Finite disturbance effect on the stability of a laminar incompressible wake behind a flat plate

An integral method is used to investigate the interaction between a two-dimensional, single frequency finite amplitude disturbance in a laminar, incompressible wake behind a flat plate at zero incidence. The mean flow is assumed to be a non-parallel flow characterized by a few shape parameters. Distribution of the fluctuation across the wake is obtained as functions of those mean flow parameters by solving the inviscid Rayleigh equation using the local mean flow. The variations of the fluctuation amplitude and of the shape parameters for the mean flow are then obtained by solving a set of ordinary differential equations derived from the momentum and energy integral equations. The interaction between the mean flow and the fluctuation through Reynolds stresses plays an important role in the present formulation, and the theoretical results show good agreement with the measurements of Sato & Kuriki (1961)

Attosecond nanoplasmonic streaking of localized fields near metal nanospheres

Collective electron dynamics in plasmonic nanosystems can unfold on timescales in the attosec- ond regime and the direct measurements of plasmonic near-field oscillations is highly desirable. We report on numerical studies on the application of attosecond nanoplasmonic streaking spectroscopy to the measurement of collective electron dynamics in isolated Au nanospheres. The plasmonic field oscillations are induced by a few-cycle NIR driving field and are mapped by the energy of photoemitted electrons using a synchronized, time-delayed attosecond XUV pulse. By a detailed analysis of the amplitudes and phase shifts, we identify the different regimes of nanoplasmonic streaking and study the dependence on particle size, XUV photoelectron energy and emission position. The simulations indicate that the near-fields around the nanoparticles can be spatio-temporally reconstructed and may give detailed insight into the build-up and decay of collective electron motion.Comment: Revised versio

On the Experimental Estimation of Surface Enhanced Raman Scattering (SERS) Cross Sections by Vibrational Pumping

We present an in-depth analysis of the experimental estimation of cross sections in Surface Enhanced Raman Scattering (SERS) by vibrational pumping. The paper highlights the advantages and disadvantages of the technique, pinpoints the main aspects and limitations, and provides the underlying physical concepts to interpret the experimental results. Examples for several commonly used SERS probes are given, and a discussion on future possible developments is also presented.Comment: To be submitted to J. Phys. Chem.

Silver Nanoparticle Aggregates as Highly Efficient Plasmonic Antennas for Fluorescence Enhancement

The enhanced local fields around plasmonic structures can lead to enhancement of the excitation and modification of the emission quantum yield of fluorophores. So far, high enhancement of fluorescence intensity from dye molecules was demonstrated using bow-tie gap antenna made by e-beam lithography. However, the high manufacturing cost and the fact that currently there are no effective ways to place fluorophores only at the gap prevent the use of these structures for enhancing fluorescence-based biochemical assays. We report on the simultaneous modification of fluorescence intensity and lifetime of dye-labeled DNA in the presence of aggregated silver nanoparticles. The nanoparticle aggregates act as efficient plasmonic antennas, leading to more than 2 orders of magnitude enhancement of the average fluorescence. This is comparable to the best-reported fluorescence enhancement for a single molecule but here applies to the average signal detected from all fluorophores in the system. This highlights the remarkable efficiency of this system for surface-enhanced fluorescence. Moreover, we show that the fluorescence intensity enhancement varies with the plasmon resonance position and measure a significant reduction (300×) of the fluorescence lifetime. Both observations are shown to be in agreement with the electromagnetic model of surface-enhanced fluorescence

Scattering by nonspherical systems

Scattering by nonspherical particles with size of order of wavelength - scattering by axisymmetric penetrable particles using approximate matching of boundary condition