Spectral LADAR: active range-resolved three-dimensional imaging spectroscopy

We present the concept and experimental results for Spectral LADAR, an augmented LADAR imager combining three-dimensional (3D) time-of-flight ranging with active multispectral sensing in the shortwave infrared (1080-1620 nm). The demonstrated technique is based on a nanosecond regime pulsed supercontinuum transmitter and spectrally multiplexed receiver that computes a high-resolution range value for each of 25 spectral bands. A low frame-rate prototype unit is described. Results demonstrating 3D imaging and material type classification of objects, especially those obscured by camouflage, are shown at effective stand-off ranges exceeding 40 m. These capabilities and the highly eye safe wavelengths at which the system operates make it suitable for applications in military imaging and robotic perception.     

Capacitive system for three-dimensional imaging of fluidized-beddensity

The U.S. Department of Energy's Morgantown Energy Technology Center has been developing a capacitance imaging system (CIS) to support its fluidized-bed research programs. A second-generation system for capacitively imaging a cold, laboratory-scale, 15.24-cm diameter fluidized bed is described. The CIS acquires interelectrode, bed-crossing displacement current data to provide 193-pixel density values at four 2.54-cm vertically spaced levels and presents a three-dimensional density display at a rate of 30 maps per second in real time. The CIS also stores displacement current data at a rate of 60 density maps per level per second for post-run analysis. Different means of data processing are described that produce one method for real-time display and two methods for post-run analysis of data. The results of calibration and fluidization tests are presented, together with the errors associated with each of the methods for the known pixel densities in the calibration tests. Improvement in the calibration procedure to reduce these errors is proposed. Test results indicate the CIS would be a useful tool for research and monitoring operations in two-phase systems     

Miniaturized digital holography sensor for distal three-dimensional endoscopy

A miniaturized sensor head for endoscopic measurements based on digital holography is described. The system was developed to measure the shape and the three-dimensional deformation of objects located at places to which there is no access by common measurement systems. A miniaturized optical sensor, including a complete digital holographic interferometer with a CCD camera, is placed at the end of a flexible endoscope. The diameter of the head is smaller than 10 mm. The system enables interferometric measurements to be made at speeds of as many as five reconstructions per second, and it can be used outside the laboratory under normal environmental conditions. Shape measurements are performed with two wavelengths for contouring, and the deformation is measured by digital holographic interferometry. To obtain full three-dimensional data in displacement measurements we illuminate the object sequentially from three different illumination directions. To increase the lateral resolution we use temporal phase shifting.     

Optical design and evaluation of a three-dimensional imaging and ranging system based on time-correlated single-photon counting

The design and operation of a noncontact surface profilometry system based on the time-correlated single-photon-counting technique are described. This system has a robust optomechanical design and uses an eye-safe laser that makes it particularly suitable for operation in an uncontrolled industrial environment. The sensitivity of the photon-counting technique permits its use on a variety of target materials, and its mode of operation does not require the continual presence of an operator. The system described has been optimized for a 1-25-m standoff, has a distance repeatability of <30 microm, and has a transverse spatial resolution of approximately 60 microm at a 2-m standoff and approximately 400 microm at a 13-m standoff.     

Research and realization of an auto-calibration technique based on stereovision

The purpose of this research is to analyse the present-day state of calibration techniques and to realize an auto-calibration technique based on a projected grating 3D measuring system. An auto-calibration technique, called multiple target tracking for detecting outlines based on random placing and regular numbers, was proposed. The practical algorithm was also presented at the same time. According to this arithmetic, the relevant experimental result was gained. Furthermore, the precision of the calculation result was analyzed. The results showed that the operation was simplified, the orientation precision of image outline edges was ensured and calibration precision was kept within 0.02–0.05 mm by using the arithmetic in this work. The research verified the feasibility of auto-calibration, providing arithmetic that is extremely useful for the industrial application of computer vision technologies. The paper deals with experimental work on innovative techniques for which the data have not been seen in the literature. In particular, an original auto-calibration technique, which is named as multiple target tracking for detecting outlines based on random placing and regular numbers, was provided.     

Comparison of passive ranging integral imaging and active imaging digital holography for three-dimensional object recognition

We present an overview of three-dimensional (3D) object recognition techniques that use active sensing by interferometric imaging (digital holography) and passive sensing by integral imaging. We describe how each technique can be used to retrieve the depth information of a 3D scene and how this information can then be used for 3D object recognition. We explore various algorithms for 3D recognition such as nonlinear correlation and target distortion tolerance. We also provide a comparison of the advantages and disadvantages of the two techniques.     

