H-LAK2A by CDGM

$$n(\lambda) = \sqrt{1 + \frac{0.914808\,\lambda^2}{\lambda^2 - 82.3261} + \frac{1.00522\,\lambda^2}{\lambda^2 - 0.00450504} + \frac{0.803416\,\lambda^2}{\lambda^2 - 0.0183713}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-5.16 \times 10^{-6} + 2(1.42 \times 10^{-8})\,\Delta T + 3(-4.62 \times 10^{-11})\,\Delta T^2 + \frac{5.61 \times 10^{-7} + 2(5.14 \times 10^{-10})\,\Delta T}{\lambda - 0.155}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$