Digital Holography And Its Application In Displacement Measurement

Digital holography is a novel optical branch compound of conventional optic holography and computer technology. Besides the advantages of conventional holography, it avoids the wet chemic process, and obtains the object wave easily. Digital holography has been widely used in many fields in information processing, but the theory and applications are not enough systemic and mature. This paper aims at the record conditions and reconstruction algorithms, and also makes some improvements in the measure of displacement and deformation based on digital holography.A primary work of this paper analyzes the spatial frequency distribution of digital hologram in the CCD frequency domain under different optical setups by the concept of spatial frequency. The separation conditions of spatial frequency and the recording capability are derived. It shows that the angle between the plane reference wave and the Z-axis in the digital holography is larger than the way in the conventional holography, and the point source location is the same as with spherical wave .The recording capability with the spherical wave is larger than with the plane wave. It supplies a way of designing the optical arrangement.On the basis of the separation conditions of the spatial frequency, the records and reconstructions of digital holography are simulated under the off-line and in-line optical setups with spherical and plane reference wave respectively. The simulated results are in accordance with the theory. By analyzing the characteristic of the phase-shifted in-line digital holography, an arbitrary single phase-shift in-line digital holography is proposed. In this method, the phase-shifted frame is not joins the calculation of the object wave, but corrects the sign of object wave. So, it is not sensitive to the phase-shifted error.The last work is the applications of digital holography in the measurement of the displacement and deformation. A thought of double-exposure in measuring the displacement is proposed in order to reduce the complexity of the experimental procedure and the high requirement of equipment produced by several sensitivity vectors recording.