S-LAH65 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.68191\,\lambda^2}{\lambda^2 - 0.00776684} + \frac{0.49378\,\lambda^2}{\lambda^2 - 0.0288916} + \frac{1.45683\,\lambda^2}{\lambda^2 - 99.2574}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[3.21 \times 10^{-6} + 2(1.28 \times 10^{-8})\,\Delta T + 3(-3.45 \times 10^{-11})\,\Delta T^2 + \frac{4.22 \times 10^{-7} + 2(5.14 \times 10^{-10})\,\Delta T}{\lambda - 0.275}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$