H-LAK52 by CDGM

$$n(\lambda) = \sqrt{1 + \frac{0.648529\,\lambda^2}{\lambda^2 - 0.000165816} + \frac{1.2845\,\lambda^2}{\lambda^2 - 0.0158114} + \frac{1.23775\,\lambda^2}{\lambda^2 - 85.7406}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[6.32 \times 10^{-7} + 2(1.75 \times 10^{-8})\,\Delta T + 3(-2.89 \times 10^{-11})\,\Delta T^2 + \frac{5 \times 10^{-7} + 2(3.79 \times 10^{-10})\,\Delta T}{\lambda - 0.163}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$