This paper proposes a visualization technique to detect the three-dimensional configuration of a single bubble. Such research is motivated by the fact that, by employing a conventional visualization technique, in which a backlight illuminates the bubble from behind, it is difficult to obtain the information concerning the geometry of the bubble along the depth direction. In principle, the three-dimensional structure of a bubble can be detected, by capturing several slices of the cross-sectional images of the bubble, via a laser light sheet. However, such visualization technique has not been developed for a single rising gas bubble, and for the gas-liquid two-phase flow, due to the overexposure occurring around the bubble surface. To avoid the overexposure, a laser induced fluorescence (LIF) is produced within a mixture of the liquid and rhodamine B (fluorescent dye). A high-pass optical filter, placed ahead the CMOS camera, covers the bubble region but leaves the contour of gas-liquid interface uncovered. Since the fluorescent light is passing with a wavelength of about 590 nm through the liquid phase, and with an attenuated wavelength of 532 nm through the gas phase, the geometric structure of a bubble is revealed. Additionally, in order to gain better contrast of the photographed contour of gas-liquid interface, the Ronchi-ruling was applied. In this way, from both the point of reflection and the behavior of the specular reflection we were able to identify the shape of the gas-liquid interface.

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