D-FK61A-25 by CDGM

$$n(\lambda) = \sqrt{1 + \frac{0.714581\,\lambda^2}{\lambda^2 - 0.0108379} + \frac{0.502175\,\lambda^2}{\lambda^2 - 0.0013231} + \frac{0.838296\,\lambda^2}{\lambda^2 - 153.776}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-1.94 \times 10^{-5} + 2(2.54 \times 10^{-9})\,\Delta T + 3(-2.83 \times 10^{-11})\,\Delta T^2 + \frac{3.05 \times 10^{-7} + 2(-9.31 \times 10^{-11})\,\Delta T}{\lambda - 0.242}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$