LASFN30 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.78301\,\lambda^2}{\lambda^2 - 0.00872506} + \frac{0.388968\,\lambda^2}{\lambda^2 - 0.0308085} + \frac{1.3015\,\lambda^2}{\lambda^2 - 92.7744}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[3.32 \times 10^{-6} + 2(1.12 \times 10^{-8})\,\Delta T + 3(-8.52 \times 10^{-12})\,\Delta T^2 + \frac{5.88 \times 10^{-7} + 2(7.13 \times 10^{-10})\,\Delta T}{\lambda - 0.209}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$