Applications Of Digital Holography For Microstructure Measurements

Recent technological trends based on miniaturization of mechanical devices to the microscopic scale, have lead to the development of electronic engineering, mechanism and communication system. In turn, the demand of researching new measurement methodologies is of extreme importance. Digital holography is a new holographic imaging technique and can be used as a fast, simple and robust method, showing important advantages and promising prospect in microstructure testing. Digital lensless Fourier transform holography, permitting sufficient utilization of the limited sensor area of CCD, has more predominance in deformation analysis and shape measurement, then allowing to calculate a variety of material parameters of microcomponents. This thesis focuses on digital lensless Fourier transform holography and its applications in microscopic objects measurement. The main contents are as follows:(1) Based on Fresnel transformation and its fast algorithm by FFT, the principle of numerical reconstruction of digital lensless Fourier transform hologram and the spatial resolution, as well as the lateral resolution of the reconstructed images plane are elaborated. The serious recording limitations due to the finite size of CCD and the space-bandwith products of an off-axis system and a lensless Fourier transform system are discussed. As in optical holography, lensless Fourier transform arrangement applies less constraint to the lateral size of an object and helps to relax the requirement on spatial resolution of CCD sensor, which is favorable for micromeasurement.(2) The numerical reconstruction of digital lensless Fourier transform holography for microstructures measurement is experimentally shown. Then based on holographic interferometry, the out-of-plane displacement of a deformed steel cantilever and deformed field of a heated resistor under different voltages are measured. The influence to the result by sensitivity vector, which depends on the geometry of the setup, is detailed discussed. The theory of two-source method for shape registration is presented. In experiment, the main influencing factors for experimental results and the settlement approach are further analyzed.(3) A smart fiber digital holographic system based on self-focusing lens is introduced. It is shown by the experimental results that with the use of a self-focusing lens by its special imaginary property, the fiber system presented here can be used for measurement of small areas of an object or objects difficult to access, while the whole setup is compact and more flexible.