L-LAH85 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.9389\,\lambda^2}{\lambda^2 - 0.00996382} + \frac{0.397879\,\lambda^2}{\lambda^2 - 0.0369751} + \frac{1.49938\,\lambda^2}{\lambda^2 - 107.951}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[4.03 \times 10^{-6} + 2(1.06 \times 10^{-8})\,\Delta T + 3(-9.93 \times 10^{-12})\,\Delta T^2 + \frac{7.49 \times 10^{-7} + 2(7.76 \times 10^{-10})\,\Delta T}{\lambda - 0.222}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$