The main aim of this article is to obtain the correlation between the thermal cycle and the mechanical properties in the weld seam and the heat-affected zone of mild and stainless steels. Key targeted process is welding using electron beam, laser and plasma. Since these processes are characterized by high heating and cooling rates, wide temperature range, small heat affected zones, they are difficult to control and automize. As a consequence, the quality of the product varies over a large range. Because either temperature measurement on one spot or quasi steady- state surface temperature distribution in a large area are generally unsuitable, temperature gradients need to be controlled directly on-line with a high accuracy. This requires the use of a two dimensional temperature control. An infrared camera systems can be used in order to investigate the cooling process in the weld seam area as well as in the heat affected zone. On the one hand the aim of the experiments is the estimation of the microstructure, especially of the hardness distribution using welding-time- temperature-conversion-diagrams and equations of regression. On the other hand the observation of the cooling cycle allows trends of mechanical diagrams and equations of regression. On the other hand the observation of the cooing cycle allows trends of mechanical properties like stretch limit, tensile strength, breaking elongation to be predicted. Simultaneously it is possible to recognize and to localize pores, voids and bonding defects, losses in penetration, problems with gap and height, appearing during the cooling of the weld.

Recent research work has shown, that 'focusing' of laser radiation down to a few nanometer can be obtained y using lasers in combination with nearfield technology (known from scanning tunneling microscope 'STM' or atomic force microscope 'AFM'). Lateral external illumination of STM- or AFM-probe tips with laser radiation can cause tremendous intensity enhancement in the nearfield underneath the tip. This effect can be explained by various electrostatic as well as electrodynamic effects known from surface enhanced raman spectroscopy. This effect was utilized to concentrate laser radiation with high intensity between a tip and a substrate in the nearfield. FOLANT-technique (focusing of laser radiation in the nearfield of a tip) enables intensity enhancement up to 10⁶ in a narrow localized zone underneath the tip. The interaction area with nanometer scale can be applied for material processing even down to atomic dimensions. Using STM- laser-combination, hillocks, pits and grooves with lateral dimensions down to 10 nm have been obtained on gold substrates. AFM- laser-combination enabled nanostructures down to 20 nm on dielectric materials as for example polycarbonate.

Laser cladding by powder coaxial injection was experimented for the repair of motor shafts. In this process, iron, nickel and molybdenum powders were clad onto carbon steel shafts. The microstructure, microhardness and wear resistance of the laser clad coatings and base materials were investigated. Test results show that the laser clad coatings have excellent metallurgical bonding with the substrate, have higher microhardness compared to conventional flame spray/plasma spray, and have better wear resistance properties than that of the base material.

In this paper, formation of single c-axis oriented wurtzite gallium nitride films on various substrates as fused silica, Si and sapphire with ZnO buffer layers by liquid target pulsed laser deposition is reported. The deposition conditions were optimized with a temperature of 600 degrees C and an ammonia pressure of 750mTorr. X-ray diffraction, scanning electron microscopy, tunneling electron microscopy, room temperature Hall effect measurement, UV/VIS spectrometry, Rutherford backscattering spectroscopy and x- ray photoelectron spectroscopy were used to characterize the as-grown films. It is shown that high quality single c-axis orientation stoichiometric gallium nitride films could be formed with a thin zinc oxide buffer layer. The FWHM of x- ray rocking curve of the peak of GaN grown on ZnO/sapphire was as narrow as 0.52 degrees. It was also found that the surface morphology was greatly improved with the zinc oxide buffer.

Thin films of Ti:sapphire were fabricated by KrF laser ablation on (0001) and (1102) sapphire, on (001) quartz and on fused silica substrates from crystalline Ti:sapphire targets. Substrates were heated during the deposition at low temperatures or at high temperatures. Films luminescence, crystallinity, fluorescence lifetime, dopants content, waveguiding and surface morphology of created Ti:sapphire films were studied. Results are presented and discussed.

The reliability of solder joints has been regarded as one of the most critical problems in surface mount technology because of large stress developed at the joints due to thermal expansion mismatch between components and the substrate in operation. uNderstanding the deformation modes of surface mount assemblies and obtaining stress and strain values of joints allow the designer to predict the fatigue life of the solder joints. This study is directed toward a comprehensive evaluation of thermomechanical behavior through 3D deformation measurements of a typical surface mount assembly having gull-wing leads soldered on a printed circuit board by means of laser interferometric techniques. In this paper we describe the application of real-time holographic interferometry and Moire interferometry to measure the 3D formation of the device under power cycling. By combining the measured results of the out-of-plane and the in-plane displacements, together with the temperature distribution of the assembly, the stress distributions of the leads and solder joints were evaluated. It was estimated that the mechanical stress will exceed the yield stress of solder material when the PQFP assembly operates at the rated temperature of 75 degrees C. Then, the deformation of solder joints might change from elastic to plastic.

