Micro-deformable mirror for next-generation adaptive optical systems

Next generation giant telescopes as well as next generation instrumentation for 10m-class telescopes relies on the availability of highly performing adaptive optical systems. Different types of AO systems are currently under study, including Multi-Conjugate AO (MCAO), high dynamic range AO, and low-order AO for distributed partial correction AO. These systems require a large variety of deformable mirrors with very challenging parameters. The development of new technologies based on micro-opto-electro-mechanical systems (MOEMS) is promising for future deformable mirrors. The major advantages of the micro-deformable mirrors (MDM) are their compactness, scalability, and specific task customization using elementary building blocks. We are currently developing a MDM based on an array of electrostatic actuators with attachments to a continuous mirror on top. A high optical quality mirror is the most challenging building block for this device. The originality of our approach lies in the elaboration of a sacrificial layer and of a structural layer made of polymer materials. With this structure, very efficient planarization has been obtained: the long-distance flatness is below 0.2 μm, the print-through of localized 9μm steps is reduced to below 0.5μm and a rms roughness of 15 nm has been measured over the surface. The integration of this mirror surface on top of an actuator array is under investigation.