S-BAL35R by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.31153\,\lambda^2}{\lambda^2 - 0.00706993} + \frac{0.175894\,\lambda^2}{\lambda^2 - 0.0254908} + \frac{1.06787\,\lambda^2}{\lambda^2 - 104.811}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[3.29 \times 10^{-6} + 2(1.32 \times 10^{-8})\,\Delta T + 3(-6.16 \times 10^{-12})\,\Delta T^2 + \frac{4.02 \times 10^{-7} + 2(3.7 \times 10^{-10})\,\Delta T}{\lambda - 0.203}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$