Generation of Ultrasonic Waves from an Optically Driven GaAs Thin Film

We demonstrate an optically driven MEMS that moves when irradiated by light. The MEMS is constructed from a GaAs/InGaAs thin film. High-frequency optical pulses drive mechanical vibration of the film to generate ultrasonic waves in air. We also measured photoluminescence (PL) from the sample to explore the cause of the optical drive. Laser irradiation caused a redshift of the GaAs PL up to 960 nm as the laser power increased. Our result implies a local heating in the thin film that causes the PL redshift, which drives the thin film by thermal expansion