Transient plasmon-like modes in multi-level quantum emitter systems

Abstract

We model a nanoparticle of organic dye molecules as an ensemble of multi-level quantum systems in order to determine the conditions necessary to yield temporal optical field enhancement for different probe energies. By utilizing a time-dependent density-matrix approach and by examination of the role played by both radiative and non-radiative decay processes between energy levels, we explore how optical pump and probe fields may be used to control the permittivity of the nanoparticle as a function of time. When an appropriate value of the permittivity occurs, a plasmon-like mode will be produced. In this work, we investigate systems in which these plasmon-like modes can be generated at probe energies detuned from the atomic transitions and sustained for timescales dependent on the lifetime of a meta-stable level in our system. Our results suggest that these plasmon-like modes may generate temporal optical field enhancement and that such nanostructures open a new realm in nanophotonics in which transient behaviour can lead to phenomena that cannot be attained in the steady-state regime.