S-LAH55 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.95616\,\lambda^2}{\lambda^2 - 0.00979339} + \frac{0.319216\,\lambda^2}{\lambda^2 - 0.0376836} + \frac{1.39173\,\lambda^2}{\lambda^2 - 94.8775}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[2.4 \times 10^{-6} + 2(1.26 \times 10^{-8})\,\Delta T + 3(-2.98 \times 10^{-11})\,\Delta T^2 + \frac{6.81 \times 10^{-7} + 2(8.19 \times 10^{-10})\,\Delta T}{\lambda - 0.211}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$