Digital Holographic Study Of High Precision Measuring Technology

Digital holography is one of the most important tools of modern optical testing technology. It uses CCD instead of traditional dry plate as a record medium to realize the digital holographic recording, which can reproduce the recorded objects with the assist of computer through some algorithms. In accordance with the different recording system, digital holography can be divided into coaxial digital holography and off-axis digital holography. Multiple images are required or phase shifting device is needed in coaxial digital holography to separate the reconstructed image and conjugate image. Whereas, off-axis digital holography can easily realize the separation by adjusting the optical path structure, thus, off-axis digital holography possess a more extensive research and application value. Furthermore, digital holography is a real-time and non-destructive detecting method which can reproduce the object’s three dimensional morphology. Therefore, it is necessary to conduct studies on digital holographic detecting. In this paper, detecting methods are studied and finally achieved a high precision. The main contents of this paper are:Firstly, the main theories of digital holographic measurement are been analysed, aiming at solving the common problems of poor accuracy, difficulties in getting the accurate phase information and the disturbances of zero-order image and conjugate image in digital holography, this paper determine to use the no preamplifier off-axis digital holographic system as a basis for research. Through theoretical analysis, key factors of the influence from recording optic path to the reproduction results are definited, recording distance and the angle between object and reference wave are theoretical analysed, digital holographic recording and reproduction process are simulated through MATLAB. By modulating the experimental parameters of recording and reproducing, the effects of these factors to the holographic reconstruction results are verified.Secondly, based on theoretical calculations and analysis, devices are selected and experiment platform are built, through the constant modify of the recording system, high quality holograms are acquired.Finally, the reconstruction algorithm are analysed and MATLAB procedures are wrote by computer, acquired holograms are preprocessed by spectrum filtering method to eliminate the spectrums of zero-order image and conjugate image. Three dimensional image of the objects is reconstructed through angular spectrum method and achieve a high precision. Afterwards, the extracted phase diagram is unwrapped and distortion eliminated to get the real phase information and the surface morphology is got. Through measurement of the same sample, the system and processing algorithms are proved to have a high accuracy, through measurement of different samples, they are proved to have an universal applicability.