We report nanometer-sized silicon (Si) crystallites prepared by pulsed laser ablation in constant pressure inert gas ambient. Size distribution of the Si ultrafine particles depends on the pressure of inert gas ambient. It is verified that the size of the Si ultrafine particles is approximately 3 nm and greater in diameter. The nanoscaled ultrafine particles has a crystallinity similar to that of bulk Si. Furthermore, optical properties of the Si nanocrystallites have been studied in terms of the particle size. Visible photoluminescence (PL) bands in the red and green spectral regions appear at room temperature after an oxidation process. The red PL band is independent of the particle size and is stable without degradation by the irradiation of excitation light. In contrast, the green PL band depends on the particle size. The green PL intensity decreases during the irradiation of excitation light in air, and then recovers in the subsequent vacuum evacuation.

This paper shows that the electronic speckle pattern interferometry (ESPI) using large capacity image memory makes possible to measure the large deformation distribution of a rough surface object precisely. A simple experiment to measure the large deformation of a cantilever which cannot be measured by a conventional ESPI is performed and its analysis shows the measurement error is small.

Due to the increasing range of high-speed and high-accuracy applications in material processing, especially in laser beam welding and cutting, the temporal stability of the laser beam parameters becomes more and more important. In this paper a laser beam diagnostic device is presented, that allows the determination of the intensity-profiles of high- power CO₂ lasers with high time-resolution. The detector of this device consists of two linear arrays of room- temperature HgCdTe-detectors, arranged perpendicularly to each other across the center of the beam. The data of the 70 detector elements is acquired simultaneously at rates up to 15 kS/sec for single shot events and several 100 kS/sec for repetitive laser pulses. Due to the use of a digital signal processor (DSP) and an especially adapted software, it is possible to analyze the fluctuations of the intensity distribution on-line. By help of a partially transmitting mirror in the beam delivery system, measurements can be performed during material processing. Therefore, the interaction of the laser beam source itself with the material processing due to beam reflection as well as influences of the industrial environment to the laser can be detected. The calculation of the local variance and mean values enables the dependence of the laser's short- and long-term stability to be investigated due to changes in the resonator alignment, the stability of the power supply, the gas composition etc., as well as to the influence of the processing. For the pulse-mode of a laser, its transient behavior like changes of the intensity distribution can be determined with high time-resolution. For the improvement of drilling processes, the calculation of further statistical functions by the DSP makes it possible to estimate the uniformity of the laser pulses on-line as well.

Semiconductive iron disilicide (beta) -FeSi₂ is an attractive material for optoelectronic and thermoelectric devices that can be integrated on Si substrates. Advantages arise from the direct band-gap, high absorption coefficient and high thermoelectric power figure of merit. We present here the semiconductor properties of (beta) -FeSi₂ films on Si(100) substrate prepared by laser ablation (LA) method. We compare these results with those obtained from (beta) - FeSi₂ films prepared by ion beam synthesis using high- energy ion implantation and electron beam deposition methods. As for laser ablation, two independent growth processes were adopted using two different target materials, The first one was Fe deposition on Si (100) substrate by LA using Fe target and subsequent high-temperature annealing leading to solid phase epitaxy. The second was LA using (beta) -FeSi₂ bulk polycrystal as a target material which was grown by horizontal gradient freeze method. (beta) - FeSi₂ films prepared by the two processes were heat- treated as a function of annealing temperature and duration time. Structural characterizations were made by reflection high-energy electron diffraction, x-ray diffraction, Raman scattering and optical absorption spectroscopy measurements at room temperature, which revealed that high-quality semiconducting (beta) -FeSi₂ films can be fabricated by two LA processes.

Laser induced permanent electrical conductivity was observed in polyimide and in initially non-conducting Ag/polyimide composites using the fourth harmonic of a Q-switched Nd:YAG laser. The critical number of laser pulses required for the metal-insulator phase transition in polyimide was less than 100, compared to the 300-350 pulses required when using a KrF excimer laser. The presence of the Ag in the composite contributed to the conducting volume fraction in the material and therefore further lowered the critical number of laser pulses to less than 50. These experiments represent a unique experimental demonstration of 'two-color' percolation, in which percolation occurs with two different types of conductors.

Microscopic bumps of heights being tens of nm can be produced on a smooth nickel-phosphorus disk substrate using Q-switched laser pulses from a diode-pumped laser. This technique is being used in the manufacture of high-end disk drives where tens of thousands of such bumps are produced to form a dedicated landing-zone racetrack for the magnetic head to land and takeoff without stiction.

