S-FSL5 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.17447\,\lambda^2}{\lambda^2 - 0.00841855} + \frac{0.0140056\,\lambda^2}{\lambda^2 - -0.0581791} + \frac{1.19272\,\lambda^2}{\lambda^2 - 129.6}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-6.33 \times 10^{-6} + 2(1.8 \times 10^{-8})\,\Delta T + 3(-5.04 \times 10^{-12})\,\Delta T^2 + \frac{3.3 \times 10^{-7} + 2(2.62 \times 10^{-10})\,\Delta T}{\lambda - 0.208}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$