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Interferometric imaging schemes have gained significant interest due to their superior sensitivity over imaging techniques that are solely based on scattered signal. In this study, we outline the theoretical foundations of imaging and characterization of single nanoparticles in an interferometric microscopy scheme, examine key parameters that influence the signal, and benchmark the model against experimental findings.

We present an approach for rational design and optimization of plasmonic arrays for ultrasensitive surface enhanced infrared absorption (SEIRA) spectroscopy of specific protein analytes. Motivated by our previous work that demonstrated sub-attomole detection of surface-bound silk fibroin [Proc. Natl. Acad. Sci. U.S.A. 106, 19227 (2009)], we introduce here a general framework that allows for the numerical optimization of metamaterial sensor designs in order to maximize the absorbance signal. A critical feature of our method is the explicit compensation for the perturbative effects of the analyte's refractive index which alters the resonance frequency and line-shape of the metamaterial response, thereby leading to spectral distortion in SEIRA signatures. As an example, we leverage our method to optimize the geometry of periodic arrays of plasmonic nanoparticles on both Si and CaF 2 substrates. The optimal geometries result in a three-order of magnitude absorbance enhancement compared to an unstructured Au layer, with the CaF 2 substrate offering an additional factor of three enhancement in absorbance over a traditional Si substrate. The latter improvement arises from increase of near-field intensity over the Au nanobar surface for the lower index substrate. Finally, we perform sensitivity analysis for our optimized arrays to predict the effects of fabrication imperfections. We find that <20% deviation from the optimized absorbance response is readily achievable over large areas with modern nanofabrication techniques.

Our recent work has showed that diffractively coupled nanoplasmonic arrays for Fourier transform infrared (FTIR) microspectroscopy can enhance the Amide I protein vibrational stretch by up to 10(5) times as compared to plain substrates. In this work we consider computationally the impact of a microscope objective illumination cone on array performance. We derive an approach for computing angular- and spatially-averaged reflectance for various numerical aperture (NA) objectives. We then use this approach to show that arrays that are perfectly optimized for normal incidence undergo significant response degradation even at modest NAs, whereas arrays that are slightly detuned from the perfect grating condition at normal incidence irradiation exhibit only a slight drop in performance when analyzed with a microscope objective. Our simulation results are in good agreement with microscope measurements of experimentally optimized periodic nanoplasmonic arrays.

It is generally accepted that the lifetimes of the localized plasmonic excitations are inherently controlled by the type of the metals and the shape of the nanoparticles. However, extended plasmonic lifetimes and enhanced near-fields in nanoparticle arrays can be achieved as a result of collective excitation of plasmons. In this article, we demonstrate significantly longer plasmon lifetimes and stronger near-field enhancements by embedding the nanoantenna arrays into the substrate. Our approach offers a more homogeneous dielectric background allowing stronger diffractive couplings among plasmonic particles leading to strong suppression of the radiative damping. We observe near-field enhancements well beyond than those achievable with isolated nanoparticles. Enhanced fields obtained in these structures could be attractive for biosensing and non-linear photonics applications.

We experimentally demonstrate that hybridized nanocavities in optically thick metal films radiate in coherence, and act as an efficient single-polarized plasmonic nano-antenna array. We employ propagating and localized plasmons to enhance polarization control along one axis, with total suppression of the perpendicular polarization component. The relationship between the near-field and far-field radiation is established through a quasi-static model connecting the individual nano-antenna behavior to the phenomenon of extraordinary light transmission. Hybridized nanocavity antennas, with length scales below the conventional diffraction limit, present opportunities for potential applications in photovoltaics, optoelectronic devices and optical sensors.

We introduce two nanoscale thickness dielectric layers on the top and bottom sides of a finite width and finite thickness metal microstrip and have calculated the fundamental symmetric plasmon-polariton mode of the 2D metal-dielectric layer waveguide. The dielectric nanolayers provide an additional degree of freedom to control the plasmon-polariton mode. When the dielectric constant of the nanolayers is smaller than that of the cladding dielectric, the travel range of the fundamental symmetric plasmon-polariton mode is extended with the trade-off of the mode confinement. The figure of merit of the mode increases as the travel range extends.

It has been reported earlier that ultra-long range surface plasmon waves can be supported if dielectric layers with lower index of refraction than that of the dielectric cladding are placed on either side of the thin metal film. In this paper, we report a further investigation of the ultra-long range surface plasmon modes and the condition to support such ultra-long propagation distances at optical frequencies. We studied the effects of the index of refraction contrast between the inner layer and the cladding dielectrics, the metal film thickness, and the dispersion with wavelength. We present a condition which must be satisfied by the waveguide structure to support the bound ultra-long range surface plasmon mode.

In this paper, we show that the propagation distance of the long range plasmon wave mode guided by a finite thickness gold metal film can be extended several orders of magnitude longer if we place intermediate dielectric layers on both sides of the metal film and choose the layer thickness properly. The propagation distance goes to infinite if the intermediate layer thickness approaches a critical thickness.

We first point out that the subpixel response function is another kernel function in digital imaging. Then we show that the subpixel response function of CMOS imaging sensor pixels can be measured with an aperture array pixel mask in a single-shot image capture. Our technique permits high-resolution subpixel response function measurement of imaging pixels for superresolution imaging applications.