with Tα = 1 2M α (-i∇ α + A α (q, R,t)) 2 the kinetic contribution of the nuclei averaged over the nuclear wavefunction. Furthermore, expressing the nuclear wavefunction ζ (R,t) and the photonic wavefunction η(q,t) in polar forms enables us to derive the equations governing the evolution of their phases, W N (R,t) and W P (q,t), respectively. Interestingly, similarly to the EF of the electron-nuclear wavefunction, these equations have the form of Hamilton-Jacobi equations, namely