S-BAL35 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{0.941357\,\lambda^2}{\lambda^2 - 0.0140334} + \frac{0.546175\,\lambda^2}{\lambda^2 - 0.000906636} + \frac{1.16169\,\lambda^2}{\lambda^2 - 114.164}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[3.66 \times 10^{-6} + 2(1.79 \times 10^{-8})\,\Delta T + 3(-4.21 \times 10^{-11})\,\Delta T^2 + \frac{3.12 \times 10^{-7} + 2(3.55 \times 10^{-10})\,\Delta T}{\lambda - 0.254}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$