L-LAH87 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.44196\,\lambda^2}{\lambda^2 - 0.00731827} + \frac{0.617507\,\lambda^2}{\lambda^2 - 0.0245371} + \frac{1.2189\,\lambda^2}{\lambda^2 - 105.976}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[6.1 \times 10^{-6} + 2(9.05 \times 10^{-9})\,\Delta T + 3(-1.35 \times 10^{-11})\,\Delta T^2 + \frac{7.87 \times 10^{-7} + 2(7.19 \times 10^{-10})\,\Delta T}{\lambda - 0.19}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$