N-SF14 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.69022\,\lambda^2}{\lambda^2 - 0.0130512} + \frac{0.28887\,\lambda^2}{\lambda^2 - 0.0613692} + \frac{1.70452\,\lambda^2}{\lambda^2 - 149.518}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-5.56 \times 10^{-6} + 2(7.09 \times 10^{-9})\,\Delta T + 3(-1.09 \times 10^{-11})\,\Delta T^2 + \frac{9.85 \times 10^{-7} + 2(1.39 \times 10^{-9})\,\Delta T}{\lambda - 0.287}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$