N-LASF40 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.9855\,\lambda^2}{\lambda^2 - 0.0109583} + \frac{0.274057\,\lambda^2}{\lambda^2 - 0.0474552} + \frac{1.28946\,\lambda^2}{\lambda^2 - 96.9085}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[8.1 \times 10^{-6} + 2(1.25 \times 10^{-8})\,\Delta T + 3(-1.73 \times 10^{-11})\,\Delta T^2 + \frac{8.27 \times 10^{-7} + 2(1.08 \times 10^{-9})\,\Delta T}{\lambda - 0.238}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$