Performance of long-wave infrared band of microstructured heavily doped InAsSb on type II superlattice layer part 1: the photonic study.

This article deals with the optical study of nanostructured components which absorb light across the entire long-wave infrared (LWIR) spectral band. The components are made of type-II superlattice (T2SL) absorber and highly doped InAsSb, the latter being nanostructured to ensure multiple resonances. We studied two components: in the first one, the T2SL has a thickness of 1.6 µm, and in the second its thickness is 300 nm. The calculated absorption spectra were shown and the components revealed high absorption thanks to optical resonance and high angular acceptance. A fabrication process has been developed, and optical measurements have confirmed the reliability of the model.

Experimental Investigation of the Thermal Emission Cross Section of Nanoresonators Using Hierarchical Poisson-Disk Distributions.

Effective cross sections of nano-objects are fundamental properties that determine their ability to interact with light. However, measuring them for individual resonators directly and quantitatively remains challenging, particularly because of the very low signals involved. Here, we experimentally measure the thermal emission cross section of metal-insulator-metal nanoresonators using a stealthy hyperuniform distribution based on a hierarchical Poisson-disk algorithm. In such distributions, there are no long-range interactions between antennas, and we show that the light emitted by such metasurfaces behaves as the sum of cross sections of independent nanoantennas, enabling direct retrieval of the single resonator contribution. The emission cross section at resonance is found to be on the order of λ_{0}^{2}/3, a value that is nearly 3 times larger than the theoretical maximal absorption cross section of a single particle, but remains smaller than the maximal extinction cross section. This measurement technique can be generalized to any single resonator cross section, and we also apply it to a lossy dielectric layer.

Helmholtz Resonator Applied to Nanocrystal-Based Infrared Sensing.

While the integration of nanocrystals as an active medium for optoelectronic devices progresses, light management strategies are becoming required. Over recent years, several photonic structures (plasmons, cavities, mirrors, etc.) have been coupled to nanocrystal films to shape the absorption spectrum, tune the directionality, and so on. Here, we explore a photonic equivalent of the acoustic Helmholtz resonator and propose a design that can easily be fabricated. This geometry combines a strong electromagnetic field magnification and a narrow channel width compatible with efficient charge conduction despite hopping conduction. At 80 K, the device reaches a responsivity above 1 A·W-1 and a detectivity above 1011 Jones (3 µm cutoff) while offering a significantly faster time-response than vertical geometry diodes.

High-efficiency second-harmonic generation in coupled nano Fabry-Perot thin resonators.

In this paper we experimentally demonstrate second-harmonic generation (SHG) enhancement in thin 1D periodic plasmonic nanostructures on GaAs in the infrared spectral range. Due to the properly designed coupling of horizontal Fabry-Perot nanoresonators that occurs inside these structures, the obtained conversion efficiencies go up to the 10-7 W-1 range. Moreover, we demonstrate that the engineering of the plasmonic nanoantenna dimensions on the same GaAs layer can lead to SHG enhancement for pump wavelengths ranging from 2.8 µm to 3.3 µm.

Experimental demonstration of second-harmonic generation in high χ2 metasurfaces.

Metasurfaces able to concentrate light at various wavelengths are promising for enhancing nonlinear interactions. In this Letter, we experimentally demonstrate infrared second-harmonic generation (SHG) by a multi-resonant nanostructure. A 100 GaAs layer embedded in a metal-insulator-metal waveguide is shown to support various localized resonances. One resonance enhances the nonlinear polarization due to the transverse magnetic (TM)-polarized pump wavelength near 3.2µm, while another is set near the TE-polarized generated wavelength (1.6µm). The measured SHG efficiency is higher than 10-9W-1 for pump wavelengths ranging from 2.9 to 3.3µm, which agrees with theoretical computations. This is typically 4 orders of magnitude higher than the equivalent GaAs membrane.

Near-Field and Far-Field Thermal Emission of an Individual Patch Nanoantenna.

