This PDF file contains the front matter associated with SPIE Proceedings Volume 12312, including the Title Page, Copyright information, Table of Contents, and Conference Committee Page.

Electronic ceramic substrates have been widely used in various markets, which include the automotive industry, electronics, aviation, and sensor due to their good thermal conductivity and thermal stability. The holes in ceramic substrates are very important for their application, many techniques are studied to drill holes of different sizes. This research presents the results of UV ultrashort pulse laser drilling of ceramic substrates with different laser parameters. Normally, the ultrashort pulse laser can be used to process materials due to its less heat-affected zone, so the heat-affected zone of the hole is also observed around the laser-drilled holes.

This study optimizes the distribution function of laser light intensity inside the material, based on the interaction between a femtosecond laser of 800 nm wavelength and quartz crystal, comprehensively considering the changes in absorption coefficient and reflectivity caused by material anisotropy. Throughout the simulation of multi-pulse machining, the influence of processing parameters such as the number of pulses and pulse energy on the hole depth, hole taper, and cross-sectional topography was investigated. Finally, the three-dimensional topography processed at various scanning rates was researched, and the correlation between the spot overlap ratio and the bottom surface topography was examined.

The point defects exist in the SiO₂ thin films can cause high absorption, which is known to be responsible for laser induced damage of the films under high power nanosecond (ns) laser irradiation. Laser conditioning of the film is beneficial to eliminate the film defects and improve the ability of films to resist ultraviolet (UV) ns laser damage. In this article, femtosecond laser is proposed to modify the SiO₂ films in the hope of improving the damage resistance of films to UV lasers. After femtosecond laser conditioning, the film properties of ALD SiO₂ films were characterized in terms of surface morphology, UV laser damage induced threshold (LIDT) and optical properties. The results show that significant improvement in laser damage resistance is achieved after femtosecond laser conditioning, the LIDT of the 300 nm SiO₂ thin film increased from 1.55 J/cm² to 16.69 J/cm², and the LIDT of the 600 nm SiO₂ thin film increased from 2.01 J/cm² to 9.46 J/cm².

By utilizing customized intra-cavity optical elements including graded-phase mirrors, variable reflectivity mirrors, aspherical mirrors, diffractive optical elements and spatial light modulators, the mode discrimination of the cavity is enhanced and a pre-determined transverse mode, usually flat-top beams such as super-Gaussian beams or flattened- Gaussian beams, can be generated in the cavity. The design of such laser cavities oscillating in a predetermined transverse mode is commonly based on the concept of phase conjugation, whereby the desired phase profile of optical element is obtained by reversely propagating the predetermined transverse mode and creating a conjugate field to propagate back. However, this procedure is only accurate under the assumption that the mirror size is infinite and the propagation process is in a lossless manner. Moreover, the parameters of the pre-determined mode, such as beam size and amplitude distribution, must be carefully chosen or else non-negligible errors would occur due to finite-size apertures and associated truncation. Here, we report on a simple and effective approach for intra-cavity mode control based on optimizing the single-mode power factor, which represents the total power extracted by a single mode from the active medium. By optimizing the single-mode power factor of the desired mode, the cavity can be designed to operate in mono-mode, increasing the mode purity significantly. Our method is verified on a digital laser with a spatial light modulator as the rear mirror and the loaded phase profile is acquired by a simulated annealing algorithm. As a result, when the single-mode power factor of TEM00 mode is optimized, the resonator operates in a single fundamental mode. When the single-mode power factor of the vortex mode with a topological charge of 1 is optimized, the output mode purity is close to 100%.

In the framework of laser technology, blue-light pumped Pr-doped materials are ideal candidates for blue, green, orange, red and deep red laser emission due to abundant transitions in visible band of praseodymium ions (Pr3+). In this communication, for the first time to our knowledge, we report on direct generations of an orthogonally polarized continuous-wave (CW) laser with dual-wavelength at 639nm and 721nm by means of a diode-pumped Pr:YLF laser platform. Without any extra thermal control on the crystal, the adjustment of pumping power or the cavity length enables the shift of the bi-chromatic output from one wavelength to the other. The stability of the output dual-wavelength laser is significantly improved when the resonator is appropriately misaligned. This work provides a simple way for direct generation and convenient control of an orthogonally polarized dual-wavelength laser at red and deep red with compact structure, high conversion efficiency and high beam quality.

