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5 November 2014 Freeform metrology based on phase retrieval and computer-generated hologram
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Recently, interferometric null-testing with computer-generated hologram has been proposed as a non-contact and high precision solution to the freeform optics metrology. However, the interferometry solution owns some typical disadvantages such as the strong sensitivity to the table vibrations or temperature fluctuations, which hinders its usage outside the strictly controlled laboratory conditions. Phase retrieval presents a viable alternative to interferometry for measuring wavefront and can provide a more compact, less expensive, and more stable experimental setup. In this work, we propose a novel solution to freeform metrology based on phase retrieval and computer-generated hologram (CGH). The CGH is designed according to the ray tracing method, so as to compensate the aspheric aberration related to the freeform element. With careful alignment of the CGH and the freeform element in the testing system, several defocused intensity images can be captured for phase retrieval. In this paper the experimental results related to a freeform surface with 18×18mm2 rectangular aperture (its peak-to-valley aspherity equals to 193um) are reported, meanwhile, we also have compared them with the measurement results given by the interferometry solution, so as to evaluate the validity of our solution.
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Fa Zeng, Qiaofeng Tan, Yi Liu, Huarong Gu, Zhehai Zhou, and Guofan Jin "Freeform metrology based on phase retrieval and computer-generated hologram", Proc. SPIE 9272, Optical Design and Testing VI, 92720E (5 November 2014);

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