H-BAF2 by CDGM

$$n(\lambda) = \sqrt{1 + \frac{0.131856\,\lambda^2}{\lambda^2 - 0.040423} + \frac{1.28687\,\lambda^2}{\lambda^2 - 0.00807407} + \frac{1.00683\,\lambda^2}{\lambda^2 - 113.575}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-2.16 \times 10^{-6} + 2(1.57 \times 10^{-8})\,\Delta T + 3(-3.1 \times 10^{-11})\,\Delta T^2 + \frac{4.71 \times 10^{-7} + 2(6.41 \times 10^{-10})\,\Delta T}{\lambda - 0.268}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$