N-KZFS8 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.62694\,\lambda^2}{\lambda^2 - 0.0108809} + \frac{0.243699\,\lambda^2}{\lambda^2 - 0.0494208} + \frac{1.62007\,\lambda^2}{\lambda^2 - 131.009}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[7.93 \times 10^{-7} + 2(6.47 \times 10^{-9})\,\Delta T + 3(-5 \times 10^{-12})\,\Delta T^2 + \frac{7.71 \times 10^{-7} + 2(1.01 \times 10^{-9})\,\Delta T}{\lambda - 0.254}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$