LAFN24 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.7096\,\lambda^2}{\lambda^2 - 0.00836252} + \frac{0.308713\,\lambda^2}{\lambda^2 - 0.0324825} + \frac{1.24764\,\lambda^2}{\lambda^2 - 84.8077}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[5.99 \times 10^{-6} + 2(1.32 \times 10^{-8})\,\Delta T + 3(-2.3 \times 10^{-11})\,\Delta T^2 + \frac{4.63 \times 10^{-7} + 2(7.15 \times 10^{-10})\,\Delta T}{\lambda - 0.247}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$