H-F51 by CDGM

$$n(\lambda) = \sqrt{1 + \frac{1.1988\,\lambda^2}{\lambda^2 - 118.703} + \frac{0.146782\,\lambda^2}{\lambda^2 - 0.058692} + \frac{1.46655\,\lambda^2}{\lambda^2 - 0.0111709}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-2.03 \times 10^{-6} + 2(1.5 \times 10^{-8})\,\Delta T + 3(-4.64 \times 10^{-11})\,\Delta T^2 + \frac{7.77 \times 10^{-7} + 2(8.08 \times 10^{-10})\,\Delta T}{\lambda - 0.275}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$