Substrate-transferred GaAs/AlGaAs crystalline coatings for gravitational-wave detectors: A review of the state of the art

Abstract

In this Perspective we summarize the status of technological development for large-area and low-noise substrate-transferred GaAs/AlGaAs (AlGaAs) crystalline coatings for interferometric gravitational-wave (GW) detectors. These topics were originally presented in a workshop† bringing together members of the GW community from the laser interferometer gravitational-wave observatory (LIGO), Virgo, and KAGRA collaborations, along with scientists from the precision optical metrology community, and industry partners with extensive expertise in the manufacturing of said coatings. AlGaAs-based crystalline coatings present the possibility of GW observatories having significantly greater range than current systems employing ion-beam sputtered mirrors. Given the low thermal noise of AlGaAs at room temperature, GW detectors could realize these significant sensitivity gains, while potentially avoiding cryogenic operation. However, the development of large-area AlGaAs coatings presents unique challenges. Herein, we describe recent research and development efforts relevant to crystalline coatings, covering characterization efforts on novel noise processes, as well as optical metrology on large-area (~10 cm diameter) mirrors. We further explore options to expand the maximum coating diameter to 20 cm and beyond, forging a path to produce low-noise AlGaAs mirrors amenable to future GW detector upgrades, while noting the unique requirements and prospective experimental testbeds for these novel materials.

13pages, 3 figures

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• Sensitivity and Performance of the Advanced LIGO Detectors in the Third Observing Run
• Titania-doped tantala/silica coatings for gravitational-wave detection
• Direct Frequency Comb Measurement of OD + CO -> DOCO Kinetics
• Monocrystalline AlGaAs heterostructures for high-reflectivity high-Q micromechanical resonators in the MHz regime
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Cited by in corpus (9)

• Mid-infrared supermirrors with finesse exceeding 400 000
• Simultaneous Measurement of Mid-Infrared Refractive Indices in Thin-Film Heterostructures: Methodology and Results for GaAs/AlGaAs
• A laser with instability reaching $4\times 10^{-17}$ based on a 10-cm-long silicon cavity at sub-5-K temperatures
• Ultrastable lasers: investigations of crystalline mirrors and closed cycle cooling at 124 K
• Global optimization of multilayer dielectric coatings for precision measurements
• Experimental demonstration of frequency downconverted arm length stabilization for a future upgraded gravitational wave detector
• Photo-birefringent effects in crystalline AlGaAs mirror coatings
• Thermal Noise Reduction in Ternary Optical Coatings: From Ti::GeO${}_2$-Based Ternary Systems to High Index Materials
• Birefringence of AlGaAs/GaAs Coatings under Above-Band-Gap Illumination, GR Noise and Photo-Optic Transfer Function