S-LAH55VS by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.92591\,\lambda^2}{\lambda^2 - 0.00961152} + \frac{0.348953\,\lambda^2}{\lambda^2 - 0.0365133} + \frac{1.42231\,\lambda^2}{\lambda^2 - 103.364}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[2.82 \times 10^{-6} + 2(1.01 \times 10^{-8})\,\Delta T + 3(-4.98 \times 10^{-12})\,\Delta T^2 + \frac{6.79 \times 10^{-7} + 2(6.67 \times 10^{-10})\,\Delta T}{\lambda - 0.229}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$