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Ag mesh transparent conductive films (TCFs) were prepared on the commercial FTO/Glass substrate by ultrafast laser direct writing, trying to improve its overall photoelectric performances. The effects of laser scanning speed, laser fluence and Ag mesh height on photoelectric properties of the Ag mesh/FTO TCFs were systematically studied. The results indicated that a small scanning speed or a high laser fluence would cause excessive ablation of the FTO film and result in an increased Ag mesh line width, which was detrimental to the photoelectric properties of the resulting TCF. It was found that the optimal parameters for fabricating Ag mesh/FTO TCFs were a laser scanning speed of 2200 mm/s, a laser fluence of 0.050 J/cm2 and an Ag mesh height of 2500 nm. The as-fabricated TCF possessed the highest figure of merit of 13.03 × 10−2 Ω−1, which was significantly superior to that of the commercial FTO film. Finally, transparent heaters (THs) were prepared respectively based on the optimal Ag mesh/FTO TCF and the FTO/Glass substrate. The Ag mesh/FTO TH exhibited a more excellent heating performance than the FTO TH, further confirming that the overall photoelectric performance of the FTO/Glass substrate had been greatly improved.

In this study, we used a water-assisted femtosecond laser drilling method to drill holes in alumina ceramics. The morphology, diameter, taper angle, cross-section area, and sidewall characteristics of the holes were investigated, and the hole characteristics obtained in the presence of air were compared with those obtained under water assistance. Finally, the mechanism underlying the water-assisted femtosecond laser drilling of alumina ceramics was investigated. The results revealed that the drilling efficiency and quality of the holes improved significantly by using the water-assisted femtosecond laser drilling method, and the effect was considerably obvious at lower pulse repetition rates. At the pulse repetition rate of 25 kHz, the taper angle decreased by 64.19% to 4.20° and the hole cross-section area increased by 46% under water assistance. In addition, water assistance could reduce the amount of the residual debris and redeposition of ablated material on the hole sidewalls, and there were almost no residual debris and redeposition of ablated material on the hole sidewalls near the hole exit. Compared to the case when the drilling was carried out in the presence of air, the composition of the hole sidewalls changed slightly when the drilling was carried out in the presence of water. With an increase in the pulse repetition rate, more plasma was formed and the plasma shielding effect strengthened, which weakened the effect of water assistance. Therefore, in order to obtain high drilling efficiency and quality during the water-assisted femtosecond laser drilling of alumina ceramics, it is necessary to use a low pulse repetition rate. The results of this study will find potential application in the field of ceramic manufacturing.

Preparation and property optimization of silver (Ag)-embedded fluorine-doped tin oxide (FTO) films were achieved based on laser etching, sputtering Ag layers, furnace annealing, sputtering aluminum-doped zinc oxide (AZO) layers and laser annealing. Specifically, a nanosecond pulsed laser (λ = 532 nm) was used to etch grooves on FTO films before sputtering 5-nm-thick Ag layers, with an aim for enabling the Ag nanoparticles from the furnace-annealed Ag layers to be intensively embedded in the grooves under the thermal-induced dewetting effect. The optimal laser fluence for laser etching and temperature for furnace annealing were found to be 0.4 J/cm2 and 300 °C, respectively. The as-obtained Ag-embedded FTO film exhibited significantly improved optical and electrical properties, being attributed mainly to the decreased coverage area of the Ag nanoparticles on the FTO film surface and the furnace annealing effect. The subsequently sputtered 10-nm-thick AZO layer suppressed the internal light reflection from the Ag nanoparticles, and laser annealing further facilitated grain growth in the film. Therefore, the resulting film had the best comprehensive property with the highest figure of merit of 20.94 × 10–3 Ω–1, which was much higher than that of the original FTO film (7.65 × 10–3 Ω–1). This work may provide a new combined processing method for high-performance transparent conductive films.

A laser etching method was performed to achieve the dual purpose of fabricating grating structures and laser annealing on aluminum-doped zinc oxide (AZO) thin films, and thus improve the film photoelectric performances. Different line spacings and laser fluences were adopted to systematically explore the optimal laser etching condition. Too narrow line spacings or too high laser fluences led to light reflections at the grating external surface to cause more light dissipation, and too wide line spacings or too low laser fluences resulted in relatively small total grating lateral areas being detrimental to multiple internal light reflections. Moreover, too narrow line spacings brought about laser-caused lattice disorder and too high laser fluences produced laser-ablated spots or overburned traces. Therefore, using the medium line spacing and laser fluence, e.g. 40 μm and 0.6 J/cm2 in the present work, was more suitable for synchronously realizing grating structure fabrication and laser annealing. The corresponding AZO film exhibited the maximum figure of merit of 2.89 × 10−2 Ω−1, which was 1.6 times that of the untreated AZO film. This study is expected to expand performance improvement methods of TCO films and promote the application of laser-etched grating structures.

