角江 崇

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 present a fast computational system for highspeed parallel phase-shifting digital holography. The image reconstruction process of parallel phase-shifting digital holography consists of the following processes: decomposition of recorded phase-shifted hologram, interpolation of vacant pixels in decomposed holograms, phase-shifting interferometry, and light propagation. We accelerated phase-shifting interferometry and light propagation processes, whose computational load was much heavier than that of the others, by a graphics processing unit (GPU). We adopted Compute Unified Device Architecture (CUDA) as a software development environment. A GPU with CUDA can achieve 6.3x and 9.0x faster computational times in phase-shifting interferometry and light propagation processes than a CPU, respectively.

We applied the spectral estimation technique to digital holography to demonstrate spectral estimation of object, whose spectral reflectance has been unknown. In this technique, we use three lasers operating at different wavelengths (red, green, and blue) to record the complex amplitude of the object, and three different reconstructed images are obtained by each wavelength. These three monochrome images are used to estimate the continuous spectrum reflectance information of the object by spectral estimation technique. The effectiveness of the digital holographic spectroscopy was confirmed by an experiment. © 2013 IEEE.

We found out a problem that the non-diffraction wave was not completely removed in parallel phase-shifting digital holography (PPSDH) system using a polarization imaging camera. To solve this problem, we introduce an algorithm for compensating the reconstructed image, which can remove the residual non-diffraction wave. In the algorithm, the phase-shifted holograms generated by image reconstruction algorithm of PPSDH and the intensity distribution of the reference wave are divided into multiple segments. Then, each segment is multiplied by each proper correction constant to make the intensity of the non-diffraction wave equal. After employing the algorithm, the non-diffraction wave can be removed by applying the calculation of phase-shifting interferometry. To confirm the effectiveness of the compensation method, we conducted an experiment. The residual non-diffraction wave of the reconstructed image was successfully removed by the algorithm in the experiment. © 2013 IEEE.

Thanks to parallel phase-shifting digital holography using a high-speed camera, we succeeded in phase-shifting interferometry at the rate of up to 262,500 frames/s. Motion pictures of three-dimensional images of fast phenomena are demonstrated. © 2013 IEEE.

Computer-Generated Holograms (CGHs) can be generated from three-dimensional objects composed of point light sources by overlapping zone plates. A zone plate is a grating that can focus an incident wave and it has circular symmetry shape. In this study, we propose a fast CGH generating algorithm using the circular symmetry of zone plates and computer graphics techniques. We evaluated the proposed method by numerical simulation. (C) 2012 Optical Society of America

We propose a color digital holography using four recording wavelengths to improve the color reproduction of three-dimensional imaging of objects. In conventional color digital holography, three-wavelength light beams corresponding to red, green, and blue are used for recording holograms. In this paper, a laser-emitting yellow light is added to the conventional color digital holography. Also spectral estimation technique is introduced to the four-wavelength recording technique to improve the color reproduction of color digital holography. The effectiveness of the proposed method was numerically confirmed. Also the proposed technique was experimentally demonstrated using four lasers operated at 473, 532, 561, and 633 nm, respectively. When Macbeth color chart consisting of 24 color patches was used as objects, in comparison to conventional technique, the average color differences between the objects and the reconstructed images by the proposed technique for the 24 colors are decreased from 7.88 to 6.24 in numerical simulation and from 10.02 to 8.63 in experiment, respectively.

