L-LAH83 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.82332\,\lambda^2}{\lambda^2 - 0.00911469} + \frac{0.548626\,\lambda^2}{\lambda^2 - 0.032842} + \frac{1.63183\,\lambda^2}{\lambda^2 - 123.611}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[3.99 \times 10^{-6} + 2(9.76 \times 10^{-9})\,\Delta T + 3(-1.73 \times 10^{-11})\,\Delta T^2 + \frac{7.56 \times 10^{-7} + 2(7.71 \times 10^{-10})\,\Delta T}{\lambda - 0.225}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$