Manifestation of Planar and Bulk Chirality Mixture in Plasmonic Λ‑Shaped Nanostructures Caused by Symmetry Breaking Defects

We report on the coexistence of planar and bulk chiral effects in plasmonic Λ-shaped nanostructure arrays arising from symmetry breaking defects. The manifestation of bi- (2D) and three-dimensional (3D) chiral effects are revealed by means of polarization tomography and confirmed by symmetry considerations of the experimental Jones matrix. Notably, investigating the antisymmetric and symmetric parts of the Jones matrix points out the contribution of 2D and 3D chirality in the polarization conversion induced by the system whose eigenpolarizations attest to the coexistence of planar and bulk chirality. Furthermore, we introduce a generalization of the microscopic model of Kuhn, yielding to a physical picture of the origins of the observed planar chirality, circular birefringence, and dichroism, theoretically prohibited in symmetric Λ-shaped nanostructures

Quantum Yield of Polariton Emission from Hybrid Light-Matter States

The efficiency of light-matter strong coupling is tuned by precisely varying the spatial position of a thin layer of cyanine dye J-aggregates in Fabry–Perot microcavities, and their photophysical properties are determined. Placing the layer at the cavity field maximum affords an interaction energy (Rabi splitting) of 503 meV, a 62% increase over that observed if the aggregates are simply spread evenly through the cavity, placing the system in the ultrastrong coupling regime. The fluorescence quantum yield of the lowest polaritonic state P– integrated over k-space is found to be ∼10^–2. The same value can be deduced from the 1.4 ps lifetime of P– measured by femtosecond transient absorption spectroscopy and the calculated radiative decay rate constant. Thus, the polariton decay is dominated by nonradiative processes, in contrast with what might be expected from the small effective mass of the polaritons. These findings provide a deeper understanding of hybrid light-molecule states and have implications for the modification of molecular and material properties by strong coupling

Mueller Polarimetry of Chiral Supramolecular Assembly

Supramolecular organizations of achiral molecules are known to undergo spontaneous mirror symmetry breaking, materializing chiral macroscopic structures with enantiomeric excess. Using Mueller polarimetry, we show that the hierarchy at play in the self-assembly of an achiral amphiphilic cyanine molecule, C8O3, can be encoded in a hierarchical evolution of the states of polarization of a light beam interacting with the self-assembly. We propose a methodology to monitor the formation, growth and bundling of supramolecular assemblies in solution by tracing, at each stage of assembly, the circular and linear dichroisms together with degree of depolarization. This systematic polarization monitoring of the self-assembly allows us to investigate the various stages of the chiral nucleation process. In particular, we reveal that mirror symmetry breaking is driven, at the earliest stage of the self-assembly, by hydrophobic forces. Chiral excitons are then formed in tubular J-aggregates by a secondary nucleation, before an amplification of the chiral signal is observed in the final stage of assembly, corresponding to exciton coupling aided by the bundling of the tubular aggregates

Waveguide and Plasmonic Absorption-Induced Transparency

Absorption-induced transparency (AIT) is one of the family of induced transparencies that has emerged in recent decades in the fields of plasmonics and metamaterials. It is a seemingly paradoxical phenomenon in which transmission through nanoholes in gold and silver is dramatically enhanced at wavelengths where a physisorbed dye layer absorbs strongly. The origin of AIT remains controversial, with both experimental and theoretical work pointing to either surface (plasmonic) or in-hole (waveguide) mechanisms. Here, we resolve this controversy by carefully filling nanoholes in a silver film with dielectric material before depositing dye on the surface. Our experiments and modeling show that not only do plasmonic and waveguide contributions to AIT both exist, but they are spectrally identical, operating in concert when the dye is both in the holes and on the surface

π‑Electronic Co-crystal Microcavities with Selective Vibronic-Mode Light Amplification: Toward Förster Resonance Energy Transfer Lasing

