S-BAH11 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.57139\,\lambda^2}{\lambda^2 - 0.00910808} + \frac{0.147869\,\lambda^2}{\lambda^2 - 0.0402402} + \frac{1.28093\,\lambda^2}{\lambda^2 - 130.399}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[2.98 \times 10^{-6} + 2(1.09 \times 10^{-8})\,\Delta T + 3(-3.44 \times 10^{-11})\,\Delta T^2 + \frac{5.52 \times 10^{-7} + 2(7.15 \times 10^{-10})\,\Delta T}{\lambda - 0.244}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$