S-BAH32 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.58024\,\lambda^2}{\lambda^2 - 0.0103578} + \frac{0.137505\,\lambda^2}{\lambda^2 - 0.0548393} + \frac{1.60603\,\lambda^2}{\lambda^2 - 147.983}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[3.61 \times 10^{-6} + 2(1.09 \times 10^{-8})\,\Delta T + 3(-2.95 \times 10^{-11})\,\Delta T^2 + \frac{7.14 \times 10^{-7} + 2(9.64 \times 10^{-10})\,\Delta T}{\lambda - 0.254}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$