分类： 物理学 >> 交叉学科物理及相关领域的科学与技术 提交时间： 2025-02-25
摘要： An optimal iterated function system (OIFS) based fast fractal decoding method was proposed inthis study. Based on the minimum domain block set (MDBS) which can effectively remove redundantdomain blocks and accelerate the decoding process, we found that there still exist redundant domain blocksin MDBS, and the decoding process can be accelerated further. By introducing the definition of minimumiterated function system (MIFS) and multilevel MIFSs, the redundant domain blocks can be removed levelby level, and finally the optimal iterated function system (OIFS) can be obtained. Before the first iterationat decoding phase, the OIFS can be firstly established by removing the redundant domain blocks outsideOIFS. Then, only the range blocks inside OIFS were reconstructed from the first to penultimate iterations,and the computations of reconstructing the range blocks outside OIFS can be saved. Finally, the wholeimage were reconstructed in the last iteration. Three fractal coding methods were adopted to assess theperformance of the proposed method. Experimental results show that about 1%-10% of total computationsin decoding process can be further saved regarding the MDBS based method.
分类： 物理学 >> 交叉学科物理及相关领域的科学与技术 提交时间： 2024-03-23
摘要： To predict the fractal decoded image quality more efficiently, an accumulated collage error coefficient (ACEC) based method was proposed in this study. Firstly, the definition of ACEC was introduced to describe the relationship among the upper bound, lower bound, and actual value of theaccumulated collage error of all range blocks. Moreover, the definition and monotonicity of the relative error of ACEC were also defined and discussed. While the relative error of ACEC reaches a relatively small value, the average collage error (ACER) can be estimated approximately, and then the encoding process can be terminated to directly predict the peak signal-to-noise ratio (PSNR) quality of decoded images. Experimental results show that compared with the previous method, the proposed method can predict the decoded image quality more accurately with fewer computations.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Non-Hermitian photonic lattices combine the peculiar consequences of energy non-conservation with the physics of bandstructures, giving rise to a variety of exotic properties not found in conventional materials or photonic metamaterials. In this tutorial, we introduce the key concepts in the design and implementation of non-Hermitian photonic lattices, including the general features of non-Hermitian lattice Hamiltonians and their bandstructures, the role of non-Hermitian lattice symmetries, and the topological chracterization of non-Hermitian bandstructures. We survey several important non-Hermitian lattice designs, as well as the photonic platforms on which they can be realized. Finally, we discuss the possibilities for future developments in the field.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： In this study, we propose and experimentally demonstrate a novel kind of Tamm plasmon topological superlattice (TTS) by engineering Tamm photonic crystals (TPCs) belonging to a different class of topology. Utilizing specifically designed double-layer metasurfaces etching on planar multilayered photonic structures, the TPC that supports the Tamm plasmon photonic bandgap is realized in the visible regime. Through the coupling of topological interface states existing between different TPCs, hybrid topological interface states of Tamm plasmon, called supermodes, are obtained that can be fully described by a tight-binding model. Meanwhile, we can achieve a tunable bandwidth of supermodes via varying the etching depth difference between double-layer metasurfaces. We show that the bandwidth decreases with the increase of etching depth difference, resulting in a nearly flat dispersion of supermodes with strong localization regardless of excitation angles. All the results are experimentally verified by measuring angular-resolved reflectance spectra. The TTS and supermodes proposed here open a new pathway for the manipulation of Tamm plasmons, based on which various promising applications such as integrated photonic devices, optical sensing, and enhancing light-matter interactions can be realized.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： The recent discovery of higher-order topology has largely enriched the classification of topological materials. Theoretical and experimental studies have unveiled various higher-order topological insulators that exhibit topologically protected corner or hinge states. More recently, higher-order topology has been introduced to topological semimetals. Thus far, realistic models and experimental verifications on higher-order topological semimetals are still very limited. Here, we design and demonstrate a three-dimensional photonic crystal that realizes a higher-order Dirac semimetal phase. Numerical results on the band structure show that the designed three-dimensional photonic crystal is able to host two four-fold Dirac points, the momentum-space projections of which at an edge are connected by higher-order hinge states. The higher-order topology can be characterised with the calculation of the \chi(6) topological invariant at different values of k_z. An experiment at microwave frequencies is also presented to measure the hinge state dispersion. Our work demonstrates the physical realization of a higher-order Dirac semimetal phase and paves the way to exploring higher-order topological semimetals phases in three-dimensional photonic systems.