Grégory Vincent

Free-standing subwavelength metallic gratings for snapshot multispectral imaging

A mosaic of ten spectral filters has been fabricated in a single 20 mm2 membrane drilled by nanoslits and coated by a gold layer. The nanostructured core-shell gratings exhibit 70% average maximum transmission efficiency in 15% aperture area, which represents a fivefold enhancement compared to the geometrical transmission. This mosaic of bandpass filters regularly spaced in the 3–5 μm wavelength range is used to demonstrate real-time spectral imaging in a multichannel camera.

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.

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.

Quadriwave lateral shearing interferometry in an achromatic and continuously self-imaging regime for future x-ray phase imaging

We present in this Letter a type of quadriwave lateral shearing interferometer for x-ray phase imaging. This device is based on a phase chessboard, and we take advantage of the large spectrum of the source to produce interferograms with a propagation-invariant contrast. Such a grating has been created for hard x-ray interferometry and experimentally tested on a synchrotron beamline at Soleil.

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.

Metal–dielectric bi-atomic structure for angular-tolerant spectral filtering

We theoretically study metal-dielectric structures made of bi-atomic metallic gratings coupled to a guided-mode dielectric resonator. The bi-atomic pattern grating allows tailoring of the Fourier spectrum of the inverse grating permittivity in order to adapt the frequency gap and obtain a flat dispersion band over a wide angular range. A significant enhancement (two-fold) of the angular tolerance as compared to a simply periodic structure is obtained.

Large-area dielectric and metallic freestanding gratings for midinfrared optical filtering applications

The authors present a fabrication process of large-area (1.7×1.7 mm2) dielectric and metal-coated lamellar freestanding gratings structured at the micrometer scale. Both the stress management and the drying problems have been carefully optimized for the fabrication of drilled membranes. Transmission spectra measurements of freestanding gold-coated gratings demonstrate the achievement of high quality, accurately controlled optical filters in the midinfrared wavelength range.The authors present a fabrication process of large-area (1.7×1.7 mm2) dielectric and metal-coated lamellar freestanding gratings structured at the micrometer scale. Both the stress management and the drying problems have been carefully optimized for the fabrication of drilled membranes. Transmission spectra measurements of freestanding gold-coated gratings demonstrate the achievement of high quality, accurately controlled optical filters in the midinfrared wavelength range.

X-ray phase contrast imaging and noise evaluation using a single phase grating interferometer.

In this paper we present some quantitative measurements of X-ray phase contrast images and noise evaluation obtained with a recent grating based X-ray phase contrast interferometer. This device is built using a single phase grating and a large broadband X-ray source. It was calibrated using a reference sample and finally used to perform measurements of a biological fossil: a mosquito trapped in amber. As phase images, noise was evaluated from the measured interferograms.

Wollaston prism-like devices based on blazed dielectric subwavelength gratings

A Wollaston prism-like binary dielectric grating is presented and analyzed. It behaves like a transmission grating, differentially and symmetrically blazed for the two crossed polarization states, TE and TM. The phase profile is obtained by means of subwavelength structures etched in a high optical index isotropic dielectric medium (gallium arsenide, for instance). The performance of the device is illustrated by numerical examples and sketched in terms of spectral bandwidth and of extinction ratio. Some practical issues related to the fabrication are discussed.

Realization of sinusoidal transmittance with subwavelength metallic structures

We propose to use hybrid dielectric-metallic subwavelength structures to code complex transmittance (module and phase) in the mid-infrared wavelength range. As a demonstrator, we have designed and fabricated large-area (2 mm×2 mm) metallic gratings with transmittance levels ranging from 37% to 98%. Optical transmission measurements are in very good agreement with numerical computations. It demonstrates the ability to control the transmission intensity with high accuracy by the use of lateral structuration of metal at the nanoscale. A nonresonant process ensures a large spectral band. We discuss the integration of this concept to code a laterally modulated sinusoidal transmittance pattern. The phase shift induced by metal structures is analyzed. A technologically viable solution is proposed to reduce this parasitic effect in our application. Such devices allow one to obtain optical beams with a lateral, two-dimensional sinusoidal modulation and can answer the growing needs of optical wavefront analysis applications.