A comparison of techniques for extracting transverse speed from photon Doppler velocimetry signal content

We recently demonstrated that a single optical probe is capable of simultaneously measuring a surface's velocity along the beam axis and its speed transverse to the beam axis. Doppler shifts in the measured data are related to axial motion, while intensity fluctuations, induced by speckle dynamics, are related to transverse motion. While it is readily apparent that speckle dynamics manifest themselves in the measured data, the ability to extract transverse speed from a particular (speckle-induced) signal feature is feature-dependent. In this paper, we relate a signal's coherence, variance, and frequency content to surface dynamics, in an effort to determine the suitability of each of these features for calculating transverse motion (classification release number: LA-UR 13-26315).