CO2激光焊接船用铝合金T型材的焊缝成形控制

分析了船用铝合金T型材的特点,提出激光焊接船用铝合金T型材的方法。采用CO2激光填丝焊接方法实现了6.0mm厚船用5083铝合金T形构件角焊缝的焊接。在平板扫描焊接实验的基础上,重点研究了激光束入射角度、作用位置及焊接速度与送丝速度的匹配关系对角焊缝成形的影响。针对6.0mm的5083铝合金,采用Ar和He混合保护气在激光功率为3300～3500W,离焦量为0的情况下进行焊接。激光入射角度为22°～25°,激光作用于竖板距横板0.8～1.0mm处,焊接速度2.2～2.5m/min,送丝速度2.5～2.8m/min的条件下,能够得到满意的角焊缝成形。同时,讨论了船用铝合金T型材CO2激光焊接过程中产生气孔和过程不稳定的原因。     

Environmentally Stable Mode-Locked Fiber Laser With Dispersion Compensation by Index-Guided Photonic Crystal Fiber

We exploit the anomalous dispersion generated by an index-guided photonic crystal fiber (PCF) for dispersion compensation in an ytterbium fiber laser passively mode-locked with a semiconductor saturable absorber. A PCF, reasonably compatible with standard fiber, and a Faraday rotator in the cavity allow for robust all-fiber subpicosecond operation at 1 m, insensitive to environmental disturbance.     

Asynchronous Congestion Control in Multi-Hop Wireless Networks With Maximal Matching-Based Scheduling

We consider a multi-hop wireless network shared by many users. For an interference model that constrains a node to either transmit to or receive from only one other node at a time, and not to do both, we propose an architecture for fair resource allocation that consists of a distributed scheduling algorithm operating in conjunction with an asynchronous congestion control algorithm. We show that the proposed joint congestion control and scheduling algorithm supports at least one-third of the throughput supportable by any other algorithm, including centralized algorithms.      

光子晶体光纤激光器的研究现状

光子晶体光纤作为一种新型特种光纤具有许多传统光纤所无法比拟的优越特性,尤其是掺杂光子晶体光纤。本文主要介绍了光子晶体光纤激光器的研究进展和应用前景。     

基于参数自适应PID控制算法激光准直系统的研制

提出并研制了一种基于参数自适应比例、积分和微分(PID)控制算法的激光准直控制系统,从根本上解决了传统PID控制方法的存在的精度低、实时性差等不足。在50min内,x向(水平方向)的角漂移量为22nm／150mm,y向(垂直方向)的角漂移量为15nm／150nm;x向的平漂移量为26nm／150nm,y向平漂移量为28nm／150nm。实验证明：采用参数自适应PID控制算法,激光准直系统的准值精度和鲁棒性得到显著提高。     

Thermal Investigation of GaN-Based Laser Diode Package

We investigated thermal behavior of GaN-based laser diode (LD) packages as a function of cooling systems, die attaching materials, chip loading conditions, and optical performances. The electrical thermal transient technique was employed for the thermal measurement of junction temperature and thermal resistance of LD packages. The results demonstrate that the total thermal resistance of LD packages is controlled mainly by the packaging design rather than the chip structure itself. Significant changes in thermal resistance with input current were observed under a natural cooling system because of the sensitive change in the heat transfer coefficient with the change in temperature. Employment of PbSn as a die attachment was more advantageous over the Ag-paste in the thermal behavior of LD packages. The LD package with epi-down structure resulted in the lower thermal resistance compared to one with epi-up structure. A continuous increase in junction temperature was measured after lasing. It was attributed to an increase in the thermal resistance of LD when it took the optical power into an account. Effective input power was decreased by the lasing and led to high thermal resistance values.     

