Laser has been widely applied for advanced material processing,such as welding of advanced high strength steels (AHSS) for automotive applications and Pt,Ti,and Nitinol alloys for medical applications. Recently,ultrafast pulse laser,especially femtosecond laser,is identified as powerful tools for joining and surface engineering of nanomaterials. This paper reviews our research on these fields at the Centre of Advanced Materials Joining,University of Waterloo. Representative conclusions are listed for laser material processing at three continuing scales. 1) For AHSS welding,a thin Al layer can dramatically enhanced the weldability of galvannealed AHSS. The movement of the welding line and softening in the vicinity has significantly influence on global mechanical properties in dual phase (DP) and transformation induced plasticity (TRIP) steels. The increase of the strength ratio decreases the formability and results in the non-uniform strain distribution. 2) For medical micro-welding,oxygen is found to be a key role for welding strength and microstructure. The formation of intermetallics reduces the relative ductility and increases the susceptibility of cracking. Different laser processing parameters can significantly influence weld mechanical performance. 3) For femtosecond laser nanofabrication,the joining of Au nanoparticles is successfully achieved by controlling laser energy. Surface nanostructure of Ag induced by femtosecond laser irradiation can work effective probes for surface enhanced Raman spectroscopy.

Deeply penetrated welds can be produced with high-power-density lasers. Thus the factors affecting laser weld penetration,laser-induced plume behavior and the interaction between a laser beam and a plume,keyhole behavior,melt flows in the molten pool,and the generation and prevention of bubbles and porosity were investigated. Consequently,the effects of plasma and plume on the weld penetration were interpreted in CO2 and fiber lasers welding,respectively. The formation of spattering,underfilled beads,and humping was understood. It was confirmed that porosity was easily formed at high powers and low welding speeds due to the generation of many bubbles from the tip of a keyhole.

Behavior of welding arc plasma,characteristic of welding voltage,local changes of electron temperature and electron density were investigated respectively with high speed camera,inductance gauge of current and voltage,spectrometer in low power YAG laser-gas metal arc welding (GMAW) hybrid welding process comparing with simple GMAW welding case. Based on the experimental results,behaviors of hybrid welding arc plasma were explained by plasma theory of thermodynamic equilibrium. The results indicated that,due to the input of YAG laser,the GMAW arc was attracted and constricted,electron temperature and electron density of local arc were increased to (15400±900) K and (1.265±0.101)×1017cm-3,the voltage output of GMAW source was decreased,and the formation of local thermodynamic equilibrium (LTE) of hybrid welding arc plasma was accelerated.

Welding is one of the key technologies in pipeline construction. The corresponding welding technology should be meeting the requirements of the pipeline construction due to the rapid development of advanced pipeline steel. The advantages and disadvantages of laser welding for pipeline steel are analyzed. X52 pipeline steels with a thickness of 16 mm are welded using high power CO2 laser. Cracks in the weld are not detected by X-ray. Solidification properties and microstructure of laser welded joint have been studied by optical microscope. The mechanical tests of the welded joint have been conducted according to American Petroleum Institute Specification API SPEC 5 L.The results show that the ultimate tensile strength is 480 MPa ,fracturing in parent metal,without any cracks in 180°bend specimens;and Charpy notch toughness at -20 ℃ is CVN＝279 J in weld metal,CVN＝282 J in fusion zone and CVN＝212 J in heat affected zone. The maximum hardness of butt welded joint is about 270 HV,which locates in the bottom of weld. All the mechanical properties of weld produced by using laser welding can meet the welding technical requirements of X52 pipeline steel.

Laser consolidation (LC) is a novel computer-aided manufacturing process developed by the Industrial Materials Institute of National Research Council of Canada (NRC-IMI). This rapid manufacturing process produces net-shape functional metallic parts layer-by-layer directly from a computer aided design (CAD) model by using a laser beam to melt the injected powder and re-solidifying it on the substrate or previous layer. As an alternative to the conventional machining process,this novel manufacturing process builds net-shape functional parts or features on an existing part by adding instead of removing material. In this review paper,LC of CPM-9V tool steel,Ni-based IN-625 and IN-718 superalloys,and Ti-6Al-4V alloy will be discussed. The microstructures and functional properties of these laser consolidated materials will be examined along with several potential industrial applications.

