Designing nanoantenna that could strongly and efficiently concentrate incident light into deep subwavelength volumes is a key issue to locally enhance the electric field and thus produce strong light-matter interactions. Many existing designs are inspired by structures widely used in the radiofrequency domain such as bowtie or Yagi-Uda antennas.
Here, we rather use an analogy between acoustics and electromagnetism wave equations, in order to adapt the acoustic Helmholtz resonator to optics. This structure is made of a tiny slit above a larger cavity and exhibits several appealing features: total absorption at resonance, absence of harmonic resonance, giant field intensity enhancement in the whole slit volume, angular independence of the Helmholtz resonance [1-3]. We demonstrate experimentally various structures with Helmholtz-like resonances, and we take advantage of the huge field enhancement in the resonator for sensing applications. In particular, we show how this resonator can be used for both surface plasmon resonance sensing (SPR) and surface enhanced infrared absorption (SEIRA), in order to detect and identify molecules. We demonstrate experimentally that the SEIRA signature of 2,4-dinitrotoluene (DNT) is enhanced by several orders of magnitude, leading to reflectivity variations up to 15%. Similar experiments have been done on various nitrosamines molecules, each having its own infrared fingerprint. These results are promising for the use of these Helmholtz-like resonators as specific and sensitive sensor of molecules.
 P. Chevalier, P. Bouchon, R. Haïdar, and F. Pardo, Appl. Phys. Lett. 105, 071110(2014)
 P. Chevalier et al, P. Bouchon, J.J Greffet, J.L. Pelouard, R. Haïdar, and F. Pardo, Phys. Rev. B 90, 195412 (2014)
 P. Chevalier et al., Appl. Phys. Lett. 112, 171110 (2018)
The growing field of quantum plasmonics lies at the intersection between nanophotonics and quantum optics. QUantum plasmonics investigate the quantum properties of single surface plasmons, trying to reproduce fundamental and landmark quantum optics experiment that would benefit from the light-confinement properties of nanophotonic systems, thus paving the way towards the design of basic components dedicated to quantum experiments with sizes inferior to the diffraction limit. Several groups have recently reproduced fundamental quantum optics experiments with single surface plasmons polaritons (SPPs). We have investigated two situations of quantum interference of single SPPs on lossy beamsplitters : a plasmonic version of the Hong-Ou-Mandel experiment, and the observation of plasmonic N00N states interferences. We numerically designed and fabricated several beamsplitters that reveal new quantum interference scenarios, such as the coalescence and the anti-coalescence of SPPs, or quantum non-linear absorption. Our work show that losses can be seen as a new degree of freedom in the design of plasmonic devices.
Mid to far infrared is an important wavelength band for detection of substances. Incandescent sources are often used in
infrared spectroscopy because they are simple and cost effective. They are however broadband and quasi isotropic. As a
result, the total efficiency in a detection system is very poor. Yet it has been shown recently that thermal emission can be
designed to be directional and/or monochromatic. To do so amounts to shape the emissivity. Any real thermal source is
characterized by its emissivity, which gives the specific intensity of the source compared to the blackbody at the same
temperature. The emissivity depends on the wavelength and the direction of emission and is related to the whole
structure of the source (materials, geometry below the wavelength-scale...). Emissivity appears as a directional and
chromatic filter for the blackbody radiation. Playing with materials and structure resonances, the emissivity can be
designed to optimize the properties of an incandescent source. We will see how it is possible to optimize a plasmonic
metasurface acting as an incandescent source, to make it directional and quasi monochromatic at a chosen wavelength.
We will target a CO2 detection application to illustrate this topic.
Here we present a 2D slit-box electromagnetic nanoantenna inspired by the acoustic Helmholtz resonator. It is able to concentrate the energy into tiny volumes, and a giant field intensity enhancement is observed throughout the slit. Noteworthily, we have shown that this field intensity enhancement can also be obtained in three dimensional structures that are polarization independent. In the Helmholtz nanoantenna, the field is enhanced in a hot volume and not a hot point, which is of great interest for applications requiring extreme light concentration, such as SEIRA, non-linear optics and biophotonics.
To engineer a cheap, portable and low-power optical gas sensor, incandescent sources are more suitable than expensive quantum cascade lasers and low-efficiency light-emitting diodes. Such sources of radiation have already been realized, using standard MEMS technology, consisting in free standing circular micro-hotplates. This paper deals with the design of such membranes in order to maximize their wall-plug efficiency. Specification constraints are taken into account, including available energy per measurement and maximum power delivered by the electrical supply source. The main drawback of these membranes is known to be the power lost through conduction to the substrate, thus not converted in (useful) radiated power. If the membrane temperature is capped by technological requirements, radiative flux can be favored by increasing the membrane radius. However, given a finite amount of energy, the larger the membrane and its heat capacity, the shorter the time it can be turned on. This clearly suggests that an efficiency optimum has to be found. Using simulations based on a spatio-temporal radial profile, we demonstrate how to optimally design such membrane systems, and provide an insight into the thermo-optical mechanisms governing this kind of devices, resulting in a nontrivial design with a substantial benefit over existing systems. To further improve the source, we also consider tailoring the membrane stack spectral emissivity to promote the infrared signal to be sensed as well as to maximize energy efficiency.
