Investigation of Key Problems on Fresnel Incoherent Correlation Holography
|School||Beijing University of Technology|
|Keywords||Digital holography Incoherent digital holography Phase mask Numerical aperture of hologram Single-shot|
Comparing with traditional digital holography, incoherent digital holography hasmany advantages such as demanding lower coherence of the light source. Incoherentdigital holography expands the application of holography to white light imaging andfluorescent imaging field. Various of methods for recording holograms underincoherent illumination have been developed recently. Fresnel Incoherent CorrelationHolography (FINCH) is an relatively innovative technology, which can achieveincoherent holograms by using the correlation between the object information and aFresnel Zone Plate. In this method, the optical wavefront scattered from an objectpropagates and incidents to a spatial light modulator which a phase mask is mountedon, and then the optical beam is split and phase shifted. A series of holograms withinstepped phase differences are obtained to suppress the twin images in thereconstruction. In this article, the key problems of Fresnel Incoherent CorrelationHolography are investigated. We study the effect of characteristics of elements and theparameters in this system on the hologram recording and reconstructing, and proposean optimized scheme base on the experimental results of theoretical analysis.The history and principle of incoherent holography are firstly reviewed in thisarticle. We describe some methods of acquiring incoherent holograms. The principleand development of Fresnel incoherent correlation holography are demonstrated. Inconnection with the problems in FINCH, the investigation is carried out.The effect of white light source characteristics on the quality of imaging inFINCH is discussed. The uniform circular light sources with different diameters areused as the original objects of the system. We record the holograms in the cases ofillumination by different diameter light sources. The modulations of holograms arecalculated in order to evaluate the effect of spatial coherence of the light source on theholograms recording. For a given light source, the effects of changing the radius ofspherical waves on the modulation and numerical aperture of holograms are alsoinvestigated. We propose a method that the valid numerical aperture of holograms canbe used to investigate the resolution of reconstructed images.To study the effect of phase-shifting technology on the holograms recording andreconstruction in FINCH, different number of phase-shifting step and phase-shiftingincrement are applied during the recording process, respectively. We compare thequality of reconstructed images by using signal-to-noise ratio, resolution andcorrelation coefficient. The feasibility of the single-exposure phase-shifting combining with FINCH is analyzed, and the analysis is verified by computersimulation based on Matlab.