Selective laser melting (SLM) is currently the subject of major research studies with the objective to directly manufacture high performance metal alloys and metal matrix composite (MMC) parts by consolidating metal and its composite powders. The successful fabrication of the parts by SLM is related with proper selection of materials and processing parameters to provide sufficient densification and consolidation of the powder materials and generate suitable microstructures and mechanical properties. It is also important to minimize or eliminate typical issues such as porosity,balling effect,and thermal stress associated with the powder melting and consolidation at high temperature conditions during SLM process. This paper presents the fundamental material and process aspects,address the technical issues,and review the recent research development in the SLM of metal and MMCs.

The technological and economic advantages of laser direct manufacturing of large titanium structural components in comparison to the traditional forging process are briefly summarized and their industrial application potentials in the aerospace industries are prospected. State of the art on processing optimization,microstructure and mechanical properties control,equipment development and engineering applications in aerospace industries are reported. The technological challenges facing the further development of the technology is reviewed. Physical and metallurgical complexities of laser direct manufacturing of large titanium structural components are analyzed with a special emphasis on the thermal physics of the deposition process,extraordinary metallurgical kinetics of the laser induced high-temperature melt pool,the forming mechanisms of the unique non-equilibrium rapidly solidified structures and various inherent internal defects. It is pointed out that efficient prevention of “component distortion and cracking” as well as control of “internal structure and defects” are currently the two “bottle-neck” obstacles challenging the further development and industrial applications of the revolutionary advanced manufacturing technology. Intensive basic research and more fundamental understanding on the non-steady state evolution and interaction behaviors of internal stresses and the forming mechanisms of rapid solidification microstructures and internal defects are needed in order to effectively overcome the above “bottle-neck” problems.

Samples of Ti-6Al-4V used in the test of plane strain fracture toughness (KIC) test is fabricated by laser solid forming (LSF). Primary β grain,with a characteristic of epitaxial growth along the depositional direction,shows an average width of 100-400 μm and length of several centimeters. Within β grains,lathy α needles and fine-weaved dense Widmanstatten α+β laths are observed. KIC≥52.6 MPa·m1/2 reaches the forging standard. And as same as the tensile property of LSF Ti-6Al-4V sample,KIC property presents remarkable anisotropism which is caused by the microstructure characteristic. Fine-weaved dense Widmanstatten α+β laths owns strong ability in anti-crack-propagation,in result,crack-propagation shows sentivites to β grain boundary. If crack propagation runs the direction perpendicular to β grain boundary,KIC value reaches maximum;if crack propagation runs the direction along β grain boundary,the longer the boundary,the higher the KIC value. It is more easier for crack propagation with a small angle between crack-propagation direction and β grain boundary(0-90°). The bigger angle and smaller β grain both result in difficulties in crack-propagation.

Thin wall samples from TA12 titanium alloy have been prepared on TA15 substrates by laser direct deposition of coaxially fed metallic powders under protective gas. The microstructure,phases and mechanical properties of the deposited materials were investigated. The results indicated that the deposited materials are fully dense,and metallurgically bonded with the substrate. The as-deposited TA12 titanium alloy tendes to be equiaxed grains,within which is basketweave widmannstatten structure formed of many fine α lamella and small amount of β with different direction. And the size of the original β-Ti grains increases a little with increasing the laser power used for depositing. The tensile strength at room temperature and under 550 ℃ for the as-deposited materials along the scanning direction reaches the value for the annealed bar.

