P-SF8 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.5537\,\lambda^2}{\lambda^2 - 0.0116583} + \frac{0.206333\,\lambda^2}{\lambda^2 - 0.0582088} + \frac{1.39709\,\lambda^2}{\lambda^2 - 130.748}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-4.27 \times 10^{-6} + 2(8.16 \times 10^{-9})\,\Delta T + 3(-2 \times 10^{-11})\,\Delta T^2 + \frac{9.02 \times 10^{-7} + 2(1.22 \times 10^{-9})\,\Delta T}{\lambda - 0.272}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$