D-LAK6-25 by CDGM

$$n(\lambda) = \sqrt{1 + \frac{1.223\,\lambda^2}{\lambda^2 - 94.0859} + \frac{0.47121\,\lambda^2}{\lambda^2 - 0.022783} + \frac{1.33929\,\lambda^2}{\lambda^2 - 0.00665285}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[1.33 \times 10^{-6} + 2(1.27 \times 10^{-8})\,\Delta T + 3(-2.36 \times 10^{-11})\,\Delta T^2 + \frac{5.62 \times 10^{-7} + 2(7.08 \times 10^{-10})\,\Delta T}{\lambda - 0.199}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$