This PDF file contains the front matter associated with SPIE Proceedings Volume 6825, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Sheets of AZ31B wrought magnesium alloy were welded by CO₂ laser. Welds of "partial penetration", "weld pool penetration", "keyhole penetration" and "excessive penetration" were obtained, and the "keyhole penetrated" weld possessed the best quality. The light emission of welding plasma was monitored by photo-diode, and it was found that the photo-diode signal varied with different penetration statuses. When the welds were "weld pool penetrated" and "keyhole penetrated", the average signal amplitude A reached its minimum value. R, which defined as ratio of A and standard deviation ^δs of signal was introduced to describe the fluctuation tendency of plasma, and the ratio reached its maximum value (which meant the lowest plasma stability) when welds were "weld pool penetrated". By detecting the minimum value of A and R, "keyhole penetration" can be differentiated from "weld pool penetration" and "excessive penetration".

Tailor welded blanks were widely used in the automobile industry for their special advantages. A combination of different materials, thickness, and coatings could be welded together to form a blank for stamping car body panels. With the gradually growing consciousness on safety requirement of auto body structural, the business of laser tailor welded blanks is developing rapidly in China. Laser tailor welded blanks were just the semi products between steel factory and automobile manufacturers. As to the laser welding defects such as convexity and concavity, automobile industry had the strict requirement. In this paper, quality standard on laser tailor welded blanks were discussed. As for the production of laser tailor welded blanks, online quality control of laser tailor welded blanks was introduced. The image processing system for welding laser positioning and weld seam monitoring were used in the production of laser tailor welded blanks. The system analyzes images from the individual cameras and transmits the results to the machine control system via a CAN bus.

This paper focused on a systemic solution to high power laser welding for high thickness shipbuilding steel. The laser induced plasma not only absorbs laser energy but also affect welding process stability especially when laser power is higher than 10 kW. The electron density, electron temperature and plasma height are analyzed in paper with high speed camera and spectrometer in this paper. Laser Supported Combustion (LSC) result in instable laser welding process and cause bad seam quality. As an effective method to suppress plasma and keep stable welding process, flow rate of side blowing gas is analyzed. The relationship between Seam shape, its mechanical properties and welding parameters is studied. Experiments results showed that High power laser welding is a qualified and efficient method for high thickness shipbuilding steel.

Aluminum alloys are among the most important parts of advanced materials being of strategic significance. Laser beam welding is a fast growing technology that offers new opportunities in the joining of aluminum alloys. Alloys such as the Al 7000 series that are unweldable with conventional techniques are readily joined by laser welding to produce welds with high strength. However, the high reflectivity, the high thermal conductivity, the high fluidity, the high chemical reactivity as well as the low ionization energy of Al element make the physical processes complex in laser welding of aluminum and its alloys. In this paper, the key scientific problems and issues are reviewed and some novel processes and techniques are introduced mainly based on the author's research achievements financially supported by the "863 Program" of the Ministry of Science and Technology of China, the Program for New Century Excellent Talents in University of the Ministry of Education of China and other programs.

A novel laser coating-texturing (LCT) technique was proposed to achieve appropriate surface topographies and frictional behaviour. The LCT process was realized by applying laser pulses at very high repetition rates to produce innumerable micro-craters with the required shape profile on the surface of the workpiece. Moreover, surface alloying of the dimples was carried out by melting submicron WC-Ni alloy powder on the substrates. Morphology and microstructures of the texturing layers were characterized using optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). Mechanical properties of the textured samples were evaluated by abrasive resistance tests and microhardness measurement. Experimental results show that good fusion bonding between the texturing layers and the substrate has been formed, and the texturing layers is mainly composed of dense and hard fine-grained structures. The abrasive wear resistance of the laser coating textured surface was 5 times higher than that of the substrates. The average surface microhardness values were as high as 850HV.

The coupled numerical simulation on fluid flow, heat transfer and mass transfer in the process of laser cladding was undertaken on the basis of the continuum model. In the simulation of mass transfer in the laser molten pool, the concentration distribution in the regions on different sides of the interface between cladding layer and the substrate was calculated separately and coupled at the co-boundary. The non-equilibrium solute partition coefficient was obtained from equilibrium solute partition coefficient according to the Sobolev model. By using the developed software, the distribution of Fe in laser molten pool in an experiment of cladding Stellite 6 on 12CrMoV was calculated. The obtained results well coincide with the experimental ones.

A three-dimensional energy coupling model for evaporative laser cutting nonmetallic material is established through theoretical analysis and the reflective transmission and energy absorption of laser against real bended cutting front and both two walls are analyzed. The front and wall's energy absorption is mainly determined by the first three incident beams, that is two reflections. The multiple reflections from the front will increase the power intensity of the bottom and the multiple reflections from the wall will increase the power intensity from the center to the bottom. Due to the multiple reflections, the power intensity distributes over the total front. Due to the cutting speed, the laser axis moves toward the front. The differences of absorptive power intensity among the three polarizations light are much smaller than those of metal. Both two walls will have waveguide effects on the incident light which will mutual reflect against both walls and transmit toward the bottom of the cut, which is so-called "wall focusing effects".

