Digital holography and 3D imaging: Introduction to the feature issue

This feature issue contains a representative selection of topics that were presented at the inaugural OSA Topical Meeting on Digital Holography and 3D Imaging as well as additional relevant papers.     

Digitized holography: modern holography for 3D imaging of virtual and real objects

Recent developments in computer algorithms, image sensors, and microfabrication technologies make it possible to digitize the whole process of classical holography. This technique, referred to as digitized holography, allows us to create fine spatial three-dimensional (3D) images composed of virtual and real objects. In the technique, the wave field of real objects is captured in a wide area and at very high resolution using the technique of synthetic aperture digital holography. The captured field is incorporated in virtual 3D scenes including two-dimensional digital images and 3D polygon mesh objects. The synthetic field is optically reconstructed using the technique of computer-generated holograms. The reconstructed 3D images present all depth cues like classical holograms but are digitally editable, archivable, and transmittable unlike classical holograms. The synthetic hologram printed by a laser lithography system has a wide viewing zone in full-parallax and give viewers a strong sensation of depth, which has never been achieved by conventional 3D systems. A real hologram as well as the details of the technique is presented to verify the proposed technique.     

Digital in-line holography of microspheres

We have used digital in-line holography (DIH) with numerical reconstruction to image micrometer-sized latex spheres as well as ferrimagnetic beads suspended in gelatin. We have examined in detail theoretically and experimentally the conditions necessary to achieve submicrometer resolution of holographic reconstructions. We found that both transparent and opaque particles could be imaged with a resolution that was limited only by the wavelength of the light used. Simple inspection of intensity profiles through a particle allowed an estimate to be made of the particle's three position coordinates within an accuracy of a few hundred nanometers. When the derivative of a second-order polynomial fitted to the intensity profiles was taken, the X, Y, Z position coordinates of particles could be determined within +/-50 nm. More-accurate positional resolution should be possible with the help of more-advanced computer averaging techniques. Because a single hologram can give information about a large collection of distributed particles, DIH offers the prospect of a powerful new tool for three-dimensional tracking of particles.     

High-speed 3D imaging using photorefractive holography with novel low-coherence interferometers

The paper reports recent progress in developing high speed 3D imaging systems based on low coherence photorefractive holography with high-speed depth-sectioned imaging at 476 frames per second. It is demonstrated that photorefractive holography can utilize a wide variety of sources of differing spatial and temporal coherence, including a novel all-solid-state broadband laser. Also presented is a novel real-time optical sectioning technique based on structured illumination combined with photorefractive holography that provides real-time optical sectioning when imaging with reflected light or with fluorescence.     

3D atomic imaging of SiGe system by X-ray fluorescence holography

X-ray fluorescence holography (XFH) provides three-dimensional atomic images around specific elements without any assumption of the structural model. Six X-ray holograms of Si_0.8Ge_0.2/Si at different energies were measured at the synchrotron radiation facility of SPring-8. Si and/or Ge atoms within 0.7 nm of a radius were clearly visible in the atomic images reconstructed from the holograms. From these images, slight displacements of the images at each shell in between Si_0.8Ge_0.2/Si and the Ge bulk were distinctly revealed. This demonstrated that the XFH method has a great potential to quantitatively analyze a three-dimensional local lattice structure in epitaxial crystals.     

2-D array for 3-D ultrasound imaging using synthetic aperture techniques

A two-dimensional (2-D) array of 256 X 256 = 65,536 elements, with total area 4 X 4 = 16 cm2, serves as a flexible platform for developing acquisition schemes for 3-D rectilinear ultrasound imaging at 10 MHz using synthetic aperture techniques. This innovative system combines a simplified interconnect scheme and synthetic aperture techniques with a 2-D array for 3-D imaging. A row-column addressing scheme is used to access different elements for different transmit events. This addressing scheme is achieved through a simple interconnect, consisting of one top, one bottom single-layer, flex circuits that, compared to multilayer flex circuits, are simpler to design, cheaper to manufacture, and thinner so their effect on the acoustic response is minimized. We present three designs that prioritize different design objectives: volume acquisiton time, resolution, and sensitivity, while maintaining acceptable figures for the other design objectives. For example, one design overlooks time-acquisition requirements, assumes good noise conditions, and optimizes for resolution, achieving -6 dB and -20 dB beamwidths of less than 0.2 and 0.5 mm, respectively, for an F/2 aperture. Another design can acquire an entire volume in 256 transmit events, with -6 dB and -20 dB beamwidths in the order of 0.4 and 0.8 mm, respectively.     

