S-BAL41 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.24344\,\lambda^2}{\lambda^2 - 0.0116397} + \frac{0.166301\,\lambda^2}{\lambda^2 - -0.00890465} + \frac{1.10586\,\lambda^2}{\lambda^2 - 114.111}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[1.27 \times 10^{-6} + 2(1.2 \times 10^{-8})\,\Delta T + 3(-4.09 \times 10^{-11})\,\Delta T^2 + \frac{3.6 \times 10^{-7} + 2(6.17 \times 10^{-10})\,\Delta T}{\lambda - 0.254}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$