We propose a single-shot phase unwrapping technique using a single wavelength. In the proposed technique, an object is illuminated by two laser beams, which are emitted from the same laser, whose illumination angles and polarizations are different. Then two types of the object waves generated by the two beams are separately and simultaneously recorded by a polarization imaging camera. We conducted an experiment and a 2.5mm height object, which was 9400 times height of the wavelength of the laser, was reconstructed without wrapping. (C) 2012 Optical Society of America

The angular spectrum method (ASM) calculates diffraction calculation in a high numerical aperture, unlike Fresnel diffraction. However, this method does not allow us to calculate at different sampling rates on source and destination planes. In this Letter, we propose a scaled ASM that calculates diffraction at different sampling rates on source and destination planes using the nonuniform fast Fourier transform. (C) 2012 Optical Society of America

Holographic projection is for laser displays and has the merits of being aberration free, producing high-contrast images, having the ability of color reconstruction with one spatial light modulator, and so on. In this paper, we propose a zoomable holographic projection without using a zoom lens and verify the proposed method by using numerical simulation. Although such a system can be readily realized to use the features of holography, which is capable of recording a large image exceeding the hologram size, the required calculation is very time consuming. For acceleration, we used shifted Fresnel diffraction for setting different sampling rates on a hologram and projected image. The proposed method can project any zoom-in and zoom-out image between zeroth-order and first-order lights, and the processing time and required memory for the zoom are constant.

Parallel phase-shifting digital holography is capable of three-dimensional measurement of a dynamically moving object with a single-shot recording. In this letter, we demonstrated a parallel phase-shifting digital holography using a single femtosecond light pulse whose central wavelength and temporal duration were 800 nm and 96 fs, respectively. As an object, we set spark discharge in atmospheric pressure air induced by applying a high voltage to between two electrodes. The instantaneous change in phase caused by the spark discharge was clearly reconstructed. The reconstructed phase image shows the change of refractive index of air was -3.7 x 10(-4). (C) 2012 Optical Society of America

We succeeded in 3-D motion-picture imaging for dynamic motion of biological objects swimming at different depths by parallel phase-shifting digital holographic microscopy (PPSDHM). PPSDHM is a technique for high-quality instantaneous 3-D imaging of specimens in the microscopic field of view by single-shot recording of multiple phase-shifted holograms. We constructed a PPSDHM for recording high-speed dynamic phenomena and then motions of biological objects in water were recorded at 20 000 and 150 000 frames/s, respectively, which is the fastest among the previous reports on 3-D imaging of biological objects.

An electro holography is one of the techniques for achieving three-dimensional television. We developed special-purpose computer HORN-7 for kinoform, which records the phase information of an object light. The HORN-7 can create a 2M pixels hologram of 16, 000 object points in 0.4 sec.

Holographic projection is of laser display. The holographic projection has the merits of being aberration-free, producing high contrast images. We have already proposed a zoomable monochrome holographic projection without using a zoom lens. The method can reconstruct a magnified image between the Oth and ±lst order diffraction lights. In this paper, we advance the zoomable monochrome holographic projection to color one.

We succeeded in accelerating computational time of image reconstruction process of parallel phase-shifting digital holography. A GPU with CUDA can achieve 12× and 14× faster computational times of phase-shifting interferometry and angular spectrum method in the process than a CPU, respectively.

We succeeded in digital light-in-flight recording by holography by use of a femtosecond pulsed laser. We recorded and reconstructed a moving picture of femtosecond light pulse propagation on a diffuser plate on which a test chart pattern was printed. A mode-locked Ti:sapphire laser was used as a femtosecond pulsed laser. The center wavelength and the duration of the light pulse were 800 nm and 96 fs, respectively. We conducted a numerical simulation in order to validate the proposed technique. We confirmed that the technique was capable of recording the moving picture of femtosecond light pulse propagation. In addition, we experimentally demonstrated the technique and successfully observed femtosecond light pulse propagation for 576 fs. The experimental results agreed well with the simulation results.

