H-TK9 by CDGM

$$n(\lambda) = \sqrt{1 + \frac{1.4878\,\lambda^2}{\lambda^2 - 0.00771068} + \frac{0.895205\,\lambda^2}{\lambda^2 - 127.355} + \frac{0.0957464\,\lambda^2}{\lambda^2 - 0.0376689}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-1.74 \times 10^{-5} + 2(6.65 \times 10^{-9})\,\Delta T + 3(-1.55 \times 10^{-11})\,\Delta T^2 + \frac{4.7 \times 10^{-7} + 2(1.18 \times 10^{-10})\,\Delta T}{\lambda - 0.217}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$