Numerical Hologram Research Articles

Acoustic cloning

Cloning refers to producing copies of objects that cannot be distinguished from the original based on their behavior or response. Here, we present a general methodology to clone objects that scatter acoustic waves and demonstrate it experimentally. We acquire digital twins and bring them back to life—a simple two-step process. First, we place the scattering object in a circular receiver aperture and insonify it from the outside using simple speakers. From the recorded data, which may be reverberative, we retrieve the object's scattering Green's functions for radiation conditions using a technique called multi-dimensional deconvolution. This process recovers the temporal and spatial bandwidth and removes the scattering interactions with the boundaries of the experimentation domain, if present. In the second step, the acoustic scatterer is removed and reconstructed holographically using the acquired scattering Green's functions. The hologram scatters arbitrary incident wavefields in real-time exactly like the original object. Low-latency feedback enables reproducing all orders of wave interactions between physical scatterers and the numerical hologram. The two-step process is demonstrated by cloning several rigid scatterers in a two-dimensional acoustic waveguide. Applications range from fully realistic digital scattering models to efficient meta-material experimentation. [Work supported by SNSF grant 197182.]

JPEG Pleno holography presents the numerical reconstruction software for holograms: an excursion in holographic views.

Digital reconstructions of numerical holograms enable data visualization and serve a multitude of purposes ranging from microscopy to holographic displays. Over the years, many pipelines have been developed for specific hologram types. Within the standardization effort of JPEG Pleno holography, an open-source MATLAB toolbox was developed that reflects the best current consensus. It can process Fresnel, angular spectrum, and Fourier-Fresnel holograms with one or more color channels; it also allows for diffraction-limited numerical reconstructions. The latter provides a way to reconstruct holograms at their intrinsic physical instead of an arbitrarily chosen numerical resolution. The Numerical Reconstruction Software for Holograms v10 supports all large public data sets featured by UBI, BCOM, ETRI, and ETRO, in their native and vertical off-axis binary forms. Through the release of this software, we hope to improve the reproducibility of research, thus enabling consistent comparison of data between research groups and the quality of specific numerical reconstructions.

Parallax limitations in digital holography: a phase space approach

The viewing direction in Digital Holography can be varied if different parts of a hologram are reconstructed. In this article parallax limitations are discussed using the phase space formalism. An equation for the parallax angle is derived with this formalism from simple geometric quantities. The result is discussed in terms of pixel size and pixel number of the image sensor. Change of perspective is demonstrated experimentally by two numerical hologram reconstructions from different parts of one single digital hologram.

Enhancement of three-dimensional perception of numerical hologram reconstructions of real-world objects by motion and stereo

We investigated the question of how the perception of three-dimensional information reconstructed numerically from digital holograms of real-world objects, and presented on conventional displays, depends on motion and stereoscopic presentation. Perceived depth in an adjustable random pattern stereogram was matched to the depth in hologram reconstructions. The objects in holograms were a microscopic biological cell and a macroscopic metal coil. For control, we used real physical objects in additional to hologram reconstructions of real objects. Stereoscopic presentation increased perceived depth substantially in comparison to non-stereoscopic presentation. When stereoscopic cues were weak or absent e.g. because of blur, motion increased perceived depth considerably. However, when stereoscopic cues were strong, the effect of motion was small. In conclusion, for the maximization of perceived three-dimensional information of holograms on conventional displays, it seems highly beneficial to use the combination of motion and stereoscopic presentation.

Holographic display of synthetic 3D dynamic scene

A synthetic scene of real-word objects is obtained through the multiplexing of several digital holograms. Moreover, by an opportune numerical hologram deformation, it is possible to synthesize 3D dynamic scenes that can be displayed by means of a spatial light modulator. In fact, the spatial adaptive deformation of digital holograms allows the control of the object position and size in a 3D volume with a high depth of focus. Through this novel technique a 3D dynamic scenes can be projected as an alternative to difficult and heavy computations needed to generate realistic-looking computer generated holograms. Finally we report the result of a pilot experiment to evaluate how viewers perceive depth in a conventional single-view display of these dynamic 3D scenes.

Information extraction from digital holograms for particle flow analysis

The goal of our project is to observe the distribution of steady and moving colloidal polystyrene particles within a micro-optofluidic canal system. To this end, we apply a classical in-line holographic setup with a magnifying telescope and a digital camera sensor. The capabilities of numerical hologram reconstruction and the subsequent image processing offer new possibilities concerning the digital hologram analysis. We demonstrate new concepts for a four-dimensional particle flow observation using a captured holographic video as well as the potentials for information extraction.

