Multiphonon, Raman, and Two-Photon Excitation of Rare-Earth Ions in Crystals: Photon and Phonon Noise in 10-μ Quantum Counters

Abstract
Noise arising from strong laser pumping and 77-K internal phonon noise upconversion in the proposed supposedly noiseless 10-μ quantum counters using rare-earth-doped crystals is described. The discussions are specialized to the crystals states of the Eu3+ ion. It is shown that at the pump power (∼50 kW cm−2) necessary for background-limited 10-μ quantum counter upconversion detection at 77 K, all the three major processes of noise generation discussed are insignificant compared to the background thermal (300 K) radiation considered previously in arriving at realistic theoretical quantum efficiencies of the proposed 10-μ quantum counters.