Accurate deflection measurement is vital in evaluating the structural integrity of transportation infrastructures, with bridges being fascinating. In this study, we propose a novel image stabilization technique integrated into the sampling moiré method, which leads to a dependable approach for measuring bridge deflection through drone aerial photography. Our experimental verification entailed conducting drone tests on an actual bridge, utilizing a passing test vehicle, and the results showcased deflection measurements comparable to those obtained through conventional methods. This newly developed technology eliminates the need for ground-fixed cameras mounted on tripods, thus enabling precise deflection measurement at the millimeter level for bridges in challenging environments, including marine and mountainous areas.
KEYWORDS: Microscopes, Digital holography, Phase shifts, 3D metrology, 3D image reconstruction, Holograms, Image processing, Cameras, 3D acquisition, Optical components
Significance: Parallel phase-shifting digital holographic microscope (PPSDHM) is powerful for three-dimensional (3D) measurements of dynamic specimens. However, the PPSDHM reported previously was directly fixed on the optical bench and imposed difficulties case, thus it is required to modify the specification of the microscope or transport the microscope to another location.
Aim: We present a modularized PPSDHM. We construct the proposed PPSDHM and demonstrate the 3D measurement capability of the PPSDHM.
Approach: The PPSDHM was designed as an inverted microscope to record transparent objects and modularized by integrating the optical elements of the PPSDHM on an optical breadboard. To demonstrate the effectiveness of the PPSDHM, we recorded a 3D motion-picture of moving Volvoxes at 1000 frames / s and carried out 3D tracking of the Volvoxes.
Results: The PPSDHM was practically realized and 3D images of objects were successfully reconstructed from holograms recorded with a single-shot exposure. The 3D trajectories of Volvoxes were obtained from the reconstructed images.
Conclusions: We established a modularized PPSDHM that is capable of 3D image acquisition by integrating the optical elements of the PPSDHM on an optical breadboard. The recording capability of 3D motion-pictures of dynamic specimens was experimentally demonstrated by the PPSDHM.
A parallel phase-shifting digital holographic microscope achieves motion-picture phase imaging of a dynamic minute specimen. However, much time and skill are required to construct the optical system of the microscope. The authors designed and constructed an optical system of a parallel phase-shifting digital holographic microscope in which the optical components of the microscope were integrated on a breadboard standing perpendicular to an optical table. The lateral and longitudinal magnifications of the microscope are 10 and 100, respectively. The authors experimentally demonstrated the motion-picture phase imaging of a dynamic minute specimen by the microscope. The holograms were recorded at 1,000 fps and the shutter speed was 0.5 ms.
KEYWORDS: Digital holography, Phase shifts, 3D image reconstruction, Crystals, Stereoscopy, 3D image processing, Holograms, Digital imaging, Refractive index, Image sensors
Parallel phase-shifting digital holography is a powerful technique for recording motion picture of holograms with an image sensor and numerically reconstructing the motion picture of the high-quality three-dimensional (3-D) images of the object in a computer. This technique provides high-quality images of light intensity and phase of the object at a time instant at arbitrary depth position. Therefore, the technique achieves 3-D motion-picture imaging of a dynamic object. The technique provides not only large depth of field and high temporal resolution at the same time but also a motion picture of an invisible object. It is difficult for other 3-D imaging techniques to achieve these features of parallel phase-shifting digital holography. The authors review two experiments demonstrating the 3-D imaging by the technique and the features of the technique. One experiment demonstrated the motion-picture 3-D imaging of a minute crystal, sinking down in solution, by refocusing the amplitude images of the crystal. The result was obtained for the first time, to the best of our knowledge. The other demonstrated the motion-picture 3-D imaging of refractive indices of dynamic invisible gas flow by applying the Abel inversion to the phase images of the flow obtained by the technique.
Parallel phase-shifting digital holography is a technique capable of recording three-dimensional (3D) motion picture of dynamic object, quantitatively. This technique can record single hologram of an object with an image sensor having a phase-shift array device and reconstructs the instantaneous 3D image of the object with a computer. In this technique, a single hologram in which the multiple holograms required for phase-shifting digital holography are multiplexed by using space-division multiplexing technique pixel by pixel. We demonstrate 3D motion picture of dynamic and transparent gas flow recorded and reconstructed by the technique. A compressed air duster was used to generate the gas flow. A motion picture of the hologram of the gas flow was recorded at 180,000 frames/s by parallel phase-shifting digital holography. The phase motion picture of the gas flow was reconstructed from the motion picture of the hologram. The Abel inversion was applied to the phase motion picture and then the 3D motion picture of the gas flow was obtained.
