L-LAH86 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{2.11103\,\lambda^2}{\lambda^2 - 0.0120714} + \frac{0.370368\,\lambda^2}{\lambda^2 - 0.0532464} + \frac{1.62687\,\lambda^2}{\lambda^2 - 109.166}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[2.69 \times 10^{-6} + 2(1.07 \times 10^{-8})\,\Delta T + 3(-9.48 \times 10^{-12})\,\Delta T^2 + \frac{8.91 \times 10^{-7} + 2(1.11 \times 10^{-9})\,\Delta T}{\lambda - 0.274}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$