Content of ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS in our journal

Published in last 1 year |  In last 2 years |  In last 3 years |  All Please wait a minute... For selected: Download citations EndNote Ris BibTeX Toggle thumbnails Select Microwave absorption properties regulation and bandwidth formula of oriented Y2Fe17N3-δ@SiO2/PU composite synthesized by reduction-diffusion method Hao Wang(王浩), Liang Qiao(乔亮), Zu-Ying Zheng(郑祖应), Hong-Bo Hao(郝宏波), Tao Wang(王涛), Zheng Yang(杨正), and Fa-Shen Li(李发伸) Chin. Phys. B, 2022, 31 (11): 114206.   DOI: 10.1088/1674-1056/ac81ac Abstract （571）   HTML （24）    PDF （3360KB）（374）       Knowledge map    As concepts closely related to microwave absorption properties, impedance matching and phase matching were rarely combined with material parameters to regulate properties and explore related mechanisms. In this work, reduction-diffusion method was innovatively applied to synthesize rare earth alloy Y$_{2}$Fe$_{17}$. In order to regulate the electromagnetic parameters of absorbers, the Y$_{2}$Fe$_{17}$N$_{3-\delta }$ particles were coated with silica (Y$_{2}$Fe$_{17}$N$_{3-\delta }$@SiO$_{2}$) and absorbers with different volume fractions were prepared. The relationship between impedance matching, matching thickness, and the strongest reflection loss peak (${\rm RL}_{\rm min}$) was presented obviously. Compared to the microwave absorption properties of Y$_{2}$Fe$_{17}$N$_{3-\delta }$/PU absorber, Y$_{2}$Fe$_{17}$N$_{3-\delta }$@SiO$_{2}$/PU absorbers are more conducive to the realization of microwave absorption material standards which are thin thickness, light weight, strong absorbing intensity, and broad bandwidth. Based on microwave frequency bands, the microwave absorption properties of the absorbers were analyzed and the related parameters were listed. As an important parameter related to perfect matching, reflection factor ($\sqrt {ărepsilon_{\rm r}/\mu_{\rm r}}$) was discussed combined with microwave amplitude attenuation. According to the origin and mathematical model of bandwidth, the formula of EAB (${\rm RL}<-10$ dB) was derived and simplified. The calculated bandwidths agreed well with experimental results. Select Exploring fundamental laws of classical mechanics via predicting the orbits of planets based on neural networks Jian Zhang(张健), Yiming Liu(刘一鸣), and Zhanchun Tu(涂展春) Chin. Phys. B, 2022, 31 (9): 094502.   DOI: 10.1088/1674-1056/ac8d88 Abstract （484）   HTML （21）    PDF （1058KB）（112）       Knowledge map    Neural networks have provided powerful approaches to solve various scientific problems. Many of them are even difficult for human experts who are good at accessing the physical laws from experimental data. We investigate whether neural networks can assist us in exploring the fundamental laws of classical mechanics from data of planetary motion. Firstly, we predict the orbits of planets in the geocentric system using the gate recurrent unit, one of the common neural networks. We find that the precision of the prediction is obviously improved when the information of the Sun is included in the training set. This result implies that the Sun is particularly important in the geocentric system without any prior knowledge, which inspires us to gain Copernicus' heliocentric theory. Secondly, we turn to the heliocentric system and make successfully mutual predictions between the position and velocity of planets. We hold that the successful prediction is due to the existence of enough conserved quantities (such as conservations of mechanical energy and angular momentum) in the system. Our research provides a new way to explore the existence of conserved quantities in mechanics system based on neural networks. Select Orthogonal-triangular decomposition ghost imaging Jin-Fen Liu(刘进芬), Le Wang(王乐), and Sheng-Mei Zhao(赵生妹) Chin. Phys. B, 2022, 31 (8): 084202.   