An adjustable working distance Bessel lens for high-precision femtosecond laser cutting is designed. The system is composed of an axicon and a bi-telecentric optical system. By adjusting the distance between the axicon and the bitelecentric optical system, a zero-order Bessel beam with continuously adjustable working distance within a certain range can be obtained. Compared with the traditional Gaussian beam, when the central core diameter of the Bessel beam and the beam width of the Gaussian beam are the same, the non-diffracting propagation distance of the Bessel beam is much larger than the Rayleigh length of the Gaussian beam. The focusing accuracy can be effectively reduced, and a larger processing dynamic range can be achieved in laser processing. Ultra-short pulse Bessel beam generated by this method in laser cutting has longer laser focal field length and smaller light field axial intensity distribution gradient, which can provide a high-quality light source for laser cutting. In this paper, the spatial intensity distribution of Bessel beam is simulated by MatLab software. The simulation results show that, by the incidence of a femtosecond pulsed Gaussian beam whose central wavelength is 1030 nm with a certain diameter on the Bessel lens, a Bessel beam with a central core diameter of 6.7 μm, a non-diffracting propagation distance of 3.40 mm, and a continuously variable working distance from 18 mm to 21 mm can be obtained.

Aiming at tightly focusing vector polarized partially coherent vortex laser beams, this paper introduced a new kind of vortex beams, named radially polarized multi-Gaussian Schell-model (MGSM) power-exponent-phase vortex beam (PEPVB). Based on the vectorial diffraction theory, this work theoretically and numerically investigated the tight focusing properties of radially polarized MGSMPEPVB passing through a high numerical aperture objective lens. Thus, we analyzed the impact of topological charge, power exponent, beam index and coherence length on the intensity of focal zone. We discovered that by increasing beam index, the intensity distribution of focal plane gradually changed from Gaussian to flat-top. Especially, when the power exponent was a non-negative fraction close to 1, regardless of whether the topological charge was an integer or not, the circular symmetry of the focused spot at focal plane would be destroyed, showing a non-uniform and asymmetric central dark core optical intensity distribution. Besides, the value of the fractional part of the topological charge would make the hollow structure of the central dark core fully open due to the introduction of power-exponent phase, which is an improvement over the tight focusing properties of radially polarized MGSM vortex beams. This work has clearly demonstrated that by changing the values of topological charge, power exponent, beam index and coherence length, the special focal spot structures with different intensity distributions including flat-top beam and irregular hollow beam can be obtained, which have many potential applications in laser machining and particle capturing such as manipulation of certain irregular microparticles.

In the framework of laser precision machining, spherical aberrations of the laser beam increase gradually along the machining depth, which is widely observed due to the refractive index difference between the material of the working pieces and the surrounding medium. In this paper, we report on a simple and effective approach for spherical-aberration-free 3D beam forming inside the materials. This new technique is based on the modified Ewald cap which is related to the numerical aperture of the objective lens, the machining depth, and the refractive index of the material. This method is verified on a laser machining platform, where the phase loaded on the spatial light modulator is acquired by the modified 3D Gerchberg-Saxton algorithm. In the experiment, we have realized line and helical structures with SA compensation, which demonstrate that customized arbitrary intensity distribution inside the material can be realized.

Laser polishing (LP) is a promising technology for improving surface quality. An important obstacle to the practical application of LP technology is the relatively narrow process window. Lots of previous studies have demonstrated that LP is often applied below the ablation threshold, causing a large gap in the process window for different materials, which depends on many parameters such as material absorption, phase transition temperature, dynamic viscosity and so on. Through comparative studies of several materials with different properties, including glass and alloy materials, we believe that the process window of LP can be appropriately sought from the perspective of molten pool dynamics. This investigation focuses on the evolution of molten pool flowing over time during the laser polishing process based on well-designed multi-physics numerical models and experiments.

