Dynamic measurement of beam divergence angle of different fields of view of scanning lidar

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.

Investigation on the effect of beam divergence angle upon output waveform based on stimulated Brillouin scattering optical limiting

This paper investigates the effect of beam divergence angle on output waveform based on stimulated Brillouin scattering optical limiting.Output waveforms in the case of different pump divergence angles are numerically simulated,and validated in a Nd：YAG seed-injected laser system.The results indicate that a small pump divergence angle can lead to good interaction between pump and Stokes,and a platform can be easily realized in the transmitted waveform.In contrast,a peak followed by the platform appears when the divergence angle becomes large.

Optimizing depth of field in 3D light-field display by analyzing and controlling light-beam divergence angle

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.

Experimental Study on the Effects of Magnetic Field Configuration near the Channel Exit on the Plume Divergence of Hall Thrusters

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.

Measurement method and results of divergence angle of laser-controlled solid propellants used in space propulsion

The plume divergence angle is an important reference index for evaluating the thrust efficiency and propellant utilization of space propulsion systems.However,the characteristics of the dynamic variation of plume divergence angle over time cannot be measured using current methods.This paper utilizes high-speed photography and image processing methods to develop a strategy that can give a quick,non-destructive and real-time detection of the divergence angle.Effectiveness of the strategy is verified,and the characteristics of plume divergence angles of different lasercontrolled solid propellants were further analyzed and fitted.The experimental results indicate that graphene could effectively reduce the divergence angle,while oxide-doped samples had larger divergence angles than alloy-doped and carbon-doped samples.

碳类粒子对固体推进剂束流发散角度影响的实验研究

以石墨烯和碳粉两种碳类粒子作为掺杂剂定向改性固体推进剂,借助高速摄影技术和自搭建的束流发散角度测量系统,对比并分析不同掺杂比例和工作条件对改性推进剂束流发散角度的影响,确定了掺杂粒子的最优掺杂比例和工作条件。结果表明,石墨烯和碳粉的最优掺杂比例均为7%,且石墨烯的束流发散角度更小,生成稳定等离子体流的响应时间更短。同时,石墨烯更适配于小激光能量供给下的工作条件,而碳粉更适配于大激光能量供给下的工作条件。

半导体激光器结构设计与波导层的优化

针对1.31μm半导体激光器工作时,远场发散角过大以及AlGaInAs/GaAs材料体系中Al组分的氧化导致器件性能下降问题。提出了在InGaAsP/InP结构基础上,上下波导层采用GaAsP材料,与由InGaAsP材料构成的有源区形成异质结结构。相比同质结构制作的波导层,异质结波导层结构依据不同材料的折射率不同,实现有源层和波导层之间较大的折射率差,从而达到更好的波导限制。对1.31μm激光器中的In_(1-x)Ga_(x)As_(y)P_(1-y)材料组分进行理论计算,并根据该材料的折射率和晶格常数,对GaAs_(y)P_(1-y)材料组分、厚度进行理论计算。使用ALDS仿真软件,对同质结波导层和异质结波导层两种结构进行模拟分析。最后确定使用100 nm厚度的GaAs_(0.145)P_(0.855)材料分别作为波导层和限制层,有效减小远场垂直发散角,提高了激光器发射的光束在空间分布的圆对称形态。

深空激光通信终端主要参数的分析与研究

针对深空激光通信的应用环境和特性,分析了通信链路中的关键性能指标,考虑了距离光斑扩散衰减、指向控制精度衰减、大气衰减、太阳辐射、探测器暗电流噪声等因素后,确定了通信速率和通信误码率的具体计算方法。对通信链路进行建模,分析了各个参数的计算方法;通过公式推导分析了发射端望远镜口径(激光束散角)与指向控制精度对最大通信距离的影响,以数值仿真进行佐证并进一步分析了发射端望远镜口径(激光束散角)与指向控制精度的约束关系,提出了深空激光通信参数设计的方法。在此基础上进一步计算了现有激光通信能力在地月空间、地火空间场景下的激光链路性能。

不同垂直骨面型安氏Ⅱ^(1)类错[牙合]畸形成人患者拔牙矫治前后牙根吸收情况比较

目的:通过测量不同垂直骨面型的安氏Ⅱ^(1)类错[牙合]成人患者正畸治疗前后的牙体长度,分析其矫治前后牙根吸收的差异以及切牙内收量与牙根吸收的相关性。方法:从南昌大学附属口腔医院选择60例拔牙病例,按面角不同分成三组,将其治疗前后的CBCT数据分别导入Dolphin-Imaging 11.95软件,测量双侧上下中切牙、尖牙和第一磨牙牙体长度以及上下切牙切缘和根尖的矢状向移动量,所得数据进行统计学分析。结果:治疗前左右两侧同名牙牙体长度无差异,治疗后三组牙根长度均减小(P<0.01),上颌中切牙牙体长度高角组减小的最大,依次为均角和低角组(P<0.01)。上下切牙切缘和根尖内收量三组间差异无统计学意义(P>0.05),左侧上颌中切牙根尖内收量与牙体长度的减少量成正相关,三组相关性分别为低角组0.663、高角组0.618、均角组0.635(均P<0.01)。结论:不同垂直骨面型成人安氏Ⅱ^(1)类错[牙合]患者拔牙矫治后均有不同程度的牙根吸收。

