Measuring chromatic aberrations in imaging systems using plasmonic nanoparticles.

We demonstrate a method to measure chromatic aberrations of microscope objectives with metallic nanoparticles using white light. Extinction spectra are recorded while scanning a single nanoparticle through a lens's focal plane. We show a direct correlation between the focal wavelength and the longitudinal chromatic focal shift through our analysis of the variations between the scanned extinction spectra at each scan position and the peak extinction over the entire scan. The method has been tested on achromat and apochromat objectives using aluminum disks varying in size from 260-520 nm. Our method is straightforward, robust, low cost, and broadband with a sensitivity suitable for assessing longitudinal chromatic aberrations in high-numerical-aperture apochromatic corrected lenses.

Unveiling the correlation between nanometer-thick molecular monolayer sensitivity and near-field enhancement and localization in coupled plasmonic oligomers.

Metal nanoclusters, sometimes called metamolecules or plasmonic oligomers, exhibit interesting optical properties such as Fano resonances and optical chirality. These properties promise a variety of practical applications, particularly in ultrasensitive biochemical sensing. Here we investigate experimentally the sensitivities of plasmonic pentamers and quadrumers to the adsorption of self-assembled nanometer-thick alkanethiol monolayers. The monolayer sensitivity of such oligomers is found to be significantly higher than that of single plasmonic nanoparticles and depends on the nanocluster arrangement, constituent nanoparticle shape, and the plasmon resonance wavelength. Together with full-wave numerical simulation results and the electromagnetic perturbation theory, we unveil a direct correlation between the sensitivity and the near-field intensity enhancement and spatial localization in the plasmonic "hot" spots generated in each nanocluster. Our observation is beyond conventional considerations (such as optimizing nanoparticle geometry or narrowing resonance line width) for improving the sensing performance of metal nanoclusters-based biosensors and opens the possibilities of using plasmonic nanoclusters for single-molecule detection and identification.

Probing the dielectric response of graphene via dual-band plasmonic nanoresonators.

In this article, we use optical transmission spectroscopy to measure the changes in the resonance features of a Au plasmonic nanoresonator array consisting of concentric ring/disc cavity elements, when graphene is introduced as an encapsulating medium. We show that by using finite element modelling to best reproduce our experimental results the dielectric response of the graphene film can be determined. We discuss the potential of such structures for chemical sensing applications.