Abstract
Metallic nanostructures provide a toolkit for the generation of coherent light below the diffraction limit. Plasmonic based lasing relies on the population inversion of emitters (such as organic fluorophores) along with feedback provided by plasmonic resonances. In this regime, known as weak light matter coupling, the radiative characteristics of the system can be described by the Purcell effect. Strong light matter coupling between the molecular excitons and electromagnetic field generated by the plasmonic structures leads to the formation of hybrid quasi-particles known as plasmon exciton polaritons (PEPs). Due to the bosonic character of these quasi particles, exciton polariton condensation can lead to laser-like emission at much lower threshold powers than in conventional photon lasers. Here, we observe PEP lasing through a dark plasmonic mode in an array of metallic nanoparticles with a low threshold in an optically pumped organic system. Interestingly, the threshold power of the lasing is reduced by increasing the degree of light matter coupling in spite of the degradation of the quantum efficiency of the active material, highlighting the ultrafast dynamic responsible for the lasing, i.e., stimulated scattering. These results demonstrate a unique roomtemperature platform for exploring the physics of exciton polaritons in an open cavity architecture and pave the road toward the integration of this on-chip lasing device with the current photonics and active metamaterial planar technologies.
Highlights
Exciton-polaritonshybrid lightmatter quasi-particles formed by strong exciton-photon couplinghave inspired more than two decades of highly interdisciplinary research [1]
Polariton physics has largely focused on semiconductor microcavities, where the strong nonlinearities associated with quantum well excitons [2, 3] combined with the high quality factor cavities available through state-of-the-art epitaxial techniques have enabled the first observations of BoseEinstein condensation (BEC) [4] and superfluidity [5] in optics
By exploiting diffractive coupling in a metallic nanoparticle array, we obtain spectrally sharp surface lattice resonance modes leading to the formation of PEPs in a dye-doped layer above the surface of the array
Summary
Exciton-polaritonshybrid lightmatter quasi-particles formed by strong exciton-photon couplinghave inspired more than two decades of highly interdisciplinary research [1]. The cavity defining the resonator is no longer a multilayer dielectric stack possessing a complex spectral response, and facilitates the integration of exciton-polariton devices with integrated photonics circuits In these plasmonic systems, previously shown to be highly suitable for photon lasing [17,18,19,20,21], the excitonic material can be integrated by solution processing. Strong coupling between excitons in the organic molecules and collective plasmonic resonances of the array forms PEPs. By increasing the PEP density through optical pumping, we observe a pronounced threshold in the emission intensity accompanied by spectral narrowing. By increasing the PEP density through optical pumping, we observe a pronounced threshold in the emission intensity accompanied by spectral narrowing Besides these generic lasing characteristics, our system exhibits two rather distinct features: first, the threshold power for PEP lasing is reduced in parallel with a degradation of the quantum efficiency of the material. Lasing from this dark (below threshold) mode manifests in an abrupt polarization rotation of the emitted light by 90◦ above threshold
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