The laser beam divergence angle is one of the important parameters to evaluate the quality of the laser beam.It can not only accurately indicate the nature of the beam divergence when the laser beam is transmitted ove...The laser beam divergence angle is one of the important parameters to evaluate the quality of the laser beam.It can not only accurately indicate the nature of the beam divergence when the laser beam is transmitted over a long distance,but also objectively evaluate the performance of the laser system.At present,lidar has received a lot of attention as a core component of environment awareness technology.Micro-electromechanical system(MEMS)micromirror has become the first choice for three-dimensional imaging lidar because of its small size and fast scanning speed.However,due to the small size of the MEMS micromirror,the lidar scanning system has a small field of view(FOV).In order to achieve a wide range of scanning imaging,collimating optical system and wide-angle optical system are generally added to the system.However,due to the inherent properties of the optical lens,it is impossible to perfect the imaging,so the effects of collimating and expanding the beam will be different at different angles.This article aims to propose a measurement system that dynamically measures the divergence angles of MEMS scanning lidar beams in different fields of view to objectively evaluate the performances of scanning lidar systems.展开更多
A concept of divergence angle of light beams(DALB)is proposed to analyze the depth of field(DOF)of a 3D light-field display system.The mathematical model between DOF and DALB is established,and the conclusion that DOF...A concept of divergence angle of light beams(DALB)is proposed to analyze the depth of field(DOF)of a 3D light-field display system.The mathematical model between DOF and DALB is established,and the conclusion that DOF and DALB are inversely proportional is drawn.To reduce DALB and generate clear depth perception,a triple composite aspheric lens structure with a viewing angle of 100°is designed and experimentally demonstrated.The DALB-constrained 3D light-field display system significantly improves the clarity of 3D images and also performs well in imaging at a 3D scene with a DOF over 30 cm.展开更多
Experimental investigations into the effects of the magnetic field configuration near the channel exit on the plume of Hall thrusters were conducted. The magnetic field configuration near the channel exit is character...Experimental investigations into the effects of the magnetic field configuration near the channel exit on the plume of Hall thrusters were conducted. The magnetic field configuration near the channel exit is characterized by the inclination angle between the magnetic field lines and the thruster radial direction. Different inclination angles were obtained by varying the current ratio in the coils. The plume divergence angles were measured by a dual-directed probe. The results showed that the plume divergence angle increased obviously with the increase in the magnitude of the inclination angle near the channel exit. Therefore, in order to optimize the magnetic field for reducing plume divergence, the magnitude of the inclination angle should be reduced as much as possible. It suggests that the magnetic field configuration near the channel exit is another important factor that affects plume divergence.展开更多
Magnetic field design is essential for the operation of Hall thrusters.This study focuses on utilizing a genetic algorithm to optimize the magnetic field configuration of SPT70.A 2D hybrid PIC-DSMC and channel-wall er...Magnetic field design is essential for the operation of Hall thrusters.This study focuses on utilizing a genetic algorithm to optimize the magnetic field configuration of SPT70.A 2D hybrid PIC-DSMC and channel-wall erosion model are employed to analyze the plume divergence angle and wall erosion rate,while a Farady probe measurement and laser profilometry system are set up to verify the simulation results.The results demonstrate that the genetic algorithm contributes to reducing the divergence angle of the thruster plumes and alleviating the impact of high-energy particles on the discharge channel wall,reducing the erosion by 5.5%and 2.7%,respectively.Further analysis indicates that the change from a divergent magnetic field to a convergent magnetic field,combined with the upstream shift of the ionization region,contributes to the improving the operation of the Hall thruster.展开更多
