Micro-Deformable Mirror: a low cost technology for cryogenic active and adaptive optics

Electrostatically operated bi-directional deflecting silicon membranes can be created using bulk micromachining techniques. The 19-channel Micro-Deformable Mirror, potential candidate for space Active and Adaptive Optics, was built by OKO Technologies. The purpose of this project was to test the mirror, constituted from its silicon membrane and its aluminium coated mount, under cryogenic conditions. The mirror was mounted on a self designed three piece structure and several experiments were constructed to characterise the zero point drift, the maximum stroke and the dynamical response of the MDM. The membrane was tested by interferometry and showed stability within 0.34μm of the initial membrane figure (flat within (^λ)(_13), λ = 0.633μm, at room temperature). Space temperatures are down to 35K and the MDM showed great dynamical behaviour at temperatures down to 86K. Adaptive Optics require a frequency response of the order of 1kHz. C++ programs drove the MDM to frequencies of up to 1.66kHz. As it can work under cryogenic conditions and has high frequency response, the MDM leads to great expectations for inexpensive wavefront correction at infrared wavelengths.