LAFN10 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.872\,\lambda^2}{\lambda^2 - 0.00967116} + \frac{0.232399\,\lambda^2}{\lambda^2 - 0.0406266} + \frac{1.29454\,\lambda^2}{\lambda^2 - 87.1629}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[4.42 \times 10^{-6} + 2(1.18 \times 10^{-8})\,\Delta T + 3(-1.16 \times 10^{-11})\,\Delta T^2 + \frac{5.19 \times 10^{-7} + 2(6.99 \times 10^{-10})\,\Delta T}{\lambda - 0.256}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$