闪烁体光束准直光学系统设计

为更好地实现对闪烁光的高效率收集和高质量准直,提升探测效果,便于进行后续的闪烁体光束控制或偏转等实验,分别提出了同轴光束准直系统和离轴光束准直系统,设计优化了该系统中的自由曲面透镜、二次曲面反射镜等器件的参数。采用光学软件LightTools对闪烁体光束准直系统进行仿真。结果表明:所设计的同轴光束准直系统和离轴光束准直系统均能有效地实现对闪烁光的准直,其中自由曲面透镜离轴反射镜系统将光束发散角从±40°压缩为±5°,光能利用率可达96%以上,光束角内光能利用率达83%以上,实现了对光束传播方向的调控,提高了闪烁光的收集效率。

Optimization of magnetic field design for Hall thrusters based on a genetic algorithm

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.

基于MEMS可变形反射镜的激光整形研究

应用MEMS可变形反射镜进行激光光束整形技术研究。首先建立平顶光束整形的理论模型,通过近轴透镜聚焦后的光场,利用柯林斯广义衍射积分公式对高斯光束整形模拟仿真,分析不同束腰半径和发散角的高斯光束对整形成平顶光束的影响。设计基于可变形反射镜的平顶光束整形的光路实验,通过平顶光束整形的理论模型和泽尼克多项公式,得到MEMS可变形反射镜各单元的驱动电压参数,实现平顶光束整形光场分布。在基于MEMS可变形反射镜的激光整形研究分析中,利用波前传感器对整形平顶光束进行光斑分析,得到基于可变形反射镜的平顶光束整形实验结果。对实验结果和理论仿真进行对比分析,得到其规律基本一致,结果较为理想。

HL-3装置7 MW中性束传输效率研究

中性束注入加热是磁约束聚变实验中非常有效的辅助加热方法,已建成的5 MW中性束在中国环流三号(HL-3)托卡马克1 MA等离子体电流高约束模式放电中起到了重要的作用。为了实现HL-3装置2.5 MA的H模放电,计划建造3条中性束注入加热系统,总加热功率达到20 MW。为HL-3设计了7 MW中性束注入器,从中性化效率和束功率沉积两方面研究束传输效率。基于蒙特卡罗方法分析了两种束流参数下中性化器性能,给出了最佳中性化效率所需的气体靶厚,并以功率沉积的方法分析了两种束流的传输性能。结果表明:当中性化送气分别为0.6 Pa·m^(3)·s^(-1)和1.1 Pa·m^(3)·s^(-1)时,束流达到最佳中性化效率;当束散角为1.2°时,两种束流参数得到的中性束功率分别为7.2 MW和6.8 MW,束传输效率分别为0.4和0.35。因此,7 MW中性束离子源参数将优选100 kV/45 A,但注入器仍保留了提供120 keV氘束的能力。

基于光谱信息散度-光谱角的自适应密度峰值聚类波段选择方法

针对传统密度峰值聚类在波段选择时缺乏信息论角度的相似性度量以及波段数目确定问题,提出基于光谱角-光谱信息散度的自适应密度峰值波段选择方法(SSDPC:Spectral angle mapping and Spectral information divergence Density Peaks Cluster)。该方法将光谱信息散度和光谱角用于高光谱图像密度峰值聚类进行波段选择,取代传统的欧氏距离构建波段相似矩阵。通过构建波段评分策略,有效自动选择出重要的光谱波段子集。在3组高光谱数据集上调用RX(Reed-Xiaoli)算法进行异常检测,在SSDPC的相似性度量方法下,异常检测精度较欧氏距离度量方法分别平均提高1.16%、1.18%和0.07%;在自适应的SSDPC波段选择方法下,异常检测精度相较原始RX算法分别提升6.49%、2.71%和0.05%。结果表明,该算法具有良好的鲁棒性,能提升高光谱图像异常检测的性能并降低其虚警率。

