N-LAF7 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.74029\,\lambda^2}{\lambda^2 - 0.0107926} + \frac{0.226711\,\lambda^2}{\lambda^2 - 0.0538627} + \frac{1.32526\,\lambda^2}{\lambda^2 - 106.269}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[9.21 \times 10^{-7} + 2(1.1 \times 10^{-8})\,\Delta T + 3(-1.75 \times 10^{-11})\,\Delta T^2 + \frac{7.67 \times 10^{-7} + 2(1.1 \times 10^{-9})\,\Delta T}{\lambda - 0.264}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$