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Topological photonics, featured by stable topological edge states resistant to perturbations, has been utilized to design robust integrated devices. Here, we present a study exploring the intriguing topological rotated Weyl physics in a 3D parameter space based on quaternary waveguide arrays on lithium niobate-on-insulator (LNOI) chips. Unlike previous works that focus on the Fermi arc surface states of a single Weyl structure, we can experimentally construct arbitrary interfaces between two Weyl structures whose orientations can be freely rotated in the synthetic parameter space. This intriguing system was difficult to realize in usual 3D Weyl semimetals due to lattice mismatch. We found whether the interface can host gapless topological interface states (TISs) or not, is determined by the relative rotational directions of the two Weyl structures. In the experiment, we have probed the local characteristics of the TISs through linear optical transmission and nonlinear second harmonic generation. Our study introduces a novel path to explore topological photonics on LNOI chips and various applications in integrated nonlinear and quantum optics.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： There are two prominent applications of the mathematical concept of topology to the physics of materials: band topology, which classifies different topological insulators and semimetals, and topological defects that represent immutable deviations of a solid lattice from its ideal crystalline form. While these two classes of topological phenomena have generally been treated as separate topics, recent experimental advancements have begun to probe their intricate and surprising interactions, in real materials as well as synthetic metamaterials. Topological lattice defects in topological materials offer a platform to explore a diverse range of novel phenomena, such as topological pumping via topological defects, embedded topological phases, synthetic dimensions, and non-Hermitian skin effects. In this Perspective, we survey the developments in this rapidly moving field, and give an outlook of its impact on materials science and applications.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： The past decade has seen a proliferation of topological materials for both insulators and semimetals in electronic systems and classical waves. Topological semimetals exhibit topologically protected band degeneracies, such as nodal points and nodal lines. Dirac nodal line semimetals (DNLS), which own four-fold line degeneracy, have drawn particular attention. DNLSs have been studied in electronic systems but there is no photonic DNLS. Here in this work, we provide a new mechanism which is unique for photonic systems to investigate a stringent photonic DNLS. When truncated, the photonic DNLS exhibits double-bowl states (DBS), which comprises two sets of perpendicularly polarized surface states. In sharp contrast to nondegenerate surface states in other photonic systems, here the two sets of surface states are almost degenerate over the whole spectrum range. The DBS and the bulk Dirac nodal ring (DNR) dispersion along the relevant directions, are experimentally resolved.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Besides a linear momentum, optical fields carry an angular momentum (AM), which have two intrinsic components: one is spin angular momentum (SAM) related to the polarization state of the field, and the other is orbital angular momentum (OAM) caused by the helical phase due to the existence of topological azimuthal charge. The two AM components of the optical field may not be independent of each other, and the Spin-to-Orbital AM conversion (STOC) under focusing will create a spin-dependent optical vortex in the longitudinal filed. Here we demonstrate a new mechanism (or novel way, new way, specific process) for the STOC based on a radial intensity gradient. The radial phase provides an effective way to control the local AM density, which induce counterintuitive orbital motion of isotropic particles in optical tweezers without intrinsic OAM. Our work not only provides fundamental insights into the spin-orbit interaction of light, but also push towards possible applications in optical micro-manipulation.
分类： 物理学 >> 地球物理学、天文学和天体物理学 提交时间： 2024-01-09 合作期刊: 《Research in Astronomy and Astrophysics》
摘要： Black widows (BWs) are millisecond pulsars ablating their companion stars. The out-flowing material from the companion can block the radio emission of the pulsar, resulting in eclipses. In this paper, we construct a model for the radio eclipse by calculating the geometry of the bow shock between the winds of the pulsar and companion, where the shock shapes the eclipsing medium but had not been described in detail in previous works. The model is further used to explain the variations of the flux density and dispersion measure of three BW pulsars (i.e., PSR B1957+20, J2055+3829, and J2051−0827) detected by the Five-hundred-meter Aperture Spherical radio Telescope. Consequently, we constrained the parameters of the three BW systems such as the inclination angles and true anomalies of the observer as well as the mass-loss rates and wind velocity of the companion stars. With the help of these constraints, it is expected that magnetic fields of companion stars and even masses of pulsars could further be determined as some extra observation can be achieved in the future.
