H-BAF4 by CDGM

$$n(\lambda) = \sqrt{1 + \frac{1.32811\,\lambda^2}{\lambda^2 - 0.00868511} + \frac{0.126865\,\lambda^2}{\lambda^2 - 0.0440786} + \frac{1.04005\,\lambda^2}{\lambda^2 - 120.9}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-2.53 \times 10^{-6} + 2(1.58 \times 10^{-8})\,\Delta T + 3(-4.13 \times 10^{-11})\,\Delta T^2 + \frac{6.35 \times 10^{-7} + 2(4.85 \times 10^{-10})\,\Delta T}{\lambda - 0.235}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$