Study Of Digital Speckle Photography And Spatial Modulation For Electronic Speckle Pattern

Speckle metrology is an important branch of optical measurement techniques.Speckle techniques make use of laser speckles formed in space or artificial specklesdeposited on the specimen surface to monitor displacement or to carry out deformationmeasurement. In the past three decades, in addition to the study of the inherentproperties of laser speckle fields, various speckle measurement techniques aregradually developed and widely applied in different fields.In Practice, In-Plane measurement is of importance and is used far and widely,therefore digital speckle photography (DSP) has developed and becomes a significanttechnique. It employs photoelectric instruments and computer to accomplish recordingand analysis process, with the virtue of convenience, practicability and high efficiency.Electronic speckle pattern interferometry (ESPI), which uses fringe analysis fornondestructive deformation field measurements, has become an important technique inthe recent 20 years. Many ripe phase measurement techniques have been applied infringe analysis in ESPI, of which temporal phase method (TPM) and spatial phasemethod (SPM) are the main sorts. Actually, measure environment or setting is instable,thus dynamic measurement is of high value.In this dissertation, digital speckle photography and Electronic speckle patterninterferometry is detailedly discussed. The main contents are described as thefollowing:1. A review of development of Speckle metrology is prsented. The main techniques,such as speckle photography, speckle interferometry, ESPI, DSP, Phase Shift ESPI andtheir derivations are summarized.2. Principle,theory and peculiarity of DSP and ESPI are introduced. A study of DSPbased on FTM (Fourier transformation method) for displacement measurement iscompleted, a novel method for enhancement of Younge's Fringe pattern. Two specklepatterns, one before and one after deformation is transformed into spectrum field, andthen are calculated. Two new methods, unitariness method and phase method isproposed, through which the quality of Young's fringe is enhanced. Their feasibilityand practicability are validateed by experiment.3. We proposed one novel method for ESPI pattern carrier modulation anddemodulation. Spatial carrier can be introduced by tilting the object or reference whichis accurately controled by micro-motor. This technique is advantageous in dynamicmeasurement and avoids enviromental affects. In addition, we discussed its valid rangeof frequency and its effect on measurement sensitivity. Quantitative measurement ofthe deformation field is performed by ESPI. The measurement system and typicalexperiment results is presented, which proves the validity and feasibility of spatialmodulation method for electronic speckle patterns. Some problems in the experimentare discussed.