分类： 核科学技术 >> 辐射物理与技术 提交时间： 2025-02-14
Haisheng YU
Jianqiu ZHU
Jiaxing WU
Yaotian GUO
Song LI
Yan ZHANG
Xiaoxu QIAN
Jian-Qiang WANG
Linjuan ZHANG
摘要： This paper describes the design and performance of a laboratory-based tender X-ray spectrometer for X-ray absorption spectroscopy. The system enables effective absorption spectra measurement within the 2.0-9.0 keV range using Rowland circle geometry: it covers the K edge of 3d transition metals, the L edge of lanthanides and the M edge of actinides. The spectrometer is configured with a 500 mm diameter Rowland circle and integrates a 250 W liquid metal-jet X-ray source, a spherical bent crystal analyzer, and an energy-resolving silicon drift detector. The X-ray source is installed outside the vacuum chamber and remains fixed, while the analyzer crystals and detector are adjusted to change the Bragg angle while maintaining the Rowland condition. The energy resolution is 0.36 - 1.30 eV at 2.0 - 9.0 keV, and the monochromatic flux is approximately 5×105 counts/s at 7040 eV. This paper highlights the main characteristics of the spectrometer and demonstrates its capabilities through selected experimental examples. The successful development of this spectrometer especially facilitates research on actinide elements, which are often constrained in synchrotron radiation experiments due to their radioactivity, thus fostering advancements in related nuclear energy fields.
分类： 物理学 >> 核物理学 提交时间： 2023-11-16
Hua Ai
Xinmei Yang
Huajian Liu
Bingchuan Chen
Ling Han
Hua Sun
Yanjun Chen
Yuan Qian
Jian-Qiang Wang
摘要： The corrosion behavior of 316H stainless steel (SS) in the impure and purified NaCl-KCl-MgCl2 salt was investigated at 700 C . Results indicate that the main deleterious impurity induced corrosion in the impure salt was the absorbed moisture, present in the form of MgCl26H2O. 316H SS occurred severe intergranular corrosion with a corrosion depth of 130 m for 1000 h in the impure NaCl-KCl-MgCl2 salt. In contrast, the purification treatment of molten chloride salt by the dissolved Mg metal can remove the absorbed moisture, and the corresponding reactions were also discussed. As a result, the corrosiveness of NaCl-KCl-MgCl2 salt is reduced significantly. 316H SS occurred slight uniform corrosion with a depth of less than 5 m for 3000 h in the purified NaCl-KCl-MgCl2 salt.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Imaging Science Subsystem (ISS) mounted on the Cassini spacecraft has taken a lot of images, which provides an important source of high-precision astrometry of some planets and satellites. However, some of these images are degraded by trailed stars. Previously, these degraded images cannot be used for astrometry. In this paper, a new method is proposed to detect and compute the centers of these trailed stars automatically. The method is then performed on the astrometry of ISS images with trailed stars. Finally, we provided 658 astrometric positions between 2004 and 2017 of several satellites that include Enceladus, Dione, Tethys, Mimas and Rhea. Compared with the JPL ephemeris SAT427, the mean residuals of these measurements are 0.11 km and 0.26 km in right ascension and declination, respectively. Their standard deviations are 1.08 km and 1.37 km, respectively. The results show that the proposed method performs astrometric measurements of Cassini ISS images with trailed stars effectively.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Imaging Science Subsystem (ISS) mounted on the Cassini spacecraft has taken a lot of images, which provides an important source of high-precision astrometry of some planets and satellites. However, some of these images are degraded by trailed stars. Previously, these degraded images cannot be used for astrometry. In this paper, a new method is proposed to detect and compute the centers of these trailed stars automatically. The method is then performed on the astrometry of ISS images with trailed stars. Finally, we provided 658 astrometric positions between 2004 and 2017 of several satellites that include Enceladus, Dione, Tethys, Mimas and Rhea. Compared with the JPL ephemeris SAT427, the mean residuals of these measurements are 0.11 km and 0.26 km in right ascension and declination, respectively. Their standard deviations are 1.08 km and 1.37 km, respectively. The results show that the proposed method performs astrometric measurements of Cassini ISS images with trailed stars effectively.
