大芯径空气包层微结构光纤实现kW级激光传输

kW级高功率激光柔性传输是激光清洗、激光焊接、激光刻蚀等高功率激光加工领域中必备的环节,而实现高功率激光低损耗传输的光纤是其关键器件。目前高功率激光传输光纤采用大芯径传能光纤,仍然存在着弯曲损耗大、柔性差等问题,并且使用过程中要经常维护。华南师范大学特种光纤研究中心提出一种大芯径空气包层微结构光纤,利用包层的空气孔可以极大降低激光泄露的风险,降低光纤制备过程中对耐高温涂敷层的严苛要求,实验结果证实该光纤在室温无制冷条件下可实现kW级激光传输,从而为10 kW级高功率激光柔性传输奠定基础。     

High-aspect-ratio microdrilling in polymeric materials with intense KrF laser radiation

UV laser microdrilling of high-aspect-ratio holes has been studied by using an intense beam with a low numerical aperture (KrF laser). The UV laser ablation produces a minimum of thermal or mechanical damage on the target. Under some particular experimental conditions (many high-fluence pulses), it is shown that long deep holes are obtained with reproducible aspect ratio (up to K/d길) in a variety of materials. Experiments with polymers (PMMA, PC, PET, PI, PS, PEEK) show that the more absorbing the polymer is, the better the resolution. However highly absorbing materials exhibit a low ablation rate. These promising results on laser microdrilling can be extended to new applications, for example, when the beam/target relative movement is computer driven. For instance this approach can be applied to cutting micro-objects with complicated shape or to machining fragile or brittle materials.     

2 kW半导体激光加工光源

针对激光加工在金属材料焊接、熔覆、表面硬化等工业领域的应用,考虑到半导体激光器体积和重量小、效率高、免维护、成本低以及波长较短等特点,设计了功率达2 kW的半导体激光加工光源。在大通道工业水冷条件下,采用48只出射波长分别为808,880,938,976 nm的传导冷却半导体激光阵列作为发光单元,最终研制出了2 218 W高亮度光纤耦合模块。此高亮度模块可以实现柔性加工,直接应用于金属材料焊接、熔覆、表面合金化等工业领域,对于半导体激光器在工业领域的应用具有重要意义。     

激光微加工技术在集成电路制造中的应用

激光微加工技术以非接触加工方式,高效率、无污染、高精度、热影响区小的优点在微电子集成电路制造中得到了广泛应用.介绍了在集成电路制造封装中采用的激光微调、激光打孔、激光清洗、激光柔性布线和激光微焊技术.     

Rapid micromachining of high aspect ratio holes in fused silica glass by high repetition rate picosecond laser

We present multiple methods of high aspect ratio hole drilling in fused silica glass, taking advantage of high power and high repetition rate picosecond lasers and flexible beam delivery methods to excise deep holes with minimal collateral damage. Combinations of static and synchronous scanning of laser focus were explored over a range of laser repetition rates and burst-train profiles that dramatically vary laser plume interaction dynamics, heat-affected zone, and heat accumulation physics. Chemically assisted etching of picosecond laser modification tracks are also presented as an extension from femtosecond laser writing of volume nanograting to form high aspect ratio (77) channels. Processing windows are identified for the various beam delivery methods that optimize the laser exposure over energy, wavelength, and repetition rate to reduce microcracking and deleterious heating effects. The results show the benefits of femtosecond laser interactions in glass extend into the picosecond domain, where the attributes of higher power further yield wide processing windows and significantly faster fabrication speed. High aspect ratio holes of 400 μm depth were formed over widely varying rates of 333 holes per second for mildly cracked holes in static-focal positioning through to one hole per second for low-damage and taper free holes in synchronous scanning.     

Ultra-short pulse laser deep drilling of C/SiC composites in air

Ultra-short pulse laser machining is an important finishing technology for high hardness materials. In this study, it demonstrated that the ultra-short pulse laser can be used to drill the film cooling holes and square holes in aero-engine turbine blades made of C/SiC composites. Both the edges and bottoms of the drilling holes are covered with small particles. The following factors have a great effect on drilling holes according to this work: (1) circular holes can be processed only at a relative small helical lines spacing. (2) With the increase of laser scanning speed, the depth of holes reduces while the diameter rarely changes. (3) Through the holes of high aspect ratio can be obtained via high processing power.     

Effects of excimer laser illumination on microdrilling into an oblique polymer surface

In this work, we present the experimental results of micromachining into polymethy-methacrylate exposed to oblique KrF excimer laser beams. The results of low-aspect-ratio ablations show that the ablation rate decreases monotonously with the increase of incident angle for various fluences. The ablation rate of high-aspect-ratio drilling with opening center on the focal plane is almost independent of incident angles and is less than that of low-aspect-ratio ablation. The results of high-aspect-ratio ablations show that the openings of the holes at a distance from the focal plane are enlarged and their edges are blurred. Besides, the depth of a hole in the samples oblique to the laser beam at a distance from the focal plane decreases with the increase of the distance from the focal plane. The number of deep holes generated by oblique laser beams through a matrix of apertures decreases with the increase of incident angle. Those phenomena reveal the influence of the local light intensity on microdrilling into an oblique surface.     

