S-BAL22 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.16334\,\lambda^2}{\lambda^2 - 0.0118079} + \frac{0.263323\,\lambda^2}{\lambda^2 - -0.00438113} + \frac{1.12551\,\lambda^2}{\lambda^2 - 106.906}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[1.07 \times 10^{-6} + 2(1.47 \times 10^{-8})\,\Delta T + 3(-3.65 \times 10^{-11})\,\Delta T^2 + \frac{3.9 \times 10^{-7} + 2(5.2 \times 10^{-10})\,\Delta T}{\lambda - 0.186}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$