卫星激光测距望远镜系统指向误差分析及修正方法研究

望远镜指向精度是卫星激光测距系统的一项重要指标。分析了望远镜指向偏差产生的各种因素,提出了一种通过建立望远镜指向误差模型来修正望远镜指向误差的方法,建立了转台模型修正误差,并用实际观测值进行了验证。     

激光雷达系统快速准直的方法和光学装置

 研制了一种能够方便、快速调节激光雷达收发光路准直的光学装置,分析了装置楔角的选取要求、准直误差及其相应的矫正方法。该装置结构简单,主要由两个楔形光学平板组成,通过电机转动两个楔板可使出射光束方向在一定范围内任意改变,该调节范围由楔板的楔角和折射率决定。利用折射定律,严格推导了装置中两个楔形光学平板的旋转角度与出射光束方向之间的关系。提出了将该光学装置插入到激光雷达发射光路,采用螺旋式粗扫、圆形和径向细扫相结合的光束扫描方式实现对激光雷达准直的方法,并给出了系统准直调节过程中的判断准则和具体的准直步骤。     

激光导星共孔径发射接收的偏振分光效率研究

在地平式折轴望远镜上开展自适应光学瑞利激光导星实验,研究了信标光束同孔径发射和接收偏振分光技术。基于镜面膜层复振幅反射特性,采用琼斯矩阵描述方法,建立了偏振分光物理模型,研究了共孔径发射和接收偏振耦合分光的效率问题,并与实验结果进行了比较。结果表明,由于镜面膜层对s光和p光的相位延迟差异,系统偏振分光效率随着望远镜的方位角旋转会发生周期性的变化,同时也受望远镜天顶角变化的影响。在研究光路反射镜相位延迟对往返分光效率影响规律的基础上,提出了提高地平式折轴望远镜激光导星共孔径发射和接收偏振分光效率,消除受望远镜方位角和天顶角变化影响的技术途径。     

Impact of telescope seeing on laser adaptive optics

Atmospheric turbulence in the internal light path of a telescope produces noncommon path phase differences that degrade the image quality of adaptive-optics systems employing laser guide stars. The spatial covariance and rms wavefront errors produced by this effect are derived. It is found that the tilt-removed wavefront error ranges from about 12 nm for a representative 30 m telescope to 59 nm for a 100 m telescope of similar optical design. For adaptive-optics systems that aim to derive tip-tilt information from the laser guide stars the error is considerably larger, ranging from 22 nm for the 30 m telescope to 256 nm for the 100 m telescope. This effect can be a significant impediment to the performance of such systems.     

100kW功率固体激光中继镜系统对1km高度目标作用效果模拟

分析了激光中继镜技术的概念及丁作过程,建立了中继镜系统模型,并在Hufnagel-Valley 5/7大气湍流模型条件下分别计算了100 kW功率,10 km高度,发射、接收、二次发射望远镜均为外径0.5 m、内径0.2 m望远镜的固体激光中继镜系统和100 kW功率,外径0.5 m、内径0.2 m发射望远镜的常规高能激光系统对1 km高度目标作用的极值功率密度与目标水平距离的关系曲线.由于中继镜系统对目标可作用时间长,根据相关资料确定常规激光系统和中继镜系统的极值功率密度破坏阈值标准分别为4000 W/cm2和800 W/cm2.分析结果得到常规高能激光系统对目标的最大可作用距离为1.38 km,中继镜系统的最大可作用距离为12.2 km.     

合成孔径激光成像雷达(Ⅱ):空间相位偏置发射望远镜

报道一种可以进行空间相位偏置的光学望远镜,用作合成孔径激光成像雷达中的光学发射天线.在望远镜内放置相位调制平板,控制望远镜的离焦量和位相调制平板的相位函数,能够在激光望远镜的照明区产生可控制的附加空间相位二次项,灵活改变激光照明波前,以在目标回波接收信号中产生雷达运动方向上的所需的二次项相位历程,因此能够实现特定的方位向成像分辨率.     

