S-NBH58 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.71408\,\lambda^2}{\lambda^2 - 0.0116813} + \frac{0.362966\,\lambda^2}{\lambda^2 - 0.0540847} + \frac{2.56486\,\lambda^2}{\lambda^2 - 188.786}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[1.76 \times 10^{-6} + 2(8.43 \times 10^{-9})\,\Delta T + 3(-2.02 \times 10^{-11})\,\Delta T^2 + \frac{9.32 \times 10^{-7} + 2(1.24 \times 10^{-9})\,\Delta T}{\lambda - 0.276}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$