Partial coherence effects in lensless in-line digital holographic microscopy

Digital holography using the in-line configuration has been demonstrated for various applications involving imaging and tracking of microparticles and microorganisms. The twin-image problem usually associated with in-line holography is not very significant for objects on the microscopic scale. The lensless configuration is particularly attractive as the setup is inexpensive and simple. Lensless digital inline holography has been demonstrated using coherent as well as partially coherent sources. The use of partially coherent light has the advantage of reducing coherent light albeit with some loss of resolution. In this paper, we analyze a lensless digital in-line holographic set up that uses a spatially incoherent broad band light source. Light from the source after passing through a pinhole, used to control the spatial coherence, interferes with the scattered light from the object to form a hologram. The effect of the size of the pinholes and the temporal bandwidth of the source on the reconstruction is analyzed. We support our analysis with experimental results obtained from a lensless microscope using an LED and a laser diode as source.