This is a generic high speed photometer which uses an indium antimonide (InSb) crystal in a low temperature, 
    	strong magnetic field environment as the detector. In this environment, InSb which is a narrow-gap semiconductor, 
    	is sensitive to the intensity of infrared light. The nominal operating wavelength range is 2000nm to 2400nm. A large number  
    	of these were produced by several manufacturers and were in wide use in the 1960's and 1970's. Some were still in  
    	use in the early 21st century.