DOI: 10.1088/1674-1056/ac5e99 Abstract （458）   HTML （0）    PDF （1262KB）（61）       Knowledge map    Ghost imaging (GI) offers great potential with respect to conventional imaging techniques. However, there are still some obstacles for reconstructing images with high quality, especially in the case that the orthogonal measurement matrix is impossible to construct. In this paper, we propose a new scheme based on the orthogonal-triangular (QR) decomposition, named QR decomposition ghost imaging (QRGI) to reconstruct a better image with good quality. In the scheme, we can change the randomly non-orthogonal measurement matrix into orthonormal matrix by performing QR decomposition in two cases. (1) When the random measurement matrix is square, it can be firstly decomposed into an orthogonal matrix $\bm Q$ and an upper triangular matrix $\bm R$. Then let the off-diagonal values of $\bm R$ equal to 0.0, the diagonal elements of $\bm R$ equal to a constant $k$, where $k$ is the average of all values of the main diagonal, so the resulting measurement matrix can be obtained. (2) When the random measurement matrix is with full rank, we firstly compute its transpose, and followed with above QR operation. Finally, the image of the object can be reconstructed by correlating the new measurement matrix and corresponding bucket values. Both experimental and simulation results verify the feasibility of the proposed QRGI scheme. Moreover, the results also show that the proposed QRGI scheme could improve the imaging quality comparing to traditional GI (TGI) and differential GI (DGI). Besides, in comparison with the singular value decomposition ghost imaging (SVDGI), the imaging quality and the reconstruction time by using QRGI are similar to those by using SVDGI, while the computing time (the time consuming on the light patterns computation) is substantially shortened. Select Optical fiber FBG linear sensing systems for the on-line monitoring of airborne high temperature air duct leakage Qinyu Wang(王沁宇), Xinglin Tong(童杏林), Cui Zhang(张翠), Chengwei Deng(邓承伟), Siyu Xu(许思宇), and Jingchuang Wei(魏敬闯) Chin. Phys. B, 2022, 31 (8): 084204.   DOI: 10.1088/1674-1056/ac5889 Abstract （407）   HTML （0）    PDF （1535KB）（92）       Knowledge map    Electrical sensing systems, such as those involving eutectic salt, are mostly used in connection to leakage from existing airborne high-temperature air-conducting pipelines. Such complex structured systems are susceptible to external interferences and, thus, cannot meet the increasingly strict monitoring needs of a complex air-conducting pipeline system of an aircraft. In view of this point, this paper studies an alternative sensor system based on a dense array fiber grating. To obtain a compact and light-weight airborne signal processing system, a field programmable gate array is used as the main control core that controls the output of the light source. The functions of pulse modulation, analog-to-digital conversion, data buffering and transmission are integrated into a single system, while the linear sensing monitoring is obtained by detecting the time-division and wavelength-division wavelength drift signals of the fiber Bragg grating array. Our experiments show that the spatial resolution of the linear sensing system approaches 5 cm, the temperature measurement accuracy reaches 2 ℃, the temperature measurement range is between 0-250 ℃, and the response time is within 4 s. Compared with the existing electrical monitoring systems, various monitoring indicators have been greatly improved and have broad application prospects. Select Experimental demonstration of a fast calibration method for integrated photonic circuits with cascaded phase shifters Junqin Cao(曹君勤), Zhixin Chen(陈志歆), Yaxin Wang(王亚新), Tianfeng Feng(冯田峰), Zhihao Li(李志浩), Zeyu Xing(邢泽宇), Huashan Li(李华山), and Xiaoqi Zhou(周晓祺) Chin. Phys. B, 2022, 31 (11): 114204.   DOI: 10.1088/1674-1056/ac8737 Abstract （404）   HTML （4）    PDF （1208KB）（180）       Knowledge map    With the development of research on integrated photonic quantum information processing, the integration level of the integrated quantum photonic circuits has been increasing continuously, which makes the calibration of the phase shifters on the chip increasingly difficult. For the calibration of multiple cascaded phase shifters that is not easy to be decoupled, the resources consumed by conventional brute force methods increase exponentially with the number of phase shifters, making it impossible to calibrate a relatively large number of cascaded phase shifters. In this work, we experimentally validate an efficient method for calibrating cascaded phase shifters that achieves an exponential increase in calibration efficiency compared to the conventional method, thus solving the calibration problem for multiple cascaded phase shifters. Specifically, we experimentally calibrate an integrated quantum photonic circuit with nine cascaded phase shifters and achieve a high-precision calibration with an average fidelity of 99.26%. Select Numerical investigation of the nonlinear spectral broadening aiming at a few-cycle regime for 10 ps level Nd-doped lasers Xi-Hang Yang(杨西杭), Fen-Xiang Wu(吴分翔), Yi Xu(许毅), Jia-Bing Hu(胡家兵), Pei-Le Bai(白培乐), Hai-Dong Chen(陈海东), Xun Chen(陈洵), and Yu-Xin Leng(冷雨欣) Chin. Phys. B, 2022, 31 (9): 094206.   