L-LAM69 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.74039\,\lambda^2}{\lambda^2 - 0.0103399} + \frac{0.176997\,\lambda^2}{\lambda^2 - 0.0484823} + \frac{1.76775\,\lambda^2}{\lambda^2 - 136.672}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[1.81 \times 10^{-7} + 2(7.4 \times 10^{-9})\,\Delta T + 3(-3.48 \times 10^{-11})\,\Delta T^2 + \frac{7.12 \times 10^{-7} + 2(8.78 \times 10^{-10})\,\Delta T}{\lambda - 0.249}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$