Improved rare-earth trichloride infrared quantum counter sensitivity

More efficient pumping and fluorescence collection, plus restricted infrared bandwidth, have enabled us to obtain a noise equivalent power (NEP) of 3\times10^{-9} watts (Hz)^{\frac-{1}{2}} for the 4.2°K Pr 3+ :LaCl 3 infrared quantum counter (IRQC) as a narrow-band detector of 2.03-micron radition. This is approximately a four order of magnitude improvement over the most recently reported NEP in this material. The significant role of the lattice is demonstrated in a comparison of Pr 3+ IRQC action in the LaCl 3 and LaF 3 hosts. The inferiority of the latter is explained in terms of nonradiative quenching of the infrared levels, using recently published data on multiphonon emission rates. The dominant source of noise in the present device is described, and prospects for further sensitivity improvement are discussed.