H-ZK20 by CDGM

$$n(\lambda) = \sqrt{1 + \frac{0.812249\,\lambda^2}{\lambda^2 - 0.0181754} + \frac{0.755251\,\lambda^2}{\lambda^2 - 0.00247828} + \frac{1.15074\,\lambda^2}{\lambda^2 - 144.031}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[3.38 \times 10^{-7} + 2(1.59 \times 10^{-8})\,\Delta T + 3(-2.45 \times 10^{-11})\,\Delta T^2 + \frac{6.4 \times 10^{-7} + 2(4.47 \times 10^{-10})\,\Delta T}{\lambda - 0.192}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$