We comparatively evaluated two types of image-reconstruction algorithms in two types of single-shot phase-shifting digital holography techniques to investigate which algorithm is more suitable for high-quality and instantaneous three-dimensional imaging. Two types of image-reconstruction algorithms were proposed for each single-shot phase-shifting interferometry so far. One generates multiple phase-shifted holograms from the recorded single hologram by utilizing interpolation and derives the complex amplitude of the object wave by applying the calculation of phase-shifting interferometry to the multiple phase-shifted holograms. The other does not use interpolation but applies the calculation of phase-shifting interferometry to the neighboring pixels in the recorded hologram to derive the complex amplitude. We experimentally evaluated the qualities of the image reconstructed by the algorithms in each single-shot phase-shifting technique. It was clarified that the former algorithm is more effective for high-quality imaging free from the unwanted images in single-shot technique using an array of optical elements. In single-shot technique using spatial carrier, although the latter algorithm is able to reconstruct a brighter image for wide area than the former, spatial-filtering technique is needed for removing the conjugate image. (c) 2012 SPIE and IS&T. [DOI: 10.1117/1.JEI.21.1.013021]

We succeeded in high-speed imaging of gas flow by means of parallel phase-shifting digital holography. This technique is capable of capturing three-dimensional (3-D) information of object and carrying out phase-shifting interferometry with a single-shot exposure because the interference fringe images in which the information of multiple phase-shifted holograms is spatially multiplexed are simultaneously recorded. We constructed a high-speed phase-shifting digital holography system by employing a quarter-wave plate and a high-speed camera. The image sensor of the camera has an anisotropic polarization-detecting function pixel by pixel. Each pixel of the polarization-detecting function corresponds to each pixel of the image sensor. The phase retardation of the reference wave is determined by the direction of the polarization axis of the each pixel. A compressed gas flow sprayed from a nozzle was set as an object. We attained the reconstructed images of phase variation caused by the gas flow. We also succeeded in phase imaging at the rate of 180,000 frames per second when the number of pixels of the captured image was 128 x 128. Additionally, we also obtained temporal subtraction images of the reconstructed images. The achieved frame rate was the fastest among not only phase-shifting digital holography but also digital holography and phase-shifting interferometry which have been ever reported, for our knowledge. It is expected that parallel phase-shifting digital holography and the constructed system can contribute to 3-D moving picture measurement of dynamically moving objects such as particle flows, shock waves, mechanical vibration, and so on.

We demonstrate motion pictures of femtosecond light pulse propagation by use of digital holography. We adopted light-in-flight recording by holography as a technique for observation of femtosecond light pulse propagation. We successfully observed femtosecond light pulse propagation for 530 fs by using a femtosecond light pulse whose center wavelength and temporal duration were 800 nm and 96 fs, respectively.

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 x 128-pixel images.

We succeeded in accelerating computational time of image reconstruction process of parallel phase-shifting digital holography. A GPU with CUDA can achieve 12x and 14x faster computational times of phase-shifting interferometry and angular spectrum method in the process than a CPU, respectively.

An electro holography is one of the techniques for achieving three-dimensional television. We developed special-purpose computer HORN-7 for kinoform, which records the phase information of an object light. The HORN-7 can create a 2M pixels hologram of 16,000 object points in 0.4 sec.

Holographic projection is of laser display. The holographic projection has the merits of being aberration-free, producing high contrast images. We have already proposed a zoomable monochrome holographic projection without using a zoom lens. The method can reconstruct a magnified image between the 0th and +/- 1st order diffraction lights. In this paper, we advance the zoomable monochrome holographic projection to color one.

We propose a color digital holography by using spectral estimation technique to improve the color reproduction of objects. In conventional color digital holography, there is insufficient spectral information in holograms, and the color of the reconstructed images depend on only reflectances at three discrete wavelengths used in the recording of holograms. Therefore the color-composite image of the three reconstructed images is not accurate in color reproduction. However, in our proposed method, the spectral estimation technique was applied, which has been reported in multispectral imaging. According to the spectral estimation technique, the continuous spectrum of object can be estimated and the color reproduction is improved. The effectiveness of the proposed method was confirmed by a numerical simulation and an experiment, and, in the results, the average color differences are decreased from 35.81 to 7.88 and from 43.60 to 25.28, respectively. (C) 2011 Optical Society of America

