A laser two focus velocimeter with high spatial resolution using confocal optical system

Measurement of flow velocity using optical techniques has advantages to measure flow velocity in a microscopic region without disturbing it. However the decrease of the depth of the measuring region (the length of the measuring region) is very difficult in the optical techniques. In this study a new velocimeter with high spatial resolution is proposed. The velocimeter was based on a laser two focus velocimeter (L2F) and its optical system was constructed with a confocal system to decrease the depth of the measuring region. The advantage of the confocal optical system is that the light from the only part within the focal region is detected strongly. The depth of the measuring region of proposed L2F was about 10 μm. The reliability of the L2F with the confocal system was confirmed by measuring velocities of moving a tungsten wire. The results of experiments show that the proposed laser two focus velocimeter using the confocal optical system achieved the velocity measurement with high spatial resolution and it is extremely effective instrument to measure the flow velocity in microscopic regions