This PDF file contains the front matter associated with SPIE Proceedings Volume 13234, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

This paper experimentally investigated the effects of laser beam oscillation and hot-wire process parameters on the surface and cross-sectional morphologies of aluminum alloy welds during oscillating laser hot-wire welding. The study revealed a competitive relationship between laser beam oscillation and the hot-wire in influencing weld morphology. As the hot-wire current increases, the weld surface quality initially improves and then deteriorates, with spatter gradually increasing and weld penetration (depth of fusion) first increasing and then decreasing. Similarly, as the oscillation frequency rises, surface quality improves and then declines, spatter decreases and then slightly increases, and the weld penetration gradually decreases. Optimal process parameters were identified within the studied range, achieving a weld with high penetration, excellent surface quality, minimal spatter, and high weld stability by coupling the effects of laser beam oscillation and hot-wire input.

Plastics and metals are highly complementary in terms of strength and density, leading to a growing demand for plastic-metal dissimilar joining, particularly in electronics, rail transportation, and aerospace. For this reason, in this study, dissimilar welding of PA66/304 stainless steel and PET/304 stainless steel was realized by introducing an oscillating laser into conventional laser welding, respectively. The results show that the oscillating laser can improve the interfacial temperature uniformity through customized energy distribution, thus achieving high quality joining of different plastic species with metals. In addition to this, different plastic-to-metal joints were explored in detail in terms of tensile fracture failure forms. The sensitivity of the PA66 base material to heat input resulted in poor fracture molding of the joints. In contrast, the PET and 304 stainless steel joints showed excellent mechanical properties comparable to those of the base material. Through the research of the morphology of different regions of the fracture surface, it was found that the mechanical properties of the joints varied greatly in different weld positions, which was specifically manifested in the gradual enhancement of the joint toughness from the center of the weld to the two sides. Further analysis and testing of the fracture interface composition revealed the interfacial enhancement mechanism in the oscillating laser-induced heterogeneous joints.

Achieving nanometer-level alignment precision in lithography is essential for the advancement of semiconductor manufacturing. This study introduces an innovative laser self-reference technique that leverages the interference of two coherent beams on a reflective grating with a matching period. By incorporating a wedge-shaped beam splitter, a reference interference fringe is generated, establishing a direct correlation between the incident interference pattern and the reference grating, thus enabling real-time spatial alignment monitoring. A theoretical model was developed to elucidate the phase relationship. The experimental apparatus comprised a high-precision laser system, a piezoelectric transducer (PZT) for minute phase adjustments, and a high-speed CMOS camera for instantaneous analysis. The technique was evaluated using three displacement inversion algorithms, with the image phase correlation algorithm outperforming the others, achieving control of deviations to below 3.2 nm. Laser self-referencing technology not only provides a nanoscale alignment method, but also meets the fine control required for multi-layer grating manufacturing, improving the quality and reliability of the lithography process, and addressing a critical challenge in the production of semiconductor chips.

The laser interference lithography shows great potential in the field of sub-wavelength gratings which can be used for polarizer arrays. However, due to the difficulty in further reducing the wavelength of the laser source, the further reduction of the grating period is limited. A widely used method to reduce the minimum size of patterns is immersion lithography. Especially in the interference lithography, using the prism to reduce laser wavelength and grating period has been explored. However, total internal reflection between the prism and the photoresist layer on the wafer surface extraordinarily reduces the energy efficiency of the incident light, making it impossible to obtain interference stripes with smaller periods. This paper proposes a laser interference lithography combined with immersion lithography that can process the gratings with the smaller period and illustrates the principle. To achieve better processing quality, the constraint conditions that the prism bottom angle and the diameter of the laser beam should satisfy are obtained through calculation, which provides a theoretical basis for laser interference lithography combined with immersion lithography for processing the gratings with the smaller period.

