S-BAL14 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.27554\,\lambda^2}{\lambda^2 - 0.00749692} + \frac{0.146083\,\lambda^2}{\lambda^2 - 0.0310422} + \frac{1.16755\,\lambda^2}{\lambda^2 - 128.947}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-5.94 \times 10^{-7} + 2(1.27 \times 10^{-8})\,\Delta T + 3(-3.65 \times 10^{-11})\,\Delta T^2 + \frac{3.93 \times 10^{-7} + 2(3.72 \times 10^{-10})\,\Delta T}{\lambda - 0.26}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$