D-QK3L-25 by CDGM

$$n(\lambda) = \sqrt{1 + \frac{0.834888\,\lambda^2}{\lambda^2 - 90.1036} + \frac{0.140256\,\lambda^2}{\lambda^2 - 0.0199283} + \frac{1.04638\,\lambda^2}{\lambda^2 - 0.00608196}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-9.26 \times 10^{-6} + 2(1.71 \times 10^{-8})\,\Delta T + 3(-1.54 \times 10^{-11})\,\Delta T^2 + \frac{3.26 \times 10^{-7} + 2(5.95 \times 10^{-10})\,\Delta T}{\lambda - 0.187}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$