We demonstrate room-temperature strong-coupling between a mid-infrared (λ=9.9 µm) intersubband transition and the fundamental cavity mode of a metal-insulator-metal resonator. Patterning of the resonator surface enables surface-coupling of the radiation and introduces an energy dispersion which can be probed with angle-resolved reflectivity. In particular, the polaritonic dispersion presents an accessible energy minimum at k=0 where potentially polaritons can accumulate. We also show that it is possible to maximize the coupling of photons into the polaritonic states andsimultaneously -to engineer the position of the minimum Rabi splitting at a desired value of the in-plane wavevector. This can be precisely accomplished via a simple post-processing technique. The results are confirmed using the temporal coupled mode theory formalism and their significance in the context of the concept of strong critical coupling is highlighted.Light emitting devices based on microcavity polaritons have experienced a tremendous development in the last two decades with the successful demonstration of electroluminescent diodes and optically pumped "bosonic lasers" operating at near-infrared wavelengths 1,2 . The extension of such devices to mid-infrared (mid-IR) and Terahertz (THz) wavelengths (λ > 10µm) has been recently explored, taking advantage of the design flexibility offered by intersubband (ISB) transitions in semiconductor quantum wells. The strong coupling between an ISB transition (or more precisely an ISB plasmon 3 ) and a microcavity photonic mode was first demonstrated in the mid-IR 4 and then in the THz range 5 . Devices based on microcavity ISB polaritons hold great potential since in the strong-coupling regime a periodic energy exchange between the light and matter degrees of freedom takes place on an ultrafast time scale (the Rabi oscillation time). On one hand, ISB polaritons can in principle exhibit radiatiave decay times faster than a bare ISB transition. This effect could yield more efficient electroluminescent devices at such wavelengths 6,7 . On the other hand, due to their bosonic nature, ISB polaritons are subject to final state stimulation, as it is also the case for their excitonic counterparts, and they can potentially lead to the demonstration of bosonic mid-IR or THz lasers 8-10 , which would not rely on population inversion. Quantum cascade structures embedded in microcavities have been used to demonstrate electrically pumped light emitting polaritonic devices in the mid-IR 11 . Furthermore, phonon-assisted polariton scattering processes have been observed 12 . This constitutes an encouraging step towards the development of efficient electroluminescent polaritonic devices, since it is possible to rely on a proven scattering process.However, in the polaritonic light emitting devices (LED) demonstrated to date a key parameter is missing. It is not possible with a total internal reflection cavity geometry to obtain an energy minimum at very low in-plane wavevector (k ) values, where the density of states...

We report a crucial step towards single-object cavity electrodynamics in the mid-infrared spectral range using resonators that borrow functionalities from antennas. Room-temperature strong light-matter coupling is demonstrated in the mid-infrared between an intersubband transition and an extremely reduced number of sub-wavelength resonators. By exploiting 3D plasmonic nano-antennas featuring an out-of-plane geometry, we observed strong light-matter coupling in a very low number of resonators: only 16, more than 100 times better than what reported to date in this spectral range. The modal volume addressed by each nano-antenna is sub-wavelength-sized and it encompasses only ≈4400 electrons.

The authors present their work in the preparation of nanoporous gold layers and their patterning with an original procedure preserving the porosity, to obtain the phenomenon of extraordinary transmission of light with a porous material. The design, fabrication, and characterization of nanoslit arrays made with bulk gold and nanoporous gold films are presented and their sensing performances are compared after coating with thiolated organic molecules. Thanks to a greatly enhanced surface-to-volume ratio, nanoporous gold reveals benefits for better reaction efficiency and detection sensitivity. Moreover, plasmonic properties in the near-IR range assure employment in plasmonic devices.

We investigate the focusing effect on circularly distributed planar tapered plasmonic waveguides by means of three-dimensional (3D) finite elements simulations. The proposed configuration allows nanofocusing on four faced planar nanotips, showing efficient condensation of surface plasmons polaritons (SPPs) at the silver/air interface toward the endpoint of the tips. By means of a plasmonic vortex lens it is possible to illuminate the tips with SPP waves carrying orbital angular momentum (OAM), namely plasmonic vortices. Our 3D simulations show that by acting on the topological charge of the plasmonic vortex the electric field charge distribution at the tips apex can be controlled accordingly to the input electric field phase distribution. The results for three particular OAM values are shown, along with a generalization for arbitrary plasmonic vortex angular momentum values.