Digital holography for recording of incoherent-object hologram as complex spatial coherence function

Abstract

We propose and demonstrate the recording of hologram of an incoherently illuminated object by using a Sagnac radial shearing interferometer, a Pockels cell and an 8 bit CCD camera. An approach based on statistical optics is used for understanding the concept of recording of an incoherent-object as complex spatial coherence function. The Sagnac radial shearing interferometer is used for the correlation of optical fields and the Pockels cell is used to shift the phase of the interfering fields. The fringe contrast and fringe phase that jointly represent the complex spatial coherence function are measured by applying a 5-step phase shifting algorithm while recording the interferograms. The results of recording and reconstruction of an object illuminated using a light emitting diode, Luxeon Star LXHL-MMID, having spectral width at half maximum of about 35nm at wavelength 530nm, are presented. Due to the implementation of the phase shift by using a Pockels cell, the system is mechanics free and has the potential for automated fast measurement which can be applied for the investigation of dynamic situations. Moreover, the interference of the optical field even with low temporal coherent light is achieved without using any interference filter and a reliable 3-D object reconstruction can be achieved even in an outdoor environment due to the inherent stability provided by the common path interferometer. By changing the shearing parameter, we can tailor the range of the measured coherence function depending on object under test. This could enable one to use it as coherence zooming microscope.