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Surface-enhanced infrared absorption (SEIRA) spectroscopy is a powerful technique for a label-free identification of molecular species. The low infrared absorption cross sections of molecules are made up for the huge electromagnetic field enhancement provided by the resonant excitation of collective electron oscillations in metallic nanoantennas. Since these surface plasmons are localized at the nanometer scale, a minute amount of materials is detected leading to a weak SEIRA signal. The design of actual plasmonics detectors is a trade-off between the detection of very small volumes of molecules and the signal to noise ratio level. We demonstrate that an epsilon-near-zero (ENZ) material combined with nano-slits lifts this constraint and provides both extreme enhancement factor up to 107 and highly contrasted SEIRA signal for an extremely low amount of material of interest. These results are explained by the modification of the electromagnetic field of the gap plasmon mode sustained by the slits in the presence of the ENZ material. We propose to implement this concept with a semiconductor whose doping level engineering provides a versatile way to scan the whole molecules' fingerprint frequency range.

International audience; We study the effect of electron spill-out and of nonlocality on the propagation of light inside a gap between two semi-infinite metallic regions. We compare the predictions of a local response model taking into account only the spill-out, to the predictions of a quantum hydrodynamic model able to take both phenomena into account. We show that only the latter is able to correctly retrieve the correct limit when the gap closes, while the local model suffers from undesirable features (divergence of the fields, overestimation of the losses). Finally, we show that, to a certain extent, the correct results can be retrieved using a simple local approach without spill-out or a conventional Thomas-Fermi approximation, but considering an effective gap width.

The ultraconfined light of plasmonic modes put their effective wavelength close to the mean free path of electrons inside the metal electron gas. The Drude model, which can not take the repulsive interactions of electrons into account, then clearly begins to show its limits. In an intermediate length scale where a full quantum treatment is computationally prohibitive, the semiclassical hydrodynamic model, instrinsically non-local, has proven successful. Here we generalize the expression for the absorption volume density and the reciprocity theorem in the framework of this hydrodynamic model. We validate numerically these generalized theorems and show that using classical expressions instead leads to large discrepancies., 10 pages, 8 figures

International audience; We optimize multilayered anti-reflective coatings for photovoltaic devices, using modern evolutionary algorithms. We apply a rigorous methodology to show that a given structure, which is particularly regular (i.e. essentially periodic), emerges spontaneously and systematically for a very broad range of conditions. The very regularity of the structure allows for a thorough physical analysis of how the design operates. This allows to understand that the central part is a photonic crystal utilized as a buffer for light, and that the external layers have the purpose of reducing the impedance mismatch between the outer media and the Bloch mode supported by the photonic crystal. This shows how optimization can suggest new design rules and be considered as a source of inspiration. Finally, we fabricate these structures with easily deployable techniques.

The production of pairs of entangled photons simply by focusing a laser beam onto a crystal with a nonlinear optical response was used to test quantum mechanics and to open new approaches in imaging. The development of the latter was enabled by the emergence of single-photon-sensitive cameras that are able to characterize spatial correlations and high-dimensional entanglement. Thereby, new techniques emerged, such as ghost imaging of objects — in which the quantum correlations between photons reveal the image from photons that have never interacted with the object — or imaging with undetected photons by using nonlinear interferometers. In addition, quantum approaches in imaging can also lead to an improvement in the performance of conventional imaging systems. These improvements can be obtained by means of image contrast, resolution enhancement that exceeds the classical limit and acquisition of sub-shot-noise phase or amplitude images. In this Review, we discuss the application of quantum states of light for advanced imaging techniques. Using quantum states of light for imaging both reveals quantum phenomena and enables new protocols that result in images that surpass classical limitations. Such systems require both quantum light sources and often the ingenious use of detector technologies.

