Different weight ratio of titanium, zirconium, WC and Fe-based alloy powders were mixed, and cladded onto a medium carbon steel substrate using a 3kW continuous wave CO₂ laser, aiming at producing Ceramic particles- reinforced metal matrix composites (MMCs) layers. The microstructures of the layers are typical hypoeutectic, and the major phases are Ni₃Si₂, TiSi₂, Fe₃C, FeNi, MC, Fe₇Mo₃, Fe₃B, γ(residual austenite) and M(martensite). The microstructure morphologies of MMCs layers are dendrites/cells. The MC-type reinforcements are in situ synthesis Carbides which main compositions consist of transition elements Zr, Ti, W. The MC-type particles distributed within dendrite and interdendritic regions with different volume fractions for single and overlapping clad layers. The MMCs layers are dense and free of cracks with a good metallurgical bonding between the layer and substrate. The addition ratio of WC in the mixtures has the remarkable effect on the microhardness of clad layers.

In the research hotspot of particle reinforced metal-matrix composite layer produced by laser cladding, in-situ reinforced particles obtained by adding strong-carbide-formation elements into cladding power have been attracting more attention for their unique advantage. The research has demonstrated that when adding strong-carbide-formation elements-Ti into the cladding powder of the Fe-C-Si-B separately, by optimizing the composition, better cladding coating with the characters of better strength and toughness, higher wear resistance and free of cracks. When the microstructure of cladding coating is hypoeutectic microstructure, its comprehensive performance is best. The research discovered that, compositely adding the strong-carbide-formation elements like Ti+V, Ti+Zr or V+Zr into the cladding coating is able to improve its comprehensive capability. All the cladding coatings obtained are hypoeutectic microstructure. The cladding coatings have a great deal of particulates, and its average microhardness reaches HV_0.2700-1400. The research also discovered that the cladding coating obtained is of less cracking after adding the Ti+Zr.

The morphologies of roll surfaces are modified with pulsed Nd:YAG laser and characterized by topography measuring instrument (WYKO-16 DRT2TC). Sombrero shaped bumps with diameters of 230-250 μm and heights of 2-4 μm are produced by out-of-focus laser beam. In laser surface heating, the cooling rate is high enough for all the material that undergoes austenitic transformation to be transformed into martensite. To explain the mechanism leading to the surface topography resulting from the Nd:YAG laser texturing of roll surface. A quantitative model is proposed to predict the bump formation during martensitic transformation. The results show: the bump height caused by martensitic transformation is very small. The key factor of macroscopic bump formation on roll surface during laser texturing is surface tension of molten metal.

There are many expensive types of equipment in oil field on the sea from U.S.A or Europe in China. Some important components due to wear and erosion do not work; the large economic challenge needs laser recondition of the expensive parts. We have developed new laser cladding process for re-fabricating the long axle shaft and the body case in transferring oil pump in oil field on the sea. Using 5KW-CO₂ lasers and the powder feeder, the cladding layer of NiCrSiB alloy on 40CrMo steel axle shaft with no crack and pores has been performed. The control distortion of long axle shaft during laser cladding has been researched. The laser re-fabricating has now been used to repairing production in the Bohai oil field in China.

Laser strengthening of U71Mn rail steel was performed under different parameters using a narrow line-shaped CO₂ laser beam formed by newly developed binary optics. The microstructure, microhardness and wear resistance of the strengthened layers were investigated. Laser strengthening of PD₃ rail steel was performed using a normal circle-shaped beam, and the contact fatigue resistance of samples obtained by optimized laser processing parameters was investigated. The research results showed that a layer with fine martensite was produced on the surface of the rail steels after laser strengthening. The wear resistance to sliding friction was improved over 1.3-2.5 times than that of original steel U71Mn. And the rolling contact fatigue property was improved over 4-5 times than that of steel PD₃. The results also indicated that the laser strengthening processing parameters should be selected not to melt and overheat the surface.

The samples of semiconductor’s surface temperature increased abruptly, when illuminated by laser pulse. The sample’s surface melted and remained liquid phase for a few hundreds ns. That caused reflectivity enhancement of the sample surface. In this article, numerical calculation was carried out on HgCdTe and PbS. And a 1mm-thick HgCdTe was used as the sample in the experiments. In the experiments, the sample was illuminated by laser pulse of 60ns duration from a Q-switched Nd:YAG laser. A beam from He-Ne laser was used as the monitor beam to illustrated the reflectivity changes of the sample. The results of the experiments were the conclusive evidences of our numerical calculation of the dynamic behavior in the sample.

Laser processing of material surface is a rapid and non-equilibrium process. Under the action of laser beam, the material surface melts and solidifies very quickly, and there exists very high thermal gradient. Accordingly, the topography, microstructure and performance of material surface will all change. To analyze these phenomena, the heat transfer and the fluid flow issues during laser surface processing need to be studied in-depth. In this paper, a hybrid analytical-numerical solution model is developed for the heat transfer and fluid flow during laser surface processing. Taking the laser texturing of GCr15 roll surface as example, the model is solved through the surface tension model developed for the melt formed in laser texturing and the numerical results from finite element analysis on the temperature field during laser texturing of roll surface. The laser textured roll surface roughness profile is then theoretically predicted using the solution to the hybrid model. The roll surface topography obtained experimentally agrees very well with the theoretical prediction, which proves the validity of the analytical-numerical solution model.

Laser rapid manufacturing based on laser cladding is a novel layer additive manufacturing technology, which can be well used for producing specific material, geometry and properties components normally unavailable or very costly by conventional methods. This paper presents a project research work on laser rapid manufacturing of special pattern Inco 718 nickel based alloy component with special pattern for aeronautical application. The required pattern Inco 718 nickel based alloy component was manufactured directly by laser deposition with optimized parameters: laser power: 800W, laser beam diameter: 0.8 mm, scanning speed: 0.5 m/min, powder feeding rate: 3g/min; The basic microstructure of laser deposited sample is directionally solidified columnar structure, with metallurgical bound to the substrate. Laser deposited component has good metallurgical and compositional and hardness homogeneity. The average hardness is about Hv_0.2 440. The tensile strength of the laser deposited Inco 718 sample is respectively 121 and 116 kgf/mm² at room temperature and at 650°C, which are a little bit less than the data of forged Inco 718 plate 142 and 127 kgf/mm² due to its directional solidified columnar structure perpendicular to the tensile test force.

Laser rapid forming (LRF) is a new and advanced manufacturing technology that has been developed on the basis of combining high power laser cladding technology with rapid prototyping (RP) to realize net shape forming of high performance dense metal components without dies. Recently we have developed a set of LRF equipment. LRF experiments were carried out on the equipment to investigate the influences of processing parameters on forming characterizations systematically with the cladding powder materials as titanium alloys, superalloys, stainless steel, and copper alloys. The microstructure of laser formed components is made up of columnar grains or columnar dendrites which grow epitaxially from the substrate since the solid components were prepared layer by layer additionally. The result of mechanical testing proved that the mechanical properties of laser formed samples are similar to or even over that of forging and much better than that of casting. It is shown in this paper that LRF technology is providing a new solution for some difficult processing problems in the high tech field of aviation, spaceflight and automobile industries.

