S-NBH55 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.83145\,\lambda^2}{\lambda^2 - 0.0122443} + \frac{0.287818\,\lambda^2}{\lambda^2 - 0.0573877} + \frac{2.15208\,\lambda^2}{\lambda^2 - 186.099}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[1.02 \times 10^{-6} + 2(7.99 \times 10^{-9})\,\Delta T + 3(-1.8 \times 10^{-11})\,\Delta T^2 + \frac{9.25 \times 10^{-7} + 2(1.17 \times 10^{-9})\,\Delta T}{\lambda - 0.276}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$