Synchrotron radiation (SR) stimulated surface process has been actively studied as anew application field of the SR in the last decade. The reaction mechanism study with these surface photochemical process is necessary to make clear the characteristics unique to the SR stimulated process and the develop an essentially new process technology. In situ observation of SR stimulated Si gas source molecular beam epitaxy by infrared reflection absorption spectroscopy and SR irradiation effects on the dimenthylalumium hydride condensed layer by x-ray photoelectron spectroscopy suggest the potential important of the site specific chemical reaction in the condensed system induced by the core electron excitations. A new process technique, selective core electron excitation process using a monochromatized SR beam, is proposed.

A pulsed XeCl laser was used to ablate copper and aluminum samples in vacuum or in ambient atmosphere. The space- and time-resolved emission spectroscopy of the ablated plasma plume was studied. The structure and composition of the synthesized products, copper oxide, alumina and aluminum nitride ultrafine powders were analyzed by x-ray diffraction and x-ray induced photoelectron spectroscopy. The morphology and size distribution were investigated using a transmission electron microscope and particle size analyzer. Preliminary results are presented and discussed.

A novel liquid-target pulsed laser deposition (LTPLD) technique has been developed. The technique has overcome the problem of solid target deterioration under high power laser irradiation and has prevented large particulates on the growing film. The LTPLD is simple and safe to operate and the cost of source materials is much lower than that in chemical vapor depositions. Choosing an organic liquid containing carbon and hydrogen as a target material, we have obtained crystalline diamond film in the presence of reactive gases H₂O₂/O₂. The film, as revealed by atomic force microscopy, raman spectroscopy, and x-ray diffraction, is composed of cube-shaped diamond crystals with most of them aligned in 220 directions. The results give some evidence that hydroxyl ions, together with atomic oxygen can indeed promote diamond formation. Since gallium is a melt above 29.8 degrees C, it is an ideal material system for LTPLD. Using ammonia as a nitrogen supplier we have succeeded in obtaining gallium nitride thin films at low deposition temperatures. By choosing an appropriate buffer layer we have grown c-axis oriented wurtzite gallium nitride films on several kinds of substrates including fused silica. With addition of indium into gallium target, InGaN films can also be prepared by LTPLD.

The self-limited etching characteristics of digital etching employing an UV laser/Cl₂GaAs system are presented. The self-limiting nature is the key mechanism and plays an important role in digital etching for obtaining etch rates independent of etching parameters. Surface processes based on photodissociation of physisorbed chlorine on GaAs with diffusion of negatively charged Cl into GaAs are also discussed.

This paper reports the fruits of the research on fundamental theory, application basis and application of laser heat treatment since 1979 in China. Also the technical development and spreading of laser heat treatment is reported. Over 20 academic exchange activities home or abroad were organized by our country. In China, there are near 1,000 units and about 5,000 intermediate and senior scientists and engineers engaged in the research, development and production of laser heat treatment. More than 3,000 academia articles have been published home and abroad. About 2,000 Bachelors, Masters and Doctors whose major is laser application have been cultivated. In domestic plants, near 1,000 production lines of laser heat treatment on the cylinder bodies and covers of automobiles and tractors have been set up, which were deeply welcomed by the automobile makers and repairmen. There are other production lines running in some factories and making good effects, such as laser glazing production line for steel ring, laser quenching production line for master reed in elastic shaft coupling and laser quenching production line for big gears, etc.

This is a review of the Chinese research and production in the field of the lasers used in materials processing and their industrial applications of cutting technology, the state of the art.

Surface corrugations with periodic of 2 micrometers and a depth of approximately 150 nm have been fabricated in lithium tantalate (LiTaO₃) monocrystal wafers. Morphologies of the corrugations were studied with an atomic force microscope. These corrugations were first produced by a single excimer laser pulse through a diffractive optical element, and the optical quality of the periodic structures is demonstrated by its characteristics as a gratings coupler in a LiTaO₃ planar waveguide.

Intense atomic nitrogen beams have been produced by a novel arc-heated source for pulsed-laser-ablation deposition. The arc discharge has been carried in pure nitrogen gas and maintained stable in arc pressure of 30-300 Torr. The average beam kinetic energy changes with the arc pressure from 0.8 to 2 eV. Strong atomic emission lines in 383-433 nm spectral region indicated that the arc-heated source generated an appreciable flux of nitrogen atoms. Nitrogen atoms, rather than N2 molecules in the arc, have been considered as the most likely nitrogen-arc species responsible for doping and synthesis of nitride film such as CNx, ZnSe:N, GaN, etc.

