FN11 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.41573\,\lambda^2}{\lambda^2 - 0.010375} + \frac{0.143334\,\lambda^2}{\lambda^2 - 0.0568804} + \frac{1.27299\,\lambda^2}{\lambda^2 - 119.664}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[7.11 \times 10^{-7} + 2(1.13 \times 10^{-8})\,\Delta T + 3(-3.37 \times 10^{-11})\,\Delta T^2 + \frac{7.48 \times 10^{-7} + 2(9.36 \times 10^{-10})\,\Delta T}{\lambda - 0.267}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$