L-LAH94 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{2.00621\,\lambda^2}{\lambda^2 - 0.0105499} + \frac{0.34703\,\lambda^2}{\lambda^2 - 0.0445845} + \frac{1.41688\,\lambda^2}{\lambda^2 - 105.995}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[5.03 \times 10^{-6} + 2(1.04 \times 10^{-8})\,\Delta T + 3(-9.78 \times 10^{-12})\,\Delta T^2 + \frac{8.28 \times 10^{-7} + 2(9.04 \times 10^{-10})\,\Delta T}{\lambda - 0.25}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$