Long-range Fourier ptychographic imaging of the dynamic object with a single camera.

Fourier ptychographic imaging technology is a new imaging method proposed in recent years. This technology captures multiple low-resolution images, and synthesizes them into a high-resolution image in the Fourier domain by a phase retrieval algorithm, breaking through the diffraction limit of the lens. In the field of macroscopic Fourier ptychographic imaging, most of the existing research generally focus on high-resolution imaging of static objects, and applying Fourier ptychographic imaging technology to dynamic objects is a hot research area now. At present, most of the researches are to use camera arrays combined with multiplexed lighting, deep learning or other algorithms, but the implementation of these methods is complicated or costly. Based on the diffraction theory of Fourier optics, this paper proposes that by expanding and focusing the illumination area, we can apply Fourier ptychographic imaging technology with a single camera to moving objects within a certain range. Theoretical analysis and experiments prove the feasibility of the proposed method. We successfully achieve high-resolution imaging of the dynamic object, increasing the resolution by about 2.5 times. This paper also researches the impact of speckles in the illuminated area on imaging results and proposes a processing method to reduce the impact of speckles.

Ghost imaging based on Fermat spiral laser array designed for remote sensing.

We propose a Fermat spiral laser array as illumination source in ghost imaging. Due to the aperiodic structure, the Fermat spiral laser array generates illuminating light field without spatial periodicity on the normalized second-order intensity correlation function. A single-pixel detector is used to receive the signal light from object for image reconstruction. The effects of laser array parameters on the quality of ghost imaging are analyzed comprehensively. Through experimental demonstration, the Fermat spiral laser array successfully achieves ghost imaging with high quality by combining with the compressive sensing reconstruction algorithm. This method is expected to be applied in remote sensing by combining with phased and collimated fiber laser array equipped with the high emitting power and high-speed modulation frequency.

Fast object imaging and classification based on circular harmonic Fourier moment detection.

Limited by the number of illumination fields and the speed of a spatial light modulator, single-pixel imaging (SPI) cannot realize real-time imaging and fast classification of an object. In this paper, we proposed the circular harmonic Fourier single-pixel imaging (CHF-SPI) for the first time to realize fast imaging and classification of objects. The light field distribution satisfies the circular harmonic Fourier formula, and the light intensity values of the single-pixel detector are equivalent to the circular harmonic Fourier moments. Then the target can be reconstructed under low sampling ratio by inverse transformation. Through simulation and experimental verification, clear imaging can be performed at a sampling ratio of 0.9%. In addition, circular harmonic Fourier moments are used to construct multi-distortion invariant to classify objects with rotation and scale change. The scale change multiples of objects can be calculated and the objects can be classified by using 10 light fields. It is of great significance to classify objects quickly without imaging.

Efficient and noise-resistant single-pixel imaging based on Pseudo-Zernike moments.

An efficient and noise-resistant single-pixel imaging (SPI) technique based on Pseudo-Zernike moments (PZ-SPI) is proposed. In this technique, the illumination light fields are modulated to satisfy the Pseudo-Zernike polynomials. Then the modulated light fields are projected onto the object. And the single-pixel detector is used to measure the reflected light intensities to calculate the Pseudo-Zernike moments. Finally, the object image is reconstructed by iterative summation of the product of the Pseudo-Zernike polynomials and the Pseudo-Zernike moments. Through the numerical simulation and experimental demonstration, PZ-SPI can effectively reconstruct image at low sampling ratios. Besides, comparing with the Fourier-SPI and Zernike-SPI, PZ-SPI has good robustness to background noise in SPI system. These advantages expand the application of PZ-SPI in complex environments.

Cosinusoidal encoding multiplexed structured illumination multispectral ghost imaging.