DOI: 10.1088/1674-1056/ac685e Abstract （403）   HTML （2）    PDF （2058KB）（167）       Knowledge map    We present a cascaded nonlinear spectral broadening scheme for Nd-doped lasers, featuring with long pulse duration and high average power. This scheme is based on two multi-pass cells (MPCs) and one multiple-plate supercontinuum generation (MPSG), and the numerical investigation is driven by a home-made Nd-doped fiber laser with 12 ps pulse duration, 50 kHz repetition rate and 100 W average power. The MPC-based first two stages allow us to broaden the pulse spectrum to 4 nm and 43 nm respectively, and subsequently, the MPSG-based third stage allows us to reach 235 nm spectral bandwidth. This broadened spectrum can support a Fourier-transfer-limited pulse duration of 9.8 fs, which is shorter than three optical cycles. To the best of our knowledge, it is the first time to demonstrate the possibility of few-cycle pulses generation based on the 10 ps level Nd-doped lasers. Such few-cycle and high average power laser sources should be attractive and prospective, benefiting from the characteristics of structure compact, low-cost and flexibility. Select Dynamically tunable multiband plasmon-induced transparency effect based on graphene nanoribbon waveguide coupled with rectangle cavities system Zi-Hao Zhu(朱子豪), Bo-Yun Wang(王波云), Xiang Yan(闫香), Yang Liu(刘洋), Qing-Dong Zeng(曾庆栋), Tao Wang(王涛), and Hua-Qing Yu(余华清) Chin. Phys. B, 2022, 31 (8): 084210.   DOI: 10.1088/1674-1056/ac7e39 Abstract （389）   HTML （6）    PDF （7099KB）（138）       Knowledge map    A dynamically tunable multiband plasmon-induced transparency (PIT) effect in a series of rectangle cavities coupled with a graphene nanoribbon waveguide system is investigated theoretically and numerically by tuning the Fermi level of the graphene rectangle cavity. A single-PIT effect is realized using two different methods: one is the direct destructive interference between bright and dark modes, and the other is the indirect coupling through a graphene nanoribbon waveguide. Moreover, dual-PIT effect is obtained by three rectangle cavities side-coupled with a graphene nanoribbon waveguide. Results show that the magnitude of the dual-PIT window can be controlled between 0.21 and 0.74, and the corresponding group index is controlled between 143.2 and 108.6. Furthermore, the triple-PIT effect is achieved by the combination of bright-dark mode coupling and the cavities side-coupled with waveguide mechanism. Thus, sharp PIT windows can be formed, a high transmission is maintained between 0.51 and 0.74, and the corresponding group index is controlled between 161.4 and 115.8. Compared with previously proposed graphene-based PIT effects, the size of the introduced structure is less than 0.5 μm2. Particularly, the slow light effect is crucial in the current research. Therefore, a novel approach is introduced toward the realization of optical sensors, optical filters, and slow light and light storage devices with ultra-compact, multiband, and dynamic tunable. Select Multi-target ranging using an optical reservoir computing approach in the laterally coupled semiconductor lasers with self-feedback Dong-Zhou Zhong(钟东洲), Zhe Xu(徐喆), Ya-Lan Hu(胡亚兰), Ke-Ke Zhao(赵可可), Jin-Bo Zhang(张金波),Peng Hou(侯鹏), Wan-An Deng(邓万安), and Jiang-Tao Xi(习江涛) Chin. Phys. B, 2022, 31 (7): 074205.   