2024

• Record 205 of
  
  Title:Airborne Small Target Detection Method Based on Multimodal and Adaptive Feature Fusion
  
  Author(s):Xu, Shufang(1,2); Chen, Xu(1); Li, Haiwei(3); Liu, Tianci(4); Chen, Zhonghao(1); Gao, Hongmin(1); Zhang, Yiyan(1)
  Source:IEEE Transactions on Geoscience and Remote Sensing
  Volume: 62  Issue:   DOI: 10.1109/TGRS.2024.3443856  Published: 2024  
  Abstract:The detection of airborne small targets amidst cluttered environments poses significant challenges. Factors such as the susceptibility of a single RGB image to interference from the environment in target detection and the difficulty of retaining small target information in detection necessitate the development of a new method to improve the accuracy and robustness of airborne small target detection. This article proposes a novel approach to achieve this goal by fusing RGB and infrared (IR) images, which is based on the existing fusion strategy with the addition of an attention mechanism. The proposed method employs the YOLO-SA network, which integrates a YOLO model optimized for the downsampling step with an enhanced image set. The fusion strategy employs an early fusion method to retain as much target information as possible for small target detection. To refine the feature extraction process, we introduce the self-adaptive characteristic aggregation fusion (SACAF) module, leveraging spatial and channel attention mechanisms synergistically to focus on crucial feature information. Adaptive weighting ensures effective enhancement of valid features while suppressing irrelevant ones. Experimental results indicate 1.8% and 3.5% improvements in mean average precision (mAP) over the LRAF-Net model and Infusion-Net detection network, respectively. Additionally, ablation studies validate the efficacy of the proposed algorithm's network structure. © 1980-2012 IEEE.
  Accession Number: 20243416917605
• Record 206 of
  
  Title:Dual-parameter controlled reconfigurable metasurface for enhanced terahertz beamforming via inverse design method
  
  Author(s):Wu, Qi(1,2); Fan, Wen-Hui(1,2,3); Qin, Chong(1,2); Jiang, Xiao-Qiang(1,2)
  Source:Physica Scripta
  Volume: 99  Issue: 6  DOI: 10.1088/1402-4896/ad43c3  Published: June 1, 2024  
  Abstract:Recently, reconfigurable metasurfaces have emerged as a promising solution for wavefront manipulation in the terahertz (THz) region, providing enhanced beamforming capabilities. However, traditional single-parameter control methods fail to achieve independent phase and amplitude modulation, constraining their modulation capabilities. Meanwhile, forward design methods based on phase matching ignore the structural responses of the non-ideal unit, leading to degraded beamforming performance. Here, we introduce an electrically reconfigurable metasurface composed of bilayer graphene strips based on dual-parameter control. Full-wave simulations demonstrate independent amplitude and phase modulation, achieving the full 360° phase coverage and an adjustable amplitude range from 0 to 0.8 at 2.6 THz. To optimize beamforming performance, particularly for the responses of the non-ideal unit away from the designed frequency, we employed an inverse design method based on a hybrid evolutionary algorithm. This novel approach significantly enhances beam steering, achieving a maximum 60% increase in beam directivity and maintaining over 90% of ideal directivity across a broad frequency range from 1.6 THz to 5 THz. Especially, it achieves a maximum deflection angle of 75°. Meanwhile, the adaptability of the inverse design method is further demonstrated to various optimized objectives. For beam focusing, even with limited phase control (below 210°), this method significantly enhances the focusing quality (up to 150% enhancement) and increases the focusing efficiency from 25% to 40%. Additionally, it effectively mitigates the impact of quantized phase errors on beamforming. This research not only demonstrates potential applications in high-speed THz wireless communication and compact imaging systems but also paves the way for innovative designs in reconfigurable metasurfaces. © 2024 IOP Publishing Ltd.
  Accession Number: 20242016080491
• Record 207 of
  
  Title:Linearly polarized RABBIT beyond the dipole approximation
  
  Author(s):Liao, Yijie(1); Chen, Yongkun(1); Dahlström, Jan Marcus(2); Pi, Liang-Wen(3); Lu, Peixiang(1,4); Zhou, Yueming(1,5)
  Source:Physical Review A
  Volume: 110  Issue: 2  DOI: 10.1103/PhysRevA.110.023109  Published: August 2024  
  Abstract:We theoretically investigate nondipole effects in the reconstruction of attosecond beating by interference of two-photon transitions (RABBIT) of helium using linearly polarized extreme ultraviolet and infrared fields. By scanning the time delay between the two fields, we observe modulations in sidebands (SBs) both for angular-integrated photoelectron yield and forward-backward asymmetry in photoelectron distribution along the light-propagation direction. The SB modulations of the forward-backward asymmetry reveal Wigner and continuum-continuum time delays of the electron wave packets ionized via nondipole paths, different from the conventional RABBIT where only the dipole paths are involved. Furthermore, the time delays extracted from the forward-backward asymmetry show an abrupt jump as a function of polar emission angle of photoelectrons, due to the competition among continuum partial waves in nondipole laser-assisted photoionization. © 2024 American Physical Society.
  Accession Number: 20243516927919
• Record 208 of
  
