BASF10 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.47553\,\lambda^2}{\lambda^2 - 0.0101493} + \frac{0.177121\,\lambda^2}{\lambda^2 - 0.0477578} + \frac{0.942502\,\lambda^2}{\lambda^2 - 118.726}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-4.33 \times 10^{-7} + 2(1.24 \times 10^{-8})\,\Delta T + 3(-2.2 \times 10^{-11})\,\Delta T^2 + \frac{9.4 \times 10^{-7} + 2(9.51 \times 10^{-10})\,\Delta T}{\lambda - 0.23}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$