DOI: 10.1088/1674-1056/ac4021 Abstract （389）   HTML （0）    PDF （2071KB）（147）       Knowledge map    We utilize three parallel reservoir computers using semiconductor lasers with optical feedback and light injection to model radar probe signals with delays. Three radar probe signals are generated by driving lasers constructed by a three-element laser array with self-feedback. The response lasers are implemented also by a three-element lase array with both delay-time feedback and optical injection, which are utilized as nonlinear nodes to realize the reservoirs. We show that each delayed radar probe signal can be predicted well and to synchronize with its corresponding trained reservoir, even when parameter mismatches exist between the response laser array and the driving laser array. Based on this, the three synchronous probe signals are utilized for ranging to three targets, respectively, using Hilbert transform. It is demonstrated that the relative errors for ranging can be very small and less than 0.6%. Our findings show that optical reservoir computing provides an effective way for applications of target ranging. Select Watt-level, green-pumped optical parametric oscillator based on periodically poled potassium titanyl phosphate with high extraction efficiency Hang-Hang Yu(俞航航), Zhi-Tao Zhang(张志韬), and Hong-Wen Xuan(玄洪文) Chin. Phys. B, 2022, 31 (12): 124203.   DOI: 10.1088/1674-1056/ac8346 Abstract （381）   HTML （0）    PDF （1029KB）（201）       Knowledge map    We report a compact, efficient optical parametric oscillator (OPO) based on a periodically poled potassium titanyl phosphate (PPKTP) crystal pumped by a 532 nm laser, which generated 1.51 W of average power at the signal wavelength of 709 nm with the pulse duration of ～ 1.0 ns. The extraction efficiency was up to 59%. To the best of our knowledge, this is the first report on Watt-level green-pumped PPKTP-based singly resonant oscillator OPO (SRO-OPO). The precise build-up time of OPO was determined to be 1.6 ns benefitting from the characteristic of twin-peak pulse profile of pump beam. The spectrum width of the idler was also measured to be 4.2 nm with the central wavelength of 2134 nm at 0.2 nm spectral resolution of optical spectrum analyzer. In addition, the beam quality of M2 < 1.9 of generated signal exhibits a good consistency with M2 < 1.5 for the pump source. Select Spatio-spectral dynamics of soliton pulsation with breathing behavior in the anomalous dispersion fiber laser Ying Han(韩颖), Bo Gao(高博), Jiayu Huo(霍佳雨), Chunyang Ma(马春阳), Ge Wu(吴戈),Yingying Li(李莹莹), Bingkun Chen(陈炳焜), Yubin Guo(郭玉彬), and Lie Liu(刘列) Chin. Phys. B, 2022, 31 (7): 074208.   DOI: 10.1088/1674-1056/ac4023 Abstract （364）   HTML （0）    PDF （3236KB）（72）       Knowledge map    We have numerically and experimentally observed the soliton pulsation with obvious breathing behavior in the anomalous fiber laser mode-locked by a nonlinear polarization rotation technique. The numerical study of the soliton pulsation with breathing behavior was analyzed through the split-step Fourier method at first, and it was found that the phase difference caused by the polarization controller would affect the breathing characteristics. Then, taking advantage of the dispersive Fourier transform technique, we confirmed the breathing characteristic of soliton pulsation in the same fiber laser as the simulation model experimentally. These results complement the research on the breathing characteristic of soliton pulsation. Select High sensitivity dual core photonic crystal fiber sensor for simultaneous detection of two samples Pibin Bing(邴丕彬), Guifang Wu(武桂芳), Qing Liu(刘庆), Zhongyang Li(李忠洋),Lian Tan(谭联), Hongtao Zhang(张红涛), and Jianquan Yao(姚建铨) Chin. Phys. B, 2022, 31 (8): 084208.   DOI: 10.1088/1674-1056/ac4a68 Abstract （361）   HTML （0）    PDF （865KB）（83）       Knowledge map    The optical control ability of photonic crystal fiber (PCF) is a distinctive property suitable for improving sensing and plasma performance. This article proposes a dual-core D-channel PCF sensor that can detect two samples simultaneously, which effectively solves the problems of coating difficulty and low wavelength sensitivity. The PCF has four layers of air holes, which dramatically reduces the optical fiber loss and is more conducive to the application of sensors in actual production. In addition, by introducing dual cores on the upper and lower sides of the central air hole, reducing the spacing between the core and the gold nanolayer, a stronger evanescent field can be generated in the cladding air hole. The optical fiber sensor can detect the refractive index of two samples simultaneously with a maximum sensitivity of 21300 nm/RIU. To the best of our knowledge, the sensitivity achieved in this work is the highest sensitivity with the dual sample synchronous detection sensors. The detection range of the refraction index is 1.35-1.41, and the resolution of the sensor is 4.695×10-6. Overall, the sensor will be suitable for medical detection, organic chemical sensing, analyte detection, and other fields. Select Numerical simulation of the thermal non-equilibrium flow-field characteristics of a hypersonic Apollo-like vehicle Minghao Yu(喻明浩)†, Zeyang Qiu(邱泽洋), Bo Lv(吕博), and Zhe Wang(王哲) Chin. Phys. B, 2022, 31 (9): 094702.   