Abstract
We present a digital holographic method to increase height range measurement with a reduced phase ambiguity using a dual-directional illumination. Small changes in the angle of incident illumination introduce phase differences between the recorded complex fields. We decrease relative phase difference between the recorded complex fields 279 and 139 times by changing the angle of incident 0.5° and 1°, respectively. A two cent Euro coin edge groove is used to measure the shape. The groove depth is measured as ≈300 μm. Further, numerical refocusing and analysis of speckle displacements in two different planes are used to measure the depth without a use of phase unwrapping process.
Highlights
Noninvasive characterization of surface shape and deformation is very important in many industrial applications such as on-line quality control and reverse engineering [1]
Dual-directional illumination quantitative phase imaging with a single wavelength light source is another unwrapping solution [22,23,24,25,26]
By introducing a small change on the angle of incident, it is possible to scale the phase difference between two recorded complex fields
Summary
Noninvasive characterization of surface shape and deformation is very important in many industrial applications such as on-line quality control and reverse engineering [1]. When phase variation spans more than 2π in a measured field, it results in phase ambiguity To remedy this problem, different methods have been presented [7,8,9,10,11,12,13,14,15]. Dual-directional illumination quantitative phase imaging with a single wavelength light source is another unwrapping solution [22,23,24,25,26]. As the method uses a single wavelength light source, there is no error due to the chromatic aberrations This method usually requires two different images to be obtained consecutively within a certain time interval, they can be obtained in a single shot method in order to be used in real-time measurements [26]. A combination of two methods can make a robust system since the analysis is based on phase differences but is based on speckle displacements
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