A novel laser percussion drilling technology assisted by an electric field with lateral air blowing is reported. The lateral air blowing is first proposed for assisting the E-field assisted laser drilling for improving hole-drilling performance, quality and efficiency by blowing away the vapor plume and cooling the target workpiece. A high-speed camera is first used for observing and characterizing the transient laser percussion drilling process with and without an electric field and/or a lateral airflow. It was indicated that the transverse electric force and/or the side air blowing expedited the spatial motion with dispersion and density reduction of the vapor-plasma plume for enhancing laser drilling efficiency via weakening the plume-induced shield effect. The recast layer was reduced by using the transverse E-field assistance with and without lateral air blowing, and the combined assistance of a transverse E-field together with a lateral airflow was more effective for reducing the recast layer. Interestingly, as a result of the dynamic air cover across the sample surface induced by the lateral air blowing, the laser-vapor interaction inside a drilling hole was greatly enhanced together with the laser-material interaction, leading to the rapidly-accumulated expansion and then the sudden explosion of the laser-induced plume inside a drilling hole. The enhanced vertical scouring and flowing effect resulting from the accelerated vertical plume-motion inside a drilling hole, which was caused by the accumulated pressure difference inside and outside of the hole due to the enhanced outside motion-dispersion effect (especially induced by the electric force) of the plasma-vapor plume, expedited the uniform molten material removal and distribution along the hole sidewall. Importantly, a transverse E-field with and without a side airflow effectively refined the grains of the heat affected zone (HAZ) near the fusion zone of a through hole via increasing the average grain size number. The micro hardness was improved after laser hole-drilling by loading a transverse E-field with and without a side airflow due to a grain refinement effect with and without an airflow cooling effect. It was demonstrated that the lateral air blowing used was more effective to increase laser drilling efficiency for drilling through the workpiece than the E-field used, and the hole-drilling efficiency was further increased if using the combined assistance of a transverse E-field and a side airflow. After the workpiece was drilled through, the hybrid plume signal was effectively suppressed primarily above the hole entrance by using a transverse E-field and/or a side airflow, especially in case of using the transverse E-field assistance.

The magnet-assisted laser hole-cutting in magnesium alloys was explored systematically with and without using water immersion, including femtosecond laser multilayer center-oriented hole-cutting and millisecond laser helical hole-cutting of both blind holes and through holes. The effect of the magnetic field and water immersion on laser hole-cutting quality, efficiency and performance is first reported for magnesium alloys with mechanism analysis and comparable discussion. It was shown that the magnetic assistance and/or the water medium improved the hole wall formation especially for underwater laser cutting of blind holes. Compared to laser hole-cutting in air, the underwater laser hole-cutting generated higher-quality holes in magnesium alloys. For laser hole-cutting in magnesium alloys in water, it is first reported that the magnetic field increases the entrance diameters for blind and through holes while decreases the blind-hole depth. The water cooling-insulating effect prevented the molten and vaporized material from re-solidifying and re-depositing onto the workpiece, and the laser-induced ignition and explosion were also prevented by water. The local laser-induced ignition and explosion were weakened when increasing the magnetic flux density. The local oxidation and carbonization reactions in air as a result of the laser-induced ignition and explosion were suppressed while the laser hole-cutting efficiency was enhanced by using the transverse magnetic assistance. The blind-hole recast layer was significantly reduced nearly without accumulated residues and carbonized or oxidized debris by using underwater laser hole-cutting, indicating that the water suppressed the laser-induced melting, vaporization, ignition and explosion and blocked the re-solidification and re-deposition surrounding the hole entrance and onto the hole wall for the recast layer formation. The average grain size number in the heat affected zone (HAZ) near the hole was improved for grain refinement by increasing the magnetic flux density, demonstrating the magnetic field-induced reduction for the local excessive thermal effect of the femtosecond laser-generated plasma on laser hole-cutting and recrystallization. The micro hardness was improved after laser hole-cutting with and without magnetic assistance mainly due to the HAZ recrystallization-induced grain refinement, and the hardness value roughly increased with the magnetic flux density.

An effective method based on laser etching and driving layer strategy was proposed to prepare patterned Ag nanoparticles (Ag NPs) on fluorine-doped tin oxide (FTO)/glass substrate and thus to enhance the photoelectric properties. This method successively included depositing an aluminum-doped zinc oxide (AZO) driving layer, laser etching, depositing an Ag layer, furnace annealing and laser removal. Different AZO and Ag layer thicknesses were adopted, and the surface morphology, crystal structure and photoelectric properties were investigated. An Ag NPs/FTO/glass sample without an AZO driving layer was prepared for comparison. It was found that furnace annealing of the Ag layer combined with the AZO driving layer, rather than that without the AZO driving layer, was more conducive to generating patterned Ag NPs. Using a 20-nm-thick AZO layer and a 150-nm-thick Ag layer led to the formation of uniformly distributed Ag NPs being aligned along the laser-etched grooves to form a pattern. The as-obtained sample had the best comprehensive photoelectric property with an average transmittance of 79.95%, a sheet resistance of 7.11 Ω/sq and the highest figure of merit of 1.50 × 10−2 Ω−1, confirming the feasibility of the proposed method and providing enlightenment for related researches of transparent conductive oxide-based films.

This study focused on utilizing a boron nitride (BN) layer to improve the photoelectric property stability of the flexible Al/Cu/ZnO multilayer thin film, which was prepared on a polyethylene terephthalate (PET) substrate by radio frequency (RF) magnetron sputtering. By analyzing surface morphology, chemical composition and photoelectric properties of flexible BN/Al/Cu/ZnO multilayer films with different BN layer thicknesses, the BN/Al/Cu/ZnO film with a 100-nm-thick BN layer (BN100/Al/Cu/ZnO), which had the best comprehensive photoelectric property with a figure of merit of 0.82 × 10−3 Ω−1, was chosen to further study the performance stability with storage temperature and time. It was found that as compared to the Al/Cu/ZnO film, the BN100/Al/Cu/ZnO film had more stable photoelectric properties at different storage temperatures and times, which was inferred to be attributed to the excellent heat and oxidation resistances of the BN layer that were conducive to avoiding surface damage and oxidation of the film. The results in this work demonstrate the key role of the BN layer in enhancing photoelectric property stability of the flexible Al/Cu/ZnO film, and may provide a feasible strategy for improving thermal and long-time stability of single-layer or multilayer flexible transparent conductive films.

