Surface bound waves and optical interactions in excitonic thin films

Abstract

Excitonic films such as J-aggregate-doped polymer films can exhibit sharp Lorentzian dispersions and thus have various optical features in the visible region. They can even show an optically metallic response and can be considered as alternative plasmonic materials. However, there were no systematic studies on optical interactions in such excitonic films. Here, we perform theoretical investigations on optical modes and interactions in planar excitonic thin films. We gradually vary the dye concentration and the film thickness and study optical coupling to surface bound waves (surface polariton modes and epsilon-near-zero modes). We also investigate thin-film interferences in high-loss and low-loss regimes. Finally, we discuss the freespace impedance matching that can result from the Lorentzian dispersion in excitonic films. Our work enables in-depth understandings on optical interactions in excitonic films and it can provide guidelines for various nanophotonic applications in the visible region.

Perfect Absorption and Strong Coupling in Supported MoS2 Multilayers

“…One way to overcome this is to use an asymmetrical surrounding with a suppressed transmission channel. The latter is usually implemented with a backside mirror (Salisbury screen) or a prism substrate enabling realization of the total internal reflection (TIR) scheme. − Then, the perfect absorption corresponds to the complete suppression of the reflection, which is typically achieved by satisfying the critical-coupling condition (the radiative loss balances the nonradiative one). The critical-coupling condition can be fulfilled for homogeneous thin films with sufficient thickness and material losses only for some discrete frequencies and angles of incidence.…”

“…In excitonic thin films, enhanced absorption has been reported for J -aggregates in the backside mirror configuration, even reaching perfect absorption . The latter has also been observed in the TIR configuration. , The high oscillator strength and intrinsic losses of excitons in transition metal dichalcogenides (TMDs) enhance light–matter interactions . Therefore, several studies have focused on enhancing TMDs absorption using various fabrication strategies, − reaching nearly perfect absorption even in monolayers. − Importantly, the same excitonic characteristics make TMDs great candidates also for strong light–matter coupling.…”

“… 12 The latter has also been observed in the TIR configuration. 4 , 5 The high oscillator strength and intrinsic losses of excitons in transition metal dichalcogenides (TMDs) enhance light–matter interactions. 13 Therefore, several studies have focused on enhancing TMDs absorption using various fabrication strategies, 14 − 16 reaching nearly perfect absorption even in monolayers.…”

Determining the Dielectric Tensor of Microtextured Organic Thin Films by Imaging Mueller Matrix Ellipsometry

“…This causes a metal-like shiny-golden appearance of the SQIB platelets to the eye, which is not because of a metal-like behavior (free conduction electrons) but caused by localized Frenkel excitons with large oscillator strength. However, molecular J-aggregated thin films have been demonstrated to support propagating surface exciton–polariton (SEP) modes, − just as metallic films support surface plasmon–polariton (SPP) modes. These J-aggregated thin films typically are noncrystalline leading to an effectively isotropic optical response.…”