250 research outputs found
Strong Modification of the Nonlinear Optical Response of Metallic Subwavelength Hole Arrays
The influence of hole shape on the nonlinear optical properties of metallic subwavelength hole arrays is investigated. It is found that the amount of second harmonics generated can be enhanced by changing the hole shape. In part this increase is a direct result of the effect of hole shape on the linear transmission properties. Remarkably, in addition to enhancements that follow directly from the linear properties of the array, we find a hot hole shape. For rectangular holes the effective nonlinear response is enhanced by more than 1 order of magnitude for one particular aspect ratio. This enhancement can be attributed to slow propagation of the fundamental wavelength through the holes which occurs close to the hole cutoff
Plasmon dispersion in metal nanoparticle chains from angle-resolved scattering
We present angle and frequency resolved optical extinction measurements to
determine the dispersion relation of plasmon modes on Ag and Au nanoparticle
chains with pitches down to 75 nm. The large splitting between transverse and
longitudinal modes and the band curvature are inconsistent with reported
electrostatic near-field models, and confirm that far-field retarded
interactions are important, even for -sized structures. The data
imply that lower propagation losses, larger signal bandwidth and larger maximum
group velocity then expected can be achieved for wave vectors below the light
line. We conclude that for the design of optical nanocircuits coherent
far-field couplings across the entire circuit need to be considered, even at
subwavelength feature sizes.Comment: 4 pages, 4 figures, colo
Dissipative eigenvalue problems for a Sturm-Liouville operator with a singular potential
We present a study of optical signatures of salmon lice and the ability to distinguish them from a reference zooplankton species. This forms the basis for developing an instrument for detecting salmon lice in situ
Accurate distance control between a probe and a surface using a microcantilever
We demonstrate a method to accurately control the distance between a custom
probe and a sample on a {\mu}m to nm scale. The method relies on the
closed-loop feedback on the angular deflection of an in-contact AFM
microcantilever. High performance in stability and accuracy is achieved in this
method by taking advantage of the small mechanical feedback path between
surface and probe. We describe how internal error sources that find their
origin in the microcantilever and feedback can be minimized to achieve an
accurate and precise control up to 3 nm. In particular, we investigated how
hysteresis effects in the feedback caused by friction forces between tip and
substrate, can be minimized. By applying a short calibration procedure,
distance control from contact to several micrometers probe-sample distance can
be obtained with an absolute nanometer-scale accuracy. The method presented is
compatible with any probe that can be fixed on a microcantilever chip and can
be easily built into existing AFM systems
Bulk viscosity of gauge theory plasma at strong coupling
We propose a lower bound on bulk viscosity of strongly coupled gauge theory
plasmas. Using explicit example of the N=2^* gauge theory plasma we show that
the bulk viscosity remains finite at a critical point with a divergent specific
heat. We present an estimate for the bulk viscosity of QGP plasma at RHIC.Comment: 5 pages, 4 figure
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