DOI: 10.1088/1674-1056/ac6ed6 Abstract （361）   HTML （0）    PDF （7678KB）（114）       Knowledge map    In order to investigate the relationship between the flow-field parameters outside the vehicle and the altitude, this paper takes the Atmospheric Reentry Demonstrator (ARD) with an angle of attack of -20° as the research object and adopts a two-temperature model coupled with the shear-stress transport k-ω turbulence model to focus on the variation of flow-field parameters including flow-field pressure, Mach number and temperature with the reentry altitude. It is found that the flow-field high-pressure region and low-Mach region both appear in the shock layer near the head of the ARD, while the maximum pressure of the surface appears on the windward side of the ARD's head with a toroidal distribution, and the numerical magnitude is inversely proportional to the radius of the torus. With fluid through the shoulder of the ARD flow expansion plays a dominant role, the airflow velocity increases, the Mach number of the windward side of the rear cone increases and the flow-field pressure and surface pressure rapidly decrease. When the fluid passes through the shock layer, the translational-rotation temperature will increase before the vibration-electron temperature, there is a thermal non-equilibrium effect and the two temperatures will rapidly decrease again when approaching the surface of the ARD due to the existence of temperature gradient. At the same time, both the windward side of the shoulder and the back cover of the ARD suffer from a large thermal load and require thermal protection. Select Full color ghost imaging by using both time and code division multiplexing technologies Le Wang(王乐), Hui Guo(郭辉), and Shengmei Zhao(赵生妹) Chin. Phys. B, 2022, 31 (11): 114202.   DOI: 10.1088/1674-1056/ac7e33 Abstract （357）   HTML （0）    PDF （1058KB）（88）       Knowledge map    We propose a new full color ghost imaging scheme using both time and code division multiplexing technologies. In the scheme, the speckle patterns of three colors (red, green and blue) are modulated with different time slots and codes. The light intensity is sampled by one bucket detector. Then based on the modulated time slots and codes, we can effectively and simultaneously extract three detection component signals corresponding to three color components of objects from the sampling signal of the bucket detector. Finally, three component images resulting from the three component detection signals can be synthesized into a full color image. The experimental results verify the feasibility of our scheme under the limit of the number of time slots and codes. Moreover, our scheme reduces the number of bucket detectors and can realize high quality imaging even in a noisy environment. Select Nonlinear inversion of ultrasonic guided waves for in vivo evaluation of cortical bone properties Xiaojun Song(宋小军), Tiandi Fan(樊天地), Jundong Zeng(曾俊冬), Qin-Zhen Shi(石勤振), Qiong Huang(黄琼), Meilin Gu(顾美琳), Petro Moilanen, Yi-Fang Li(李义方), and Dean Ta(他得安) Chin. Phys. B, 2022, 31 (7): 074301.   DOI: 10.1088/1674-1056/ac3eca Abstract （355）   HTML （3）    PDF （1009KB）（67）       Knowledge map    Ultrasonic guided waves (UGWs), which propagate throughout the entire thickness of cortical bone, are attractive for the early diagnosis of osteoporosis. However, this is challenging due to the impact of soft tissue and the inherent difficulties related to multiparametric inversion of cortical bone quality factors, such as cortical thickness and bulk wave velocity. Therefore, in this research, a UGW-based multi-parameter inversion algorithm is developed to predict strength-related factors. In simulation, a free plate (cortical bone) and a bilayer plate (soft tissue and cortical bone) are used to validate the proposed method. The inversed cortical thickness (CTh), longitudinal velocity (VL) and transverse velocity (VT) are in accordance with the true values. Then four bovine cortical bone plates were used in in vitro experiments. Compared with the