L-PHL2 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.08137\,\lambda^2}{\lambda^2 - 0.0059421} + \frac{0.313258\,\lambda^2}{\lambda^2 - 0.0198012} + \frac{0.879193\,\lambda^2}{\lambda^2 - 109.894}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-4.53 \times 10^{-6} + 2(8.19 \times 10^{-9})\,\Delta T + 3(-3.49 \times 10^{-11})\,\Delta T^2 + \frac{4.89 \times 10^{-7} + 2(4.76 \times 10^{-10})\,\Delta T}{\lambda - 0.221}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$