S-NBH59 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.7369\,\lambda^2}{\lambda^2 - 0.0107867} + \frac{0.287363\,\lambda^2}{\lambda^2 - 0.0458085} + \frac{1.85126\,\lambda^2}{\lambda^2 - 149.647}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[9.61 \times 10^{-7} + 2(7.15 \times 10^{-9})\,\Delta T + 3(-1.75 \times 10^{-11})\,\Delta T^2 + \frac{8.39 \times 10^{-7} + 2(9.27 \times 10^{-10})\,\Delta T}{\lambda - 0.245}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$