Lenticular array for spatial filtering velocimetry of laser speckles from solid surfaces

Abstract

We present a low-cost optical design for the detection of speckle translation, which can provide measures of in-plane translation or the rotation of a solid structure. A nonspecular target surface is illuminated with coherent light. The scattered light is propagated through an optical arrangement that has been particularly designed for the type of mechanical measurand for which the sensor is intended. The dynamics of the speckle field that arise from the target surface are projected onto a lenticular array, constituting a narrow spatial bandpass filter for the speckle spectrum. The filter provides access to the full phase information of the temporal quasi-sinusoidal intensity output; thus differential arrangements of photodetectors can provide suppression of low-frequency oscillations and higher harmonics, and the direction of the speckle translation can be determined. The spatial filter of the sensor is characterized, and the precision of the sensor when it is integrated with an electronic zero-crossing-detection processor is investigated. The best measurement accuracy obtained at constant velocity is 1% at 1.6-mm translation; the relative standard deviation decreases with the square root of the distance traveled.

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

“…A more detailed description of this type of system can also be found in [14]. Table 2 lists the parameters and orientation of the spatial filters used in the measurements.…”

“…This is a well-known property of rectangular detector arrangements. It has been shown [14] that the Kth harmonics can, under certain conditions, be suppressed by selecting W d ¼ Λ=K. Given the detector configuration described above, the fourth harmonic will be suppressed but the third and fifth harmonics may constitute significant passbands in the spatial power spectrum of the spatial filter.…”

“…Previously, such methods have been demonstrated [10,12] and more recently described in a similar application [13]. The measurement of the out-of-plane motion is facilitated by an integrated optical spatial filter due to its high sensitivity [14]. The proposed method is intended for use in real-time studies where 3D translational velocity is of interest.…”

Liquid crystal-based lenticular lens array with laterally shifting capability of the focusing effect for autostereoscopic displays

“…Combined with head detection and tracking systems, our lenticular lens array will be directly applicable for a new class of autostereoscopic 3D display systems. Moreover, it is expected to play a versatile role in the crosstalk reduction of optical signal processing [29] and optical data storage [30]. …”

Speckles and their dynamics for structured target illumination: optical spatial filtering velocimetry

“…In the detector plane a differential pair of photodetectors is positioned with a centre spacing of d 180 . For a successful implementation of an optical spatial filter both with differential-detection, and a rectangular-weighted rectangular-array transmission function (2), the optics must fulfil the following relation [12]:…”