共查询到20条相似文献,搜索用时 15 毫秒
1.
The successful results of a feasibility experiment for tracking underwater vehicles equipped with laser beacons by aircraft equipped with detectors are presented. The system design focuses on tracking limited payload vehicles such as torpedoes in shallow-water (0-200 m) environments during Navy test and evaluation exercises. A compact, battery operated, Q-switched, frequency-doubled, dual-pulse Nd:YAG laser operating at 532 nm was used. The upward-pointing laser with a diffuse 14° output beam was mounted to a stationary buoy at a depth of five attenuation lengths. Aboard an SH3 helicopter at 5000 ft (1524 m), a 14° field-of-view avalanche photodiode detector system detected the first pulse that triggered an image-intensified CCD camera to image the second pulse at the ocean surface. When the results were scaled, we concluded that a coverage diameter of 14,375 m could be achieved at an aircraft elevation of 1 mile (1.6 km) with a signal-to-noise ratio of 10:1 for depths of ten attenuation lengths. 相似文献
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Using a very short laser pulse and camera gate in a range-gated optical imaging system, we have demonstrated an improvement in imaging in turbid water. A 0.5-ns FWHM laser pulse at 532 nm and a camera gate time ranging down to 120 ps were used to record images of 0.635-cm-bar-resolution targets at 6.5 attenuation lengths through 4.572 m of turbid water. With a four-channel version of this camera, coupled to a CCD camera, we can observe a quasi-three-dimensional image in real time. 相似文献
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Klann M Koch C 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2005,52(9):1546-1554
The measurement of spatial cross sections of ultrasound pressure fields is an essential element of exposimetry of ultrasonic medical equipment. An optical technique is presented that allows the two-dimensional (2-D) determination of ultrasound pressure using an optical multilayer hydrophone in which a laser beam with suitable wavelength is partially reflected from a dielectric optical multilayer system. By detecting the change in reflectivity of the multilayer coating induced by the incident ultrasound, the pressure time waveform can be determined. A 2-D data acquisition covering an area of at least 15 mm x 5 mm was realized by two complementary approaches. A serial detection scheme was set up by scanning the sensing point across the area of interest by a micromechanically engineered scanning mirror and acquiring pressure time waveforms sequentially and pointwise. This allows the measurement of repeating ultrasonic waveforms with a spatial resolution of better than 70 microm and a minimal detectable pressure of 50 kPa (bandwidth: 50 MHz) in a few seconds. In an alternative approach exploiting the parallel processing capabilities of a charge-coupled devices (CCD) camera chip, the probe was strobe-illuminated by a large-diameter collimated beam of a pulsed laser diode. The 2-D pressure distribution at a particular moment was derived from captured reflectivity distributions with a spatial resolution of 75 microm. By successive delaying of the laser pulse with respect to the ultrasound pulse, the complete 2-D pulse waveform was acquired with high spatial resolution. Measurement results on ultrasound fields from plane and focusing transducers are presented and compared to simulation results. Individual advantages and drawbacks of both approaches are discussed. A combined setup merging both detection schemes into a single device was developed and represents a milestone on the way toward constructing an optical ultrasound measuring camera. 相似文献
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A novel measuring system based on a single CCD camera and two laser projectors to record images and perform three-dimensional measurement of a distant object is proposed here. Because of the alignment of the laser beams which form in parallel with the optical axis of the CCD camera, projected spots will appear on the same scan line in a CCD image. As a result processing of a single scan line rather than the whole image is only required to identify the projected spots in the CCD image. Complex computation of video signals of the whole image via either pattern recognition or image analysis methods is therefore circumvented. On the basic of an established relationship between the distance and pixel counts between the projected spots in the CCD image, the proposed system not only measures the distance from a distant object but also the length of two arbitrarily designated points on the object. To provide better accuracy, intrinsic parameters of the CCD camera are taken into consideration in the measurement. Furthermore, the effect of laser diffusion is also proved to be irrelevant to the measuring accuracy here. Experimental results have demonstrated that the proposed measuring method is capable of yielding accurate results of three-dimensional measurement for a distant object in a very responsive way. 相似文献
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K. A. Stetson W. R. Brohinsky Jawed Wahid Thomas Bushman 《Journal of Nondestructive Evaluation》1989,8(2):69-76
This paper reports the use of a real-time arithmetic image processor in an electro-optic holography system. A speckle interferometer is used to combine an image of an object, lit by laser light, with a mutually coherent reference beam. A CCD TV camera detects the interference pattern, and the phase of the reference beam is advanced by 90° between frames. An image is generated from each set of four sequential TV frames by subtracting alternate frames, squaring, and adding the two results. The result is improved picture quality compared with the use of binary pixels and compared with electronic speckle pattern interferometry. Experimental results are shown. 相似文献
7.
