Importance of multiple-phonon interactions in molecular dissociation and nanofabrication using optical near fields

A quasi-particle (exciton-phonon polariton) model, as a simple model of an optical near-field probe, is proposed to investigate an unresolved problem in photochemical processes, i.e., why a vapor molecule can be dissociated by an incident photon with less energy than the dissociation energy only if, not a propagating far field, but an optical near field is used, and what is the mechanism leading to the photon flux dependence of the deposition rates. Incident photon energy and intensity dependences of Zn deposition rates are analyzed, and good agreement between the theoretical and experimental results is obtained. It suggests that the probe system plays an important role in vibrational transitions as well as electronic transitions in photodissociation processes, and that the couplings between the optical near field and molecular vibrations are enhanced to permit a nonresonant photodissociation inherent in the optical near field.