Abstract: The invention presents means for protecting a remote sensing device such as missile seeker unit from damaging radiation outside of the sensing band of the detector and interrogating radiation attempting to determine the operating band of the sensor, its modulation rate, timing signal, or similar data which might be used to deteriorate the performance of the sensor.

Abstract: An improved apparatus and technique for providing frequency selective seng and tracking. An optical radar transmitter is constructed using a dye laser controlled by a Faraday cell having two end polarizers. The Faraday cell extends to intercept the return beam from the transmitting laser. Using a magnetic field to control the Faraday cell, the frequency of transmission can be selectively varied while the receiver-detector is automatically ganged to the transmitted frequency. The particular frequency selectivity provides significant isolation of the sensing beam from unwanted and interfering radiation allowing highly selective optical beam tracking.