N-LASF31 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.71317\,\lambda^2}{\lambda^2 - 0.00819172} + \frac{0.718575\,\lambda^2}{\lambda^2 - 0.0297802} + \frac{1.72332\,\lambda^2}{\lambda^2 - 138.461}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[2.29 \times 10^{-6} + 2(8.93 \times 10^{-9})\,\Delta T + 3(-1.59 \times 10^{-11})\,\Delta T^2 + \frac{6.52 \times 10^{-7} + 2(8.09 \times 10^{-10})\,\Delta T}{\lambda - 0.236}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$