The information dimension obtained by multispectral ghost imaging is more abundant than in single-band ghost imaging. Existing multispectral ghost imaging systems still meet some shortages, such as complex structure or reconstruction time-consuming. Here, an approach of cosinusoidal encoding multiplexed structured illumination multispectral ghost imaging is proposed. It can capture the multispectral image of the target object within one projection cycle with a single-pixel detector while maintaining high imaging efficiency and low time-consuming. The core of the proposed approach is the employed novel encoding strategy which is apt to decode and reconstruct the multispectral image via the Fourier transform. Specifically, cosinusoidal encoding matrices with specific frequency characteristics are fused with the orthogonal Hadamard basis patterns to form the multiplexed structured illumination patterns. A broadband photomultiplier is employed to collect the backscattered signals of the target object interacted by the corresponding structured illumination. The conventional linear algorithm is applied first to recover the mixed grayscale image of the imaging scene. Given the specific frequency distribution of the constructed cosinusoidal encoding matrices, the mixed grayscale image can be converted to the frequency domain for further decoding processing. Then, the pictures of multiple spectral components can be obtained with some manipulations by applying Fourier transform. A series of numerical simulations and experiments verified our proposed approach. The present cosinusoidal encoding multiplexed structured illumination can also be introduced in many other fields of high-dimensional information acquisition, such as high-resolution imaging and polarization ghost imaging.

Scanning single-pixel imaging lidar.

Long-range light detection and ranging (lidar) of active illumination optical imaging has widespread applications, such as remote sensing, satellite-based global topography, and target recognition and identification. Here, to make trade-offs among imaging efficiency, resolution, receiving field of view, divergence angle, and detected distance, we demonstrate a scanning single-pixel imaging lidar (SSPIL), enjoying the merits of the traditional pointing-by-pointing scanning imaging and single-pixel imaging. The imaging strategy of SSPIL is divided into scanning search and staring imaging processes. These strategies can save most time consumption for imaging background areas and thus improve imaging efficiency. Three imaging experiments were conducted in real urban atmospheric conditions. The preliminary results show SSPIL has the ability for long-range imaging with high efficiency, high resolution, and a large receiving field of view. Also, from the imaging results, we found that multiple samples can improve the SNR of imaging in the real urban atmosphere. The present work may provide a valuable alternative approach in the long-range active illumination optical imaging fields.

Single-pixel imaging using discrete Zernike moments.

A novel single-pixel imaging (SPI) technique based on discrete orthogonal Zernike moments is proposed. In this technique, the target object is illuminated by two sets of Zernike basis patterns which satisfy the Zernike polynomials. The Zernike moments of object image are obtained by measuring the reflected light intensities through a single-pixel detector. And the object image is reconstructed by summing the product of Zernike polynomials and detected intensities iteratively. By theoretical and experimental demonstrations, an image with high quality is retrieved under compressive sampling. Moreover, the Zernike illuminating patterns are used for object classification due to the rotation invariant of Zernike moments. By measuring the amplitudes of a few specific Zernike moments through the SPI system, the rotated images with different angles and the same content are classified into the same class on experiment. This classification technique has the advantages of high efficiency and high accuracy due to the high modulation speed and high sensitivity of SPI system.

Anti-motion blur single-pixel imaging with calibrated radon spectrum.

Single-pixel imaging (SPI), a novel computational imaging technique that has emerged in the past decades, can effectively capture the image of a static object by consecutively measuring light intensities from it. However, when SPI is applied to imaging the dynamic object, severe motion blur in the restored image tends to appear. In this Letter, a new SPI scheme is proposed to largely alleviate such a problem by leveraging a calibrated radon spectrum. Such a spectrum is obtained by translating the acquired one-dimensional projection functions (1DPFs) according to the positional relationship among the 1DPFs. Simulation and experimental results demonstrate that, without prior knowledge, our approach can effectively reduce motion blur and restore high-quality images of the fast-moving object. In addition, the proposed scheme can also be used for fast object tracking.

Complementary moment detection for tracking a fast-moving object using dual single-pixel detectors.

