S-LAH58 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.78765\,\lambda^2}{\lambda^2 - 0.00847379} + \frac{0.652636\,\lambda^2}{\lambda^2 - 0.0313126} + \frac{1.79915\,\lambda^2}{\lambda^2 - 132.788}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[2.37 \times 10^{-6} + 2(1.28 \times 10^{-8})\,\Delta T + 3(-3.08 \times 10^{-11})\,\Delta T^2 + \frac{6.33 \times 10^{-7} + 2(5.04 \times 10^{-10})\,\Delta T}{\lambda - 0.248}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$