KZFN2 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.12337\,\lambda^2}{\lambda^2 - 0.00712847} + \frac{0.177618\,\lambda^2}{\lambda^2 - 0.0317291} + \frac{0.849213\,\lambda^2}{\lambda^2 - 84.9657}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[3.51 \times 10^{-6} + 2(1.97 \times 10^{-8})\,\Delta T + 3(-1.93 \times 10^{-11})\,\Delta T^2 + \frac{6.02 \times 10^{-7} + 2(7.23 \times 10^{-10})\,\Delta T}{\lambda - 0.143}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$