PBL35Y by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.31885\,\lambda^2}{\lambda^2 - 0.0101475} + \frac{0.125015\,\lambda^2}{\lambda^2 - 0.0481636} + \frac{0.215794\,\lambda^2}{\lambda^2 - 28.5517}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[-1.48 \times 10^{-6} + 2(1.41 \times 10^{-8})\,\Delta T + 3(-1.47 \times 10^{-11})\,\Delta T^2 + \frac{8.54 \times 10^{-7} + 2(6.15 \times 10^{-10})\,\Delta T}{\lambda - 0.229}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$