Study On Quasi-co-linear Common-path Shearography With A Zero-approaching Shear Amount

Speckle interferometry is an important branch of optical measurement technology.Because of its full-field,high accuracy and non-contact character,Speckle interferometry is gradually applied in medicine,water conservancy,machinery,mechanics,aerospace and other fields.Speckle shearography is a new method to measure the derivative of displacement developed on the basis of speckle interferometry.It has a simpler optical path,lower environmental requirements and more extensive applications.In recent years,with the development of computers,Speckle shearography has ushered in a digital revolution,which is called shearography shear speckle pattern interferometry now,For the data processing and the measurement method in the Speckle shearography system has been developed from electronic processing to digital processing and from static measurement to real-time dynamic respectively.Nowadays,more and more scenes have the demand of real-time measurement.In order to meet this demand,it is necessary to both improve the performance and optimize the single measurement time period of speckle shearography.In the aspect of performance improvement,the quasi-co-linear common-path shearography is commonly used,which has the advantages of simple operation and strong anti-interference ability,and can improve the quality of the phase map obtained.However,the arrangement of all optical components on one axis makes the shear amount in the system strongly correlated with the spatial carrier frequency,and the shear amount of the system cannot approach zero.In terms of time optimization,phase map filtering occupies most of the time in the whole measurement process,and the commonly used filtering method is sine-cosine filtering.However,the sinecosine filtering framework consumes about 70% of the computation time in the whole filtering process to recalculate the sine-cosine components of the intermediate phase map in each filtering process,which limits its real-time measurement ability.This topic has carried out in-depth theoretical analysis and experimental research on speckle shearography realtime measurement technology.After a detailed investigation of the quasi-common-path structure,the working principle of Wollaston prism and the introduction way of shear amount are also studied,solutions for the above two problems are proposed respectively.The main contents are as follows:(1)An idea of creating an intermediate real image plane is proposed to solve the two problems of strong correlation between spatial carrier frequency and shear amount and nonzero shear amount in the basic quasi-common shear speckle interferometry technology.The proposed quasi-co-linear common-path speckle shearography system consists of a carrier frequency control unit and a shear imaging unit.The carrier frequency control unit can independently control the carrier frequency,while the shear imaging unit can control the shear amount approach to zero.(2)A real-time strain measurement system for aluminum plate is set up based on the quasi-co-linear common-path speckle shearography.The ability of the system to control the carrier frequency and the ability of the system to obtain qualified speckle phase distribution map under the condition of zero-approach shear amount are verified by experiments respectively.(3)A complex amplitude domain filtering framework is proposed,which can improve the filtering efficiency while ensuring the filtering quality.The feature of the framework is that the filtering is carried out before obtaining the phase map,and it does not need to carry out the sine and cosine transform operation back and forth,which saves the filtering time.(4)The digital speckle interferometry system and the digital speckle shearography system are built respectively to obtain the real annular phase map and the butterfly pattern phase diagram.The algorithm of complex amplitude domain filtering framework is written.In this framework,different filters are used to filter the two types phase map,and the same process is carried out in the sine and cosine filtering framework for performance comparison.