N-SK10 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.34972\,\lambda^2}{\lambda^2 - 0.00736272} + \frac{0.238588\,\lambda^2}{\lambda^2 - 0.0253765} + \frac{0.966734\,\lambda^2}{\lambda^2 - 103.503}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[5.05 \times 10^{-7} + 2(1.16 \times 10^{-8})\,\Delta T + 3(-1.53 \times 10^{-11})\,\Delta T^2 + \frac{4.9 \times 10^{-7} + 2(5.1 \times 10^{-10})\,\Delta T}{\lambda - 0.183}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$