PBM8Y by Ohara

$$n(\lambda) = \sqrt{1 + \frac{1.35351\,\lambda^2}{\lambda^2 - 0.0105625} + \frac{0.130213\,\lambda^2}{\lambda^2 - 0.0496607} + \frac{0.158337\,\lambda^2}{\lambda^2 - 20.7966}}$$

$$\frac{dn}{dT} = \frac{n_0^2 - 1}{2\,n_0}\left[6.76 \times 10^{-7} + 2(1.49 \times 10^{-8})\,\Delta T + 3(-3.72 \times 10^{-11})\,\Delta T^2 + \frac{9.2 \times 10^{-7} + 2(8.07 \times 10^{-10})\,\Delta T}{\lambda - 0.227}\right] \Delta T = T - T_0, \quad T_0 = 25\,°\text{C}$$