S-LAH52 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.85391\,\lambda^2}{\lambda^2 - 0.00955321} + \frac{0.297926\,\lambda^2}{\lambda^2 - 0.0393817} + \frac{1.39382\,\lambda^2}{\lambda^2 - 102.707}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[5.34 \times 10^{-6} + 2(1.23 \times 10^{-8})\,\Delta T + 3(6.91 \times 10^{-12})\,\Delta T^2 + \frac{7.5 \times 10^{-7} + 2(8.12 \times 10^{-10})\,\Delta T}{\lambda - 0.219}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$