Electrostatically operated micromirrors for Hadamard transform spectrometer

The paper presents the development of a linear micromirror array which can be used as a switchable entrance mask for a double-array Hadamard transform spectrometer, In addition to the detector array, the double-array spectrom eter has a linear multislit array realized by independently switchable micr omirrors at the entrance side, Two different switch positions of the electr ostatically operated mirrors allow the reflection of light into or away fro m the spectrometer. With this arrangement (mirror array, concave grating, a nd array detector) and the use of the Hadamard transform principle it is po ssible to increase the signal-to-noise ratio and the resolution of the syst em compared to conventional spectrometers of the same size, In order to use a micromirror array as an entrance mask the dimensions of the switching el ements must be similar to those of entrance slits and the mirror surface mu st have a high reflectivity in the desired spectral range, To obtain a high resolution a given pitch between the mirrors must be realized, Using thin- film technology we developed a linear array with 18 tiltable mirrors, The m irrors consist of a multilayer system of aluminum and silicon nitride depos ited on a structured sacrificial layer of polyimide, The aluminum has a com paratively high reflectivity in the UV/VIS region and the silicon nitride y ields good mechanical properties for realizing stress reduced mirrors and b ending structures, After etching of the sacrificial layer, the mirrors can be switched electrostatically, The angle between on and off position is abo ut 5 degrees. Low switching voltages in the range of 15-45 V can be realize d.