Laser ablation of anisotropic conductive adhesive

A laser ablation process has been developed and optimized for the rework of anisotropic conducting adhesive bonds. Ablative photodecomposition of the adhesive matrix and simultaneous removal of the conductive particles is a dry, controllable, and readily implemented alternative for removal of these materials and preparation of the substrate for reprocessing. The ultraviolet absorption spectrum was evaluated, and ablation results evaluated at both λ=193 nm and λ=248 nm. The λ=193 nm wavelength was determined to be optimal for complete adhesive removal and minimal thermal damage to the substrate. A systematic evaluation of the fluence level, angle of incidence, and cumulative exposure established the parameter range between complete adhesive removal and substrate damage. The surface topology of reworked samples showed little change from the original, but a resistance increase was observed for the rebonded circuits. This process appears superior to competing methods because it is both dry and restores the bonding surface to nearly original condition     

激光光敏消融动脉粥样硬化斑块

本文综述了激光光敏消融动脉粥样硬化斑块的研究现状、光敏剂选择性聚集于斑块的机理,光敏消融机制及其应用前景。     

Laser ablation and micromachining with ultrashort laser pulses

The mechanisms of ultrashort-pulse laser ablation of materials are discussed, and the differences to that of long laser pulses are emphasized. Ultrashort laser pulses offer both high laser intensity and precise laser-induced breakdown threshold with reduced laser fluence. The ablation of materials with ultrashort pulses has a very limited heat-affected volume. The advantages of ultrashort laser pulses are applied in precision micromachining of various materials. Some femtosecond laser pulse micromachining results, including comparison with long pulses, are presented. Ultrashort-pulse laser micromachining may have a wide range of applications where micrometer and submicrometer feature sizes are required     

真空及大气下激光对复合材料的烧蚀试验对比

激光与物质相互作用受到环境因素的影响。为了研究真空及大气环境下激光对复合材料的烧蚀模式和烧蚀规律,开展了激光辐照碳纤维复合材料对比试验。在不同辐照能量水平下,研究了两种环境中激光对复合材料的烧蚀特征,获得了复合材料瞬态温度响应数据,并对烧蚀样品进行了显微观测。试验结果表明,环境因素的影响与入射激光能量水平紧密相关。在低辐照能量水平下,复合材料表面烧蚀形貌具有差异,但瞬态热响应非常接近。在较高辐照能量水平下,复合材料烧蚀形貌差异较大:在真空环境下复合材料的环氧树脂发生热解和挥发,碳纤维束发生脱层;在大气环境下复合材料的环氧树脂发生明显的氧化反应,碳纤维束轻微脱层。最后,结合样品显微观测结果,分析了真空及大气环境下激光对复合材料烧蚀模式差异的原因,为建立激光烧蚀理论模型提供了参考。     

Laser ablation of atherosclerotic blood vessel tissue under variousirradiation conditions

A quantitative analysis is presented of the destruction of normal wall and atherosclerotic plaque areas of blood vessels by laser radiation. Threshold laser radiant exposure values were measured experimentally in vitro, along with the ablation efficiency for various laser wavelengths and irradiation conditions. Correlations were found between the ablation efficiency and fluence thresholds on the one hand and the optical properties of the blood vessel tissues on the other. Fibrous plaque was demonstrated to be selectively destroyed by the second-harmonic output from a pulsed Nd:YAG laser at lambda = 532 nm.     

金红石型纳米TiO2的液相激光烧蚀合成

利用浸入聚乙烯基吡咯烷酮(PVP)水溶液中的金属钛片为靶材,采用1064nm红外脉冲激光进行液相激光烧蚀制备了金红石型纳米TiO2。应用XRD、TEM、HRTEM和Raman对产物进行表征,并对其形成机理进行了探讨。结果表明:金红石型纳米TiO2可通过液相激光烧蚀法在室温下一步合成,颗粒平均粒径约50nm,尺寸分布比较窄,分散性较好。脉冲激光诱导的瞬间等离子体可能是金红石型纳米TiO2形成的主要原因。     

Laser ablation as a processing technique for metallic and polymerlayered structures

A study of the laser ablation process for application in processing metallic and polymer layered structures is presented. The central result of this study is that, by operating with laser pulses of different fluences, it is possible to selectively remove polymer overlayers on metallic films and metallic films from polymer layers, provided the metallic films are sufficiently thin. Careful choice of the fluence allowed both of these processes to be carried out with minimal damage to the underlying material. The damage produced has been characterized by laser processing through visual inspection, profilometry, and electron microscopy. In the case of polymer layers, the effect of exposure to laser irradiation through spectroscopic studies in the infrared, visible, and ultraviolet portion of the spectrum has also been studied. For the metallic layers, we have correlated the visible damage observed with changes in the electrical resistivity of the films     

ZnO clusters: Laser ablation production and time-of-flight mass spectroscopic study

Zinc oxide clusters have been produced by laser ablation of bulk powder zinc peroxide in vacuum and investigated by time-of-flight mass spectroscopy. Experimental results revealed unpredicted and hitherto unknown (ZnO)_n clusters of enhanced stability (“magic clusters”) at n=34, 60 and 78. Cage-like structures for the magic clusters have been suggested, supported by first-principles calculations.     

