H-F52 by CDGM

$$n(\lambda) = \sqrt{1 + \frac{0.145719\,\lambda^2}{\lambda^2 - 0.0588532} + \frac{1.3881\,\lambda^2}{\lambda^2 - 0.0106276} + \frac{1.21907\,\lambda^2}{\lambda^2 - 126.468}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-4.58 \times 10^{-6} + 2(1.65 \times 10^{-8})\,\Delta T + 3(-4.33 \times 10^{-11})\,\Delta T^2 + \frac{7.2 \times 10^{-7} + 2(7.3 \times 10^{-10})\,\Delta T}{\lambda - 0.284}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$