Three-wave Lateral Shearing Interferometry With Partially Coherent Light
Abstract: This thesis contains an examination of a method for quantitative phase imaging using lateral shearing interferometry. The focus is on how the degree of spatial coherence in the light source effect the image. The method is examined by first creating a simulation of the system, then looking at some analytical solutions for the interaction between some parameters, and finally conducting an experiment with a simplified implementation of the system. One problem with classic holography is that it is very sensitive to vibrations, another is that you can get speckles due to using a temporally coherent light source. The method in this thesis uses lateral shearing, where the reference is not split ahead of the object. This has been shown to be more robust against vibrations. The method works by translating part of a wavefront in a lateral direction, creating a kind of shear between original wavefront and the translated part. From the interference between the two the difference in phase can be extracted. The method used to extract the phase requires the wavefronts to be shifted in spatial frequency. It is shown that this allow one to perform the shear by defocusing after the frequency shift. This is indeed how the experimental setup demonstrated is implemented. The simulation is built upon the theory of some simpler imaging theory and diffraction. Some significant time has been spent optimizing its implementation in Matlab. The simulation allows one to examine the statistical properties of the system with very little work. The work method of creating a simulation and then solving analytically for some parameters complemented each other very well. When either does not agree with that of the other one immediately knows there is an error. The simulation also provides what parameters actually are important, so you do not have to do a lot of work that leads to boring conclusions.
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