reference values, the relative errors for cortical thickness were 3.96%, 0.83%, 2.87%, and 4.25%, respectively. In the in vivo measurements, UGWs are collected from the tibias of 10 volunteers. The theoretical dispersion curves depicted by the estimated parameters (VT, VL, CTh) match well with the extracted experimental ones. In comparison with dual-energy x-ray absorptiometry, our results show that the estimated transverse velocity and cortical thickness are highly sensitive to osteoporosis. Therefore, these two parameters (CTh and VT) of long bones have potential to be used for diagnosis of bone status in clinical applications. Select Wave mode computing method using the step-split Padé parabolic equation Chuan-Xiu Xu(徐传秀) and Guang-Ying Zheng(郑广赢) Chin. Phys. B, 2022, 31 (9): 094301.   DOI: 10.1088/1674-1056/ac6940 Abstract （354）   HTML （1）    PDF （4777KB）（143）       Knowledge map    Models based on a parabolic equation (PE) can accurately predict sound propagation problems in range-dependent ocean waveguides. Consequently, this method has developed rapidly in recent years. Compared with normal mode theory, PE focuses on numerical calculation, which is difficult to use in the mode domain analysis of sound propagation, such as the calculation of mode phase velocity and group velocity. To broaden the capability of PE models in analyzing the underwater sound field, a wave mode calculation method based on PE is proposed in this study. Step-split Padé PE recursive matrix equations are combined to obtain a propagation matrix. Then, the eigenvalue decomposition technique is applied to the matrix to extract sound mode eigenvalues and eigenfunctions. Numerical experiments on some typical waveguides are performed to test the accuracy and flexibility of the new method. Discussions on different orders of Padé approximant demonstrate angle limitations in PE and the missing root problem is also discussed to prove the advantage of the new method. The PE mode method can be expanded in the future to solve smooth wave modes in ocean waveguides, including fluctuating boundaries and sound speed profiles. Select Enhancing performance of GaN-based LDs by using GaN/InGaN asymmetric lower waveguide layers Wen-Jie Wang(王文杰), Ming-Le Liao(廖明乐), Jun Yuan(袁浚), Si-Yuan Luo(罗思源), and Feng Huang(黄锋) Chin. Phys. B, 2022, 31 (7): 074206.   DOI: 10.1088/1674-1056/ac597c Abstract （342）   HTML （0）    PDF （607KB）（68）       Knowledge map    The effects of GaN/InGaN asymmetric lower waveguide (LWG) layers on photoelectrical properties of InGaN multiple quantum well laser diodes (LDs) with an emission wavelength of around 416 nm are theoretically investigated by tuning the thickness and the indium content of InGaN insertion layer (InGaN-IL) between the GaN lower waveguide layer and the quantum wells, which is achieved with the Crosslight Device Simulation Software (PIC3D, Crosslight Software Inc.). The optimal thickness and the indium content of the InGaN-IL in lower waveguide layers are found to be 300 nm and 4%, respectively. The thickness of InGaN-IL predominantly affects the output power and the optical field distribution in comparison with the indium content, and the highest output power is achieved to be 1.25 times that of the reference structure (symmetric GaN waveguide), which is attributed to the reduced optical absorption loss as well as the concentrated optical field nearby quantum wells. Furthermore, when the thickness and indium content of InGaN-IL both reach a higher level, the performance of asymmetric quantum wells LDs will be weakened rapidly due to the obvious decrease of optical confinement factor (OCF) related to the concentrated optical field in the lower waveguide. Select Design of an all-dielectric long-wave infrared wide-angle metalens Ning Zhang(张宁), Qingzhi Li(李青芝), Jun Chen(陈骏), Feng Tang(唐烽),Jingjun Wu(伍景军), Xin Ye(叶鑫), and Liming Yang(杨李茗) Chin. Phys. B, 2022, 31 (7): 074212.   