高功率VCSEL激光器光束发散角的测量方法

垂直腔面发射激光器(Vertical Cavity Surface Emitting Laser,简称VCSEL)由于其能发射出垂直于腔面光束的特性使得多个VCSEL激光器可以在同一片芯片上紧密集成,而不需要大量的空间;且VCSEL激光器使用共振腔的反射镜来增强光并放大,从而实现高效的光发射;通常情况下,VCSEL激光器的发光效率可以达到40至60之间,与传统的激光器相比,VCSEL激光器更容易实现高效率。由于VCSEL激光器的可集成性好、效率高等特点,使其广泛应用于3D感知、自动驾驶、光通信等领域。因此,VCSEL激光器的质量检测工作也显得越来越重要。随着VCSEL激光器进军高功率领域,其发光束的模式也经历了从基模变为高阶模的过程,光束已经从类高斯光束变为了类拉盖尔-高斯空心圆环光束。虽然传统的1/e^(2)、D86等算法在测量基模下的类高斯光束的发散角较为精确,但对于高阶模式下的类拉盖尔-高斯空心圆环光束,这些方法则出现了明显的误差。考虑到VCSEL激光器在自动驾驶等重要领域的广泛应用,其光束精确度的要求也随之提高。因此,本文采用了D4σ算法,针对类拉盖尔-高斯空心圆环光束进行发散角测量,与1/e^(2)、D86等传统算法进行了比较。结果显示,新方法在发散角测量准确度上最高提升了230。

圆锥面拟合的太赫兹发散角精密测量研究

针对太赫兹(THz)光束发散角精密测量问题,以单频连续波太赫兹源为研究对象,搭建了基于圆锥面拟合的太赫兹发散角测量装置。通过研究太赫兹光束的传播模式,分析其在空间上的光强分布特性,提出将太赫兹输出光束在远场范围内视作圆锥曲面,利用太赫兹探测器采集光斑图像,根据图像的边缘点坐标构建圆锥曲面,借助间接平差对边缘点数据做预处理并进行参数迭代与圆锥面拟合计算出光束发散角数值。结果表明,被测100 GHz的太赫兹源发散角为2.73°,相对扩展不确定度为3.8%(k=2)。

Theoretical analysis of some problems in the measurement of beam divergence angle for EAST neutral beam injector

Beam angular divergence is one of the indicators to evaluate the beam quality. Operating parameters of the beam extraction system could be adjusted to gain better beam quality following the measurement results, which will be helpful not only to study the transmission characteristics of the beam and the power distribution on the heat load components, but also to understand the real-time working condition of the ion source and beam extraction system. This study includes: (1) the theoretical analysis of beam extraction pulse duration for measurement of beam angular divergence; (2) the theoretical analysis of beam intensity distribution during beam transmission for Experimental Advanced Superconducting Tokomak (EAST) neutral beam injector. Those theoretical analyses could point the way to the measurement of beam divergence angle for EAST neutral beam injector.

利用切伦科夫辐射进行电子束发散角及分布概况的测量技术研究

针对切伦科夫辐射特点,采用厚度尽量小的石英薄片作为转换靶,并将电子束以切伦科夫辐射角入射转换靶的形式构成一种电子束发散角分布的测量布局,并基于焦平面成像原理,研制了相应的电子束发散角光学测量系统。在强流脉冲直线感应加速器上完成了装置研制和测试工作,显示了电子束发散角分布测量系统可以获得电子束一定方向上的散角分布概况,测量结果具有一定的可信度,具有装置结构简单、数据处理难度低及速度快等特点。

一种大功率宽波段激光束散角的校准测试方法

在大功率激光系统的评价与分析中,激光器的光束品质是系统光束品质的决定性因素,也是激光器验收、鉴定的重要指标,其中束散角是判别激光光束质量的重要参数。本系统测试激光波长的范围比较宽,一般在0.532μm~10.6μm之间,没有合适的探测器能够覆盖整个波段,所以采用了一种新的方法来解决宽波段束散角的测量问题。选用CCD成像和扫描狭缝相结合的方法来实现宽波段激光光束束散角的测量,可见光和近红外波段(0.532μm~1.2μm)激光光束采用CCD法测量激光束散角,中红外波段(1.2μm~10.6μm)激光光束采用扫描狭缝法测量激光束散角。两种方法的结合可以较为精确地测量出不同波段的激光束散角。

850nm窄发散角单模半导体激光器材料研究

短距离激光雷达技术应用广泛,但是要求器件的发散角比较小。针对器件的发散角,通过商用软件和波导模拟软件,设计850nm GaAs/AlGaAs扩展波导外延材料结构。采用非对称波导结构设计,有助于降低内部光学损耗,提高激光器的斜率效率,降低激光器功耗。通过优化腐蚀阻挡层GaInP的掺杂浓度,消除能带不连续导致器件电压升高问题。采用MOCVD生长了带有腐蚀阻挡层的AlGaAs/GaAs非对称扩展波导外延片,并制作成条宽2.5μm、腔长1mm的激光器芯片。测试结果表明,室温条件直流条件测试下,阈值电流为35mA,斜率效率为1.2 W/A,输出功为200mW@200mA,快轴发散角测试为15°。