The effects of heat treatment on the microstructure and mechanical properties of laser solid forming Inconel 718 superalloy have been investigated. As compared with as-deposited samples,direct aged (DA) microstructure of laser solid formed (LSF) Inconel 718 changed little,and still presents the microstructural characteristic of columnar dendrites which grow epitaxially from the substrate. However,the hardness and tensile strength of DA samples increase obviously. Three technology of homogenization,solution and double aging heat-treatment (960STA) result in complete dissolution of interdendritic Laves phase and the reduction of Nb segregation. Further the solution treatment results in the precipitation of acicular δ phase along grain boundaries,and the tensile strength and plasticity both reach the wrought standard of Q/3B 548-1996 at room and high temperature. The tensile fracture surface of DA samples presents anisotropic feature of dimples along deposition orientation of columnar dendrites array,which is similar to that of the as-deposited samples. It is found that the distribution anisotropy of dimples in LSF samples disappeared through 960STA treatment.

Based on Ansys secondary development language APDL,a parametric temperature/stress finite element model for metal laser solid forming (MLSF) process was developed. The model allows for non-linear behavior of material properties,Gaussian distribution of laser energy,thermal convection and radiation boundary condition,phase change,free deformation constraints condition et al. A full finite element model of MLSF process is established by transition mesh technology. Accuracy of simulation is improved and the element number is reduced under the model. The temperature/stress evolution of MLSF process is simulated based on moving laser beam and element birth and death technology. On the basis of the temperature distribution is evolution,the reason of inducing the compress plastic stress,tensile plastic stress and unloading zones is analyzed. The influence of MLSF process conditions on temperature/stress can be studied by utilizing the parametric finite element model in order to optimize the MLSF process.

Study on the technology of selective laser melting (SLM) is carried out on Dimetal-280 system with 200 W fiber laser. Orthogonal experiment of six factors and five levels is designed to optimize parameters for 316L stainless steel powder. Six typical surface profiles are summarized,and the relative density and dimensional accuracy along z-direction are measured correspondingly. Results show that the density of samples is high when powders are fully melted and low when partially melted. Practical manufacturing layer trends thicker,which affects the dimensional accuracy. Considering the comprehensive effects of surface profile,relative density and dimensional accuracy,optimal parameters are obtained. Special specimen with sharp-angled and overhang features for geometrical performance test is manufactured. The relative density,dimensional accuracy and surface roughness Rz are 89%,96.8% and 25 μm respectively,which show a good result.

Reliable and efficient power generation is a major global issue due to both political and environmental concerns. Nevertheless many critical components,particularly the blades of the low pressure (LP) side of power generating steam turbines,are subjected to failure due to severe erosion at the leading edges. Since taking machines off-line for maintenance and removal of damaged blade for repair is extremely expensive,increasing the service life of these critical components can offer significant economic and political benefits. Conventional techniques to increase service life include brazing of an erosion shield at the leading edge of the turbine blades,open arc hardfacing,and cladding with erosion resistant materials using gas tungsten,manual metal or plasma transferred arc welding. We have been investigating for the past eight years the potential of laser cladding to deposit a high quality and erosion resistant protection shield on the leading edge of LP blades. Laser cladding offers unique advantages over the conventional techniques. The project to-date has demonstrated the feasibility of in-situ repair of turbine blades in trials conducted at a power station using a fibre delivered Laserline diode laser and a robot. A company (Hardwear Pty. Ltd.) has been established to commercialise the technology and has delivered two commercial contracts.

Laser additive manufacturing (LAM) of tungsten carbide metal matrix composites (MMCs) has been evaluated for surface modification of hot die forming tools,cutting edges,glass tooling,extrusion mandrels,and other abrasive wear applications. This work focuses on transitions from tool steels to MMCs through a single pass laser powder deposition operation. Issues related to the application of various metal powders and carbides used include surface hardness,porosity,cracking,and dilution. These issues along with factory results that were obtained during this project are discussed.

This paper investigates the effects of porosity of the forming parts by laser cladding method. In the experiment,the laser cladding has been applied to build up the bulk clad on the thin layers formed by selective laser sintering,and the surface porosity with various laser powers has been characterized by imprint method. In the numerical analysis,a computation model was developed to analyze the porosity based on the surface tension and energy of cladding powders at various temperatures. The results show a good conformity between the numerical analysis and the experimental measurement.

