H-ZK21 by CDGM

$$n(\lambda) = \sqrt{1 + \frac{0.894249\,\lambda^2}{\lambda^2 - 0.00384522} + \frac{0.696413\,\lambda^2}{\lambda^2 - 0.017413} + \frac{1.07122\,\lambda^2}{\lambda^2 - 102.206}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[8.71 \times 10^{-7} + 2(1.71 \times 10^{-8})\,\Delta T + 3(-8.72 \times 10^{-11})\,\Delta T^2 + \frac{4.27 \times 10^{-7} + 2(-7.8 \times 10^{-10})\,\Delta T}{\lambda - 0.222}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$