H-QF56 by CDGM

$$n(\lambda) = \sqrt{1 + \frac{1.01194\,\lambda^2}{\lambda^2 - 116.639} + \frac{0.110712\,\lambda^2}{\lambda^2 - 0.0511037} + \frac{1.29397\,\lambda^2}{\lambda^2 - 0.0092374}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-4.86 \times 10^{-6} + 2(1.38 \times 10^{-8})\,\Delta T + 3(-3.64 \times 10^{-11})\,\Delta T^2 + \frac{7.51 \times 10^{-7} + 2(4.38 \times 10^{-11})\,\Delta T}{\lambda - 0.236}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$