Exploring Light–Matter Interaction Phenomena under Ultrastrong Coupling Regime

Exciton-polaritons are bosonic quasiparticles that arise from the normal mode splitting of photons in a microcavity and excitons in a semiconductor material. One of the most intriguing extensions of such a light–matter interaction is the so-called ultrastrong coupling regime. It is achieved when the Rabi frequency (Ω_R, the energy exchange rate between the emitter and the resonant photonic mode) reaches a considerable fraction of the emitter transition frequency, ω₀. Here, we report a Rabi energy splitting (2ℏΩ_R) of 1.12 eV and record values of the coupling ratio (2Ω_R/ω₀) up to 0.6-fold the material band gap in organic semiconductor microcavities and up to 0.5-fold in monolithic heterostructure organic light-emitting diodes working at room temperature. Furthermore, we show that with such a large coupling strength it is possible to undress the exciton homogeneous linewidth from its inhomogeneous broadening, which allows for an unprecedented narrow emission line (below the cavity finesse) for such organic LEDs. The latter can be exploited for the realization of novel monochromatic sources and near-IR organic emitting devices

Mid-Infrared Plasmonic Excitation in Indium Tin Oxide Microhole Arrays

Transparent conducting oxides (TCOs) are emerging as possible alternative constituent materials to replace noble metals such as silver and gold for low-loss plasmonic applications in the near-infrared (NIR) and mid-infrared (MIR) regimes. In particular, TCO-based nanostructures are extensively investigated for biospectroscopy exploiting their surface-enhanced infrared absorption (SEIRA). The latter enhances the absorption from vibrational and rotational modes of nearby biomolecules, making TCO nanostructures a promising candidate for IR sensing applications. Nevertheless, in order to produce inexpensive devices for lab-on-a-chip diagnostics, it would be favorable to achieve surface-enhanced infrared absorption with very simple microstructures not requiring nanosize control. In this work, we attempt to demonstrate a SEIRA effect with the least challenging fabrication, μm-scale instead of nm-scale, by tailoring both device design and charge density of the indium tin oxide (ITO) film. We show that microperiodic hole arrays in a ITO film are able to produce SEIRA via grating coupling. Such a study opens the way for innovative and disrupting biosensing devices