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High-resolution terahertz Doppler velocimetry based on frequency difference multiplication

The frequency range of the terahertz wave makes it have partial characteristics both of microwave and light waves. This also makes the terahertz wave has the advantages of strong penetrability and small influence on the detected object when applied in the field of velocity measurement compared with other non-contact velocity measurement technologies. We designed and built a non-invasive, high-precision, free-space terahertz wave Doppler velocimetry (TDV) , and amplified the Doppler frequency difference to solve the problems such as incomplete terahertz wave interference fringes and low velocity resolution due to the long wavelength of terahertz when TDV applied in the diagnosis of detonation process and other instant process with high acceleration. Combined with the velocity measurement model introduced by our optical system and terahertz interference velocity measurement method, we used high-resolution TDV to measure the flying process of flyerplate. Then we completed the extraction of flyerplate velocity and displacement at velocity up to 1.2 km/s, and proved the high velocity resolution of measurement results. The terahertz Doppler velocimetry combined with the frequency difference multiplication provides a non-destructive, non-contact, high-resolution measurement method for the research of detonation and shock wave physics, internal vibration detection of large equipment, and many other fields.