H-QF6A by CDGM

$$n(\lambda) = \sqrt{1 + \frac{0.0830015\,\lambda^2}{\lambda^2 - 0.0493974} + \frac{1.22223\,\lambda^2}{\lambda^2 - 0.00830689} + \frac{1.01475\,\lambda^2}{\lambda^2 - 114.774}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-5.28 \times 10^{-6} + 2(2.18 \times 10^{-8})\,\Delta T + 3(-9.29 \times 10^{-11})\,\Delta T^2 + \frac{4.95 \times 10^{-7} + 2(4.67 \times 10^{-10})\,\Delta T}{\lambda - 0.262}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$