Finite element simulation and modeling of 2-D arrays for 3-D ultrasonic imaging

Issues of modeling and design of 2-D arrays in three dimensions with finite element code are discussed. These ultrasonic arrays are used for real time dynamic imaging of the heart. Topics include optimization, sensitivity, and performance and methods to speed up the run times required for computer simulations of large three-dimensional models. Empirical results from 45×45 2-D arrays are also presented     

Lensless imaging by spatial Fourier synthesis holography

The technique of Fourier synthesis holography is extended to the spatial domain. A spatially extended source is decomposed into its Fourier components, and a hologram of an object distribution is formed at each spatial frequency and stored in a computer. Upon synthesis in the computer a clear image can be formed of the object without the use of lenses.     

Spectral holography for imaging through scattering media

Absorbers were imaged through a highly scattering material by application of spectral holography. A broad-spectrum source forms the spectral hologram of light transmitted by a diffuser, and computer processing reconstructs a series of images of the diffuser as it would have appeared with scattered light that traveled different path lengths. One of these reconstructed images is certain to be an image formed with first-arriving light and is therefore an image of the diffuser as seen with the least-scattered light. Experimental results present an image of an absorber hidden by a diffuser in which the gating was done by computer.     

Polarization imaging by use of digital holography

We present what we believe to be a new digital holographic imaging method that is able to determine simultaneously the distributions of intensity, phase, and polarization state at the surface of a specimen on the basis of a single image acquisition. Two reference waves with orthogonal polarization states interfere with the object wave to create a hologram that is recorded on a CCD camera. Two wave fronts, one for each perpendicular polarization state, are numerically reconstructed in intensity and phase. Combining the intensity and the phase distributions of these two wave fronts permits the determination of all the components of the Jones vector of the object-wave front. We show that this method can be used to image and measure the distribution of the polarization state at the surface of a specimen, and the obtained results indicate that precise quantitative measurements of the polarization state can be achieved. An application of the method to image the birefringence of a stressed polymethyl methacrylate sample is presented.     

Digital in-line soft x-ray holography with element contrast

Digital in-line soft x-ray holography (DIXH) was used to image immobilized polystyrene and iron oxide particles and to distinguish them based on their different x-ray absorption cross sections in the vicinity of the carbon K-absorption edge. The element-specific information from the resonant DIXH images was correlated with high-resolution scanning electron microscopy (SEM) pictures. We also present DIXH images of a cell nucleus and compare the contrast obtained for nuclear components with the appearance in optical microscopy.     

Real-time 3-D ultrasound imaging using sparse synthetic aperture beamforming

A method for real-time three-dimensional (3-D) ultrasound imaging using a mechanically scanned linear phased array is proposed. The high frame rate necessary for real-time volumetric imaging is achieved using a sparse synthetic aperture beamforming technique utilizing only a few transmit pulses for each image. Grating lobes in the two-way radiation pattern are avoided by adjusting the transmit element spacing and the receive aperture functions to account for the missing transmit elements. The signal loss associated with fewer transmit pulses is minimized by increasing the power delivered to each transmit element and by using multiple transmit elements for each transmit pulse. By mechanically rocking the array, in a way similar to what is done with an annular array, a 3-D set of images can be collected in the time normally required for a single image.     