This paper presents a special CAD/CAM software for rapid manufacturing thin wall metal parts by laser cladding, which is based on the developing of AutoCAD. It mainly consists of solid modeling, layering and section data processing, NC code generation module, processing path simulating and data transferring module.

This paper presents the research on direct laser deposition of Inconel 738 alloys on directionally solidified (DS) Ni-base supperalloy substrate in order to strengthen or repair the DS gas turbine blades. The results indicate that cracks occur very easily during the deposition process and cracks in laser deposited Inconel 738 on DS Ni-base supperalloy substrate are mostly thermal cracks which may originate on the interface between deposited layers and DS substrate, and develop to multi-deposited layers. The low melting temperature point eutectics between the grain boundaries of DS Ni-base superalloy substrate are the main sources of thermal cracks. Strict control of the heat input of the deposition process can dramatically decrease the cracking tendency. Layers with the DS characteristics are achieved by direct laser deposition on Ni-base superalloy substrate with good shaping and free of cracks by optimizing the deposition technique and laser parameters. Compared with the substrate, the microstructure of the layers is much finer, the average primary spacing of the dendrites is about 5μm. The microhardness of Inconel 738 multi-deposited layers is very uniform, indicating the structure of the layers is homogeneous. The results demonstrate the feasibility and great foreground in repairing and fabricating local parts on DS Ni-base superalloy turbine blades by direct laser fabrication technology.

Laser direct manufacturing and re-fabricating by co-axis feeding have been widely used in space, aircraft and power station. Due to lack of evaluation method of powder stream, its industrial application is limited in. A new Digital Particle Image Velocimetry (DPIV) system has been developed to measure the powder stream outside co-axis feeding head. The DPIV system is as follows: A double pulse Nd⁺:YAG laser, λ=532nm, single pulse energy 220mJ, pulse repeat frequency 10Hz, pulse width 6ns; Nd⁺:YAG laser beam shaping device; Frame straddle CCD camera, 30 frames/s, 8bit image plate and special image software. The transverse and longitudinal distributions of concentration and velocity fields have been measured by CCD camera respectively. It is shown that the focus parameters (focus diameter, focus length), concentration field, flow velocity field of powder stream can be successfully evaluated by the DPIV technique.

With deep studying on the process of laser rapid forming (LRF) the researchers gradually meet the knowledge that it is very important to understand the mechanism of interaction between the laser and the powder particles since it is the key point to realize the effective control of the LRF process. The high-speed photography has been employed to realize in situ observation on the delivery process of powdered materials for the first time. A group of parameters -- delivery parameters of powder is put forward to characterize the delivery process in quantitative by dealing with the digital images obtained. On the basis of quantitative description of the powder delivery, an analytical model is presented to study the attenuation of the laser power caused by the cloud of the power particles. Another analytical model is also presented to study the temperature rise of the particle irradiated by the laser. It can be found that the attenuation ratio is determined together by the powder specifications, the powder feeding parameters and the powder delivery parameters. With the off axial powder nozzle being employed in the paper, the diameter of the powder steam was always bigger than the diameter of laser spot, thus the laser processing parameters have no effect on the laser attenuation. The temperature rise of the particle is determined by the powder specifications and the powder delivery parameters too. Meanwhile the laser processing parameters also affects the temperature rise of the particle. With the decreasing of the particle radius, the irradiation heating effect increases remarkably.

Laser forming of sheet is a forming technology of sheet without a die that the sheet is deformed by internal thermal stress induced by partially irradiation of a laser beam. In this paper, the bending behavior of common stainless steel 1Cr18Ni9Ti sheet is studied after being irradiated by straight line with a Nd:YAG pulse laser beam. The aim of the investigation is to find out the relationship of the bending angles with the pulse parameters of the laser. The experimental results show that higher width of pulse is advantageous to increase the bending angles if the total outer power and the rate of the pulse are constant. The bending angle increases as the rate of the pulse increase and begins to decrease at a certain processing parameters. And the bending angle firstly increases with the pulse energy increasing and begins to decrease at a certain processing parameters, as there is a certain pulse energy parameter resulting in a maximum bending angle for a certain material and processing parameters. The pulse energy is the most important factor influences the bending angles of pulse laser forming in the pulse parameters. By qualitative analysis of experimental result, the conclusion obtained may provide basis for theoretical investigation and possible industrial application of laser bending process in the future.

The Laser Rapid Forming (LRF) has been used to build up default free and nonoxidation Ti- 6Al- 4V samples in atmosphere controlled LRF equipment. The microstructure and mechanical properties of as-deposited and heat-treatment are analyzed. It has been found that the macrostructure of as-deposited Ti- 6Al- 4V alloys takes the shape of huge columnar prior beta grains (PβG) with continuous boundary and epitaxial growth along the vertical direction (Z) of the laser scanning. Between cladding layers there are bands of coarse structures resulting from the reheating by laser beam when the prior cladding layers forming. The substructure in prior beta grains is mainly of the fine acicular α and basketweave matrix of α+β. After high temperature annealing treatment, little basketweave matrix of α+β remains and the acicular α changes into α laths with clear β outlines. After quenching-aging treatment, the substructures are mainly of the α laths and basketweave matrix of α+β. Multi-quenching -aging heat treatments produce bi-modal structure. The physical property test shows that the tensile strength and plasticity at the vertical direction (Z) of the laser scanning are higher than those at the direction of parallel (X). After high temperature-annealing treatment, the Ti-6Al-4V alloy has lower level of tensile strength and plasticity while quenching-aging treatment decreases tensile strength and increases plastic slightly.

This article designs a system for coaxially monitoring and penetration control in CO₂ laser welding with a visual sensor. The key techniques for imaging the keyhole and eliminating the plasma-induced severe interference have been developed. The two-dimensional image of the keyhole has been obtained clearly in real time. It shows that once the penetration status changes from “partial penetration” or “weld pool penetration” (keyhole not penetrates workpiece) to “moderate full penetration” (keyhole penetrates workpiece), a lower grayscale spot appears in the center of the keyhole image and the grayscale curve presents a concavity in the center. This criterion of penetration recognition is suitable for most welding conditions. An image processing method that compares the average grayscale of a central image window at the keyhole center (vector Fc) and the average grayscale of an annular window surrounding the keyhole center (vector F_R) has been proposed to quickly recognize “moderate full penetration”, based on which, the closed-loop control of penetration can be carried out and the weld bead can be kept at “moderate full penetration” during welding.

Tailor welded blanks had been widely used in the automobile industry. A tailor welded blank consists of several flat sheets that were laser welded together before stamping. A combination of different materials, thickness, and coatings could be welded together to form a blank for stamping car body panels. As for the material for automobile industry, this technology was one of the development trend for automobile industry because of its weight reduction, safety improvement and economical use of materials. In this paper, the characters and production of tailor welded blanks in the market were discussed in detail. There had two major methods to produce tailor welded blanks. Laser welding would replace mesh seam welding for the production of tailor welded blanks in the future. The requirements on the edge preparation of unwelded blanks for tailor welded blanks were higher than the other steel processing technology. In order to produce the laser welded blank, there had the other process before the laser welding in the factory. In the world, there had three kinds of patterns for the large volume production of tailor welded blanks. In China, steel factory played the important role in the promotion of the application of tailor welded blanks. The competition for the supply of tailor welded blanks to the automobile industry would become fierce in the near future. As a result, the demand for the quality control on the production of tailor welded blanks would be the first priority concern for the factory.