Cold-rolled steel sheets of thickness ranging from 0.7 (with zinc coating) to 2.0 mm were used to produce tailor laser welded blanks (TLWBs) with various thickness ratios, the maximum of which reaches 2.86:1. In this study, the laser weldability and formability of the TLWBs, as well as the mechanical characteristics of the weld zones, were analyzed experimentally under the effects of various thickness ratios of TWLBs. The results showed that the hardness of the weld beads are 1.9 times higher than respective parent metal at most but the formability of TLWBs as evaluated by the Erichsen cup test was lower than that of the parent material.

Based on the theoretical model of uniform pulsed laser beam irradiating on the optical material, the stress distribution of the transparent material when laser with different beam spatial distribution - circle beam spot and dark-cross beam spot - irradiated to the inner of optical material was discussed. The experiment that 532nm Q-switched laser pulse was focused to the inner of silicate glass was taken, which the beam spatial distribution of the output laser was dark-cross beam spot. According to the theory, the experimental results and phenomena were analyzed and the damage micro-configurations were explained. The theory and experiment could be accordant well.

In this paper, 5Kw CO₂ laser and a special CNC table were used to weld automobile double-linked gears with 20CrMnTi material and Y gap. A lot of evaluations on microstructure, defects and mechanical properties for welding seam were examined by OM, SEM and X-ray diffraction. It was shown that deep penetration welding in the double-linked gear could be achieved at optimum parameters of 2.6~2.8KW and 2M/min. Laser welding had a small distortion of 0.0408mm in gear diameter. Microstructure of fine martensite and austenite was observed in the welding seam. Mechanical tests of hardness of HV400 and tordional strength of 1512Nm were measured. The welding seam had a comprehensive intensity and toughness. The defects of blowhole and crack could be reduced or avoided by adjusting parameter and preheating before welding. The allowable standard of laser welding of automobile double-linked gears was recommended.

NiTi alloy has excellent biocompatibility. This paper presents a novel technology of direct shaping of this promising biomaterial with selective laser melting (SLM). The frequently encountered defects of the SLM metal alloy parts such as non-fully melting, thermal deformation and balling were analyzed theoretically and experimentally, and the microstructure of the parts was analyzed on microscope. The results show that an appropriate selection of laser mode and scanning strategy assures a satisfying quality of the final parts; they also reveal that the SLM technology can be expected as a potential technology to directly manufacture the artificial implant of NiTi alloys.

Due to the excellent performance in high strength, anti-temperature and anti-wear, ceramics reinforced metal base composite material was used in some important fields of aircraft, aerospace, automobile and defense. The traditional bulk metal base composite materials are the expensive cost, which is limited in its industrial application. Development of laser coating of ceramics reinforced metal base composite is very interesting in economy. This paper is focused on three laser cladding ceramics coatings of SiC particle /Al matrix , Al₂O₃ powder/ Al matrix and WC + Co/mild steel matrix. Powder particle sizes are of 10-60μm. Chemical contents of aluminum matrix are of 3.8-4.0% Cu, 1.2-1.8% Mg, 0.3-0.99% Mn and balance Al. 5KW CO₂ laser, 5 axes CNC table, JKF-6 type powder feeder and co-axis feeder nozzle are used in laser cladding. Microstructure and performance of laser composite coatings have been respectively examined with OM,SEM and X-ray diffraction. Its results are as follows : Microstructures of 3C-,6H- and 5H- SiC particles + Al + Al₄SiC₄ + Si in SiC/Al composite, hexagonal α-Al₂O₃ + cubic γ-Al₂O₃ + f.c.c Al in Al₂O₃ powder/ Al composite and original WC particles + separated WC particles + eutectic WC + γ-Co solid solution + W₂C particles in WC + Co/steel coatings are respectively recognized. New microstructures of 5H-SiC in SiC/Al composite, cubic γ-Al₂O₃ in Al₂O₃ composite and W₂C in WC + Co/ steel composite by laser cladding have been respectively observed.

It is easy to produce molten dross by using traditional laser cutting technology in laser cutting silicon steel sheet. The main reason is that oxidizing reaction will take place inevitably by using oxygen as aided gas, so high pressure and high purity N₂ or inert gases is used as aided cutting gas in laser cutting process. Although the cut quality is improved, the cutting efficiency is dropped because of the lack of energy resulting from an exothermic oxidation reaction. A fire new laser cutting technology by using an additional nozzle put under the workpiece that will form lateral gas flow to control the direction of the flowing dross gas is raised. In this technology oxygen is still used as aided gas, the laser power is reduced and the cut is fine. The experiments prove that by controlling the technical parameter reasonably, glossy and dross-free cutting kerfs are obtained. The gas flow acting under the workpiece is simulated by Finite Element Method (FEM). The varieties of pneumatic fields when the additional nozzle is in different degree and flow velocity are analyzed, which provides academic basis for controlling the flowing direction of the dross gas more reasonably. This laser cutting technology is practical and feasible.

