The indices of refraction of ADP, KDP, and deuterated KDP were measured at temperatures between the Curie point and room temperature. The estimated accuracy of the data is ±0.0001. The empirical equation Δn= (n2+an+b)c(298-T) where n is the index at room temperature, Δn is the change in index, and T is the temperature in °K, fits the measurements to within experimental error. The values of the constants a, b, and c are tabulated for each material, permitting n to be calculated for any temperature.
RICHARD A. PHILLIPS, "Temperature Variation of the Index of Refraction of ADP, KDP, and Deuterated KDP," J. Opt. Soc. Am. 56, 629-632 (1966)