In this paper, the effect of CeO₂ on the cladded Ni-base alloy coatings was studied. Based on a comparison of the microstructure and properties of laser cladded coatings containing CeO₂ or without it, it is clear that the addition of CeO₂ can refine the microstructure, increase the microhardness, deduce the inclusion percentage and modify the friction and wear properties. A discussion was also offered in this paper.

Measurements of laser induced shock pressures are made using polyvenyliden fluoride (PVDF) gauges which were stoke on the back of 0.04 and 0.2 mm thick targets, covered with polymethyl methacrylate (PMMA) windows and irradiated by laser pulses of 33 ns duraction, at incident intensity between 10⁸ and 10⁹ W/cm². The integral shock profiles on the front face of PVDF and the decay of laser induced shocks were obtained by measuring the shock pressures in aluminum targets with different thickness. The experimental results are analyzed by the way of computer simulations to illustrate the decay of the shock peak pressures and the shock profile evolution.

It is known that at 1200-1400 degrees C the polycarlosilane (PC) can be converted into silicon carbide (SiC) by electric furnace heating. However, the production cycle is longer than ten hours owing to the limit to the raising rate of furnace temperature. A method of laser heat-treatment for preparation of SiC fiber is presented in this paper. As soon as PC precursor is made by a fiber spinning machine, it is converted into SiC fiber of diameter about 12 micrometers under nitrogen flow. X-ray crystallogram show cubic system of (beta) -SiC was formed. The production cycle is shorter than 5 seconds, when the CO₂ laser power density is about 30 W/mm². The defect, such as bubble and hole inside the fiber, was monitored, which are formed by too large heating rate. The chemical and physical mechanism to avoid defect, together with the design of multi-beam optical setup for heating the moving fiber, is discussed.

Bright layers covering 80 percent of the melt area have been achieved by laser glazing on Fe-C-Si-B eutectic matrix prealloyed by laser on nodular iron substrates, which are verified to be metallic glasses by TEM electron diffraction. It is demonstrated in the paper that epitaxial growth from the crystalline substrate in melt bottom is the universal phenomenon and critical factor during laser glazing. The principal condition for glass forming is the abrupt stop of the epitaxial growth during solidification, which is comprehensively dependent upon the eutectic composition, composition homogeneity, microstructure fineness, laser glazing power density and scanning velocity.

We present the surface morphology of YBCO films deposited by laser ablation and optimization procedure of laser ablation to obtain epitaxial films with good surface quality. The optimization of the surface morphology of the films can be performed by carefully controlling the laser power to determine the growth rate and the homogeneity of films can be improved by rotating the ablating laser beam. These methods allow us to obtain high quality films with the transition width less than 1K, T_c of more than 90K and J_c more than 10⁶A/cm² at 77K. The optimized films were used to fabricate an 8-element high T_c superconducting microbridge with the size of 20 X 100 micrometers ². The optical response characteristics of the microbolometer array wee investigated in the region of 8-14 micrometers . The average noise equivalent power was 3.1 X 10^-12WHz^-1/2, the average normalized detectivity was 1.44 X 10⁹cmHz^1/2W^-1 and the nonuniformity of the average normalized detectivity was less than 10 percent.

The oxide ceramic powders have been sintered with a high power CW CO₂ laser. The products of Al₂(WO₃)₂ as a new compound which can not be found in 2D equilibrium phase diagrams. The hardness of laser synthesized materials are shown to be higher than that produced with the general sintering method in furnace. The microstructure and character is of oxide ceramics synthesis using CW CO₂ laser have investigated. We found that the products of laser sintering Al₂O₃-50mol percent WO₃ have the electrical resistance characters varied linearly of negative temperature coefficient from the room temperature to 220 degrees C.

A high current density YBa₂Cu₃O_7-x (YBCO) superconducting thick film on a flexible NiCr alloy substrate tape with ZrO₂ + 10 percent Y₂O₃ (YSZ) as buffer layer was prepared by pulsed laser deposition. The buffer layer YSZ of thickness 0.3 micrometers was formed on the NiCr alloy substrate tape of length 6.0 cm by ion-assisted pulsed laser deposition. The YBCO superconducting thick film with thickness 1.5 micrometers was deposited on the YSZ/NiCr alloy substrate tape by a KrF laser. The x-ray diffraction pattern indicates that the YBCO superconducting thick film is with strongly C-axis oriented. The critical current densities versus temperature and magnetic field were measured by standard four-point probe method, the values of critical current density and the critical temperature of the YBCO/YSZ/NiCr alloy superconducting tape are 8.75 X 10⁴ A/cm² and 88.7 K, respectively.

