F14 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.3195\,\lambda^2}{\lambda^2 - 0.00980475} + \frac{0.181107\,\lambda^2}{\lambda^2 - 0.0465331} + \frac{0.92185\,\lambda^2}{\lambda^2 - 109.855}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[2.3 \times 10^{-6} + 2(1.85 \times 10^{-8})\,\Delta T + 3(-2.46 \times 10^{-11})\,\Delta T^2 + \frac{9.22 \times 10^{-7} + 2(6.14 \times 10^{-10})\,\Delta T}{\lambda - 0.236}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$