L-BAL35 by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.16263\,\lambda^2}{\lambda^2 - 0.0125957} + \frac{0.325661\,\lambda^2}{\lambda^2 - -0.00326911} + \frac{1.35132\,\lambda^2}{\lambda^2 - 119.215}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[5.03 \times 10^{-6} + 2(1.22 \times 10^{-8})\,\Delta T + 3(-3.81 \times 10^{-11})\,\Delta T^2 + \frac{4.93 \times 10^{-7} + 2(5.76 \times 10^{-10})\,\Delta T}{\lambda - 0.16}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$