Lensless fiber microendoscopes enable optical diagnostics and therapy with minimal invasiveness. Because of their small diameters, multimode fibers are ideal candidates, but mode scrambling hinders the transmission of structured light fields. We present the generation of a localized fringe system at variable distances from the distal fiber end by exploiting digital optical phase conjugation. The replayed fringe system was used for quantitative metrology. Velocity measurements of a microchannel flow in the immediate proximity of the fiber end without the use of any imaging lenses are shown. Lensless multimode fiber systems are of interest especially for biomedical imaging and stimulation as well as technical inspection and flow measurements.

No abstract

No abstract

The tungsten carbide films were deposited by reactive magnetron sputtering in an industrial-scale coating chamber at different bias voltages and gas (argon/acetylene) flows. As substrate materials, silicon wafers and 100Cr6 steel sheets were used. The films were characterized using electron probe microanalysis with wavelength-dispersive X-ray spectroscopy (EPMA/WDX) and in situ hightemperature X-ray diffraction (HTXRD). EPMA revealed the chemical composition of the films; HTXRD gave overview over the thermally activated phase transformations and stabilization of metastable phase through the microstructure defects. The as-deposited films contain metastable phases WC1-x and W2C with distorted crystal structures. With increasing temperature and/or longer annealing time, the crystal structure of the high-temperature W2C phase recovered, although the annealing temperature was below the temperature, which is required to make W2C thermodynamically stable. The density of the microstructure defects in W2C was reduced, but some defects persisted. The structure relationships between individual phases will be discussed. Further heat treatment resulted in a decomposition of W2C, which was accompanied by the formation of metallic tungsten. The EPMA results confirmed that this decomposition is accelerated by the reaction of carbon with oxygen impurities in the annealing atmosphere. When the 100Cr6 steel is used as substrate material, W3Fe3C forms at the interface between the substrate and the coating. The presence of this carbide influences the decomposition of W2C.

No abstract