Real world objects: capturing using in-line digital holography, projecting using spatial light modulators

Abstract

Digital holography is the process where an object's phase and intensity information is retrieved from intensity images obtained using a digital camera (CCD or CMOS sensor). Unlike off-axis holography, object information is not modulated onto carrier fringes, thus in-line digital holography makes optimum use of the recording device's sampling bandwidth resulting in higher resolution digital holograms. However, reconstructed images are obscured by the linear superposition of the unwanted out of focus twin images. In addition to this, speckle noise degrades overall quality of the reconstructed images. The speckle effect is an optical phenomenon arising when laser sources are used in digital holographic systems. Minimizing the effects due to speckle noise, removal of the twin image and using the full sampling bandwidth of the capture device, aids overall reconstructed image quality. Using interferometric techniques, it is possible to record whole field information about an object. Digital processing of the reconstructed holograms can remove or suppress the twin image while effects from speckle noise can also be reduced numerically. Machine vision techniques can then be applied to segment and distinguish objects of interest in the hologram. Coding the resulting phase information onto a spatial light modulator (SLM), real world, three dimensional images of objects can be reconstructed using the computer generated hologram.

Advanced holographic wavefront sensor

“…The combination terahertz digital holography takes the advantages of both the terahertz radiation and the digital holography, thus making up the defects of conventional holographic systems and in fact broadens the applications of holography [4][5][6][7]. It is known that due to various applications such as fast processing, compatibility and computer generated holograms (CGHs) to name a few, the use of photoelectric sensors (CCD, CMOS) in recording interferograms (i.e., digital holography) and numerical reconstruction have received wide attention [8][9][10][11][12].…”

“…Digital holography (DH) is a discrete whole-field imaging technique where both the intensity and phase components of a wave-field are captured using the holographic principle [13]. Numerical reconstruction of the digitally recorded intensity hologram enables access to the intensity and phase of the object field [12]. One common problem in recording and processing digital holograms is voluminous dataset, i.e., a huge amount of information have to recorded and processed which makes the process extremely (computationally) difficult.…”

Sparsity based terahertz reflective off-axis digital holography

“…Numerical reconstruction of the digitally recorded intensity hologram enables access to the intensity and phase of the object field [12]. One common problem in recording and processing digital holograms is voluminous dataset, i.e., a huge amount of information have to recorded and processed which makes the process extremely (computationally) difficult.…”