Parallel phase-shifting digital holography can obtain three-dimensional information of a dynamically moving object with high accuracy by using space-division multiplexing of multiple holograms required for phase-shifting interferometry. We demonstrated high-speed parallel phase-shifting digital holography and obtained images of the phase variation of air caused by a compressed gas flow sprayed from a nozzle. In particular, we found the interesting phenomenon of periodic phase distributions. Reconstructed images were obtained at frame rates of 20,000 and 180,000 frames per second. (C) 2011 Optical Society of America

We propose a portable parallel phase-shifting digital holography system. Parallel phase-shifting digital holography is a technique capable of instantaneous and three-dimensional measurement of objects. This technique has been verified by an experiment on anti-vibration optical tables, but had not been realized as a system for practical use yet. Then, we designed a portable system of parallel phase-shifting digital holography for the purpose of practical use. The size and weight of the system are 450 mm (L) x 250 mm (W) x 200 mm (H) and less than 7 kg, respectively. We designed the configuration of the system in a way which can be easily changed to implement two types of parallel phase-shifting digital holographies. The system was constructed by the use of ready-made optical components. To confirm the validity of the system, the capability of the three-dimensional imaging free from the superimposition of the unwanted images, which was the problem accompanied with conventional in-line digital holography, with a single-shot exposure was successfully demonstrated. (C) 2011 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.3596177]

We succeeded in recording and observing femtosecond light pulse propagation as a form of moving picture by means of light-in-flight recording by holography using a rewritable holographic material, for the first time. We used a femtosecond pulsed laser whose center wavelength and duration were 800 nm and similar to 120 fs, respectively. A photo-conductor plastic hologram was used as a rewritable holographic material. The femtosecond light pulse was collimated and obliquely incident to the diffuser plate. The behavior of the cross-section between the collimated femtosecond light pulse and the diffuser plate was recorded on the photo-conductor plastic hologram. We experimentally obtained a spatially and temporally continuous moving picture of the femtosecond light pulse propagation for 58.3 ps. Meanwhile, we also investigated the rewritable performance of the photo-conductor plastic hologram. As a result, we confirmed that ten-time rewriting was possible for a photo-conductor plastic hologram. (C) 2011 Elsevier B.V. All rights reserved.

We propose single-shot digital holography which is capable of simultaneously capturing both the information of multiple phase-shifted holograms and the distribution of the polarization. In this technique, a single image sensor records both the information required for phase-shifting interferometry and that of the polarization states of objects using an array of polarizers. The essence of the technique is the capability of imaging the distribution of the polarization of three-dimensional objects with a single-shot exposure by using the space-division multiplexing of holograms. The validity of the proposed technique was confirmed by the preliminary experiments. (C) 2011 Optical Society of America

Although we have constructed parallel phase-shifting digital holography systems using an array of micropolarizers, we found that the zeroth-order diffraction wave was not removed completely. Then, we report the reason why the zeroth-order diffraction wave is not always removed completely and propose an algorithm to remove the residual zeroth-order diffraction wave. In the algorithm, phase-shifted holograms obtained by parallel phase-shifting digital holography and the intensity distribution of the reference wave are divided into segments and the pixel values in the segments are multiplied by proper correction constants. The effectiveness of the proposed algorithm was experimentally verified. (C) 2011 The Japan Society of Applied Physics

We succeeded in recording and observing a spatially and temporally continuous moving picture of visible femtosecond light pulse propagation by using light-in-flight recording by holography, for the first time. We applied second-harmonic generation (SHG) to a NIR femtosecond light pulse from a mode-locked Ti:sapphire laser to generate a visible femtosecond light pulse. The center wavelength and duration of the generated light pulse were 400 nm and similar to 100 fs, respectively. We acquired a moving picture of a visible and collimated femtosecond light pulse that propagated on a diffuser plate for 145 ps. (C) 2011 The Japan Society of Applied Physics

