S-LAH66 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.39281\,\lambda^2}{\lambda^2 - 0.00608475} + \frac{0.679577\,\lambda^2}{\lambda^2 - 0.0233925} + \frac{1.38702\,\lambda^2}{\lambda^2 - 95.8354}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[3.03 \times 10^{-6} + 2(1.36 \times 10^{-8})\,\Delta T + 3(-3.27 \times 10^{-11})\,\Delta T^2 + \frac{5 \times 10^{-7} + 2(6.02 \times 10^{-10})\,\Delta T}{\lambda - 0.218}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$