S-LAL21 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{0.935251\,\lambda^2}{\lambda^2 - 0.0180836} + \frac{0.905989\,\lambda^2}{\lambda^2 - 0.00408453} + \frac{1.43351\,\lambda^2}{\lambda^2 - 138.683}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[9.29 \times 10^{-6} + 2(1.17 \times 10^{-8})\,\Delta T + 3(-1.68 \times 10^{-11})\,\Delta T^2 + \frac{5.62 \times 10^{-7} + 2(4.97 \times 10^{-10})\,\Delta T}{\lambda - 0.193}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$