Research And Experiment On The Method To Improve Fresnel Digital Holography Reconstructed Image Quality

The holographic information is directly recorded on a charge-coupled device (CCD) camera in digital and the optical reconstruction is replaced by a computer numerical reconstruction, so the holographic full process including recording, memory and reconstruction is entirely digital. holography can develop its advantage and achieve extensive application. such as 3D profilometry, cell viewing, microcircuit examination, grain size analysis, experimental stress analysis, transparent field measurement etc.(1) Basic mathematical model for recording and numerical reconstruction of digital hologram is elaborated. The core of digital holography is the algorithm of numerical reconstruction. Two different approaches for numerical reconstruction of digitally sampled holograms are investigated, namely the Fresnel transform algorithm and the frequency domain algorithm.(2) The serious recording limitations due to the finite size and resolution of CCD are discussed. It's shown that the setup for recording hologram with spherical reference wave can make full use of the spatial bandwidth of CCD.(3) Various digital image-processing techniques for suppression of undesired components and enhancement of quality in numerical reconstruction images are considered, such as HRO subtraction, average value subtraction.(4) Combining phase-shifting technique with synthetic aperture technique is a kind of optimum method to solve the problem of reconstructing separation requirement and to improve the ratio of signal to noise of reconstructing image.