KZFSN5 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.47728\,\lambda^2}{\lambda^2 - 0.00975488} + \frac{0.191687\,\lambda^2}{\lambda^2 - 0.0450495} + \frac{0.897334\,\lambda^2}{\lambda^2 - 67.8786}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[5.51 \times 10^{-6} + 2(1.48 \times 10^{-8})\,\Delta T + 3(-2.21 \times 10^{-11})\,\Delta T^2 + \frac{6.22 \times 10^{-7} + 2(7.05 \times 10^{-10})\,\Delta T}{\lambda - 0.23}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$