On acoustic emissions in percussion laser drilling

Laser drilling is a well established sheet metal processing method. The development of a monitoring system capable of assessing the dimensions of holes is the subject of this work. This paper investigates the applicability of an acoustic-based monitoring system for the percussion laser drilling process. Correlation between the sensor output and the hole's geometry, determined by its depth and upper diameter, is investigated and the results are presented. In general, the results indicate that a correlation exists between the acoustic signal output and the depth of the hole.     

连续Nd:YAG激光光纤耦合效率的实验

对0.6mm芯径3m长光纤输出100W连续Nd:YAG激光的光纤耦合效率进行了实验分析。围绕光纤耦合效率相关的量:激光模式、发散角、数值孔径、焦斑直径、精密光纤耦合器等问题进行了讨论;并给出实验结果:3m长光纤输出0～100W激光耦合效率典型值≥87%,最佳值为90%.     

Design of precision measurement system for metallic hole

For most of the high-speed hole diameter measuring process, a contact measuring method is undesirable due to its slow and destructive touching process. Thus, an optical method is usually chosen for non-contact measurement. Unfortunately, for most holes in precise manufacturing, especially those with a high aspect ratio, the optical method cannot be used. In our study, we developed a simple and low-cost precision capacitive hole measuring system. By using a simple alignment mechanism, we prove that a high-resolution hole diameter can be achieved. Comparing a traditional measuring method like coordinate measuring machine with our system, over 99% correlation is easily obtained. The paper also presents a multilayer hole measuring probe and sensor probe for non-through-hole measurement.     

基于人工神经网络的激光点焊焊点形态预测

建立适用于激光点焊焊点形态预测的人工神经网络模型,以点焊过程中的三个主要工艺参数(激光功率、点焊时间和离焦量)作为模型输入,输出为焊点表面、熔合面、背面直径以及熔深和横截面面积五个焊点形态参数。在此基础上,建立焊点形态模型,模型输入为神经网络的预测结果,输出为焊点形态。所建立的神经网络预测模型和焊点形态模型结合之后,可以实现激光点焊焊点的形态预测。网络测试结果显示实际值与网络预测值之间的RMS误差为0.1左右,模型输出的预测焊点形态与实际焊点形态之间较为吻合。根据模型的仿真结果,进一步研究点焊参数对焊点尺寸和形态的影响规律。结果表明未熔透焊点形态为Y形,而熔透焊点则存在多种形态,形态之间的转变主要受激光功率的影响。     

半导体激光鼓膜造孔术的光学系统设计

设计并研制了一套可在视频监控和红光指示下实施半导体激光鼓膜造孔术的光学系统.首先,利用光束整形和波长合束技术将半导体激光单管出射的650 nm激光和半导体激光列阵出射的810 nm激光耦合到芯径为200 μm,数值孔径为0.22的光纤中;然后,利用消色差透镜准直光纤出射的双波长激光,再利用另一个消色差透镜将光束聚焦到耳鼓膜上,该聚焦镜可通过机械部件沿光轴方向移动,从而调节鼓膜上光斑的大小;成像部分则直接使用商用视频耳镜;热反射镜用于使激光和成像光同轴.手术时,根据显示器上的红色指示光斑确定造孔位置.测量结果显示:该系统出光孔处的激光功率在0～13.3 W间连续可调,造孔直径在1～3mm内连续可调.使用本系统可缩短手术时间,减少并发症;儿童患者手术时无需全身麻醉.另外,该系统还具有整机体积小、重量轻、电光转换效率高等优点.     

Φ25mm火炮身管直线度光电测量方法

基于激光准直和光电探测原理与技术,并借鉴象限探测法、精密机械、伺服控制技术和计算机技术研制了一种用于Φ25mm火炮身管直线度的光电测量系统.给出了系统的总体结构,对系统的测量原理进行了理论分析,得到了身管直线度的计算公式,建立了解决光电靶偏心的数学模型.并将测量系统应用于长1.15m的Φ25mm精加工孔标准件进行两组采样,每组采样步长为100mm.实测的结果表明:测量系统分辨率可以达到0.005mm,测量误差小于0.015mm,重复性测量精度优于±0.009mm,说明测量方法是可行的.     

