SK16 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.34318\,\lambda^2}{\lambda^2 - 0.00704687} + \frac{0.241144\,\lambda^2}{\lambda^2 - 0.0229005} + \frac{0.994318\,\lambda^2}{\lambda^2 - 92.7509}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-2.37 \times 10^{-8} + 2(1.32 \times 10^{-8})\,\Delta T + 3(-1.29 \times 10^{-11})\,\Delta T^2 + \frac{4.09 \times 10^{-7} + 2(5.17 \times 10^{-10})\,\Delta T}{\lambda - 0.17}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$