π-conjugated organic microcrystals often act as optical resonators in which the generated photons in the crystal are confined by the reflection at the crystalline facets and interfere to gain lasing action. Here, we fabricate microcrystals from a mixture of carbon-bridged oligo-<i>para</i>-phenylenevinylenes (COPVs) with energy-donor (D) and energy-acceptor (A) characters. Upon weak excitation of the single D–A co-crystal, Förster resonance energy transfer (FRET) takes place, exhibiting spontaneous emission from A. In contrast, upon strong pumping, stimulated emission occurs before FRET, generating lasing action from D. Lasing occurs with single- and dual-vibronic levels, and the lasing wavelength can be modulated by the doping amount of A. Time-resolved spectroscopic studies reveal that the rate constant of lasing is more than 20 times greater than that of FRET. Furthermore, microcrystals, vertically grown on a Ag-coated substrate, reduce the lasing threshold by one-fourth. This study proposes possible directions toward organic solid FRET lasers with microcrystalline resonators

Electronic Light–Matter Strong Coupling in Nanofluidic Fabry–Pérot Cavities

Electronic light–matter strong coupling has been limited to solid molecular films due to the challenge of preparing optical cavities with nanoscale dimensions. Here we report a technique to fabricate such Fabry–Pérot nanocavities in which solutions can be introduced such that light–molecule interactions can be studied at will in the liquid phase. We illustrate the versatility of these cavities by studying the emission properties of Chlorin e6 solutions in both the weak and strong coupling regimes as a function of cavity detuning. Liquid nanocavities will broaden the investigation of strong coupling to many solution-based molecular processes

π‑Electronic Co-crystal Microcavities with Selective Vibronic-Mode Light Amplification: Toward Förster Resonance Energy Transfer Lasing

π-conjugated organic microcrystals often act as optical resonators in which the generated photons in the crystal are confined by the reflection at the crystalline facets and interfere to gain lasing action. Here, we fabricate microcrystals from a mixture of carbon-bridged oligo-<i>para</i>-phenylenevinylenes (COPVs) with energy-donor (D) and energy-acceptor (A) characters. Upon weak excitation of the single D–A co-crystal, Förster resonance energy transfer (FRET) takes place, exhibiting spontaneous emission from A. In contrast, upon strong pumping, stimulated emission occurs before FRET, generating lasing action from D. Lasing occurs with single- and dual-vibronic levels, and the lasing wavelength can be modulated by the doping amount of A. Time-resolved spectroscopic studies reveal that the rate constant of lasing is more than 20 times greater than that of FRET. Furthermore, microcrystals, vertically grown on a Ag-coated substrate, reduce the lasing threshold by one-fourth. This study proposes possible directions toward organic solid FRET lasers with microcrystalline resonators

Coherent Coupling of WS₂ Monolayers with Metallic Photonic Nanostructures at Room Temperature

Room temperature strong coupling of WS₂ monolayer exciton transitions to metallic Fabry–Pérot and plasmonic optical cavities is demonstrated. A Rabi splitting of 101 meV is observed for the Fabry–Pérot cavity. The enhanced magnitude and visibility of WS₂ monolayer strong coupling is attributed to the larger absorption coefficient, the narrower line width of the <i>A</i> exciton transition, and greater spin–orbit coupling. For WS₂ coupled to plasmonic arrays, the Rabi splitting still reaches 60 meV despite the less favorable coupling conditions, and displays interesting photoluminescence features. The unambiguous signature of WS₂ monolayer strong coupling in easily fabricated metallic resonators at room temperature suggests many possibilities for combining light–matter hybridization with spin and valleytronics

Vibro-Polaritonic IR Emission in the Strong Coupling Regime

The strong coupling regime of light–matter interaction has recently been extended to IR active molecular vibrations coupled to microcavities, resulting in the formation of so-called vibro-polaritonic states. Here we demonstrate the emissivity of such hybrid states. Using thermal excitation, we achieve polaritonic IR emission from a strongly coupled polymer. Thermal excitation of vibro-polaritons, thus, constitutes an original way of establishing sizable excited-states populations in strongly coupled systems and opens new routes to the study of interacting vibro-polaritons