Performance of laser-pumped quantum counters

Narrow-band quantum counters with less than unit internal quantum efficiency are analyzed. The pump power dependent expressions for the transient and steady-state quantum efficiencies are derived. These quanties are discussed for "typical" trivalent and divalent rare-earth-doped insulator crystals, and the performance of two specific systems is presented. It is shown that to achieve high quantum efficiency in trivalent rare-earth-doped quantum counter systems, the pump source must be highly nonblackbody in spectral character, i.e., a laser, and resonant with the transition between the relevant excited states. Performance limiting factors for laser-pumped quantum counters are pointed out.