This PDF file contains the front matter associated with SPIE Proceedings Volume 11456, including the Title Page, Copyright information, and Table of Contents.

Laser pressure welding of dissimilar metal aluminum and copper can be realized at high welding speed. The microstructural evolution of the weld are characterized by using scanning electron microscope (SEM) and transmission electron microscopy (TEM). The investigation results indicate that the weld mainly consists of four zones, namely (I) the fusion zone between the aluminum base metal and the interface is mainly the Al solid solution and Al-Cu eutectic alloy; (ii) the interface zone between the copper and the fusion zone mainly composes of Al-Cu eutectic alloy and the intermetallic compounds (IMCs), such as Al2Cu and Al2Cu3; and (iii) the base metal of aluminum and copper.

In this paper, investigation on fiber laser cutting of CFRP was carried out through establishing a multi-physical finite element model and cutting experiment. A multi-physical field model of laser cutting of CFRP was established. Experiments on 1 kW fiber laser cutting of 1 mm CFRP was performed. The relationship between cutting quality (slit width, notch taper, and HAZ width) and laser process parameters such as laser power and cutting speed was investigated. The results show that the transfer of laser energy in CFRP is mainly along the direction of fiber laying, and the heat transfer speed in carbon fiber is much faster than that in resin. The width of the slit, HAZ and the notch taper all increase with the increasing of laser power. However, the width of slit and HAZ decrease as the cutting speed increase and the notch taper increased first and then decreased. When the laser power is 150 W and the cutting speed is 1 m/min, the cutting quality is better.

The Galvanized steel sheet is used as the automotive body material, and the evaporation of zinc into the weld seam will cause welding defects during the laser welding process. The multi-point laser beam has great development potential in automobile industry, because it can effectively reduce the integration of the galvanized layer into the weld seam during welding. In this paper, a panda-shaped three-point beam (panda beam) is proposed to replace the original single beam used in welding and three methods to realize the panda beam have been discussed. The beam splitting of the diffraction grating is performed, and the three, five and four beam-splitting ratio Daman gratings are obtained but with relatively high energy loss. Additionally, based on the theory of grating diffraction, a panda beam has been obtained by splitting the 4kW incident laser through the Bragg grating. The single front beam radius is 0.6mm with a power of 1.1261kW, and the distance between the two front beams is 3.8mm. The radius of the main beam is 1mm with a power of 1.7168kW, and the distance from the front beam to the main beam is 9.7mm. Lastly, based on the beam splitting theory of geometric optics, the multi-point beam and the panda beam are realized by the ridge reflector with an energy loss of 14.09%, which shows the great advantage of laser beam splitter compared with multi-light source structure in practical application. When welding with the panda beam, two functions of zinc coating and solder melting are carried out respectively, which can avoid zinc vapor entering the molten pool and improve the welding quality

The metallurgical and thermophysical process in the laser melting filer wire process are complex, and the interaction between the laser - metal wire - substrate makes the energy distribution requirements more demanding. In order to study the energy coupling mechanism in the high deposition efficiency achieved by inducing a boiling front, the existing characteristics are firstly explored. The author studies the laser energy distribution rules on the boiling front and the substrate surface by the main process parameters and gives an optimal parameter adjustment range theoretically, which has a guiding significance for the actual machining process. In addition, comparing the heat conduction loss of the new method and the common additive manufacturing process (feeding solid wire into the melting pool of substrate), the calculating result reveals that the new additive manufacturing method proposed by our group plays a more positive role on improving the energy coupling efficiency.

Common organic modification of metal superhydrophobic surface has these problems such as serious environmental pollution, high thermal resistance, low processing efficiency, and easy to fall off. A chemical-free direct laser selective texturing technology is proposed to enhance condensation heat transfer performance on stainless steel surface. A micro-textured steel plate was processed by nanosecond pulsed laser to obtain a superhydrophilic surface of a square grid groove-convex structure. After heat treatment, the superhydrophilic surface changed to be superhydrophobic. The superhydrophobic surface was then laser selective textured to get a wedge-shaped superhydrophilic-superhydrophobic surface. Surface morphology, chemical composition and three-dimensional profile were analyzed. By comparing the superhydrophobic and superhydrophilic surfaces, the back-surface temperature and the average detached diameter of the condensed droplets was measured. Furthermore, the surface condensation heat transfer coefficient of samples was calculated according to the relevant condensing heat transfer theory. At the same time, samples with different area ratios of laser textured superhydrophilic-superhydrophobic were designed for heat transfer analysis. Condensation results showed that the heat transfer coefficient of the selective-textured surfaces was enhanced compared to the full laser textured superhydrophobic surface. After the condensed droplet grew to the superhydrophobic boundary of the laser selected area, it was restricted to grow and merge quickly and then was removed by self-transport in the wedge-shaped superhydrophilic area. The laser textured patterns showed a smaller detachment diameter than the fully superhydrophobic surface and had enhanced condensation heat transfer coefficient, as laser textured superhydrophilic-superhydrophobic areas are equal.