Large-scale diffraction gratings, ranging from sub-meter to meter in size, play a vital role in spectrometers and various measurement technologies. The primary method for fabricating these gratings is holographic exposure, which requires large-aperture laser beams and low-aberration wavefronts, limiting the size of gratings that can be fabricated in a single exposure. To expand the grating size, we employ a mosaic exposure method, where different areas of the substrate are sequentially exposed by repositioning the beams. This requires compensation for mosaic errors, including phase, period, and tilt errors. Mosaic errors are monitored by observing the interference fringes formed by the -1st and 0th-order diffraction waves of a reference grating. By analyzing the variations in the reference fringes caused by these errors, we correct them through adjustments to the phase, incidence angle, and azimuth angle of the laser beams. In our experiments, we achieved a 2×1 mosaic grating area of (9+9) mm × 9 mm. Fizeau interferometer measurements showed that the -1st-order diffraction wavefront error had a PV value of 0.1595λ and an RMS value of 0.0259λ.

Neural networks are powerful tools for solving many modern problems. One of the options for the optical implementation of a neural network is a diffraction neural network, which consists of one or several layers of different-sized pixels on which radiation diffracts. The pixel parameters are tightly bound with the desired radiation wavelength. In this work, we printed masks for diffraction neural networks for the optical range using two-photon laser lithography. Applying coordinate stabilization approach and preserving temperature and humidity allowed to print pixels with up to 10 nm height difference and 2.3 nm average surface roughness.

The High Temperature Co-fired Ceramic (HTCC) substrate boasts advantages such as high structural strength, high thermal conductivity, and good chemical stability, thus showing broad application prospects in high-power microcircuits. As the circuit board material, it is necessary to use mechanical or laser drilling on the raw porcelain, and the aperture of through hole and position accuracy directly affect the yield and final electrical properties of the substrate. In recent years, laser processing technology has the advantages of high precision, high efficiency, stable performance and no contact, which increasingly become one of the most critical processes of multi-layer ceramic packaging technology. In this paper, the ultraviolet (UV) picosecond laser with pulse width of 15 ps was used for HTCC drilling with thickness of 0.14mm. The laser has a maximum power of 30W at a repetition rate of 600 kHz, a spot size of 20 μm after focusing, and a wavelength of 355nm. By optimizing the process parameters, including laser power, frequency, scanning speed, and repetitions, a minimum through-hole with diameter of 100 μm, with an accuracy of ±5 μm for entrance and exit holes were achieved. Under optical microscope, roundness, taper, and Heat-Affected Zone (HAZ) of hole under different conditions were obtained and analyzed. These results prove that ultra-fast laser processing can be an efficient HTCC drilling technique.

We present the fs laser inscription of ring-shaped random structures using Spatial Light Modulator (SLM) in multimode GRIN fiber. The use of SLM allows one to modulate the phase of the fs radiation incident on it and to write various structures with complex geometries inside the static fiber core. We optimized the fs laser inscription parameters: pulse energy, SLM frame rate, overall length and distances along the fiber of the structures to enhance Rayleigh backscattering level at minimal insertion losses. In particular, scattering structures with random distances along the fiber were written using the Line-by-Line method in single mode fiber at the optimal inscription parameters (pulse energy of 3 μJ, SLM frame rate of 5 Hz, the overall of 2 mm and random distances along the fiber in the range of 5 μm). Further, we created the ring-shaped random structures in 100/140 μm GRIN multimode fiber with enhanced Rayleigh backscattering level by +66 dB/mm relative to the intrinsic fiber level. Owing to the variation of random distances along the fiber and ring’s diameters of structures in range of 0.5 μm and 20 μm, respectively, allows one to obtain a broadband reflection spectrum within 88 nm with a reflection coefficient of 0.01%. The low threshold generation with ring-shaped output beam of the Raman fiber laser with random distributed feedback based on the SLM-inscribed random structures in the multimode fiber is demonstrated for the first time.

Copper alloys with addition of the refractory metals have been widely used due to their excellent conductivity and ablative resistance. In this work, the Cu-Ta deposited alloy was successfully fabricated by laser directed energy deposition. The microstructures of the Cu-Ta deposited alloy were characterized and the arc-ablation properties were studied. Results show that the Cu-Ta deposited alloy is mainly composed of Ta and Cu and the morphology of Ta is spherical. The ablation area of the Cu-Ta deposited alloy is smaller than that of the CuCrZr substrate and the percentages of the arc erosion region ratio are 5.48% and 20.50%, which indicates that the Cu-Ta deposited alloy has more excellent arc-ablation property. We hope that the results will be helpful for the further development of the copper alloys with addition of the refractory metals.

