Sensitivity of Pr+3: LaCl3infrared quantum counter

The NEP
λ
and response time of the Pr
³⁺
:LaCl
3
Infra-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
NEP_{2.03_\mu} = 2 \times 10^{-5}
watts
(c/s)^{-1/2}
and a temperature independent response time of 20-30 ms.