Target tracking has found important applications in particle tracking, vehicle navigation, aircraft monitoring, etc. However, employing single-pixel imaging techniques to track a fast-moving object with a high frame rate is still a challenge, due to the limitation of the modulation frequency of the spatial light modulator and the number of required patterns. Here we report a complementary single-pixel object tracking approach which requires only two geometric moment patterns to modulate the reflected light from a moving object in one frame. Using the complementary nature of a digital micromirror device (DMD), two identical single-pixel detectors are used to measure four intensities which can be used to acquire the values of zero-order and first-order geometric moments to track the centroid of a fast-moving object. We experimentally demonstrate that the proposed method successfully tracks a fast-moving object with a frame rate of up to 11.1 kHz in the first two experiments. In the third experiment, we compare previous works and find that the method can also accurately track a fast-moving object with a changing size and moving speed of 41.8 kilopixel/s on the image plane. The root mean squared errors in the transverse and axial directions are 0.3636 and 0.3640 pixels, respectively. The proposed method could be suitable for ultrafast target tracking.

Detection and imaging of distant targets by near-infrared polarization single-pixel lidar.

Single-pixel imaging (SPI) is a new technology with many applications and prospects. Polarization detection technology can improve the detection and identification ability of the imaging system. A near-infrared polarization SPI lidar system is designed to realize detection and polarization imaging of outdoor long-range targets. The depth, intensity, linear polarization, and polarization degree images of typical remote targets are obtained. The results show that the polarization image contains many details and contour information of the target, and the intensity image contains brightness and reflectivity information. Intensity and polarization information complement each other. The characteristics of intensity and polarization images at different spatial frequencies are analyzed for the first time, to our knowledge, by taking advantage of the Fourier modulation mode. We found that the proportion of high-frequency information in the polarization image is much higher than that of the intensity image. The sampling strategy of collecting only low-frequency components is applicable in intensity imaging but needs further improvement in polarization imaging. The polarization SPI lidar system can enrich the target information acquired, improve imaging contrast, and have significant application value for target detection and identification in complex backgrounds.

Multi-Object Positioning and Imaging Based on Single-Pixel Imaging Using Binary Patterns.

Single-pixel imaging (SPI) is a new type of imaging technology that uses a non-scanning single-pixel detector to image objects and has important application prospects and value in many fields. Most of the modulators currently used in SPI systems are digital micromirror device (DMD) modulators, which use a higher frequency for binary modulation than other alternatives. When modulating grayscale information, the modulation frequency is significantly reduced. This paper conducts research on multiple discrete objects in a scene and proposes using binary patterns to locate and image these objects. Compared with the existing methods of using gray patterns to locate and image multiple objects, the method proposed in this paper is more suitable for DMD-type SPI systems and has wider applicability and greater prospects. The principle of the proposed method is introduced, and the effectiveness of the method is experimentally verified. The experimental results show that, compared to traditional SPI methods, the number of patterns required by the proposed method is reduced by more than 85%.

Single-pixel tracking of fast-moving object using geometric moment detection.

Real-time tracking of fast-moving object have many important applications in various fields. However, it is a great challenge to track of fast-moving object with high frame rate in real-time by employing single-pixel imaging technique. In this paper, we present the first single-pixel imaging technique that measures zero-order and first-order geometric moments, which are leveraged to reconstruct and track the centroid of a fast-moving object in real time. This method requires only 3 geometric moment patterns to illuminate a moving object in one frame. And the corresponding intensities collected by a single-pixel detector are equivalent to the values of the zero-order and first-order geometric moments. We apply this new approach of measuring geometric moments to object tracking by detecting the centroid of the object in two experiments. The root mean squared errors in the transverse and axial directions are 5.46 pixels and 5.53 pixels respectively, according to the comparison of data captured by a camera system. In the second experiment, we successfully track a moving magnet with a frame rate up to 7400 Hz. The proposed scheme provides a new method for ultrafast target tracking applications.

Computational-weighted Fourier single-pixel imaging via binary illumination.