High-precision mechanical sensors are critical for devices and systems with extremely high accuracy. By combining the mechanical and optical properties of specific materials, it is possible to fabricate sensors that meet specific performance requirements by using ultraprecise micro/nano fabrication, and optical sensing methods. In this work, we introduce a probe fabricated on the end face of an optical fiber using two-photon polymerization 3D printing technology. The 3D-printed probe and the optical fiber form a Fabry–Pérot cavity, which converts the minute mechanical signals received by the probe into optical signals for demodulation. The sensitivity of the probe depends on the material properties, structure, and sizes. The material we used has a lower Young’s modulus than normal 3D-printing photoresist, so the probe could achieve higher resolution. Depending on the specific requirements of different application conditions, various materials and different designs for 3D printing can be selected. The structure of this nano-mechanics sensor was demonstrated in this work. We also conducted mechanical testing on it. The verification results show that the sensor achieves an ultra-high resolution. The optical fiber nano-mechanics sensor that shows high force resolution has potential for high accuracy measurement applications, and the results reveal a potential design strategy for special optical probes with unique physical properties.

Laser assisted Electrochemical Surface Modification (LESM) technology is a general term for coupling laser and electrochemical treatment technology to improve the surface properties of metal. Due to combining the advantages of laser and electrochemical processing, LESM has developed rapidly in recent years and gets applications in many fields, such as aerospace, aviation, navigation, and medicine. On the one hand, LESM can break through the limitations of single processing in environmental protection, efficiency, quality, and performance improvement. On the other hand, it can use the thermal, mechanical, and photoelectric effects provided by laser irradiation to change the thermodynamics and dynamics of the electrochemical reaction, and then control the electrochemical reaction process. LESM enables divided into three types based on the processing objective, including material removal (electrochemical machining), additive manufacturing (electrodeposition), and surface strengthening treatment (anodic/micro-arc oxidation). Simultaneously, according to the composite mode, it can also be divided into process composite and energy field composite. Thus, the typical methods of LESM are reviewed in this paper, and the recent developments in laser-assisted electrodeposition, laser-assisted electrochemical machining, and laser-assisted micro-arc oxidation technologies are introduced at the same time. Finally, the future development trends and challenges of LESM prospect in aspects of efficiency, quality, performance, and equipment development.

CO₂ laser polishing process can significantly improve the surface quality and the Laser-Induced Damage Threshold (LIDT) of fused silica optics. However, due to the thermal history of the laser polishing process, the increment of the fictive temperature inside the modification layer would cause densification and residual stress, which critically affect the surface accuracy and the service life of fused silica optics. In this work, a 3D multi-physical coupling model including temperature, fluid flow and fictive temperature was established. Based on the fictive temperature distribution of the fused silica polished by CO₂ lasers, the mechanism of laser annealing on the modified layer was revealed. The annealing results of fused silica were defined as three states including incomplete annealing, perfect annealing and over annealing. Based on the simulation results, the fictive temperature inside the modified layer was completely reduced with no increment of modified layer depth under the perfect annealing state. Additionally, the residual stress and the fictive temperature after the laser annealing were characterized by the Raman spectrum. The fictive temperature was reduced by 16.8 % and the residual stress was effectively reduced. This work can provide theoretical and experimental guidance for the control of surface modification and residual stress of fused silica optics polished by CO₂ lasers.

Superhydrophobic surfaces are the most commonly used functional surfaces. Femtosecond laser processing technology has emerged as a useful instrument for producing micro- and nanoscale structures on superhydrophobic surfaces because of its extremely high processing accuracy and highly controlled features. The substrate materials used in this work are AH36 steel plates. By varying the laser processing parameters, the microstructure shapes of steel plate surface are produced. After processing, the samples were allowed to rest in air for 30 days before characterizing their hydrophobicity. The optical and scanning electron microscopy were used to analyze its morphology, and the contact angles were measured. The study demonstrated that the surface roughness, microstructure, and hydrophobicity of AH36 steel plate samples vary with laser parameters. As a result, the AH36 steel plate exhibits the creation of a superhydrophobic surface when the contact angle reaches 151.2°, with a scanning interval of 100 μm between two lines, scanning speed of 10 mm/s, and an energy density of 3.67 J/cm². This is an important result for promoting femtosecond laser in preparing hydrophobic structures on marine metal surface.

