SK10 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.31659\,\lambda^2}{\lambda^2 - 0.00712229} + \frac{0.271656\,\lambda^2}{\lambda^2 - 0.0244417} + \frac{0.968688\,\lambda^2}{\lambda^2 - 105.082}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[2.69 \times 10^{-7} + 2(1.11 \times 10^{-8})\,\Delta T + 3(-8.91 \times 10^{-12})\,\Delta T^2 + \frac{4.89 \times 10^{-7} + 2(6.13 \times 10^{-10})\,\Delta T}{\lambda - 0.182}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$