分类： 光学 >> 量子光学 提交时间： 2023-02-24
Zhen Wang
Qiang Wang
Hui Zhang
Simone Borri
Iacopo Galli
Angelo Sampaolo
Pietro Patimisco
Vincenzo Luigi Spagnolo
Paolo De Natale
Wei Ren
摘要： Photoacoustic spectroscopy (PAS) based gas sensors with high sensitivity, wide dynamic range, low cost, and small footprint are desirable across a broad range of applications in energy, environment, safety, and public health. However, most works have focused on either acoustic resonator to enhance acoustic wave or optical resonator to enhance optical wave. Herein, we develop a gas sensor based on doubly resonant PAS in which the acoustic and optical waves are simultaneously enhanced using combined optical and acoustic resonators in a centimeter-long configuration. Not only the lower detection limit is enhanced by the double standing waves, but also the upper detection limit is expanded due to the short resonators. As an example, we developed a sensor by detecting acetylene (C2H2), achieving a noise equivalent absorption of 5.7*10-13 cm-1 and a dynamic range of eight orders. Compared to the state-of-the-art PAS gas sensors, the developed sensor increases the sensitivity by two orders of magnitude and extends the dynamic range by three orders of magnitude. Besides, a laser-cavity-molecule locking strategy is proposed to provide additional flexibility of fast gas detection.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
Sixin Zhu
Dan Li
Jianlu Wang
Qiang Wang
Yongpeng Wu
Liang Xiong
Zhangfeng Jiang
Huihong Lin
Zhirui Gong
Qi Qin
Xingjun Wang
摘要： In this work, a hybrid integration of few-layer transition metal dichalcogenides (TMDCs) and ferroelectric polymer is designed to achieve passive control of optical properties in-situ. The electrical polarization in ferroelectric P(VDF-TrFE) polymer can regulate the photoluminescence (PL) in few-layer TMDCs. The total PL intensity is substantially suppressed or enhanced under opposite polarization in bilayer WSe2. This is because electrons transfer between valley K and {\Lambda} in the conduction band induced by the built-in electric field in P(VDF-TrFE) polymer. This charge transfer further changes the competing dynamics between direct and indirect exciton recombination path and overall optical radiation efficiency. We also illustrate that the engineered PL originates from external electric field dependent transferred electron effect. The theoretical result matches the experimental data well. This work demonstrates a device platform in which passive regulation is achieved using 2D TMDCs modulated by polarized ferroelectric materials.
分类： 天文学 >> 天文学 提交时间： 2024-08-14 合作期刊: 《Research in Astronomy and Astrophysics》
摘要： For real-time processing of ultra-wide bandwidth low-frequency pulsar baseband data, we designed and implemented an ultra-wide bandwidth low-frequency pulsar data processing pipeline (UWLPIPE) based on the shared ringbuffer and GPU parallel technology. UWLPIPE runs on the GPU cluster and can simultaneously receive multiple 128 MHz dual-polarization VDIF data packets preprocessed by the front-end FPGA. After aligning the dual-polarization data, multiple 128M subband data are packaged into PSRDADA baseband data or multi-channel coherent dispersion filterbank data, and multiple subband filterbank data can be spliced into wideband data after time alignment. We used the Nanshan 26 m radio telescope with the L-band receiver at 964 ∼ 1732 MHz to observe multiple pulsars. Finally, we processed the data using DSPSR software, and the results showed that each subband could correctly fold out the pulse profile, and the wideband pulse profile accumulated by multiple subbands could be correctly aligned.
