Abstract: An optical filter (18) includes a first layer (22) of material having a bandgap and being doped with an impurity having an energy level in the bandgap such that the first layer absorbs optical energy below a first wavelength and transmits optical energy thereabove. The filter further includes a second layer of optical material (26) disposed on said first layer (22) which transmits optical energy at a second wavelength, above the first wavelength, and reflects optical energy at a third wavelength above the second wavelength. The first and second layers in combination provide a filter (18) with high transmission in-band, low transmission out-of-band and a sharp cutoff therebetween.

Abstract: An optical filter for an infrared detector is provided by creating an impurity band in a semiconductor substrate onto which the infrared detector is epitaxially grown. The impurity band provides a range of absorption and a long wavelength pass band characteristic. The range of absorption is broadened by doping the substrate with a dopant of different photoelectric threshold from the dopant used to create the impurity band.

Abstract: Optical elements, such as windows for forward-looking, infrared radiation-receiving devices have at least one substantially flat surface adapted for exposure to incident radiation and, within such elements, one or more doped regions having predetermined, desired, non-flat shapes or having doping concentrations. These doped regions are adapted for exposure to the same incident radiation, and are also adapted to reflect, refract or scatter one or more predetermined, desired wavelengths of the incident radiation while transmitting other predetermined, desired wavelengths of the same incident radiation. Methods for making these devices include growing the doped regions on the preformed surface of optical element blocks; immersing such blocks in a molten bath of the material from which the dopant is made; and placing one or more doped inserts into a preformed region of an optical element block.

Abstract: Uniform electrical heating of a circular, single crystal germanium window (18) uses its bulk resistance and pairs of electrodes (20) equally spaced about the window's periphery. The electrode pairs are sequentially switched at a rate high enough to avoid thermal switching transients.

Abstract: A reflector and method for fabricating diffraction gratings in reflectors comprises the steps of placing one or more layers (38, 56-64) of a dielectric reflective enhancing material on a reflective surface (34, 54), and forming grooves (40, 66) only in the top layer (38, 64) of the dielectric material to form the gratings. Precise control of the efficiency is obtained by decreasing the thickness (b', b") of the grooved layer and adjusting the ratio (b'/b") of the material under the grooves and adjacent to the grooves.

Abstract: A sun shield (16) is placed in front of an RF reflector (12) for thermal protection thereof. The shield comprises a Kapton substrate (20) with a thin aluminum capacitive grid (26) on the shield's reflector side (24), and a partially reflecting layer (28) of germanium on its sun side (22). Other materials and combinations thereof may be placed on either or both sides singly or in layers to obtain desired reflectance and thermal energy rejection away from the reflector.