A portable and compact laser peening (LP) device was developed to apply LP to infrastructure maintenance. LP treatment of metal materials was performed by this device, and residual stress measurements and fatigue tests were conducted. Even at a pulse energy of less than 10 mJ, compressive residual stress was imparted in a near surface layer of high strength steel (HT780) and aluminum alloy (A7075) to a depth of 0.2 mm and 0.5 mm respectively. The fatigue properties of the materials were also improved.

Laser-arc hybrid additive manufacturing with beam oscillation (O-LHAM) was introduced to fabricate AZ31 magnesium alloy thin-wall components. The effect of the beam oscillating frequency on the morphological characteristics, internal porosity, microstructure, and mechanical properties was investigated. It was found that increasing oscillating frequency is effective to suppress the imperfections of lack of fusion, height differences, and wavy hump, as well as the number and size of internal porosity. The beam oscillation was beneficial to fragmentizing the average grain size and promoting the precipitation of Al8Mn5 and Mg17Al12 phases by generating stirring laminar flow in the molten pool, and it can disrupt the grain structure and provide more nucleation sites. Compared to the case without beam oscillation, the average grain size range decreased from 22-32 μm to 18-20 μm when the frequency increases to 300 Hz, while the precipitation percentage increased from 1.42-1.61% to 2.55-3.32%. For the components without porosity detected by the X-ray nondestructive test, the ultimate tensile strength and the elongation were 205 MPa and 20.7%, respectively, which are higher than those of AZ31 cast magnesium alloy. The tensile fracture has characterized the dimples with a small part of ductile tearing ridges, showing good ductility. The results indicated that O-LHAM would be effective to solve the tough problems in deposition quality and efficiency of additively manufactured Mg alloys.

Thin-wall specimens of near-β titanium alloy Ti-55531 were manufactured by laser melting deposition (LMD), followed by the post-processing using the electroshock treatment (EST). The results show that the microstructure of the as-manufactured alloy is mainly composed of fine columnar grains and equiaxed grains, showing a unique structure of alternating short columnar grains-equiaxed grains-short columnar grains. EST is shown to change the microstructure and grain size of the specimens. Besides phase variation, EST can also reduce the orientation concentration and weaken the texture. Meanwhile, the lattice constant and the microscopic strain were increased after EST. From the tensile test results, the yield strength and tensile strength increased, and the elongation decreased after EST. The results showed that EST is an effective approach for optimizing the microstructure and improving the mechanical properties of LMD near-β titanium alloy.

To address the problem of directional selective removal of multilayer composite heterogeneous materials, an integrated processing and detection system based on galvanometer scanning processing and coaxial spectral monitoring was proposed. Combining laser processing and spectral detection technology, aiming at the selective removal of FR-4 multilayer composite copper clad laminate (CCL), the influence rules between material interface and characteristic spectrum, characteristic spectrum intensity ratio and residual rate, spectral signal-to-noise ratio and energy density were systematically explored. The spectral criterion of laser selective processing was established based on the residual rate index, which realizes the patterned precision processing copper layer, and simultaneously realizes the in-situ online analysis and two-dimensional to three-dimensional mapping characterization of the composition and content of the processed materials, the coordinated regulation mechanism of real-time online monitoring and element closed-loop feedback was established.

The Ti-25Ta alloy was fabricated by LPBF using mechanically mixed powders. It was found that the relative density, phase composition, and surface roughness were quite different with different LPBF preparation parameters. The Ti-25Ta alloy samples have a high relative density (>99.9%) with better surface roughness at faster scan speed, and thereby lower laser energy density. However, the amount of unmelted Ta particles increased at a lower energy density. In addition, the energy input of the LPBF process had a great influence on the phase formation of Ti-25Ta due to element composition differences. The α' phase was mainly dominated in Ti-25Ta samples under lower laser energy density while changing to the α" phase gradually with the increase of laser energy density. The SEM image and XRD analysis were applied to show the characteristics. The micro-hardness of Ti-25Ta samples under various LPBF parameters was tested for proving the difference in the phase composition.

