H-ZK5 by CDGM

$$n(\lambda) = \sqrt{1 + \frac{0.920219\,\lambda^2}{\lambda^2 - 109.362} + \frac{0.531425\,\lambda^2}{\lambda^2 - 0.0198986} + \frac{1.01909\,\lambda^2}{\lambda^2 - 0.0052582}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-3.46 \times 10^{-6} + 2(1.21 \times 10^{-8})\,\Delta T + 3(1.31 \times 10^{-11})\,\Delta T^2 + \frac{5.78 \times 10^{-7} + 2(6.03 \times 10^{-10})\,\Delta T}{\lambda - 0.17}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$