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

authored by: 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
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.
Organisation(s): Institute of Gravitation Physics
QuantumFrontiers
External Organisation(s): Max Planck Institute for Gravitational Physics (Albert Einstein Institute)
Thorlabs
University of Glasgow
Type: Article
Journal: Optics express
Volume: 27
Pages: 36731-36740
No. of pages: 10
ISSN: 1094-4087
Publication date: 09.12.2019
Publication status: Published
Peer reviewed: Yes
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Electronic version(s): https://doi.org/10.1364/OE.27.036731 (Access: Open)
https://doi.org/10.15488/10464 (Access: Open)

BibTeX

@article{934ed8d4bef04419a446ce7273d6d8de,
title = "Thickness uniformity measurements and damage threshold tests of large-area GaAs/AlGaAs crystalline coatings for precision interferometry",
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.",
author = "P. Koch and Cole, {G. D.} and C. Deutsch and D. Follman and P. Heu and M. Kinley-Hanlon and R. Kirchhoff and S. Leavey and J. Lehmann and P. Oppermann and Rai, {A. K.} and Z. Tornasi and J. W{\"o}hler and Wu, {D. S.} and T. Zederbauer and H. L{\"u}ck",
note = "Funding information: Deutsche Forschungsgemeinschaft (EXC-2123/1); Max Planck Research School on Gravitational Wave Astronomy.",
year = "2019",
month = dec,
day = "9",
doi = "10.1364/OE.27.036731",
language = "English",
volume = "27",
pages = "36731--36740",
journal = "Optics express",
issn = "1094-4087",
publisher = "OSA - The Optical Society",
number = "25",
}