Study On The Phase Processing And Applications Of Digital Holography

Digital holography has been developed rapidly in the recent 20 years with the improvement of computer technique and opto-electric imaging device and applied in many fields such as three-dimensional display,three-dimensional measurement of contour and deformation,and stress analysis.In digital holography,phase processing is the key technology because measured quantities are usually given by phase.Unfortunately,phase processing is very difficult because of the esistance of noise and dislocations et al in the real phase map.In this paper,phase processing technology was studied in more depth,and digital holographic interferometry was applied in the measurement of transparent objects and analysis of damage and fracture.The content and conclusions of this paper are shown as following:1.Two phase unwrapping algorithms were proposed in this paper.The first one is improved phase unwrapping based on least-squares and iteration(PULSI),and the second is calibrated phase unwrapping based on least-squares and iteration(CPULSI).Both algorithms were utilized to unwrap the simulated and experimental phase data with speckle noise and compared with other classical algorithims.The results exibit that PULSI is the fastest for the phase data with lower speckle noise,and CPULSI has the best processing ability and highest accuracy for that with high speckle noise and faster than other classical algorithms adpt to high noise.2.Two approaches for the unwrapping and de-noising of phase data with high speckle noise were proposed in this paper.The first is de-noising with windowed fourier transform filtering firstly and unwrapping with PULSI then(WFTF+PULSI).The second is unwrapping with CPULSI firstly and de-noising with median filtering then(CPULSI+MedF).Both approached were verificated with simulated and experimental pahse data.The results exibit that WFTF+PULSI is more accurate and faster than CPULSI+MedF.3.For the phase data with dislocations,a restoration approach based on the detection and masking with second-order phase gradient,unwrapping with PULSI and inpainting with interpolation was proposed.This approach was utilized to restore the simulated phase data and experimental phase data in holographic flow measurement and compared with other restoration approaches.The results demonstrate that the proposed approach has better accuracy and speed.4.For the phase data with high speckle noise and dislocations,a robust processing approach was proposed in this paper.The process of the proposed approach is that,firstly,the phase map is de-noising with WFTF,then,phase dislocation is detected and Masked with 2nd phase gradient,then,masked phase is unwrapped with PULSI,and lastly,the unwrapped phase is in-painted with Interpolation(WMPI).It was demonstrated with simulated phase data and comparision with other approaches exibite that WMPI is a robust,accurate and fast approach for the restoration of phase data with high speckle noise and.dislocations.5.The proposed phase processing methods were applied in transmission digital holographic interferometry(DHI).The quantilized measurement for the stress-optic constant,stress field and deformation was realized and comparison to the theoretical results of elasticity and the results in literature demonstrated the feasibility of the proposed approach.6.The stress field of the rigid inclusion and interference stress field of two circular void inclusions were measured with DHI.The results show that the stress concentration appears in the regions near to the ends of the diameter of the rigid inclusion verticle to the load which are prone to be damaged which are opposite to the results of single void inclusion.The results are in accordance with those of in-situ SEM observation for Cu/WCp composites under tensile load.The interference stress field around two void inclusions is related to the configuration of the inclusions.When the line connecting the centers of inclusions is verticle to the load,the stress concentration appears in the region between the inclusions which will result cracks in this region and connect the voids.When the line is parallel to the load,the stress in the region between the voids will decrease and the maximum stress will also decrease compared with those of the above two cases which will protect the materials.7.The stress field and stress intensity factor KI near the mode I crack in the transparent plate were measured with DHI and the method to retrieve KI was given.The experimental phase data with high speckle noise was unwrapped successfully with CPULSI and the stress field near the crack was obtained.The KI under different load were calculated from stress field and their errors versus to the treoretical results are less which demonstrates the feasibility of the damage and fracture analyzing of materials with DHI.