During CO₂ laser deep penetration welding, the laser-induced plasma significantly effects the process stability and efficient. In this study, the method of three-dimension synchrony high-speed photography is adopted to record the charge of plasma during laser deep penetration welding. The primary version image is in the image plane directly, the vertical view and the side view image also are in the same image plane by two optical fibers and finally three images distribute at the different area of a film. It is clear that the direction variation of laser welding plasma is acute. The reason is that the change of keyhole shape leads to the impact direction variation of the metal vapor to the plasma and it finally affects the motion direction of the laser-induced plasma. The plasma is in the state of irregular rotation and wobbling in space during the laser welding process. The area change curve on continuous 80 frames image are given out. The change extent of relative area on the three images are calculated and the curves of the relative area are showed. It is found that the shape of plasma change quickly and the maximum relative area ratio of the side view image is up to 40 during laser welding.

The aluminum alloy, 5A06, was used in the experiment. High power Nd:YAG laser was adopted as the source and argon as shielding gas. The laser welding of Al alloy with thin plate was a difficult thing especially in the butt form of the thickness 0.5mm to 0.5mm and the fillet form of unequal thickness case. Blow hole and pore in the welding bead and deformation, usually, were the main defects. The welding parameters were tested and determined in the study. For the butt welding, the parameters of 1200W laser power with pulse mode and 1.8m/min welding rate were used for making a full penetration of weld bead and a smooth weld surface. The blow hole and pore were easily kept in weld bead when the power of 800W and 1500W was used. It was strongly depended on the pore tendency of Al-Mg alloy in the laser welding and the unstable welding process. For the fillet welding, the parameters of 1300W to approximately 1500W laser power with pulse mode, 1.8m/min welding rate, an angle of 15 degree between laser beam and vertical plane were used to get a high quality weld bead. In order to control the distortion of plate, a special method was designed and made for fixing the parts and keeping them in correct position. The experimental data showed that the best result was got when the copper cooling board was employed.

Hybrid laser-arc welding is becoming one of the most significant laser welding technologies in industry due to its higher welding efficiency, higher tolerance to gaps between plates, and adjustment of composition and microstructure of the weld metal. Comparing with common off axis hybrid laser-arc welding, coaxially combined laser beam and arc can provide a symmetrical circular thermal source on the workpiece surface, which is convenient for 3-D welding. This paper introduces a coaxial hybrid CO2 laser-pulsed MIG welding system and conducts experiments of welding Al-Mg alloy plates under different welding conditions. The basic physical phenomena during welding are observed and the weld bead shape (penetration depth, weld width) are measured. The results show that hybrid laser-MIG can stabilize the arc, remarkably increase the total welding efficiency and improve the quality of weld bead formation. In addition, process and control techniques for hybrid laser-MIG welding are also proposed.

Laser welding of A5083 aluminum alloys with high power CO₂ laser is experimental studied in this paper. The study shows that under determinated welding condition, an additional plasma control tube would achieve good plasma suppression, which results in good welding quality. The shielded gas flow acting on the keyhole in CO₂ laser welding of A5083 aluminum alloy is numerical simulated by finite element method. From the ANSYS numerical simulation diagrams of the keyhole’s gas flow field, it can be seen that the additional plasma control tube would achieve good plasma suppression to maintain the keyhole.

Tailor welded blanks were used in the automotive industry to consolidate parts, reduce weight, and increase safety. In recent years, this technology was developing rapidly in China. In Chinese car models, tailor welded blanks had been applied in a lot of automobile parts such as rail, door inner, bumper, floor panel, etc. Concerns on the properties of tailor welded blanks had become more and more important for automobile industry. A lot of research had shown that the strength of the welded seam was higher than that of the base metal, such that the weld failure in the aspect of strength was not a critical issue. However, formability of tailor welded blanks in the stamping process was complex. Among them, the metal flow of tailor welded blanks in the stamping process must be investigated thoroughly in order to reduce the scrap rate during the stamping process in automobile factories. In this paper, the behavior of metal flow for tailor welded blanks made by the laser welding process with two types of different thickness combinations were studied in the deep drawing process. Simulations and experiment verification of the movement of weld line for tailor welded blanks were discussed in detail. Results showed that the control on the movement of welded seam during stamping process by taking some measures in the aspect of blank holder was effective.

A hybrid Nd:YAG laser beam welding technique has been investigated in welding of aluminum alloy. Connecting the filler wire with one pole of a DC power supply and the workpiece with the other, a closed electric circuit is built. By this means, the wire is resistively preheated, so that less energy from the laser beam is dissipated in melting the filler metal. On the other hand, the current flowing in the weld pool generates a magnetic field and electromagnetic forces which affect the fluid flow of the weld pool and then the welding process. It is found that the weld depth increases and the weld seam becomes slender when a certain current is supplied. To clarify which effect, the thermal effect or the electromagnetic effect, dominates, welding with pure hot wire was carried out. The experimental results demonstrate that the pure hot wire addition has no obvious affect on the welding efficiency and the weld cross section, but worsens the process instability. Thus we can conclude that the influences of the current do not result from the resistive heat from the wire, but the electromagnetic effects. This new approach provides a possibility to increase the processing efficiency and flexibility, improve the process stability and weld quality, and also shape the seam cross section.

In this paper the effect of activating flux on plasma during laser welding is studied and the Activating Flux-Laser Beam Welding (A-LBW) is proposed. The stainless steel (1Cr18Ni9Ti) is respectively welded by using activating flux and by not using activating flux. And the shape variation of plasma during laser welding is recorded directly by using three-dimension synchrony high-speed photography separately. It is found that the penetration of using activating flux is larger than the penetration not using it. When not using activating flux, there are so many negative effects such as reflection, scatter, absorption and refraction etc, which resulted in power density of acting on the work piece surface decreases and the penetration is lower. But when using activating flux, its molecules evaporated could trap electrons in the plasma to form negative corpuscles. Although the total number of the electron in the laser welding plasma aren’t decreased, but the mass of negative corpuscle is larger and then these corpuscles also became the background of the motion of electrons. Eventually the effective electron density is decreased and then the penetration is increased.

800MPa grade RPC steel is the recently developed new generation steel, which was produced by relaxation-precipitation controlling transformation (RPC) processing. The microstructure and mechanical properties of the heat affected zone (HAZ) in laser welding of 800MPa grade RPC steel were investigated by using a 4kW YAG laser and a Gleeble-1500 thermal simulator in this paper. The experimental results indicate that: (1) The size of prior austenite grains of HAZ increases with increasing heat input. (2) Granular bainite is the main microstructure of the HAZ of laser welding. (3) As the heat input increases, the hardness of HAZ decreases, but it is higher than that of the base metal, indicating no softened zone after laser welding. (4) As t_8/5 increases, the impact toughness of HAZ increases at first and then decreases. The impact energy of HAZ is much higher than that of the base metal when t_8/5 is between 3s and 8s. It indicates that excellent low temperature toughness can be obtained under appropriate laser welding conditions.