高强铝合金的激光焊接头组织及力学性能

采用CO2激光器对高强铝合金2519-T87进行焊接,研究了其激光焊接头组织和力学性能特征,并与熔化极气体保护焊(MIG)焊接头的组织和力学性能进行了对比。实验结果表明,激光焊焊缝组织细小,晶界共晶相呈短棒状均匀分布,时效后焊缝中有大量细小θ′相均匀析出,且熔合线附近没有形成等轴晶区,而熔化极气体保护焊焊缝组织晶粒粗大,晶界共晶相呈长条网络状分布,时效后焊缝中的θ′相尺寸大,数量少,且分布不均匀,熔合线附近还存在一个较宽的等轴晶区。焊后时效激光焊接头抗拉强度可达到母材的74%,并且随着焊接速度的增加,接头抗拉强度随之增加,而熔化极气体保护焊焊接头抗拉强度仅仅只有母材的61%,且激光焊接头的热影响区(HAZ)中没有明显的软化区。     

双包层光子晶体光纤激光器研究进展

光子晶体光纤(PCF)具有许多传统光纤难以实现的诸多优良特性,以光子晶体光纤为增益介质的高功率光纤激光器受到了普遍关注.介绍了光子晶体光纤及由其构成的光子晶体激光器的原理,重点介绍了双包层光子晶体光纤激光器国内外的最新研究进展.     

激光诱导液晶定向研究

报道了一种新的激光诱导液晶定向技术。用偏振激光辐照两块涂有聚乙烯醇（ＰＶＡ）和甲基橙（ＭＯ）混合物薄膜的玻璃基片,再按激发光偏振态相互垂直的方向组装为液晶（ＬＣ）盒,用光诱导法获得盒内液晶分子的扭曲向列排列,该盒可使入射线偏振光旋转９０°。用１ＧＷ／ｃｍ２强激光辐照后,盒内ＬＣ分子取向不变,因而可望用于制备强激光系统中偏光控制器以改善光束质量。     

Coherence of Photonic Crystal Vertical-Cavity Surface-Emitting Laser Arrays

We measure and compare the coherence properties of 2 times 1 arrays of photonic crystal vertical-cavity surface-emitting lasers. Antenna array theory applied to the measured far field intensity patterns is used to determine the phase of the complex degree of coherence, which is found to vary with current injection. The amplitude of the complex degree of coherence is determined by calculating the visibility from the far field patterns and making near field measurements of the relative intensities between lasing defects. We find that the amplitude and phase of the complex degree of coherence are correlated, such that coherence is maximized near in-phase and out-of-phase coupling conditions, and controllable by independent current injection to each array element     

半导体激光器边缘绝热封装改善慢轴光束质量

为了削弱激光器工作时芯片横向温度不均而导致的热透镜效应对慢轴发散角的影响,提高慢轴的光束质量,引入了边缘绝热封装方式,即在激光器芯片两侧与过渡热沉之间加入空气隙,以降低两侧的传导散热。利用有限元分析软件ANSYS 18.0对该封装结构中激光器芯片的温度进行仿真。结果表明:当工作电流为1.6 A,芯片与热沉的接触宽为200μm时,慢轴发散角由普通封装时的11.5°减小至8.2°,降幅为28%,光束参数积和光束质量因子也分别降低了28%和24%,热阻增大了6%。边缘绝热封装对器件激射波长、阈值电流、电光转换效率的影响很小。     

Novel Design of Current Driven Photonic Crystal Laser Diode

Contrary to the great possibilities of photonic crystal (PC), a practical laser diode with a PC cavity has not yet been developed. This is mainly due to the lack of electrically driven devices; Since a two-dimensional PC slab cladded by air is often employed to realize strong light confinement, it is difficult to inject carriers into a cavity in such an air-bridge structure. An electrically driven laser using a tiny semiconductor pillar for current injection has been reported; however, a large cross-section of the pillar (or low electrical resistance) trades-off a large $Q$-factor sufficient for lasing. In this letter, we propose a novel design of PC laser diode in which light confinement and carrier injection are highly compatible.      

