We probe the dynamics of objective laser speckles as the axial distance between the object and the observation plane
changes. With the purpose of measuring out-of-plane motion in real time, we apply optical spatial filtering velocimetry
to the speckle dynamics. To achieve this, a rotationally symmetric spatial filter is designed. The spatial filter converts the
speckle dynamics into a photocurrent with a quasi-sinusoidal response to the out-of-plane motion. Our contribution
presents the technology and discusses the selectivity of the spatial filter. Specifically, we discuss how the selectivity of
the spatial filter with regard to radial speckle motion is influenced by a concurrent in-plane speckle motion. The spatial
filter is emulated with a CCD camera, and is tested on speckle acquisitions obtained from a controlled set-up.
Experiments with the emulated filters illustrate performance and potential applications of the technology.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.