A “low-deformation mirror” micro-oscillator with ultra-low optical and mechanical losses

We report on the mechanical losses measured in a “low-deformation mirror” micro-oscillator designed to reduce as much as possible the strain in the coating layer and the resulting energy dissipation. The deposition of the highly reflective coating layer has been fully integrated in the micro-machining process. We measured at cryogenic temperature a mechanical quality factor up to 10^5 and an optical finesse of about 4x10^4, and simulations show that the device can manage input powers of a few mW at 4.2 K. These features make the device very promising for quantum optics experiments.