Telescopic resonators for large-volume TEM00-mode operation

A stable resonator incorporating a suitably adjusted telescope gives reliable operation of an Nd:YAG laser with a large-volume TEM₀₀ mode. The telescope adjustment is chosen to minimize the effect of focal length variations in the laser rod and at the same time ensures the optimum mode-selection properties of a confocal resonator. Simple approximations applied to the ray transfer matrices allow a detailed analysis of the resonator to be performed. This analysis yields simple design equations relating the mode spot sizes, resonator length, telescope magnification and defocusing, and diffraction losses. Experimental results show excellent agreement with the results of this analysis.     

自动聚焦激光诱导击穿光谱远程测量系统

激光诱导击穿光谱(LIBS)技术具有非接触测量、无需样品预处理以及快速多元素同时分析等特点,适合于高温、高压、真空、有毒以及敌对环境等仪器和操作人员无法靠近观测对象的应用中。LIBS技术结合望远镜系统可以实现物质成分的远距离检测与分析。搭建了一套可自动聚焦的LIBS远程测量系统。该系统中的望远镜采用Schwarzschild结构,由一块凹球面反射镜和一块凸球面反射镜组成。两块球面反射镜共轴安装。其中凸面反射镜安装在电控精密平移台上,电动平移台可带动凸面反射镜沿光轴移动。通过调整凸面反射镜的位置,改变凸面反射镜和凹面反射镜的间距,进而改变系统的焦距,实现对不同距离的样品进行光谱测量。该结构的优点在于：激光聚焦光路与信号光采集光路相同,便于安装和调试;望远镜系统采用全反射式光路,适用于紫外波段检测;只包括两个球面反射镜,结构紧凑,元件容易加工。望远镜系统调焦距离为1.5～3.6 m,聚焦光斑直径约为0.5~1.0 mm。使用该系统对铜样品进行了LIBS实验,确认了Cu元素的特征谱线。通过测量Cu元素的LIBS特征谱线(Cu Ⅰ 223.01 nm, Cu Ⅰ 224.43 nm)峰面积和反射镜间距之间关系,得到了激光的最优聚焦位置。实验结果表明,该系统能够完成样品的远程激发和LIBS光谱测量,并能够对不同距离的样品进行自动聚焦。     

用于高能激光系统的共孔径光学装置设计

高能激光系统的主要工作方式是利用其精跟踪模块将发射激光传输聚焦至闭环跟踪条件下的目标上,使之受到毁伤或失效。为实现该工作方式,本文研究设计了一套共孔径光学收发装置。该装置的发射系统主要由离轴两反式主望远镜模块、伽利略透射式调焦望远镜模块和光束馈送模块共同组成二级扩束系统,接收系统主要由离轴两反式主望远镜模块、精跟踪成像模块和光束馈送模块共同组成长焦距光学系统,其中光束馈送模块由二向色镜、快速反射镜等光学元件组成。以非相干空间合束的基模高斯光作为激光光源,利用光学设计软件对该装置进行了优化设计。对于发射系统,获得了激光经过调焦望远镜模块不同的调焦量调制后,传输至0.5~5 km处的光斑分布情况,且激光波前像差RMS值均优于λ/20;对于接收系统,由各模块一同构成的成像光学系统的性能经优化后接近衍射极限,其中系统传递函数在70 lp/mm时大于0.6,最后通过样机实验也验证了设计的正确性。本文的设计和实验结果证实了该共孔径光学收发装置结构合理,性能可靠,满足高能激光系统的工程应用需求。     

共路外差法分析牛顿望远镜偏振特性

应用共路外差干涉法分析了牛顿望远镜的偏振特性。根据菲涅耳定律求出了入射光s-偏光和p-偏光入射到望远镜各点的反射率公式。给出了共路外差干涉法测量牛顿望远镜偏振特性的实验装置原理图。采用632.8nm的外差光源,分析了牛顿望远镜对s-偏光和p-偏光反射系数、相位差以及对入射光偏振度的影响,根据入射角度的不同绘制了相应的变化曲线。结果表明：镀有铝膜的牛顿望远镜对入射光偏振特性影响较小,s-偏光和p-偏光反射系数相差不到0.01,偏振度变化不超过0.07,适用于激光遥感偏振成像的接收系统。     

