S-NBH5 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.47545\,\lambda^2}{\lambda^2 - 0.00955837} + \frac{0.19306\,\lambda^2}{\lambda^2 - 0.046043} + \frac{1.50939\,\lambda^2}{\lambda^2 - 126.423}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[3.81 \times 10^{-6} + 2(1.36 \times 10^{-8})\,\Delta T + 3(-4.15 \times 10^{-11})\,\Delta T^2 + \frac{6.52 \times 10^{-7} + 2(7.31 \times 10^{-10})\,\Delta T}{\lambda - 0.252}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$