Optical emission monitoring for defocusing laser percussion drilling

This paper presents a novel method for controlling the laser-drilling process for a hole by monitoring induced plasma emission. The variation of light brightness from laser-induced plasma is used as an indicator to control laser percussion drilling. Through on-line plasma emission acquisition and analysis, we obtain the positive association between the increased depth and the optical signal output. A coaxial photodiode is used to estimate the brightness levels of laser-induced plasma. The above constitute an inexpensive and practical on-line feedback system that can be easily implemented in the laser systems. All of the processing work is performed in air under standard atmospheric conditions without gas assist. The acquired signal for drilling could also be used as an input to a focus point process control scheme. Moreover, the technology demonstrates the feasibility to develop an automated laser micromachining system. Experimental results show that drilling efficiency was increased 47% by applying the proposed defocusing laser percussion drilling.     

Nanometer edge profile measurement of diamond cutting tools by atomic force microscope with optical alignment sensor

This paper describes an atomic force microscope (AFM) based instrument for nanometer edge profile measurements of diamond cutting tools. The instrument is combined with an AFM unit and an optical sensor for alignment of the AFM probe tip with the top of the diamond cutting tool edge in the submicrometer range. In the optical sensor, a laser beam from a laser diode is focused to generate a small beam spot with a diameter of approximately 10 μm at the beam waist, and then received by a photodiode. The tool edge top and the AFM probe tip are brought to the center of the beam waist, respectively, through monitoring the variation of the photodiode output. To reduce the influence of the electronic noise on the photodiode output so that the positioning resolution can be improved, a modulation technique is employed that modulates the photodiode output to an AC signal by driving the laser diode with a sinusoidal current. Alignment experiments and edge profile measurements are carried out.     

Development of a laser-guiding-type deep small-sized hole-measurement system: Measurement accuracy

In this study, a system for measuring small-sized holes with a 17–21 mm diameter and 1000 mm length was constructed. The system comprises a laser interferometer to detect hole accuracy, a probe connected to a measurement bar, and an optical apparatus for detecting the probe attitude (position and inclination). The probe was supported by supporting pads. A steel workpiece with 18 -mm diameter and 800 mm length was used for the performance test. During the experiment, errors were found in terms of hole deviation and roundness profile. Further experiments, using new experimental apparatus and analysis, revealed the causes of errors: electrical noise that increased with time, two periodic stylus swings in the longitudinal direction of the hole per rotation of the measurement unit, and the excessive spring force pushing the tip of the stylus, causing a large frictional force with the hole wall, etc. If these errors are corrected, high accuracy in the measurement of hole deviation and roundness can be achieved.     

808nm高亮度半导体激光器光纤耦合器件

针对单个808nm单管半导体激光器输出功率低,采用端面泵浦方式对光纤激光器进行泵浦时受到限制的问题,本文利用空间合束技术制成高亮度半导体激光器光纤耦合模块来提高808nm单管半导体激光器泵浦掺Nd3+双包层光纤激光器的效率。首先,通过微透镜对每个单管半导体激光器进行快慢轴准直;然后,使用反射棱镜对每个激光器发出的光进行空间合束;最后,利用自行设计的扩束系统将合束后的光束进行扩束,聚焦进入光纤,从而极大地提高光纤耦合模块的亮度。实验中将4只连续输出功率为5W的单管半导体激光器发出的光束耦合进芯径为105μm、数值孔径(NA)为0.2的光纤,当工作电流为5.8A时,通过光纤输出的功率为15.22W,耦合效率达到74%,亮度超过1.4MW/cm2.sr。     

