S-LAH93 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{2.17884\,\lambda^2}{\lambda^2 - 0.0115761} + \frac{0.325509\,\lambda^2}{\lambda^2 - 0.0495983} + \frac{1.70609\,\lambda^2}{\lambda^2 - 128.914}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[2.48 \times 10^{-6} + 2(9.67 \times 10^{-9})\,\Delta T + 3(-3.51 \times 10^{-12})\,\Delta T^2 + \frac{8.57 \times 10^{-7} + 2(9.77 \times 10^{-10})\,\Delta T}{\lambda - 0.258}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$