N-SSK5 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.59223\,\lambda^2}{\lambda^2 - 0.00920285} + \frac{0.103521\,\lambda^2}{\lambda^2 - 0.042353} + \frac{1.05174\,\lambda^2}{\lambda^2 - 106.927}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[7.29 \times 10^{-7} + 2(1.17 \times 10^{-8})\,\Delta T + 3(-1.5 \times 10^{-11})\,\Delta T^2 + \frac{6.08 \times 10^{-7} + 2(7.66 \times 10^{-10})\,\Delta T}{\lambda - 0.189}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$