Study On Algorithm Of Digital Holography With Applicationto Microstructure Topography Measurement

With the development of the processing technology of micro-structure, many techniques for measuring the microsturcture are continually updating due to the requirements of the measurement of mico-structures’ surface profile being higher and higher. How to measure the surface profile of micro-structure has attracted much attention. Digital holography has been developing as the Con-temporary integration technology advances, it is the result of combining optics with digital technique. In the digital holography, the holographic plate has been substituted with charge-coupled device(CCD), so the amplitude and phase can be stored in the computer. In contrast to pure optical hologram, the renconstruction process is completely accomplished by means of computer programming, which makes the analysis of3D-profile and phase more precise. Digital holography has a extensive application on account of it’s advantage that flexibility, digitization, non-contact and no damage.This dissertation primarily studies the algorithms of digital holography for measuring the mico-structures’ surface profile, including three calssical recon-struction algorithms, spectrum filtering method, self-focusing algorithms, phase aberration compensation algorithms and phase unwrapping algorithms. All the algorithms have been studied with the aid of MATLAB, the main content of this thesis is shown as follows:(1) The theory of recording and reconstructing digital hologram has been analysed, as well the light path used in digital holography microscopy(DHM). It focus on studing the theory of DHM for measuring structures, deriving the recording conditions of digital holography. It also reproduces the image at different recording conditions and reconstruction algorithms has been reproduced, and the clarity of each image has been compared.(2) The equation of digital holographic resolution is derived. The dissertationanalyses and compares the methods for eliminating zero-order image and conjugate image. Self-focusing problem of off-axis digital holography is analysed and simulated. Through comparing focusing evaluation function of four algorithms, the reconstructed distance is calculated with Fourier spectrum function.(3) The algorithms of phase unwrapping is studied. Here, the classical unwrap-ping algorithm ranks by point and least-squares unwrapping algorithm are analysed and improved. Unwrapping phase is gained with the different unwapping algorithms in MATLAB. (4) Two algorithms of phase aberration compensation are analysed. Through the simulation in MATLAB，the wrapped phase is compensated. Meanwhile, after unwrapping the phase, the true phase distribution is gained.