We propose an algorithm for compensating the phase-shift error of polarization-based parallel two-step phase-shifting digital holography, which is a technique for recording a spatial two-step phase-shifted hologram. Although a polarization-based system of the technique has been experimentally demonstrated, there had been the problem that the phase difference of two phase-shifted holograms had been changed by the extinction ratio of the micropolarizer array attached to the image sensor used in the system. To improve the performance of the system, we established and formulated an algorithm for compensating the phase-shift error. Accurate spatial phase-shifting interferometry in the system can be conducted by the algorithm regardless of phase-shift error due to the extinction ratio. By the numerical simulation, the proposed algorithm was capable of reducing the root mean square errors of the reconstructed image by 1/4 and 1/5 in amplitude and phase, respectively. Also, the algorithm was experimentally demonstrated, and the experimental results showed that the system employing the proposed algorithm suppressed the conjugate image, which slightly appeared in the image reconstructed by the system not employing the algorithm, even when the extinction ratio was 10:1. Thus, the effectiveness of the proposed algorithm was numerically and experimentally verified. (C) 2010 Optical Society of America

高速度カメラを用いた並列位相シフトディジタルホログラフィック顕微鏡法による生体の3次元動画イメージングに成功したので報告する。並列位相シフトディジタルホログラフィは高画質瞬時3次元イメージング可能な技術であり,その顕微鏡応用技術である本顕微鏡法がこれまで提案,実証されてきた。今回,倍率が試料の奥行き位置に依存しないディジタルホログラフィック顕微鏡システムと高速度カメラを用いて本顕微鏡法を水中の生体に適用することで,機械的な焦点合わせなしに泳動の様子を詳細に可視化することに成功した。毎秒20,000フレームでの生体の3次元動画イメージングを行い,生体の3次元イメージングにおいて世界最高速を達成した。

We propose an in-line color digital holography that can suppress a 0th-order diffraction image and a conjugate image. This technique reconstructs the image of an object from two holograms that are formed at two different distances from the object for each primary color. We numerically simulated the proposed technique and confirmed that it enabled the reconstruction of higher-quality images of an object than the Fresnel transform alone, which is the simplest reconstruction algorithm in digital holography. The effectiveness of the proposed technique was also quantitatively shown by evaluating the reconstructed images using root-mean-square errors. Thus, it was confirmed that the proposed technique was capable of recording and reconstructing both three-dimensional information and color information of an object. (C) 2011 The Japan Society of Applied Physics

We demonstrate high-speed parallel phase-shifting digital holography capable of three-dimensional measurement of a dynamically moving object. We constructed the recording system by using a quarter-wave plate and a high-speed polarization-imaging camera. Moving pictures of two vibrating elastic bands located on different depth plane were clearly and individually reconstructed by the technique.

We present single-shot phase-shifting digital holographic microscopy using space-division multiplexing of holograms. The technique has the capability of clearly imaging the temporal change of a three-dimensional movement, mu m-order structures, and the phase distribution of an object. The experimental result for a moving object was demonstrated.

We propose a parallel phase-shifting digital holography capable of simultaneously capturing both outside three-dimensional (3D) information of the object such as a surface of an object which human being can perceive (visible information) and internal 3D information of the object (invisible information) using a visible laser light and an invisible laser light. This technique can carry out phase-shifting interferometry for each light with a single-shot exposure, because an interference fringe image in which the information of each light and each phase-shift is spatially multiplexed is recorded by a phase-shifting array device and a wavelength-filter array. We numerically simulated the proposed technique, and the effectiveness of the proposed technique was shown by evaluating the simulation results using a correlation coefficient. Also we conducted a preliminary experiment using a red filter and a near-infrared filter placed 8 cm apart from each other as objects containing both visible and invisible 3D information. A He-Ne laser operated at 633 nm and a diode laser operated at 830 nm were used as a visible light source and an invisible light source, respectively. The 3D imaging capability of the proposed technique was successfully demonstrated by the preliminary experiment, and the validity of the technique was also confirmed by evaluating root mean square errors of the reconstructed images. Also the capability for simultaneously 3D capturing of outside (visible) information and internal (invisible) information was demonstrated by a preliminary experiment.

