N-LASF9 by Schott

$$n(\lambda) = \sqrt{1 + \frac{2.0003\,\lambda^2}{\lambda^2 - 0.0121426} + \frac{0.298927\,\lambda^2}{\lambda^2 - 0.0538736} + \frac{1.80692\,\lambda^2}{\lambda^2 - 156.531}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[1.05 \times 10^{-6} + 2(1.02 \times 10^{-8})\,\Delta T + 3(-2.38 \times 10^{-11})\,\Delta T^2 + \frac{9.19 \times 10^{-7} + 2(1.18 \times 10^{-9})\,\Delta T}{\lambda - 0.257}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$