Numerical simulation of process dynamics during laser beam drilling with short pulses

In the last years, laser beam drilling became increasingly important for many technical applications as it allows the contactless production of high quality drill holes. So far, mainly short laser pulses are of industrial relevance, as they offer a good compromise between precision and efficiency and combine high ablation efficiency with low thermal damage of the workpiece. Laser beam drilling in this pulse length range is still a highly thermal process. There are two ablation mechanisms: evaporation and melt expulsion. In order to achieve high quality processing results, a basic process understanding is absolutely necessary. Yet, process observations in laser beam drilling suffer from both the short time scales and the restricted accessibility of the interaction zone. Numerical simulations offer the possibility to acquire additional knowledge of the process as they allow a direct look into the drill hole during the ablation process. In this contribution, a numerical finite volume multi-phase simulation model for laser beam drilling with short laser pulses shall be presented. The model is applied for a basic study of the ablation process with μs and ns laser pulses. The obtained results show good qualitative correspondence with experimental data.     

Laser processing integrated into machine tools — design,applications, economy

In the last few years, lasers have found new applications in production engineering as tools for surface treatment, cutting, welding, drilling and marking. So far, the laser has mainly been used in special laser processing machines (laser-only) directly integrated into a production line or serving as stand-alone stations in the workshop. By combining conventional metal cutting technologies with laser processes in one machine, complete processing of a workpiece with different technologies in one setting can be realized. The main advantages are a reduction of the material flow between the production machines, which leads to a reduction in processing time and logistics, and an enhancement of manufacturing quality due to the processing in one setting. In addition to this approach, new processing technologies such as laser-assisted machining are possible.Applications of laser caving, hardening, welding and drilling of production parts in combination with the cutting process in one setting have been investigated with the aim of adapting these technologies to the characteristics of the machines and the typical parts spectra. Furthermore, various technical solutions for the integration of lasers into milling centres and lathes have been elaborated. In both situations the laser tool is handled like a standard tool and can be exchanged automatically. The main results will be reported, together with a brief discussion of the economic aspects of laser processing integrated into machine tools.This article is based on an invited paper presented at LANE '94, Erlangen, 12–14 October 1994.     

Beamforming array techniques for acoustic emission monitoring of large concrete structures

This paper introduces a novel method of acoustic emission (AE) analysis which is particularly suited for field applications on large plate-like reinforced concrete structures, such as walls and bridge decks. Similar to phased-array signal processing techniques developed for other non-destructive evaluation methods, this technique adapts beamforming tools developed for passive sonar and seismological applications for use in AE source localization and signal discrimination analyses. Instead of relying on the relatively weak P-wave, this method uses the energy-rich Rayleigh wave and requires only a small array of 4–8 sensors. Tests on an in-service reinforced concrete structure demonstrate that the azimuth of an artificial AE source can be determined via this method for sources located up to 3.8 m from the sensor array, even when the P-wave is undetectable. The beamforming array geometry also allows additional signal processing tools to be implemented, such as the VESPA process (VElocity SPectral Analysis), whereby the arrivals of different wave phases are identified by their apparent velocity of propagation. Beamforming AE can reduce sampling rate and time synchronization requirements between spatially distant sensors which in turn facilitates the use of wireless sensor networks for this application.     

Laser fabrication of high-aspect-ratio holes and grooves in photoresist by time constant manipulation

We report on the cw-laser fabrication of sharp-edged holes and grooves in organic-dye-sensitized photoresists for g-line or i-line by manipulating its intensity and scanning rate. The laser fabrication is performed to locally control the reaction time constant of the photoresist. By scanning a tightly focused laser focal spot inside the transparent photoresist, various micron/submicron meter structures have been produced based on the reaction time constant depending on the beam intensity. The proposed method is considered to be a cost-effective technique for high-aspect-ratio holes and grooves fabrication.     

Direct-write pulsed laser processed silver nanowire networks for transparent conducting electrodes

Metal nanowire networks are promising alternatives for transparent conducting layers in flexible electronics. However, the inverse relationship between transparency and conductivity limits their viability in many critical applications. In this work, we demonstrate a direct-write refining technique in which a solution-processed nanowire network, deposited by spin coating, is exposed to monochromatic UV pulsed laser processing near a plasmonic resonance. Our results exhibit a 75?% reduction in surface resistance along with marginal improvements in optical transparency. The local nature of the laser technique enables direct-write or large area processing on a variety of substrates including flexible, and organic materials.     

Power ultrasound and its applications: A state-of-the-art review

Ultrasonic processing has attracted increasing attention by people because ultrasonic technology may represent a flexible ‘green’ alternative for energy efficient processes. The major challenges for the power ultrasound application in real situations are the design and development of specific power ultrasonic systems for large-scale operations. Thus, new families of power ultrasonic transducers have been developed in recent years to meet actual needs, and this contributes to the implementation of power ultrasound of application in many fields such as chemical industry, food industry and manufacturing. This paper presents the current state of ultrasonic transducers of magnetostrictiv type and piezoelectric type as well as applications of power ultrasound in various industrial fields including chemical reactions, drying/dehydration, welding, extraction, heat transfer enhancement, de-ice, enhanced oil recovery, droplet atomization, cleaning and fine particle removal. The review paper helps to understand the current development of power ultrasonic technology and its applications in various situations, and induce extended applications of power ultrasound to more and more fields.     

