SF10 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.61626\,\lambda^2}{\lambda^2 - 0.0127535} + \frac{0.259229\,\lambda^2}{\lambda^2 - 0.0581984} + \frac{1.07762\,\lambda^2}{\lambda^2 - 116.608}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[5.31 \times 10^{-6} + 2(1.59 \times 10^{-8})\,\Delta T + 3(-4.07 \times 10^{-11})\,\Delta T^2 + \frac{1.28 \times 10^{-6} + 2(1.32 \times 10^{-9})\,\Delta T}{\lambda - 0.27}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$