We report the violation of a Bell inequality within full-field coincidence images of a phase object probed by entangled photons., The violation of a Bell inequality not only attests to the nonclassical nature of a system but also holds a very unique status within the quantum world. The amount by which the inequality is violated often provides a good benchmark on how a quantum protocol will perform. Acquiring images of such a fundamental quantum effect is a demonstration that images can capture and exploit the essence of the quantum world. Here, we report an experiment demonstrating the violation of a Bell inequality within observed images. It is based on acquiring full-field coincidence images of a phase object probed by photons from an entangled pair source. The image exhibits a violation of a Bell inequality with S = 2.44 ± 0.04. This result both opens the way to new quantum imaging schemes based on the violation of a Bell inequality and suggests promise for quantum information schemes based on spatial variables.

International audience; Recent experiments with film-coupled nanoparticles suggest that the impact of spatial dispersion is enhanced in plasmonic structures where high wavevector guided modes are excited. More advanced descriptions of the optical response of metals than Drude's are thus probably necessary in plasmonics. We show that even in classical prism coupler experiments, the plasmonic enhancement of spatial dispersion can be leveraged to make such experiments two orders of magnitude more sensitive. The realistic multilayered structures involved rely on layers that are thick enough to rule our any other phenomenon as the spill-out. Optical evanescent excitation of plasmonic waveguides using prism couplers thus constitutes an ideal platform to study spatial dispersion.

Quantum ghost diffraction harnesses quantum correlations to record diffraction or interference features using photons that have never interacted with the diffractive element. By designing an optical system in which the diffraction pattern can be produced by double slits of variable width either through a conventional diffraction scheme or a ghost diffraction scheme, we can explore the transition between the case where ghost diffraction behaves as conventional diffraction and the case where it does not. For conventional diffraction the angular extent increases as the scale of the diffracting object is reduced. By contrast, we show that no matter how small the scale of the diffracting object, the angular extent of the ghost diffraction is limited (by the transverse extent of the spatial correlations between beams). Our study is an experimental realisation of Popper’s thought experiment on the validity of the Copenhagen interpretation of quantum mechanics. We discuss the implication of our results in this context and explain that it is compatible with, but not proof of, the Copenhagen interpretation.

Ghost imaging uses optical correlations to enable an alternative and intriguing image acquisition technique: even though information from either one of the detectors used for the acquisition does not yield an image, an image can be obtained by harnessing the optical correlations. This Review describes a variety of both quantum and classical ghost imaging techniques, and seeks to point out where these techniques may have practical applications.

Engineering apparatus that harness quantum theory promises to offer practical advantages over current technology. A fundamentally more powerful prospect is that such quantum technologies could out-perform any future iteration of their classical counterparts, no matter how well the attributes of those classical strategies can be improved. Here, for optical direct absorption measurement, we experimentally demonstrate such an instance of an absolute advantage per photon probe that is exposed to the absorbative sample. We use correlated intensity measurements of spontaneous parametric downconversion using a commercially available air-cooled CCD, a new estimator for data analysis and a high heralding efficiency photon-pair source. We show this enables improvement in the precision of measurement, per photon probe, beyond what is achievable with an ideal coherent state (a perfect laser) detected with 100% efficient and noiseless detection. We see this absolute improvement for up to 50% absorption, with a maximum observed factor of improvement of 1.46. This equates to around 32% reduction in the total number of photons traversing an optical sample, compared to any future direct optical absorption measurement using classical light.

The repulsion between free electrons inside a metal makes its optical response spatially dispersive, so that it is not described by Drude's model but by a hydrodynamic model. We give here fully analytic results for a metallic slab in this framework, thanks to a two-mode cavity formalism leading to a Fabry-Perot formula, and show that a simplification can be made that preserves the accuracy of the results while allowing much simpler analytic expressions. For metallic layers thicker than 2.7 nm modified Fresnel coefficients can actually be used to accurately predict the response of any multilayer with spatially dispersive metals (for reflection, transmission, or the guided modes). Finally, this explains why adding a small dielectric layer [Y. Luo et al., Phys. Rev. Lett. 111, 093901 (2013)] allows one to reproduce the effects of nonlocality in many cases, and especially for multilayers.