Analysis of silicon via hole drilling for wafer level chip stacking by UV laser

For stacking wafers/dies, through-silicon-vias (TSVs) need to be created for electrical connection of each wafer/die, which enables better electrical characteristics and less footprints. And for via hole processing, chemical methods such as DRIE (Deep Reactive Ion Etching) are mostly used. These methods suffer the problems of slow processing speed, being environment-unfriendly and damage on the existing electric circuits due to high process temperature. Furthermore, masks are also needed. To find an alternative to the methods, researches on the laser drilling of via holes on silicon wafer are being conducted. This paper investigates the silicon via hole drilling process using laser beam. The percussion drilling method is used for this investigation. It is also examined how the laser parameters- laser power, pulse frequency, the number of laser pulses and the diameter of laser beam- have an influence on the drilling depth, the hole diameter and the quality of via holes. From these results, laser drilling process is optimized. The via hole made by UV laser on the crystal silicon wafer is 100μm deep, has the diameter of 27.2μm on the top, 12.9μm at the bottom. These diameters deviate from the target values by 2.8μm and 0.4μm respectively. These values correspond to the deviation from the target taper angle of the via hole by less than 1°. The processing speed of the laser via hole drilling is 114mm/sec, therefore, etching process can be replaced by this method, if the number of via holes on a wafer is smaller than 470,588. The ablation threshold fluence of silicon is also determined by a FEM model and is verified by experiment.     

激光透射法磁珠浓度测量系统

磁珠广泛应用于免疫检测、细胞分离等生物实验中,磁珠浓度的检测对于评价实验效果具有重要意义。本文提出了基于激光透射法的双光路磁珠浓度测量系统,通过测量入射激光强度与透射激光强度的比值来确定磁珠浓度。利用该系统对多个浓度的磁珠悬浊液进行了实验测量,每个浓度下测量多组实验数据,共采集了8 000组数据。通过拟合测量数据,建立了磁珠浓度与测量值的关系函数,二者呈现指数函数关系,拟合残差平方和为0.000 088 89,确定系数可达0.997 1,说明函数具有良好的拟合性能。实验结果表明,相对测量误差在2.5%以内,输出值相对波动范围在2.5%以内,测量系统具有较高的测量精度和良好的重复性。     

数字X线影像仪中激光扫描光学系统的设计

数字X线影像仪是计算机和激光技术快速发展的产物,而其中的激光扫描光学系统是其核心技术之一。针对数字X光影像仪的使用特点,对激光扫描系统中的Fθ镜头、光束扩展器、扫描器这几个关键部件进行了较详细的论述分析,提出并解决了其中一些关键问题,如光阑位置浮动对像质的影响、影响系统扫描光点大小的因素、扫描器的确定等。最后用ZEMAX光学设计软件对系统的光学性能进行了设计模拟,得到扫描光斑直径小于0.1mm、焦距和视场满足线性关系的设计结果。像质评价分析结果表明,所设计的镜头像质优良,轴上与轴外质量相当,像质达到衍射极限。     

LD泵浦的全固体绿激光器研究

主要论述了用激光二级管(LD)泵浦、内腔倍频的绿激光器的原理和结构。在激光阈值、斜效率的讨论中指出:当LD的泵浦光束在激光晶体中的尺寸越小,光功率密度越高,激光阈值就越低,转换效率就越高;在放大基波的结构中,激光腔镜对基波的反射度越高,基波的放大倍数就越大,转换效率就越高;重点讨论了内腔倍频激光器中的“绿光问题”,指出造成“绿光问题”是由于模式正交分量之间的和频效应与空间烧孔形成的横向饱和;用Poincare图分析了激光器中出现的混沌行为;对如何克服“绿光问题”,得到稳定激光输出提出了几种方案。针对LD的光形状是一个椭圆光锥,选择了用多组透镜准直、棱镜对扩束的泵浦光传输系统方案;对腔体、激光膜层作了概述,具体提出了用平凹腔结构,并把激光膜层直接做在晶体上,可以减少腔内损耗;对YAG-KTP,YVO₄-KTP组合的绿激光器作了研究。在内腔倍频YAG激光器中观察到的实验现象很好地附合理论结果。在YVO₄-KTP的绿激光器中,比内腔倍频YAG激光器较容易得到YAG-KTP组合绿激光器,最大连续输出功率为14.4mW,阈值15.0mW,光-光斜效率为4.1%.YVO₂-KTP绿激光器:最大连续输出120mW,阈值100mW,光-光斜效率为6.3%.     

