Refractive-index measurements and Sellmeier coefficients for zinc germanium phosphide from 2 to 9 µm with implications for phase matching in optical frequency-conversion devices

Recent experiments in mid-IR frequency conversion reveal that older Sellmeier models for zinc germanium phosphide are inadequate for predicting phase-matching loci in zinc germanium phosphide optical frequency-conversion devices. This results in compromised device performance. We conduct a complete study of the refractive indices of zinc germanium phosphide from 2 to 9 µm and calculate new Sellmeier coefficients. The phase-matching calculations based on our new refractive-index data predict much more closely the results of several different mid-IR frequency-conversion experiments.