Velocity and thickness measurement of a thin-liquid film via a single-tip optical fiber probe micro-fabricated by femtosecond pulse laser

Optical fiber probing is a simple and compact measurement system for a gas-liquid two phase flow. This probe detects a gas-liquid interface responsively. We have developed a new measurement technique for a thin-liquid-film that utilizes a single-tip optical fiber probe (Fs-TOP) micro-fabricated through femtosecond laser pulses. The Fs-TOP is installed horizontally along the channel base, and vertically traversed to the other side of the base. The signal from the Fs-TOP is sufficiently understood by using the originally developed 3D ray-tracing-numerical simulation. The maximum liquid film thickness was measured as well as the average liquid film thickness. Based on the simulation, it was found out that when a fraction of liquid phase is 52{\%}, the installed position of the Fs-TOP is equal to the average liquid film thickness. We measured velocity of the liquid film by the Fs-TOP and visualization. The results accorded with each other, and implied that the Fs-TOP measurement was superior to the visualization, against a high-velocity flow.