分类： 物理学 >> 地球物理学、天文学和天体物理学 提交时间： 2024-02-01 合作期刊: 《Research in Astronomy and Astrophysics》
摘要： To address the problem of real-time processing of ultra-wide bandwidth pulsar baseband data, we designed and implemented a pulsar baseband data processing algorithm (PSRDP) based on GPU parallel computing technology. PSRDP can perform operations such as baseband data unpacking, channel separation, coherent dedispersion, Stokes detection, phase and folding period prediction, and folding integration in GPU clusters. We tested the algorithm using the J0437-4715 pulsar baseband data generated by the CASPSR and Medusa backends of the Parkes, and the J0332+5434 pulsar baseband data generated by the self-developed backend of the NanShan Radio Telescope. We obtained the pulse profiles of each baseband data. Through experimental analysis, we have found that the pulse profiles generated by the PSRDP algorithm in this paper are essentially consistent with the processing results of Digital Signal Processing Software for Pulsar Astronomy (DSPSR), which verified the effectiveness of the PSRDP algorithm. Furthermore, using the same baseband data, we compared the processing speed of PSRDP with DSPSR, and the results showed that PSRDP was not slower than DSPSR in terms of speed. The theoretical and technical experience gained from the PSRDP algorithm research in this article lays a technical foundation for the real-time processing of QTT (Qi Tai radio Telescope) ultra-wide bandwidth pulsar baseband data.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
Gui-Geng Liu
Zhen Gao
Peiheng Zhou
Qiang Wang
Yuan-Hang Hu
Maoren Wang
Chengqi Liu
Xiao Lin
Shengyuan A. Yang
Yihao Yang
Yidong Chong
Baile Zhang
摘要： Weyl semimetals are gapless three-dimensional (3D) phases whose bandstructures contain Weyl point (WP) degeneracies. WPs carry topological charge and can only be eliminated by mutual annihilation, a process that generates the various topologically distinct 3D insulators. Time reversal (T) symmetric Weyl phases, containing a minimum of four WPs, have been extensively studied in real materials, photonic metamaterials, and other systems. Weyl phases with a single WP pair - the simplest configuration of WPs - are more elusive as they require T-breaking. Here, we implement a microwave-scale gyromagnetic 3D photonic crystal, and use field-mapping experiments to track a single pair of ideal WPs whose momentum space locations depend strongly on the biasing magnetic field. By continuously varying the field strength, we observe the annihilation of the WPs, and the formation of a 3D Chern insulator, a previously unrealised member of the family of 3D topological insulators (TIs). Surface measurements show, in unprecedented detail, how the Fermi arc states connecting the WPs evolve into TI surface states.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Cheng-Min Zhang
Xiang-Han Cui
Di Li
De-Hua Wang
Shuang-Qiang Wang
Na Wang
Jian-Wei Zhang
Bo Peng
Wei-Wei Zhu
Yi-Yan Yang
Yuan-Yue Pan
摘要： The evolutions of a neutron star's rotation and magnetic field (B-field) have remained unsolved puzzles for over half a century. We ascribe the rotational braking torques of pulsar to both components, the standard magnetic dipole radiation (MDR) and particle wind flow ( MDR + Wind, hereafter named MDRW), which we apply to the Crab pulsar (B0531 + 21), the only source with a known age and long-term continuous monitoring by radio telescope. Based on the above presumed simple spin-down torques, we obtain the exact analytic solution on the rotation evolution of the Crab pulsar, together with the related outcomes as described below: (1) unlike the constant characteristic B-field suggested by the MDR model, this value for the Crab pulsar increases by a hundred times in 50~kyr while its real B-field has no change; (2) the rotational braking index evolves from \sim3 to 1 in the long-term, however, it drops from 2.51 to 2.50 in \sim45 years at the present stage, while the particle flow contributes approximately 25% of the total rotational energy loss rate; (3) strikingly, the characteristic age has the maximum limit of \sim10 kyr, meaning that it is not always a good indicator of real age. Furthermore, we discussed the evolutionary path of the Crab pulsar from the MDR to the wind domination by comparing it with the possible wind braking candidate pulsar PSR J1734-3333.
点击量
通过
点击量
下载量
评论
待评议