Terahertz imaging system based on a backward-wave oscillator

We present an imaging system designed for use in the terahertz range. As the radiation source a backward-wave oscillator was chosen for its special features such as high output power, good wave-front quality, good stability, and wavelength tunability from 520 to 710 GHz. Detection is achieved with a pyroelectric sensor operated at room temperature. The alignment procedure for the optical elements is described, and several methods to reduce the etalon effect that are inherent in monochromatic sources are discussed. The terahertz spot size in the sample plane is 550 microm (nearly the diffraction limit), and the signal-to-noise ratio is 10,000:1; other characteristics were also measured and are presented in detail. A number of preliminary applications are also shown that cover various areas: nondestructive real-time testing for plastic tubes and packaging seals; biological terahertz imaging of fresh, frozen, or freeze-dried samples; paraffin-embedded specimens of cancer tissue; and measurement of the absorption coefficient of water by use of a wedge-shaped cell.     

Depth fingerprint map of active range-gated imaging for real-time three-dimensional measurement of foreground objects

We present a depth fingerprint map to obtain three-dimensional (3D) spatial information from objects in a large deterministic background by active range-gated imaging, for night remote surveillance. This method first gives the depth fingerprint map of the region of interest in the background by gate viewing in the form of contour bands in range. The map is then embedded in the range-gated laser surveillance system. Finally, 3D spatial information such as target scale and location can be estimated by segmenting the target from the background and matching them with the depth fingerprint map. The measurement is performed by computer background processing. Therefore, the method has no influence on the frame rate of surveillance systems and can realize real-time surveillance. In this paper, the approach to acquisition of the depth fingerprint map is also demonstrated without an echo-broadening effect.     

基于Vega Prime的多通道三维仿真系统的实现

论文以2010年上海世博会广州案例馆360度内环幕虚拟体验区的软件系统为原型,叙述了基于Vega Prime的多通道三维仿真系统的实现。首先对系统进行概述,描述了实现原理及开发流程,然后对系统实现展开讨论,重点叙述了三维建模、构建仿真系统、场景编辑3个主要的步骤,给出单机演示的技术要点及演示效果,并把新旧系统做了对比。     

Hybrid digital holographic imaging system for three-dimensional dense particle field measurement

To apply digital holography to the measurement of three-dimensional dense particle fields in large facilities, we have developed a hybrid digital holographic particle-imaging system. The technique combines the advantages of off-axis (side) scattering in suppressing speckle noise and on-axis (in-line) recording in lowering the digital sensor resolution requirement. A camera lens is attached to the digital sensor to compensate for the weak object wave from side scattering over a large recording distance. A simple numerical reconstruction algorithm is developed for holograms recorded with a lens without requiring complex and impractical mathematical corrections. We analyze the effect of image sensor resolution and off-axis angle on system performance and quantify the particle positioning accuracy of the system. The holographic system is successfully applied to the study of inertial particle clustering in isotropic turbulence.     

Enhanced three-dimensional integral imaging system by use of double display devices

We propose an enhanced three-dimensional (3D) integral imaging system using multiple display devices. Experimental results with double devices prove the improvement in the image depth for a given image quality. We present experiments on an enhanced 3D integral imaging system using double display devices, in which two 3D subimages that cover different depth ranges are separately generated in each device, and then they are combined with a beam splitter to reconstruct the whole 3D image with an enhanced depth of view. In a similar manner, the double-device system can also be used to obtain a wider viewing angle by combining two images with different viewing angle ranges. We discuss the possibility of 3D integral imaging systems using multiple display devices as extensions of the system with double display devices.     

Medical diagnostic system based on simultaneous multispectral fluorescence imaging

A multicolor fluorescence imaging system applied to medical diagnostics is described. The system presented simultaneously records four fluorescence images in different wavelength bands, permitting low-resolution spectroscopy imaging. An arithmetic function image of the four spectral images is constructed by a pixel-to-pixel calculation and is presented on a monitor in false-color coding. A sensitive detector is required for minimizing the excitation energy necessary to obtain an image and thus avoid side effects on the investigated tissue. Characteristics of the system of importance for the detector sensitivity as well as image quality are discussed. A high degree of suppression of ambient background light is reached with this system by the use of a pulsed laser as an excitation source together with gated detection. Examples of fluorescence images from tumors on the hind legs and in the brain of rats injected with Photofrin are given.     

