We exploit the versatility provided by metal-dielectric composites to demonstrate controllable coherent perfect absorption (CPA) or anti-lasing in a slab of heterogeneous medium. The slab is illuminated by coherent light from both sides, at the same angle of incidence and the conditions required for CPA are investigated as a function of the different system parameters. Our calculations clearly elucidate the role of absorption as a necessary prerequisite for CPA. We further demonstrate the controllability of the CPA frequency to the extent of having the same at two distinct frequencies even in presence of dispersion, rendering the realization of anti-lasers more flexible.

Abstract:Plasmonic metasurfaces are able to modify the wavefront by altering the light intensity, phase and polarization state. Active plasmonic metasurfaces would allow dynamic modulation of the wavefront which give rise to interesting application such as beam-steering, holograms and tunable waveplates. Graphene is an interesting material with dynamic property which can be controlled by electrical gating at an ultra-fast speed. We use a graphene-integrated metasurface to induce a tunable phase change to the wavefront. The metasurface supports a Fano resonance which produces high-quality resonances around 7.7 microns. The phase change is measured using a Michleson interferometry setup. It is shown that the reflection phase can change up to 55 degrees. In particular the phase can change by 28 while the amplitude is nearly constant. The anisotropic optical response of the metasurface is used to modulate the ellipticity of the reflected wave in response to an incident field at . We show a proof of concept application of our system in potentially ultra-fast laser interferometry with sub-micron accuracy.Introduction:

The surface second-harmonic generation from interacting spherical plasmonic nanoparticles building different clusters (symmetric and asymmetric dimers, trimers) is theoretically investigated. The plasmonic eigenmodes of the nanoparticle clusters are first determined using an ab initio approach based on the Green's functions method. This method provides the properties, such as the resonant wavelengths, of the modes sustained by a given cluster. The fundamental and second-harmonic responses of the corresponding clusters are then calculated using a surface integral method. The symmetry of both the linear and nonlinear responses is investigated, as well as their relationship. It is shown that the second-harmonic generation can be significantly enhanced when the fundamental field is such that its second harmonic matches modes with suitable symmetry. The role played by the nanogaps in second-harmonic generation is also underlined. The results presented in this article demonstrate that the properties of the second-harmonic generation from coupled metallic nanoparticles cannot be fully predicted from their linear response only, while, on the other hand, a detailed knowledge of the underlying modal structure can be used to optimize the generation of the second harmonic.

Using full-wafer processing, we demonstrate a sophisticated nanotechnology for the realization of an ultrahigh sensitive cavity-coupled plasmonic device that combines the advantages of Fabry-Perot microcavities with those of metallic nanostructures. Coupling the plasmonic nanostructures to a Fabry-Perot microcavity creates compound modes, which have the characteristics of both Fabry-Perot and localized surface plasmon resonance (LSPR) modes, boosting the sensitivity and figure-of-merit of the structure. The significant trait of the proposed device is that the sample to be measured is located in the substrate region and is probed by the compound modes. It is demonstrated that the sensitivity of the compound modes is much higher than that of LSPR of plasmonic nanostructures or the pure Fabry-Perot modes of the optical microcavity. The response of the device is also investigated numerically and the agreement between measurements and calculations is excellent. The key features of the device introduced in this work are applicable for the realization of ultrahigh sensitive plasmonic devices for biosensing, optoelectronics, and related technologies.

We show bending of light on the same side of the normal in a free-standing corrugated metal film under bidirectional illumination. Coherent perfect absorption (CPA) is exploited to suppress the specular zeroth order leading to effective back-bending of light into the "-1" order, while the "+1" order is resonant with the surface mode. The effect is shown to be phase sensitive, yielding CPA and superscattering in the same geometry.

The far-field polarization of the optical response of a plasmonic antenna can be tuned by subtly engineering of its geometry. In this paper, we develop design rules for nano antennas which enable the generation of circular polarized light via the excitation of circular plasmonic modes in the structure. Two initially orthogonal plasmonic modes are coupled in such a way that a rotational current is excited in the structure. Modifying this coupling strength from a weak to a strong regime controls the helicity of the scattered field. Finally, we introduce an original sensing approach that relies on the rotation of the incident polarization and demonstrates a sensitivity of 0.23 deg·nm −1 or 33 deg·RIU −1 , related to changes of mechanical dimensions and the refractive index, respectively. KEYWORDS: Plasmonics, antennas, coupling strength, polarization, sensors I n the past few decades, localized plasmon resonances supported by metallic nanostructures have attracted significant attention thanks to their applications in a variety of fields, such as biosensing, 1 photovoltaics, 2 and optoelectronics.3 It is now well-known that, with appropriate tuning of a plasmonic nanostructure, it is possible to engineer both its near and far-field response.4−8 In the optical regime, plasmonic nanostructures react similarly to antennas in the sense that incident light can be collected and stored in the near-field, and conversely, energy stored in the near-field can be radiated into the far-field. The far-field emission pattern of planar plasmonic structures is determined by the near-field distribution. As a consequence, it is possible by engineering the near-field of a plasmonic nanostructure to design its response in a way such that a linearly polarized excitation results in a circular polarized (CP) response.9−18 Recently, nanostructures supporting not only one single plasmon mode but also multiple interacting plasmonic modes have been developed. 19−23 The interaction between such plasmonic modes allows energy transfer between the particular modes within the corresponding wavelength range, and consequently, different modes can indirectly be excited through their near-field. In line with the observed asymmetric scattering spectra, these modes are named Fano resonances. 24 Potential applications of such structures exhibiting Fano line shapes include sensing, energy storage, and spectroscopy enhancement.25−28 Most of those applications rely on the modulation of the intensity of the scattered light induced by the interaction of the plasmonic modes over different spectral regions. It has already been shown that light polarization can be altered using plasmonic nano antennas 29−31 or plasmonic metamaterials. 32−34 In this paper, we show that the polarization of the scattered light can be controlled by introducing a perturbation into a system with initially orthogonal plasmonic modes. Furthermore, we demonstrate that such structures can be used for the generation of CP light from an incident linearly polarized plane wave. ...

Metasurface-enhanced infrared reflection spectroscopic cytopathology (MEIRSC) is used for label-free distinguishing between normal and cancerous colon cell lines.

Polarization is one of the important properties of light, and its detection is of significant interest for various fundamental and practical applications. We demonstrate a mid-infrared polarimetry device using a gatetunable graphene-integrated anisotropic metasurface. The Stokes parameters of the incident light are extracted by sweeping the gate voltage applied to the device and subsequent fitting of the measured reflected intensities. Considering subpicosecond carrier relaxation times in graphene, the polarization measurement rate of our device is governed only by the speed of the gate voltage sweep. Thus, our work serves as a proof-of-principle demonstration for high-speed microscale polarimetric devices.