H-LAK71 by CDGM

$$n(\lambda) = \sqrt{1 + \frac{1.12851\,\lambda^2}{\lambda^2 - 101.092} + \frac{0.562112\,\lambda^2}{\lambda^2 - 0.0213537} + \frac{1.27965\,\lambda^2}{\lambda^2 - 0.00668008}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[7.88 \times 10^{-6} + 2(1.46 \times 10^{-8})\,\Delta T + 3(-1.42 \times 10^{-11})\,\Delta T^2 + \frac{5.79 \times 10^{-7} + 2(5.52 \times 10^{-10})\,\Delta T}{\lambda - 0.193}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$