K10 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.15687\,\lambda^2}{\lambda^2 - 0.00809424} + \frac{0.0642625\,\lambda^2}{\lambda^2 - 0.0386051} + \frac{0.872376\,\lambda^2}{\lambda^2 - 104.748}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[4.86 \times 10^{-6} + 2(1.72 \times 10^{-8})\,\Delta T + 3(-3.02 \times 10^{-11})\,\Delta T^2 + \frac{3.82 \times 10^{-7} + 2(4.53 \times 10^{-10})\,\Delta T}{\lambda - 0.26}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$