In this study, the method of three-dimension reconstruction of laser welding plasma on the basis of three-dimension synchrony high-speed photo is proposed. The method of anti-RADON transformation is used to finish three-dimension reconstruction. The anti-RADON transformation utilizes the projected data to reconstruct the initial image, which bases on the projection of the parallel beam. It is found that there are the cavitations on most section images and the area of cavitations is ever-changing. The space shape of plasma represents irregularity on the different surface.

In this paper, a kind of absorptive thin film, for the first time, was used in laser welding of SiO₂, Si and L_iN_bO₃. This absorptive thin film of three-layer metal-dielectric-metal structure is designed for further reducing the high reflectance of the Nd:YAG laser beam in the surface of the tin layer that is utilized as solder between the transparent parent materials. The actual absorption exceeds 99%. This combination of absorber and solder transformed the laser energy into heat effectively and decreased the minimum necessary incident laser power transmitting through the transparent parent materials. As a result, the damage of the parent materials, which is suffered from laser transmission, is avoided; on the other hand, the laser power is of full utilization and saved.

Many factors influence laser cutting quality. In this paper, the influence of laser head movement on 3D laser cutting is investigated. Except normal movement which laser head is vertical to work piece surface, three types of movement defined in 3D laser cutting are considered. Experimental design method is used to analyse cutting result. In order to quantitatively describe the relationship between cutting quality and cutting parameters, artificial neural network (ANN) has been setup. The quality marks system is used to evaluate cutting result. The test shows the calculated quality points by ANN is very similar with actual cutting result. The laser head forward movement is better than the others. The ANN is very useful to optimize cutting parameters, predict cutting result and deduce new information.

Evaluation of the cut quality is extremely significant to industrial applications of laser cutting. The relationship between cut quality and processing conditions has been investigated by using one of the measurable cut qualities, such as kerf width, striations, dross, roughness and so on. However, each of these qualities can only partially represent the cut quality. In this paper, a synthetic evaluation method for laser cutting quality has been proposed. A 3KW CO₂laser was used to perform cutting experiments with 1.0mm thick mild steel sheets. The cut quality indicators, including kerf width, striations, dross, roughness, under different cutting conditions have been studied. A Synthetic Quality Number (SQN) has been presented as the evaluation indicator by quantitatively analyzing the conventional indicators. A neural network based method to anticipate laser cutting quality has been presented with SQN as the evaluation indicator.

In this paper, the experiments of cutting titanium alloy sheet with Nd:YAG pulsed laser were carried out and the effects of the type of shielding gases, gas pressure and laser parameters on kerf width, surface quality and metamorphic layer thickness were studied. The results showed that compressed air is suitable for laser cutting of titanium alloy, the Argon gas does better, while Oxygen gas has undesirable effects; the metamorphic layer is thicker with compressed air as assisted gas in comparison to that with Argon gas; the kerf width increases as the power density, pulse frequency and pulse width increase; higher cutting speed can be applied and the cutting quality is improved when the pulse frequency is increased.

Laser trimming adjusts the resistance of chip resistors accurately. The laser-cutting path that is vertical to the current flow is called transverse cutting. It increases the resistance quickly. The laser-cutting path that is parallel to the current flow is called ordinate cutting. It increases the resistance slowly. Using numerical results of resistance-calculation formula, the influence of transverse cutting on the resistance is analyzed. With resistor-subsection method, the relationship of resistance and ordinate cutting is studied. And quantitative formulae of them are given. The conclusions can provide some control strategies to improve the trimming precision and trimming efficiency.

Based on the comparison of traditional laser and fiber laser cutting system, a fiber laser based micro-machining system is designed. The main modules of the micro-machining system and the key techniques are analyzed and the corresponding solution is proposed. In particular, the driving, control and modulation system are focused on, in which an SOC system is built up, and the corresponding hardware and software are described in detail. The pulse width and frequency modulation are achieved with software, by setting the related parameters via keyboard. The power, pulse length and pulse frequency can be tunable in our modulation system, which can meet the different laser requirement in various kinds of stents cutting and micro-machining.

The positional precision of laser scribing and laser marking in precision metrological tools, such as scale plate and scale dial, is of the order of µm. The control of scribing must be very accurate. The laser beam parameters, focal length of the lens, and the position of the focal spot must be carefully selected and accurately controlled. The workpiece must also be accurately and repeatedly positioned. Any deviation from the required parameters would seriously affect the product quality. This paper studied an Nd:YAG laser scribing system specially designed for scribing of extremely high precision dial scale used in petroleum drilling machine. The relevant parameters were carefully selected and optimized. CAD, CAM, NC and automatic control technology were employed in the system. The integration of optics, mechanics, electronics and computer ensured high precision laser scribing.

Microstructures develop spontaneously on silicon surface under the cumulative short laser pulses irradiation in different ambient atmospheres. The experimental results suggest that the ambient atmospheres and the laser pulse duration play key roles on the microstructures formation. Only in SF₆ ambient, the sharp conical spikes develop. Under the picosecond laser irradiation, silicon surface is melted before the spike arrays formed, while under the femtosecond laser irradiation, the formation of spike array does not pass through the liquid phase. The optical absorption increases remarkably from ultraviolet (~0.25 μm) to the infrared (~19μm) for the microstructured silicon material, which promises for new device applications, such as solar cells, infrared photo-detector.

Femtosecond laser is suitable to machine a variety of materials, such as metals, semiconductors, polymers, oxide ceramics, silica aerogels, optical glasses, crystals, deep sea sands and even explosives because of its high peak power density and low heat affected zone. In this paper, the femtosecond laser micromachining of different materials and for different processing is presented, including structuring in optical glasses, and the cutting of metals and the deep-sea (South China Sea) sands. The laser used in the experiment is a commercial Ti:Sapphire laser with the pulse width of 50 and 100 fs, wavelength of 800 nm, maximum pulse energy up to 2 mJ and the repetition rate of 1 kHz. The evolution of material eruption as a function of the number of laser pulses and intensity is studied. The dependence of ablation rate with laser intensity and the number of the pulses is characterized by measuring the maximum laser penetration depth in different materials.

Based on the avalanche model, the mechanism of femtosecond laser-induced ablation in fused silica was investigated. The three microscopic processes, including the production of conduction band electrons (CBE), the deposition of laser energy, and the diffusion of CBE and energy, were solved by a finite element method (FEM) of two-dimension cylinder coordinate. The conduction band electrons (CBE) were produced through photoionization and impact ionization, which were calculated via Keldysh theory and Double-flux model, respectively. The accumulated charge and the electrostatic field were also calculated, and the evolution of microexplosion was discussed based on this model. The results indicate that the CBE and energy diffusion plays an important role in the ablation of dielectrics by femtosecond laser pulse.

