S-LAL20 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.06788\,\lambda^2}{\lambda^2 - 0.00518896} + \frac{0.758735\,\lambda^2}{\lambda^2 - 0.0204004} + \frac{1.02805\,\lambda^2}{\lambda^2 - 120.826}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-6.99 \times 10^{-6} + 2(8.4 \times 10^{-9})\,\Delta T + 3(-7.12 \times 10^{-12})\,\Delta T^2 + \frac{6.14 \times 10^{-7} + 2(5.44 \times 10^{-10})\,\Delta T}{\lambda - 0.202}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$