Owing to the exceptional physical and mechanical properties, alumina ceramics are widely applied in industrial manufacturing, where laser technology is pivotal for achieving high-precision cutting. This study investigates the laser ablation of alumina ceramics using fiber lasers, complemented by simulation to optimize processing parameters. The laser has a maximum average power of 150 W with a fiber core diameter of 25 μm. By varying laser power, frequency, and scanning speed, at an average power of 90W and a frequency of 400 Hz, the ablation efficiency and surface quality are enhanced while minimizing heat-affected zone of 50 μm. Simulation results accurately predict temperature distribution and material removal, aligning well with experimental data, thus advancing the precise machining of hard ceramics.

Laser Powder Bed Fusion (LPBF) technologies are now being widely adopted across the global industrial landscape. New LPBF systems with multiple lasers and an expanded work area are entering the market, thereby enhancing both the production speed and the maximum size of 3D parts that can be produced. The aim was to investigate the aspects of upscaling LPBF processing parameters on the characteristic formation of stable single tracks, which are the primary building blocks for this technology. A number of LPBF systems were employed in this study, each operating independently and utilizing distinct parameter regimes, to produce the single tracks on a solid substrate deposited with a thin powder layer. The results demonstrated that the geometrical characteristics of single tracks are predominantly influenced by laser power and scanning speed when scanning a thin powder layer. The results also indicate that higher laser power and spot size can be used to produce stable tracks with increasing linear energy input. However, there are a number of nuances to be considered in increasing the performance.

High-performance piezoelectric sensors play a crucial role in transduction and monitoring applications, and the piezoelectric performance of piezoelectric materials is affected by strain. Therefore, processing various microstructures on piezoelectric thin films by using a mask template method to cause stress concentration when they are subjected to force is a common method to improve their piezoelectric performance. However, the mask template method has disadvantages of low efficiency, low precision, complex template preparation, and high cost. Here, we demonstrate a simple and effective femtosecond laser direct writing method, and prepared adjustable size micro drum packaging, crater, groove, and other structures on the surface of Lead Zirconate Titanate (PZT) piezoelectric thin films, and detailed analysis of different structured thin film piezoelectric signal changes. The results show that compared with the unprocessed PZT thin film, there is no significant enhancement in the output voltage of the samples with the surface as groove and crater structures, and the output voltage of the sample with a bulge structure of 450 nm height is increased by about 30%. Theoretical analysis shows that this is due to a stress concentration phenomenon at the top of the bulge. In addition, we applied hydrophobic treatment to the film and the 450nm sample and tested the response of samples with different surface structures to water droplets of different volumes and falling frequencies. The research results show that both the film and the structured samples can well identify each droplet. Compared to the unprocessed PZT thin film, the 450 nm sample has stronger piezoelectric feedback to water droplets, and the feedback effect increases with the increase in droplet volume, and it can clearly identify the impact signal of a single droplet under higher frequency impact. This technology has potential application value in the field of rainfall monitoring.

Multispot laser peening was conducted on austenitic stainless steel (SUS316L) using a Nd:YAG laser as the laser source to generate a high-intensity pulse ranging from 0.5–4 GW/cm². A liquid-crystal-on-silicon spatial light modulator (LCOS-SLM) was used for laser division to create multiple spots on the target. Multiple laser pulses irradiating a metal surface simultaneously induce multiple shock waves. This approach leads to a thicker plastically deformed layer compared with laser-induced shock waves produced by a single pulse. The laser peening performance was evaluated by measuring the magnitude of the compressive residual stress, hardness difference, and magnitude of the laser-induced shock wave. The laser intensity and laser irradiation patterns were adapted as the laser peening parameters throughout the experiment.

Laser peening is a surface-enhancement technique that uses a high intensity of several gigawatts for the cold working of metal samples. The most notable feature of this technique is its effective treatment of the depths of metal samples. A transparent coating, known as a plasma confinement layer, is typically used in laser peening to suppress the expansion of the plasma away from the metal surface. The ability to confine the plasma significantly affects the effectiveness of laser peening. Water is commonly used as a plasma confinement layer due to its transparency, cost-effectiveness, ease of handling, and its ability to conform to the shape of metal as a liquid. However, in high-vacuum environments, only solid-state media can be used as plasma confinement layers. In this study, laser peening was performed in a high-vacuum environment using silicone rubber (polydimethylsiloxane) as the plasma confinement layer. It is softer and conforms to the shape of metal in a vacuum environment. Through experiments, the appropriate process window for laser irradiation was explored by varying the intensity and number of laser shots.