The random occurrence of component burn damage is a major challenge for laser soldering, but there is no effective solution so far. In order to solve the problem, two processes of constant power mode and constant temperature mode were used for laser soldering. The corresponding change curves of power and temperature were collected. In condition, the dynamic change of laser reflectivity during the whole welding process was tested. The process can be divided into five stages. It is found that the increase of reflectivity (64%) and peak power(＞70W) in the final stage is the main cause of the burnout. Finally, the cooperation control methods of power mode and temperature mode were adopted to restrain the burnout. The results provide an effective way to dynamically adjust the wettability of laser soldering and improve the reliability of solder joints.

Shaped plates with a special shape of texture on the front surface are widely used in the production of products of complex shapes from heat-resistant materials. An important stage of technological preparation for the formation of a system for the automated production of plates using laser ablation is the assignment of recommendations for the shape of the front surface. The technical result is ensured by the rational shape of the front surface of the replaceable multifaceted plate, which meets the requirements of manufacturability and increased performance when using it. Placement on the front surface of a microrelief, which is formed by a set of holes in the form of a group of micro-holes with a radius of 20-40 μm, a depth of 20-40 μm, which ensures the placement and retention of a suspension based on molybdenum disulfide during drilling, and the coordinates of the centers of the holes are determined by new analytical dependencies. This technological solution will significantly increase the speed of writing programs to control machines for laser ablation.

Three-tooth drills have been used relatively recently. However, even now their application gives an important technical result. Increase processing performance up to 2-3 times. In this regard, the article proposes a new approach to the automated design of teeth of drills with a special shape of the front surface machining by laser ablation. The system is based on fast interpolation splines, allowing continuous control of the laser ablation machine and thus greatly improving the processing efficiency.

In order to improve the performance of robotic laser medical operations, various methods are used to control the distance from the laser head or objective optics to the surface to be treated, and algorithms for correcting robot movements are built on their basis, which makes it possible to achieve high-precision processing. This study evaluated data of the reflected laser emission feedback sensor on uneven surfaces for use in robotic laser processing automation. As an uneven surface, a produced on a 3D printer detail with different profiles was used, which had been measured on conturograph before the experiments. Then, data were obtained from the feedback sensor of laser when passing along these profiles using a CMM and a robot. In the course of comparing the obtained results, it was found that the values of standard deviations from the real (highly-precise measured) surface do not exceed 600 μm. This value can be reduced by exclusion the identified problems that affect the data, the solution or leveling of which will be given in the further works of the authors. In general, it can be concluded that this method can be applied in robotic laser processing.

To study the influence mechanism of process parameters on the temperature field and the repair performance in Inconel718 nickel-base-superalloy laser additive repairing process, numerical research was carried out. A three-dimensional finite element model was established, and the finite element software ANSYS was used to simulate the temperature field. The influence of the laser power, the scanning speed on the laser additive repairing temperature distribution and the penetration depth and width of the repair zone were analyzed. The numerical result and the experimental measurement result was compared, and the result showed that as the laser power is in the range of 229~668W and the cladding speed is in the range of 6~16mm/s, the metallurgical bond was formed between the repair layer and the matrix material. The maximum temperature at the interface between the repair layer and the substrate is proportional to the laser power and inversely proportional to the scanning speed. The theoretically calculated penetration depth and penetration width of the repair zone are basically consistent with the experimental measurement results. The theoretical simulation can provide theoretical guidance for the parameter optimization in the laser additive repairing process.

