D-ZK21 by CDGM

$$n(\lambda) = \sqrt{1 + \frac{1.31515\,\lambda^2}{\lambda^2 - 103.989} + \frac{1.08358\,\lambda^2}{\lambda^2 - 0.0143813} + \frac{0.513109\,\lambda^2}{\lambda^2 - -0.000363924}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[4.26 \times 10^{-6} + 2(1.53 \times 10^{-8})\,\Delta T + 3(-2.43 \times 10^{-11})\,\Delta T^2 + \frac{4.86 \times 10^{-7} + 2(2.51 \times 10^{-10})\,\Delta T}{\lambda - 0.199}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$