KEYWORDS: Digital holography, High speed cameras, Phase shifts, 3D image reconstruction, Holograms, Digital imaging, Cameras, Image sensors, Polarization, Image quality
Parallel phase-shifting digital holography is one of digital holographic techniques and good at high-speed recording of moving object. The phase distribution of the object can be calculated from recorded hologram so that the technique has been actively applied in high-speed three-dimensional measurement. In this paper, we review a high-speed parallel phase-shifting digital holography system consists of a high-speed polarization-imaging camera (FASTCAM-SA5-P, Photoron, Inc.) and a Nd:YVO4 laser with 532 nm wavelength, 150 mW output power. In the experiment, a simple electrical discharging equipment was set for the fast object, and the electrical discharging phenomenon was successfully recorded at the rate of 25,000 fps, and 1,000,000 fps respectively.
KEYWORDS: Digital holography, Phase shifts, 3D image reconstruction, Holograms, Cameras, Image sensors, Imaging systems, Digital imaging, 3D metrology, 3D image processing
As a high-speed three-dimensional (3D) imaging technique, parallel phase-shifting digital holography is presented. This technique records a single hologram of an object with an image sensor having a phase-shift array device and reconstructs the instantaneous 3D image of the object with a computer. In this technique, a single hologram in which the multiple holograms required for phase-shifting digital holography are multiplexed by using space-division multiplexing technique pixel by pixel. Also, we present a high-speed parallel phase-shifting digital holography system. The system consists of an interferometer, a continuous-wave laser, and a high-speed polarization imaging camera. Motion pictures of dynamic phenomena at the rate of up to 1,000,000 frames per second have been achieved by the high-speed system.
High-speed multicolor 3D motion-picture recording of a 3D object was experimentally demonstrated by using multiwavelength parallel phase-shifting digital holography. Parallel phase-shifting digital holography is a technique for obtaining the complex amplitude distribution of an object wave from a single hologram, based on space-division multiplexing of multiple phase-shifted holograms. The combination of parallel phase-shifting with angular multiplexing is proposed to capture multicolor information simultaneously using a monochromatic image sensor. 3D space, phase, and wavelength information is simultaneously reconstructed by recording a monochromatic hologram using an image sensor with polarization-detection function. Color 3D motion-picture recording of objects that move at the speed of more than 20 km/h was achieved at 20,000 frames per second. This result is the first experimental demonstration of multiwavelength parallel phase-shifting digital holography.
One of advantages of parallel phase-shifting digital holography (PPSDH) compared with other digital holography
techniques is the fast recording of three-dimensional (3D) objects. During the fast recording of a multiplexed hologram
that contains at least three amounts of phase retardation, the optical energy of the hologram becomes smaller. Therefore,
it is important to assess the minimum optical energy that can reconstruct the object with moderate reconstruction error.
In this paper, we investigate experimentally the optical energy to reconstruct the object under weak light condition in
PPSDH. We compare the numerical and experimental results. The experiment is in good agreement with numerical
results when the sensitivity of the image sensor is taken into account.
KEYWORDS: Digital holography, Phase shifts, Holography, Microscopy, Holograms, Image sensors, Digital recording, 3D image reconstruction, Digital imaging, Wave plates
Three-dimensional (3-D) motion-picture recording by parallel phase-shifting digital holographic microscopy that has the
ability of instantaneous 3-D recording of dynamic phenomena in the microscopic field of view is presented. Parallel
phase-shifting digital holography is a scheme to record multiple phase-shifted holograms with a single-shot exposure,
and to achieve 3-D motion-picture recording of objects with high accuracy and wide 3-D area, based on space-division
multiplexing of phase-shifted holograms. Parallel phase-shifting digital holographic microscopy is implemented by an
optical interferometer and an image sensor on which polarization-detection function is introduced pixel by pixel. This
time, we constructed a parallel phase-shifting digital holographic microscope for recording high-speed dynamic
phenomena, and then motions of biological objects in water were recorded at more than 10,000 frames per second, which
is the fastest among the previous reports on 3-D imaging of biological objects.
We demonstrate motion pictures of femtosecond light pulse propagation. We adopted digital light-in-flight recording by
holography as a technique for observation of femtosecond light pulse propagation. We recorded and reconstructed a
moving picture of femtosecond light pulse propagating on a diffuser plate on which a test chart pattern was printed. The
center wavelength and the duration of the light pulse were 800 nm and 96 fs, respectively. We successfully observed
femtosecond light pulse propagation for 530 fs by the technique.
KEYWORDS: Digital holography, Phase shifts, 3D image reconstruction, Holograms, Imaging systems, High speed cameras, Image sensors, Cameras, 3D metrology, Polarization
A technique of single-shot phase-shifting interferometry called as parallel phase-shifting digital holography is described. This technique records multiple holograms required for phase-shifting digital holography using space-division multiplexing technique. The authors constructed a system based on the parallel phase-shifting digital holography consisting of a Mach–Zehnder interferometer and a high-speed polarization imaging camera. High-speed motion pictures of three-dimensional image and phase image of dynamically moving objects at the rate up to180,000 and 262,500 frames per second were achieved, respectively, for the 128 × 128-pixel images.
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