This study defines measurements of three-dimensional rigid-body shapes by using a fiber optic Lloyd’s mirror. A fiber optic Lloyd's mirror assembly is basically a technique to create an optical interference pattern using the real light point sources and their images. The generated fringe pattern thanks to this technique is deformed when it is projected on an object's surface. The introduced surface profilometry algorithm depends on a multi-step phase shifting process. The deformed fringe patterns containing information of the object's surface profile are captured by a digital CCD camera. While each frames are captured, required π∕2 phase shifts for interference fringe pattern are obtained by mechanically sliding the Lloyd assembly via an ordinary micrometer stage. Some preprocess algorithms are applied to the frames and are processed with an algorithm to accomplish 3D topographies. Finally, the continuous data determines the depth information and the surface topography of the object. The experimental setup is simple and low cost to construct, and is insensitive to the ambient temperature fluctuations and environmental vibrations that cause unwanted effects on the projected fringe pattern. Such a fiber optic Lloyd’s system which provides an accurate non-contact measurement without contaminating and harming the object surface has a wide range of applications from laser interference based lithography in nano-scale to macro-scale interferometers.
This study defines measurements of three-dimensional rigid-body shapes by using a fiber optic Lloyd’s mirror.
A fiber optic Lloyd's mirror assembly is basically a technique to create an optical interference pattern using real light
point sources and their images. The generated fringe pattern thanks to this technique is deformed when projected on an
object's surface. The deformed fringe pattern containing information of the object's surface profile is captured by a digital
CCD camera. The two-dimensional Fourier transformation is applied to the image, which is digitized with a frame
grabber card. After applying a band-pass filter to this transformed data in its spatial frequency domain, the twodimensional
inverse Fourier transform is applied. Using the complex data obtained by the inverse Fourier transform, the
phase information is determined. A phase unwrapping algorithm is applied to eliminate discontinuities in the phase
information and to make the phase data continuous. Finally, the continuous data determines the depth information and
the surface topography of the object. It is illustrated for the first time that the use of such a fiber optic Lloyd's system
increases the compactness and the stability of the fringe projection system. Such a fiber optic Lloyd’s system which
provides an accurate non-contact measurement without contaminating and harming the object surface has a wide range
of applications from laser interference lithography (LIL) in nano-scale to macro-scale interferometers.
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