The NEP
λand response time of the Pr
3+:LaCl
3Infra-red Quantum Counter have been measured for the wavelengths 1.48 μ, 1.58 μ, 2.03 μ and 2.33 μ at the nominal temperatures of 300°K, 77°K, and 4.2°K. The experimental arrangement is described and suggestions for improvement are made. The best results obtained are an

watts

and a temperature independent response time of 20-30 ms.