Refined Sellmeier equations for AgGaSe2 up to 18 µm

We present refined Sellmeier equations for AgGaSe2 that provide good reproduction of the phase-matching angles for frequency upconversion of CO2 laser radiation in the 1.7652–10.5910 µm range and for frequency downconversion in the 1.85–18 µm range thus far reported in the literature.