Quantum Efficiency Determination by Fluorescence in an Integrating Sphere: Consistency of a Simple, Transparent Solution with a More Complex, Widely Used Solution

Quantum efficiency QE is an important factor in determining the overall efficiency of a solid-state laser, but can be very difficult to measure. One approach to obtain an absolute value for the QE of a laser material involves fluorescence and scattering measurements in an integrating sphere. A successful method for such measurements was developed by de Mello et al. and has been applied by a number of groups. Yet its base equations leave open questions as to the accuracy of some terms, and the form of their solution for QE is not easy to interpret. Since this leaves open the possibility that their approach is not as accurate as might be hoped, we have undertaken an analysis that accounts for the photons at each stage of the measurement, using the same underlying assumptions about the physical processes as de Mello et al. We find a much simpler solution whose interpretation is quite transparent and show that it is fully consistent with their solution.