KEYWORDS: Holograms, 3D image reconstruction, Digital holography, Fringe analysis, Spatial frequencies, Beam splitters, Data modeling, 3D acquisition, Speckle, 3D metrology
A new method is proposed for instantaneous measurement of 3-D shape of moving objects with rough surface by using
one-shot digital holography. The principle of proposed method consists of projection of interference fringes with a
constant period on surfaces, one-shot recording of the complex-amplitude in-line hologram, elimination of speckle from
reconstructed images, and calculation of depth from focus. The acquisition time is less than 1 micro-second needed for
recording one hologram. Speckles appeared in reconstructed images are eliminated into a low level by filtering.
Following the method of depth of focus, we can precisely determine 3-D position of each point on the surface. Accuracy
higher than 0.01% is obtained in the experiment of depth measurement because of low-level speckles.
Single-shot digital holography is developed for instantaneous recording of the complex-amplitude inline hologram by
applying spatial heterodyne modulation and spatial frequency filtering. The complex-amplitude in-line hologram can be
precisely extracted from one off-axis hologram for the reference light beam with general spatial phase distribution.
Bandwidth of the complex-amplitude hologram is enlarged up to a half of the spatial sampling frequency by eliminating
the zero-order term from the off-axis hologram, which is a theoretical upper limit in the single-shot recording.
Experimental results show that fine images are reconstructed from the complex-amplitude hologram as a result of
elimination of the direct light beam and the conjugate beam.
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