KZFS8 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.60299\,\lambda^2}{\lambda^2 - 0.0106585} + \frac{0.267572\,\lambda^2}{\lambda^2 - 0.0476203} + \frac{0.976091\,\lambda^2}{\lambda^2 - 76.4326}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[6.08 \times 10^{-6} + 2(1.48 \times 10^{-8})\,\Delta T + 3(-2.26 \times 10^{-11})\,\Delta T^2 + \frac{9.93 \times 10^{-7} + 2(1.02 \times 10^{-9})\,\Delta T}{\lambda - 0.215}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$