Silver (Ag) films were deposited on glass substrates by radio frequency (RF) magnetron sputtering and then ablated by a 532 nm nanosecond pulsed laser. The effects of laser fluence and defocusing amount on the width and depth of laser-ablated grooves on 100- and 600-nm-thick Ag films were systematically investigated under single- and multi-scan ablation. The results suggested that the Ag films could be successfully removed from the substrate owing to laser-induced thermoelastic force or vaporization. It was confirmed that laser fluence and defocusing amount played very important roles in controlling the width and depth of the laser-ablated grooves. In the present work, grooves with widths ranging from 53 to 196 μm and depths ranging from 56 to 196 nm were obtained on 100-nm-thick Ag films by single-scan laser ablation, and laser ablation or removal with controllable depths was realized on 600-nm-thick Ag films by adopting single- or multi-scan (i.e., scanning numbers of 1–6). Furthermore, square spiral Ag patterns were successfully obtained by single- and multi-scan laser ablation and showed good electrical conductivity in a simple circuit. This work may have great potential applications in various fields that demand width and depth control of laser ablation/removal.

A systematic investigation was reported for observing and analyzing the process and performance of millisecond laser drilling with and without magnetic assistance and/or assist gas using a self-developed real-time monitoring system based on high-speed photography. The systematic and corresponding comparisons between the effects of longitudinal magnetic assistance and co-axial assist gas for millisecond laser drilling of both blind holes and through holes using high-speed photography were first reported. Using a direct comparable visual method based on comparable observations using high-speed camera, the effects of the co-axial assist gas and/or the longitudinal magnetic assistance on millisecond laser drilling process, drilling efficiency and drilling quality were systematically analyzed by correspondingly comparing and correlating the real-time observations with the measurements for laser drilled specimens, including the characterizations and analyses for material removal, plume expansion and dispersion, specimen spatters, hole geometry/morphology, hole sidewall recast layer and micro hardness performance. It was shown that the metal vapor and plasma induced by a millisecond laser mixed with each other as a hybrid plume. The co-axial assist gas flow was observed to be much more effective than the longitudinal magnetic field for promoting plume dispersion and enhancing drilling efficiency during the processes of blind-hole drilling and through-hole drilling. When using the assistance of a co-axial argon flow together with a longitudinal magnetic field, the blowing and cooling effects of assist gas were dominant during the laser drilling process, and the longitudinal magnetic assistance further vertically squeezed and horizontally stretched the plasma, greatly reducing the shielding effect of laser-induced plume for effectively increasing laser drilling efficiency and quality.

Effusion cooling holes are commonly drilled in nickel super-alloy aero-engine components using electro-discharge machining (EDM) or pulsed laser drilling. While drilling quality of EDM is high, its machining efficiency is normally relatively low, in addition to its high tooling cost. The drilling efficiency of a millisecond pulsed laser is much higher, while a recast layer often forms on the hole wall. In this paper, an ultrasonic-assisted laser trepanning technology is reported for trepanning blind and through holes in nickel super-alloy samples. The influence of ultrasonic vibrations on hole geometry, morphology, microstructure, recast layer thickness and mechanical performance was investigated through comparing holes trepanned with and without ultrasonic assistance. It was found that ultrasonic vibrations contributed to laser trepanning process mainly by means of grain refinement strengthening, hard phase precipitation and dispersion strengthening, and led to recast layer reduction and negative taper for the through hole trepanned. The percentage of the measured recast layer reduction induced by ultrasonic vibrations approximately ranged from 15.73% to 31.82%. Besides, a maximum percentage of around 19.43% was achieved for micro hardness improvement induced by ultrasonic vibrations. However, the width of laser trepanned heat affected zone (HAZ) was increased by around 36.00% due to ultrasonic vibration assistance. In addition, the HAZ grains near the recast layer was refined via increasing the trepanning speed, decreasing pulse width. Compared with the base metal, the impact toughness was increased by using ultrasonic-enhanced laser trepanning mainly due to grain refinement strengthening.

In this study, the fluorine-doped tin oxide (FTO) film on a glass substrate was etched by using a femtosecond pulsed laser with a wavelength of 1030 nm, a repetition rate of 1 MHz and a pulse duration of 262 fs. The effect of laser fluence and scanning speed on the quality of the groove etched on the FTO film surface was systematically studied, trying to improve the groove quality. The results indicated that in order to obtain high quality grooves for use on touch screens, a balance needed to be achieved between laser fluence and scanning speed. Excessive laser fluence caused cracks at the bottom of the groove with shoulder protrusions formed at the edge of the groove, and the scanning speed had a considerable influence on the groove width at the same time. After discussing and comparing the results of five groups of experiments, the best groove quality was determined at the scanning speed of 3000 mm/s and the laser fluence of 1.1 J/cm2. In this case, the edge of the groove was sharp without obvious cracks and shoulder-like protrusions, and the groove width was 7.92 μm, which made it possible to process small etched areas for touch screen. Furthermore, the optimal parameters were confirmed to be available for processing a pattern on the touch screen sensor layer with a line spacing of 5 μm.

Selective laser ablation (SLA) of silver (Ag) films, which were deposited on glass substrates by radio frequency (RF) magnetron sputtering, was performed by using a 532 nm nanosecond (ns) pulsed laser. Two kinds of simple and mask-free SLA strategies featured by two new scanning paths (i.e. frame-typed serial scanning, FTSS, and frame-line combined scanning, FLCS) were proposed to improve the edge quality and optical transmittances of the SLA patterns. The effects of laser scanning speed (v), hatch distance (HD) and scanning path on edge quality of the laser-ablated grooves and SLA patterns were systematically studied. The results indicated that compared with the conventional line-typed cyclic scanning (LTCS) path, which resulted in unsmooth edge with semicircle-shaped boundaries and some Ag residues, the proposed scanning paths of FTSS and FLCS produced clean and smooth edges without obvious heat-affected zone and Ag residues under the condition of using a v value of 15 mm/s and an HD value of 90 μm. As a result, the as-obtained SLA patterns exhibited relatively high optical transmittances. The simple methods of adopting the FTSS or FLCS path for improving the edge quality during SLA and thus the optical transmittance of SLA patterns may have great potential application in various fields.

