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.

Modern data acquisition technology and off-the-shelf optical telecommunications devices now enable the assembly of PDV systems within reasonable budgets.

The fundamental mechanism of PDV is the interference pattern created by two electromagnetic waves with a small difference in frequency.

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 gigahertz.

In theory, the analysis of a PDV data signal is quite simple, where the apparent velocity of the moving surface (

Consequently, Fourier transform analysis is used to extract the most probable frequency components, which can then be used to calculate the velocity history.

PDV can measure a wide range of velocities (limited primarily by the time resolution of the signal recording equipment), and is relatively easy to set up and use.

Depending on the quality of the data signal and parameters of the FFT, the inherent error in PDV measurements can be high.

Beat frequency obtained from the interference of a 193.4 THz EM wave with a 193.40032 THz EM wave. The shifted frequency corresponds to a surface moving toward the observer at a velocity of 500 m/s.