H-BAK7 by CDGM

$$n(\lambda) = \sqrt{1 + \frac{0.65947\,\lambda^2}{\lambda^2 - 0.00076601} + \frac{0.762197\,\lambda^2}{\lambda^2 - 0.0177403} + \frac{1.19936\,\lambda^2}{\lambda^2 - 129.975}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[6.07 \times 10^{-7} + 2(1.74 \times 10^{-8})\,\Delta T + 3(-3.75 \times 10^{-11})\,\Delta T^2 + \frac{5.69 \times 10^{-7} + 2(2.67 \times 10^{-10})\,\Delta T}{\lambda - 0.188}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$