Room-temperature photoinduced effects in elasticity and mechanical loss of GaAs for applications in high-precision optical metrology

\nCrystalline coating materials like AlGaAs/GaAs have the potential to revolutionise applications in high-precision optical metrology, such as ultra-stable laser cavities or gravitational wave interferometers. The primary driver for that is the promise of reduced noise and, thus, enhanced stability and measurement sensitivity. However, recent investigations revealed that the aspired noise level could be out of reach as an additional noise source is present, seemingly originating from intrinsic material properties and being related to the illumination of the material. To contribute to understanding this effect, we employ mechanical spectroscopy to explore the illumination-dependent mechanical loss of GaAs flexures at mechanical frequencies from 100 Hz to 94 kHz. The results indicate that photoinduced effects in bulk GaAs change the elasticity and mechanical loss with relaxation times of several minutes.\n