Simulating translation-induced laser speckle dynamics in photon Doppler velocimetry.

Historically, single-beam optical velocimetry has been limited to measuring only the component of velocity along the beam. However, theoretical work and recent experimental results have shown that laser speckle dynamics may be exploited to measure lateral motion, thereby gaining information about surface dynamics across an additional degree of freedom. In the use of photon Doppler velocimetry (PDV), this new information is considered "free" in that it is already contained within the PDV signal, needing only to be extracted and interpreted correctly.

Defining parametric dependencies for the correct interpretation of speckle dynamics in photon Doppler velocimetry.

Laser speckle dynamics manifest themselves in photon Doppler velocimetry (PDV) data as low-frequency amplitude fluctuations, and analysis of these fluctuations provides insight into the transverse speed of the surface under observation. We previously demonstrated that a single measurement probe is capable of simultaneously measuring (1) axial motion, through frequency analysis of Doppler shifts, and (2) transverse speed, through analysis of the speckle's coherence time. However, the performance of this technique hinges on a correct understanding of the speckle pattern's response to surface motion.

Note: Simultaneous measurement of transverse speed and axial velocity from a single optical beam.

A method is introduced for simultaneously measuring transverse speed and axial velocity using a single optical beam and a standard photon Doppler velocimetry (PDV) sensing architecture. This result is of particular interest given the recent, widespread use of PDV and the fact that optical velocimetry has thus far been limited to measuring motion in one dimension per probe. Further, this result demonstrates that both axial velocity data and transverse speed data (at least qualitative) may be obtained entirely through signal analysis; not requiring hardware modification.