H-F5 by CDGM

$$n(\lambda) = \sqrt{1 + \frac{1.43542\,\lambda^2}{\lambda^2 - 0.0108395} + \frac{0.133105\,\lambda^2}{\lambda^2 - 0.0581528} + \frac{1.22152\,\lambda^2}{\lambda^2 - 120.768}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-7.35 \times 10^{-7} + 2(1.37 \times 10^{-8})\,\Delta T + 3(-1.86 \times 10^{-11})\,\Delta T^2 + \frac{7.71 \times 10^{-7} + 2(6.53 \times 10^{-10})\,\Delta T}{\lambda - 0.265}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$