The far-field spectral and near-field spatial responses of an individual metal-insulator-metal nanoantenna are reported, using thermal fluctuations as an internal source of the electromagnetic field. The far-field spectra, obtained by combining Fourier transform infrared spectroscopy with spatial modulation based on a light falloff effect in a confocal geometry, have revealed two distinct emission peaks attributed to the excitation of the fundamental mode of the nanoantenna at two distinct wavelengths. Superresolved near-field images of the thermally excited mode have been obtained by thermal radiation scanning tunneling microscopy. Experimental results are supported by numerical simulations showing that it is possible to excite the same mode at different wavelengths near a resonance of the insulating dielectric material forming the antenna.

Extraordinary optical extinctions through dual metallic gratings.

We report on multiple extraordinary optical extinction (EOE) phenomena achieved through encapsulated dual metallic gratings. They are evidenced in TM polarization by angularly and spectrally resolved transmission measurements in the mid-infrared wavelength range. We show that EOE can be achieved on both sides of the extraordinary optical transmission (EOT) resonance, leading to pass-band filters with an improved rejection rate.

Over-coupled resonator for broadband surface enhanced infrared absorption (SEIRA).

Detection of molecules is a key issue for many applications. Surface enhanced infrared absorption (SEIRA) uses arrays of resonant nanoantennas with good quality factors which can be used to locally enhance the illumination of molecules. The technique has proved to be an effective tool to detect small amount of material. However, nanoresonators can detect molecules on a narrow bandwidth so that a set of resonators is necessary to identify a molecule fingerprint. Here, we introduce an alternative paradigm and use low quality factor resonators with large radiative losses (over-coupled resonators). The bandwidth enables to detect all absorption lines between 5 and 10 µm, reproducing the molecular absorption spectrum. Counterintuitively, despite a lower quality factor, the system sensitivity is improved and we report a reflectivity variation as large as one percent per nanometer of molecular layer of PMMA. This paves the way to specific identification of molecules. We illustrate the potential of the technique with the detection of the explosive precursor 2,4-dinitrotoluene (DNT). There is a fair agreement with electromagnetic simulations and we also introduce an analytic model of the SEIRA signal obtained in the over-coupling regime.

Free-standing guided-mode resonance band-pass filters: from 1D to 2D structures.

We study experimentally and theoretically band-pass filters based on guided-mode resonances in free-standing metal-dielectric structures with subwavelength gratings. A variety of filters are obtained: polarizing filters with 1D gratings, and unpolarized or selective filters with 2D gratings, which are shown to behave as two crossed-1D structures. In either case, a high transmission (up to ≈ 79 %) is demonstrated, which represents an eight-fold enhancement compared to the geometrical transmission of the grating. We also show that the angular sensitivity strongly depends on the rotation axis of the sample. This behavior is explained with a detailed description of the guided-mode transmission mechanism.

Optical extinction in a single layer of nanorods.

We demonstrate that almost 100% of incident photons can interact with a monolayer of scatterers in a symmetrical environment. Nearly perfect optical extinction through free-standing transparent nanorod arrays has been measured. The sharp spectral opacity window, in the form of a characteristic Fano resonance, arises from the coherent multiple scattering in the array. In addition, we show that nanorods made of absorbing material exhibit a 25-fold absorption enhancement per unit volume compared to unstructured thin film. These results open new perspectives for light management in high-Q, low volume dielectric nanostructures, with potential applications in optical systems, spectroscopy, and optomechanics.

Harvesting light at the nanoscale by GaAs-gold nanowire arrays.

A nanoscale metal-semiconductor-metal photodetector with a 40 nm-thick GaAs absorbing layer has been studied numerically and experimentally. A gold nanowire array is the top mirror of a Fabry-Perot cavity and forms interdigitated Schottky contacts. Nearly perfect absorption is achieved in TE polarization. It is shown numerically that the gold nanowire array induces light absorption in GaAs nanowires with tiny sections (100 nm × 40 nm). High external quantum efficiency (η > 40 %) is demonstrated.

Guided mode resonance in subwavelength metallodielectric free-standing grating for bandpass filtering.

We present the experimental study of a free-standing metallic guided-mode resonant structure, for bandpass filtering applications in the mid-IR wavelength range. Structure consists of a subwavelength gold grating with narrow slits deposited on a silicon nitride membrane. High optical transmission is measured with up to 78% transmission at resonance. Angularly resolved spectra are presented revealing Fano-type resonance.

