H-LAK6A by CDGM

$$n(\lambda) = \sqrt{1 + \frac{1.13018\,\lambda^2}{\lambda^2 - 81.4541} + \frac{1.60589\,\lambda^2}{\lambda^2 - 0.00817223} + \frac{0.207869\,\lambda^2}{\lambda^2 - 0.0303803}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[3.08 \times 10^{-6} + 2(1.57 \times 10^{-8})\,\Delta T + 3(-1.21 \times 10^{-11})\,\Delta T^2 + \frac{5.18 \times 10^{-7} + 2(5.95 \times 10^{-10})\,\Delta T}{\lambda - 0.182}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$