H-ZF52A by CDGM

$$n(\lambda) = \sqrt{3.25069 - 0.0133942\,\lambda^2 + 0.0483626\,\lambda^{-2} + 0.00314443\,\lambda^{-4} - 0.000197074\,\lambda^{-6} + 3.47646 \times 10^{-5}\,\lambda^{-8}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-6.9 \times 10^{-6} + 2(1.71 \times 10^{-8})\,\Delta T + 3(-4.57 \times 10^{-11})\,\Delta T^2 + \frac{1.16 \times 10^{-6} + 2(8.99 \times 10^{-10})\,\Delta T}{\lambda - 0.285}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$