The free-form milling of gears is a modern and flexible machining process that allows the manufacturing of external gears by using standard milling tools on universal machine center. In this paper, tooth profile error of cylindrical gears manufactured by flexible free-form milling is studied. Firstly, a mathematical model is established to investigate the tool path with respect to geometric characteristic of gear surface according to the theory of spatial form milling. Then, the influence of tooth profile error related to the processing parameters such as the type of tool, the feeding strategy of tool, and the basic parameters of gear is studied. Finally, for a validation, an experiment is performed using a universal multiaxis machine center with standard end mill. The experimental results show that free-form milling of gears is an effective and economical solution for manufacturing high-quality gears while a universal machine center is available. Furthermore, the study results support the engineers in the selection of optimal processing parameters by using free-form milling method.

The sound field characteristics in a trapezoidal enclosure surrounded by a flexible wall, which is adjacent to the tilted one, are investigated and compared with the case of a rectangular enclosure. The acoustic modes of trapezoidal enclosure are obtained by the coupling of the modes of rectangular enclosure that bounds it. The coupling system model is then built between trapezoidal enclosure modes and flexible wall modes using modal coupling theory. Based on the coupled system model, the effect of flexible wall modal density on the resonance frequencies and the decay times of coupled system are analyzed. Compared with the case of rectangular enclosure, the variation of the resonance frequency and the decay time of enclosure-controlled system mode is determined by its mode indices and tilted wall location when the panel modal density is changed. When the modal indices of trapezoidal sound field in the two directions unparallel to the tilted wall are equal to zero simultaneously, the effect of inclination angle on the resonance frequencies and decay times of these coupled system modes can be neglected. Otherwise, the coupling system modes behaviors are changed with the elevation angle. In addition, the coupling selection between the modes of trapezoidal enclosure and flexible wall is discussed in detail.

A novel magnetic-ultrasonic assisted laser drilling technology, which integrates and couples water-based ultrasonic vibrations with an external transverse magnetic field for assisting the process of percussion laser drilling, is reported to carry out laser drilling experiments for improving hole drilling performance. The influence of water temperature on drilling performance for water-based magnetic-ultrasonic assisted percussion laser drilling technology is first reported. The influential mechanisms and roles of magnetic assistance and/or water-based ultrasonic assistance on the process and performance of percussion laser drilling were analysed, including both blind hole and through hole drilling. The effects of water-based ultrasonic vibrations and/or magnetic assistance on laser drilling performance were systematically studied via corresponding comparisons. It was demonstrated that the couple magnetic-ultrasonic assistance effectively increased laser drilling performance, by increasing laser energy absorption efficiency inside a drilling hole, enhancing material removal, increasing drilled depth, reducing recast layer formation and hole taper, improving microstructure and micro hardness performance, and relieving residual stress. Besides, it was reported that the uniform mechanical vibrations induced by water-based ultrasonic assistance effectively relieved residual stress (65.8% reduction) for the drilled specimen. The addition of an external transverse magnetic field could further relieve residual stress with a reduction percentage of 89.1%, resulting from the coupled magnetic-ultrasonic assistance. In addition, the water medium with a relatively high temperature was helpful for decreasing residual stress on the drilled sample. The alteration of water temperature (from 33.9 °C to 64.2 °C) not only greatly changed the value but also changed the direction of the residual stress (hole entrance: changing from −163 MPa to +32 MPa; hole exit: changing from −284 MPa to +64 MPa). However, the water temperature showed small effects on microstructure, micro hardness, recast layer thickness, hole cross-section, hole circularity deviation, and hole taper angle.

ZnO/Al/Cu/ZnO multilayer films were deposited on flexible polyethylene terephthalate (PET) substrates by radio frequency (RF) magnetron sputtering. The overall thickness of the intermediate Al and Cu metal layers maintained at 8 nm. The four different Al/Cu thickness ratios were 7:1, 6:2, 5:3 and 4:4. Other four reference samples were prepared by using the same process, i.e. ZnO single-layer film, ZnO/Al8 (8-nm-thick Al layer, the same below)/ZnO, ZnO/Cu8/ZnO and ZnO/Cu2/Al6/ZnO multilayer films. The effects of Al/Cu thickness ratio and deposition sequence of Al and Cu layers were investigated. The results revealed that with the increase of Cu layer thickness, sheet resistance of the multilayer film decreased, while transmittance increased first and then decreased. The ZnO/Al6/Cu2/ZnO multilayer film with a sheet resistance of 108 Ω/sq and an average visible transmittance of 84.73% had the optimum overall photoelectric property, being confirmed by the highest figure of merit of 1.77 × 10–3 Ω–1. Furthermore, ZnO/Cu2/Al6/ZnO and ZnO/Al6/Cu2/ZnO multilayer films exhibited almost the same average visible transmittance and sheet resistance, implying that the deposition sequence of Al and Cu layers has little influence on photoelectric properties. It is demonstrated that ZnO/Al/Cu/ZnO multilayer flexible films have great potential in various fields.

