S-FPM3 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{0.809407\,\lambda^2}{\lambda^2 - 0.00376072} + \frac{0.527007\,\lambda^2}{\lambda^2 - 0.0135655} + \frac{0.909128\,\lambda^2}{\lambda^2 - 142.504}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-1.39 \times 10^{-5} + 2(1.49 \times 10^{-9})\,\Delta T + 3(1.66 \times 10^{-11})\,\Delta T^2 + \frac{3.43 \times 10^{-7} + 2(1.65 \times 10^{-10})\,\Delta T}{\lambda - 0.218}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$