P-LASF51 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.84569\,\lambda^2}{\lambda^2 - 0.00988496} + \frac{0.339002\,\lambda^2}{\lambda^2 - 0.0378097} + \frac{1.32419\,\lambda^2}{\lambda^2 - 97.8415}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[7.79 \times 10^{-6} + 2(1.1 \times 10^{-8})\,\Delta T + 3(-2.03 \times 10^{-11})\,\Delta T^2 + \frac{7.86 \times 10^{-7} + 2(8.78 \times 10^{-10})\,\Delta T}{\lambda - 0.215}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$