PBL6Y by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.22311\,\lambda^2}{\lambda^2 - 0.00897805} + \frac{0.0811218\,\lambda^2}{\lambda^2 - 0.0445757} + \frac{0.321401\,\lambda^2}{\lambda^2 - 40.5962}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[9.75 \times 10^{-7} + 2(1.49 \times 10^{-8})\,\Delta T + 3(-3.42 \times 10^{-11})\,\Delta T^2 + \frac{6.21 \times 10^{-7} + 2(7.19 \times 10^{-10})\,\Delta T}{\lambda - 0.222}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$