SF14 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.69183\,\lambda^2}{\lambda^2 - 0.0133152} + \frac{0.28592\,\lambda^2}{\lambda^2 - 0.0612647} + \frac{1.12595\,\lambda^2}{\lambda^2 - 118.405}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[8.85 \times 10^{-6} + 2(1.81 \times 10^{-8})\,\Delta T + 3(-4.12 \times 10^{-11})\,\Delta T^2 + \frac{1.39 \times 10^{-6} + 2(1.53 \times 10^{-9})\,\Delta T}{\lambda - 0.279}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$