LASF3 by Schott

$$n(\lambda) = \sqrt{1 + \frac{1.95904\,\lambda^2}{\lambda^2 - 0.0104347} + \frac{0.219801\,\lambda^2}{\lambda^2 - 0.0465504} + \frac{1.33464\,\lambda^2}{\lambda^2 - 87.9058}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[5.24 \times 10^{-6} + 2(1.24 \times 10^{-8})\,\Delta T + 3(-7.89 \times 10^{-12})\,\Delta T^2 + \frac{6.59 \times 10^{-7} + 2(8.8 \times 10^{-10})\,\Delta T}{\lambda - 0.239}\right] \Delta T = T - T_0, \quad T_0 = 20\,°\text{C}$$