S-LAH98 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{2.28511\,\lambda^2}{\lambda^2 - 0.0122179} + \frac{0.385532\,\lambda^2}{\lambda^2 - 0.0514752} + \frac{2.06551\,\lambda^2}{\lambda^2 - 145.921}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[1.68 \times 10^{-7} + 2(8.94 \times 10^{-9})\,\Delta T + 3(-2.93 \times 10^{-11})\,\Delta T^2 + \frac{9.61 \times 10^{-7} + 2(1.11 \times 10^{-9})\,\Delta T}{\lambda - 0.254}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$