Development of precision micro-fabrication techniques for transparent materials such as crystal quartz, sapphire, silica glass is strongly desired in various industrial. During laser ablation the quality of micro-fabrication depends strongly on the optical breakdown region induced by laser irradiation. In this work, nanosecond ultraviolet laser can be used to micro-process on the surface of silica glass and microcrystal glass in air. The experiments demonstrate that number of laser pulse, scanning velocity, laser wavelength and absorption index of these materials are important factors affecting quality of micro-fabrication using ultraviolet laser.

According to the optical transmission model of laser irradiated Polyethylene terephthalate (PET) fabric, the method of measuring the surface characteristic parameters, both the equivalent optical thickness and the gain of dye strength, is presented in detail. The PET fabrics untreated and irradiated by UV laser (308 nm, mJ/cm², 10 pulses) are used in our experiment. They are dyed respectively by three disperse dyes (Ciba Terasil Red G 150%, Ciba Terasil Blue BG-02 200% and Ciba Terasil Navy GRL-C 200%) with various concentrations. The spectral reflectance distributions of the untreated and irradiated PET fabrics dyed are carried out with the color measuring and matching system (Datacolor, SF600plus). The experimental data indicated that the dye strength of disperse dye in the UV laser irradiated PET fabric was greater than that in the untreated, that the gain of dye strength is relative to dyestuff, and that the calculated reflectance of UV laser irradiated PET fabric is accordant well to the measured. The results show that the optical transmission model of laser irradiated PET fabric is reasonable and available.

Liquid water acts as an important role in laser processing. Water can be added on purpose gain better result: to avoid redeposition of debris, to cool the material, to increase plasma pressure or to conduct light. On the other hand water is the most common, cheap and safe medium and has an exceptionally high heat capacity. So many researches have been carried out in water-assisted laser processing. In this article, UV laser (wavelength: 355nm, pulse width: 10ns THG Nd:YAG laser) assisted processing of ceramics in air and in water is studied and compared with the processing quality in different environment.

This presentation introduces solid state UV laser drilling technology for electronic packaging applications which mainly includes generating microvias in high-density interconnects (HDI) printed wiring boards (PWB) and integrated circuit (IC) chip packaging devices. The first three sections discuss the drilling process technology in terms of substrate materials, via quality requirements, laser-materials interaction, via formation processes, laser beam profiles, and system hardware. The remaining sections cover some typical application examples including via drilling, soldermask ablation, and routing to explain the UV laser process capability with the common PWB materials.

In order to meet the special demands for laser materials processing, after the analysis and design of the resonator parameters and pulse parameters, a mechanical chopper Q-switched CO₂ pulse laser unit is developed. At last, a Q-switched CO₂ laser pulse with high peak power of more than 10kW and the maximum beam power of 800W (at this time the pulse repetition rate is 20kHz) and TEM₀₀ mode is obtained. The width of the pulse duration is adjustable and in order of μs.

We report on functional color centers and waveguide formed by using 800nm, 120fs, 200kHz pulse laser in alkali halide crystals such as KCl and LiF. These crystals are transparent in the wavelength ranging from 250-1000nm. After irradiated by the 800nm tightly focused femtosecond laser, the crystal changed to dark and color centers have been formed. Some of these color centers are useful and alkali halide crystal with these color centers is one type of laser crystal (color center laser crystal). And also photoinduced refractive index changes have been formed by focusing the laser beam.

Due to their attractive mechanical properties, bioinert ceramics are frequently used in the high load-bearing sites such as orthopaedic and dental implants, but they are chemically inert and do not naturally form a direct bond with bone and thus are lack of osseointegration. A CO₂ laser was used to modify the surface properties of bioinert zirconia with the aim to achieve osseointegration between the material and bone. Higher wettability characteristics generated by the CO₂ laser treatment was primarily due to the enhancement of the surface energy, particularly the polar component, determined by way of microstructural changes. An in vitro test using human fetal osteoblast cells (hFOB) revealed that osteoblast cells adhere better on the laser treated sample than the untreated sample. The change in the wettability characteristics could be the main mechanism governing the osteoblast cell adhesion on the YPSZ.

The Polyethylene terephthalate (PET) fiber is so sleek that its surface has high reflectance. Therefore it is difficulty to dye the PET fiber dark color by using the disperse dyes. In order to solve this problem, the laser processing technology is applied to change the surface dyeing property of the PET fiber. How to quantify the treated layer thickness of laser irradiated PET fabric and how to foretell its spectrum reflectivity distribution are two problems that needs the solution urgently. In this paper, both the simplified structure model and optical transmission model of PET fabric irradiated by laser are developed, the reflectance formula for laser irradiated PET fabric is derived. The characteristic parameters, both the equivalent optical thickness and the gain of dye strength, are introduced, which represented surface performance of laser irradiated PET fabric. When the equivalent optical thickness of the treated layer and the unit k/s ratio of the dyestuff are measured, the spectrum reflectivity distribution of the laser irradiated PET fabric for given concentrations of the various colorants can be calculated, thereby its tristimulus values can be obtained.

Wavelet transform was widely used in communication, data compression and image manipulation. Base on Wavelet transform, the model that is designed for enhancing the result of binary image in laser processing system was built. Software for this model to control CO₂ laser processing system was wrote out. The result which was given in this paper indicated that this model can effectively improve the output quality of binary image in CO₂ laser processing system.

Applying of laser alloying for modification of electrical resistivity of metals with significant importance in electrical and electronic engineering and utilization of this method for producing passive elements of electric circuit have been presented. The alloyed metals were obtained by means of laser beams with different wave length and various mode of working (cw or pulse), by different methods for the supplying of alloying elements. It was possible to form alloyed layers of metals forming different types of metallurgical systems: with full (Cu-Au, Cu-Ni) or partial solubility (Mo-Ni, W-Ni, Cu-Al, Ag-Sn), insoluble (Mo-Au and Cu-Cr) and immiscible (Ag-Ni and Ni-Au) metals, with metallic as well as non-metallic additions (oxide). It has been shown as well that it is possible to achieve resistive elements modified in whole cross section, in a single technological process. The results of systematic investigations into the resistivity of alloyed metals in the temperature range of 77-450 K have been presented. The alloyed layers, obtained, were characterised by a range of resistivity from 2.8 x 10^-8 Ωm (Cu-Cr) to 128 x 10^-8 Ωm (W-Ni). The microstructure and composition of alloyed layers were examined by means of SEM-microscopy and EDX analyser. In selected cases it was shown how results of investigations could be utilized for modification of surface layer of contact materials or to optimize the resistance of laser welded joints. In addition the results of investigations of new developed microtechnology -- producing micro-areas with extremely high resistivity -- have been presented.

Evolution of laser damage morphology has been studied in 112 oriented, mirror polished Indium Antimonide(InSb)samples as a function of increasing energy, pulse repetition rate and number of pulses using a Nd:Cr:GSGG laser of 1.06 μm wavelength having a pulse width of 20ns. Scanning Electron Microscope (SEM) investigations of the irradiated samples have been done to understand the evolution of damage morphology. Damage morphology is consistent with surface melting and solidification along with an evidence of subsurface overheating. Temperature profiles calculated at different fluence levels confirm substantial subsurface heating. Multiple pulse damage seen at 20Hz with increasing fluence levels is mainly thermal damage. Thermal modeling has been done to explain different morphological features.