Sub-micron ablation of metallic thin film by femtosecond pulse laser

The ability to machine very small features in a material has a wide range of applications in industry. We ablated holes into thin film of 100 nm thickness made from various metals by femtosecond pulsed laser ablation. Using a Ti:Sapphire laser which supplies a laser pulse of 150 fs duration at central spectrum wavelength of 400 nm, we have produced a series sub-micron holes, whose diameters are less than 200 nm with a focused laser spot of 1.7 μm. We found that the material damage threshold has a great influence on the quality of the produced features. Experimental results shows that the heat-affected zone and the degree of being affected reduce with the increase of threshold value.     

A statistical approach to determine process parameter impact in Nd:YAG laser drilling of IN718 and Ti-6Al-4V sheets

The numerous unique advantages afforded by pulsed Nd:YAG laser systems have led to their increasing utility for producing high aspect ratio holes in a wide range of materials. Notwithstanding the growing industrial acceptance of the technique, the increasingly tighter geometrical tolerances and more stringent hole quality requirements of modern industrial components demand that “defects” such as taper, recast, spatter etc., in laser-drilled holes are minimized. Process parameters like pulse energy, pulse repetition rate, pulse duration, focal position, nozzle standoff, type of gas and gas pressure of the assist gas are known to significantly influence hole quality during laser drilling. The present study reports the use of Taguchi design of experiments technique to study the effects of the above process variables on the quality of the drilled holes and ascertain optimum processing conditions. Minimum taper in the drilled hole was considered as the desired target response. The entire study was conducted in three phases:(a) screening experiments, to identify process variables that critically influence taper in laser drilled holes, (b) Optimization experiments, to ascertain the set of parameters that would yield minimum taper and (c) validation trials, to assess the validity of the experimental procedures and results. Results indicate that laser drilling with focal position on the surface of the material being drilled and employing low level values of pulse duration and pulse energy represents the ideal conditions to achieve minimum taper in laser-drilled holes. Thorough assessment of results also reveals that the laser-drilling process, optimized considering taper in the drilled hole as the target response, leads to very significant improvements in respect of other hole quality attributes of interest such as spatter and recast as well.     

通过光致还原调制氧化石墨烯寿命并用于微纳图形制备

氧化石墨烯因其宽带可调谐的荧光发射特性已被广泛应用于荧光成像、金属离子高灵敏检测和光电器件的制备.相比于荧光强度,氧化石墨烯荧光寿命不受材料厚度和激发功率的影响,具有更为稳定和均一的特性.本文研究了在激光还原过程中氧化石墨烯荧光寿命逐渐减小的变化行为,发现了长寿命sp~3杂化结构向短寿命sp~2杂化结构的转变.通过精确控制还原时间,结合激光直写技术,在单层氧化石墨烯薄膜上实现了二维码、条形码、图形和数字等微纳图形的制备,还在多层氧化石墨烯薄膜结构上获得了多寿命多层微纳图形.这种微纳图形的制备具有灵活无掩膜、高对比和多模式的特点,可用于高密度光学存储、信息显示和光电器件制备等诸多领域.     

High-throughput rear-surface drilling of microchannels in glass based on electron dynamics control using femtosecond pulse trains

This study proposes a rear-surface ablation enhancement approach to fabricate high-aspect-ratio microchannels by temporally shaping femtosecond laser pulse trains. In the case study of K9 glass, enhancements of up to a 56 times higher material removal rate and a three times greater maximum drilling depth are obtained by the proposed method, as compared with conventional femtosecond laser drilling at the same processing parameters. The improvements are due to the changes of photon-electron interactions by shaping femtosecond pulse train, which can effectively adjust the photon absorption and localized transient material properties by changing electron dynamics such as free electron densities.     

Excimer laser: a new tool for precision micromachining

The unique features of the pulsed UV light emitted by excimer lasers lead to a variety of innovative applications of this relatively new industrial laser type. The excimer laser is used for micromachining, surface treatment, microlithography and high-quality marking. The resolution of excimer laser processing is very high: typical structures of 100 m down to 0.2 m are produced. Moreover, typical ablation rates of about 0.1–1 m per laser pulse also allow extremely high precision in the depth of material removal.The most popular industrial applications of excimer lasers are microdrilling for highly integrated multichip modules (MCMs), TABs and FPCBs, in the manufacturing of nozzle plates for personal ink-jet printers, TFT annealing for flat panel displays, wire stripping for hard disk heads, and indelible marking for the aircraft, electronic and medical/health-care industries.In contrast to traditional and alternative methods, the use of excimer lasers allows fast and flexible production processes without pollution of the environment. Nearly all technical materials (plastics, ceramics, glass, metals, semiconductors, composites) and biological/medical materials can be processed by excimer laser methods.