Agile beams and micromachined membrane deformable mirrors

Summary form only given. A Micromachined Membrane Deformable Mirror (MMDM) consists of a thin stretched membrane suspended over an array of electrostatic electrodes. The membrane is fabricated by LPCVD deposition of a thin ∼0.5 μm layer of tensile stressed silicon nitride Si_nN_m, followed by anisotropic etching of bulk silicon to release the membrane. Pure nitride membranes are sufficiently strong for mirrors with diameter of up to 25 mm; larger membranes - up to 50 mm - can be fabricated by sandwiching a relatively thick - up to 10 μm - layer of epi-poly silicon between two nitride layers. Compactness, simplicity and high optical quality make MMDM the device of choice for a number of optical applications in laser optics, imaging, optical testing and astronomy.