This investigation aims to elucidate the morphology and mechanism of laser-induced damage on fused silica surfaces, and the temporal evolution of electron density within the irradiated areas under a 35 fs mJ-level laser system. Several ablation features, including budge and ablated structures, splash, microdroplets, and debris, were observed and subjected to detailed analysis. By distinguishing budge and ablated structures, the ablation occurred when the free-electron density exceeded the critical electron density. Additionally, to achieve a satisfactory cutting situation, a rational scan speed for the mJ-level laser system was considered within the range of 1-5 mm·s^-1, and an ablation threshold was identified around 6 J·cm^-2. The mathematical model proposed in this study provides insights into the launch conditions of ablation on fused silica and analyzes the ablation of fused silica in high energy pulse. The mathematical model could also be used in optimizing technological parameters for processing.

Maskless femtosecond laser two-photon polymerization micromachining technology is capable of inducing triggered two-photon polymerization (2PP) to fabricate three-dimensional additive templates with structural linewidths capable of exceeding the optical diffraction limit. With the help of polymer templates, disordered structural unit nanoparticles are spontaneously assembled into ordered structures through element-to-element interactions driven by free-energy minimization. In this paper, quadrilateral and hexagonal patterned tiling polymer templates were successfully fabricated by designing and tuning the processing parameters. The nanoparticle of appropriate size arrangement corresponding to the template pattern is expected to be successful in obtaining it by directed self-assembly. At the same time, the near-field and far-field optical properties of the template area under different assembly schemes were simulated and analyzed by CST Studio Suite based on finite element analysis.

Spherical and irregular powders are two prevalent materials used in 3D ceramic printing. Irregular powders are characterized by varying sizes and generally poorer surface quality. In contrast, spherical powders offer better surface morphology but are prone to splattering during the printing process, which negatively impacts the precision of sample formation. Mixing irregular powders with spherical powders can enhance the overall formation quality of samples. Consequently, this paper introduces a mixed powder technique tailored for 3D ceramic printing. Specifically, through experiments using alumina powders of different morphologies in single-track and sample formation tests, this study confirms that both types of powders are suitable for the mixed powder process and that the mixed powder formation results in superior quality.

Laser cladding is often used for surface modification or remanufacturing of H13 hot working dies. Thermo-mechanical coupled numerical simulation of laser cladding 316L+H13/20%WC composite coatings on H13 steel surface has been carried out. Distribution of the temperature field and cooling rate of the melt pool, residual stress varied with the process parameters as well as strain along different directions has been obtained. Results showed that the maximum temperature gradient was located in the bottom of the 316L cladding layer and reached 10⁶ °C/m, while the cooling rate of the melt pool has reached 10³ °C/s. The plastic strain in the scanning direction was the largest, and the cladding layer was more prone to crack in the direction perpendicular to the scanning speed. Laser cladding experiments were conducted on the surface of H13 steel using parameters obtained by numerical simulation. Dense and defects free composite cladding layers has been obtained.

H13+H13/20%WC composite coating was prepared on the surface of H13 steel using laser cladding technology. Bonding performance between the coating and substrate, microstructure and composition evolution, hardness and wear resistance of the coating has been studied and analyzed. Research results indicated that the composite coating was metallurgically bonded with the substrate. The fine and dense microstructure was mainly composed of dendrites, intergranular Fe and Cr rich eutectic and carbides. Slight elements diffusion occurred at the interface between the substrate and the composite cladding layer. The surface of the H13/20%WC coating was mainly composed of α-Fe Fe-Cr compounds, and carbides, which resulted in a high hardness of 626.9HV in average. The wear resistance of the cladding layer was better than the bare substrate. The wear patterns were abrasive wear and oxidation wear. The research results were supposed to provide a reference for the modification of H13 steel mold and die surface.

