extremely sensitive measurements in gravitational wave astronomy.Thermal noise of dielectric coatings poses a limitation to sensitivity these interferometers.To decrease coating thermal noise, new crystalline GaAs/AlGaAs multilayer mirrors have been developed.To date, surface figure and thickness uniformity alternative low-loss has not investigated.Surface errors, example, cause small angle scattering thereby limit an interferometer.Here we measure highly reflective, substrate-transferred, with custom scanning reflectance system.We exploit fact that reflectivity varies coating.To increase penetration into coating, used 1550 nm laser on reflective designed center wavelength 1064 nm.The RMS variation two inch optic was measured be 0.41 ± 0.05 nm.This result within 10% uniformity, 0.37 RMS, achieved ion-beam sputtered aLIGO detector.We additionally lower induced damage threshold 64 MW/cm 2 at nm.