S-LAL56 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.54052\,\lambda^2}{\lambda^2 - 0.00826765} + \frac{0.217749\,\lambda^2}{\lambda^2 - 0.0328534} + \frac{1.30456\,\lambda^2}{\lambda^2 - 124.527}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[2.53 \times 10^{-6} + 2(1.39 \times 10^{-8})\,\Delta T + 3(-3.57 \times 10^{-11})\,\Delta T^2 + \frac{4.25 \times 10^{-7} + 2(4.38 \times 10^{-10})\,\Delta T}{\lambda - 0.265}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$