BAFN11 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.60255\,\lambda^2}{\lambda^2 - 0.00938812} + \frac{0.116919\,\lambda^2}{\lambda^2 - 0.0440475} + \frac{1.02861\,\lambda^2}{\lambda^2 - 104.533}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[1.24 \times 10^{-6} + 2(1.1 \times 10^{-8})\,\Delta T + 3(-3.67 \times 10^{-11})\,\Delta T^2 + \frac{7.75 \times 10^{-7} + 2(4.1 \times 10^{-10})\,\Delta T}{\lambda - 0.132}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$