N-LASF31A by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.96485\,\lambda^2}{\lambda^2 - 0.0098206} + \frac{0.475231\,\lambda^2}{\lambda^2 - 0.0344713} + \frac{1.4836\,\lambda^2}{\lambda^2 - 110.74}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[1.67 \times 10^{-6} + 2(8.9 \times 10^{-9})\,\Delta T + 3(-8.73 \times 10^{-12})\,\Delta T^2 + \frac{7.47 \times 10^{-7} + 2(7.46 \times 10^{-10})\,\Delta T}{\lambda - 0.207}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$