Vivi Tornari 《Strain》2019,55(2)
Artworks are delicate objects representative of the most high values of human kind that require constant control over the situation they are in and effective actions to preserve them and deliver them safely to next generations. As such, the non‐destructive or minimally destructive nature of operator–artwork interactions has been considered as essential in this field. The complete diagnosis of the status of the art object signifying a full knowledge of invisible defects and their morphology allows its timely and correct maintenance and ensures its durability. It is herein presented the basic technical information on the development of a portable system termed Digital Holographic Speckle Pattern Interferometry (DHSPI) for the structural diagnosis of works of art. DHSPI has been tested on a variety of conservation problems over the years. It is a completely portable and fully PC driven automated system for the detection and non‐destructive diagnosis of the structural alterations of an artwork, whether they are defects lying on the subsurface or between the layers below it, the fringe number information allows the depth estimation and the complete documentation. The system exploits the benefits of a highly coherent laser beam as essential presupposition for remote on‐field access—that is the main emphasis given here—to immovable/movable art objects. It takes advantage of a CCD camera as photosensitive medium to record the interference of the retro reflected object laser beam from the object under consideration with a twin reference laser beam. The device allows micro projections of the defects on the surface of the object to be detected with a resolution that corresponds to half the wavelength of the laser beam. Local disparities, in relation to the total response of the object, are directly correlated to the detected microdisplacement of object surface as structural defects. Special tailor‐made software allows full control of the system, processing of the data, and extraction of anomalies. Direct visual qualitative observation of the displacement processes is followed as captured in the monitor. A second custom‐made software—not presented in detail here—enables further processing of the results to improve their imaging, quantification, and dimensioning. The final result is a quantitative map of alterations, the coordinates, and the classification of their risks which can be also extracted if further information is necessary. The qualitative or quantitative documentation map can be used as a guide to the conservator for maintenance and restoration work. Further on, the system also allows observation of the object's response to climate changes in order to predict the formation of alterations or the evolution of existing ones providing the only known direct tool for scheduling preservation strategies. 相似文献
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A new parallel photodisplacement technique has been developed that achieves simultaneous real-time imaging of surface and subsurface structures from a single space-frequency multiplexed interferogram, which greatly simplifies the system and the optical alignment. A linear region of photodisplacement is excited on the sample for subsurface imaging by use of a line-focused intensity-modulated laser beam, and the displacement and surface information on reflectivity and topography are detected by a parallel heterodyne interferometer with a charge-coupled device linear image sensor used as a detector. The frequencies of three control signals for excitation and detection, that is, the heterodyne beat signal, modulation signal, and sensor gate pulse, are optimized such that surface and subsurface information components are space-frequency multiplexed into the sensor signal as orthogonal functions, allowing each to be discretely reproduced from Fourier coefficients. Preliminary experiments demonstrate that this technique is capable of simultaneous imaging of reflectivity, topography, and photodisplacement for the detection of subsurface lattice defects at a remarkable speed of only 0.26 s per 256 x 256 pixel area. This new technique is promising for use in nondestructive hybrid surface and subsurface inspection and other applications. 相似文献
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This paper presents a laser speckle method for the measurement of plastic zone ahead of a Y-notch tip on metallic specimens. The method employs an unexpanded laser beam to illuminate the test object. Diffracted images are captured on a ground glass and recorded using a CCD camera. The recorded images were digitised and subsequently analysed on a personal computer. The plastic strain at the notch tip was correlated with its corresponding speckle image using a recently proposed parameter known as the integrated peak spectral intensity coefficient. Specimens containing Y-notches of various angles were tested and the resu Its compared well with that predicted by theory. 相似文献
11.
Confocal Raman spectroscopy was applied to the characterization of various states emerging in the screening of protein crystallization. Four main characterized states, namely single crystals, microcrystals, precipitates, and clear drops without solid materials, appear in a droplet for crystallization; the first three states should be critically distinguished and characterized because of the limitations of visual observation under an optical microscope. Using lysozyme and other proteins, crystallization was performed by the hanging drop vapor diffusion technique and was monitored through an automated confocal Raman system. Prior to the spectroscopic analysis, an optical microscope with a charge-coupled device (CCD) camera and associated image processing software were used to rapidly identify the XY locations to be measured spectroscopically by focusing the laser beam on a test sample. Instead of the current image analysis by optical microscopy, confocal Raman spectroscopy with a high spatial resolution was used to identify the state of protein crystallization. Such real-time Raman monitoring also distinguished real protein crystals from pseudo-protein crystals emerging in a crystallization droplet. 相似文献
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Bajt S Chapman HN Spiller EA Alameda JB Woods BW Frank M Bogan MJ Barty A Boutet S Marchesini S Hau-Riege SP Hajdu J Shapiro D 《Applied optics》2008,47(10):1673-1683