Hydrogenated amorphous silicon films have been crystallized by the irradiations of XeCl excimer laser. The crystallized films have been examined by the use of scanning electron microscopy (SEM), x-ray diffraction (XRD) and conductivity measurements to clarify their morphologies, structure and electrical properties. The results show that a high conductive super thin layer is formed by a single pulse laser irradiation with the energy density of 75mJ/cm². The conductivity increases quickly at laser energy density threshold which decreases when the hydrogen in a-Si:H films is removed by pre-annealing. During crystallization process, oxygen atoms from the air ambient have been introduced into the films and such an introducing process is hindered by the hydrogen eruption. When the oxygen content is high enough, the carrier-transport mechanism includes thermionic emission and thermionic field emission in the vicinity of room temperature, which is similar to semi-insulating polycrystalline silicon.

It is the chief difficulty of laser cladding metal-ceramics layer that cracks are liable to emerge. The processing technology and coating materials are studied to resolve the problem. Firstly, according to the calculating of temperature field distribution and analysis of thermal stress in the cladding procedure, it is considered that the scanning velocity of laser beam and initial temperature are the main technological factors of crack emergence. On the other hand, the gradient distribution of ceramic hard phase is carried out and transition layer is put in between cladding layer and substrate. The results of SEM and microhardness test show, the hardness changed smoothly from surface to substrate, coating layer is dense and free of cracks.

The amorphous layers of 250 micrometers -300 micrometers thickness are obtained using the method of CW CO₂ laser scanning the surface of Fe-based alloy and Co-based alloy. The relationship among some parameters in the procedure of forming amorphous layer is made by multi-pass laser scanning.

In this work, a new laser cladding system on larger area for industrial application has been developed. It consists of wide-band scanning mirror and automatic powder feeder by the rotating feed wheel with bucket-type scoops. It is shown that all kinds of laser cladding powders including not only Ni-base, Fe-base, Co-base, but also superfine and light ceramics powders ZrO₂ Al₂O₃ as well as superfine and heavy WC, TiC with spherical and edged grains can be fed. The powder feed rate can be continuously varied from 0.5 to 200g/min, and the measured tolerance limits are less than 2 percent in all conditions. The powder feeder can deliver powders by both side-band of 10-35mm and focusing band. Without the carrier gas the powder flow depends mainly on gravity. The powder stream at the nozzle is uniform, and the powder utilization factor is over 98 percent. Some applications in metallurgical industry have been successfully made.

Considering the variety of thermal properties of silicon material and the spatial profile of incident laser, the temperature rise in silicon material has been obtained by using a 2D model of heat conduction, the relation between the time needed for the surface to reach melting point and the power density of the incident laser has also been given out and the results have been compared with those obtained by using a 1D model.

A method for measuring laser plasma flow field on the surface of target by using laser synchronous interference system is presented. A set of measuring theory for plasma parameters including temperature, pressure, density, ionization degree is built. An interference measurement for laser plasma produced by a Q-switched Nd:YAG laser acted on Al target surface has been made and results of the plasma parameters been given.

With 495nm Ar⁺ laser as inducing light source and polymethyl methacrylate as substrate, the effects of laser power and irradiation time on the laser induced localized deposition of copper in the liquid solution are studied. The micromorphology of the deposited spot formation is analyzed by scanning electron microscope. As compared with the result of common chemical plating, laser induced localized chemical deposition reveals a depositing coating with a smooth surface and a dense and homogeneous grain distribution. The depositional thickness shows a Gaussian-like transverse distribution.

The experimental samples, coated with buckyballs and buckytubes respectively, were processed with laser and subsequent quenching. Scanning electron microscopy, transmission electron microscopy, x-ray diffraction and Raman spectroscopy were employed to investigate the treated surfaces. The experimental results showed that diamond particles dispersed in Fe-C alloy system could be obtained by CO₂ continuous laser-induced quenching of fullerene coatings on carbon steel s well as on ductile iron. The results also indicated that the treated surfaces, which reached an average macro-hardness of HRC 65-70, contained a great deal of polygonal crystallites on the order of microns and most of them were well-faceted cubic diamonds.

In high power cw-CO₂-laser welding, assisting gas is necessary. It has a great effect on the welding results, such as penetration depth, cross section, size of the heat affected zone and welds surface. Much has been done on discussing the influence of its kind and flow rate on the welding results, but little attention was given to its configurations. In this article, several configurations of assisting gas were tried and the according welding results were given. Especially, a new gas assisting configuration including three gases was suggested. Their influences on the topography and cross sections were qualitatively analyzed. Experimental results showed that the best welds were obtained with the new three-gas-configuration.

