H-QF1 by CDGM

$$n(\lambda) = \sqrt{1 + \frac{1.24414\,\lambda^2}{\lambda^2 - 0.00867592} + \frac{1.08793\,\lambda^2}{\lambda^2 - 124.771} + \frac{0.106583\,\lambda^2}{\lambda^2 - 0.0473896}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-3.37 \times 10^{-6} + 2(1.32 \times 10^{-8})\,\Delta T + 3(-5.38 \times 10^{-11})\,\Delta T^2 + \frac{6.46 \times 10^{-7} + 2(6.5 \times 10^{-10})\,\Delta T}{\lambda - 0.251}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$