Researches On Digital Holography

As a highlight in the optical research today, digital holography is a mix of optical holography, computer technology and electronic imaging technology. Digital holography is based on the theory of optical holography, but it utilizes CCD array to record Fresnel holograms and fulfills the numerical reconstruction of the object wavefront by computer. This procedure not only replaces the wet-chemical processing, but also has a number of further advantages especially in holographic metrology.After a brief review of the history of holography and a summarization of progresses in digital holography, this thesis offers researches in the theories, computer simulations and experiments of digital holography:1. Introduce fundamentals of recording and reconstruction in traditional holography. Two approaches to the theory of Fresnel transform (namely Fresnel diffraction formula) are studied: one is the scalar diffraction theory in the spatial domain and the other is the angular spectrum theory in the frequency domain. The differences between the two kinds of hologram recording configuration, in-line setup and off-axis setup, are described in the latter sections.2. Construct a mathematical model of digital holography for its recording and reconstruction. The procedure of digital recording and numerical reconstruction are discussed in detail. The interference angle limitation induced by the spatial resolution of CCD sensor through both in-line and off-axis setup is brought forward. The study of the phase-shifting technology applied in in-line holography and the frequency spectrum filtering technology used in off-axis holography is also presented.3. Demonstrate numerical simulations' procedures and results to validate the theory of digital holography. Some pretty good numerical simulation results of metrology to the transmissivity object and phase object by the two kinds of holography setup, in-line and off-axis, respectively, are offered.4. Perform the digital holography experiments. According to the current experimental conditions, we adopted the scheme of off-axis digital holography. With careful and repeated adjustments to the optical path of the experiment and the parameters of computer-constructed reference wave, some exciting results were obtained.