The thermal deformation in penetration welding with a laser has been investigated as a factor which results in the elevation on the surface of the weld. Qualitative analysis of the course of thermal deformation during which elevation is made has been presented in detail. A series of comparison laser welding experiments was done with a 5kW CO₂ laser. The experimental results showed that there were always a slight warp and a lateral shrinking of the workpiece together with the elevation on the surface, which had been predicted by the analysis. The influence exerted by shielding gas on the topography of the weld has also been discussed. The shielding gas is supposed to affect the pressure above the surface of the welding pool. The shape of the surface of the welding pool is determined by the difference between pressures on both sides of the surface in term of Laplace equation. When the distribution of the gas pressure was homogeneous within the range of the welding pool, a fairly smooth topography was experimentally obtained. Otherwise, obvious ripples were observed along the weld.

In high-power CO₂ laser welding, in addition to well- known stable heat conduction welding (HCW) and stable deep penetration welding (DPW), the authors have found a third welding process: unstable-mode welding (UWM). UMW has the feature of the two welding modes (HCW and DPW) appearing intermittently. The physical characteristics of the three welding processes and the features of their weld formation have been described. By synthesizing the effects of laser power, focal position and travel speed on welding mode and welding process, the laser welding mode-transition curves which include three kinds of welding process have been obtained. The curves precisely indicate the welding- parameter ranges of three different welding processes. During laser welding, the thermal focusing of the lens will change the focal position and may cause transition of welding mode and fluctuation of penetration and weld width. The relationships between lens focal shift, laser power and beam irradiation time have been investigated. By using welding mode-transition curve, the influence of thermal focusing on welding mode and welding process has been studied, and measures for prevention of welding process instability induced by thermal focusing have also been suggested.

A Nd/YAG pulse laser is used to drill in Sm-Co and Nd-Fe-B permanent magnetic rotor. The experimental studies and analysis on the morphology and the phase composition of the drilled rotor are described. In the center of the drilled rotor, there is a hole which diameter is equal roughly to the girdle size of the Gauss laser beam. The hole wall is rapid fused amorphous matter, which morphology and composition are obviously different from that before hole drilling. The grain in heat-affected zone fined, but the composition has not changed. The experimental results show that the reasonable selection of laser parameters according to physical properties of materials is necessary in order to improve product quality and production efficiency and that the lower laser power, the narrower pulse and the multiple- drilling and advantageous to the processing for hard-brittle materials as rare-earth magnets.

The mechanism of the marking of excimer laser to titanium enamelware is studied in this paper. This mechanism is different from the principle that matter in surface is vaporized by laser and engraved, it based on the principle that matter of surface is melted and then resolidify very quickly so as to change color and other characters. A visible and fine pattern can be gained in this way, and fluence threshold is lower. The option condition is gained from the experiment.

We obtain a microscopic lattice-dynamic Hamiltonian of a system interacting with laser based on the electronic system-specific-time-dependent Schroedinger equation and the system-specific time laser theory. From this Hamiltonian, we use the Mori formalism to develop a coupled set of equations for various physical correlation functions and obtain the inverse friction expression of the velocity-velocity self- correlation function in the high-friction limit. An analytical formula is obtained for the diffusion constant of a particle diffusion in a periodic background. The analysis of the formula shows that the effect of non-resonance interaction of laser on the migration of surface adatoms is so small that it can be ignored for ordinary-intensity laser. In other words, only resonance interaction of laser affects the migration of surface adatoms at low temperature. Our results well agree with the qualitative experiment results of laser induced epitaxy.

Laser phase transformation hardening is an important field of laser application industry, and the choice of its technological parameters influences the depth and width of hardening layer directly. In this paper, from the basic equation of heat conduction, the relationship between parameters such as laser power of Gauss distribution, out of focus and scanning velocity and the depth, width of hardening layer is obtained, and a series of computer soft about choice of technological parameters is compiled. Experiments show that the relativity error of width of hardening layer between theoretical calculation and experimental results is 5.7 percent and the error of depth is 18.7 percent.

A specially designed folded quasi-sealed-off CO₂ laser of 800W and TEM_oo mode has been successfully used for welding of smaller diamond saw blades. Process parameters such as the relative position of the focal point to the joint edge are experimentally studied. The metallurgy aspect of the weld is also investigated. The bond strength and the loading capacity of the diamond saw blades under arduous conditions, e.g., in dry cutting are greatly increased by the laser welding.

The laser molten welding of cemented carbides and steel is discussed in this paper. It presents the mechanism of dip soldering. The changes of material structure of welding seam, elements composition and the cause of fissures have been analyzed. The changes of tension of carbides and cobaltic phase in welding process are investigated. The effect of laser plasma on surface of specimen is discussed. The welding results of heterogenous materials between L135 cemented carbides and 6542 tool steel, YG15, YG12, YG8 cemented carbides and 45 steel are also discussed.

