H-LAK12 by CDGM

$$n(\lambda) = \sqrt{1 + \frac{0.786703\,\lambda^2}{\lambda^2 - 0.00202073} + \frac{1.2177\,\lambda^2}{\lambda^2 - 86.7035} + \frac{1.04087\,\lambda^2}{\lambda^2 - 0.0163643}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-1.86 \times 10^{-7} + 2(1.39 \times 10^{-8})\,\Delta T + 3(-1.79 \times 10^{-11})\,\Delta T^2 + \frac{4.74 \times 10^{-7} + 2(4.36 \times 10^{-10})\,\Delta T}{\lambda - 0.167}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$