H-ZF2 by CDGM

$$n(\lambda) = \sqrt{1 + \frac{0.167643\,\lambda^2}{\lambda^2 - 0.0605178} + \frac{1.54335\,\lambda^2}{\lambda^2 - 0.0118524} + \frac{1.17313\,\lambda^2}{\lambda^2 - 113.671}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-3.63 \times 10^{-6} + 2(1.35 \times 10^{-8})\,\Delta T + 3(-5.31 \times 10^{-11})\,\Delta T^2 + \frac{8.33 \times 10^{-7} + 2(8.4 \times 10^{-10})\,\Delta T}{\lambda - 0.278}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$