DOI: 10.1088/1674-1056/ac4026 Abstract （337）   HTML （0）    PDF （14391KB）（200）       Knowledge map    Optical metasurfaces are two-dimensional arrays of nano-scatterers that modify optical wavefronts at subwavelength spatial resolution. They achieve the effect of focusing through phase control under a subwavelength scale, and are called metalenses. They are poised to revolutionize optics by enabling complex low-cost systems. However, there are severe monochromatic aberrations in the metasurfaces. In this paper, the coma of the long-wave infrared optical system is eliminated through a single-layer metasurface. By changing the phase function, this metalens has a numerical aperture of 0.89, a focal length of 150 μm and a field of view of 120° (0.4@60 line pairs/mm) that enables diffraction-limited monochromatic imaging along the focal plane at a wavelength of 10.6 μm. The designed metasurface maintains a favorable value of the modulation transfer function at different angles. This equipment can be widely used in imaging and industrial processing. Select Dual-function terahertz metasurface based on vanadium dioxide and graphene Jiu-Sheng Li(李九生)† and Zhe-Wen Li(黎哲文) Chin. Phys. B, 2022, 31 (9): 094201.   DOI: 10.1088/1674-1056/ac5884 Abstract （333）   HTML （3）    PDF （2531KB）（147）       Knowledge map    A dual-function terahertz metasurface based on VO2 and graphene is proposed in this paper. It consists of a gold layer embedded with VO2 patches, a SiO2 spacer layer, a VO2 layer, graphene and a SiO2 spacer substrate. When the bottom VO2 layer is in the metallic state, the designed metasurface can achieve absorption. When the top VO2 patches are in the metallic state, the proposed metasurface can be used as a single-band absorber with terahertz absorptance of 99.7% at 0.736 THz. When the top VO2 patches are in the insulating state, the designed structure behaves as a dual-band absorber with an absorptance of 98.9% at 0.894 THz and 99.9% at 1.408 THz. In addition, the absorber is polarization insensitive and keeps good performance at large angles of incidence. When the bottom VO2 is in an insulating state, the metasurface shows electromagnetically induced transparency. The transparent window can be dynamically regulated by controlling the chemical potential of graphene. The proposed metasurface exhibits the advantages of terahertz absorption, electromagnetically induced transparency and dynamic control, which provides more options for the design of terahertz devices in the future. Select Imaging a periodic moving/state-changed object with Hadamard-based computational ghost imaging Hui Guo(郭辉), Le Wang(王乐), and Sheng-Mei Zhao(赵生妹) Chin. Phys. B, 2022, 31 (8): 084201.   DOI: 10.1088/1674-1056/ac6498 Abstract （333）   HTML （0）    PDF （1049KB）（34）       Knowledge map    We propose a method for imaging a periodic moving/state-changed object based on computational ghost imaging with Hadamard speckle patterns and a slow bucket detector, named as PO-HCGI. In the scheme, speckle patterns are produced from a part of each row of a Hadamard matrix. Then, in each cycle, multiple speckle patterns are projected onto the periodic moving/state-changed object, and a bucket detector with a slow sampling rate records the total intensities reflected from the object as one measurement. With a series of measurements, the frames of the moving/state-changed object can be obtained directly by the second-order correlation function based on the Hadamard matrix and the corresponding bucket detector measurement results. The experimental and simulation results demonstrate the validity of the PO-HCGI. To the best of our knowledge, PO-HCGI is the first scheme that can image a fast periodic moving/state-changed object by computational ghost imaging with a slow bucket detector. Select A 45-μJ, 10-kHz, burst-mode picosecond optical parametric oscillator synchronously pumped at a second harmonic cavity Chao Ma(马超), Ke Liu(刘可), Yong Bo(薄勇), Zhi-Min Wang(王志敏), Da-Fu Cui(崔大复), and Qin-Jun Peng(彭钦军) Chin. Phys. B, 2022, 31 (8): 084206.   DOI: 10.1088/1674-1056/ac6016 Abstract （333）   HTML （0）    PDF （1844KB）（239）       Knowledge map    A novel high-energy picosecond optical parametric oscillator (OPO) was realized by placing an OPO in a second-harmonic (SH) cavity. In a proof-of-principle experiment, we demonstrated excellent burst energy of 45 μJ for the OPO signal at 900 nm that operates at a pulse repetition rate of 10 kHz and a pulse width of 46.8 ps. The beam quality was measured as $M^{2}_{x} = 1.44$ and $M^{2}_{y} = 1.40$ in the orthogonal directions, corresponding to an average beam factor $M^{2} = 1.42$. So far, this study is the first to investigate high-energy ps OPO synchronously pumped in a second-harmonic cavity. page Page 1 of 14 Total 278 records First page Prev page Next page Last page