We propose parallel phase-shifting digital holographic microscopy (PPSDHM) which has the ability of three-dimensional (3-D) motion measurement using space-division multiplexing technique. By the PPSDHM, instantaneous information of both the 3-D structure and the phase distributions of specimens can be simultaneously acquired with a single-shot exposure. We constructed a parallel phase-shifting digital holographic microscope consisting of an optical interferometer and an image sensor on which micro polarizers are attached pixel by pixel. The validity of the PPSDHM was experimentally verified by demonstrating the single-shot 3-D imaging and phase-imaging ability of the constructed microscope. (C) 2010 Optical Society of America

Parallel two-step phase-shifting digital holography is a technique for single-shot implementation of phase-shifting interferometry and requires only the intensity distribution of the reference wave and spatial two phase-shifted holograms. We constructed a system of parallel two-step phase-shifting digital holography and experimentally demonstrated the technique, for the first time. The system uses an originally fabricated image sensor having an array of 2 x 1 micro polarizers. Each micro polarizer was attached on pixel by pixel. In the experiment, the unwanted images, the zero-order diffraction wave and the conjugate image, are removed from the reconstructed image of objects by the system, while the images superimpose on the image of objects reconstructed by Fresnel transform alone. Also the capability of single-shot and three-dimensional imaging is demonstrated by the system. (C) 2010 Optical Society of America

We propose an algorithm that can improve the quality of the reconstructed image from the single hologram recorded by the optical system of the parallel four-step phase-shifting digital holography. The proposed algorithm applies the image-reconstruction algorithm of parallel two-step phase-shifting digital holography to the hologram so as to reduce errors in the reconstructed image and eliminate ghosts. We numerically and experimentally confirmed that the proposed algorithm decreased 25% in terms of root mean square error in amplitude, and eliminated the ghosts, respectively. (C) 2010 Optical Society of America

We propose parallel phase-shifting color digital holographic microscopy (PPSCDHM) which is capable of both color imaging and three-dimensional (3-D) motion measurement by using space-division multiplexing technique. By the PPSCDHM, instantaneous information of not only the 3-D structure of specimens but also the spectral image can be simultaneously acquired with a single-shot exposure. The PPSCDHM can be implemented by using a micro-polarizer array, a micro-wavelength-filter array, and more than two wavelengths of lasers. We conducted a preliminary experiment using three wavelengths of lasers, and then much clearer image was reconstructed by the PPSCDHM than that by Fresnel transform alone for each wavelength. Thus, the effectiveness of the PPSCDHM was verified. © 2010 3D Display Research Center and Springer-Verlag Berlin Heidelberg.

We propose parallel phase-shifting color digital holography using two phase shifts. This technique enables the instantaneous acquisition of three-dimensional information of a moving color object. The interference fringe image that contains six holograms with two phase shifts for three wavelengths is recorded by a single shot exposure. Decreasing the degree of space-division multiplexing of these holograms makes it possible to suppress the degradation of the image quality owing to the aliasing caused by the multiplexing. Numerical simulation and preliminary experiments demonstrate the validity of the proposed technique; the reconstructed images of the proposed technique are clearer than those of the previously reported single-shot phase-shifting color digital holography that uses four phase steps. (C) 2009 Optical Society of America

We proposed a technique for observing ultrashort light pulse propagation in a microscopic space by using light-in-flight recording by holography. The technique introduces a microscope between the object and the holographic plate in the optical system of light-in-flight recording by holography, and can record and reconstruct a moving picture of magnified images of ultrashort light pulse propagation. A model of the microscope and a scheme of numerical simulation are established. The simulation uses ray tracing that considers coherence length. A microscope based on the technique was simulated. A microscope objective with a 10x magnification was used in the simulation. It was verified that moving picture of a 10x-magnified image of a 130fs light pulse propagation can be recorded for 4ps. (C) 2009 The Japan Society of Applied Physics