Plasmonic antennas have a profound impact on nanophotonics as they provide efficient means to manipulate light and enhance light-matter interactions at the nanoscale. However, the large absorption losses found in metals can severely limit the plasmonic applications in the visible spectral range. Here, we demonstrate the effectiveness of an alternative approach using all-dielectric nanoantennas based on silicon dimers to enhance the fluorescence detection of single molecules. The silicon antenna design is optimized to confine the near-field intensity in the 20 nm nanogap and reach a 270-fold fluorescence enhancement in a nanoscale volume of λ(3)/1800 with dielectric materials only. Our conclusions are assessed by combining polarization resolved optical spectroscopy of individual antennas, scanning electron microscopy, numerical simulations, fluorescence lifetime measurements, fluorescence burst analysis, and fluorescence correlation spectroscopy. This work demonstrates that all-silicon nanoantennas are a valid alternative to plasmonic devices for enhanced single molecule fluorescence sensing, with the additional key advantages of reduced nonradiative quenching, negligible heat generation, cost-efficiency, and complementary metal-oxide-semiconductor (CMOS) compatibility.

The photonic resonances hosted by nanostructures provide vivid colors that can be used as color filters instead of organic colors and pigments in photodetectors and printing technology. Metallic nanostructures have been widely studied due to their ability to sustain surface plasmons that resonantly interact with light. Most of the metallic nanoparticles behave as point-like electric multipoles. However, the needs of an another degree of freedom to tune the color of the photonic nanostructure together with the use of a reliable and cost-effective material are growing. Here, we report a technique to imprint colored images based on silicon nanoparticles that host low-order electric and magnetic Mie resonances. The interplay between the electric and magnetic resonances leads to a large palette of colors. This all-dielectric fabrication technique offers the advantage to use cost-effective, reliable, and sustainable materials to provide vivid color spanning the whole visible spectrum. The interest and potential of this all-dielectric printing technique are highlighted by reproducing at a micrometer scale a Mondrian painting.

When excited over a periodic metamaterial lattice of gold nanoparticles (~ 100nm), localized plasmon resonances (LPR) can be coupled by a diffraction wave propagating along the array plane, which leads to a drastic narrowing of plasmon resonance lineshapes (down to a few nm full-width-at-half-maximum) and the generation of singularities of phase of reflected light. These phenomena look very promising for the improvement of performance of plasmonic biosensors, but conditions of implementation of such diffractively coupled plasmonic resonances, also referred to as plasmonic surface lattice resonances (PSLR), are not always compatible with biosensing arrangement implying the placement of the nanoparticles between a glass substrate and a sample medium (air, water). Here, we consider conditions of excitation and properties of PSLR over arrays of glass substrate-supported single and double Au nanoparticles (~ 100-200nm), arranged in a periodic metamaterial lattice, in direct and Attenuated Total Reflection (ATR) geometries, and assess their sensitivities to variations of refractive index (RI) of the adjacent sample dielectric medium. First, we identify medium (PSLR, PSLR for air and water, respectively) and substrate (PSLR) modes corresponding to the coupling of individual plasmon oscillations at medium- and substrate-related diffraction cut-off edges. We show that spectral sensitivity of medium modes to RI variations is determined by the lattice periodicity in both direct and ATR geometries (~ 320nm per RIU change in our case), while substrate mode demonstrates much lower sensitivity. We also show that phase sensitivity of PSLR can exceed 10 degrees of phase shift per RIU change and thus outperform the relevant parameter for all other plasmonic sensor counterparts. We finally demonstrate the applicability of surface lattice resonances in plasmonic metamaterial arrays to biosensing using standard streptavidin-biotin affinity model. Combining advantages of nanoscale architectures, including drastic concentration of electric field, possibility of manipulation at the nanoscale etc, and high phase and spectral sensitivities, PSLRs promise the advancement of current state-of-the-art plasmonic biosensing technology toward single molecule label-free detection.

Substituting noble metals for high-index dielectrics has recently been proposed as an alternative strategy in nanophotonics to design broadband optical resonators and circumvent the ohmic losses of plasmonic materials. In this report, we demonstrate that subwavelength silicon nanoantennas can manipulate the photon emission dynamics of fluorescent molecules. In practice, it is showed that dielectric nanoantennas can both increase and decrease the local density of optical states (LDOS) at room temperature, a process that is inaccessible with noble metals at the nanoscale. Using scanning probe microscopy, we analyze quantitatively, in three dimensions, the near-field interaction between a 100 nm fluorescent nanosphere and silicon nanoantennas with diameters ranging between 170 nm and 250 nm. Associated to numerical simulations, these measurements indicate increased or decreased total spontaneous decay rates by up to 15 % and a gain in the collection efficiency of emitted photons by up to 85 %. Our 2 study demonstrates the potential of silicon-based nanoantennas for the low-loss manipulation of solid-state emitters at the nanoscale and at room temperature.

International audienceThin film of ZnO nanoparticles with dimension of about 5–10 nm were fabricated by the pulsed laser ablation method. By using a femtosecond laser beam at 700 nm to pump micrometer-thick films the authors observed two-photon-induced lasing at 385 nm. Experimentally obtained dependence of the threshold on the excitation spot radius r0 is closer to (1/r_0^2) than to (1/r_0), thus suggesting efficiency of the feedback by scattering-random lasing. The experimental data on nonlinear transmission of the film at the wavelength of pumping are presented

We present the results of experiments on synthesis of ZnO nanoclusters by reactive pulsed laser deposition (PLD). The nanoclusters were formed and crystallized in the gas phase and deposited on SiO 2 substrates. The nanostructured films were characterized by conventional photoluminescence (PL). The PL spectra consist of a narrow UV excitonic band and a broad visible band related to defects in the film. The film preparation conditions such as the substrate temperature, ambient gas nature and pressure, were optimized in order to increase the intensity of excitonic emission and prevent the formation of defects. A postgrowth annealing by UV laser radiation improved the optical quality of the deposited films.The photoluminescence intensity was found to be dependent significantly on the laser fluence and on the number of shots per site. The nature of the defects responsible for the observed luminescence in a visible range is discussed.

International audienceNonlinear optical conversion is studied in thin films of wide-bandgap materials. Very high conversion efficiency to the third-harmonic radiation is achieved for an unamplified femtosecond Cr 4+ :forsterite laser in a submicron-thick film of a nanocrystalline ZnO pulsed-laser-deposited on a fused silica substrate

Thanks to a high refractive index, giant optical anisotropy, and pronounced excitonic response, bulk transition metal dichalcogenides (TMDCs) have recently been discovered to be an ideal foundation for post‐silicon photonics. The inversion symmetry of bulk TMDCs, on the other hand, prevents their use in nonlinear‐optical processes such as second‐harmonic generation (SHG). To overcome this obstacle and broaden the application scope of TMDCs, MoS2 nanodisks are engineered to couple Mie resonances with C‐excitons. As a result, their alliance produces 23‐fold enhancement of SHG intensity with respect to the resonant SHG from a high‐quality exfoliated MoS2 monolayer under C‐exciton excitation. Furthermore, SHG demonstrates a strongly anisotropic response typical of a MoS2 monolayer due to the single‐crystal structure of the fabricated nanodisks, providing a polarization degree of freedom to manipulate SHG. Hence, these results significantly improve the potential of bulk TMDCs enabling an avenue for next‐generation nonlinear photonics.