Feynman's path-integral polaron treatment approached using time-ordered operator calculus

► The Feynman polaron is reformulated using a Hamiltonian formalism. ► Excited all-coupling polaron states are explicitly obtained for the first time. ► This allows to understand the nature of peaks of the polaron optical absorption. ► E.g., transitions to “Relaxed Excited' vs Franck-Condon states can be identified.