Cutting brittle materials such as ceramics and glass by lasers or traditional saw method, costly fractures and associated damage such as chips and cracks can result. In most cases, these problems were caused as a result of the stress was not controlled properly and exceeded the critical value of the fracture. In this study, a dual-laser-beam method was proposed to avoid fractures in glass laser cutting, where an off-focused CO₂-laser beam was scanning on the top surface of glass periodically and repeatedly and a preheated-band which has a proper temperature was built. This preheated-band will reduce the temperature gradients when the glass is cut by the focused CO₂-laser beam. Under these conditions, glass can be cut with melting method without any fractures. The process of cutting glass by dual CO₂-laser beams was simulated numerically with FEA method and the distribution of temperature and thermal stress was investigated. The relationships between the cutting parameters, such as laser beam diameter, laser power, cutting speed, and the profile of the cutting groove were also discussed. The result showed that thermal stress decreased with the increasing width of preheated-banding, and the smaller the diameter of laser beam, the better the quality of the cutting groove was in the same laser power situation.

The new idea of the optimum controlling of laser processing technique and parameters with multi-objectives and multi-variables was put forth. With the comprehensive discussion about the quality index of laser transformation hardening (LTH), a hierarchical structure of the LTH quality index system and a decision-making framework model of the quality control were set up. Then, based on the conclusions of the sensitivities of LTH parameters' influences on the case indexes, the principle of LTH's parameters optimization was discussed by means of fuzzy decision method. With the combination of the principle and the sectionlly changing scanning velocity technique, which can effectively the uniformity of longitudinal case-distribution, a decision-making framework for optimal controlling on the laser scanning technique and the parameters with multi-objectives were put forward. An optimization model was developed and the validity of the model was verified both by theoretical computation and experimental results.

Femtosecond laser with 775nm wavelength and 150fs pulse width was empoyed to fabricate microstructures on a photosensitive glass (FOTURAN). The fabrication procedures included three steps: focused irradiation of femtosecond laser, programmed heat treatment and wet chemical etching in 8% ultrasonic solution of hydrofluoric acid for 50 minutes. By adopting appropriate incident laser parameters, including average power, numbers of pulses and scanning velocity, several fundamental microstructures had been fabricated on FOTURAN. The morphologies of these microstructures were analyzed by optical microscope, atomic force microscope and scanning electron microscope. Concave dots with smooth wall and several tens of microns in diameter are obtained on the surface. Microholes with circular cross-section and several tens microns in diameter are fabricated by femtosecond laser longitudinal writing mode, and currently the aspect ratio value above 8 is achieved. Femtosecond laser-induced index-refractive-change structures and shallow grooves are fabricated on the surface by transverse writing mode. The influences of incident laser parameters on final fabrication results are also experimentally characterized.

The experiment is carried out with ns Q-switch 532nm laser focusing into the transparent material to research the damage characteristics. The theory models about modulated pulse series are built up. Some main parameters such as interval of modulated sub-pulse, single pulse energy, peak power, and pulse duration are studies in process of laser bulk damage in transparent material. Some useful conclusions are acquired.

We have realized three-dimensional micromachining and microfabrication in transparent materials with femtosecond laser pulses, including water-assisted drilling by ablation, hologram encoding by microexplosion, waveguide writing by refractive index increase, and nanoline and nanotip polymerization via two-photon absorption. With the water-assisted drilling, we showed that not only longitudinal holes in the laser beam propagation direction but also transverse holes perpendicular to laser beam could be drilled when the sample's rear surface was in contact with water. True three-dimensional microchannels and microchambers were fabricated. In addition, three-dimensional cutting of glass was realized with the water assistance. By using tightly focused pulse to induce microexplosion, permanent computer-generated holograms were directly written inside glass and the stored data were reconstructed by a He-Ne laser beam. A waveguide array was written inside glass by the laser induced refractive index increase, and coupling between these waveguides was observed. Nanoline and nanotips with sub-30nm feature-size were fabricated using resin SCR500 by two-photon photopolymerization.

In this paper, selective deposition of conductive copper films on glass surfaces is demonstrated with the assistance of femtosecond laser surface modification followed by electroless plating. Irradiation of femtosecond laser makes it possible to selectively deposit copper films in the irradiated area on glass surfaces coated with silver nitrate films. The influence of the laser direct writing parameters and the electroless plating process on the formation of copper films is discussed. Meanwhile, the electric properties of copper films are investigated, which confirms that copper films are conductive. A tentative mechanism of the selective deposition process is also proposed. In addition, the potential application of this technique for integrating electrical and thermal functions into microdevices is discussed.

Transparent conducting CuCr_1-xMg_xO₂ thin films were prepared by pulsed laser deposition (PLD) from polycrystalline CuCr_1-xMg_xO₂ targets. The derived CuCr_1-xMg_xO₂ films were highly c-axis oriented deposited at higher substrate temperature. The micro structural, electrical as well as optical properties were studied. It was found that the films were relatively smooth, and behaved as semiconductors. The transmittances of the films in the visible region are about 80% with direct band gaps about 3.15eV. The results suggested that CuCr_1-xMg_xO₂ films could be successfully prepared by PLD, which can broaden the applications of the transparent conducting oxides films.

