K4A by CDGM

$$n(\lambda) = \sqrt{1 + \frac{0.749532\,\lambda^2}{\lambda^2 - 0.0148034} + \frac{0.494866\,\lambda^2}{\lambda^2 - -0.000264092} + \frac{0.960169\,\lambda^2}{\lambda^2 - 95.719}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[7.37 \times 10^{-6} + 2(2.2 \times 10^{-8})\,\Delta T + 3(-6.81 \times 10^{-12})\,\Delta T^2 + \frac{4.56 \times 10^{-7} + 2(4.32 \times 10^{-10})\,\Delta T}{\lambda - 0.199}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$