Figure 4
The collection efficiency of SPDC photons (pair-to-singles ratio), and the final brightness in the SPEQS geometry, for different crystal lengths. In this graph, the pump and collection beam FWHM were fixed at 180 micron and 120 micron respectively. The collection efficiency is quite stable across the range of crystal lengths. The dependence of brightness on crystal length, however, appears to lie in two different regimes. Additional work is ongoing to characterize this dependence and a model is being developed.