A nozzle which consist of two co-axial pipes was applied to weld stainless steel with a 2.5kw CO₂ laser. Helium through the outer pipe and argon through the inner one were used as the shielding and plasma controlling gases. The influences of the gas flow rate, the angle of nozzle and the gas jet position relative to the laser beam on the weld depth, the ratio of the weld depth to width and the weld formation were studied. When the argon flow rate is 10 1/min with the nozzle angle greater than 45 degrees, the plasma can be suppressed in the keyhole, and then a weld with great penetration and ratio of weld depth to width can be obtained. At a certain welding speed, there is an optimal helium flow rate to get the deepest weld. The optimal helium flow rate corresponding to the deepest weld decreases with the increase of the welding speed. However, improper gas jet position will destroy the keyhole and cause bad weld formation.

It is interesting to theoretically discuss the role of the focus position in keyhole laser welding. Based on the energy balance between the laser power, the vaporizing energy of the material, and the energy loss by heat conduction, a mathematical model of the keyhole has been set up. The model describes the relationship between the geometrical shape of the keyhole and the laser parameters, technological parameters and the specific characteristics of the metal. From this model, an analytical expression between the focus position and the weld depth is obtained, and the influence of the defocusing on the penetration in keyhole laser welding is studied. The calculation results shows that the weld penetration reaches the peak when the focus penetrates into the material by a third of the full penetration. The theoretical result has good correspondence with the experiment results in the laser welding of carbon-steel with a high power CO₂ laser.

There are advantages of less working procedure and lower cost in cool rolling ball. But after convention heat treatment, because of bigger deformation, the workpiece must be corrected and finely burnish, which improves the cost and descends the precision. Because there is less deformation in laser surface transformation hardening, we use HJ-3 CO₂ laser machine to study the technology of the surface phase transformation hardening of cool rolling ball guide-distance is less than 0.1, the axial beat value is less than 0.02mm, surface hardness is above HRc 60 and the average depth of hardening layer is 0.2mm. Not only is it not necessary to correct and finely grind, but also the precision of guide screw is improved.

This paper deals with experimental and theoretical analyses of butt welding of 1.55 mm thick Al1050A alloy using a 1kW pulsed Nd:YAG laser, and butt weld joints are investigated for tensile strength and microhardness; then discusses effects of some main normalized welding parameters on surface quality of weld seams and penetration depth.

In the process of high-powered CO₂ laser beam welding, the plasma produced above the welding pool shields the workpiece from the laser beam. In this paper the study about the effect of an added magnetic field on the penetration is made, it is proved that a suitable added magnetic filed can reduce the shielding effect of the plasma to the laser beam. The energy absorption ratio of the workpiece to the energy of laser beam is calculated. And the principle governing the penetration of sudden changes has been analyzed.

This paper describes Ti-6Al-4V plae 1.3 mm thick welded by CO₂ laser beam. The orthogonal test of 3-level and 3- factor is adopted and technological parameters are optimized. The shielding case full of Helium is put behind the pool This experiment indicates that the tensile strength of the weld can reach up to that of parent metal, when the weld joint is regular. Moreover the joint structure is analyzed also.

This paper reports the YAG laser processing device we developed and its application in the instrument and meter industry and briefly analyzes the hybrid series-parallel converter of the switch power supply used in the device.

The rule of the distortion introduced by pressure and thermal stresses in the active cooling mirror were proved experimentally. In order to minimize the distortion of a mirror the active cooing mirror should be consisted of a thin faceplate layer, a good heat exchanger layer and a hard rigidity substrate. According to this requirement of a superthin multilayer mirror were designed. Its maximum distortion was only 0.10 micrometers , when the 8.69kw laser beam was incident on the surface of mirror and the coolant pressure was 0.13MPa.

Hollow core waveguides are becoming a potential delivery system of high power CO₂ laser for applications in medical and material processing procedures. GeO₂ as a kind of cladding material of hollow waveguide with low loss at the wavelength of CO₂ laser, has been studied recently. As we know, loss in hollow waveguide increases because of bending, twisting and other reasons. In this paper, bending losses in hollow core GeO₂ waveguide were measured by bending the waveguide for known radius of curvature, the bending plane was parallel or perpendicular to the polarization of CO₂ laser beam. We also compared our results with those of GeO₂-based hollow waveguide.

Because of the economic and technical advantages, laser processing technology has been developed rapidly in recent years. Jilin Province Laser Institute laser processing center set up a laser cutting production line, a laser heat- treatment production line, and a laser marking machine. In this paper we describe applied examples of laser cut, laser heat-treatment and laser marking.

