H-BAF6 by CDGM

$$n(\lambda) = \sqrt{1 + \frac{1.06475\,\lambda^2}{\lambda^2 - 115.354} + \frac{1.38639\,\lambda^2}{\lambda^2 - 0.00853301} + \frac{0.146161\,\lambda^2}{\lambda^2 - 0.0437435}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-3.02 \times 10^{-6} + 2(1.55 \times 10^{-8})\,\Delta T + 3(-1.32 \times 10^{-10})\,\Delta T^2 + \frac{6.09 \times 10^{-7} + 2(9.44 \times 10^{-10})\,\Delta T}{\lambda - 0.233}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$