N-BAF52 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.43903\,\lambda^2}{\lambda^2 - 0.009078} + \frac{0.0967046\,\lambda^2}{\lambda^2 - 0.0508212} + \frac{1.09876\,\lambda^2}{\lambda^2 - 105.692}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[1.15 \times 10^{-6} + 2(1.27 \times 10^{-8})\,\Delta T + 3(-5.08 \times 10^{-12})\,\Delta T^2 + \frac{5.64 \times 10^{-7} + 2(6.38 \times 10^{-10})\,\Delta T}{\lambda - 0.238}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$