S-LAH60 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.95243\,\lambda^2}{\lambda^2 - 0.0106442} + \frac{0.3071\,\lambda^2}{\lambda^2 - 0.0456735} + \frac{1.56578\,\lambda^2}{\lambda^2 - 110.281}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[6.88 \times 10^{-6} + 2(1.25 \times 10^{-8})\,\Delta T + 3(-3.24 \times 10^{-11})\,\Delta T^2 + \frac{6.63 \times 10^{-7} + 2(7.1 \times 10^{-10})\,\Delta T}{\lambda - 0.271}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$