Passive broad long wave and mid-wave infrared optical limiting prism

摘要

Method for limiting the amount of radiation impinging on a radiation sensitive detector that is responsive to signals of interest having infrared wavelengths of approximately 3 to 14 microns, such as an infrared camera. The method includes: directing a radiation signal through a prism and toward the radiation sensitive detector; permitting the radiation signal to impinge upon the radiation sensitive detector, e.g. upon an infrared focal plane array in the camera, when the radiation is below a predetermined threshold; and directing radiation associated with the radiation signal but having wavelengths different from said signals of interest—e.g., wavelengths in the visible and near-infrared range—on a path external to the prism, in order to initiate the limiting of the radiation impinging upon the radiation sensitive detector when the predetermined threshold is exceeded. Also, a Total Internal Reflection device that includes a prism having a thin film coated on the back surface of said prism. The material making up the prism and the thin film are selected so that, in the presence of radiation having an intensity less than a certain threshold, the refractive index of the thin film is lower than that of the prism, and when the radiation has an intensity higher than that certain threshold, the refractive index of the thin film is higher than that of the prism.