EFFICIENT FAR INFRARED INDUCTIVE MESH FILTERS BY PHOTOELECTROCHEMICAL ETCHING

NASA HAS NUMEROUS APPLICATIONS FOR FAR INFRARED AND SUBMILLIMETER SPECTROSCOPY, INCLUDING ORBITING OBSERVATION OF THE EARTH'S ATMOSPHERE, DETECTION OF PLANTS ORBITING NEARBY STARS, AND MAPPING OF THE INFRARED SKY. THE INSTRUMENTATION GENERALLY REQUIRES BEAMSPLITTERS AND BANDPASS OR CUTOFF FILTERS, WHICH, FOR THESE WAVELENGTHS, TYPICALLY HAVE A MESH GEOMETRY, WITH THE SHAPE AND DIMENSIONS OF THE OPENINGS DETERMINING THE OPTICAL PROPERTIES. WE PROPOSE A NEW METHOD FOR FABRICATING THESE FILTERS USING LIGHT-DRIVEN ETCHING OF SEMICONDUCTOR CRYSTALS. THE METHOD PROMISES TO PROVIDE A VARIETY OF HOLE SHAPES WITH NARROW HOLE SPACINGS AND HIGHLY VERTICAL SIDEWALLS WHICH CANNOT BE ACHIEVED BY THE PRESENT TECHNIQUESOF ETCHING THIN METAL FOILS OR WINDING FINE METAL GRIDS. PHASE I WILL BE USED TO DEFINE THE CONDITIONS FOR MAKING 1 CM(2) PROTOTYPE MESHES (E.G., 20 X 20 MU M SQUARES ON 30 MU M CENTERS) IN 50-100 MU M THICK GAAS, A CONVENIENT MATERIAL FOR INITIAL EXPERIMENTS. PHASE II WILL ENTAIL OPTIMIZING SEMICONDUCTOR SUBSTRATE MATERIALS AND PHOTOELECTROCHEMICAL PROCESSING CONDITIONS, AND FABRICATION AND EVALUATION OF A VARIETY OF FILTER STRUCTURESAND SETS WITH RELEVANCE TO SPECIFIC NASA MISSIONS.