KZFN1 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.1995\,\lambda^2}{\lambda^2 - 0.00767704} + \frac{0.163892\,\lambda^2}{\lambda^2 - 0.0352898} + \frac{0.890412\,\lambda^2}{\lambda^2 - 94.3367}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[2.25 \times 10^{-6} + 2(1.8 \times 10^{-8})\,\Delta T + 3(-2.28 \times 10^{-11})\,\Delta T^2 + \frac{5.35 \times 10^{-7} + 2(6.6 \times 10^{-10})\,\Delta T}{\lambda - 0.229}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$