Biomedical subjects

J R Krenn

Publications and source records attributed to J R Krenn.

10 recordsLinked to original sources

PubMed2006

Surface plasmon mediated near-field imaging and optical addressing in nanoscience.

We present an overview of recent progress in "plasmonics". We focus our study on the observation and excitation of surface plasmon polaritons (SPPs) with optical near-field microscopy. We discuss in particular recent applications of photon scanning tunnelling microscope (PSTM) for imaging of SPP propagating in metal and dielectric wave guides. We show how near-field scanning optical microscopy (NSOM) can be used to optically and actively address remote nano objects such as quantum dots. Additionally we compare results obtained with near-field microcopy to those obtained with other optical far-field methods of analysis such as leakage radiation microscopy (LRM).

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PubMed2005

Grating-induced plasmon mode in gold nanoparticle arrays.

We study the dipolar coupling of gold nanoparticles arranged in regular two-dimensional arrays by extinction micro-spectroscopy. When the interparticle spacing approaches the plasmon resonance wavelength of the individual particles, an additional band of very narrow width emerges in the extinction spectrum. By systematically changing the particles dielectric environment, the particles shape, the grating constant and angle of incidence, we show how this band associated to a grating induced-resonance can be influenced in strength and spectral position. The spectral position can be qualitatively understood by considering the conditions for grazing grating orders whereas the strength can be related to the strength of dipolar scattering from the individual particles.

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PubMed2005

Surface enhanced Raman scattering arising from multipolar plasmon excitation.

Visible and near infrared extinction spectra of gold nanorod regular arrays exhibit several bands assigned to high multipolar order plasmon resonances. These up to ninth order multipolar resonances generate surface enhanced Raman scattering spectra with typically 5 x 10(4) enhancement which is of similar magnitude as those obtained for dipolar excitations.

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PubMed2005

Imaging surface plasmon of gold nanoparticle arrays by far-field Raman scattering.

We present Raman spectra and Raman images of the methylene blue molecule adsorbed as a single layer on gold nanoparticles regularly arranged in periodic arrays. Spectra and images are recorded in the same spatial and spectral regions using an excitation under total internal reflection. Images of the Raman scattering appear as spots of circular shape located at the particle positions with size defined by the diffraction limit. It appears that all excited particles contribute equally to the Raman signal if the Gaussian intensity distribution of the laser beam is taken into account. These results demonstrate that Raman scattering can be a useful technique to study plasmon properties.

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PubMed2004

Surface plasmon polariton-based optical beam profiler.

We describe a surface plasmon polariton- (SPP-) based device for measuring the intensity distribution of strongly focused light beams. A gold thin film configured as a sharp step is positioned in the focal region of a light beam, converting light into SPPs. The SPPs emit directional leakage radiation into the glass substrate beneath the thin film. The intensity of the leakage radiation is proportional to the intensity of the incident local light at the position of the step, allowing us to reconstruct the optical field profile by scanning the thin film's edge through the focal region.

Journal Article↗

PubMed2004

Gold particle interaction in regular arrays probed by surface enhanced Raman scattering.

Lithographically designed two-dimensional arrays consisting of gold nanoparticles deposited on a smooth gold film are used as substrate to examine the SERS effect of the trans-1,2-bis (4-pyridyl) ethylene molecule. These arrays display two plasmon bands instead of the single one observed for the same arrays of particles but deposited on indium tin oxide coated glass. Laser excitation within the short wavelength band does not bring about any SERS spectrum, while excitation within the long wavelength band yields SERS spectra with a gain per molecule rising up to 10(8). The simultaneous investigation of extinction and Raman spectra of arrays exhibiting various topography parameters enables us to suggest an interpretation for both the occurrence of the two plasmon resonances and for the high Raman enhancement. We suggest to assign the short wavelength band to a plasmon wave propagating at the gold glass interface and the long wavelength one to an air/gold surface plasmon mode modified by particle-particle interaction.

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PubMed2004

Surface plasmon polaritons in metal stripes and wires.

Surface plasmon polaritons (SPPs) are collective electron oscillations coupled to a light field which are propagating along the interface of a metal and a dielectric. As a surface wave, SPP modes feature properties essentially different from light-field modes in all dielectric structures. These properties could allow the realization of novel photonic devices that overcome certain limitations of conventional devices. Specifically, the realization of two-dimensional optics and light-field transport in sub-wavelength SPP waveguides seems feasible. In this review we discuss recent experimental advances regarding SPP waveguides, i.e. laterally confined metal thin films that guide SPPs. Electron-beam lithography is applied to tailor these films with widths ranging from a few micrometres (stripes) to nanoscopic values (wires). We investigate SPP properties such as propagation length, mode field profile and reflection or scattering at interfaces. Various techniques for SPP excitation and detection are discussed.

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PubMed2003

Optical resonances in periodic surface arrays of metallic patches.

The transmission of light along the surface normal through an air-quartz-glass interface covered with a periodic array of thin, rectangular gold patches has been studied over the visible to infrared range. The various structures that are observed can be qualitatively understood as arising from standing-wave resonances set by the size and surroundings of the metal patches. A method-of-moments calculational scheme provides simulations in good quantitative agreement with the data. It is shown how the standing-wave picture provides a useful conceptual framework to understand and exploit such systems.

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PubMed2003

Surface plasmon micro- and nano-optics.

We report the experimental realization of key elements of a two-dimensional optics based on surface plasmon polaritons (SPPs). Local SPP sources, Bragg mirrors and beamsplitters were lithographically built from silver nanostructures. The SPP fields were imaged by detecting the fluorescence of molecules that act as local probes of the SPP near-field intensity.

Fluorescent Dyes↗

PubMed2001

Light field propagation by metal micro- and nanostructures.

The ability to sustain plasmon oscillations gives rise to unique properties of metal nanostructures, which can be exploited for the controlled manipulation of light fields on the nanoscale. In this context we investigate electromagnetic coupling effects within lithographically produced ensembles of gold nanoparticles with a photon scanning tunnelling microscope. To provide an interface between these nano-optical devices and classical far-field optics, we investigate surface plasmon propagation on microstructured metal thin films.

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