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

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

Holograms: The story of a word and its cultural uses

Holograms reached popular consciousness during the 1960s and have since left audiences alternately fascinated, bemused or inspired. Their impact was conditioned by earlier cultural associations and successive reimaginings by wider publics. Attaining peak public visibility during the 1980s, holograms have been found more in our pockets (as identity documents) and in our minds (as video-gaming fantasies and “faux hologram” performers) than in front of our eyes. The most enduring, popular interpretations of the word “hologram” evoke the traditional allure of magic and galvanize hopeful technological dreams. This article explores the mutating cultural uses of the term “hologram” as marker of magic, modernity and optimism

Compressive Holographic Video

Compressed sensing has been discussed separately in spatial and temporal domains. Compressive holography has been introduced as a method that allows 3D tomographic reconstruction at different depths from a single 2D image. Coded exposure is a temporal compressed sensing method for high speed video acquisition. In this work, we combine compressive holography and coded exposure techniques and extend the discussion to 4D reconstruction in space and time from one coded captured image. In our prototype, digital in-line holography was used for imaging macroscopic, fast moving objects. The pixel-wise temporal modulation was implemented by a digital micromirror device. In this paper we demonstrate $10\times$ temporal super resolution with multiple depths recovery from a single image. Two examples are presented for the purpose of recording subtle vibrations and tracking small particles within 5 ms.Comment: 12 pages, 6 figure