S-LAH71 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.9828\,\lambda^2}{\lambda^2 - 0.0118987} + \frac{0.316758\,\lambda^2}{\lambda^2 - 0.0527156} + \frac{2.44473\,\lambda^2}{\lambda^2 - 213.221}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-3.71 \times 10^{-7} + 2(9.01 \times 10^{-9})\,\Delta T + 3(-2.99 \times 10^{-11})\,\Delta T^2 + \frac{9.14 \times 10^{-7} + 2(1.11 \times 10^{-9})\,\Delta T}{\lambda - 0.257}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$