An Optical Radar Receiver Using Programmed Sensitivity Time Control

The return signals from a pulsed air /underwater laser radar system can have dynamic ranges that exceedthe capabilities of normal photomultiplier tubes, creating spurious signals. By actively controlling thegrid voltage of a photomultiplier tube, the usable dynamic range of a receiver can be extended. Careful active control of the grid voltage on an ITT 6 stage 4084 photomultiplier has resulted in gain changes inexcess of 50 dB in a time frame of several hundred nanoseconds. This programmed STC (sensitivity timecontrol) has allowed the recording of enhanced signal returns covering larger dynamic ranges than previouslypossible, without spurious signals resulting from multiplier overload.IntroductionThe Naval Air Development Center operates an SH -3 helicopter equipped with an air /underwater laser radar system. Applications include communication, target recognition, and oceanographic data collection.The use of a short pulse, high power, frequency doubled Nd:YAG laser yields high initial air backscatter