Power skiving is a modern and productive method in the manufacturing of cylindrical internal gears and external gears. However, the high cost of skiving tool has prevented its widespread use. Accordingly, a novel skiving tool with multiple subblades on the rake face with respect to the traditional tool is proposed. First, the mathematical model of machine setup of gear skiving and the geometry model of multiblade tool working angles are derived. Then, the influence of working angles and maximum chip thickness related to the parameters of tool such as the crossed axes angle and the number of tool teeth are studied. Meanwhile, the relation between layout of tool subblade and chip deformation is analyzed. Finally, for a validation, the analogy experiment is conducted using a traditional skiving tool. The results show that the multiblade tool is under worse cutting condition compared with the traditional skiving tool, but some advisable suggestions, which could improve the bad cutting condition when using a multiblade skiving tool, have concluded in this study. The study results support the design engineers in the optimization of the multiblade skiving tool regarding more efficient and longer tool life.

A simple transparent cover-assisted laser annealing strategy, which used a coverglass or a PET sheet as the transparent cover, was proposed to improve photoelectric properties of fluorine-doped tin oxide (FTO) thin films. Pure laser annealing was also performed for comparison. Transparent cover-assisted laser annealing was found to be more effective for producing densely distributed particles, decreasing surface roughness and increasing grain size, thus enhancing transmittance and conductivity of the film. More importantly, compared with coverglass-assisted laser annealing, PET-assisted laser annealing enabled the film surface to be covered with more uniform and denser particles and exhibit a remarkable increase in grain size. Therefore the film had the highest total transmittance of 84.32%, the highest specular transmittance of 75.88%, a slightly decreased haze of 10.01% and the lowest sheet resistance of 7.36 Ω/sq. The simple PET-assisted laser annealing method may be a promising substitution for the conventional laser annealing treatment.

A millisecond-pulsed percussion laser drilling technique using water-based ultrasonic assistance is reported for drilling nickel super-alloy GH4037 sheets with 12-mm-thickness. Influence of ultrasonic vibration on drilling quality including hole taper angle, hole sidewall quality, recast layer microstructure, and hardness distribution of hole heat affected zone (HAZ) is analyzed through comparing holes drilled without ultrasonic assistance. Recast layer reduction, grain refinement, and HAZ hardness increase induced by ultrasonic assistance are also analyzed. It is shown that ultrasonic vibration improves percussion laser drilling quality by reducing hole taper angle, cleaning hole sidewall, decreasing hole defects, reducing recast layer thickness, refining grains, decreasing hole sidewall surface roughness, and increasing micro hardness.

An ultrasonic-vibration-assisted laser annealing method was developed to enhance the performance of fluorine-doped tin oxide (FTO) thin films. The influences of ultrasonic vibration, laser scan line overlapping rate (LOR) and laser spot overlapping rate (SOR) on surface morphology, FTO layer thickness, RMS roughness, crystal structure and photoelectric properties of the FTO films were investigated. The results indicated that the presence of ultrasonic vibration during laser annealing could significantly enhance the film compactness, and using moderate LOR and SOR values resulted in significantly decreased FTO layer thicknesses and RMS roughnesses as well as slightly increased crystallite sizes, thus yielding significantly improved optical transmittance values and slightly enhanced electrical conductivity values. It was found that the optimal LOR and SOR values for ultrasonic-vibration-assisted laser annealing of the FTO films were 80% and 90%, respectively. The as-obtained film possessed the best overall photoelectric property with an average transmittance (400–800 nm) of 85.9%, a sheet resistance of 8.7 Ω/sq and a figure of merit of 2.51 × 10–2 Ω–1. This work may be of great significance in terms of performance optimization of transparent conducting oxide (TCO) thin films.

SLM process parameters such as laser power, scanning speed, layer thickness and hatch spacing play a crucial role in the quality of the processed product. In order to find the parameters suitable for SLM process, a finite element model was established to simulate the distribution of temperature field of selective laser melting (SLM) stainless steel 316L (SS316L) parts. After finite element simulation, the optimum factor levels for SLM processing SS316L were as follows: laser power of 100–200 W, scanning speed of 500–1500 mm/s, hatch spacing of 0.04–0.12 mm, and layer thickness of 0.03–0.06 mm. Then, based on a series of experiments, different laser energy densities were divided into three regions corresponding to three melting mechanisms: the partial melting zone (37.88–75.76 J/mm3), the full melting zone (75.76–151.52 J/mm3), and the over-melting zone (larger than 151.52 J/mm3). The surface roughness, density, microstructure and mechanical properties of the SLM SS316L were strongly dependent on the laser energy density. The results showed that an excellent SS316L part with a relative density higher than 99.66% and good mechanical properties could be obtained at a laser energy density of 119.05 J/mm3 with a laser powder of 200 W, a scanning speed of 700 mm/s, a hatch spacing of 0.08 mm and a layer thickness of 0.03 mm.

This paper presents a transient analysis of the wave propagation in an aluminum film caused by a femtosecond laser pulse irradiation on the surface. The hot-electron-blast is induced during interaction between a femtosecond laser pulse and the aluminum film. By employing three-dimensional solid mechanics and TTM-TEF (two-temperature and thermal-elastic-force) model, the dynamic wave propagation and dynamic shock pressure P are studied and compared with constant results obtained by previous methods. The low-reflecting boundary conditions have been used to truncate the computational domain to a reasonable size. The dynamic shock pressure P and wave propagation show dynamic change process inside of aluminum films.

