N-SF11 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.7376\,\lambda^2}{\lambda^2 - 0.0131887} + \frac{0.313747\,\lambda^2}{\lambda^2 - 0.0623068} + \frac{1.89878\,\lambda^2}{\lambda^2 - 155.236}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-3.56 \times 10^{-6} + 2(9.2 \times 10^{-9})\,\Delta T + 3(-2.1 \times 10^{-11})\,\Delta T^2 + \frac{9.65 \times 10^{-7} + 2(1.44 \times 10^{-9})\,\Delta T}{\lambda - 0.294}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$