Far-Field Wavefront Control of Nonlinear Luminescence in Disordered Gold Metasurfaces.

We demonstrate the local optimization of nonlinear luminescence from disordered gold metasurfaces by shaping the phase of femtosecond excitation. This process is enabled by the far-field wavefront control of plasmonic modes delocalized over the sample surface, leading to a coherent enhancement of subwavelength electric fields. In practice, the increase in nonlinear luminescence is strongly sensitive to both the nanometer-scale morphology and the level of structural complexity of the gold metasurface. We typically observe a 2 orders of magnitude enhancement of the luminescence signal for an optimized excitation wavefront compared to a random one. These results demonstrate how disordered metasurfaces made of randomly coupled plasmonic resonators, together with wavefront shaping, provide numerous degrees of freedom to program locally optimized nonlinear responses and optical hotspots.

Spatiotemporal Coherent Control of Light through a Multiple Scattering Medium with the Multispectral Transmission Matrix.

We report the broadband characterization of the propagation of light through a multiple scattering medium by means of its multispectral transmission matrix. Using a single spatial light modulator, our approach enables the full control of both the spatial and spectral properties of an ultrashort pulse transmitted through the medium. We demonstrate spatiotemporal focusing of the pulse at any arbitrary position and time with any desired spectral shape. Our approach opens new perspectives for fundamental studies of light-matter interaction in disordered media, and has potential applications in sensing, coherent control, and imaging.

Direct determination of diffusion properties of random media from speckle contrast.

We present a simple scheme to determine the diffusion properties of a thin slab of strongly scattering material by measuring the speckle contrast resulting from the transmission of a femtosecond pulse with controlled bandwidth. In contrast with previous methods, our scheme does not require time measurements nor interferometry. It is well adapted to the characterization of samples for pulse shaping, nonlinear excitation through scattering media, and biological imaging.

THz emission microscopy with sub-wavelength broadband source.

A versatile THz/IR near field microscope is demonstrated. Collecting the scattered light from a THz in-situ subwavelength source, this microscope provides images with resolution better than lambda/10. The physical origin of the contrast is explained by a Mie scattering diffraction model. Owing to the classical nature of this microscope working in the near field, resolution of THz/IR images is improved using deconvolution process.

Near-field excitation of nanoantenna resonance.

An array of paired elliptic nanoparticles designed to enhance local fields around the particle pair is fabricated with gold embedded in quartz. Light excites a coupled plasmon resonance in the particle pair and the system acts like a plasmonic nanoantenna providing an enhanced electromagnetic field. Near-field scanning optical microscopy and finite element modeling are used to study the local field effects of the nanoantenna system. Local illumination shows similar resonant properties as plane wave illumination: a strong, localized optical resonance for light polarized parallel to the main, center-to-center axis.

Deterministic control of broadband light through a multiply scattering medium via the multispectral transmission matrix.

We present a method to measure the spectrally-resolved transmission matrix of a multiply scattering medium, thus allowing for the deterministic spatiospectral control of a broadband light source by means of wavefront shaping. As a demonstration, we show how the medium can be used to selectively focus one or many spectral components of a femtosecond pulse, and how it can be turned into a controllable dispersive optical element to spatially separate different spectral components to arbitrary positions.