Atef Shalabney

Coherent coupling of molecular resonators with a microcavity mode

The optical hybridization of the electronic states in strongly coupled molecule–cavity systems have revealed unique properties, such as lasing, room temperature polariton condensation and the modification of excited electronic landscapes involved in molecular isomerization. Here we show that molecular vibrational modes of the electronic ground state can also be coherently coupled with a microcavity mode at room temperature, given the low vibrational thermal occupation factors associated with molecular vibrations, and the collective coupling of a large ensemble of molecules immersed within the cavity-mode volume. This enables the enhancement of the collective Rabi-exchange rate with respect to the single-oscillator coupling strength. The possibility of inducing large shifts in the vibrational frequency of selected molecular bonds should have immediate consequences for chemistry.

Figure-of-merit enhancement of surface plasmon resonance sensors in the spectral interrogation

We show that adding a thin dielectric layer with high refractive index on top of the metallic layer in surface plasmon resonance sensors in the Kretschmann-Raether configuration in the spectral mode causes a redshift of the resonance wavelength, narrowing of the resonance dip, and an enhancement to the spectral sensitivity. Surprisingly, together with the sensitivity enhancement, the dip becomes much narrower and the figure of merit is considerably improved, particularly in the IR range.

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 A 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.

Enhanced Raman Scattering from Vibro‐Polariton Hybrid States

Ground-state molecular vibrations can be hybridized through strong coupling with the vacuum field of a cavity optical mode in the infrared region, leading to the formation of two new coherent vibro-polariton states. The spontaneous Raman scattering from such hybridized light–matter states was studied, showing that the collective Rabi splitting occurs at the level of a single selected bond. Moreover, the coherent nature of the vibro-polariton states boosts the Raman scattering cross-section by two to three orders of magnitude, revealing a new enhancement mechanism as a result of vibrational strong coupling. This observation has fundamental consequences for the understanding of light-molecule strong coupling and for molecular science.

Liquid-Phase Vibrational Strong Coupling.

Light-matter strong coupling involving ground-state molecular vibrations is investigated for the first time in the liquid phase for a set of molecules placed in microcavities. By tuning the cavities, one or more vibrational modes can be coupled in parallel or in series, inducing a change in the vibrational frequencies of the bonds. These findings are of fundamental importance to fully develop light-matter strong coupling for applications in molecular and material sciences.

Ground-State Chemical Reactivity under Vibrational Coupling to the Vacuum Electromagnetic Field.

Abstract The ground‐state deprotection of a simple alkynylsilane is studied under vibrational strong coupling to the zero‐point fluctuations, or vacuum electromagnetic field, of a resonant IR microfluidic cavity. The reaction rate decreased by a factor of up to 5.5 when the Si−C vibrational stretching modes of the reactant were strongly coupled. The relative change in the reaction rate under strong coupling depends on the Rabi splitting energy. Product analysis by GC‐MS confirmed the kinetic results. Temperature dependence shows that the activation enthalpy and entropy change significantly, suggesting that the transition state is modified from an associative to a dissociative type. These findings show that vibrational strong coupling provides a powerful approach for modifying and controlling chemical landscapes and for understanding reaction mechanisms.

Dielectric coated plasmonic interfaces: their interest for sensitive sensing of analyte-ligand interactions

Abstract Surface plasmon resonance (SPR) sensors have matured over the last 2 decades into very powerful tools for the study of biomolecular interactions, chemical detection and immunoassays. The performance of the sensor depends on several parameters, such as the choice of the metal thin film where the plasmonic wave propagates, the excitation wavelength and the refractive index (RI) of the glass prism. Next to these physical parameters, the strategy selected to bind the desired receptors to the SPR chip, has a strong influence on the overall sensitivity and selectivity of the device. This review focuses on the advancement made using lamellar SPR structures, where a thin dielectric layer is deposited onto the surface plasmon active metal thin film. Silver-based SPR interfaces can be developed using this approach, as these overlayers allow an efficient protection of the underlying silver film. At the same time, these interfaces open the scope for new surface functionalization schemes, which can be employed for anchoring ligands to the SPR sensor chip. While self-assembled monolayers (SAMs) are widely used, due to the possibility of easily incorporating carboxylate, amine or hydroxyl groups, the drawbacks of such films include limited chemical and electrochemical stability. Moreover, a poor orientation and potential problems of protein adsorption and fouling, is often encountered if no synthetic effort in the synthesis of more sophisticated thiols is made. In addition, while the surface chemistry developed on gold has been of great value, the limitations of working on gold are becoming more noticeable, with increasingly complex fabrication requirements for biometric systems and arrays. Lamellar SPR interfaces represent an alternative route. Finally, the contribution of the thin dielectric top layer to the sensitivity of SPR sensors will be discussed.

Quantum Strong Coupling with Protein Vibrational Modes

In quantum electrodynamics, matter can be hybridized to confined optical fields by a process known as light-matter strong coupling. This gives rise to new hybrid light-matter states and energy levels in the coupled material, leading to modified physical and chemical properties. Here, we report for the first time the strong coupling of vibrational modes of proteins with the vacuum field of a Fabry-Perot mid-infrared cavity. For two model systems, poly(l-glutamic acid) and bovine serum albumin, strong coupling is confirmed by the anticrossing in the dispersion curve, the square root dependence on the concentration, and a vacuum Rabi splitting that is larger than the cavity and vibration line widths. These results demonstrate that strong coupling can be applied to the study of proteins with many possible applications including the elucidation of the role of vibrational dynamics in enzyme catalysis and in H/D exchange experiments.

Probing the kinetics of lipid membrane formation and the interaction of a nontoxic and a toxic amyloid with plasmon waveguide resonance

The kinetics of formation of solid-supported lipid model membranes were investigated using a home-made plasmon waveguide resonance (PWR) sensor possessing enhanced properties relative to classic surface plasmon resonance sensors. Additionally, the kinetics of interaction of two amyloid peptides with zwitterionic and anionic membranes and their effect on lipid organization were followed.

Improving the performances of surface Plasmon resonance sensor in the infrared region by adding thin dielectric over-layer

The implications of adding thin dielectric film with high refractive index (RI) on top of the transducer metallic layer in surface Plasmon resonance (SPR) sensors are extensively investigated particularly in the infrared in the spectral mode. An over-layer made of silicon with thickness of about 10 nm is introduced on top of the silver metallic layer in SPR sensors when the Kretschmann-Raether (KR) configuration is used. The spectral interrogation is considered and the thickness of the dielectric over-layer is below the cutoff thickness of the lowest guided TM mode. The additional film causes to red-shift the resonance wavelength, narrowing of the dip in the reflectance spectrum, and enhancing the spectral sensitivity and the figure of merit (FOM) of the sensor. Furthermore, adding the top dielectric film enhances the electromagnetic fields at the analyte interface, increases the penetration depth inside the sensed medium, and improves the stability of the sensor.