  Title:Robust internal model control based on a novel generalized extended state observer and its application on a two-inertia system
  
  Author(s):Wang, Fan(1,2); Cheng, Tianji(3,4,5); Jing, Feng(1,2); Liu, Peng(1,2); Xie, Meilin(1,2); Cao, Yu(1,2); Guo, Min(1,2)
  Source:ISA Transactions
  Volume: 152  Issue:   DOI: 10.1016/j.isatra.2024.07.005  Published: September 2024  
  Abstract:Disturbance observer (DOB) and extended state observer (ESO) are extensively utilized to handle external disturbances and model uncertainties in the control system. Nevertheless, the integration of these two methods to improve disturbance suppression remains an open question. In this research, the disturbance compensation mechanism of DOB is employed to compensate the disturbance estimation error of ESO, thereby achieving an effective integration of DOB and ESO. Additionally, a generalized ESO (GESO) is proposed to replace ESO. A robust internal mode control (RIMC) scheme is then developed by incorporating GESO into a two-degree-of-freedom internal mode control (TDF-IMC) framework. Moreover, the equivalence of RIMC and classical TDF-IMC is given by a rigorous derivation under the frequency domain description. Finally, the RIMC is applied to the control of a two-inertia system to verify its superiority in terms of robustness, disturbance rejection, and resonance suppression. © 2024 ISA
  Accession Number: 20242816684078
• Record 209 of
  
  Title:An enhanced gated MCP-PMT for neutron detection in laser fusion experiments
  
  Author(s):Li, Kuinian(1,2,3); Chen, Ping(1,7); Liu, Hulin(1); Wei, Yonglin(1); He, Luanxuan(1,2,3); Su, Xiao(4,6); Yang, Yang(1); Gou, Yongsheng(1); Tian, Jinshou(1); Wu, Shengli(2); Yuan, Xiaohui(4,6); Zhang, Zhe(5); Zhang, Jie(4,5,6)
  Source:Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
  Volume: 1067  Issue:   DOI: 10.1016/j.nima.2024.169726  Published: October 2024  
  Abstract:The microchannel plate photomultiplier tube (MCP-PMT) is a photodetector that utilizes microchannel plates for signal amplification, offering rapid pulse response time of sub-nanosecond with a compact design and low dark current. A series of enhanced gated MCP-PMTs have been developed by incorporating a gating electrode between the photocathode and the MCPs, which have been employed in neutron detection during the double-cone ignition laser fusion experiment at the SGII Upgrade laser facilities. © 2024
  Accession Number: 20243416890221
• Record 210 of
  
  Title:Atomistic evidence of nucleation mechanism for the direct graphite-to-diamond transformation
  
  Author(s):Luo, Duan(1); Yang, Liuxiang(2); Xie, Hongxian(3); Srinivasan, Srilok(1); Tian, Jinshou(4); Sankaranarayanan, Subramanian(1); Arslan, Ilke(1); Yang, Wenge(2); Mao, Ho-kwang(2,5); Wen, Jianguo(1)
  Source:Carbon
  Volume: 229  Issue:   DOI: 10.1016/j.carbon.2024.119538  Published: October 2024  
  Abstract:The direct graphite-to-diamond transformation mechanism has been a subject of intense study and remains debated concerning the initial stages of the conversion, the intermediate phases, and their transformation pathways. Here, we successfully recover samples at the early conversion stage by tuning high-pressure/high-temperature conditions and reveal direct evidence supporting the nucleation-growth mechanism. Atomistic observations show that intermediate orthorhombic graphite phase mediates the growth of diamond nuclei. Furthermore, we observe that quenchable orthorhombic and rhombohedra graphite are stabilized in buckled graphite at lower temperatures. These intermediate phases are further converted into hexagonal and cubic diamond at higher temperatures following energetically favorable pathways in the order: graphite → orthorhombic graphite → hexagonal diamond, graphite → orthorhombic graphite → cubic diamond, graphite → rhombohedra graphite → cubic diamond. These results significantly improve our understanding of the transformation mechanism, enabling the synthesis of different high-quality forms of diamond from graphite. © 2024 Elsevier Ltd
  Accession Number: 20243416906823
• Record 211 of
  
  Title:Generation of subcycle isolated attosecond pulses by pumping ionizing gating
  