The principles of laser ultrasonic generation and measurements with pulsed laser are presented. There are two kinds of means to actuate ultrasonic pulse: elasticity actuating and ablation actuating. The progress in laser ultrasonic about laser ultrasound generation, detection, propagation and its applications is introduced briefly. Applications in the field of Non-Destructive Testing (NDT) are reviewed. In the field of Non-Destructive Testing, according to the principle, the laser ultrasonic testing system consists of laser system, laser interferometer, photoelectric detector and receiving system with signal amplifier. Thus, long-range and non-contact on-line detection of ultrasonic testing system was realized. In view of some of the problems, the developing trends of such techniques are analyzed.

In this paper, yttria-stabilized zirconia ceramic films of fine particles in order of nanometer have been prepared by sol-gel process and the wetting ability of the ceramic thin film before and after laser ablation is discussed. The results showed that the wetting ability depended on the abundance ratio of O to Zr on the membrane surface. The smaller the ratio is, the better the wetting ability is. The oxygen deficiency occurs after laser treatment which makes the value O/Zr small. At this time, water can spread on the membrane surface. So, the membrane exhibits hydrophilicity after laser ablation. After a month aging, the oxygen in the air is absorbed onto membrane surface which makes the value O/Zr large and the water can not spread on the membrane surface.

Mn:Fe:LiNbO₃ crystals were grown using the conventional Czochalski method. The phase conjugate reflectivity and response time were measured by four-wave fixing method with Ar+ laser (488nm) as light source. Non-degenerate phase conjugate wave varying frequency was obtained in Mn:Fe:LiNbO₃ and Fe:LiNbO₃ crystals with Ar+ laser (488nm) and He-Ne laser (632.8 nm) as light source. The maximum of phase conjugate reflectivity varying frequency of Mn:Fe:LiNbO₃ crystal was up to 920%, three orders of magnitude than that of Fe:LiNbO₃ crystal. Based on Li vacancy model, we discussed the photorefractive improving mechanism of Mn:Fe:LiNbO₃ crystal.

Laser cutting had been widely used in the material processing field with the increase of the requirements on the quality and work efficiency. As to the laser cutting, there had many factors that could affect the quality of cuts. Among them, the chemical composition played an important role because laser processing was a kind of interaction among laser beam, shielding gas and materials. Compared with the other element, silicon element had a deleterious effect on the laser processing which resulted in cuts with a dross and brittleness in the welded seam. However, many kinds of steel with high amount of silicon need to be processed by laser technology in recent years. In this paper, the influence of silicon element on the quality of laser cutting and laser welding was discussed. Continuous CO₂ laser was used to cut and weld materials with different amount of silicon. Results showed that with the increase amount of silicon, the speed of laser cutting and laser welding decreased in order to obtain the good cuts and welds. Silicon had the obvious influence on the laser processing technology and quality. Microstructure of the laser welds for materials with high amount of silicon was also analyzed in this paper.

This paper introduces the principle of Shafting correction In heavy mechanical manufacturing industry, shipping industry and Nuclear industry, analyzes the effect of distribution of laser light beam spot energy to PSD measure precision. With experiment, we analyze the relation between the different distribution of laser light beam spot energy and PSD measure precision, discuss the method to compensate of shafting correction error caused by the distribution of laser light beam spot energy.

Ceramic material has favorable characteristics of high strength, bearing high temperature, bearing abrasion, bearing corrosion, which has been extensively utilized in such areas as machinery, electronics, chemical engineering and aeronautics, etc. Due to the very high degree of hardness and brittleness of ceramic material, processing ceramics is very difficult, especially the drilling particularly difficult. Since laser-processing technology has been introduced, it was firstly applied in the drilling technology because of the laser’s high power density and excellent directional property. However, as laser drilling is based on the optical characteristic of the laser and the laser beam is focused on work piece through the lens, the processed through-holes have been realized with some certain degree of the taper angle. In this paper, a new method for resolving the problem presented above is discussed. The new method -- lean-revolve method is designed for the laser precise drilling of ceramic material, in which the work piece or the laser beam is inclined with some certain degree and the work piece is revolved with a fixed axes during the process of drilling, so as to lessen the taper angle of the holes processed and resolve the problem of drilling technology of ceramic material.

The precise of artillery duplicate-aim is the important tactics index. At present many countries are making great efforts to improve the firing rate of large artillery, and the leading index of artillery in high firing rate is duplicate-aim precision. So the measure of duplicate-aim precision of artillery and evaluation of reliability are very crucial. The paper proposes a Theodolite front across-assembling method with cooperative object by which the precise of artillery duplicate-aim is non-touch detected. According to the precise demand of artillery duplicate-aim, the optimal disposition theory of theodolite front across-assembling is presented to assure high system precise. It proves that the method function with simpleness and high detecting precise and better flexibility and acclimation.

In many applications such as cylinder body, sleeve and mould side wall, vertical surfaces need to be strengthening together with horizontal surfaces. In this paper, a new powder feeding nozzle for laser vertical surface treating was designed and a whole laser surface modification system with powder feeding for vertical surfaces is developed. By using this system, experimental work on laser remelting, laser alloying with powder feeding, laser cladding with powder feeding was performed on vertical surfaces of gray iron substrates. The microstructure, composition and hardness distribution were analyzed. The results indicate that the properties of the vertical surfaces have been greatly improved after these treatments. The powder feeding nozzle and vertical processing can realize various vertical surface modifications with or without powder feeding, which has a promising prospect in industry applications.

By the analysis of the DXF file format of three-dimension image, the scheme that uses the technology of spatial and triangular transformation is formulated. The arithmetic for this scheme was given out in this paper. The control software for this arithmetic has been used in CO₂ three-dimension laser processing system. Compared with some different schemes, the advantage of using this scheme in laser processing system was also pointed out. This scheme can be popularized in the other laser processing system.

A laser ultrasonic testing system using a confocal Fabry-Perot interferometer and a pulsed Nd:YAG laser is developed for the fatigue test of materials. To stabilize the fringe pattern of the confocal interferometer, an adaptive stabilization fringe control system is developed using two photodiode signals. The closed-loop fringe control system is operated automatically. The optical system is composed of many polarization components, such as a half-wave plate, quarter-wave plates and polarization beam splitters to improve the signal to noise ratio. The laser ultrasonic system carried out performance test. The optical configuration of the interferometer system and the stabilization module are investigated in this paper. The experimental results of the basic experiments are also described.

In laser transformation hardening (LTH), it is a common phenomenon that the discrepancy of hardening effects occurs between the beginning and the end of laser scanning for those parts which have boundaries along the scanning direction, when the laser processing parameters, laser power and scanning velocity, are kept unchanged. The case depth at the end of scanning path is larger than that at the beginning. And sometime the local surface on the end may be melted. The discrepancy, which results in non-uniform hardening effect, will make the process quality bad. This paper study on the discrepancy and the effects of laser power and scanning velocity, then presents the effective method to control the discrepancy and to improve the laser process.

