20 research outputs found
Optical magnetic near-field intensities around nanometer-scale surface structures
Recently, local probes used in optical experiments added a new dimension to the study of the optical properties of small particles lying on a surface. Until now, several theoretical frameworks, developed to understand the interaction of optical fields with mesoscopic and nanoscopic objects, emphasized mainly the prediction of the electric near-field distributions generated by these structures. This paper demonstrates how such subwavelength dielectric surface structures also produce a particular confinement of the optical magnetic near field when the sample is illuminated by a surface wave
Polarization state of the optical near-field
The polarization state of the optical electromagnetic field lying several
nanometers above complex dielectric structures reveals the intricate
light-matter interaction that occurs in this near-field zone. This information
can only be extracted from an analysis of the polarization state of the
detected light in the near-field. These polarization states can be calculated
by different numerical methods well-suited to near--field optics. In this
paper, we apply two different techniques (Localized Green Function Method and
Differential Theory of Gratings) to separate each polarisation component
associated with both electric and magnetic optical near-fields produced by
nanometer sized objects. The analysis is carried out in two stages: in the
first stage, we use a simple dipolar model to achieve insight into the physical
origin of the near-field polarization state. In the second stage, we calculate
accurate numerical field maps, simulating experimental near-field light
detection, to supplement the data produced by analytical models. We conclude
this study by demonstrating the role played by the near-field polarization in
the formation of the local density of states.Comment: 9 pages, 11 figures, accepted for publication in Phys. Rev.
Creating Well-Defined Hot Spots for Surface-Enhanced Raman Scattering by Single-Crystalline Noble Metal Nanowire Pairs
Well-defined surface-enhanced Raman scattering (SERS) active systems were fabricated by single-crystal line noble metal nanowires. Crossed and parallel nanowire pairs were constructed by using a nanomanipulator to create SERS hot spots in the form of nanowire junction. SERS spectra of brilliant cresyl blue (BCB), p-mercaptoaniline (pMA), and p-mercaptobenzoic acid (pMBA) were observed at the junction of two nanowires. The SERS enhancement and polarization dependence are correlated well with the enhanced electric field intensities calculated by the finite difference time domain (FDTD) method for specific nanowire geometries. These simple and effective SERS active systems have a practical advantage that the hot spots can be readily located and visualized by an optical microscope. These well-defined SERS active systems based on noble metal nanowires can be further developed to find applications in a variety of biological and chemical sensingclose38404
Optimized factor of merit of the magneto-optical Kerr effect of ferromagnetic thin films
This paper deals with the optimization of the factor of
merit of the magneto-optical Kerr effect of a resonant multilayer
cavity including a ferromagnetic film. This optimization is of
interest in the context of optical storage technology. Using
numerical simulations based on the Green's dyadic technique, we
discuss a route to obtain magneto-optical multilayers with a vanishing
ellipticity and factors of merit (with respect to the bulk magnetic
material) larger than 3 on a broad range of wavelengths,
significantly higher than the actual state of the art
Analysis of image formation with a photon scanning tunneling microscope
International audienceThe photon scanning tunneling microscope (PSTM) is based on the frustration of a total internal reflected beam by the end of an optical fiber. Until now it has been used to obtain topographic information, generally for smooth samples. We report theoretical as well as experimental results on the observation of a step on a quartz substrate with the PSTM. These results demonstrate the effects on image formation of the distance between the fiber tip and the sample surface, the orientation of the incident beam with respect to the step, the polarization, and the coherence of the light. Good agreement exists between numerical simulations and experiments. We show that a perturbative approach, whose validity has been checked by comparison with a rigorous volume integral method, provides physical insight into the main features of the different images
Infrared near-field study of a localised absorption in a thin film
We study the conditions to perform micro-spectroscopy with a sub-wavelength lateral
resolution in the wavelength spectral range from 3 to 20 ÎŒm, taking advantage of the infrared
spectral signature of different chemical species. We utilised CLIO, a free electron laser, as the
photon source. The transmitted photons were collected by either fluoride or chalcogenide
glass fibres. Fibre tips were obtained through chemical etching by organic solvents.
Metallisation of the tips permits to achieve lateral resolution of the order of the tip size.
However, parasitic propagation of the light in the film reduces the contrast between irradiated
and non-irradiated zones. We exemplify our set up with near-field infrared spectra obtained for
polymer thin films deposited onto silicon wafers
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Fiber-optic surface-enhanced Raman system for field screening of hazardous compounds
Surface-enhanced Raman scattering permits identification of compounds adsorbed onto a metal microbase that is microlithographically produced with submicron resolution. Less than one percent of a monolayer of a Raman Active target compound offers a high signal-to-noise ratio. By depositing the microbase on the exterior of a fiber optic cable, convenient field screening or monitoring is permitted. By using highly effective microbases, it is possible to reduce laser power requirements sufficiently to allow an economical, but complete, system to be housed in a suitcase. We shall present details of SERS system of this type and shall show data on samples of interest in the screening of hazardous compounds