Hydrogen-free DLC films has been deposited by femtosecond laser pulse onto (1 0 0) p-type silicon substrates. The laser used for deposition has a pulse energy from 0.4mJ to1.6mJ and pulse width of about 50 fs with the repetition rate of 1 kHz. The laser intensities on the target are from 0.7×10¹⁴W/cm² to 2.8×10¹⁴W/cm². Uniform and wear-resistant DLC films is deposited with fs laser ablating a high purity graphite target at room temperature in vacuum. It is shown that the films has a good hardness ranged from 20 GPa to 30 GPa. Raman spectroscopy, X-ray Photoelectron Spectroscopy and micro-hardness are used to analyze the comprehensive performance of the films, and the results show that the films deposited at the laser intensity of 1.4×10¹⁴W/cm² has better hardness and a higher sp³ content. The sp³ fraction of the films is estimated to be as high as 45.6%.

A novel approach to restrain the formation of the burr during nanosecond laser ablation is reported in this paper. An assistant laser pulse, separated from the primary processing laser pulse with the pulse duration of 21 ns by temporal pulse shaping method, is used to control the formation of the melt deposit. The effect of the assistant pulse on the morphologies of the melt pools is investigated with the aid of microscope. The results of machining grooves on steel samples with the shaped pulses show a reduction of the burr at the boundary of the ablation zone. The contribution indicates a potential method for obtaining an efficient ablation as well as good processing quality in short pulse laser microfabrication.

To Construct the one-dimensional three sects photonic crystal with symmetrical structure in the form of (AB)^N1 (BA)^N2, a numerical calculation is conducted using the transfer matrix method of photonic crystal. It is found that in the main prohibitive bands of transmission spectrum there are extremely narrow single transmission peaks. The changing laws of the transmission peak position λ with the changes of the period quantities N_i (i=1,2), the refractive rate ⁿ_j (j=1,2,3) and the thickness a, b and c are analyzed. It is concluded that they can be approximately considered as linear in a small range and N₁ = N₂ = 7 is the optimal period quantities in theory. Based on these characteristics, through the adjustment of the parameters, the light needed is distilled in the mixing light in the range of 2280~2396 nm. The result is satisfactory.

Semiconductor lasers at wavelengths around 1.3μm are widely used for optic communications. For GaInNAs, the incorporation of nitrogen in the active layer can reduce the band-gap energy and allow emission wavelengths as long as 1.3μm. Ridge waveguide GaInNAs strain single-quantum-well lasers were fabricated with pulsed anodic oxidation (PAO). Using the technology PAO, we prevented the damage from the ion bombardment in the procedure of sputtering silicon dioxide used for building the insulating film. The output power of the laser with a wavelength of 1.31μm reached 14mW in CW mode at room temperature. The threshold-current was 18mA and its density was 360A/cm². The characteristic temperature of lasers was 135.1K and the quantum efficiency reached 76%.

By means of the Collins formula and finite-element method, diffraction integral equation of the square resonator with spherical mirrors is transformed to the finite-element matrix equation, mode-fields of the square aperture resonator is calculated. Experiment with square aperture resonator is done on HUST2000 high power transverse flow CO₂ laser. The results show that a square multi-mode beam with uniform comparatively intensity appeares in near field distribution. Laser quenching on 45# steel is done by using the square multi-mode beam and general circle beam. The hardened case caused by the square multi-mode beam is more uniform than general circle beam.

A numeric model of velocity and concentration distribution of shield gas-metal powder two phases flow field output by nozzle in laser cladding is established, and it is calculated by FLUENT software. In this model, the influences of momentum and mass transmission in the two phases flow are taken into consideration. The analysis on metal powder flow field velocity and concentration distribution with different process parameters (nozzle exit width w, initial gas flow velocity u and initial powder concentration c at nozzle entrance, angle of inward and outward wall of nozzle α, Φ) is conducted. The calculated results show that w mainly affects concentration and velocity magnitude, u mainly affects the focused position and velocity magnitude, c mainly affects concentration magnitude, α and Φ mainly affects the focused position and concentration magnitude. Under the process parameter conditions: w=1mm, c=0.1, u=3m/s,α=82 ° , Φ=68.5°, the same flow field is measured with DPIV technique. The calculated result agrees with the measured result, which indicates that the established model is reliable. The model can be used to understand the influences with different flow field process parameters and further design the nozzle size.

The onset of supercontinuum generation in a photonics crystal fiber is investigated experimentally and numerically as a function of pump optical power with a femtosecond pulse. The effects of optical wave breaking of higher-order solitons, Stimulated Raman scattering (SRS), and coupling between the SRS and parametric four-wave mixing on supercontinuum generation are investigated. Good agreement between experiment and simulation is obtained.