A new process for swirling flow generation in the submerged entry nozzle （SEN） in continuous casting process of steel was proposed. A rotating electromagnetic field was set up around the SEN to induce swirling flow ...A new process for swirling flow generation in the submerged entry nozzle （SEN） in continuous casting process of steel was proposed. A rotating electromagnetic field was set up around the SEN to induce swirling flow by Lorentz force. The flow and temperature fields in the SEN and round billet mold with electromagnetic swirling were numerically simulated and then verified by the electromagnetic swirling model experiment of low melting point alloy. The effects of divergent angle of the SEN on the flow and temperature fields in mold with electromagnetic swirling were investigated. The electromagnetic swirling flow generator （EMSFG） could effectively induce swirling flow of molten steel in the SEN, which consequently improved greatly the flow and temperature fields in the mold. Below the nozzle outlet in mold, with the increase of divergent angle, the stream of bulk flow diverged more widely, the high temperature zone shifted up, and the temperature field became more uniform. Above the nozzle outlet in mold, with 350 A electromagnetic swirling, when the divergent angle of the SEN increased, the upward flow velocity and the meniscus temperature first increased and then decreased. With a divergent angle of 60~, the upward flow velocity and meniscus temperature reaced the largest value.展开更多
为消除场致发射电推力器(Field emission electric propulsion,FEEP)羽流发散角度过大给推进器寿命和可靠性带来的不利影响,研究了聚焦电极阵列空间位置对羽流聚焦效果的影响,并通过正交试验法给出了最优电极分布。通过数值仿真对FEEP...为消除场致发射电推力器(Field emission electric propulsion,FEEP)羽流发散角度过大给推进器寿命和可靠性带来的不利影响,研究了聚焦电极阵列空间位置对羽流聚焦效果的影响,并通过正交试验法给出了最优电极分布。通过数值仿真对FEEP的离子运动过程建模,采用正交试验方法电极阵列进行研究,关注其在不同空间位置下的聚焦效果,得到了离子出射半角分布和推力大小。结果表明,聚焦极的位置决定了羽流的聚焦效果,其次是提取极和加速极;聚焦极径向距离发射极1600μm,且提取极径向和轴向坐标为(800μm,500μm)时能得到最优的聚焦效果。本文验证了正交试验方法在聚焦电极阵列设计上的可行性,同时还为聚焦电极阵列设计提供了有效的分析方法和设计策略。展开更多
垂直外腔面发射激光器(VECSEL)可以实现大功率的高光束质量输出。针对外腔制作工艺复杂、腔体结构松散的缺点,研制了一种介质膜集成衬底表面外腔底面发射激光器。将衬底表面生长的多层介质绝缘薄膜与N-DBR、P-DBR共同构成复合腔结构,衬...垂直外腔面发射激光器(VECSEL)可以实现大功率的高光束质量输出。针对外腔制作工艺复杂、腔体结构松散的缺点,研制了一种介质膜集成衬底表面外腔底面发射激光器。将衬底表面生长的多层介质绝缘薄膜与N-DBR、P-DBR共同构成复合腔结构,衬底充当外腔。该结构能够抑制高阶模式,进而优化输出光谱及远场发散角等光束特性。在已有的理论指导下,制作了有源区直径为200μm、外腔腔长250μm的VECSEL。室温下,向器件连续直流注入3.4 A,测试得到输出功率为260 m W,远场发散角的半角宽度为3.8°,光谱半高全宽为0.046 nm。与常规结构底面发射VCSEL进行比较,发现VECSEL器件的光束质量得到了明显改善,实验结果与理论仿真结果有较好的一致性。展开更多
基金Project supported by the National Key Scientific Instrument and Equipment Development Projects of China(Grant No.62027823)the Shenzhen Fundamental Research Program(Grant No.JCYJ2020109150808037)the National Natural Science Foundation of China(Grant No.61775048)。
文摘The laser beam divergence angle is one of the important parameters to evaluate the quality of the laser beam.It can not only accurately indicate the nature of the beam divergence when the laser beam is transmitted over a long distance,but also objectively evaluate the performance of the laser system.At present,lidar has received a lot of attention as a core component of environment awareness technology.Micro-electromechanical system(MEMS)micromirror has become the first choice for three-dimensional imaging lidar because of its small size and fast scanning speed.However,due to the small size of the MEMS micromirror,the lidar scanning system has a small field of view(FOV).In order to achieve a wide range of scanning imaging,collimating optical system and wide-angle optical system are generally added to the system.However,due to the inherent properties of the optical lens,it is impossible to perfect the imaging,so the effects of collimating and expanding the beam will be different at different angles.This article aims to propose a measurement system that dynamically measures the divergence angles of MEMS scanning lidar beams in different fields of view to objectively evaluate the performances of scanning lidar systems.
基金supported by the National Key Research and Development Program of China(No.2021YFB3600504)the National Natural Science Foundation of China(Nos.62175015 and 62075016)。
文摘A concept of divergence angle of light beams(DALB)is proposed to analyze the depth of field(DOF)of a 3D light-field display system.The mathematical model between DOF and DALB is established,and the conclusion that DOF and DALB are inversely proportional is drawn.To reduce DALB and generate clear depth perception,a triple composite aspheric lens structure with a viewing angle of 100°is designed and experimentally demonstrated.The DALB-constrained 3D light-field display system significantly improves the clarity of 3D images and also performs well in imaging at a 3D scene with a DOF over 30 cm.
