Fig. 1: Schematic of the ultraviolet/visible-to-infrared (UV/vis-to-IR) photonic downconversion process mediated by excited-state vibrational polaritons (ESVP).
An impulsive excitation by UV/vis light (blue arrow) interacts with a molecule in it’s electronic ground state, promoting the molecule to an electronic excited state through an electronic transition with frequency Ωe,g. Due to vibronic interactions, captured by a nonzero Huang–Rhys factor (S), the excitation creates ESVP with energy Sℏωv along the cavity-coupled vibration with frequency ωv. The ESVP then leak IR radiation from the cavity (red arrows). Here ℏ is Planck’s reduced constant and \({Q}_{g}^{(g)}\) (\({Q}_{g}^{(e)}\)) denotes the ground (excited) state nuclear equilibrium position.