  Author(s):Wu, Zhaohui(1); Zeng, Xiaoming(1); Li, Zhaoli(1); Zhang, Zhimeng(1); Wang, Xiaodong(1); Wang, Xiao(1); Mu, Jie(1); Zuo, Yanlei(1); Su, Jingqin(1); Peng, Hao(2); Cao, Huabao(3); Fu, Yuxi(3); Riconda, C.(4); Weber, S.(5)
  Source:Physical Review Research
  Volume: 6  Issue: 1  DOI: 10.1103/PhysRevResearch.6.013126  Published: January 2024  
  Abstract:We present an interesting approach named as pumping ionizing gating (PIG) for the generation of isolated attosecond pulses (IAPs). In this regime, a short laser is used to ionize a preexisting gas grating, creating a fast-extending plasma grating (FEPG) having an ionization front propagating with the velocity of light. A low-intensity long counterpropagating pump pulse is then reflected by a very narrow region of the ionization front, only where the Bragg conditions for resonant reflection is satisfied. Consequently, the pump reflection is confined within a subcycle region called PIG, and forms a wide-band coherent IAP in combination with the frequency up-conversion effect due to the plasma gradient. This approach results in a new scheme to generate IAPs from long picosecond pump pulses. Three-dimensional (3D) simulations show that a 1.6 ps, 1 μm pump pulse can be used to generate a 330 as laser pulse with a peak intensity approximately 33 times that of the pump and a conversion efficiency of around 0.1%. These results highlight the potential of the PIG method for generating IAPs with high conversion efficiency and peak intensity. © 2024 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.
  Accession Number: 20240615527419
• Record 212 of
  
  Title:Turbulence compensation with pix-to-pix generative adversarial networks in vector vortex beams
  
  Author(s):Zhang, Zhi(1,2,3); Xie, Xiaoping(1,3); Si, Jinhai(2); Wang, Wei(1,3); Jia, Shuaiwei(1,3); Gao, Duorui(1,3)
  Source:Physica Scripta
  Volume: 99  Issue: 10  DOI: 10.1088/1402-4896/ad74b8  Published: October 1, 2024  
  Abstract:Orbital angular momentum (OAM) has significantly propelled free space optical communication (FSOC) towards achieving ultra-large transmission capacities, but mode-crosstalk in atmospheric turbulence limits its application. Here, we propose a proof-of-concept turbulence compensation approach utilizing pix-to-pix generative adversarial networks (pix2pixGAN) that does not rely on the wavefront sensor. The model captures the complex relationships between distorted optical fields and phase screens through extensive training, after which the phase screen is directly recovered from the well-trained model by identifying the corresponding distorted image to compensate for distortions. Using this model, the Strehl ratio improvement is measured at 35.7%, 8.9%, and 1.7% under three distinct turbulence conditions, respectively. Furthermore, the recognition of vector vortex beams (VVBs) integrating with the pix2pixGAN significantly improves average mode accuracy from 2% to over 99%. Additionally, the exploration of VVB-based communication further elucidates pix2pixGAN's role in enhancing communication quality. These findings suggest a potential advancement in developing a novel neural network-based strategy to compensate for transmission distortions under intense turbulence. © 2024 IOP Publishing Ltd. All rights, including for text and data mining, AI training, and similar technologies, are reserved.
  Accession Number: 20243817043606
• Record 213 of
  
  Title:Upconversion photoluminescence of the lanthanide-doped core–shell luminescent material for anti-counterfeiting recognition
  
  Author(s):Li, Dongdong(1); Zhang, Qianqian(1); Liao, Haibin(1); Fan, Qi(2); She, Jiangbo(2)
  Source:Optics Communications
  Volume: 573  Issue:   DOI: 10.1016/j.optcom.2024.130987  Published: December 15, 2024  
  Abstract:Three different NaErF4:Tm@NaREF4:Er (RE = Y, Lu, Yb) core-shell luminescent material were successfully synthesized. XRD, XPS and other characterization techniques were used to analyze the composed material, morphology, and luminous characteristics of the produced microparticles. Especially, compared with the uncoated NaErF4:Tm, the luminescence intensity of the materials with active-shell structure were increased by 2.44 times, 3.46 times, and 4.01 times respectively under 980 nm laser excitation. Moreover, the generated UCMPs were reliably employed for anti-counterfeiting recognition labels when they were used as screen-printing materials for anti-counterfeiting ink. © 2024 Elsevier B.V.
  Accession Number: 20243516959501
• Record 214 of
  
  Title:Underwater image enhancement via color correction and multi-feature image fusion
  