高平均功率面阵二极管激光器封装

对激光二极管中冷却和界面联接热阻两个关键环节进行了分析 ,设计了一种五层结构的模块式铜微通道冷却器 ,对于腔长 0 .9mm、宽 1 0 mm的线阵激光器二极管 (DL )芯片热阻为0 .39°C/W。对冷却器进行了面阵 DL封装实验 ,在工作电流 5 2 A,电压 41 .4V时 ,封装的面阵 DL输出功率 1 0 0 5 W,电光效率 45 %,中心波长 80 7.3nm,谱宽约 2 .2 nm。经快轴准直后整个面阵输出激光的发散角小于 2°(快轴 )× 1 2°(慢轴 )。     

Nikon光刻机激光步进对准系统研究

介绍了Nikon光刻机最常用的对准方式,即激光步进对准(LSA)。从基本的光学系统出发,介绍了LSA在Nikon光刻机中的作用,搜索和增强型全局对准(EGA),详细阐述了LSA的工作原理及其对工艺的影响,最后介绍了LSA对准系统的技术指标和作用。     

交流异步电动机的矢量控制

讨论了三相异步电动机的几种控制方法,并对有否采用矢量控制技术的几种变频调速系统进行分析比较,指出它们各自的适用范围。     

AZ91D铸造镁合金激光焊接气孔研究

针对铸造镁合金的激光焊接气孔难题,以AZ91D铸造镁合金为主要材料,紧密围绕气孔产生的原因、影响因素及其控制开展研究.探讨了铸造镁合金激光焊接气孔产生的特点和机理;研究了自熔激光焊接气孔产生的原因及影响因素;研究了填充焊丝激光焊接对焊缝气孔的控制及不同对接间隙焊接的质量控制.研究结果表明:铸造镁合金的激光焊接稳定性和气孔率主要受母材微孔率影响.对于母材微孔率在1-3%的铸造镁合金,采用填充焊丝激光焊接技术,焊缝平均气孔率降低到0.31%;对于母材微孔率在6-10%的铸造镁合金,采用填充焊丝激光焊接技术,使焊缝平均气孔率由20%降低到3%,对接间隙0.4mm时可以进行正常的焊接.     

激光准直特性在主动式激光侦察告警系统设计中的应用探讨

探讨了主动式激光侦察告警系统入射高斯光束腰斑与望远镜副镜的距离对出射高斯光束准直倍率的影响.在满足入射高斯光束腰斑与望远镜副镜的距离远大于望远镜副镜的焦距的条件下,望远镜主镜的焦距与望远镜副镜的焦距的比值越大,出射高斯光束的准直效果越好.在不满足入射高斯光束的腰斑与望远镜副镜的距离远大于副镜的焦距的条件下,仿真分析了望...     

由安全极限确定激光散斑在角膜上的辐照度

激光束直接照射人眼时，对人眼角膜和视网膜会造成损伤，而焊接光的漫反射光和激光散斑在一定条件下照射到人眼上，也会引起人眼角膜和视网膜的损伤。本文根据角膜上辐照度的安全极限，导出了激光器光功率与强漫射板上光斑直径、角膜到漫射板之间距离的关系式。     

准直激光束水下光斑的变化规律研究

从光在介质中传输的物理过程出发 ,获得了准直激光束的水下光斑随深度变化的解析表达式 ,可以较好地解释不同水质、不同深度条件下光斑的变化规律     

远距离激光光斑位置高精度测量方法

为了提高激光光斑位置测量精度,考虑影响光斑测量精度的因素,并对若干关键技术进行研究。为了抑制由于气溶胶散射导致的激光后向散射,研究距离选通技术,提出一种基于四象限探测器的异步距离选通技术;为了削弱大气湍流的随机扰动对激光光斑成像的影响,提出一种改进的盲解卷积事后复原方法,并从数学上证明了该方法的收敛性;为了消除多传感器采集图像之间的差异,提出一种基于目标区域的图像配准算法;还原光斑图像并利用高斯曲面拟合法提取激光光斑的位置信息。实验结果表明,提取到的激光光斑位置精度不大于0.3pixel。