H-LAF2 by CDGM

$$n(\lambda) = \sqrt{1 + \frac{1.62865\,\lambda^2}{\lambda^2 - 0.00864219} + \frac{1.11837\,\lambda^2}{\lambda^2 - 109.901} + \frac{0.253252\,\lambda^2}{\lambda^2 - 0.0342503}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-4.12 \times 10^{-6} + 2(2.75 \times 10^{-8})\,\Delta T + 3(-1.05 \times 10^{-10})\,\Delta T^2 + \frac{8.05 \times 10^{-7} + 2(-8.24 \times 10^{-10})\,\Delta T}{\lambda - 0.107}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$