H-QK1 by CDGM

$$n(\lambda) = \sqrt{1 + \frac{0.841944\,\lambda^2}{\lambda^2 - 93.2639} + \frac{0.991785\,\lambda^2}{\lambda^2 - 0.0103999} + \frac{0.146213\,\lambda^2}{\lambda^2 - -0.00820301}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-4.39 \times 10^{-6} + 2(2.39 \times 10^{-8})\,\Delta T + 3(-3.11 \times 10^{-11})\,\Delta T^2 + \frac{3.4 \times 10^{-7} + 2(2.1 \times 10^{-10})\,\Delta T}{\lambda - 0.199}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$