Digital holography technique is the numerical version of conventional holography technique. It is widely applied in computer reconstruction for the object image, opt-electronic reconstruction and the object information measurement, in which the computer reconstruction is the basis of the others. In this paper, the computer reconstruction technique combined with digital holography is researched. It puts forward reverse transform method to realize the digital reconstruction and applies focusing function to determine the exact registering/reconstruction distance. Finally the experimental results are shown.
Digital holography is widely used as a fast, simple and robust method for the field of non-destruction and non-contact testing, especially in deformation measurement. In this paper, an in-line digital holographic interferometry setup is described, which is based on phase-shifting digital holography. Taking advantage of digital holography, the setup is able to measure the deformation of an object. In addition, two theoretical methods are briefly described: two-exposure technique and phase-shifting digital holography, which can both realize deformation measurement. This paper utilizes the whole information of the object in two different states in the hologram plane which can respectively be reconstructed onto the image plane with two different methods: two-exposure digital holographic interferometry and phase shifting digital holography interferometry, which are derived from the computer reconstruction of single hologram and reconstruction technique combined with phase shifting technique. Then the interference fringe pattern and the phase difference map between the two reconstructed images can both be obtained, which indicate the deformation of the tested object by analyzing some kind of quantitative mapping relationship. In this paper, practical measurement results are presented to verify the metrology. High precision is obtained simultaneously. Several error factors are analyzed and some corresponding suppression methods are described.
In digital holography technique, we use CCD for recording. The reconstruction executes in computer and can also realize special reconstruction like conventional holography. The computer-reconstruction can be carried out by mathematical transform for single-fringe hologram, which has larger additive error. Now we import phase-shifting technique which can improve the reconstructive precision. Meanwhile it brings new problems because this means can
only receive the object information on holography plane. In this paper, we present virtual interferometry method and reverse transform method to solve reconstruction problems in phase-shifting technique and verify the methods by simulation.
The phase-shifting algorithm via wavelength tuning based on temporal Fourier transform is according to the Fourier transform technique and the difference technique to realize the processing of the interferogram. This algorithm is applied to test some course profiles or the topography with high steps. The paper describes its main idea and presents the shortcoming of the algorithm proposed by Takeda. Then it puts forward the improved algorithml. The pape describes the realization processing and the errors of the new algorithm. Finally, it supplies the measurement result.