SF58 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.92184\,\lambda^2}{\lambda^2 - 0.0149263} + \frac{0.552192\,\lambda^2}{\lambda^2 - 0.0614139} + \frac{1.11644\,\lambda^2}{\lambda^2 - 123.45}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[4.98 \times 10^{-6} + 2(1.68 \times 10^{-8})\,\Delta T + 3(-4.44 \times 10^{-11})\,\Delta T^2 + \frac{2.37 \times 10^{-6} + 2(2.39 \times 10^{-9})\,\Delta T}{\lambda - 0.28}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$