H-K11 by CDGM

$$n(\lambda) = \sqrt{1 + \frac{0.795537\,\lambda^2}{\lambda^2 - 0.00400873} + \frac{0.500949\,\lambda^2}{\lambda^2 - 0.0175437} + \frac{0.905052\,\lambda^2}{\lambda^2 - 111.287}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-5.95 \times 10^{-6} + 2(1.38 \times 10^{-8})\,\Delta T + 3(-4.14 \times 10^{-11})\,\Delta T^2 + \frac{5.05 \times 10^{-7} + 2(5.13 \times 10^{-10})\,\Delta T}{\lambda - 0.194}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$