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A simple and reliable implementation of all-fiber velocity interferometer

This work reports a fiber velocity interferometer (FVI), mainly used for velocity profile measurements of materials in dynamic compression experiments. This FVI generates two pairs of orthogonal signals with only one fiber-coupled optical hybrid to achieve push–pull analysis, which is traditionally obtained by a set of discrete optical components in a velocity interferometer system for any reflector (VISAR). These signals are received differentially by two balanced detectors. Common mode fluctuations of signals caused by rapid changes in light intensity are suppressed in this way, and the signals will not easily exceed the dynamic range of recorders anymore. Furthermore, a dual-core fiber probe is used to reduce disturbance from unwanted lights. At the Institute of Fluid Physics, FVI has been successfully applied in high-speed measurements up to several kilometers per second with almost the same precision of the heterodyne velocimetry (HV), which is now considered to be a reliable and accurate technique.