Femtosecond laser has been widely utilized for modification of crystal structure to achieve desired functions. However, the effect of crystallographic orientation on the induced structure by femtosecond laser processing has yet been comprehensively studied. In this work, the crystallographic orientation dependence of amorphization effect of Si with femtosecond laser irradiation is studied. It is revealed that surfaces of different crystallographic orientations have different tendencies to form amorphization. Within the laser fluence range in this work, the (111) surface of Si favors generation of amorphization compared with the other crystallographic planes. This phenomenon could be explained by the lowest crystallization speed required by the (111) surface due to its smallest surface energy. Compared with nanosecond laser, non-thermal melting induced by femtosecond laser induces mild thermal gradient and favors recrystallization in the lattice.

As a mid-infrared laser with large magnification and high beam quality, carbon dioxide lasers are often used as intermediate amplifiers in picosecond terawatt laser systems. With the combination of gas discharge and optical pump, the gain spectrum in 10μm can be greatly improved. In this paper, a numerical model is set up to describe the laser amplification and kinetic processes, based on six-temperature level structure, in hybrid pump CO₂ laser amplifier system. The influences of the pump power and its amplification results compared with conventional CO₂ laser are simulated and discussed. Such a hybrid pump CO₂ laser amplifier is very promising in improving output pulse quality by reducing the pulse split.

A double-beam laser shockwave cleaning (DLSC) process is applied to clean nanoparticles on silicon wafer to eliminate the formation of uncleaned blind zone right under the plasma kernel. The size of the uncleaned blind zone in DLSC is reduced by 95% compared to the single-beam laser shockwave cleaning process. The study of the time-resolved plasma evolution suggests that the formation of multiple plasma kernels makes the nanoparticles in the blind zone exposed to the cleaning-effective zone of the nearby passing plasma. The theoretical calculation of the shockwave force distribution shows that the horizontal drag force from a nearby passing plasma in the DLSC process facilitates the nanoparticle removal in the blind zone.

Quartz tuning fork is a kind of widely used piezoelectric device. However, as a hard and brittle material, silicon dioxide crystal, which is the core component of tuning fork, is difficult to realize high precision microprocessing. In this paper, femtosecond laser is used to process silicon dioxide crystal. The laser processing parameters which affect quality of tuning fork sidewall are theoretically analyzed, and an experimental study is carried out to optimize the technological parameters and improve the quality of tuning fork crystal. In addition, a set of processing route of quartz tuning device is designed, The tuning fork sensor manufactured has the characteristics of low cost, compact structure, low power consumption and will have a wide application prospects in the future.

Investigation on single-pulse 266 nm nanosecond laser and 780 nm femtosecond laser ablation of sapphire was carried out. Diameter, depth and volume of ablated holes varying with laser density is studied. The results show that 266 nm nanosecond laser ablation of sapphire is caused by photochemical and photothermal effects. 780 nm femtosecond laser ablation of sapphire is due to “cooling”ablation. As energy density increases, thermal effect still exists, yet being much less significant, while ablation mass is greater than that by nanosecond laser. In nanosecond and femtosecond laser ablation, the ablation efficiency increase first and then decrease due to plasma shielding. Ablation efficiency is higher by nanosecond laser than by femtosecond laser at the same laser density. The ablation efficiency reaches the maximum at the energy density of 55.32 J/cm2 to 68.43J/cm2. However, 780 nm femtosecond laser could machine a microstructure with larger depth diameter ratio at lower density.

High strength steel has been used in the aviation industry and automotive body structural applications to reduce its mass through a reduction in thickness. Therefore, it is very important to enhance its mechanical property, such as microhardness. In the present research, the high strength steel samples were treated by laser shock peening (LSP) with different laser pulse energy and laser pulse width. The microhardness and residual stress were measured to compare the difference between laser energy of 3 J with 10 ns and 5 J with 20 ns. The results in the study show that the surface LSP treatment can increase the microhardness and the compressive residual stress can be found when the samples were tested by hole drilling testing.

Laser Direct Part Marking (DPM) technology is a marking technology that has proved to be feasible in the industrial environment, and can be highly automated and environmentally friendly. It has become the preferred method for completing product marking in industrial product traceability. In this paper, MOPA laser marking system with flexible control and wide adjustment range of laser parameters is used for experiment. According to ISO/IEC TR 29158 bar code technology standards, the influence of laser processing parameters(such as laser peak power, laser pulse energy, laser power, filling space, scan speed, etc.) on the quality (such as symbol level, symbol contrast, print growth, etc.)of laser direct marking DM symbol is studied. By optimizing the laser processing parameters, high-quality DM symbol on the surface of AL2024 is realized.

