Enhancement of the threshold sensitivity of infrared radiation detectors by up-conversion of radiation frequency

Experimental studies were made of some methods for enhancing the sensitivity of an infrared radiation detector by up-conversion of the radiation frequency. In one such method use was made of the intraresonator spherical focusing of a laser pump beam in a nonlinear crystal. The pump laser was operated under slow Q -switching conditions. The converted radiation was recorded by gating a photomultiplier which was used as a photon counter. In this way it was possible to record a signal of 5X10^–14 W power.