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Photon Doppler velocimetry
Photon Doppler velocimetry (PDV) is a one-dimensional Fourier transform analysis of a heterodyne laser interferometry, used in the shock physics community to measure velocities in dynamic experiments with high temporal precision. PDV was developed at Lawrence Livermore National Laboratory by Strand. 〔(Compact system for high-speed velocimetry using heterodyne techniques )〕 In recent years PDV has achieved popularity in the shock physics community as an adjunct or replacement for Velocity Interferometer System for Any Reflector (VISAR), another time-resolved velocity interferometry system. Modern data acquisition technology and off-the-shelf optical telecommunications devices now enable the assembly of PDV systems within reasonable budgets.
==Theory==
The fundamental mechanism of PDV is the interference pattern created by two electromagnetic waves with a small difference in frequency. Since most PDV systems are constructed with available telecommunications equipment, a standard laser source for a PDV system is centered at 1550 nm (or 193.4 THz). If this source is then reflected off of a moving surface with some velocity (), the reflected light will be shifted in frequency () according to the relativistic Doppler shift equation.
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If the shifted return light is then interfered with the original source, the resulting wave will have a beat frequency in the range of a few GHz. This beat frequency is slow enough that it can be monitored with a simple photo-detector and high speed oscilloscope. By recording the beat frequency over time, a complete velocity history of the surface is obtained.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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