Self-protecting infrared detector with a continuously variable attenuator

Abstract

Abstract An instrument for protecting sensitive infrared detectors, such as those d in satellites, from being damaged by exposure to high intensity radiation. The high intensity radiation may come from a high power cw laser. A gas absorption cell is used between the detector and the collecting optics to limit the amount of radiation reaching the detector. However, if it is desirable to also protect the collecting optics, then the gas absorption cell may be used in front of the collecting optics. In either case, the pressure in the absorption cell is controlled by the output reading of the detector; in that, when the rate of increase of the intensity is less than a predetermined value and the intensity is less than 90% of its saturation value then there is no gas in the absorption cell and the detector operates normally. However, when the intensity exceeds 90% of its saturation value the attenuator is actuated until the signal is decreased to say 1/10th of its saturation value at which time the attenuator is deactivated. The intensity reaching the instrument is determined from measurements of the detector output and the pressure in the attenuator. In this manner the dynamic range of the detector can be increased by several orders of magnitude. There is also a fast acting puff valve so that, when dI/dt exceeds a certain value, the attenuator can be quickly filled with the gas mixture to protect the detector from burn out. These detectors operate in certain wavelength bands like 3 to 5 μm, 8 to 14 μm, or 16 to 22 μm and the gas used in the absorption cell is different for each detector as explained below.

Inventors

• 👤 Thomas G. Roberts

Bibliographic Details