By using the nonlinear polarization rotation (NPR), we demonstrated a novel wavelength-tunable narrow linewidth erbium-doped fiber ring laser (EDFL) with a maximum tuning rang up to 25 nm (from 1532.0 nm to 1557.2 nm). The NPR effect effectively induced intensity- and wavelength-dependent loss to alleviate mode competition caused by homogenous gain broadening in erbium-doped fibers. By adjusting the polarization controllers in the cavity, the laser has a power-equalized output, and the output power fluctuation between different wavelengths is smaller than 0.2dB, the line-width of each light laser is 0.06 nm by 3 dB.

Laser marking is non-contact, non-pollution and permanence so it will be used widely. Laser marking is related essentially with the CNC machining. It is proposed that the control method and algorithm in the CNC system can be applied to the laser marking. The comparability of them is summarized on the base of analyzing the composition characters of the open-architectured CNC system and the laser marking. The mode of Laser marking includes scan mode and path one which are researched in detail in this paper. For path mode, the steps and code translation of CNC machining are applied. This method is not only useful to settle the edge effect, but also improve the marking efficiency.

As the application of the laser ultrasonics developed rapidly, there is especial call for more sensitive and convenient optical installation to detect the ultrasonic waves induced by pulsed laser. The optical beam deflection (OBD) methods have abstracted the interest of people for many years for their merits over the interference method. In this paper a novel differential OBD detection system for measuring laser-generated surface acoustic waves (SAW) is presented. The detection principle of this optical system is discussed in detail according to the scheme. And we get the linear relation between the physical parameter of the SAW and the output of the detection system. For confirm the conclusion the Monte Carlo computation method is utilized to simulate the ray propagation in the system, adding the consideration of the light spot distribution of the detection laser. The numerical result agrees with the analytic method. The linear relation between the detection system output current and the deflection angle induced by SAW is validated. Furthermore, the sensitivity and the spatial resolution of the system proposed are also calculated for comparing with the other OBD methods. The results show that this differential optical beam deflection detection system is more sensitive to the small disturbance and has higher space resolution. It has considerable potential in ultrasonic measurement.

Nondestructive and non-contact detection methods of surface defects of the elastic cylinders are urgently needed especially for the extensive application of such structure in the manufacture and daily life. In recent years there has been an increasing focus on laser ultrasonics, a novel technique in nondestructive evaluation, which can excite and receive high frequency ultrasonic waves from distance range in thermoelastic regime. This paper utilized the finite element method to investigate the transient mode conversion of circumferential guide waves by the surface crack of cylinder. The numerical model of the ultrasonic waves generated on aluminum cylinder whose diameter is 10mm by pulsed laser is established, considering the dependence of the material parameters on the temperature varying. The depth of the surface crack varies from 100 μm to 1 mm, which is much less comparing with the wavelength of the circumferential guide waves. The numerical results obtained from finite element model are presented in terms of vertical displacement, which is generated because of the localized temperature gradient on the surface. And the signals of the circumferential guide waves are analyzed by wavelet transformation. From the obtained results we can see that the amplitude of the scattered waves induced by the crack become more and more obvious as the depth of the crack increases and the time-frequency distributions of the scattered waves also change obviously. The results demonstrate the propagation of the circumferential guide waves on the surface of the cylinder can be applied in crack detection well.

In order to study the effect of viscosity on the mechanical effects during laser-metal interaction, the transient forces loading on a metal plate in various glycerol-water mixtures are investigated by a fiber-optic diagnostic technique based on optical beam deflection (OBD). The experimental results show that a target in glycerol mixtures is impacted in turn by laser-plasma ablation force and high-speed liquid-jet impulse induced by bubbles collapse in the vicinity of a solid boundary. The amplitudes of the two forces decrease monotonously with less laser energy. Furthermore, strong differences of mechanical effects are observed in the glycerol mixtures and water. Viscosity has the effect of dampening mechanical energy. And increased viscosity is seen to decrease the amplitudes of the two forces but increase bubble life-time.

Hydrogenated amorphous silicon (a-Si:H) thin films have been prepared by DC magnetron sputtering, and the effect of sputtering power, the hydrogen flow rate on deposition rate and the optical properties of a-Si:H thin films have been investigated. The hydrogen content (C_H) of the films was calculated by Fourier transform infrared (FTIR) spectroscopy method, the maximum C_H was obtained at 11at. %,and a bandgap of a-Si:H thin films was changed from 1.43 to 2.25 eV with different C_H. It was found that the refractive index (n) and extinction coefficient (k) of the prepared films decreased with the increase of C_H. The results provided experimental basis for preparing a-Si:H thin films with special performance and structure .

Investigated on TC4 titanium alloy and L3 pure aluminum laser welding of dissimilar metal, the width We of the lap joint was crucial for joint strength, and increased with the increasing of heat input, but if heat input was too high, the back of aluminum would burning loss, the joint strength would decline. Welding structures were related with penetration ratio θ, the larger the penetration ratio was, the easier the intermetallic compound formed, and the joint cracking and hardness were influenced. Choosing appropriate laser parameter, controlling aluminum melting amount, and ensuring joint width, we could acquire welding joint of meeting the need.