Digital holographic method for tomography-image reconstruction

A digital holographic method for three-dimensional reconstruction of tomography images is demonstrated theoretically and experimentally. In this proposed method, a numerical hologram is first computed by calculating the total diffraction field of all transect images of a detected organ. Then, the numerical hologram is transferred to the usual recording medium to generate a physical hologram. Last, all the transect images are reconstructed in their original position by illuminating the physical hologram with a laser, thereby forming a three-dimensional transparent image of the organ detected. Due to its true third dimension, the reconstructed image using this method is much more vivid and accurate than that of other methods. Potentially, it may have great prospects for application in medical engineering.

719 ディジタルホログラフィを用いた粒子三次元位置検出法の測定精度 : ホログラム面内位置検出精度の影響

This paper reports the influence of the accuracy of detecting in-plane particle position with digital holography on the depth measurement. In the present digital holography, particle depth detection is carried out by calculating the light intensity at the in-plane particle position over the whole range from observed in-line hologram patterns. In the performance test, numerical hologram patterns are employed. It is shown that the error in in-plane particle position affects the depth measurement accuracy of the present method and that we can recognize whether detected in-plane particle position is correct or not, by using the reconstructed light intensity at the image point.

Fresnelets: new multiresolution wavelet bases for digital holography

We propose a construction of new wavelet-like bases that are well suited for the reconstruction and processing of optically generated Fresnel holograms recorded on CCD-arrays. The starting point is a wavelet basis of L2 to which we apply a unitary Fresnel transform. The transformed basis functions are shift-invariant on a level-by-level basis but their multiresolution properties are governed by the special form that the dilation operator takes in the Fresnel domain. We derive a Heisenberg-like uncertainty relation that relates the localization of Fresnelets with that of their associated wavelet basis. According to this criterion, the optimal functions for digital hologram processing turn out to be Gabor functions, bringing together two separate aspects of the holography inventor's work. We give the explicit expression of orthogonal and semi-orthogonal Fresnelet bases corresponding to polynomial spline wavelets. This special choice of Fresnelets is motivated by their near-optimal localization properties and their approximation characteristics. We then present an efficient multiresolution Fresnel transform algorithm, the Fresnelet transform. This algorithm allows for the reconstruction (backpropagation) of complex scalar waves at several user-defined, wavelength-independent resolutions. Furthermore, when reconstructing numerical holograms, the subband decomposition of the Fresnelet transform naturally separates the image to reconstruct from the unwanted zero-order and twin image terms. This greatly facilitates their suppression. We show results of experiments carried out on both synthetic (simulated) data sets as well as on digitally acquired holograms.

Digital recording and numerical reconstruction of holograms: reduction of the spatial frequency spectrum

Direct recording of Fresnel holograms on a charge-coupled device and their numerical reconstruction is possible if the maximum spatial frequency of the holographic microstructure is adapted to the spatial resolution of the detector array. The maximum spatial frequency is determined by the angle between the interfering waves. For standard CCDs with spatial resolutions of ;100 lines/mm, the angle between ref- erence and object wave is limited to a few degrees. This limits the size of the objects to be recorded or requires a great distance between object and CCD target. A method is described in which the primary object angle is optically reduced so that objects with larger dimensions can be re- corded. The principle is demonstrated for the example of deformation analysis. Two Fresnel holograms, which represent the undeformed and the deformed states of the object, are generated on a CCD target, stored electronically, and the wave fields are reconstructed numerically. The interference phase can be calculated directly from the digital holograms, without generating an interference pattern. As an application of this method, we present the transient deformation field of a plate that is loaded by an impact. © 1996 Society of Photo-Optical Instrumentation Engineers. Subject terms: digital holography; hologram interferometry; numerical hologram reconstruction; charge-coupled devices.

Off-axis electron holography of a two-phase polymer

Electron holography enables retrieval of phase from an image wave. This phase information is lost in conventional microscopy. As part of an ongoing program to study polymer microstructure via phase-contrast imaging, we report here our first experiences applying off-axis holography to polymers.This study utilized a 48k mw styrene/butadiene diblock copolymer mixed with 30% 25k mw styrene homopolymer. The specimen was cast from toluene, annealed, cryomicrotomed, and osmium stained. Offaxis electron holography experiments were performed at Arizona State University using the Philips 400STFEG microscope operated at 100kV. Digital holograms with =0.25nm fringes, 520kx magnification and Is exposures were recorded using a Gatan slow-scan CCD camera. Numerical hologram reconstruction was performed employing Gatan's Digital Micrograph.Figure 1 shows a diffraction contrast image of the specimen showing alternating styrene-rich (light) and butadiene-rich (dark) lamellae. Absolute phases were obtained from holograms in which vacuum was used as reference (region A in Fig. 1). Typical reconstructed amplitude and phase images from region A are shown in Fig. 2.