N-BALF5 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.28386\,\lambda^2}{\lambda^2 - 0.00825816} + \frac{0.0719301\,\lambda^2}{\lambda^2 - 0.044192} + \frac{1.05049\,\lambda^2}{\lambda^2 - 107.097}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[1.14 \times 10^{-6} + 2(1.29 \times 10^{-8})\,\Delta T + 3(-1.46 \times 10^{-11})\,\Delta T^2 + \frac{5.02 \times 10^{-7} + 2(5.87 \times 10^{-10})\,\Delta T}{\lambda - 0.219}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$