laser Doppler velocimetryとは 意味・読み方・使い方

Laser Doppler velocimetry (LDV), also known as laser Doppler anemometry (LDA) is a technique for measuring the direction and speed of fluids (or any other material that is processed like metal, paper etc) like air and water. In its simplest form, LDV crosses two beams of collimated, monochromatic, and coherent laser light in the flow of the fluid being measured. The two beams are usually obtained by splitting a single beam, thus ensuring coherency between the two. The two beams are made to intersect at their waists (the focal point of a laser beam), where they interfere and generate a set of straight fringes. The sensor is then aligned to the flow such that the fringes are perpendicular to the flow direction. As particles pass through the fringes, they reflect light (only from the regions of constructive interference) into a photodetector (typically an avalanche photodiode). By measuring the Doppler equivalent frequency-shift of the scattered light, one is able to calculate the velocity of the tracer particle and thus the flow velocity of the liquid.