Bimodal fingerprint capturing system based on compound-eye imaging module

A compact imaging system called TOMBO (Thin Observation Module by Bound Optics) is proposed in which a microlens array is used for thin hardware configuration. This paper describes a fingerprint-capturing module as an application of the TOMBO. Experimental results by the TOMBO prototype system are shown to clarify the applicability of the TOMBO to the fingerprint capturing. Different types of biometrics, i.e., fingerprint and face images, are captured by the same hardware, which shows the extendability of the system for multimodal identification.     

Viewing zones in three-dimensional imaging systems based on lenticular, parallax-barrier, and microlens-array plates

The viewing zone of autostereoscopic imaging systems that use lenticular, parallax-barrier, and microlens-array plates as the viewing-zone-forming optics is analyzed in order to verify the image-quality differences between different locations of the zone. The viewing zone consists of many subzones. The images seen at most of these subzones are composed of at least one image strip selected from the total number of different view images displayed. These different view images are not mixed but patched to form a complete image. This image patching deteriorates the quality of the image seen at different subzones. We attempt to quantify the quality of the image seen at these viewing subzones by taking the inverse of the number of different view images patched together at different subzones. Although the combined viewing zone can be extended to almost all of the front space of the imaging system, in reality it is limited mainly by the image quality.     

High-resolution monochromatic x-ray imaging system based on spherically bent crystals

We have developed an improved x-ray imaging system based on spherically curved crystals. It is designed and used for diagnostics of targets ablatively accelerated by the Nike KrF laser. A spherically curved quartz crystal (d = .?, R = mm) has been used to produce monochromatic backlit images with the He-like Si resonance line (1865 eV) as the source of radiation. The spatial resolution of the x-ray optical system is 1.7 mum in selected places and 2-3 mum over a larger area. Time-resolved backlit monochromatic images of polystyrene planar targets driven by the Nike facility have been obtained with a spatial resolution of 2.5 mum in selected places and 5 mum over the focal spot of the Nike laser.     

基于水下光电成像系统研究计算机仿真技术

在引入小角度近似原理的基础上构建相关的理论模型,对水下光电成像探测系统计算机仿真技术进行一定程度的研究。从接收信号分类、系统结构模型、信号以及前向散射辐射量等方面入手,构建信号辐射演算模型。由于散射光的客观存在,在距离相对恒定的情况下,对水下成像面各要素的信号辐射量的量化、后向散射辐射量等方面展开了讨论,并进行计算机的相关仿真技术研究。     

Demonstration of literal three-dimensional imaging

In a recent paper a new technique was proposed for remote ranging and topographical mapping by using a system with a single-photon-counting detector and a low-power pulsed laser [Appl. Opt. 35, 441 (1996)]. We report on the results from the laboratory and the field demonstration of this literal three-dimensional imaging technique. Using a detector system developed at Los Alamos with a commercial pulsed laser and observing from a single remote vantage point, we demonstrate use of this technique in the literal mapping of three-dimensional topography and the probing of a complex scene. With a reasonably short exposure this system can resolve features with height variations as small as 5 cm.     

Miniaturized implantable pressure and oxygen sensors based on polydimethylsiloxane thin films

We demonstrate the application of polydimethylsiloxane (PDMS) thin films in highly sensitive pressure and oxygen sensors, designed for pressure and oxygen content measurements within the heart and blood vessels. PDMS thin film displacement as a result of pressure changes was transduced by a capacitive detection technique to produce quantitative measurement of absolute pressures. Oxygen measurements were obtained by transducing the current change between a Pt and an Ag/AgCl electrode on a glass substrate, with KCl soaked filter paper as the electrolytic media that is separated from the oxygen carrying fluid by a thin PDMS membrane. The best sensitivity for the pressure sensor was ~ 0.1 nA/KPa, with a noise limited resolution of ~ 0.09 KPa. For the oxygen sensor, the best sensitivity was ~ 2.75 µA for 1% change in oxygen content of the surrounding media, with a noise limited resolution of ~ 6.18 ppm oxygen. These experimental results agree with theoretical modeling predictions, and suggest that the semi-permeable and biocompatible PDMS can be successfully adopted as the contacting membrane in an integrated sensor design to quantify pressure and oxygen content in blood.