Speckle-based three-dimensional velocity measurement using spatial filtering velocimetry

Speckle and fringe dynamics in imaging-speckle-pattern interferometry for spatial-filtering velocimetry

“…This behavior of speckles and fringes is numerically and experimentally documented in [8] in full agreement with Eq. (19d).…”

“…The three velocity Figure 4 illustrates that the fifth and seventh harmonics of the spatial filter, responding on the speckle patterns, do overlap with the spatial frequency band of the fringe patterns, and therefore cross talk from fringe motions could possibly contaminate the measurements of speckle motion. This is demonstrated numerically in [8], with a similar setup. However, as it is demonstrated, by choosing a φ ¼ ðφ x ; φ y Þ where jφ x j ¼ jφ y j, a complete suppression of any cross talk between measurements on fringes and speckles is obtained.…”

“…However, this system will not differentiate between translation and rotation of the object. Therefore, a design [8], based on mixing a reference wave with a speckle field propagated through an imaging system, has been proposed. The reference and the speckle field mix under a well-defined angle, and spatial-filtering velocimetry [9,10] is applied to the image plane of the imaging-speckle interferometer.…”

“…This fringe pattern will translate through the image plane with a displacement/velocity that can be related directly to the out-of-plane displacement/velocity of the object. In contrast to previous studies, this configuration is designed for measuring out-of plane motion of a rigid object [8] with optical spatial-filtering velocimetry [10] having the center frequency of the spatial bandpass filter tuned to the fringe spacing. Spatialfiltering velocimetry can provide both the displacement/velocity and the direction of the fringe pattern in real time.…”

Spatial filtering velocimetry of objective speckles for measuring out-of-plane motion

“…Such techniques can be integrated conveniently into a compact optical sensor [6], providing nearly realtime measurements of one or two components of an object in-plane motion [7]. The out-of-plane component can be addressed by adding a reference field incident onto the observation plane, and designing multiple spatial filters that can deal with a compound intensity structure of random speckles and regular fringes, and thus give independent and simultaneous velocity measurements [8]. Such a velocity measurement technique is anisotropic in the sense that the out-of-plane motion will be resolved with a resolution that is one or two magnitudes higher than in the resolution for measurement of the two in-plane motions.…”