An investigation of water-based ultrasonic-assisted single-pulse laser drilling is reported for drilling thin section super-alloy sheets to show the influence of ultrasonic power on both blind-hole drilling quality and through-hole drilling quality using different single laser pulses. The effects of ultrasonic power on drilling quality (e.g., hole geometry, hole sidewall surface morphology, and hole wall recast layer, etc.) were experimentally investigated for ultrasonic-assisted millisecond single-pulse Nd:YAG laser drilling. It was found that the ultrasonic vibration incorporated into the single-pulse Nd:YAG laser drilling process could obviously improve the inner hole wall surface morphology/quality in terms of relatively clean and better-profiled hole wall surface with less defects/spattering, better uniformity, and smaller surface roughness. It was indicated that the alteration of the molten material flowing/spattering/expelling due to the contribution of ultrasonic vibration was the main reason of improving the drilling quality for ultrasonic vibration-assisted single-pulse laser drilling. It was also shown that the influencing trends of ultrasonic power on hole circularity deviation, hole sidewall surface morphology, and hole sidewall surface roughness for through holes were similar to those for corresponding blind holes. Except the sample sheet thickness difference, under the same other drilling conditions, hole cross sections and recast layers contributed to the main differences between the drilled through holes and blind holes, which was mainly caused by their difference of the flow and expelling of the molten material.

The ultrasonic vibration was introduced to assist the Nd:YAG laser trepan drilling for improving drilling quality/performance. Effects of ultrasonic power and pulse energy on geometrical and/or metallurgical quality were deciphered for the ultrasonic-assisted Nd:YAG laser trepanning. The energy dispersive spectroscopy analysis was also carried out to reveal the influence of ultrasonic vibration on the elemental compositions of the areas surrounding the drilled microhole entrance. It was shown that the axial ultrasonic vibration coupled into the Nd:YAG laser trepanning process could effectively improve the hole entrance profile/morphology with less metallurgical defects such as microcracks. Moreover, relatively high ultrasonic power was more beneficial to the improvement of laser trepan drilling quality in terms of smaller hole taper angle, thinner recast layer, and less cracks, etc. However, the oxidation of the microhole sidewall could not be effectively improved by using the ultrasonic assistance.

A phase field model (PFM) is combined with a two-dimensional two-temperature model (TTM) to simulate the evolution of dendritic growth during re-solidification of ultrafast laser-material interaction. The dynamic solidification conditions at different locations of the melting pool obtained from TTM are fed into the quantitative PFM based on the macro-micro coupled method. A series of simulations are executed to investigate the influence of laser parameters, such as laser influence and pulse duration, on melting pool characteristics and local dendrite morphology. Besides, dendrite structures calculated at different areas of the melting pool were discussed based on local solidification conditions, and the simulated dendrite arm spacing (DAS) for various cooling rates was made comparison with previously published experimental data. The simulated results reveal that the maximum temperature gradient has significant influence on the local dendritic competitive growth, while the laser parameters effect the local microstructure distinctly due to the changes of solidification conditions. This work demonstrates the potential application of PFM to predict the microstructure morphology presented in ultrashort laser-material interaction and other industrially relevant conditions with complex solidification conditions.

The fluorescence intensities of CdSe/ZnS quantum dots on a silver nanowire and a gold-silver alloy nanotube with different molar ratios of gold and silver are investigated under excitation with different polarization angles. The ratio of the fluorescence intensity of perpendicular and parallel polarization excitations is measured to be 4.05 for a silver nanowire and decreases to 1.30, 1.10 and 1.07 for nanotube with Au:Ag molar ratios of 1:4.0, 1:2.5 and 1:1.5, respectively. The numerical simulation results show that the aforementioned experimental phenomena can be attributed to the variation in the distribution of the surface plasmon electromagnetic field under perpendicular polarized light excitation. The electromagnetic field is primarily distributed on the outer surface of the silver nanowire, while the field partially penetrates the interior of the silver nanotube and becomes completely concentrated at the interior of the gold nanotube. This research also found that the productivity and robustness of the chemical synthesis of the alloy nanotubes can be greatly improved by using a microwave reactor.

An underwater femtosecond laser layered ring trepanning (FLLRT) technology is reported in this paper. The FLLRT experiments are performed in silicon carbide (SiC) ceramic sheets in air and water. The effects of water immersion and laser pulse repetition rate on laser trepanning quality and hole generation characteristics are demonstrated by altering the laser pulse repetition rate. The underwater FLLRT technology notably improves the laser hole-trepanning quality for the SiC material because of the water cooling–insulating effect, underwater bubble-cavitation effect, and water microstreaming effect. Performing FLLRT in water, the hole diameter, particularly the hole exit diameter, increased whereas the hole taper decreased when using a relatively low pulse repetition rate. Furthermore, the hole-wall formation quality and surface uniformity improved while notably reducing the hole-wall oxidation. Significantly, the redeposition of the vapourised material and the resolidification of the molten material are greatly reduced, thereby reducing the formation of the recast layer and micro cracks. When the pulse repetition rate was relatively high, the local thermal accumulation effect induced by significantly more successive laser pulses was notably enhanced for melting the SiC material despite the laser ablation-induced vapourisation.

Using the finite element method (FEM) and the element birth and death technique, a novel rotational pulsed-laser heat source model with consideration of angular velocity and laser pulse activation is reported for simulating the transient thermal process induced by circular laser hole-cutting (CLHC) of through holes in stable stainless steel sheets. The predicted through-hole geometry characteristics were validated with their measured results. It was shown that the simulated results agreed well with the experimental measurements with an acceptable prediction accuracy, and the error percentage for the simulation reported in this work ranged from 2.84% to 6.87%, demonstrating the feasibility and reliability of the rotational pulsed-laser heat source model developed. The temperature field on the workpiece transiently altered with the rotation of the laser beam. Under the combined effect of the uniform circular motion of the laser beam and the periodic irradiation induced by the successive laser pulses, the local temperature on the thermal cycle curve for a nodal location rose obviously with transient multi-peak temperature fluctuations when the rotational laser beam moved near to this calculation node. With the increase of the distance from the hole-entrance border to a certain location, the thermal effect of the rotational pulsed-laser heat source decreased, and the thermal fluctuation on the thermal cycle curve also weakened. The pulse repetition rate and angular cutting velocity slightly influenced the through-hole diameters predicted, while the beam spot size and pulse duration affected the calculated through-hole diameter more noticeably.

