L-BAL42 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.39528\,\lambda^2}{\lambda^2 - 0.0111862} + \frac{0.072552\,\lambda^2}{\lambda^2 - -0.0246749} + \frac{1.66336\,\lambda^2}{\lambda^2 - 167.718}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[3.11 \times 10^{-6} + 2(9.17 \times 10^{-9})\,\Delta T + 3(3.29 \times 10^{-15})\,\Delta T^2 + \frac{5.2 \times 10^{-7} + 2(5.23 \times 10^{-10})\,\Delta T}{\lambda - 0.184}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$