BAL35Y by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.26231\,\lambda^2}{\lambda^2 - 0.00695586} + \frac{0.225154\,\lambda^2}{\lambda^2 - 0.0221311} + \frac{0.639119\,\lambda^2}{\lambda^2 - 63.1663}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[3.6 \times 10^{-6} + 2(1.41 \times 10^{-8})\,\Delta T + 3(-3.59 \times 10^{-11})\,\Delta T^2 + \frac{4.39 \times 10^{-7} + 2(5.79 \times 10^{-10})\,\Delta T}{\lambda - 0.167}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$