星载激光相干测高计的参量设计

为使星载激光高度计实现高空间分辨力、高距离精度,提出了联合采用调频光纤激光器和相干测距的方法.详细讨论了这种方法的实现方案,并对方案中的激光发射功率、望远镜口径以及脉冲宽度对距离精度及信噪比的影响进行数值模拟.对系统参量进行分析,得到了相关参量的关系和优化的参量.结果表明,当望远镜口径为400 mm时,啁啾调频速率为1 MHz/μs,脉冲时间宽度150～350 μs, 发射功率10 W左右时,基于相干测距的星载激光高度计可以实现距离精度小于15 cm的技术指标.     

激光散斑效应对激光雷达探测性能的影响

分析了激光散斑效应对激光雷达探测性能的影响. 给出了远场情况下接收物镜所采集激光散斑数的表达式. 在物镜所采集的散斑和光电子数均较大情况下，提出了光电子所遵守的分布. 分别导出了机载和星载激光雷达的探测概率. 分析表明激光雷达探测性能与所采集的散斑数密切相关，接收的散斑数仅与激光束腰和物镜的口径有关，随着接收散斑数的增加，散斑噪声的影响将减弱. 关键词： 激光雷达 激光散斑 探测概率     

Experimental validation of a technique to measure tilt from a laser guide star

We have experimentally demonstrated for what is believed to be the first time a method for sensing wave-front tilt with a laser guide star (LGS). The tilt components of wave fronts were measured synchronously from the LGS by use of a telescope with a 0.75-m effective aperture and from the star Polaris by use of a 1.5-m telescope. The Rayleigh guide star was formed at an altitude of 6 km and at a corresponding range of 10.5 km by projection of a focused beam at Polaris from the full aperture at the 1.5-m telescope. Both telescope mounts were unpowered and bolted in place, allowing us to reduce substantially the telescope vibration. The maximum value of the measured cross-correlation coefficient between the tilt for Polaris and the LGS is 0.71. The variations of the measured cross-correlation coefficient in the range from 0.22 to 0.71 are caused by turbulence at altitudes above 6 km, which was not sampled by the laser beacon but affected tilt for Polaris, the cone effect for turbulence below 6 km, residual mount jitter of the telescopes, and variations of the signal/noise ratio. The results support our concept of sensing atmospheric tilt by observing a LGS with an auxiliary telescope and indicate that this method is a possible solution for the tip-tilt problem.     

The effect of the relativistic transformation law of angles on laser ranging of satellites moving in circular orbits equipped with a single retroreflector

It is shown that due to the relativistic transformation law of angles, a laser pulse reflected from a moving retroreflector propagates not strictly back, but at a small angle to the direction of the laser station. For this reason, the ray located on the periphery of a pulse reaches the receiving telescope of the laser station instead of the central ray of a pulse. As a result, the flux of electromagnetic energy received by the laser station is certainly less than the flux of energy in the vicinity of the central ray. The energy flux attenuation coefficient is assessed on the basis of numerical analysis. It is shown that if the receiving telescope is separated from the laser station in order to be mobile and is moving along the Earth’s surface so that the center of each spot formed by a pulse of the reflected light hits the telescope, then the electromagnetic energy flux during laser probing of the satellite will be higher by more than 100 times in comparison with the energy flux received by the stationary telescope of the laser station. From our study it follows that the maximum speed of motion of the centers of spots on the Earth’s surface does not exceed 8 km/h.     

Generation of powerful filaments at a long distance using adaptive optics

Because of its extraordinary properties (intensity clamping, white light source, km long plasma channels), filamentation represents an ideal candidate for remote sensing. However, the promising generation of filaments at long distances for such purposes remains an issue.

We propose a specially designed focusing telescope to properly deliver the laser pulses at long distance and generate powerful filaments. The telescope includes a deformable mirror (DM) that corrects the wavefront’s aberrations working in a closed loop system with a wavefront sensor (WFS). Using this setup we are able to generate extraordinarily strong nitrogen signals at a distance as far as 90 m using 40 mJ laser pulses. Compared to the chirped based filament control technique, we believe that an appropriate control of the reservoir like what we have achieved will contribute to reduce the energy of the required laser pulses and at the same time, the cost of the required laser system.     

