Tip diameter and transmission efficiency of a visible-wavelength near-field optic probe determine both the lateral spatial resolution and experimental utility of the near-field scanning optical microscope. The commonly used tip fabrication technique, laser-heated pulling of fused-silica optical fiber followed by aperture formation through aluminization, is a complex process governed by a large number of parameters. An extensive study of the pulling parameter space has revealed a time-dependent functionality between the various pulling parameters dominated by a photon-based heating mechanism. The photon-based heat source results in a temperature and viscosity dependence that is a complex function of time and fiber diameter. Changing the taper of the optical probe can affect transmission efficiency by an order of magnitude or more.

dimensions of the source are much smaller than the Near-field scanning optical microscopy (NSOM) is a scanned probe technique utilizing a subwavelength-sized light source for high-resolution imaging of surfaces. Although NSOM has the potential to exploit and extend the experimental utility of the modern light microscope, the interpretation of image contrast is not straightforward. In near-field microscopy the illumination intensity of the source (probe) is not a constant value, rather it is a function of the probe-sample electronic environment. A number of dielectric specimens have been studied by NSOM to elucidate the contrast role of specimen type, topography and crystallinity; a summary of metallic specimen observations is presented for comparative purposes. Near-field image contrast is found to be a result of lateral changes in optical density and edge scattering for specimens with little sample topography. For surfaces with considerable topography the contributions of topographic (Z) axis contrast to lateral ( X , Y ) changes in optical density have been characterized. Selected near-field probes have also been shown to exhibit a variety of unusual contrast artefacts. Thorough study of polarization contrast, optical edge (scattering) contrast. as well as molecular orientation in crystalline specimens. can be used to distinguish lateral contrast from topographic components. In a few cases Fourier filtering can be successfully applied to separate the topographic and lateral contrast components.

Outdoor education at this university-sponsored program was at least as safe as traditional college sports. Overall, college students were less likely to be injured while participating in COE courses than while participating in NCAA sports, even after excluding high-contact sports from the comparison.

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We report on a conceptual design and feasibility demonstration for a scanned beam endoscope, with advantages over present CCD imaging technology in image resolution and quality, light source power, and package diameter. Theoretical calculations were made by optical modeling and finite element analysis of the performance projected for a design meeting size constraints. To verify the design target of 5 mm for the endoscope diameter, we conducted a design study of the deformation and resolution characteristics of a scan mirror small enough to fit within a 2.5 mm capsule within the endoscope. The results show that performance similar to the test system can be achieved. A functional prototype was then built and tested to validate the theory used. The test system consisted of a photonics module with red (635 nm), green (532 nm) and blue (473 nm) lasers, combined by dichroic mirrors and launched to a single mode fiber. The light emerging from the fiber is formed into a beam and reflected from a commercially available bi-axial MEMS scanner with a 1.56 mm square mirror, and a scan angle of 6 degrees zero to peak mechanical, at a frequency of 19.7 kHz. Scanned beam power from 1 to 3 mw impinges the test object at a range from 10 to 100 mm, and the scattered light is collected by several 3 mm diameter multimode fibers and conducted one-meter to detectors. The detected light was digitized and then reconstructed to form an image of the test object, with 800 by 600 output pixels. Several such images will be presented.