S-LAH53 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.91812\,\lambda^2}{\lambda^2 - 0.0102148} + \frac{0.253724\,\lambda^2}{\lambda^2 - 0.0433176} + \frac{1.39474\,\lambda^2}{\lambda^2 - 101.938}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[5.52 \times 10^{-6} + 2(1.63 \times 10^{-8})\,\Delta T + 3(2.71 \times 10^{-12})\,\Delta T^2 + \frac{8.93 \times 10^{-7} + 2(5.67 \times 10^{-10})\,\Delta T}{\lambda - 0.188}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$