用于激光接收/目视瞄准镜的共光路光学系统设计

为实现多传感器光轴校准并达到小型化轻量化的设计要求,将目视瞄准镜作为校轴光学基准,采用共用摄远型物镜组,并利用在立方棱镜斜面镀制光谱分光膜,实现高精度目视瞄准镜与激光接收的共光路系统设计。该目视瞄准镜放大倍率为7×、视场为5°、出瞳直径为3.7 mm、出瞳距离不小于20 mm;激光接收系统视场为1 mrad、接收口径为50 mm,设计结果满足指标要求。     

Compact TEM<Subscript>00</Subscript> grazing-incidence Nd:GdVO<Subscript>4</Subscript> laser using a folded cavity

A compact diode-side-pumped Nd:GdVO₄ laser system using a folded cavity and grazing-incidence configuration is presented. The highest multimode output power obtained was 21.8 W at 36 W of effective diode pump power. Highest optical-to-optical conversion efficiency of 61.5% was achieved at 33 W of effective diode pump power with 20.3 W of multimode output power. For single-mode TEM₀₀ operation, an intracavity telescope was adopted for mode matching in the horizontal direction. Because of the folded cavity and the intracavity telescope, this laser head was the most compact to our knowledge of the TEM₀₀ grazing-incidence laser geometry. At last, an output power of 15 W was produced at 36 W of effective diode pump power. The stable Q-switching operation was also obtained. PACS 42.55.-f; 42.55.Xi; 42.60.Gd     

共孔径偏振耦合分光系统中反射镜造成的相位延迟差的测量

 激光信标共孔径发射接收偏振分光系统的动态相位补偿需要测量望远镜各反射镜对s光和p光的相位延迟差。利用Stokes矢量和Mueller矩阵建立了物理模型，并推导出用测得的回光功率计算相位延迟差的解析式。提出一种通过实验测量回光功率计算反射镜相位延迟差的方法，解决了在0～2p范围内唯一确定反射镜相位延迟差的问题。实际测量了两块反射镜的相位延迟差，并将测量结果用于动态相位补偿偏振分光实验，验证了该方法的正确性。分析了偏振分光棱镜、法拉第旋光器以及近似计算这3个主要的测量误差源，并估计总测量误差约为1°。     

空间引力波探测望远镜初步设计与分析

引力波的直接观测已开启引力波天文学的新篇章,爱因斯坦的百年预言终获证实。空间引力波探测器使得探测0.1 m Hz~1 Hz频段丰富的引力波源成为可能,与地面引力波探测器互为补充,才可实现更加宽广波段的引力波探测,揭开宇宙早期的更多秘密。空间激光干涉引力波探测采用外差干涉测量技术,测量间距百万公里的两自由悬浮测试质量间10 pm量级的变化量。望远镜是激光干涉测量系统的重要组成部分,1 pm的光程稳定性及苛刻的杂散光要求,不同于传统的几何成像望远镜。本文根据空间太极计划任务需求,对望远镜的功能及技术要求进行了分析,并完成了原理样机的初步方案设计,针对百万公里远场波前分布,分析了望远镜系统的敏感性,同时完成了在轨光机热集成仿真,为后面原理样机的研制奠定了技术基础。     

合成孔径激光成像雷达(Ⅲ):双向环路发射接收望远镜

提出了一种用于合成孔径激光成像雷达的双向环路结构的发射接收望远镜,双向环路包括发射4-f转像系统、接收4-f转像系统和独立的望远镜.发射通道中设置离焦和相位调制平板偏置,接收通道中设置离焦和相位平板偏置.控制发射离焦量,发射相位调制甬数.接收离焦量.接收相位调制甬数.用同一个望远镜可以同时实现空间二次项相位附加偏置的激光发射和消除目标点散射回波接收波面像差的离焦光学接收,并产生雷达运动方向上合适的和可控制的相位二次项历程.从而实现孔径合成成像.详细介绍了系统设计,给出了从发射到光电外差接收的全过程传输方程.