Laser induced damage in the visible window glass, such as K9 glass, irradiated with Nd:YAG laser operating at 1.064μm wavelength and approximately 10ns pulse duration was investigated in the present experiments. The pulse energy, duration, and beam spot size were taken as changeable factors to study the laser damage results. The experimental arrangement consists of a Q-switched Nd:YAG laser with pulse duration of about 10ns operating at 1.064μm, a lens of 40cm focal length which focus the laser beam onto the sample, a diaphragm to adjust the incident laser energy, a power stabilized He-Ne laser at 0.6328μm providing a diagnostic beam onto the Nd:YAG spot size, a detector which can measure the 0.6328μm reflected from the spot during the pulses beating. Images analysis was conducted at different laser induced damage level. At last, the dynamic damage threshold measuring method was discussed.

In this paper, an automatic fillet weld pre-tracking system for welding the work piece of lorry back boards with several bend in haul automobile is developed basing on laser trigonometry. The optical measuring head based on laser-PSD trigonometry is used as position sensor. It is placed in front of the traveling direction of welding wire to get the distances from welding wire to the two side boards of the welding lines, upper board and bottom board of the fillet weld respectively. A chip of AT89S52 is used as the micro controller in this system. The AC servomotors, ball-screws and straight guide rails constitute the sliding table to take welding wire move. The laser-PSD sensors pass through the vertical board, upper board and bottom board of the fillet weld when welding wire moves and then get the distance. The laser-PSD sensors output the analog signals. After A/D conversion, the digital signal is input into AT89S52 and calculated. Then the information of the position and lateral deviation of the welding wire when welding a certain position are gotten to control welding wires. So the weld pre-tracking for welding the work piece with long distance and large bend in haul automobile is realized. The position information is input into EEPROM to be saved for short time after handled by AT89S52. The information is as the welding position information as well as the speed adjusting data of the welding wire when it welds the several bend of the work piece. The practice indicates that this system has high pre-tracking precision, good anti-disturb ability, excellent reliability, easy operating ability and good adaptability to the field of production.

Non-contact and nondestructive monitoring of subsurface defects are urgently required especially in the line production of such products. In this paper a two-dimensional plane stress finite element model with absorbing boundary condition has been developed to investigate the ultrasonic wave generated by nanosecond pulsed laser propagation in two-layer material. The pulsed laser is assumed to be transient heat source, and the Surface acoustic wave is computed based on the thermoelastic theory, which propagated on the top surface of the plate. The defects located on the interface can be modeled as the subsurface slits of the Al/Cu layers. The numerical results include the three cases which the subsurface slit located in different positions of the interface of the Al/Cu layers. After performing Wigner-Ville analysis on the displacement data, frequency domain feature analysis is done. This study of the SAW was demonstrated to be promising in evaluating the bond quality as well as identifying the location of subsurface lateral defects.

This paper utilized the Finite Element Method to investigate the transient scattering of Rayleigh wave by a surface crack in a plate. The incident wave models the guided waves generated by a pulsed line source laser irradiation on the top surface of the plate. The pulsed laser is assumed to be transient heat source, and the surface acoustic wave is calculated based on the thermoelastic theory. We have computed the different results of the Al plates with the varied depth surface-breaking crack, then attained the temporal characteristics of reflected waves and transmitted waves which are generated by the initial surface acoustic waves interacted with the surface breaking cracks with different depth. The artificial neural networks (ANN) are applied to establish the mapping relationship between the characteristic of the reflected waveform and the crack depth. The results of crack damage detection for Al plates show that the method developed in this paper can be applied to online structural damage detection and health monitoring for various industrial structures.

In this paper, attenuation of laser power by coaxial powder flow was studied. Given that the distribution of laser power as well as that of powder concentration was defined as a Gaussian function and no grain was shielded from laser by other grains, resolution model of laser power attenuated by coaxial powder flow was established. The attenuation of laser power by powder flow was a function of process parameters such as powder feed rate, moving velocity of grains, spraying angles and waist positions and diameters of laser beam and powder flow, grain diameter and run of laser beam through powder flow. The attenuation coefficient increased with powder feed rate or run of laser beam through powder flow and decreased with rise in grain diameter or moving velocity. The impacts of spraying angles and waist positions and diameters of laser beam and powder flow on attenuation coefficient were complicated. In practice, powder feed rate and run of laser beam through powder flow were both often adjusted, and other parameters were usually constant under certain conditions. In the presented experiment, the experimental results agreed well with the calculation results, and it was demonstrated that attenuation of laser power by coaxial powder flow rose with powder feed rate or run of laser beam through powder flow.

The time-dependent optical reflectivity of HgCdTe detector at 0.63μm has been measured during irradiating by a 1.06-μm Q-switched Nd:YAG laser of 50-ns duration. The reflectivity was observed to increase abruptly to a value and to remain at that value for a period of time, which ranged from several nanoseconds to several hundreds of nanoseconds, depending on the irradiating pulse intensity. The duration of the “flat-top” portion of the reflectivity waveform represents the total time that the surface is melting. Subsequently, the reflectivity dropped abruptly to a value less than the initial one. The difference shows that the damage takes place in the incidence point. By measuring the time-resolved reflectivity and simulating physical structures of PbS and HgCdTe detector, whose dynamic mathematical model was created. By solving the equations of energy transport and thermal diffusion, the temperature rises of PbS and HgCdTe detector irradiated by pulse laser beam were studied, the relationship of power and temperature rises were discussed and the numerical solutions of dynamic temperature field were obtained. The experimental result of the reflectivity of HgCdTe detector was compared with calculated result. The results show finite element analysis is effective in solving the temperature field.

The measuring of geometrical profile and tread defects of wheel set is an important step for the safety of train vehicle running. The paper researched an automatic measuring system of comprehensive parameters of wheel set based on optoelectronic detecting technique. The system used precision laser displacement sensor, digital image processing and motion control technology to realize the non-contact automatic measuring of wheel set parameters. The tread and flange profile were captured using laser source and high resolution CCD sensor. The image SNR was gained through narrow band-pass optical filters which wavelength matched with laser source. In order to detect the irregular tread failures formed in running of train vehicle, the paper used precision laser displacement sensor to scan the tread and acquire the position while the wheel set was rotating slowly. The displacement data of different positions were transformed to digital image. Then digital image processing and mode recognition algorithm was used to distinguish and judge the failures. The repeatability and accuracy of the system can meet the demand of wheel set maintaining.

The new design about a CW, digital all-solid-stated LD pumped Nd:YVO₄ controller is introduced. The stable output power of this digital laser controller which adopts Digital Signal Processor (TMS320C31) is approximately 20mW. The whole system is composed of constant- current source, protection circuit, pulse-width modulation circuit, Si-photo-detector and amplified circuit and Digital Signal Processor control system, etc. In terms of error deviation Based on nonlinear control curves of LD power output by Si-photo-detector, the region control can be obtained by means of the PID control algorithm in the software platform, that is, error amendment and high stability laser power output can be achieved. And the precision of temperature control can reduce from ±0.2°C to ±0.04°C. By adopted integral separated mode PID control algorithm, the LD output power instability (σ%) down to ±2%. By way of adopting the new digital design, the work to protect the laser diode, including the continuous adjustable output power with high accuracy and stability, is easily obtained. The internal-external modulation control of the laser power based on digital optical feedback can be accomplished with stable power output. At last, the bringing reasons of noise are analyzed and the solving methods are put forward in this paper.

