BAF3 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.32064\,\lambda^2}{\lambda^2 - 0.00887799} + \frac{0.133573\,\lambda^2}{\lambda^2 - 0.042029} + \frac{0.885522\,\lambda^2}{\lambda^2 - 111.729}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[1.41 \times 10^{-6} + 2(1.73 \times 10^{-8})\,\Delta T + 3(-1.51 \times 10^{-11})\,\Delta T^2 + \frac{5.76 \times 10^{-7} + 2(4.68 \times 10^{-10})\,\Delta T}{\lambda - 0.267}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$