Harnessing the unique properties of quantum mechanics offers the possibility of delivering alternative technologies that can fundamentally outperform their classical counterparts. These technologies deliver advantages only when components operate with performance beyond specific thresholds. For optical quantum metrology, the biggest challenge that impacts on performance thresholds is optical loss. Here, we demonstrate how including an optical delay and an optical switch in a feed-forward configuration with a stable and efficient correlated photon-pair source reduces the detector efficiency required to enable quantum-enhanced sensing down to the detection level of single photons and without postselection. When the switch is active, we observe a factor of improvement in precision of 1.27 for transmission measurement on a per-input-photon basis compared to the performance of a laser emitting an ideal coherent state and measured with the same detection efficiency as our setup. When the switch is inoperative, we observe no quantum advantage.

We propose a universal design which provides simple scaling laws that can be used as a recipe to realize ultra-thin perfect absorbers operating from infrared to microwave frequencies independently of the choice of the materials (i.e metal and dielectric) involved and for all polarization states of light.

Decades of work on beam deformation on reflection, and especially on lateral shifts, have spread the idea that a reflected beam is larger than the incident beam. However, when the right conditions are met, a beam reflected by a multilayered resonant structure can be 10\% narrower than the incoming beam. Such an easily measurable change occurs on a very narrow angular range close to a resonance, which can be leveraged to improve the resolution of sensors based on the detection of surface plasmon resonances by a factor three. We provide theoretical tools to deal with this effect, and a thorough physical discussion that leads to expect similar phenomenon to occur for temporal wavepackets and in other domains of physics.

The spatial resolution of an optical system is limited by diffraction. Various schemes have been proposed to achieve resolution enhancement by employing either a scanning source/detector configuration or a two-photon response of the object. Here, we experimentally demonstrate a full-field resolution-enhancing scheme, based on the centroid estimation of spatially quantum-correlated biphotons. Our standard-quantum-limited scheme is able to image a general non-fluorescing object, using low-energy and low-intensity infrared illumination (i.e., with

We report ghost imaging of a single non-reproducible temporal signal in the range of tens kHz by using pseudo-thermal speckle light patterns and a single detector array with a million of pixels working without any temporal resolution. A set of speckle patterns is generated deterministically at radio-frequency rate, multiplied by the temporal signal and time integrated in a single shot by the camera. The temporal information is retrieved by computing the spatial intensity correlations between this time integrated image and each speckle pattern of the set., 6 pages, 4 figures

We propose a design for an universal absorber, characterized by a resonance frequency that can be tuned from visible to microwave frequencies independently of the choice of the metal and the dielectrics involved. An almost perfect absorption up to 99.8% is demonstrated at resonance for all polarization states of light and for a very wide angular aperture. These properties originate from a magnetic Fabry-Perot mode that is confined in a dielectric spacer of λ/100 thickness by a metamaterial layer and a mirror. An extraordinary large funneling through nano-slits explains how light can be trapped in the structure. Simple scaling laws can be used as a recipe to design ultra-thin perfect absorbers whatever the materials and the desired resonance wavelength, making our design truly universal.

Superstructured hyperbolic metamaterials (HMs) have been recently introduced to realize media with effective index $\ensuremath{-}1$ with the ultimate goal of designing flat lenses of super-resolution power for optical imaging applications. In this work, we analyze the impact on their effective optical properties of defect metallic layers periodically added in HMs. The effective index and losses are systematically calculated in both homogenization and diffractive regimes and with respect to the ratio of dielectric and metallic layers. Although the superstructuring can dramatically decrease the effective losses, we demonstrate that the extent of the hyperbolic dispersion curve in $k$ space plays an even more fundamental role for breaking the diffraction limit. Optimized superstructured HMs working in a regime between the homogenization and diffractive regimes are shown to present simultaneously low effective losses and a high optical resolution for visible light. These superstructured HMs present an effective index of $\ensuremath{-}5$ and extend the subwavelength focalization distance up to $2\ensuremath{\lambda}$, which is twice as large as for regular HMs.

International audience; We analyze the impact of nonlocality on the waveguide modes of metallo-dielectric multilayers and optical patch antennas, the latter formed from metal strips closely spaced above a metallic plane. We model both the nonlocal effects associated with the conduction electrons of the metal, as well as the previously overlooked response of bound electrons. We show that the fundamental mode of a metal-dielectric-metal waveguide, sometimes called the gap-plasmon, is very sensitive to nonlocality when the insulating, dielectric layers are thinner than 5 nm. We suggest that optical patch antennas, which can easily be fabricated with controlled dielectric spacer layers and can be interrogated using far-field scattering, can enable the measurement of nonlocality in metals with good accuracy.