SLS烧结参数对原型精度影响的正交试验分析

通过对轴对称圆柱孔等典型几何形状的烧结成型,研究了SLS中激光功率、加热温度以及切片厚度这三个烧结参数对圆柱孔形位公差以及直径和圆柱度的误差的影响。采用正交试验方法,在两种不同的切片方式下,分析了各种误差产生的主要原因,以及获得较高原型精度的工艺参数值。     

四程抽运Yb:YAG盘式激光器

报道了激光二极管阵列(LDA)抽运Yb:YAG盘式激光器。Yb:YAG晶体掺杂浓度10-at.%,几何尺寸为Φ10mm×300μm,采用铟焊工艺将其焊接到水冷系统上,用可调式恒温水箱对其进行温度控制。利用蒙特卡罗方法对抽运光斑的大小进行了计算,将反射镜轴向与光纤头轴向夹角控制在120以内,以使抽运光斑半径与基模光斑半径比符合模式匹配原则。使用两个Φ=30mm,R=50mm的球面反射镜,完成了四程抽运。在LDA抽运功率为4.13W时,获得了最高功率为670mW的1030nm连续激光输出,光-光转换效率为16.2% 。     

Portable optical particle (0.06 microm) counter

An improved portable optical counter, using a He-Ne laser with 8 mW output, measures particles ranging in size from 0.06 to 10 microm in diameter in situ.     

An optically pumped XeF(C-A) laser with repetitive rate of 10 Hz

A novel XeF(C-A) laser which can be operated in repetition mode has been developed based on surface discharge optical pumping technique. Its maximum repetitive rate is up to 10 Hz. The influence of repetitive rate and gas flow rate on the stability of output energy is studied and the main factor which influences the stability of output energy is analyzed. The experimental results show that increasing the gas flow rate into laser chamber can improve the stability of the output energy. The ideal output energy results of 20 laser pulses under different repetitive rates and their optimal experimental conditions are presented. Output energies of more than 4 J and better stability can be obtained when the laser device operates at 1, 2, and 5 Hz, respectively. When the gas feed rate is larger than 53 l/s, the stability of output energy is improved obviously at the repetitive rate of 10 Hz, and the average energy of 20 laser pulses is up to 3.2 J.     

Novel approach to indirect measurements of alternating current based on the interrogation of an all-fiber laser

This paper proposes and demonstrates a novel alternative to measure alternating current (AC) in an indirect manner, based on the interrogation of an Erbium-doped all-fiber laser. The principle of operation is based on sensing the temperature of an electrical wire AWG-22 caused by Joule effect. The heat transfer between a sensing Fiber Bragg Grating and the electrical wire modulates the intensity of the optical output power of the fiber laser. The intensity variation of the fiber laser is caused by the wavelength overlapping process into the fiber laser. The advantage of the proposed alternative is measuring AC current through the optical power from the fiber laser. The linear increment of optical output power as a function of temperature allows for the measurement of the AC current, which is an advantage over other methods.     

纳秒激光加工2.5维Cf/SiC复合材料的烧蚀孔洞特征

针对新型材料2.5维碳纤维增强陶瓷基（Cf/SiC）复合材料采用传统机械加工难以去除加工的问题，采用纳秒激光烧蚀2.5维Cf/SiC复合材料，烧蚀后采用扫描电子显微镜观察其烧蚀孔洞形貌特征，并分析其烧蚀去除机制，讨论激光加工参数对烧蚀孔径的影响。研究表明，Cf/SiC复合材料的激光烧蚀区域出现烧蚀孔洞、重凝、纤维断口、末端气胀，以及长轴与纤维方向一致的椭圆形材料性能变化区域等烧蚀现象；激光烧蚀Cf/SiC复合材料过程中存在氧化的化学变化现象；烧蚀产生的孔径随烧蚀功率的增加和烧蚀时间的延长而增大，烧蚀时间和烧蚀功率均较大时，可能存在烧蚀孔洞被重凝材料堵塞或部分堵塞的情况。计算出纳秒激光的束腰半径为223 μm，纳秒激光烧蚀Cf/SiC复合材料的烧蚀阈值为0.32 J/cm2。