Nearly perfect Fano transmission resonances through nanoslits drilled in a metallic membrane.

We report nearly perfect optical transmission (87%) through freestanding metallic gratings with narrow slits, as the experimental demonstration of the theoretical prediction by Porto et al. [Phys. Rev. Lett. 83, 2845 (1999)10.1103/PhysRevLett.83.2845]. In addition, we show that the Fano line shape of transmission spectra reveals the interplay between localized and propagating surface plasmon resonances, and allows us to determine the nonradiative losses. It provides the limits for the transmission efficiency and resonance quality factor. As an illustration, a mosaic of various bandpass filters has been achieved in a single membrane.

Tailoring radiative and non-radiative losses of thin nanostructured plasmonic waveguides.

Thin nanostructured metal films allow to control radiative and non-radiative losses of surface plasmon polariton modes without changing their group velocities. This effect is studied in plasmonic waveguides made of thin gold films drilled with very narrow slits and deposited on a GaAs substrate. The analysis is supported by high-resolution angle-resolved transmission measurements and rigorous electromagnetic calculations. We show that the excitation of air/gold and gold/GaAs surface waves leads to Fano-type resonances with specific light localization into the slits. As a result, gold/GaAs surface waves induce a modulation of radiative and non-radiative losses of air/gold surface waves. The minimum and maximum of the Fano-type resonance introduce two propagation regimes. In the radiative propagation regime, the losses due to the absorption are negligible, whereas an efficient inhibition of free-space coupling is demonstrated in low-loss propagation regime.

High energy resolution five-crystal spectrometer for high quality fluorescence and absorption measurements on an x-ray absorption spectroscopy beamline.

Fluorescence detection is classically achieved with a solid state detector (SSD) on x-ray absorption spectroscopy (XAS) beamlines. This kind of detection however presents some limitations related to the limited energy resolution and saturation. Crystal analyzer spectrometers (CAS) based on a Johann-type geometry have been developed to overcome these limitations. We have tested and installed such a system on the BM30B/CRG-FAME XAS beamline at the ESRF dedicated to the structural investigation of very dilute systems in environmental, material and biological sciences. The spectrometer has been designed to be a mobile device for easy integration in multi-purpose hard x-ray synchrotron beamlines or even with a laboratory x-ray source. The CAS allows to collect x-ray photons from a large solid angle with five spherically bent crystals. It will cover a large energy range allowing to probe fluorescence lines characteristic of all the elements from Ca (Z = 20) to U (Z = 92). It provides an energy resolution of 1-2 eV. XAS spectroscopy is the main application of this device even if other spectroscopic techniques (RIXS, XES, XRS, etc.) can be also achieved with it. The performances of the CAS are illustrated by two experiments that are difficult or impossible to perform with SSD and the complementarity of the CAS vs SSD detectors is discussed.

Angle-resolved transmission measurements through anisotropic two-dimensional plasmonic crystals.

We report on high-accuracy angle-resolved optical transmission measurements through anisotropic 2D plasmonic crystals made of gold films with large-area rectangular arrays of nanoscale square holes, deposited on GaAs substrates. The measurements reveal the dispersion relations of air-gold and gold-GaAs surface plasmon polaritons. The crystal anisotropy induces a separation between plasmonic modes propagating in different directions. Their symmetry and dispersion properties are discussed.

Spherically bent analyzers for resonant inelastic X-ray scattering with intrinsic resolution below 200 meV.

Resonant inelastic X-ray scattering with very high energy resolution is a promising technique for investigating the electronic structure of strongly correlated materials. The demands for this technique are analyzers which deliver an energy resolution of the order of 200 meV full width at half-maximum or below, at energies corresponding to the K-edges of transition metals (Cu, Ni, Co etc.). To date, high resolution under these conditions has been achieved only with diced Ge analyzers working at the Cu K-edge. Here, by perfecting each aspect of the fabrication, it is shown that spherically bent Si analyzers can provide the required energy resolution. Such analyzers have been successfully produced and have greatly improved the energy resolution in standard spherically bent analyzers.