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Thickness uniformity measurements and damage threshold tests of large-area GaAs/AlGaAs crystalline coatings for precision interferometry
Authors
G.D. Cole
C. Deutsch
+14 more
D. Follman
P. Heu
M. Kinley-Hanlon
R. Kirchhoff
P. Koch
S. Leavey
J. Lehmann
H. Lück
P. Oppermann
A.K. Rai
Z. Tornasi
D.S. Wu
J. Wöhler
T. Zederbauer
Publication date
1 January 2019
Publisher
Washington, DC : OSA - The Optical Society
Doi
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Abstract
Precision interferometry is the leading method for extremely sensitive measurements in gravitational wave astronomy. Thermal noise of dielectric coatings poses a limitation to the sensitivity of these interferometers. To decrease coating thermal noise, new crystalline GaAs/AlGaAs multilayer mirrors have been developed. To date, the surface figure and thickness uniformity of these alternative low-loss coatings has not been investigated. Surface figure errors, for example, cause small angle scattering and thereby limit the sensitivity of an interferometer. Here we measure the surface figure of highly reflective, substrate-transferred, crystalline GaAs/AlGaAs coatings with a custom scanning reflectance system. We exploit the fact that the reflectivity varies with the thickness of the coating. To increase penetration into the coating, we used a 1550 nm laser on a highly reflective coating designed for a center wavelength of 1064 nm. The RMS thickness variation of a two inch optic was measured to be 0.41 ± 0.05 nm. This result is within 10% of the thickness uniformity, of 0.37 nm RMS, achieved with ion-beam sputtered coatings for the aLIGO detector. We additionally measured a lower limit of the laser induced damage threshold of 64 MW/cm2 for GaAs/AlGaAs coatings at a wavelength of 1064 nm. © 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreemen
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Last time updated on 10/01/2020
Institutionelles Repositorium der Leibniz Universität Hannover
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Last time updated on 11/04/2021