Investigation of Interference Phenomenon of Astigmatic Pick-up Head and its Application in Displacement Measurement
Date Issued
2011
Date
2011
Author(s)
Chen, Yen-Hung
Abstract
Astigmatic pickup head is developed for capturing nano-scale data from the DVD disc. It can also be applied to measure nano-scale displacement by using its linear region of the focus error signal (FES), but the linear measurement range is only about 6 um. In order to extend its measurement range, object lens with long focal length is chosen, but it also induces resolution reduction.
In order to derive large measurement range and high resolution, the goal of this thesis is to study the interference phenomenon of the astigmatic pickup head and apply it to develop a laser interferometer. Through realizing parallel laser beam by removing the object lens, the astigmatic pickup head can also generate interference fringes on its projection plane by using the interference principle and half mirror. Two photoelectric sensors are utilized to capture the fringe change, which is induced by the displacement of a reflective mirror. Its displacement measurement resolution depends on the laser wave length, and the parallel laser beam reaches a longer measurement range.
This research includes the development of the astigmatic interferometer system with two precision 2-axes adjustment stages, which make the complicated alignment easily among the pickup head, the half mirror and the measured reflective mirror. Besides the interferometric analysis between the interference fringe and the output signal, our developed laser interferometer from the astigmatic pickup head is also verified by displacement measurement experiments. Its displacement measurement range is extended from 6 um to 100 mm, and its maximum resolution achieves 5 nm.
Subjects
Astigmatic pickup head
Astigmatic phenomenon
Displacement measurement
Michelson interferometer
Laser interferometer
Type
thesis
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