Circular-array ultrasound holography imaging using the linear-array approach

A circular-array, pulse-echo, ultrasound holography imaging method is presented. The configuration of the measurement system is much simpler than that of traditional computed-tomography (CT) and compound beta-scan imaging. Wide-beam insonification is used. The geometrical differences of the circular array compared with a linear array system are corrected in the frequency domain of the hologram. The computation time of the reconstruction process for a circular image is practically the same as that of a linear array imaging process using the backward propagation (BP) principle. A fast Fourier transform (FFT) algorithm is directly used in the reconstruction process. Computer simulation shows that the resolution of this imaging method can surpass that of a linear-array system. In the preliminary experiments, 2-mm resolution was achieved in both the lateral and radial directions with an ultrasound frequency of 2 MHz.     

A 256 x 256 2-D array transducer with row-column addressing for 3-D rectilinear imaging

We present simulation and experimental results from a 5-MHz, 256times256 2-D (65536 elements, 38.4times38.4 mm) 2-D array transducer with row-column addressing. The main benefits of this design are a reduced number of interconnects, a modified transmit/receive switching scheme with a simple diode circuit, and an ability to perform volumetric imaging of targets near the transducer with transmit beamforming in azimuth and receive beamforming in elevation. The final dimensions of the transducer were 38.4 mm times 38.4 mm times 300 mum. After a row-column transducer was prototyped, the series resonance impedance was 104 Omega at 5.4 MHz. The measured -6 dB fractional bandwidth was 53% with a center frequency of 5.3 MHz. The SNR at the transmit focus was measured to be 30 dB. At 5 MHz, the average nearest neighbor crosstalk was -25 dB. In this paper, we present 3-D images of both 5 pairs of nylon wires embedded in a clear gelatin phantom and an 8 mm diameter cylindrical anechoic cyst phantom acquired from a 256 times 256 2-D array transducer made from a 1-3 composite. We display the azimuth and elevation B-scans as well as the C-scan for each image. The cross-section of the wires is visible in the azimuth B-scan, and the long axes can be seen in the elevation B-scan and C-scans. The pair of wires with 1-mm axial separation is discernible in the elevational B-scan. When a single wire from the wire target phantom was used, the measured lateral beamwidth was 0.68 mm and 0.70 mm at 30 mm depth in transmit beamforming and receive beamforming, respectively, compared with the simulated beamwidth of 0.55 mm. The cross-section of the cyst is visible in the azimuth B-scan whereas the long axes can be seen as a rectangle in the elevation B-scan and C-scans.     

3-D X-ray diffraction imaging with nanoscale resolution using incoherent radiation

A novel approach to X-ray diffraction data analysis for nondestructive determination of the shape of nanoscale particles and clusters in three-dimensions is illustrated with representative examples of composite nanostructures. The technique is insensitive to the X-ray coherence, which allows 3-D reconstruction of a modal image without tomographic synthesis and in situ analysis of large (over a several cubic millimeters) volume of material with a spatial resolution of few nanometers, rendering the approach suitable for laboratory facilities.     

连续太赫兹波数字全息相衬成像

太赫兹波具有独特的低能性、高穿透性、惧水性等成像特性,将其应用于相衬成像能够反映物体的内部结构和更加丰富全面的生物信息,在生物医学检测等领域具有重要的应用。其中,太赫兹波数字全息成像是一种可以给出定量的振幅和相位信息的非接触、全场相衬成像方法,是太赫兹成像技术领域的重要研究方向之一。本文基于连续太赫兹源,从离轴式和同轴式数字全息成像的相衬成像原理、光路系统和再现算法多个方面,介绍了相关技术的研究现状,分析了太赫兹源、再现算法等因素对成像分辨率的影响,并对太赫兹数字全息的发展趋势进行了展望。     

Multi-plane imaging for arbitrary reconstruction positions in digital holography

A novel method for multi-plane imaging in digital holography is proposed: holograms of objects located at various places are recorded and then reconstructed simultaneously through one-step Fresnel diffraction using the quadratic distorted phase factor (QDPF). The theory of one-step Fresnel diffraction with the QDPF is deduced and experimental results support the theoretical investigation.     

Digital image decoding for in-line X-ray holography using two holograms

Abstract

A novel solution to twin-image disturbance in in-line X-ray holography is presented. By computer simulation, this two-hologram-based digital way is proved to be efficient, while conditions relating to experiments are taken into account.