Early nuclear power plant components were normally made with stainless steel AISI 316L due to its good anticorrosion property. After long time running,316L nuclear components are facing severe intergranular stress corrosion under rigorous radiation conditions. To rejuvenate the as-eroded 316L components is vital for long-term sustainable and safe operation of the nuclear power plants. It is approved that the resistance to intergranular stress corrosion cracking and intergranular attack is significantly dependent on the Cr content in the material. In this paper,the coating was deposited by CO2 and Nd∶YAG laser using Inconel 690. Investigation on main influence factors on the Cr content in the coating including the dilution rate,laser types,beam energy distribution and laser processing parameters,were discussed. A rectangular beam can achieve low dilution,high Cr content and high deposition efficiency than a Gaussian beam. The coating produced by Nd∶YAG laser shows more excellent properties than CO2 laser.

High power diode laser (HPDL) is advanced portable equipment with the high value electrical to optical conversion efficiency. Diode lasers have seen wide applications in material fabrication and processing. Aggregate WC-Ni based superhard composites were fabricated on 304 stainless steel substrate. Wear-resistant coatings were fabricated by a 3 kW diode laser with direct injection powders into the molten pool. The coating had excellent bonding with the substrate and was free of pores and cracks. The morphology of laser cladding layer was observed by scanning electronics microscope (SEM),composition analysis was applied by energy dispersive spectroscopy (EDS),and the phase transformation was characterized by X-ray diffraction (XRD). The results showed that WC-Ni based superhard composites was fabricated by high power diode laser with high content tungsten carbide (60%) and low dilution. The main structure of diode laser cladding WC-Ni based alloy was γ-Ni,WC,W2C,Ni3B,CrB2 etc. The hardness of the laser clad layer is inhomogeneously distributed with the average value of HV 1100,higher than the substrate of HV 350. The hardness in the transition region is gradient distributed with steep reduction.

The laser surface cladding of AZ91D magnesium alloy with Ni-Cr-B-Si+WC powders has been investigated. Laser surface cladding was conducted using a continuous wave CO2 laser. As a result,a good metallurgical bond interface was obtained between Mg alloy substrate and coating. The microstructure and phase analysis of the coating were carried out by scanning electron microscope (SEM) and X-ray diffraction (XRD). The hardness and the corrosion properties of the coating were also measured. The experimental results show that the cladding layer is composed of AlNi3,Al3Ni2,Ni(Cr2O4) and different kinds of carbide. The cracks and porosity of coating are decreased with the join of 25% WC particles. The hardness of the cladding layer is significantly improved by 9.4 times higher than that of the AZ91D substrate,and the modulus is about twice higher than that of the substrate. The corrosion resistance of the laser modified samples is considerably improved as compared to the substrate.

Ti-6Al-4V/B/C mixed powder which pre-pasted on a Ti-6Al-4V substrate was scanned by a 500 W pulsed YAG laser to induced in situ formation of a titanium composite coating contained TiBx and TiC ceramic reinforced phases. The influences of laser processing parameters including pulse frequency (PF),pulse width (PW),laser power (P) and scanning speed (V) on the microstructure and properties of the coating were investigated. Microstructure,phase components and micro-hardness of the coating were analyzed by optical microscopy (OM),scanning electron microscopy (SEM),X-ray diffraction (XRD) and micro-hardness tester respectively. The optimized processing parameters of a single path laser scanned specimen in this case are as follow:PF=15 Hz,PW=3 ms,laser line energy about 11 J/mm. Multi-path laser scanned specimens were formed under the above processing parameters. TiB and TiC ceramic were formed evenly reinforced in the matrix of Ti-6Al-4V with the morphology of needle,tiny dendrites and disperse particles. No crack and porous are found in the single and multi-path specimens. Metallurgical bonding is formed between the coating and the substrate. The maximum micro-hardness of a multi-path layer is up to 800 HV,which is 2 times of that of the substrate (394 HV). The wear weight loss of a multi-path laser scanned specimen formed under the optimized processing parameters is 21% less than that of the substrate.

