Study Of The Phase-shifting Technique In ESSPI

Speckle metrology is an important branch of optical measurement techniques. Speckle techniques make use of laser speckles formed in space or artificial speckles deposited on the specimen surface to monitor displacement or to carry out deformation measurement. In the past three decades, in addition to the study of the inherent properties of laser speckle fields, various speckle measurement techniques are gradually developed and widely applied in different fields.Electronic speckle pattern interferometry (ESPI), which uses fringe analysis for nondestructive deformation field measurements, has become an important technique in the recent 20 years. Electronic Speckle-shearing Interferometry (ESSPI) is a new method which developed from Electronic speckle pattern interferometry (ESPI).The method has many advantages of the whole-field measurement, the simple optical road, the easy modulation and the low demand for environment. The phase-shifting method which is used in ESSPI can improve the precision of the measurement greatly. So the phase-shifting method is used in Non Destructive Testing (NDT) widely.In this dissertation, Electronic Speckle-shearing Interferometry (ESSPI) and the phase-shifting technique are detailedly discussed. The main contents are described as the following:1,A review of development of Speckle metrology is presented. The main techniques, such as Electronic speckle pattern interferometry (ESPI) and Speckle-shearing Interferometry (ESSPI) are summarized.2,Principle of the phase measurement method is introduced. The principle, the method and the arithmetic of the phase-shifting technique is specially introduced.3,Because two shearing object beams travel in the same direction when Wollaston prism is used as image-shearing device in traditional speckle shearing interferometry. It is difficult to realize phase-shifting technique by separating the two beams. The phase-shifts method of the translating Wollaston prism can introduce additional phase without separating the two beams. This paper gives the theoretical analysis of the method. The relationship between the displacement and additional phase is offered. The errors of the output angle and the position of the prism in ESSPI are analyzed. The mathematic relationship and the figure of the relative error are offered. A typical experiment about the method is carried out by using a centrally loaded clamped circular plate. The result is offered. It shows that the method of translating Wollaston prism phase-shifting technique could effectively obtain displacement derivative field from fringe patterns of test object.