D-PK3-25 by CDGM

$$n(\lambda) = \sqrt{1 + \frac{0.513408\,\lambda^2}{\lambda^2 - 0.00173535} + \frac{0.923806\,\lambda^2}{\lambda^2 - 95.3262} + \frac{0.781225\,\lambda^2}{\lambda^2 - 0.011835}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-3.49 \times 10^{-6} + 2(1.52 \times 10^{-8})\,\Delta T + 3(-7.04 \times 10^{-11})\,\Delta T^2 + \frac{4.13 \times 10^{-7} + 2(3.57 \times 10^{-10})\,\Delta T}{\lambda - 0.131}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$