Study on aberration suppressing methods in digital micro-holography |
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Authors: | Wenjing Zhou Yingjie Yu Anand Asundi |
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Institution: | 1. Department of Precision Mechanical Engineering, Shanghai University, Shanghai 200072, PR China;2. School of Mechanical & Aerospace Engineering, Nanyang Technological University, Singapore 639798, Singapore |
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Abstract: | This paper discusses methods to eliminate and/or suppress aberrations in digital micro-holography (DMH) with specific examples for post-magnification DMH and lens-less DMH along with a phase subtraction approach. In post-magnification DMH, the reference wave interferes with the object wave to form a hologram, which is then magnified by a microscope objective (MO) and recorded by CCD. This compensates for the quadratic phase error usually present in the pre-magnification DMH and also it is easier to isolate the useful information in pre-processing. In this paper differences between post-magnification and pre-magnification DMH are compared and analyzed with the specimen of a phase grating with period 30 lines/mm and height 0.3 μm. A lens-less DMH is also described that can eliminate the quadratic error and most of wave-front errors of the projecting light. Finally, a phase subtraction method is demonstrated which can eliminate most of the system aberrations. |
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