Showing papers by "Franz R. Aussenegg published in 1999"

Squeezing the Optical Near-Field Zone by Plasmon Coupling of Metallic Nanoparticles

Abstract: We report on the experimental observation of near-field optical effects close to Au nanoparticles using a photon scanning tunneling microscope (PSTM). Constant height operation of the PSTM allowed an unprecedented direct comparison with theoretical computations of the distribution of the optical near-field intensity. An unexpected squeezing of the optical near field due to plasmon coupling was observed above a chain of Au nanoparticles.

Resonant and Off-Resonant Light-Driven Plasmons in Metal Nanoparticles Studied by Femtosecond-Resolution Third-Harmonic Generation

Abstract: We report on a femtosecond-resolution study of the plasmon fields in gold nanoparticles using third-harmonic generation. Controlled resonant and off-resonant plasmon excitation is achieved by tailoring the nanoparticle sample by an electron-beam-lithographic method. Comparing the measured third order interferometric autocorrelation function of the plasmon field with simulations based on a simple harmonic oscillator model we extract the temporal characteristic of the plasmon oscillation. For off-resonant excitation of particle plasmons we find a beating between the driving laser field and the plasmon field which demonstrates clearly the nature of the plasmon as a collective electron oscillation.

SHG studies of plasmon dephasing in nanoparticles

Abstract: . The necessary high SHG efficiency is obtained by nanoparticles produced by an electron beam lithographic method, which enables us to fabricate a two-dimensional array of nearly identical, parallel oriented particles of designed shape without centrosymmetry, essential for high SHG efficiency and the tuning of the plasmon resonance to the driving laser wavelength of 780 nm.

Direct observation of localized surface plasmon coupling

Abstract: We report on the direct observation of localized surface plasmon coupling using a photon scanning tunneling microscope. The surface plasmons are excited in gold nanostructures tailored by electron beam lithography. Electromagnetic energy transfer from a resonantly excited nanoparticle to a nanowire, which is not directly excited by the incident light is observed. Our experimental results appear to be in good agreement with theoretical computations based on Green's dyadic technique.

Particle-plasmon decay-time determination by measuring the optical near-field's autocorrelation : influence of inhomogeneous line broadening

Abstract: A detailed analysis of the influence of inhomogeneous plasmon absorption band broadening on particle-plasmon decay-time determination by an interferometric autocorrelation method is reported. We present model calculations based on the representation of plasmons in an array of non-uniformly shaped particles by an ensemble of harmonic oscillators. Considering carefully the extent of the inhomogeneous broadening our theoretical treatment yields an unambiguous correlation between the autocorrelation function and the plasmon decay time. As an experimental example we find a plasmon decay time of 6 fs for a gold nanoparticle sample.

Optical nanocluster microchips for human diagnostics

Abstract: Metal clusters excited by light exhibit high local field enhancement and nanoscale resonant behavior. Absorptive properties of these metal clusters bound to a surface are the basis of various new and highly promising setups to transduce biorecognitive interactions into an optical signal. Multilayered highly resonant systems had been proposed and recently demonstrated employing a metal mirror, a nanometric polymer distance layer, a biomolecule interaction layer and biorecognitively bound metal nano clusters. The optochips clearly exhibit strong reflection minima induced by the resonant behavior of the metal cluster layer. At least one narrow reflection minimum can be shifted to the red or infra red spectral range and therefore far away from spherical gold colloids (less than 520 nm) and human plasma absorption. The setup enabled us to replace conventional binding assays (like ELISA) overcoming the various technological limits as there are multiple incubation steps, harmful reagents and spatial resolution. A modified setup (the metal island coated swelling polymer over mirror system) employing an optical thin-layer system consisting of a metal mirror, an active analyte-induced swelling polymer, and a metal cluster (island) film as the topmost layer was used to transduce human plasma ion concentrations.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Optical Near-Field Properties of Lithographically Designed Metallic Nanoparticles

Abstract: We report on the experimental observation of localized surface plasmons sustained by small metallic particles using a photon scanning tunneling microscope (PSTM). The surface plasmons are excited in gold nanostructures tailored by electron beam lithography. The constant height operation of the PSTM allowed a direct comparison with theoretical computations of the distribution of the optical near-field intensity. Plasmon coupling above a chain of Au particles and electromagnetic energy transfer from a resonantly excited nanoparticle to a nanowire are demonstrated. Our experimental results appear to be in good agreement with theoretical computations based on the Green’s Dyadic Technique.