High contrast, cryogenic, large micromirror array for multi-object spectroscopy

Next generation of multi-object spectrographs (MOS) in astronomy will use MEMS-based programmable slit masks. Large micromirror arrays with 2048 tiltable micromirrors were fabricated using bulk and surface micro-machining, and wafer level bonding for the assembly. Micromirror size is 100µm × 200 µm and they exhibit very good surface flatness. Mirror architecture as well as a large mechanical tilt angle of 25° lead to a high contrast device, in the order of 1000∶1, large enough for objects and background rejection in the MOS field of view. Finally, the micromirrors could be successfully actuated before, during and after cryogenic cooling at 162K.