The properties of high peak pulsed laser induced damage to fused-silica fibers are investigated using damage experiments. The laser source is Q-switched Nd:YAG pumped dye laser system, the pulse width is 15.2 ns, and the wavelength is 1064 nm. The experimental results show that all the damaging scenes are fiber entry faces. Damaging patterns can be classified as three types: pit damage, fusion damage and sputtering damage. Pit damage occurs most frequently. Scaffolding defects come into being pits when the laser irradiation is lower. Fusion damage is related to the laser energy, but sputtering damage occurs frequently when the laser energy or power density is very high (>10⁷W/cm²~109W/cm², ns pulse). The damage photos illustrate that fiber end damage is mainly due to laser ablation and gasification. Impurities of fiber material or contaminant particles adhere to fiber end are stress-raisers, which absorbed enough laser energy, make local temperature rises up quickly, ulterior fusion or gasification, and finally strong tensile stress. When stress goes beyond the tensile strength of fused-silica, damage occurs. The main damage mechanisms appear to be thermal effect and plasma ionization. The origin for the decline of laser induced-damage to fibers threshold appears to be extrinsic defect. The damage criterion and damage threshold test method are presented. The zero probability damage threshold is calculated by linear fitting, that is 58.6J/cm². The damage process of fiber end faces could be divided into six steps. The origin for the decline of laser induced-damage to fibers threshold appears to be extrinsic defects which are closely related to the end-face quality.

FAF(Fast Axial Flow) CO₂ lasers are widely used in the areas of welding, cutting and texturing etc. These applications require the laser power supply with higher performance. In the paper, a switch power supply for the FAF CO₂ laser was developed, which can provide continuous and pulsed discharge voltage. It makes a FAF CO₂ laser to be competent for complex machining. The switch power supply adopts the half-bridge resonant switching circuit. IGBT was adopted as the switch device, which integrates the drive circuit and protection circuit. A microchip was used in the power as the control core, which translates the control signal from users to corresponding driving signal for IGBT, gathers and deals with the faults of the switch power supply. The experiment of the switch power supply was made on a fast axial flow CO₂ laser. The experiments show that the switch power supply can work on the FAF CO₂ laser well. The discharge current can be adjusted from 5mA to 120mA. It can switch the discharge freely between continuous mode and pulse mode. The pulse frequency can be adjusted from 20 to 2000Hz. Utilizing the switching power supply, the efficiency of the laser was improved. The dissipation power of the IGBT is very small, and the power supply brings fewer high frequency harmonic, lower interference.

Aiming to the special high power CO₂ laser surface treatment, the paper developed the integrated control system based on S7-200 PLC of transverse flow CO₂ laser. The selection of key technology and components, detection and control of signals, integrated control of complete circuit, technology of human machine interface and process control of system have been researched. Double closed loop power control system was realized, so that the stability of the laser power was in ±2%. Also, the giving power can be controlled by the laser controller or by the processing machine, thus, the users can control the laser more efficiently when processing. A series of experiments have been performed on 5kW transverse flow CO₂ laser, the output laser power was stable at discharge current of 9A for 8 hours, and the maximal power was 5.42 kW. The new type of transverse flow CO₂ Laser with Integrated Control System has been applied for special laser cladding with power-modulating on the metallic surface of the oil industry production.

Microcrystalline silicon (μc-Si) thin film transistors (TFTs) can be provided with higher mobility and stability than a-Si and better uniformity than poly-Si TFTs, it would be more suitable to be applied in larger area AMOLED. By using 2ωYAG laser annealing, crystalline μc-Si thin film on plastic substrate has been investigated and the proper laser energy needed for crystallization has been indicated. It has been found that the dehydrogenation process at 300~450 °C for a few of hours could be omitted by decreasing the H content in the crystallization precursor, which is suitable for laser crystallization on plastic substrate. The crystalline volume fraction (Xc) and the grain size of the resulted μc-Si could be adjusted by controlling the laser energy. By this method, the μc-Si on plastic substrate with the Xc and the grain size are 85% (at the maximum) and 50nm respectively has been achieved.

Due to thermal mismatch, stresses develop in n-type diamond thin films when cooled down to room temperature from deposition temperature. In this investigation, thermal stresses in diamond films deposited on silicon substrate are calculated, the influence of temperature and film thickness on thermal stresses are also discussed. The results show that thermal stresses are sensitive to deposition parameters, the thermal stresses increase with the increase of deposition temperature, reach the maximum value of 0.724GPa at 1000k, and then begin to decrease. With the increase of diamond thickness and substrate thickness, the thermal stresses decrease and increase respectively.

