Search results for "Microscope"

From Measurement to Control of Electromagnetic Waves using a Near‐field Scanning Optical Microscope

2013

Near-field optical response of a two-dimensional grating of gold nanoparticles

2001

Laboratoire de Physique, Optique Submicronique, Universite´de Bourgogne, Boite Postale 47870, F-21078 Dijon, France~Received 1 August 2000; published 4 April 2001!This article reports on the near-field optical response of a small square grating of gold nanoparticles tailoredby electron-beam lithography. The investigation of the grating is aimed at a deepened understanding ofelectromagnetic interaction among particles due to scattered light fields. Therefore, a photon scanning tunnel-ing microscope is applied to acquire near-field optical images. Two different incident wavelengths are used tocharacterize the intensity and the spatial localization of the electromagnetic near field both in and out…

Simultaneous observation of light localization and confinement in near-field optics

2001

We report on the observation, in direct space, of both light localization and confinement effects near lithographically designed structures. The sample is observed in the optical near-field zone with a Photon Scanning Tunneling Microscope (PSTM). Several patterns composed of a few periods of TiO2 dots, arranged as a hexagonal lattice, have been investigated. When the central dot of the pattern is removed, a phenomenon of light localization above the vacancy can be observed in the PSTM image. The occurrence of this phenomenon can be related to the variation of the electromagnetic local density of state.

Quasi-isotropic 3-D resolution in two-photon scanning microscopy.

2009

One of the main challenges in three-dimensional microscopy is to overcome the lack of isotropy of the spatial resolution, which results from the axially-elongated shape of the point spread function. Such anisotropy gives rise to images in which significant axially-oriented structures of the sample are not resolved. In this paper we achieve an important improvement in z resolution in two-photon excitation microscopy through spatial modulation of the incident beam. Specifically, we demonstrate that the design and implementation of a simple shaded ring performs quasi-isotropic three-dimensional imaging and that the corresponding loss in luminosity can be easily compensated by most available fe…

Reduction of focus size in tightly focused linearly polarized beams

2004

The electromagnetic theory predicts that when a linearly polarized collimated field is focused by a high-angle focusing system, components perpendicular to the initial polarization are generated. The use of annular masks to reduce the area of the focal spot usually increases the magnitude of this phenomenon, known as depolarization. We present a class of masks, the three-ring masks, which are important because they narrow the central lobe of the focal intensity distribution without increasing the depolarization. This can be very useful in modern optical applications, such as confocal microscopy or multiphoton scanning microscopy.

Maximizing the information gain of a single ion microscope using bayes experimental design

2016

We show nanoscopic transmission microscopy, using a deterministic single particle source and compare the resulting images in terms of signal-to-noise ratio, with those of conventional Poissonian sources. Our source is realized by deterministic extraction of laser-cooled calcium ions from a Paul trap. Gating by the extraction event allows for the suppression of detector dark counts by six orders of magnitude. Using the Bayes experimental design method, the deterministic characteristics of this source are harnessed to maximize information gain, when imaging structures with a parametrizable transmission function. We demonstrate such optimized imaging by determining parameter values of one and …

Dielectric versus topographic contrast in near-field microscopy

1996

Using a fully vectorial three-dimensional numerical approach (generalized field propagator, based on Green's tensor technique), we investigate the near-field images produced by subwavelength objects buried in a dielectric surface. We study the influence of the object index, size, and depth on the near field. We emphasize the similarity between the near field spawned by an object buried in the surface (dielectric contrast) and that spawned by a protrusion on the surface (topographic contrast). We show that a buried object with a negative dielectric contrast (i.e., with a smaller index than its surrounding medium) produces a near-field image that is reversed from that of an object with a posi…

Near-field optics theories

1996

The development of near-field optics theory is reviewed. We first recall that near-field optics is not limited to near-field microscopy. Broadly speaking, it concerns phenomena involving evanescent electromagnetic waves. The importance of such waves was ignored for a long time in optical and surface physics until the emergence of scanning near-field optical microscopes. Taking evanescent waves into account prevents the use of any simple approximation in the set of Maxwell's equations. The various theoretical approaches of near-field optics are discussed from the point of view of their ability to assess evanescent electromagnetic waves. We discuss the main results of the application of the v…

Imaging of test quartz gratings with a photon scanning tunneling microscope Experiment and theory

1995

We use the differential formalism of the electromagnetic theory of gratings to interpret the images of test sinusoidal or lamellar quartz gratings obtained with a photon scanning tunneling microscope. The period of the grating is 0.5 μm, and the height of the rule is 0.2 μm. It is shown that the images depend strongly on several parameters, such as polarization or angle of incidence, with respect to the ruling direction. A systematic study of the isointensity lines above the gratings as a function of polarization is presented, and it is shown that the image contrast can be increased or decreased depending on the sample–probe distance. To model the interaction of the fiber probe with the ele…

Experimental demonstration of Bloch mode parity change in photonic crystal waveguide

2004

We experimentally show coupling between two photonic crystal waveguide Bloch modes having a different parity. A monomode ridge waveguide etched in a silicon-on-insulator substrate and connecting to the photonic crystal waveguide allows us to excite the even Bloch mode. Transmission measurements, performed on a broad spectral range, show the even mode propagation along the defect line. Then, spectrally resolved near-field patterns obtained by using a scanning near-field optical microscope in collection mode for wavelengths, inside and outside the multimode region of the photonic crystal waveguide, clearly demonstrate coupling phenomenon between even and odd modes.