In this paper, an effective method applied in laser spot center determination is described, which is based on multi-spectrum digital image processing. The laser collimation technique combined with digital image processing technique is adopted to realize the measurement of parallel cylindrical tubes with mono axis or multi-axes. The advantages of detection are non-invasive, high measuring accuracy; easily realizing the measuring procedure with automation and intelligence.

Deep penetration laser welding is associated with violent plasma generation characterized by high charge densities. Plasma resides both outside and inside the keyhole, known as plasma plume and keyhole plasma, respectively. Plasma plume outside the keyhole has been studied extensively due to its convenient observation; however, very little work has concentrated on the analysis of the keyhole plasma. In this article, a specially designed setup was used to take firsthand measurements of the light emission of the keyhole plasma in deep penetration laser welding aluminum films clamped in between two pieces of GG17 glass that we called it a “sandwich” sample, triumphantly eliminating the impact of the plasma plume covering the keyhole on the observation of keyhole plasma. Results of spectroscopic measurements of both plasma plume and keyhole plasma under welding conditions were obtained with orthogonal experimental design. It was shown that keyhole plasma had considerable effects on the energy transfer efficiency of the incident laser beam to the material, exhibiting various melting width and depth; deeper welding depth as well as lower temperature of the keyhole plasma was obtained when decreasing the densities of the keyhole plasma by reducing the thickness of aluminum films.

The experiment of laser heat treatment of workpieces with a sharp board milled to be 90°, 55°, 45° and 35° has been finished to investigate the influences of the sharp board on the temperature field and the heat-affected zone. The spot of laser has been sampled using the thermal paper in two planes of different height h₁ and h₂, and the power distribution of laser has been simulated numerically. A finite element model of numerical calculation is developed to simulate the transient three-dimensional temperature field, and the shade plot and isotherm can be output in any longitudinal and transverse sections and then the hardened zones are determined. The several cross sections of treated workpieces are chosen to make the metallographical analysis and the comparisons with the numerical results. It has proved that the numerical results are in a good agreement with the experimental data and the sharp boards have a great influence on the temperature and the heat-affected zone when laser approaches to the sharp board of workpiece.

Laser energy distributions of 20 μm and 40 μm glass microspheres were calculated with different laser wavelengths. Most simulation results show similar energy distributions in which laser energies are focused at the backside of the microsphere. Using time-resolved optical shadow images and Schlieren images, initial breakdown location and shockwave propagation from the breakdown were investigated for 20 μm glass microsphere which was ablated by Nd:YAG laser with a wavelength of 1.064 μm. Time-resolved imaging showed the location of the initial breakdown and the shockwave motion over its first 300 μm of expansion. Measured shockwave velocities were in the range of 1-10 km/s and showed a linear dependence on laser fluence within 30 ns.

We report the experimental fabrication of optical elements with femtosecond pulses. The laser source we adopted is a low power Ti: sapphire laser oscillator, with a central wavelength of 790 nm and pulse duration of 100 fs. Positive-photoresist-coated film acts as the sacrificial material. To obtain the optical elements, three microobjectives with high numerical aperture 0.25 and 0.1 were used to focus the light beam of femtosecond laser. Due to the extreme high intensity of the tightly focused femtosecond laser beam, nonlinear effect occurred between photoresist and the laser pulses, which enable the ablation of the photoresist. In the experiments, we use a translational stage that hold the sample by a pump through a ventage. Various gratings and phase plates are fabricated by this method. The obtained gratings patterns are checked with a conventional optical microscopy. The fabricating widths and depths are measured with the Taylor Hobson equipment. With the same method, photomask for microelectronics can also be fabricated. From the experimental results, we see that the fabrication of the different microobjectives can be achieved with this method. This technique can be applied to the fields of microoptics and microelectronics. The mechanism between femtosecond laser and photoresist is also investigated. The processing mechanics is considered as laser ablation. Fabrication of optical elements with femtosecond laser reflects a new trend for fabrication of microoptical elements.

Based on the theory of phase transformation, computational mechanics, thermal non-elasticity and the character of laser phase transformation, a non-linear heat conduction equation considering phase transformation and a model of the relationship between the phase transformation products and the properties of 40Cr steel are established and solved by means of Finite Element Method (F.E.M). Comparing the calculated results with those of experiments, satisfying agreement is found. It might be valuable for some practical applications and for the development of theory.

High-density optical storage and the three-dimension (3D) microstructures in the side-chain azobenzene polymer material were studied. Two interfering orthogonal (± 45° to the incident plane) linearly polarized laser beams from an Ar⁺ laser at 514.5 nm as recording beams intersected on the surface of the sample with an angle which could be adjusted to form the holographic gratings storage. And a He-Ne laser at 633nm was used for a reading beam. By rotating the sample, there were 20 sets of gratings stored on the same spot in a side-chain copolymer PGMAA-20 film. Utilizing the stable optical storage property of this material, a rectangular microstructure and a complicated double layers nesting six-pointed star microstructure were also inscribed in the samples by using the same simple two-wave couple (TWC) setup in regular recording sequence, including rotating the sample and adjusting the incident angle of the recording beams. In the recording process of the high-density multiple gratings structure with different periodicity and incident angle, we found that the recording order of gratings with different periodicity made a crucial effect on the final forming of the microstructures. The microstructures in the samples were shown by an optical phase contrast microscope (Nikon TE300). And the simulation results were in accordance with what we had observed through a microscope.

The quality of laser remanufacturing depends on temperature field distribution in laser molten pool. In this paper, two-dimensional temperature field model and CCD measurement of temperature field were developed. According to radiant transfer function, bright of light signal of temperature field grabbed by CCD was transformed to spectral radiant signal. A new system model for CCD measurement of temperature filed was proposed. It concluded optical system, CCD camera, image plate, orientating laser, special image software and computer. Thermal image signal received by CCD is transformed to digital signal by image plate. After processing digital image signal by computer, Temperature field distribution can be obtained by thermal image displaying. It was proved that CCD Measurement of molten pool temperature field was available. Automatic control of laser remanufacturing processing could be achieved by feedback control of thermal radiant signal.

Laser cladding technology has led to the development of a unique method for repairing, providing fast, near net shape reconstruction of components to blueprint dimensions. However, when the direction of the coaxial nozzle is out of the vertical with repairing surface, the powder feeder with carrying gas must be need. In this paper, the movement of gas particle two phase flow has been simulated with ANSYS software. The powder feed equipment with carrier-gas has been developed due to optimum design parameters. It mainly consists of two parts as follows: part one is alloy powder measurement unit, part two is convey powder unit with carrying gas. Lots of tests of powder transport with carrying gas with Ni02(45) _aWC, were performed. The result is shown that it can solve problems of the superfine powders type transport and powder feed stabilization, moreover, it makes the precise feeding of powders possible, the powder feed rate 5~80g/min, catch efficiency up to 20%.