The experiment of micro-ablating diamonds, natural diamond and HTHP manmade diamond, has demonstrated that F₂ 157nm laser can break the chemical bonds of hard material with low laser pulse power, and ionizes them rapidly. The ablation thresholds of these two kind of diamonds were tested as 2.0J/cm² and 3.0J/cm² respectively. Stair ablation on the polished surface of the natural diamond showed that a pulse could ablate 17nm depth on a 25μm×25μm square, however, for the polished surface of HTHP diamond, the depth was 12nm. The edges of ablating square were sharp, few spatters were observed, and 3-D ablation quality was good. The thermal calculation shows that the temperature rise was not very seriously. The interaction and the mechanism of ablative photo decomposition between the photons of 157nm laser and the atoms of diamond are presented. Diamond is a covalent crystal. Covalent bonds associate carbon atoms. The cohesive energy of diamond is 7.36eV, and its binding energy is 3.68eV. Comparing with 7.9eV of 157nm photon energy, it can be inferred that the mechanism of interactions between 157nm laser and diamond is a process of single-photon absorption.

During laser heating of a metal material, the continuity of material confines its free expansion, thermal stresses arise. On one hand the thermal expansion of the heated zone of the material increases with the increase of temperature, the thermal stress level increases correspondingly; on the other hand the mechanical properties of the material will change with the increase of temperature, especially the elastic modulus, yield strength and tensile strength drop significantly, which is the so-called thermal softening problem. Due to the effect of the two factors, as the heating time or the intensity of the laser beam increases, it is possible that the stress levels of the heated zone of the material exceed the yield strength, which leads the material to come into a plastic stage. Thus, a thermal plastic problem occurs. In this study, thermal elasto-plastic stresses during laser heating of a metal plate are computed by the finite element method (FEM) based on thermal elasto-plastic constitutive theory. The mechanical behaviors of the metal material during the laser heating are analyzed. By the analysis of the results, it is found that thermal expansion leads to the increase of stress level early during the laser irradiating, and thermal softening causes the decrease of stress levels in the plastic zone and the slow growth and even decrease of stress levels in elastic zone later. The radial stresses are all compressive stresses, and the hoop stresses are compressive stresses within about the laser spot and are tensile stresses at other place. This work may be beneficial to the laser processing of metal materials.

Advanced High Strength Steels (AHSS) are gaining considerable market shares in the automotive industry. The development and application of Dual Phase (DP) steel is just a consistent step towards high-strength steel grades with improved mechanical behavior. Tailor welded blanks with DP steel are promoted in the application of Body-In-White (BIW) structure by the automotive industry. A tailor welded blank consists of several flat sheets that are laser welded together before stamping. Applied cases of tailor welded blanks of high strength steels on the automotive structural parts are investigated in this paper. The mechanical behavior of laser welded joints for DP steel is studied. Microstructure of laser welded joints for DP steel was observed by SEM. Martensite in the weld seam explains the higher strength of welded joints than the base metal. Results show that the strain safety tolerance of laser welded seam for high strength steel can meet the requirement of automobile parts for stamping if the location of laser welded seam is designed reasonably.

Si and SiO₂ as two materials are composed of one-dimensional photonic crystal. Using transfer matrix method, the optical transmission properties in 1-D photonic crystals is analyzed, and the band gap property of 1-D photonic crystal is obtained. According to thermo-optical effect and thermal-expansion effect the optical depth and index of the materials can vary when the temperature varies. So the structure of 1/4 wave-plate stack in traditional photonic crystals is destroyed and the band structure varies. And the band edges shift. The relationship between temperature and the band edges of one-dimensional photonic crystals is analyzed numerically. The result shows that it is linear relationship between the temperature of photonic crystal and the wave-length of the band edges. And analytical expression of the linear relationship is proposed. The temperature can be measured by the wavelength shift value. The result can provide theoretical guideline for the design and application of temperature sensor.

On propagation characteristic of material surface wave in laser ultrasonic, design of laser ultrasonic measure system have attracted the extensive attention and recognition. Laser ultrasonic technology is on studying material structure, characters, parameters (thickness, density, flexibility module), now as a important means and development aspect it has been used to detect whether material is scatheless. Firstly, this paper introduces Test principle of Fizeau Fiber Interferometer, and designs the measure system based on laser SAW. Finally through experiment data, this system provides high sensitivity of laser ultrasonic and also has the merits of no contacted measurement, high space resolution of laser ultrasonic, low environment demand, simple configuration, easy adjustment and high frequency response, highly adapts to laser ultrasonic measure.

This paper (SPIE Paper 68251G) was removed from the SPIE Digital Library on 19 August 2008 upon learning that two individuals listed as additional co-authors on the manuscript had no prior knowledge of the paper, did not contribute to it, and did not consent to having their names included as co-authors. The names of these two individuals have been or will be deleted from this and all other bibliographic records as far as possible since they have no connection to this paper. Additionally, the names now associated with this publication record, Xiang-Wen Xiong and Wynn L. Bear, are actually the same individual and not two different authors. This is not sanctioned by SPIE. As stated in the SPIE Guidelines for Professional Conduct and Publishing Ethics, "SPIE considers it the professional responsibility of all authors to ensure that the authorship of submitted papers properly reflects the contributions and consent of all authors." A serious violation of these guidelines is evident in this case. It is SPIE policy to remove papers from the SPIE Digital Library where serious professional misconduct has occurred and to impose additional sanctions as appropriate.

