S-LAH64 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.83021\,\lambda^2}{\lambda^2 - 0.00904823} + \frac{0.291564\,\lambda^2}{\lambda^2 - 0.0330757} + \frac{1.28544\,\lambda^2}{\lambda^2 - 89.3676}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[3.03 \times 10^{-6} + 2(1.2 \times 10^{-8})\,\Delta T + 3(-3.49 \times 10^{-11})\,\Delta T^2 + \frac{4.09 \times 10^{-7} + 2(4.61 \times 10^{-10})\,\Delta T}{\lambda - 0.277}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$