Digital holography and hybrid opto-acoustic imaging system for vibration analysis

Official URL: http://192.168.1.20/record=b1301367 (Table of Contents)

Holography is a true three dimensional (3D) imaging technique that has real life applications varying from high resolution 3D microscopy to interferometric analysis. In this thesis a hybrid opto-acoustic vibration analysis system is designed and implemented which is combination of a digital holographic interferometer and an acoustic microphone array. The system is capable of analyzing broad range of vibration amplitudes by utilizing acoustic microphone array for coarser analysis and holographic interferometer for small scale analysis on the order of few hundred nanometers. In the design process of the system, a comprehensive research on holography is performed both from theoretical and practical perspectives. In the theoretical part, a discrepancy that exists in the literature for the numerical reconstruction of digital holograms is clarified and a new method for diffraction pattern calculation is presented which we call Planar Layers Method (PLM). PLM is a fast method based on the idea of representing 3D computer synthesized objects with discrete planar layers and evaluating the diffraction patterns efficiently using Fast Fourier Transform (FFT) based Fresnel Transform. In the practical issues about holography, a new holographic recording scheme is presented in which there is no need for a separate reference wave. In the method reference beam is generated from the reflecting object wave, therefore path length equalization can be done automatically.