SF6G05 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.62114\,\lambda^2}{\lambda^2 - 0.0113479} + \frac{0.506586\,\lambda^2}{\lambda^2 - 0.053584} + \frac{10.4032\,\lambda^2}{\lambda^2 - 1118.84}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[6.9 \times 10^{-6} + 2(1.76 \times 10^{-8})\,\Delta T + 3(-3.17 \times 10^{-11})\,\Delta T^2 + \frac{1.89 \times 10^{-6} + 2(1.5 \times 10^{-9})\,\Delta T}{\lambda - 0.256}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$