LAH80 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{2.06636\,\lambda^2}{\lambda^2 - 0.0122134} + \frac{0.349316\,\lambda^2}{\lambda^2 - 0.055596} + \frac{1.91746\,\lambda^2}{\lambda^2 - 125.474}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[2.6 \times 10^{-6} + 2(1.15 \times 10^{-8})\,\Delta T + 3(-3.36 \times 10^{-11})\,\Delta T^2 + \frac{8.82 \times 10^{-7} + 2(1.2 \times 10^{-9})\,\Delta T}{\lambda - 0.279}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$