We analyse wave scattering by an interface between a positive refractive index medium and a medium for which both the permittivity and the permeability are negative. We show that the negative refraction effect can be deduced directly from Maxwell equations, without references to causality or losses.

6174,Route de Gray 25030 Besanc¸on Cedex, FRANCE(Dated: July 20, 2012)We demonstrate Einstein-Podolsky-Rosen (EPR) entanglement by detecting purely spatial quan-tum correla-tions in the near and far fields of spontaneous parametric down-conversion generatedin a type-2 beta barium borate crystal. Full-field imaging is performed in the photon-countingregime with an electron-multiplying CCD camera. The data are used without any postselection,and we obtain a violation of Heisenberg inequalities with inferred quantities taking into accountall the biphoton pairs in both the near and far fields by integration on the entire two-dimensionaltransverse planes. This ensures a rigorous demonstration of the EPR paradox in its original position-momentum form.

International audience; We propose a scheme to evidence the Einstein-Podolsky-Rosen (EPR) paradox for photons produced by spontaneous down conversion, from measurement of purely spatial correlations of photon positions both in the near- and in the far-field. Experimentally, quantum correlations have been measured in the far-field of parametric fluorescence created in a type II BBO crystal. Imaging is performed in the photon counting regime with an electron-multiplying CCD (EMCCD) camera.

International audience; When a thin structure in which negative refraction occurs (a metallo-dielectric or a photonic crystal) is illuminated by a beam, the reflected and transmitted beam can undergo a large negative lateral shift. This phenomenon can be seen as an interferential enhancement of the geometrical shift and can be considered as a signature of negative refraction.

Le journal, Open Access, demande à ce qu'on ne dépose pas d'exemplaire du papier sur un autre serveur. https://www.jeos.org/index.php/jeos_rp/article/view/10025; International audience; When coupled modes are excited in a multilayered structure, the profile of the reflected beam presents exotic characteristics like unexpectedly large lateral shifts or beam enlargment. These results are surprising because they are not accounted for by classical approaches (Artmann's formula or Tamir's description of the reflected beam's profile). Studying such situations requires reliable numerical tools - that is why our programmes are published with this paper. Such tools can be used to understand the behaviour of any multi-layered structure.

International audience; Using complex plane analysis we show that left-handed slab may support either leaky slab waves, which are backward because of negative refraction, or leaky surface waves, which are backward or forward depending on the propagation direction of the surface wave itself. Moreover, there is a general connection between the reflection coefficient of the left-handed slab and the one of the corresponding right-handed slab (with opposite permittivity and permeability) so that leaky slab modes are excited for the same angle of incidence of the impinging beam for both structures. Many negative giant lateral shifts can be explained by the excitation of these leaky modes.

Spatially entangled twin photons provide a test of the Einstein-Podolsky-Rosen (EPR) paradox in its original form of position (image plane) versus impulsion (Fourier plane). We show that recording a single pair of images in each plane is sufficient to safely demonstrate an EPR paradox. On each pair of images, we have retrieved the fluctuations by subtracting the fitted deterministic intensity shape and then have obtained an intercorrelation peak with a sufficient signal to noise ratio to safely distinguish this peak from random fluctuations. A 95% confidence interval has been determined, confirming a high degree of paradox whatever the considered single pairs. Last, we have verified that the value of the variance of the difference between twin images is always below the quantum (poissonian) limit, in order to ensure the particle character of the demonstration. Our demonstration shows that a single image pattern can reveal the quantum and non-local behavior of light, without any need of averaging after repeating the experiment.

We show the existence of a Goos-Hänchen effect when a monochromatic beam illuminates a photonic crystal inside a photonic band gap.

We demonstrate sub-shot-noise spectroscopy, near to the ultimate quantum limit. We use heralded single photons as the optical probe and compare using single photon detectors and a CCD to demonstrate sub-shot-noise performance.