LASF35 by Schott

$$n(\lambda) = \sqrt{1 + \frac{2.45506\,\lambda^2}{\lambda^2 - 0.013567} + \frac{0.453006\,\lambda^2}{\lambda^2 - 0.0545803} + \frac{2.38513\,\lambda^2}{\lambda^2 - 167.905}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[1.43 \times 10^{-7} + 2(8.71 \times 10^{-9})\,\Delta T + 3(-2.71 \times 10^{-11})\,\Delta T^2 + \frac{1.02 \times 10^{-6} + 2(1.5 \times 10^{-9})\,\Delta T}{\lambda - 0.263}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$