Optical dispersion and phase matching in gallium nitride and aluminum nitride

Precise measurements of the index of refraction for oriented single crystal samples of gallium nitride and aluminum nitride are reported. Dispersion and birefringence were determined from 450 to 1950 nm using internal reflection from a calibrated rutile prism. Values for dn/dT were measured between 20 and 105 degrees C. Measurements of refractive dispersion allow for predictions of the conditions needed for nonlinear frequency conversion. The stronger birefringence and weaker dispersion displayed by AlN are shown to allow for a limited range of bulk birefringent phase matching. Both crystals are promising candidates for quasi-phase matched nonlinear frequency conversion.