Laser annealing has important significance for performance improvement of transparent conductive oxide (TCO)-based thin films. In this study, we further developed the simple flexible polyethylene terephthalate (PET) mask reinforced laser annealing (FPLA) process through covering a transparent PET sheet on the film surface to achieve performance improvement of fluorine-doped tin oxide (FTO) films. Scan control strategy during FPLA involving scanning speed and scan line spacing was determined by analyzing surface morphology, surface roughness, crystal structure and photoelectric properties of the films. It was found that line-by-line round-trip scanning using the optimal scanning speed of 10 mm/s and scan line spacing of 20 μm resulted in the more effective FPLA effect. The as-obtained FTO film exhibited a low-fluctuated surface with remarkably enlarged and dense particles, the lowest RMS roughness, the largest grain size, and thus the maximum figure of merit of 3.05 × 10−2 Ω−1, which was about 1.8 times that of the direct laser-annealed FTO film using the same parameters. The effectiveness of the PET sheet used for FPLA in redepositing the film materials and inhibiting the decrease of oxygen vacancies was further confirmed by mechanism analysis using SEM, EDX and XPS characterizations.

Using simultaneous assistance of the water-based ultrasonic vibrations and a side-loaded magnetic field, the transient real-time observation and metallurgical examination were carried out for laser percussion drilling in stainless steel sheets, aiming for demonstrating the effect of the magnetic-ultrasonic assistance on the hole-drilling process and the metallurgical alteration characteristics. The effect of the camera shooting distance on the signal detection below the hole exit was discussed for laser drilling of through holes. The laser drilling efficiency was characterized based on the real-time observation. It was found that the camera shooting distance affected the signal observation below the hole exit after a workpiece was drilled through due to an optical shield effect of its border side. The influence of the magnetic-ultrasonic assistance was much more notable when the dominant or sufficient heat input for drilling through a hole could not be provided by using a smaller pulse energy, a smaller pulse duration or a bigger laser fluence. The average recast layer thickness of the through-hole middle generated using a millisecond laser could be less than around 5 μ m when using the water-based ultrasonic assistance accompanied with the magnetic assistance. Compared to the corresponding case without external assistance, a reduction of 40 μ s was achieved for drilling through a hole by using the simultaneous magnetic-ultrasonic assistance. The average grain size number became bigger for validating the grain refinement in the heat affected zone after laser drilling using the water-based ultrasonic vibrations with and without magnetic assistance.

A new ultrafast laser direct writing process to fabricate completely embedded silver mesh flexible transparent electrodes (TEs) using sputtered silver thin films and their applications for flexible transparent heaters (FTHs) are reported. The optimal laser etching parameters were determined, and the effects of mesh pitch and height on photoelectric properties of the silver mesh flexible TEs were systematically studied, with an aim to obtain a TE with excellent comprehensive performance. The resulting TE had a lower sheet resistance (0.86 Ω/sq) and a higher optical transmittance (91.26%) than traditional TEs. Good environmental stability of the TE, i.e. maintaining good electrical conductivity in air or deionized water without significant changes for 40 days, was also demonstrated. The fabricated representative FTH also presented stable heating performance, reaching a high temperature in 60 s under a DC voltage of 1.0 V and finally stabilizing at 98 ℃. This heating performance was confirmed to be stable and consistent after 20 cycles or under the conditions of bending and twisting. In addition, a deicing experiment was performed to illustrate the possible application of the FTH. The results indicated the availability of the laser direct writing method for fabricating high-performance metal mesh-based flexible TEs.

We developed a kind of Cu/Ag composite mesh transparent conductive electrodes (TCEs) with low reflection on glass substrates through a simple and effective method, and successfully applied them to fabricate transparent heaters with high performance. By combining laser direct writing and PVP coating-assisted localized removal of sputtered metal layers, Cu/Ag composite mesh TCEs with excellent optical and electrical properties were efficiently prepared and showed a low average reflectance down to 5.71% while maintaining a high average transmittance of 86.49% and a low sheet resistance of 0.43 Ω/sq. The transparent heater based on the as-obtained Cu/Ag composite mesh TCE exhibited an effective and rapid heating performance, being confirmed by achieving a steady-state temperature of ~131 °C within 100 s under an ultra-low applied voltage of 0.8 V. A deicing test of an ice block on the transparent heater was also successfully demonstrated. Good optical and electrical properties as well as excellent thermal stability and reliability imply that the transparent heaters based on the Cu/Ag composite mesh TCEs hold great promise in windshield deicing devices.

This paper reports two optical models of temperature dependent reflectivity, R, and absorption coefficient, α, during femtosecond laser interaction with aluminum. After a comparison with existing experimental data, the critical point model (CPM) was incorporated into a two-temperature model (TTM) to simulate laser energy deposition and thermal response in an aluminum film irradiated by femtosecond laser pulses. The dynamic change of optical properties R and α, distribution of laser heat density, electron and lattice temperature of an aluminum film were investigated. Compared with constant reflectivities and absorption coefficients, dynamic reflectivities and absorption coefficients are recommended to be employed in modeling ultrafast laser heating.