The precise control of fluid transport is of significant importance in intelligent systems and microfluidics. However, current research typically involve either the directed transport of a single type of fluid or requires complex preparation processes. This work utilities the complementary superwetting surface of polyimide/Poly tetra fluoroethylene to achieve the spontaneous directional transport of water droplets and underwater bubbles through single femtosecond laser processing. This technology enables the preparation of flexible and diverse structures for complex fluid control. This work presents a novel approach to the control of fluid transport, with a multitude of applications in aerospace, medical and intelligent transportation.

In high-precision mechanical engineering, the need for small-sized products has been steadily increasing over the past decades and, thus, small-sized cutting tools are used for their production. Laser processing has become one of the most convenient and effective technologies. A new approach to manufacturing micro-cutting three-prong drills is based on the laser ablation technology, which allows to remove material from the workpiece surface regardless of its and has a small zone affected by heating. Laser ablation does not cause workpiece deformation or wear, which ensures high precision of shaping. The work presents a special technology of continuous impact on a section of the front and rear surfaces when forming a sharpening in the form of a set of B-splines. The splines are arranged in such a way that, as a result of removing material from the end of the drill, the cutting wedge forms an angle close to constant with a minimum duration of laser exposure, ensuring in this way the edge. Thus, the algorithm allows forming the working part of a three-tooth drill depending on the diameter, offset of the cutting edge, angle of inclination of the helical flute, front and rake angles of the blade. The new technology allows, for the first time, to form a point and back surface with constant angles on microcutting three-tooth drills with a minimum duration of laser exposure, in particular, when restoring restoration or cyst pointing of the cutting part of the drill. Unlike the known model of the tool is not discredited by the edge sections and the formation of the standard form of the flank surface but creates geometry along the freely formed cutting edge. The goal of minimizing the number of necessary physical tests while expanding the capabilities of the modeling results is achieved. The mathematical model of the process of forming the main rear surface of the drill will ensure the constancy of the normal clearance angle along the cutting edge of a freely shape.

With the progress of national defense science and technology, the thermal effect of components in aerospace technology has greatly hindered the operation of devices. In order to solve the problem of high interface thermal resistance between materials, a new method of femtosecond processing combined with thermal interface materials was proposed to reduce interface thermal resistance. By using the high-efficiency positioning response method and the non-material selectivity and low thermal effect of femtosecond laser, the micro-structure with low roughness is precisely machined on the surface of copper based on the laser five-axis machining system, and the internal structural roughness, depth and width of the micro-structure are characterized. Then the surface is covered with thermal interface materials to achieve the purpose of reducing the interface thermal resistance between materials. At the same time, the effect of microstructure on interface thermal resistance is simulated with simulation software. A uniform array structure was obtained on the surface of copper substrate with a roughness less than 0.3μm, and the measured linear roughness of the microstructure was 0.23μm, which was consistent with the surface roughness of copper. Firstly, in order to verify that the surface heat conduction efficiency of the material with a microstructure surface is higher, the heat transfer time of the composite substrate with a microstructure is 0.0073s after simulation, which is faster than that of the composite substrate without a microstructure. Then, the thermal conductivity of the composite substrate with low roughness is 355 W·m^-1 ·K^-1, while that of the composite substrate with high roughness is 325 W·m^-1 ·K^-1 . Through the ultrafine processing, the heat transfer efficiency of the prepared composite substrate is increased by 17%, and the heat transfer efficiency is higher with lower roughness, which provides a research basis for high energy consumption devices.

Operation in aggressive environmental conditions and the interaction of friction pairs impose increased demands on modern parts used in aircraft engine manufacturing and electrical power engineering. Often, working in such conditions leads to the premature failure of parts and equipment, as well as energy loss due to friction and wear processes. Advanced technologies for surface modification and coating deposition by various methods can enhance the performance characteristics of such parts. The technology of laser cladding for wear-resistant coatings, combined with preliminary surface modification, allows the creation of a protective layer on the surface and strengthens it. This paper provides an overview of modern methods for surface modification and deposition of protective coatings using various physical techniques, highlighting their advantages and disadvantages. The most promising method is the laser cladding of wear-resistant coatings with preliminary surface modification. An algorithm for the laser cladding process has been developed for this technology. The paper proposes the use of a new wear-resistant coating made from powder materials based on chromium and molybdenum carbides. The influence of the mixture composition on the properties of the synthesized coating has been determined. Adhesion strength and coating thickness have been evaluated.