We describe a camera to record coherent scattering patterns with a soft-x-ray free-electron laser (FEL). The camera consists of a laterally graded multilayer mirror, which reflects the diffraction pattern onto a CCD detector. The mirror acts as a bandpass filter for both the wavelength and the angle, which isolates the desired scattering pattern from nonsample scattering or incoherent emission from the sample. The mirror also solves the particular problem of the extreme intensity of the FEL pulses, which are focused to greater than 10(14) W/cm2. The strong undiffracted pulse passes through a hole in the mirror and propagates onto a beam dump at a distance behind the instrument rather than interacting with a beam stop placed near the CCD. The camera concept is extendable for the full range of the fundamental wavelength of the free electron laser in Hamburg (FLASH) FEL (i.e., between 6 and 60 nm) and into the water window. We have fabricated and tested various multilayer mirrors for wavelengths of 32, 16, 13.5, and 4.5 nm. At the shorter wavelengths mirror roughness must be minimized to reduce scattering from the mirror. We have recorded over 30,000 diffraction patterns at the FLASH FEL with no observable mirror damage or degradation of performance. 相似文献
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We demonstrate a compact, automated, long working distance optical tweezer system using a novel mechanism for controlling the position of the optical trap. Our system uses a single focusing lens with a working distance of 4.5?mm and the trapping beam is steered by moving the lens with a miniature coil-magnet assembly. The sample is imaged through a 100×?microscope objective and a CCD camera captures the magnified image. A custom image processing software detects the position of the laser beam and identifies the sample objects. This information is used to generate appropriate electrical signals to drive the coils which move the focusing lens along the desired path. The system is fairly simple and power efficient due to minimal usage of optical elements in the laser path; hence our setup is simple, low-cost and requires low optical power. Computer-generated arbitrary trapping paths and time-shared trapping patterns are successfully demonstrated. Efficient trapping of micron size spheres with laser powers as low as 1.5?mW is observed. 相似文献
14.
J. Upadhyay J. A. Chakera C. P. Navathe P. A. Naik A. S. Joshi P. D. Gupta 《Sadhana》2006,31(5):613-620
A single-frame X-ray framing camera has been set up for fast imaging of X-ray emissions from pulsed plasma sources. It consists
of two parts, viz. an X-ray pin-hole camera using an open-ended microchannel plate (MCP) detector coupled to a CCD camera,
and a high voltage short duration gate pulse for the MCP. The camera uses a 10-Μm pin-hole aperture for imaging on the MCP
detector with a magnification of 6 X. The high voltage pulser circuit generates a pulse of variable duration from 5 to 30
ns (at 70% of peak amplitude) with variable amplitude from 800 V to 1.25 kV, and is triggered through a laser pulse synchronized
with the event to be recorded. The performance of the system has been checked by recording X-ray emission from a laser-produced
copper plasma. A reduction factor of ∼ 6.5 is seen in the dark current contribution as the MCP gate pulse is decreased from
250Μs to 5 ns duration. 相似文献
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We describe an interferometer system that uses two separate wavelengths to measure step height. The overlapping interference images detected by a CCD camera are easily separated by an ordinary integrating-bucket method and time-sharing sinusoidal phase modulation, in which two laser diodes are alternately modulated with a sinusoidal signal. A phase map is obtained only for the laser diode into which the modulation signal is injected. In this instance, a 1-microm step height was accurately detected. 相似文献
17.
Talbot interferometry is used to study the surface profile of a transparent object. Periodic patterns are produced by illuminating a grating with a collimated laser beam. The object is placed on the self-image plane of the grating. The deformed grating image, which interferes with another grating, results in the Talbot interferometric fringes. The fringe pattern is recorded on a CCD camera for subsequent analysis, and the phase variation is achieved by a linear translation stage. In this application two specimens are tested to demonstrate the validity of the method; one is a transparent object with a spherical shape with a height of less than 350 microm, and the other is a transparent object with an uneven surface of 50-microm average height. The experimental results are compared with the test results obtained with the mechanical stylus method. 相似文献
18.
A comparison of several endoscopes as object image carriers in pulsed digital holography is presented. Three multicore flexible fiber endoscopes of different spatial resolution and one rigid endoscope are investigated. The four endoscopes are integrated in a setup for the recording of digital holograms on a CCD camera. A double-pulsed ruby laser is used as the light source. A spatial carrier is introduced by an off-axis reference beam, which permits quantitative evaluation of the phase difference between two holograms recorded with a short time separation (5-600 micros). From reported studies it may be inferred that the quality of the phase maps so derived from digital holographic interferometry has a strong correlation to the spatial resolution of the multicore fiber used in these endoscopes. With the endoscopic technique combined with pulsed digital holography a number of useful applications (in areas such as medical endoscopy, micromechanics, and microelectronics) are envisaged for which access to the objects of interest is otherwise difficult. 相似文献
19.
A fluorescence detection scheme coupled to a highly sensitive nitrogen-cooled CCD camera is used to image the spatial distribution of a low-density falling rubidium atomic cloud released from an optical trap. The falling cloud passes through a thin probe laser beam tuned to resonance. The performance of the scheme is illustrated in the analysis of cold atomic clouds collimated by pinholes during their free fall under the influence of gravity. Clouds of approximately 10(4) atoms and with typically 10(6) at./cm(3) density are analyzed spatially with 24-mum resolution. This method is compared with different atomic cloud imaging techniques. 相似文献