Formulation of off-axis single reference beam and two angle views for digital holography

Abstract

Photo-plates used in classical holography have several advantages, mainly a high resolution and the ability to overlap several holograms. Conversely, they suffer from chemical processing and delays in getting the useful signal. In contrast to film holography, digital holography offers quick and easy access to the desired information but suffers from the low resolution of the CCD sensors and their small detecting areas. This is why many holographers were limited to the in-line scheme, because of its simplicity and ability to overcome this resolution problem. But it still suffers from several problems when recording particles such as depth of focus, superposition of twin images and others. This is why, in spite of a more complex optical arrangement, we propose an appropriate off-axis scheme and a theoretical formulation that enables us to record simultaneously two holograms on the same CCD sensor from two angle views using a single reference beam. Furthermore, such a scheme, simpler than other off-axis proposals, provides spatially separate reconstruction of the two views and overcomes the above cited problems. As the aim of our development is to measure the influence of concentration of solid particles on their velocity for mixing flows, we show here examples without extended analysis.

Two beams two orthogonal views particle detection

“…Boucherit et al [14,15] developed a technique based on two orthogonal object beams and one reference beam for better localizing tracer particles in a flow. Unfortunately, in this configuration, the recording and therefore the reconstructing distances were relatively large: more than three meters (360 cm for the direct view and 380 cm for the orthogonal view).…”

“…Furthermore, all multiplexing techniques use a separate reference wave for each view. Boucherit et al [14,15] described an angular multiplexing technique using only one reference beam for two views. This is not very convenient for the proposed experimental set-up in which the space of handling optical components with their mechanical holders is much too limited due to the critical angle imposed by the Shannon sampling theorem in off-axis digital holography.…”

An ultra-compact multiplexed holographic microscope using a multiple-pinhole aperture

“…In 2010, Larbi's team [22] developed an off-axis imaging system which only uses a single reference wave and two object waves to form a multiplexed hologram. Their system simplified previous multiplexed off-axis systems where paired object waves and reference waves are applied.…”