L-PHL1 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.07571\,\lambda^2}{\lambda^2 - 0.00591654} + \frac{0.33502\,\lambda^2}{\lambda^2 - 0.0203433} + \frac{0.810998\,\lambda^2}{\lambda^2 - 106.182}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-5.46 \times 10^{-6} + 2(7.3 \times 10^{-9})\,\Delta T + 3(-4.11 \times 10^{-11})\,\Delta T^2 + \frac{5.89 \times 10^{-7} + 2(6.92 \times 10^{-10})\,\Delta T}{\lambda - 0.202}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$