SK14 by Schott

$$n(\lambda) = \sqrt{1 + \frac{0.936155\,\lambda^2}{\lambda^2 - 0.00461717} + \frac{0.594052\,\lambda^2}{\lambda^2 - 0.0168859} + \frac{1.04375\,\lambda^2}{\lambda^2 - 103.736}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[1.58 \times 10^{-6} + 2(1.22 \times 10^{-8})\,\Delta T + 3(-8.04 \times 10^{-12})\,\Delta T^2 + \frac{4.46 \times 10^{-7} + 2(5.22 \times 10^{-10})\,\Delta T}{\lambda - 0.15}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$