Single-pixel imaging has the ability to generate images at nonvisible wavelengths and under low light conditions and thus has received increasing attention in recent years. Fourier single-pixel imaging (FSI) utilizes deterministic basis patterns for illumination to greatly improve the quality of image reconstruction. However, the original FSI based on grayscale Fourier basis illumination patterns is limited by the imaging speed as the digital micro-mirror devices (DMD) used to generate grayscale patterns operate at a low refresh rate. In this paper, a new approach is proposed to increase the imaging speed of DMD-based FSI without reducing the imaging spatial resolution. In this strategy, the grayscale Fourier basis patterns are split into a pair of grayscale patterns based on positive/negative pixel values, which are then decomposed into a cluster of binary basis patterns based on the principle of decimalization to binary. These binary patterns are used to illuminate the imaged object. The resulting detected light intensities multiply the corresponding weighted decomposed coefficients and are summed, and the results can be used to generate the Fourier spectrum for the imaged object. Finally, an inverse Fourier transform is applied to the Fourier spectrum to obtain the object image. The proposed technique is verified by a computational simulation and laboratory experiments. Both static and dynamic imaging experiments are carried out to demonstrate the proposed strategy. 128 × 128 pixels dynamic scenes at a speed of ~9 frames-per-second are captured under 22 KHz projection rate using a DMD. The reported technique accelerates the imaging speed for DMD-based FSI and provides an alternative approach to improve FSI efficiency.

Polarimetric ghost imaging.

For conventional ghost imaging (GI) systems, the object image is obtained based on the reflective or transmissive character of the object. When the object and its background have the same reflectivity or transmittance, conventional GI is helpless in detecting the object from the background. An improvement is to use the polarization components of the reflected or transmitted light. We propose a polarimetric GI system that employs a polarization state generator and a polarization state analyzer. This feature allows for the first time, to the best of our knowledge, imaging the object buried in the same reflectivity or transmittance background, which represents a breakthrough for GI applications. Using a combination of intensity and polarization information, we are better able to distinguish between the background and the different material objects.

Temperature-Induced Variations in Slip Behavior of Single Crystal Aluminum: Microstructural Analysis.

The simultaneous increase in strength and plasticity of aluminum and its alloys at cryogenic temperatures has been shown in previous research, but the deformation mechanism was still unclear. Therefore, the purpose of this investigation was to reveal the relationship between slip behavior and mechanical response at low temperatures. A quasi-in situ scanning electron microscope was used to observe the evolution of slip bands in the selected aluminum single crystals with two typical orientations at 25 °C, -100 °C, and -180 °C. The results showed that irrespective of orientation, the density of the slip plane was increased with the decline in temperature, which inhibited slip localization and significantly improved plasticity and work hardening. In detail, at RT, the slip bands were widening until the micro-cracks were generated, causing early failure during deformation. When the temperature was decreased to -180 °C, the slip plane density was increased, and the deformation was more homogenous. Moreover, the slip mode was influenced by orientation and temperature. In particular, a single slip system was activated in the sample with the [112] orientation at all the temperatures investigated. Multiple slip systems were found to activate at 25 °C and -100 °C, and only the primary slip system was activated in the sample with [114] orientation at -180 °C. These findings deepen the understanding of slip behavior at cryogenic temperatures, providing new insights into the deformation mechanism of aluminum and its alloys.

Solid-state fermentation by S. cerevisiae with high resistance to ferulic acid improves the physicochemical properties of wheat bran and quality of bran-rich Chinese steamed bread.

Wheat bran has numerous health benefits, but its poor processing and sensory properties limit its application in the staple food industry. Fermentation by S. cerevisiae changes the performance of wheat bran. However, high levels of ferulic acid (FA) inhibit S. cerevisiae. The effects of solid-state fermentation of S. cerevisiae with high resistance to FA on the physicochemical properties of wheat bran and the quality of bran-rich Chinese steamed bread (CSB) were investigated. The results showed that the growth of S. cerevisiae was inhibited by FA in a dose-dependent manner. Short-term adaptation strategies efficiently improved the tolerance of S. cerevisiae to FA stress. Compared with the parental strain (PS), fermentation of the short-term adapted strains (adapted strains) significantly increased the FA, total phenol, and soluble dietary fiber content in wheat bran. Wheat bran fermented by the adapted strains had a higher antioxidant capacity than wheat bran fermented by PS. In addition, compared with the PS, the wheat bran fermented by the adapted strains can decrease the hardness, improve the specific volume, and the quality of CSB. Thus, solid-state fermentation of the adapted strain is a potentially effective method to improve the nutritional and physicochemical properties of wheat bran as a cereal food ingredient.