In-situ synthesis of the system of TiB ceramic particle reinforced Co-base alloy composite coating has been produced on titanium alloy surface by CO2 flow transverse laser to improve the comprehensive properties of the material. Analysis shows that β-Ti,γ-Co,TiB and TiB2 ceramic phase and CO2Ti reinforcement phase lie in the coating. Studies of microstructure on the coating by scanning electronic microscope (SEM),electron probe microzone analysis (EPMA) show that in-situ synthesis of TiB2 and TiB major ceramic phases disperse homogeneously in the γ-Co based alloy. With the increase of the content of Ti and B in cladding zone the form of reinforcement phase varies with chemical composition of the coating,and the small dispersed sheet and massive structure transform into column crystal structure with regularly oriented and uniform distribution. The wear resistance of the coating was evaluated with wear test. The wear loss of the coating is approximately 1/10 of the substrate material. Wear resistance of the composite coating is significantly improved.

Intermetallic matrix composite (IMC) surface layer has been formed on Ni-based alloy surface by laser cladding via CO2 laser. The Ni3Si composite coating of NbC particles reinforced was prepared by in situ contact reaction with preplaced powder mixtures of Ni-Si-Nb-C. It was found that compound material cladding coating mainly consists of NbC particles,Ni3Si intermetallic and Ni solid solution. An excellent bonding between the coating and the substrate was ensured by the strong metallurgical interface and good wettability between the reinforced NbC and the coating matrix. The NbC particles were about 2-4 μm in size and dispersed in the coating. The crystal structure of NbC and the growth kinetics of laser cladding play an important role in controlling the growth morphology of carbide.

In order to improve the wearing properties of the mild steel,in-situ synthesis of TiC-Mo2C particles reinforced composite coatings has been prepared by laser cladding using ferrotitanium,ferromolybdenum,graphite and iron. The microstructure and properties of the composite coatings were investigated by optical microscopy,X-ray diffractometer (XRD),electron probe microanalyzer (EPMA) and microhardness tester. Results indicate that TiC-Mo2C particles were produced by direct metallurgical reaction between ferrotitanium,ferromolybdenum and graphite during laser cladding process. It was also found that the fine carbides are dispersed in the matrix in form of graininess and petaliform. The hardfacing layer with high hardness and good wear properties could be obtained when the amounts of ferrotitanium,ferromolybdenum and graphite were controlled within a range of 30%40%,3%6%,3%4%,respectively.

To strengthen the surface performance of medium steel,Ni-P-Al2O3 electroless composite plating was produced on 45# steel,and then treated by pulsed Nd:YAG laser beam. Optical microscope (OM) and scanning electron microscope (SEM) were used to observe the microstructure of the coating. X-ray energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) were employed to analyze the phases and elements of the coating. The micro-hardness of pulse laser processing was tested. The results reveal that the hardened coating has good performance with uniform components and fined microstructure. The phases in hardened layer obviously change,the coating is divided into five regions from the surface to inner as follows:dendrite region,cystiform crystal zone,columnar crystal zone,fusion zone,heat affected zone (HAZ) and substrate. After laser process,the coating obviously transits from amorphous state to crystalline state,where non-equilibrium phases such as Al5FeNi,FeNi and Fe0.64Ni0.36 were found. The microhardness of hardened region is about 1.7 times of as-deposited layer and 4.5 times of the substrate owing to dispersion and transformation strengthening.

Laser assisted machining (LAM) takes the advantages of local heating and softening of workpiece by laser beam in front of the cutting tool. The local softening of workpiece at the shear zone enables much easier plastic deformation during machining. This paper reviews the up-to-date progress on LAM of ceramics. It covers the laser beam integration with cutting tools,analysis of temperature distribution around the cutting region,material removal mechanism,tool wear mechanism,and optimization of LAM. The benefit of LAM and its optimization are discussed in terms of material removal temperature.