Tamm plasmons are interface modes formed at the boundary between a metallic layer and a dielectric Bragg mirror.
They present advantages associated both to surface plasmons and to microcavities photonic modes. One of their
striking properties is that they can be spatially confined by structuring only the metallic part of the structure, thus
reducing the size of the mode and allowing various geometries without altering the optical properties of the active
layer. These modes are very good candidates for optimizing the emission properties of semiconductor
nanostructures. In particular, due to the relatively low damping and the versatility of the Tamm geometries, they
open new perspective for the development of hybrid metal/semiconductor lasers. In this paper, we will show that a
laser effect can be achieved in a bidimensional Tamm structure under pulsed optical pumping. We will also
demonstrate that the mode can be spatially confined, and that this results in a reduction of the pump power at
In the past years, reducing the thickness of the absorber layer in CIGS-based solar cells has become a key issue to reduce the global Indium consumption and thus increased its competitiveness. As the absorber thickness is reduced, less photons are absorbed and consequently the efficiency decreases. It is well known that scattering light in the absorbing layer increases the effective optical length, which results in enhanced absorption. In this study, we have deposited a transparent conductive oxide as a back contact to the cell with a white paint on the rear surface to diffuse the light back to the cell. A proof of concept device is realized and optically characterized. Modeling scattering by rough surfaces can be done by brute force numerical simulations but does not provide a physical insight in the absorption mechanisms. In our approach, we regard the collimated solar light and its specular reection/transmission as coherent. On an irregular surface, part of the collimated light is scattered in other directions. To model this diffuse light, we adopt the formalism of the radiative transfer equation, which is an energy transport equation. Thus, interference effects are accounted for only in the coherent part. A special attention is dedicated to preserving reciprocity and energy conservation on the interface. It is seen that most of the absorption near the energy bandgap of CIGS is due to the diffuse light and that this approach can yield very significant photocurrent gains below 500nm absorber thickness.
This study addresses the potential of different approaches to improve the generated current density in ultrathin
Cu(In,Ga)Se<sub>2</sub> (CIGSe) based solar cells down to 0.1 μm. Advanced photon management, involving both absorption
enhancement and reflection reduction in the absorber, is studied. In this contribution, the three main approaches used
- The reduction of the CIGSe thickness by chemical etching which combines thickness reduction and smoothing effect
on the absorber.
- Optical management by front contact engineering and by the replacement of the back contact by the "lift-off" of CIGSe
layer from the Mo layer and the deposition of a new reflective back contact.
- Application of plasmonic structures to CIGSe solar cells enabling light confinement at the subwavelength scale.
We propose an experimental demonstration of a THz modulator with a visible optical command. The device is a n-doped
GaAs grating with subwavelength dimensions. The principle of this modulator is the control of the THz resonant
absorption by surface waves supported by the grating. This absorption is modulated with low power visible light, leading
to a modulation of the reflected THz beam. From experimental polarized THz reflectivity measurement of the grating,
we show that a depletion layer at the surface of the doped GaAs has to be taken into account to correctly describe the
observed resonant absorption. From experimental observation and modeling we are able to ascribe this absorption to the
coupling of incident THz light with surface plasmon-phonon polariton mode propagating along each wall of the grating.
Thus, each wall acts as a nano-antenna that resonantly absorbs light. The grating can be viewed as a metamaterial
composed of individual resonators. The theoretical model indicates that the reflectivity dip linked to the surface wave is
sensible to the electronic density in the walls of the grating. We performed an experiment to measure the THz
reflectivity while illuminating the grating with visible photons having energy higher than the bandgap of GaAs. The
created photoelectrons change the effective mode index, leading to a shift of the resonant absorption frequency. This
demonstrates the modulation of THz radiation around 8.5 THz with a visible optical command at room temperature.
Plasmonic structures can be advantageous for single photon sources due notably to their large Purcell factor
over a relatively large frequency range. Here, we compare thin disks and optical patch antenna configurations.
We analyze the physics involved in the modification of the Purcell factor, and discuss how the structures can be
seen as plasmonic cavities. We also discuss briefly the implications for single photon sources.
In this paper, we establish the form of the spectral degree of spatial coherence of the field thermally emitted by a planar opaque surface. Our approach is based on the fluctuation-dissipation theorem. Several new properties are derived. It is shown that for lossy media, the coherence length in a plane very close to the surface is essentially the skin depth. Thus, it can be much smaller than the wavelength. However, if the metal can support a surface wave, the coherence length can be much larger than the wavelength.
We consider the scattering of light by a system of randomly distributed particles above an interface. It is shown that this system can produce backscattering enhancement even for a very dilute system such that multiple scattering is negligible. A physical mechanisms is proposed and the role of the Fresnel reflectivity of the interface is examined. Differences between the behavior of s and p-polarization are considered.