This paper introduces the fundamental compositions and functions of a newly developed 5KW CO₂ laser processing equipment CGJ-93 controlled by microcomputer in Changchun Institute of Optics and Fine Mechanics. The laser processing equipment consists of a 5KW CO₂ laser, multifunction beam guidance systems, modular processing machine, water cooling system and CNC systems. The equipment has the ability to heat-treat not only the internal holes and outer circular surfaces but also space holes and three dimensional curved surfaces. The equipment can heat-treat workpieces up to 3000mm length, 1500mm diameter and 3000kg weight. The longitudinal table allows moving speed of 0.8-12000mm per minute with 3600mm effective moving range and 0.069mm position accuracy. The transverse table allows moving speed of 5-12000mm per minute with 1000mm effective moving range and 0.028mm position accuracy. The laser head allows longitudinal moving speed of 0.1-12000mm per minute. Its effective moving range and position accuracy are 540mm and 0.03mm respectively.

The effect of several parameters to accuracy and speed of final part in selective laser sintering process is discussed in this paper, as well as some improved methods.

In this paper, the Nd:YAG laser engraving system is studied for the purpose of engraving image, figure, and characters on the surface of metal, ceramic, plastic, leather, etc. First of all, the high repetition and high power Nd:YAG laser is set up; secondly, the 2-mirror 2-axis optic scan system is analyzed and designed; third, the software is developed to control the laser beam in vector mode or in dot matrix mode. The expanded laser beam is directed toward the worksurface through a f-(theta) lens by computer controlled X and Y axis mirror, and moves in a fixed path, a mark is engraved or marked. As a result, the marking field of 100 X 100mm and spot size of 0.088mm are obtained.

The development of laser imaging system, namely laser radar extends the radar technique from the microwave to the optical wavebands, including visible and infrared wavebands and combines the high-technology laser with the mature radar technique, and injects new vigor into the development of the radar technique. The paper is a review in which the basic concept, relative techniques, research status and development perspective of the synthetic aperture laser radar are introduced.

High speed UPC bar code has become a standard mode of data capture for supermarkets in the US, Europe, and Japan. The influence of the ergonomics community on the design of the scanner is evident. During the past decade the ergonomic issues of cashier in check-outs has led to occupational hand-wrist cumulative trauma disorders, in most cases causing carpal tunnel syndrome, a permanent hand injury. In this paper, the design of a side scanner to resolve the issues is discussed. The complex optical module and the sensor for aforesaid side scanner is described. The ergonomic advantages offer the old counter mounted vertical scanner has been experimentally proved by the industrial funded study at an independent university.

Laser shock processing (LSP) is a new technology for strengthening the materials. The feasibility of using a high energy, pulsed beam to shock-harden the localized stress concentration zone, i.e. small holes in 2024-T62 aluminum alloy was investigated in this paper. Confining plasma technique was used in our study. In order to generate the pressure which is required to exceed the dynamic yield strength of 2024-T62 aluminum alloy, laser parameters were optimized. The fatigue life of specimens was studied before and after laser shocking. The fatigue tests showed that the fatigue life of 2024-T62 aluminum alloy treated by LSP had been improved significantly. With 95 percent confidence, the median fatigue life of shocked specimens was 1.9 to 2.5 times that of unshocked ones. It is expected that LSP will e used as a good treatment for improving the fatigue life of aviation structures.

The emergence of commercially available diode pumped solid state lasers in the 3-10 watt power range has created alternative laser sources for many light industrial applications. Laser marking, micro-machining, resistor trimming, disk texturing, and rapid prototyping are some of the applications which can benefit from this technology. In this paper, we describe fiber-coupled diode bar pumped Nd:YAG and Nd:YVO₄ lasers with short pulse, high energy, and relatively high average power developed for these applications. Our design emphasizes system efficiency and simplicity to minimize the cost of ownership. The excellent beam spatial quality and pulse-to-pulse stability of these devices results in improved process yields for the end user.

A synthetic type of distance ranging system is described in this paper. In this system, one frequency-modulated laser beam and two multimode laser beams that come from different lasers, having different wave length, are input to a Michelson interferometer together with the same path. When the systems start to run, the computer may send out signals driving the reference reflector to find or keep the zero optical path difference, according to the principle of frequency-modulated ranging and quasi-white light positioning with the interferometer. In the meantime, the shifted value of the reference reflector would be measured by another interferometer. Lastly, the distance can be accurately detected by that value and the environment parameters through calculating with computer. Some fundamental experiments have been done, proving the feasibility of this synthetic method.