When the galvanized auto-body panel steel sheets were cut by CO2 laser and the three-dimensional (3D) laser cutting machine,problems such as collision and burn-off are easily generated in the uphill,downhill and corner. So the corresponding improvement measurements are proposed in this paper. Experimental results indicate that to obtain 3D cutting workpiece with good cutting quality,high cutting precision and small hot effect width,the incident angle changed along with the pose of cutting head should be limited less than 20°. The collision can be eliminated by increasing craft spot,adjusting cutting direction and changing incident angle. Burn-off in uphill,downhill and corner can be effectively avoided by decreasing laser power,and opting pulse laser and reducing its duty ratio and using the air to take as auxiliary gas and so on. At the same time,the cutting quality is evaluated from the kerf width,cutting surface roughness,cutting surface ripple and hot affected width.

Methods for interference detection between laser head and part,and correction of laser head posture were proposed. The stero lithography (STL) model of laser heads was built and divided into two types of concave and convex. The interference areas were found out by using the ubiety of the disperse points on STL model and normal vector of triangles that are composed of laser head model. A method to avoid the interference by rotating the laser head and to calculate critical rotating angle by using a series of cutting planes cutting the laser head model was presented. The algorithms were implemented by using VC++ and OpenGL. The case studies show that the method can primely detect the interference areas of laser head and part,and correct the posture of laser head so as to avoid the interference. The whole process of detection and correction are stable and reliable.

The ZrO2 ceramic sample has been shocked by laser pulse with 35 J energy and determined with scanning electron microscope (SEM) for researching on the impact toughness. The results show that a compact layer with 90 μm thickness that there is no cracks in is formed in the laser irradiated surface of the sample,and a lot of micro-cracks which its density increased as nearing to the back were observed under the compact layer,while the spallation occurred in the back of the sample. The X-ray phase analysis for ZrO2 ceramic indicate that the impact phase transition from tetragonal phase to monoclinic phase has occurred in some materials,which may lead to the volume of metallographic structure increasing. The residual stress produce by the transition in the tip of cracks will hinder cracks expanding,so the cracks have no expandability. A ceramic sample has been shocked by laser pulse with 10 J energy repeatedly,and then shocked by laser pulse with 42 J energy,the pretreatment results show that the spallation tendency appears in the sample back,but no spallation occurred in there,so it suggests that the laser shocking pretreatment can increase the impact toughness.

The aluminum alloy 2A02 coated with ethyl-silicate black paint was laser shocked using the laser setup with the 1.054 μm output wavelength and the 20 ns short pulse,then the fatigue experiment was carried out. The effect of laser shock processing upon the fatigue behavior of the aluminum 2A02 was analyzed via the comparison of microstructures,hardness and fatigue life of the material before and after the shock. The experiment results indicated that the residual compressive stress of the laser-shocked test material can reach 120 MPa above,and the strengthened depth can reach 1.5 mm,which makes the fatigue life of the material be increased 1.835-2.882 times,comparing to that non-laser-shocked. The scanning electronic microscope (SEM) analysis of the fatigue fracture morphology revealed that the fatigue fracture consists of fatigue crack′s initiation,fatigue crack propagation zone and final rupture,and the fatigue crack initiation on the laser-shocked specimen moves towards the inner layer of laser-hardened surface. The residual compressive stress effectively postpones the initiation of the fatigue cracks,slow-downs the propaganda rate of the cracks,and the cyclic hardening inhabits or reduces the secondary cracks to emerge,therefore the fatigue life of the laser shocked aluminum 2A02 can be remarkably increased.

Multi-beam ultra-fast laser parallel microprocessing using spatial light modulation is demonstrated in this paper. Diffractive multi-beam patterns are generated with a spatial light modulator (SLM),which is driven by computer generated holograms (CGHs). The CGHs calculated by appropriate algorithms are displayed on the SLM to split an input laser beam to a number of beamlets and digitally manipulate their positions and intensity. The undesired damage by the energetic zero order beam can be avoided by either installing a 4f optical system to block the zero order at the Fourier plane or adding a Fresnel zone lens on the CGH to defocus the zero order at the processing plane. The surface ablation of materials using multi-beam patterns synchronised with a scanning galvanometer system shows flexible and high throughput parallel processing. By tightly focusing the diffractive beams with an objective into transparent materials,high speed dynamic femto-second laser two-dimensional (2D) and three-dimensional (3D) internal structuring is also presented. The results demonstrate the high precision micro-processing with higher efficiency,showing the potential for ultra-fast laser parallel processing in real industrial applications.

