Abstract

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. In this paper, we model the origination of the speckle pattern, and we describe a methodology for calculating the speckle’s coherence time from the autocorrelation of a noisy signal. We then test a suite of optical probes over a range of standoff distances, demonstrating a significant reduction in the speckle’s coherence time, which correlates to the increase in speckle boiling when the target surface is located near a probe’s focal length. We show that spatial regions of decreased coherence time may be predicted a priori by a probe’s parameters, since they stem from boiling dominance. We analyze this result as a function of probe parameters for a surface-scattering target and a volume-scattering target. Although the coherence time’s behavior in the focal plane makes velocity extraction difficult, far from the probe’s focal lengths, we are able to measure rigid body transverse speeds exceeding 20m/s with an absolute accuracy of ±15% using the speckle dynamics measured by a PDV setup.

© 2013 Optical Society of America

Full Article  |  PDF Article

References

You do not have subscription access to this journal. Citation lists with outbound citation links are available to subscribers only. You may subscribe either as an OSA member, or as an authorized user of your institution.

Contact your librarian or system administrator
or
Login to access OSA Member Subscription

Cited By

You do not have subscription access to this journal. Cited by links are available to subscribers only. You may subscribe either as an OSA member, or as an authorized user of your institution.

Contact your librarian or system administrator
or
Login to access OSA Member Subscription

Figures (11)

You do not have subscription access to this journal. Figure files are available to subscribers only. You may subscribe either as an OSA member, or as an authorized user of your institution.

Contact your librarian or system administrator
or
Login to access OSA Member Subscription

Tables (1)

You do not have subscription access to this journal. Article tables are available to subscribers only. You may subscribe either as an OSA member, or as an authorized user of your institution.

Contact your librarian or system administrator
or
Login to access OSA Member Subscription

Equations (11)

You do not have subscription access to this journal. Equations are available to subscribers only. You may subscribe either as an OSA member, or as an authorized user of your institution.

Contact your librarian or system administrator
or
Login to access OSA Member Subscription

Metrics

You do not have subscription access to this journal. Article level metrics are available to subscribers only. You may subscribe either as an OSA member, or as an authorized user of your institution.

Contact your librarian or system administrator
or
Login to access OSA Member Subscription