Laser ablation sampling for induction coupled plasma source quadrupole mass spectrometry of Cd-Zn-Te materials

A method to measure the elemental composition of both major and minor species that is spatially resolved along and below the surface of Cd-Zn-Te (CZT) crystal specimens is described. This method uses laser ablation sampling (LAS) for material introduction into an inductively coupled plasma (ICP) source quadrupole mass spectrometer (QMS) system for subsequent elemental analysis. Mass spectra are acquired at discrete locations on the surface of each CZT specimen, mounted inside a LAS cell. This cell allows argon sweep gas to transport the ablation products into the ICP-QMS for analysis. Since three component movement of the CZT specimen surface relative to the LAS site is possible under computer control, elemental analysis at specific locations on the surface can be obtained. Additional mass spectra are obtained by repetitive LAS at progressively deeper locations beneath the surface at a fixed position, and at difference sites of interest anywhere on the surface of the CZT specimen. These spectra are analyzed to obtain the relative ionic abundances of all detectable isotopes of the major (CZT matrix) and the minor (trace) elements. From these data, the ensemble atom mass concentrations are calculated for each LAS procedure. The relative mass fraction of each element specie within a particular LAS data set is then determined by calculating the ratio of its abundance to the whole ensemble mass in that sample.     

Laser ablation of SiO2 for locally contacted Si solar cells with ultra‐short pulses

We apply ultra‐short pulse laser ablation to create local contact openings in thermally grown passivating SiO₂ layers. This technique can be used for locally contacting oxide passivated Si solar cells. We use an industrially feasible laser with a pulse duration of τ_pulse ∼ 10 ps. The specific contact resistance that we reach with evaporated aluminium on a 100 Ω/sq and P‐diffused emitter is in the range of 0·3–1 mΩ cm². Ultra‐short pulse laser ablation is sufficiently damage free to abandon wet chemical etching after ablation. We measure an emitter saturation current density of J_0e = (6·2 ± 1·6) × 10⁻¹³ A/cm² on the laser‐treated areas after a selective emitter diffusion with R_sheet ∼ 20 Ω/sq into the ablated area; a value that is as low as that of reference samples that have the SiO₂ layer removed by HF‐etching. Thus, laser ablation of dielectrics with pulse durations of about 10 ps is well suited to fabricate high‐efficiency Si solar cells. Copyright © 2007 John Wiley & Sons, Ltd.     

八0四高山台数字电视覆盖分析和技术方案探讨

通过对八〇四发射台发射地面数字电视的覆盖分析,论证了在牡丹江地区特定的山地条件下,采用高山台站大功率覆盖的可行性。八〇四台发射相对高度950 m左右,采用3 kW数字功率,理论上可有效覆盖60 km半径,在该范围内牡丹江地区的11个乡镇和90多个行政村可良好接收8套左右的本地数字电视节目,接收点理论场强可达到55~66 d BμV/m。与常规中小功率、多点发射相比,该大功率、单点发射方案可以大大减少林口县、海林市境内的11个乡镇设备投入,为国家节省大量资金。     

一起VSAT站干扰微波站的实例分析

在C波段由于微波与卫星通信共用,地球站建站前我们一般都要进行电磁环境测试和相关的电磁兼容分析,鉴于微波通信系统干扰卫星通信系统的情况比较多见,我们在做分析时往往只注意地球站收信区电磁兼容分析,而忽略了地球站的发信区电磁兼容分析。最近我省发生了一起VSAT站干扰微波站的事件,我们及时进行了查找和分析,现将测试及分析情况提供给大家参考。 2000年底我站收到河北省长传局的干扰申诉,反映该局石家庄－唐山PDH数字微波电路A微波站收B站方向发现干扰。并呈一定的规律性：上午9：00以后较频繁,下午1：00以后又出现约2小…     

传统基站到有源天线基站的演进

随着无线网络的发展,基站架构也不断演进。详细介绍了传统基站、分布式基站、有源天线基站的架构,对比了其优缺点,说明了演进到有源天线基站的必然性。针对有源天线,明晰其概念,给出了设计思路,探讨了其技术优势。有源天线可通过波束成形覆盖更多小区,完全可满足未来低能耗、低成本绿色移动通信系统的发展要求,将成为基站演进的必然趋势。     

激光二极管双端抽运Tm:YAP激光器

简要分析了掺铥铝酸钇(Tm∶YAP)晶体的能级结构及吸收光谱特性,报道了一种室温条件下的激光二极管(LD)双端面抽运Tm∶YAP激光器。激光器输出的中心波长为1996 nm,2μm连续激光输出功率为40.7 W,光-光转换效率为30.4%,斜率效率为41.1%。经过声光(AO)调制后获得重复频率为10 kHz的脉冲激光输出,输出功率为34.6 W,激光脉冲宽度为92.08 ns,光-光转换效率为25.9%,斜率效率为32.9%。光束发散角x方向为11.6 mrad,y方向为12.2 mrad。     

激光物理与激光隐身技术

文章探讨了激光隐身的途径和方法,并对激光隐身技术的现状进行了分析。     

基站建设及基站天线的设计与分析

移动基站建设是为人们提供良好通信基础的重要途径,在移动基站建设过程中必须要选择合适的位置,提高基站的维修和运行成本,同时提高运行可靠性和稳定性。文章对通信基站建设以及基站的天线分布进行设计,旨在提高基站的工作效率。     

风生水起的移动电台

随着现代人工作、生活节奏不断加快,娱乐文化需求日趋多样化,优质原创内容急剧增加,同时各项信息通信技术超常发展,传统广播业被颠覆,移动电台却由此风生水起。移动电台打破了传统音频与互联网的壁垒,突破了时间和地域的限制,以其强烈的伴随性,受到越来越多人的喜爱,各种移动电台如雨后春笋般涌现。     

全向小区与定向小区共站解决覆盖断点

针对目前一些全向基站信号覆盖不理想问题 ,提出了有效解决办法 :在全向基站增加一定向小区 ,专门覆盖该盲区 ,解决覆盖断点问题