Laser technology as one of the most important manufacturing tools in industry has entered the solar cell production processes in almost all aspects. Laser processing is extensively applied in the complete production line of major parts of high efficiency solar cells based on silicon wafer today,including laser edge isolation,grooving,drilling,soldering,etc. The thin-film solar cells which are on the threshold between development and mass production exhibit further potential in the reduction of production costs and also provide many opportunities for laser processing like laser scribing,laser edge deletion,etc.

Although significant progress has been made in large scale and high quality single-walled carbon nanotube (SWNT) synthesis,the fabrication of SWNT-based functional devices still faces many challenges due to the lack of good methods to precisely control over SWNTs growth location,orientation,alignment,and electronic properties. Hence,development of practical methods for well-controlled SWNT-based device fabrication has drawn great interests from both academics and industry. Due to numerous advantages,laser-based techniques are applied in controlled fabrication of SWNT devices. In this paper,we first introduce the laser assisted chemical vapor deposition (LCVD) process,and then different aspects of controllability in device fabrication are described in three sections:1) location and orientation control of SWNT channels integration using optical near-field effects;2) alignment control of SWNTs arrays using electrical biasing polarities;3) SWNTs electronic property control using laser-induced breakdown technique. Our experimental results show that well-organized individual SWNT channels or arrays with location,orientation,alignment,and electronic property control can be achieved through laser assisted fabrication process,which is a promising solution for the fabrication of future SWNT-based devices.

Large area uniform micro-nanostructures are fabricated by single-beam femtosecond laser ablating titanium alloy Ti-6Al-4V surface. These micro-nanostructuring metal surfaces show a great change of their optical properties. Three significantly different surface structures,such as sub-micron ripple structures,ripple-covered bulge structure and the micro-porous structure,are obtained by controlling the processing parameters. These three types of surface structure,which correspond to different visual effects,make the titanium alloy exhibit“rainbow-like color”,“blue” and “black”,respectively. The formation mechanisms of these surface structures,as well as the roles of these structures in changing metal-surface optical properties are also discussed.

Using excimer laser with 157 nm wavelength,experimental studies on micro-ablation of LED-GaN semiconductor films have been performed. The primary etching performance and mechanism of GaN-based semiconductor materials have been investigated and analyzed. The results show the etching rate above 50 nm/pulse can be achieved as the laser fluence is higher than 2.5 J/cm2. For 157 nm laser direct writing,the etched surface with roughness lower than 30 nm-Ra which can be obtained when the laser repetition rate is smaller than 16 Hz and the scanning velocity is higher than 0.25 mm/min. Using laser scanning approach for GaN film etching,a sidewall with about 75° sharpness can be fabricated. The potential of the 157 nm laser for micro-machining of three-dimensional (3D) micro-structures has been proven. Photo-chemical reaction induced by single photon absorption ionization plays a dominant role in GaN-based material etching with 157 nm laser.

A 10 W and 355 nm Nd:YAG laser is used for the blind hole drilling experiment of a 4 layer flexible circuit board (FPC). The interaction mechanism with UV laser and copper and polyimide (PI) is analysised,and the etching depth of single pulse under certain conditions on polyimide and copper is simulated. The effects of the processing methods on the micro-drilling quality are investigated and analyzed. Finally,the optimization of process parameters are obtained,that firstly using the power of 3.9 W,the frequency of 80 kHz,then secondly using the power down to 1.4 W with other parameters unchanged. The recast layer roughness and the bottom surface roughness are 0.88966 μm and 1.063 μm respectively. The scanning electron microscope (SEM) photograph,the 3D profile of bottom surface and the 2D profile of section of the blind hole measured by surface profile measuring system are given.