ZBAF17 by CDGM

$$n(\lambda) = \sqrt{2.71148 - 0.0083031\,\lambda^2 + 0.0237332\,\lambda^{-2} + 0.000281977\,\lambda^{-4} + 3.94099 \times 10^{-5}\,\lambda^{-6} + 7.17563 \times 10^{-7}\,\lambda^{-8}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[3.29 \times 10^{-8} + 2(1.54 \times 10^{-8})\,\Delta T + 3(-1.58 \times 10^{-11})\,\Delta T^2 + \frac{7.94 \times 10^{-7} + 2(1.05 \times 10^{-9})\,\Delta T}{\lambda - 0.24}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$