基金supported by National Natural Science Foundation of China(No.50676026)the Program for Chair Professors of"Cheung Kong Scholars Program"of China in 2008
文摘Experimental investigations into the effects of the magnetic field configuration near the channel exit on the plume of Hall thrusters were conducted. The magnetic field configuration near the channel exit is characterized by the inclination angle between the magnetic field lines and the thruster radial direction. Different inclination angles were obtained by varying the current ratio in the coils. The plume divergence angles were measured by a dual-directed probe. The results showed that the plume divergence angle increased obviously with the increase in the magnitude of the inclination angle near the channel exit. Therefore, in order to optimize the magnetic field for reducing plume divergence, the magnitude of the inclination angle should be reduced as much as possible. It suggests that the magnetic field configuration near the channel exit is another important factor that affects plume divergence.
基金funded by Shanghai Natural Science Foundation(No.12ZR1414700)。
文摘Magnetic field design is essential for the operation of Hall thrusters.This study focuses on utilizing a genetic algorithm to optimize the magnetic field configuration of SPT70.A 2D hybrid PIC-DSMC and channel-wall erosion model are employed to analyze the plume divergence angle and wall erosion rate,while a Farady probe measurement and laser profilometry system are set up to verify the simulation results.The results demonstrate that the genetic algorithm contributes to reducing the divergence angle of the thruster plumes and alleviating the impact of high-energy particles on the discharge channel wall,reducing the erosion by 5.5%and 2.7%,respectively.Further analysis indicates that the change from a divergent magnetic field to a convergent magnetic field,combined with the upstream shift of the ionization region,contributes to the improving the operation of the Hall thruster.
基金Item Sponsored by Fundamental Research Funds for Central Universities of China(N100409010)Project for Key Laboratory of Liaoning Province of China(LS2010065)"111 Project"of Northeastern University of China(B07015)
文摘A new process for swirling flow generation in the submerged entry nozzle （SEN） in continuous casting process of steel was proposed. A rotating electromagnetic field was set up around the SEN to induce swirling flow by Lorentz force. The flow and temperature fields in the SEN and round billet mold with electromagnetic swirling were numerically simulated and then verified by the electromagnetic swirling model experiment of low melting point alloy. The effects of divergent angle of the SEN on the flow and temperature fields in mold with electromagnetic swirling were investigated. The electromagnetic swirling flow generator （EMSFG） could effectively induce swirling flow of molten steel in the SEN, which consequently improved greatly the flow and temperature fields in the mold. Below the nozzle outlet in mold, with the increase of divergent angle, the stream of bulk flow diverged more widely, the high temperature zone shifted up, and the temperature field became more uniform. Above the nozzle outlet in mold, with 350 A electromagnetic swirling, when the divergent angle of the SEN increased, the upward flow velocity and the meniscus temperature first increased and then decreased. With a divergent angle of 60~, the upward flow velocity and meniscus temperature reaced the largest value.
文摘为消除场致发射电推力器(Field emission electric propulsion,FEEP)羽流发散角度过大给推进器寿命和可靠性带来的不利影响,研究了聚焦电极阵列空间位置对羽流聚焦效果的影响,并通过正交试验法给出了最优电极分布。通过数值仿真对FEEP的离子运动过程建模,采用正交试验方法电极阵列进行研究,关注其在不同空间位置下的聚焦效果,得到了离子出射半角分布和推力大小。结果表明,聚焦极的位置决定了羽流的聚焦效果,其次是提取极和加速极;聚焦极径向距离发射极1600μm,且提取极径向和轴向坐标为(800μm,500μm)时能得到最优的聚焦效果。本文验证了正交试验方法在聚焦电极阵列设计上的可行性,同时还为聚焦电极阵列设计提供了有效的分析方法和设计策略。
文摘垂直外腔面发射激光器(VECSEL)可以实现大功率的高光束质量输出。针对外腔制作工艺复杂、腔体结构松散的缺点,研制了一种介质膜集成衬底表面外腔底面发射激光器。将衬底表面生长的多层介质绝缘薄膜与N-DBR、P-DBR共同构成复合腔结构,衬底充当外腔。该结构能够抑制高阶模式,进而优化输出光谱及远场发散角等光束特性。在已有的理论指导下,制作了有源区直径为200μm、外腔腔长250μm的VECSEL。室温下,向器件连续直流注入3.4 A,测试得到输出功率为260 m W,远场发散角的半角宽度为3.8°,光谱半高全宽为0.046 nm。与常规结构底面发射VCSEL进行比较,发现VECSEL器件的光束质量得到了明显改善,实验结果与理论仿真结果有较好的一致性。
