Developing a High-Speed Electronic Speckle Pattern Interferometer:Experimental demonstration of time-stepping quadrature phase shifting method
Date Issued
2006
Date
2006
Author(s)
Liu, Chien-Wei
DOI
zh-TW
Abstract
After many years development and improvement, microscopy has been getting to be one of the most important precision metrology techniques. To meet the demand of the rapidly advanced micro-electro-mechanical system and nanotechnology, many instruments were invented by further integrating microscope into their systems. In the field of full-field measurement, high-speed electronic speckle pattern interferometry (ESPI) developed using high-speed CCD camera was first developed in 1978. Phase shifting interferometry was used to transform the speckle intensity information into the more desirable phase information. However, it is necessary to introduce a phase shifting device in the reference arm if phase shifting interferometry is to be implemented. However, adding phase shifting device significantly increases the system cost. Moreover, the measurement precision suffers due to the errors induced by the phase shifting device. For example, hysteresis of piezoceramic actuator can introduce errors in the range of several micrometers. The goal of this research is thus to develop a new ESPI system that can measure full-field and dynamic vibrations up to nanometer resolutions without the need to adopt the traditionally used phase shifting device. With the development of an innovative optical design and the associated signal-processing algorithm, phase shifting device is removed successfully from the optical system. Alignment and other related alignment and operational procedures is thus greatly simplified.
In this dissertation, high-speed CCD camera was used as the image system. An eight-wave retardation plate was added within the optical path to remove the phase shifting device. By means of short exposure time and precise time sequency control, transient information in a series of time scales could be obtained successfully. In image processing part of ESPI, time stepping quadrature phase shifting method, direct correlation method, noise reduction median filter, and path-independent phase unwrapping method were all integrated to reconstruct surface profile of specimen. By demonstrating the feasibility of time stepping quadrature phase shifting method, we successfully remove the phase shifting device from the system and basically eliminated the errors induced by the inaccurate phase modulation.
With regards to the experimental verifications, the electronic speckle image processing interface was developed by LabVIEW and the feasibility of the newly proposed optical configuration is demonstrated by optical simulation software. Finally, the feasibility of time stepping quadrature phase shifting method is verified experimentally.
Subjects
光學檢測
電子斑點
optical metrology
ESPI
Type
thesis
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