Femtosecond laser with different polarizations can induce different types of periodic structures in fabrication of metal, semiconductor and dielectric materials. Most previous works reported that direction of the laser induced periodic surface structure (LIPSS) is perpendicular to the polarization direction of the laser. Polarization state of the vectoral polarized beam exerts an axisymmetric distribution in the beam cross-section. Over the years, femtosecond laser fabrication based on vectoral beams is attracting more and more attentions, which indicates novel properties and applications for induction of microstructures on surface. In this work . we used vortex wave plate to convert linearly polarized light into first-order and second-order vector beams respectively. We produced various types of LIPSS by single-point ablation on the SiC surface and analyzed period of the LIPSS by Fourier transform. In addition, we also analyzed variations of the LIPSS at different scanning speeds on the SiC surface.

We developed a longitudinally excited CO₂ laser with controllable a laser pulse waveform, and a simple, compact and low cost device. We investigated 146-μm-thickness borosilicate glass drilling depended on a fluence to consider applications of a longitudinally excited CO₂ laser. The laser processing system was consisted of the CO₂ laser with the repetition rate of 1 Hz, CaF₂ attenuators, a beam expander, a ZnSe focusing lens with the focal length of 12.7 mm and the glass sample. The focus spot was on the sample surface. An assist gas for cooling the sample and removing debris was not used. The CO₂ laser produced a short laser pulse had a spike pulse with the pulse width of 300 ns, a pulse tail with the length of 100 µs and the energy ratio of the energy of the spike pulse part to the energy of the pulse tail part of 1:25. The short laser pulse produced a crack-free piercing hole without assist gas. On the other hand, a heat affected zone (HAZ) was produced around a piercing hole. In this work, the smallest piercing hole diameter in each condition was about 50% of the irradiation diameter of 125 μm.

In this paper, we presented a study of fabricating nano-grooves on GaAs substrate through laser direct writing (LDW). GaAs (001) substrate with homo-deposition of 500nm buffer layer was linearly scanned (pixel by pixel) by a focused UV laser (405nm) to directly create nano-grooved structures. The dependence of laser power and dwelling time (the exposure duration for each scanning pixel) on the patterned grooves were carefully observed. First, with the fixed setting of dwelling time at 10000ns, the laser power was varied from 110mW to 140mW. It can be found that there is an ablation threshold power between 115mW-120mW. As the power exceeds 125mW, as well as the depth, the average full width at half maximum (FWHM) of grooves could be effectively turned with a positive correlation to the power. Then, with the fixed setting of power at 130mW, a wide dwelling time variation from 10000ns to 10ns was systematically investigated. It is observed, in the range of 10ns-4000ns, the average depth can be continuously tuned by the dwelling time following an approximately linear positive relation, but once above 4000ns, the average depth will be saturated at ~77nm. While for the average FWHM, the saturation will show up early just when the dwelling time is above 100ns and the saturated value is ~90nm. Moreover, if the dwelling time is set too small (below 50ns), a by-product of nano-dots can form in the grooves.

In this paper, 266 nm nanosecond solid-state laser machining of SiC was experimentally investigated. Atomic force microscope and optical microscopy are used to detect the ablation morphology of specimens. The changes in the diameter of the ablated holes and depth of single and multi-pulse laser ablation of SiC were studied and the removal mechanism was analyzed. The results show that in the single-pulse ablation experiment, as the laser energy density increases, the diameter of the ablated holes gradually increases, and the ablation depth increases first and then decreases. In the multi-pulse machining experiment, the average depth per pulse increases as the laser density increasing when the number of the laser pulse is less than 125 pulses. When the number of laser pulses is more than 125 pulses, the average depth per pulse increases as the laser density at lower laser density; whereas, the average depth per pulse keeps a constant value at higher laser density.

In order to realize laser additive manufacturing and damage repair of complex parts with different sizes, an adjustable variable spot size laser cladding optical system is proposed. The system is an off-axis three-mirror optical system, which is composed of three aspherical reflectors. It can adjust the spot size by moving an asperical mirror with an step motor. It can eliminatesolves the problem of light energy loss fixed spot size of traditional refractive optical systems. The proposed solution is high efficient in complex parts clading process and cost effective. and lift the application limitation of high-power lasers in laser cladding. In this paper, the physical model of off-axis three-mirror optical system is established by means of Zemax software. A 4000 W fiber laser in non-sequence mode was used to simulate the intensity distribution of the spot cross-section. By defocusing, the spot diameter at the working face can change continuously from 6mm to 12mm.