Liquid-Metal-Assisted Synthesis of Patterned GaN Thin Films for High-Performance UV Photodetectors Array.

GaN's outstanding physical characteristics allow for a wide range of applications in numerous industries. Although individual GaN-based ultraviolet (UV) photodetectors are the subject of in-depth research in recent decades, the demand for photodetectors array is rising as a result of advances in optoelectronic integration technology. However, as a prerequisite for constructing GaN-based photodetectors array, large-area, patterned synthesis of GaN thin films remains a certain challenge. This work presents a facile technique for pattern growing high-quality GaN thin films for the assembly of an array of high-performance UV photodetectors. This technique uses UV lithography, which is not only very compatible with common semiconductor manufacturing techniques, but also enables precise patterning modification. A typical detector has impressive photo-response performance under 365 nm irradiation, with an extremely low dark current of 40 pA, a high Ilight /Idark ratio over 105 , a high responsivity of 4.23 AW-1 , and a decent specific detectivity of 1.76 × 1012 Jones. Additional optoelectronic studies demonstrate the strong homogeneity and repeatability of the photodetectors array, enabling it to serve as a reliable UV image sensor with enough spatial resolution. These outcomes highlight the proposed patterning technique's enormous potential.

Two-wavelength ghost imaging through atmospheric turbulence.

Recent work has indicated that ghost imaging might find useful application in standoff sensing where atmospheric turbulence is a serious problem. There has been theoretical study of ghost imaging in the presence of turbulence. However, most work has addressed signal-wavelength ghost imaging. Two-wavelength ghost imaging through atmospheric turbulence is theoretically studied in this paper. Based on the extended Huygens-Fresnel integral, the analytical expressions describing atmospheric turbulence effects on the point spread function (PSF) and field of view (FOV) are derived. The computational case is also reported.

Effect of the Second Phases on Composite Spinning-Extrusion Forming and Mechanical Properties of Al-Cu-Li Alloy.

The aim of this work is to investigate the effect of different second phases on the composite spinning-extrusion forming and mechanical properties of Al-Cu-Li alloy. With that purpose, four kinds of second phases blanks were controlled using preheating treatment, composite spinning-extrusion forming and mechanical properties test. Then, the correlation between the second phases and mechanical properties was further analyzed using electron backscattered diffraction and transmission electron microscopy. The results indicated that different second phases of Al-Cu-Li alloy can be regulated via reasonable preheating treatment. In addition, different second phases in the blank have various influences on composite spinning-extrusion forming, microstructure and mechanical properties of cylindrical parts. Dissolving the coarse second phases particles and precipitating the Al3Zr dispersoid in the blank can effectively improve the composite spinning-extrusion forming, inhibit the abnormal growth of recrystallized grains, and significantly enhance the mechanical properties of cylindrical parts with ribs. After regulation, the average grain size of the cylindrical parts is refined from about 90 µm to about 45 µm, and the average diameter of T1 phase is refined from 107 nm to 77 nm. In addition, the ultimate tensile strength, yield strength and elongation of cylindrical parts are increased from 555 MPa to 588 MPa, 530 MPa to 564 MPa, and 9.1% to 11%, respectively.

Adaptive optical ghost imaging through atmospheric turbulence.

We demonstrate for the first time (to our knowledge) that a high-quality image can still be obtained in atmospheric turbulence by applying adaptive optical ghost imaging (AOGI) system even when conventional ghost imaging system fails to produce an image. The performance of AOGI under different strength of atmospheric turbulence is investigated by simulation. The influence of adaptive optics system with different numbers of adaptive mirror elements on obtained image quality is also studied.