A role of evanescent light in the characteristic measurements of scintillating fibers

To study the light attenuation behavior of a scintillating fiber in some detail, the measurements are used for both core light and cladding light. We have developed the analytical expression for each on-axis component, and applied it to the past data. In such a measurement, the core light and the cladding light were expected to show up the concentric distributions separated by some dark space. We have tried observation of such images by photography, and found a radial distribution of cladding light much narrower than the Monte Carlo simulation result of the off-axis traveling light. It was suggested that the evanescent wave might have contributed in detaching the cladding light from the fiber