A dark field infrared telescope. Energy from an infrared scene is focused by a lens (10) onto a thermoptic modulator (12) comprising an optical structure (16) containing a thin film of vanadium dioxide disposed to form the faceplate of a conventional cathode ray tube. The modulator, normally nonreflecting of infrared energy, may have reflecting spots written at selected coordinates thereon by an electron beam from the cathode ray tube. A reflecting spot written on the modulator optically couples a selected element of the scene imaged on the modulator to an infrared detector (52) maintained at low temperature. A retroreflecting mirror (30), cold spectral filter (46), field lens (47), cold field stop (48) and cold pupil stop (50) are provided ahead of the detector to produce a low background flux cavity with the detector at one end and the retroreflecting mirror at the other. In its unswitched state, the modulator is nonreflecting and the scene image is not coupled to the detector. The cold detector thus looks back upon itself and sees a "dark field." Under the control of the sensor microprocessor (22), the electron beam is synchronously switched on and off to modulate the detector signal. The detector signal is then synchronously demodulated by a signal processor (56) to reduce the noise of the detector and preamplifier. By reducing background flux and detector noise, the sensor approaches a signal shot noise or electronic noise limited condition.
A spectral filter for use in optical systems receiving field-of-view (FOV) optical beams at differing angles refracts all FOV beams onto a single plane focal surface. The spectral filter comprises a combination of lens having varied thicknesses incorporated into a single filter unit. Each thickness, or step, of the spectral filter corresponds to a different one of the received FOV beams.
5065026 - Thermal black-hole mask - Owned by The United States of America as represented by the Secretary of the Army (Washington, DC)
The black hole which a cryogenically-cooled infrared (thermal) detector ctes in a scene being observed by another such detector is obscured by inserting a partial transmitter-reflector on the optical axis of the detector. A black-body radiator projects an ambient-temperature image the same size and shape as the black hole onto the transmitter-reflector such that the other detector sees a combined image with no apparent black hole.
A vanadium oxide compound having the formula VO.sub.2 is disclosed for the purpose of selectively shielding an electromagnetic transmitter or receiver. Vanadium oxide exhibits a marked and rapid transition from dielectric and transparent to electromagnetic radiation to metallic and impervious to such radiation at a specific temperature, 68.degree. C. The compound is preferably mounted as a thin layer on a substrate which has been specifically selected for the desired application. The transmission of radiation is then temperature selected. The preferred method of deposition is an organic hydrolysis reaction.
A switchable shield which precludes transmission or receipt of radio frequency or microwave energy. The shield comprises a substrate of highly transmissive material with an active film layer disposed on the substrate. This active film layer is switchable upon heating from a high transmissivity, high resistivity mode which permits transmission or receipt of rf or microwave radiation, to a low transmissivity, low resistivity mode which precludes transmission or receipt of rf or microwave radiation through the shield.
An infrared detector has its sensor chip assembly (10,12,14) cooled to a relatively low temperature required for its operation, whereas a preamplifier (56) required to be positioned close to the sensor chip assembly and which generates considerably more heat than does the sensor chip assembly, is thermally isolated from the sensor chip assembly and its support (16) and is cooled to a higher temperature to thereby significantly reduce the power dissipated to the coldest refrigerator stage (90).