  Author(s):Ke, Ke(1,2,4); Zhang, Biyun(3); Zhang, Chunmin(1,2); Yao, Baoli(4); Guo, Shiping(1,2); Tang, Feng(1,2)
  Source:Measurement Science and Technology
  Volume: 35  Issue: 9  DOI: 10.1088/1361-6501/ad4dca  Published: September 2024  
  Abstract:The light attenuation underwater causes the actual underwater images to suffer from color cast, low contrast, and weak illumination. To address these issues, an effective fusion-based method is proposed, which realizes color correction (CC), brightness adjustment, contrast, and detail enhancement of underwater images. Concretely, we first design an adaptive CC method via dominant color channel judgment and lower color channel compensation. Then, we detect the brightness of each input image and propose a gamma correction function based on the gradient of the cumulative histogram to adjust the brightness of the low-light images. Subsequently, global histogram stretching and adaptive fractional differentiation techniques are employed to process the brightness-adjusted image, and then the global contrast-enhanced version and detail-enhanced version are generated respectively. To integrate the advantages of both versions, a channel fusion method based on the Lab color space is used to fuse the luminance and color of the two versions separately. The experimental results demonstrate the effectiveness of the proposed method in improving the color and illumination of underwater images, as well as enhancing the clarity of images. Moreover, the testing results on multiple datasets validate the excellent stability of this method. © 2024 IOP Publishing Ltd.
  Accession Number: 20242616532375
• Record 215 of
  
  Title:Simultaneous transmission of multi-format signals in the mid-infrared over free space
  
  Author(s):Su, Yulong(1); Xue, Jiayi(1); zheng, Yunqiang(1,2); Wang, Wei(2); Tian, Wenlong(1); zhu, Jiangfeng(1)
  Source:Optics Communications
  Volume: 573  Issue:   DOI: 10.1016/j.optcom.2024.131019  Published: December 15, 2024  
  Abstract:Mid-infrared (MIR) light within the 3–5 μm spectrum offers distinct advantages over the 1.5 μm band, particularly in adverse atmospheric conditions, rendering it a favorable option for free-space optical (FSO) communication. The transmission capacity within the 3–5 μm band is relatively low due to the immature state of its devices. In this study, we demonstrate multi-format signals FSO transmission with a total of 40 Gbps capacity in the 3 μm band, utilizing our developed MIR transmitter and receiver modules. These modules facilitate wavelength conversion between the 1.5 μm and 3 μm bands through the utilization of difference-frequency generation (DFG) effect. The MIR transmitter effectively produces three MIR signals: On-Off Keying (OOK), Binary Phase Shift Keying (BPSK), and Quadrature Phase Shift Keying (QPSK) optical signals. The generated MIR power is 7.8 dBm, covering a wavelength range from 3.5864 to 3.5885 μm. The MIR receiver regenerates the three format signals with a power of −29.6 dBm. Relevant results of regenerated signal demodulation have been collected in detail, including bit error ratio (BER), constellation diagram, and eye diagram. The required powers for the 10 Gbps OOK, BPSK, and QPSK are −37.82, −40.24, and −39.4 dBm at BER of 1 × 10−6. It is expected to further push the data capacity to the terabit-per-second level by adding more 1.5 μm band laser sources and using wider-bandwidth chirped nonlinear crystals. © 2024 Elsevier B.V.
  Accession Number: 20243516960710
• Record 216 of
  
  Title:439 MHz, 94 fs, low-threshold mode-locked all fiber ring laser
  
  Author(s):Huang, Xiwei(1); Guo, Xiaoxiao(1); Li, Xiaohui(1); Tang, Xu(1); Zhang, Rui(1); Zhang, Yan(1); Wang, Yishan(2); Zhao, Wei(2)
  Source:Optics and Laser Technology
  Volume: 179  Issue:   DOI: 10.1016/j.optlastec.2024.111336  Published: December 2024  
  Abstract:Pulsed fiber lasers with high repetition rates play a crucial role in applications such as high-efficiency processing and bio-optical imaging. However, many ring fiber mode-locked lasers primarily focus on shortening the cavity length to achieve high repetition rate pulse output. Attention is often directed towards the gain fiber and cavity structure, with less consideration given to the challenge of increasing mode-locking threshold power. In this study, we present a high-repetition-rate annular all-fiber laser system with dispersion management. Through strategic adjustment of the intracavity dispersion away from the near-zero dispersion region and careful control of the intracavity gain strength, we have successfully lowered the mode-locking threshold power. This approach can generate pulses with a repetition rate of 439.71 MHz and a mode-locking threshold power of approximately 600 mW. Following pulse compression, the achieved pulse width is 94.8 fs. Its time-bandwidth product is 0.368. To our knowledge, this represents the highest fundamental repetition rate currently attained using a ring all-fiber resonator, accompanied by the lowest mode-locking threshold. Our work introduces a ring fiber laser system characterized by a low mode-locking threshold and a high repetition rate, offering a valuable method for achieving higher fundamental repetition rate pulses. © 2024 Elsevier Ltd
  Accession Number: 20242516285052