S-LAH51 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.82587\,\lambda^2}{\lambda^2 - 0.00935297} + \frac{0.283023\,\lambda^2}{\lambda^2 - 0.0373803} + \frac{1.35964\,\lambda^2}{\lambda^2 - 100.656}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[5.3 \times 10^{-6} + 2(1.13 \times 10^{-8})\,\Delta T + 3(2.62 \times 10^{-12})\,\Delta T^2 + \frac{8.44 \times 10^{-7} + 2(1.11 \times 10^{-9})\,\Delta T}{\lambda - 0.169}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$