Aiming at the 3kW transverse flow CO₂ laser, a hybrid power system and its compatibility with pin-to-flat discharge structure has been studied in the paper, CW/pulse output laser has been obtained. The DC high voltage output consists of switching power supply and main transformer, and three-phase SCR power supply is replaced by switching power supply. The pulse parameters are frequency from 0Hz to 1kHz, duty ratio from 0% to 100%. The pulse waveform of discharge voltage and discharge current are measured. The results show that row resistances have been moved, pin resistances have been reduced to 10kΩ. When the pressure P is 8.45kPa, the highest efficiency of electric-photo conversion of laser is up to 14.8%.The laser output power can be modulated in the state of continuous and pulse at arrange of 3kW. Then particular laser cladding is performed on the airplane engine blade, the laser cladding crack produced in continuous state is solved, and the heat-affected zone of laser cladding is also narrowed.

Laser-induced breakdown spectroscopy (LIBS) has been shown to be a useful technique in elemental analysis with many advantages including rapid analysis, simultaneous multi-element detection, in-situ or stand-off analysis capability. To evaluate the potential application of LIBS for quantitative analysis, some experimental investigations into the laser induced plasma process were undertaken with brass alloy sample, in the laboratory. The plasma was generated by a Q-switched Nd:YAG laser operating at 532 nm with pulse width of 10ns and repeat frequency of 10 Hz. The LIBS signal was coupled to the spectrometer and recorded with OMA system and a PMT in conjunction with a computer controlled Boxcar integrator. The temporal characteristic of the plasma was investigated with the emission line of Cu atom at 324.75 nm, 327.40 nm and the emission line of Zn atom at 330.25 nm. The optimum delay time range for 324.75 nm from Cu atoms and 330.25 nm from Zn atoms is from 300 to 600 ns. The self-absorption of Cu atomic lines at 324.75 nm and 327.40 nm can be reduced by increasing the laser energy and recording the spectra in the early stage of the plasma formation. The experimental results are effective for improving the slope of calibration curve.

Remanufacture engineering, which has become an important way to sustainable society progress, and its recent development were introduced. Laser remanufacturing technology utilizes high energy density laser beam to remanufacture the worn or failed components. As laser processing is important and advanced technology for remanufacturing, laser remanufacturing was introduced on connotation, characteristics and technical sorts. Research and application status of laser remanufacturing was reviewed, and two laser remanufacturing examples were described to show that laser remanufacturing can solve the difficult problems in equipment maintenance and remanufacturing. It pointed out that the main problems of laser remanufacturing technology for further developing lies in high power laser system, laser remanufacturing technique or processing, supports from government and enterprises. It stated out the developing trends of laser remanufacturing technology, and showed that laser remanufacturing can bring great economic and social benefits.

SiO₂-TiO₂ strip optical waveguides have been fabricated by laser densification of SiO₂-TiO₂ sol-gel films using a Ytterbium fiber lasers and following chemical etching process. Effects of laser processing parameters and dried temperature of SiO₂-TiO₂ sol-gel films on the dimensions of strip optical waveguides were systematically studied. And the mechanism on laser densification of SiO₂-TiO₂ films was discussed. The experimental results demonstrate that the width and thickness of strip waveguides increase with laser power density until SiO₂-TiO₂ films are damaged by laser irradiation. The available range of laser power density for laser densification increase through enhancing dried temperature of SiO₂-TiO₂ films, which mainly thanks to the increasing stress capacity in the films. The width of strip optical waveguides can be markedly decreased from 110 to 25 μm in the case of the same thickness by enlarging available range of laser power density. The mechanism on laser densification of SiO₂-TiO₂ films is mainly based on shrinkage of nanoscale pore within SiO₂-TiO₂ films duo to the energy transferred from silicon substrate.

In order to investigate the tribological performance of laser clad coatings on die steel, laser cladding techniques were adopted with Fe-based alloy powders. The wear tests were carried out by using laser clad layers as low samples and GCr15 steel ball as upper samples with HT-500 wear tester. The morphologies of wear scars were observed with optical microscopy, and the wear width and the depth of the wear samples were measured. In the meantime, the wear rate was calculated theoretically. Under dry sliding condition, As the tests show, friction coefficient decreased with the load increase gradually, then increased. And the wear performance of 300g load was better than that of 500g load under dry sliding condition. Under lubricant condition, with the increase of load, the friction coefficient decreased gradually. And the friction coefficient, wear rate and wear width under lubricant are smaller than that under dry friction with the same load.

Analyzing the laser processing system basic structure, the model of CO₂ laser processing system with remote control has been given. A new scheme of this system is carried out. In this system, the control module of CO₂ laser processing system is designed to accept the instruction which comply with HTTP protocol. The hardware structure and the software framework are described in detail in this paper. The scheme basing on standard protocol is value to design and manufacture of CO₂ laser processing system.