H-ZLAF68N by CDGM

$$n(\lambda) = \sqrt{1 + \frac{1.49455\,\lambda^2}{\lambda^2 - 109.763} + \frac{2.07574\,\lambda^2}{\lambda^2 - 0.0104041} + \frac{0.361138\,\lambda^2}{\lambda^2 - 0.0412621}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-9.92 \times 10^{-9} + 2(1.31 \times 10^{-8})\,\Delta T + 3(-2.62 \times 10^{-11})\,\Delta T^2 + \frac{7.34 \times 10^{-7} + 2(7.89 \times 10^{-10})\,\Delta T}{\lambda - 0.237}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$