The effect of initial dislocation density on subsequent dislocation evolution and strain hardening in FCC aluminium alloy under laser shock peening (LSP) was investigated by using three-dimension discrete dislocation dynamics (DD) simulation. Initial dislocations were randomly generated and distributed on slip planes for three different dislocation densities of 4.21 × 1012, 8.12 × 1012 and 1.26 × 1013 m−2. Besides, variable densities of prismatic loops were introduced into the DD cells as nanoprecipitates to study the dislocation pinning effect. The flow stresses as a function of strain rate obtained by DD simulation are compared with relevant experimental data. The results show a significant dislocation density accumulation in the form of dislocation band-like structures under LSP. The overall yield strength in FCC aluminium alloy decreases with increasing initial dislocation density and forest dislocation strengthening becomes negligible under laser induced ultra-high strain rate deformation. In...

We demonstrate the unity absorption of visible light with an ultra-narrow 0.1 nm linewidth. It arises from the Bloch surface wave resonance in alternating TiO2/SiO2 multilayers. The total absorption and narrow linewidth are explained from the radiative and absorptive damping, which are quantitatively determined by the temporal coupled mode theory. When a silver film with proper thickness is added to the absorber, the perfect absorption is achieved with only 3 structural bilayers, in contrast with 8 bilayers required without Ag. Furthermore, significant field enhancement and an ultrahigh 2600/RIU sensing figure-of-merit are simultaneously obtained at resonance, which might facilitate applications in nonlinear optical devices and high resolution refractive index sensing.

A facile and highly-efficient laser scanning process coupled with a simple silanization modification was used to prepare textured titanium (Ti) surfaces with stable superhydrophilicity and superhydrophobicity. Femtosecond pulsed laser scanning along two mutually perpendicular directions led to the formation of binary structures featuring micrometer-scale spikes covered with nanometer-scale ripples. The period of the spikes significantly increased and the period of the ripples irregularly changed in the narrow range of 550–600 nm with the increase of laser fluence. The obtained laser-textured Ti surfaces were hydrophilic or even superhydrophilic, and the superhydrophilic laser-textured Ti surface using a laser fluence of 1.5 J/cm2 was observed to retain its wetting property after 30 days of storage in ambient atmosphere. After silanization, all the laser-textured Ti surfaces exhibited high hydrophobicity or superhydrophobicity, and the superhydrophobic laser-textured Ti surfaces using laser fluences of 1.5 and 1.8 J/cm2 remained stable when stored in air for over 30 days. The results imply the potential applications of these surfaces in a variety of fields.

Power skiving is a modern and productive method in the manufacturing of cylindrical internal gears and external gears. However, pose errors of workpiece and cutter are caused by clamping, cutting force, and deformation of heat, which make the tooth deviation present a feature of complexity and diversity in the process of gear skiving. First, a mathematical model with workpiece and cutter pose errors is proposed to investigate the influence of sensitive error on tooth deviation by an example of internal gear skiving. Second, the correlation of tooth deviation with respect to eccentric error of workpiece, eccentric error of cutter, tilt error of cutter, and the multiple errors is studied. The sensitive errors are derived from the tooth deviation by using an orthogonal analysis with workpiece and cutter pose errors. Last, the experimental results show the validity of the numerical analysis results, and the influence of sensitive pose errors on tooth deviation can be used to identify the possible error in power skiving, as well as in gear generating method.

This work focuses on the fabrication of antireflection grating structures on Ag/F-doped SnO2 (FTO) films by ultrasonic-vibration-assisted laser irradiation to compensate the optical transmittance loss due to coating the Ag layers. The effects of laser fluence and ultrasonic vibration on formation of laser-induced grating structures are investigated. The results indicate that ultrasonic-vibration-assisted laser irradiation can not only contribute to generating a complete and uniform periodic grating structure, it can also bring about a laser annealing effect to the film. Ultrasonic vibration is considered to play an important role in generating the grating structure by changing the defocusing amount of the film surface, inputting energy and providing mechanical vibration. Moreover, under the favorable influence of ultrasonic vibration, the laser parameter values can be lowered, and the interference of the laser-excited surface plasmons (SPs) with the incident laser can be facilitated. In this present work, the optimal grating-structured Ag/FTO film has the highest figure of merit of 3.26 × 10−2 Ω−1, showing significant increases compared to the untreated FTO (1.13 × 10−2 Ω−1) and the ultrasonic-vibration-free laser-irradiated Ag/FTO (2.34 × 10−2 Ω−1) films. This work may be of important enlightening and reference significance for preparing high-performance transparent conductive films.

With the ultrashort timescale and high-power density, femtosecond laser is a powerful tool for localized material ablation with high processing accuracy and cleanliness. In this work, femtosecond laser direct writing was used to selectively ablate and remove the copper/silver (Cu/Ag) double-layer metal films on glass substrates for fabricating mesh-type transparent conductive electrodes (TCEs). In particular, the effects of laser fluence and laser scanning speed on surface morphology and photoelectric properties of the TCEs were studied. By using a laser fluence of 1.1 J/cm2 and a laser scanning speed of 400 mm/s, the optimal removal result of the Cu/Ag double-layer metal film was achieved with the minimal damage to the glass substrate. The as-obtained TCE showed a high average transmittance of 87.89% and a low sheet resistance of 1.36 Ω /sq. As an application, a transparent heater based on the as-obtained TCE exhibited an efficient, rapid and stable heating performance, being confirmed by achieving a high temperature of ∼ 144 °C under a low applied voltage of 2.0 V. The femtosecond laser selective ablation strategy for laser patterning of metal-based films provides a unique scheme for the rapid fabrication of metal mesh-type TCEs under the mask-free condition and room temperature.