The most problematic aberrations in 3D DLW are related to mismatched refractive index at surface of the sample. Adaptive optical element placed in a plane conjugate to the objective pupil can be used to apply the correcting phase, providing a promising aberration correction. Currently, the calculation of correcting phase are all based on the assumption of ideal objective lens. In practice, secondary aberration is introduced due to the use of actual objective lens, and has not been researched. In this paper, we compare ideal objective lens and actual objective lens in theory, and simulate the energy distribution inside of sample. The effect of secondary aberration on DLW performance is reported. We make compensation for the secondary aberration, and contract the energy distribution of correcting secondary aberration and without correcting secondary aberration. Correction of secondary aberration caused by actual objective lens provides a more accurate correcting method of 3D DLW.

Narrow gap oscillating laser welding of 6061/2024 dissimilar aluminum alloys with hot wire was carried out. The effects of processing parameters on weld formation were investigated. The results show that increasing the laser power (P) and the wire current (I) can suppress the lack-of-fusion, while increasing the oscillation frequency (f) can effectively eliminate the weld porosity. Furthermore, 20mm-thick joint was fabricated with optimized process parameters and the microstructure and mechanical properties were analyzed. The weld center exhibits an equiaxed microstructure composed of α-Al matrix, eutectic on the grain boundary, and point-like precipitation phase in the grain, while the interlayer weld exhibits a gradient microstructure composed of columnar grains, coarse grains, and equiaxed grains. The joint shows good consistency in hardness and tensile properties. The highest tensile strength and elongation are 215 MPa and 9%, which are 69% and 66% of the 6061 aluminum alloy, respectively.

In this paper, the IC10 alloy joints are prepared by laser welding. The effect of process parameters on thermal crack is discussed, and the formation mechanism of welding thermal crack in different types during laser welding of IC10 alloy are analyzed by micro means. The microstructure, element distribution and phase composition of the thermal cracks are studied. When the laser scanning direction is perpendicular to the grain growth direction of the substrate, the crack sensitivity is greater. With the increase of laser power and the decrease of shielding gas flowing, the crack sensitivity is also greater. A faster welding speed could cause thermal stress and increase crack sensitivity. The choice in an appropriate laser scanning speed range could effectively control the tendency of crack formation. According to the analysis of the formation mechanism of different cracks, the results of SEM and EDS showed that IC10 alloy was susceptible to crystallization cracking due to the high content of low melting point eutectic between grains and grain boundaries, and the tendency to produce liquefaction crack becomes greater when coarse carbides precipitate, both types of cracks belong to the thermal cracks caused by liquid films. In IC10 alloy, ductility dip cracking (DDC) is thermal crack caused by the sharp drop of intergranular plasticity, which is closely related to the state of grain boundaries and interstitial phase precipitated from grain boundary. The crack susceptibility of DDC cracks is easier to control than the above mentioned two type thermal cracks.

Particulate reinforced composites are expected to solve the problem of grain growth and strength reduction caused by multiple thermal cycles during additive manufacturing. In this work, TiB₂/2319Al composite was fabricated by oscillating laser-arc hybrid additive manufacturing (O-LAHAM). The microstructure, mechanical properties and fracture of tensile samples were studied. The results show that TiB₂/2319Al composites were composed of fine equiaxed grains due to the stirring effect of laser beam and the particle strengthening effect of TiB₂. Although ultimate tensile strength (UTS) of the TiB₂/2319Al composite did not increase significantly, it had a higher yield strength (YS), especially stimulated by T6 heat treatment. Compared with 2319 aluminum alloy, YS of the as-deposited and heat-treated composites was 137 MPa and 355 MPa, respectively, which increased by 19% and 10%. However, the elongation decreased significantly, which is caused by the presence of micro pores that promoted crack propagation.

Microcutters are one of the important elements of the technological system for high-speed machining. A new approach to the automated design of micromills using spline interpolation is proposed. Existing methods do not allow to form a continuous contour of the front helical surface for processing in one pass. In this regard, the trajectory of the laser head was calculated and analytical approximation of the profile with given geometric parameters of the cutter was derived that allows applying laser ablation technology for the manufacture of helical surfaces of micromills.