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Wavefront aberration compensation with a thermally deformable mirror

First generation gravitational wave interferometer performances were affected by thermal effects and non-optimal coupling of the light into several optical cavities. Slow thermally induced beam-wavefront distortions can be compensated using deformable mirrors driven by thermal actuators. We propose a new device, where the set of heating actuators is placed in direct contact with the reflecting surface of the mirror, enabling an efficient control of its refractive index and shape. This system is particularly useful for an in-vacuum environment, where low noise remote actuation is required. It is therefore well suited for Advanced Gravitational Wave Detectors where many optical cavities will require active optimal coupling for optimizing their quantum noise sensitivity without producing motion of the rest of the optics, which could interrupt the control acquisition sequence. In this paper, a prototype for such a thermally deformable mirror is described, and first results are presented. The proposed system promises to perform with good stability and efficiency.