Nanosecond Laser Research Articles

Ablation threshold, structural modification, and sensing of graphene oxide thin film induced by UV nanosecond laser

Reduction of graphene oxide by laser irradiation is crucial for developing conductive thin films. This study investigates the ablation threshold, reduction of graphene oxide, and high-precision patterning by UV nanosecond laser irradiation of graphene oxide films on flexible substrates. The ablation threshold of graphene oxide thin film was evaluated by examining the relationship between micropore diameters and laser pulse energy density. The single pulse ablation threshold was 2.29 J/cm², indicating that the UV nanosecond laser energy density is sufficient for the ablation of graphene oxide. Based on ablation threshold evaluation, graphene oxide was reduced by UV nanosecond laser irradiation, and laser-irradiated graphene oxide-based flexible thin film with four different line widths was fabricated. UV nanosecond laser irradiation graphene oxide-based grid structure patterns on the flexible substrates were fabricated by analyzing these different line widths. In addition, laser-irradiated graphene oxide-based grid structure flexible electrode were used to monitor human hand motion and finger press sensing. This study underscores the significance of laser irradiation of graphene oxide, a controllable strategy, and highlights the novelty and practical applications for fabricating flexible graphene oxide-based electronics.

Selective nanosecond laser removal of retinal pigment epithelium for cell therapy

Retinal pigment epithelial (RPE) cells play a crucial role in the health of the retina, and their dysfunction is associated with various ocular diseases. The transplantation of RPE cells has been proposed as a potential treatment for numerous degenerative diseases, including geographic atrophy from macular degeneration. However, current models to induce RPE damage in animal models prior to transplantation involve mechanical scraping, chemical administration, or laser photocoagulation techniques, which can damage the overlying neurosensory retina. This study aims to investigate the feasibility and efficacy of nanosecond duration laser treatment to safely remove large areas of RPE cells without causing damage to the adjacent tissue or affecting the retinal architecture. Twelve pigmented rabbits were treated with a nanosecond laser on each eye at a laser energy ranging from 200 to 800 nJ with a treated area of 5 × 5 mm2. Human induced pluripotent stem cells-differentiated to RPE (hiPSC-RPE) cells labeled with indocyanine green (ICG), an FDA approved dye, were transplanted subretinally into the damaged RPE areas at day 14 post-laser treatment. The RPE atrophy and hiPSC-RPE cell survival was evaluated and monitored over a period of 14 days using color photography, fluorescein angiography (FA), photoacoustic microscopy (PAM), and optical coherence tomography (OCT) imaging. All treated eyes demonstrated focal RPE loss with a success rate of 100%. The injured RPE layers and the transplanted hiPSC-RPE cells were visualized in three dimensions using PAM and OCT. By performing PAM at an optical wavelength of 700 nm, the location of hiPSC-RPE cells were identified and distinguished from the surrounding RPE cells, and the induced PA signal increased up to 18 times. Immunohistochemistry results confirmed the grafted hiPSC-RPE replaced regions of RPE damage. This novel technique has the potential to serve as an animal model of RPE degeneration, to improve models of RPE transplantation, and may help accelerate translation of this therapeutic strategy for clinical use.

Influence of crystallinity on micro-nano structure response of Zr-based alloys treated by nanosecond laser

Understanding the processes and mechanisms of laser-matter interaction is fundamental to the treatment of materials by using laser-based methods, but it is quite challenging because the response of matter to laser irradiation is influenced by many factors, especially the intrinsic properties of the matter. In this study, the influence of crystallinity on micro-nano structure response of Zr-based alloys (Zr41.2Ti13.8Cu12.5Ni10Be22.5) treated by nanosecond laser is investigated. The microscopic topographies and geometrical dimensions of the laser-induced micro-nano structures formed on the surface of Zr-based alloys with different crystallinity have been explored and compared. The experimental results indicate that the microstructural transformation between micro-concave and micro-convex is observed for both amorphous and crystallized Zr-based alloys, i.e., independent of the arrangement of the internal atomic structure. The geometrical dimensions of the laser-induced micro-nano structures and the critical peak laser power intensity required for the microstructural transformation are different, which can be attributed to the difference in thermal conductivity. Inspired by laser-induced micro-convex, a point-by-point laser patterning technique has been proposed for highly efficient and flexible preparation of micro-nano patterns. Importantly, this patterning technique exhibits ultra-high processing efficiency with a material accumulation rate of more than 1012 μm3/s. This work paves an avenue for understanding the laser-matter interaction and is expected to facilitate the advanced functional applications of Zr-based alloys in many fields.

Evolution and persistence of SiO emission in nanosecond laser ablation plumes

Abstract Analyzing laser-produced plasmas in a controlled oxygen-containing environment provides insight into the formation and evolution of molecular species through gas-phase oxidation. This study explores the role of ambient pressure and oxygen availability in forming SiO molecular species in laser ablation plumes. The self-emission emanating during the reactive ablation of Si targets was characterized by optical emission spectroscopy and optical time-of-flight techniques. Our results showed that the SiO species formation was greatly influenced by both the ambient pressure and oxygen availability. The intensity and the persistence of SiO emission bands are lower at higher oxygen concentrations, indicating they are depopulated by the formation of more complex silicon oxides. The oxygen partial pressure effects on plume chemistry showed that SiO formation is favored even with a minimal oxygen concentration in the environment.

Rapid Fabrication of Antilunar Dust Aluminum Surface by Nanosecond Laser Etching.

Although a dust-repellent surface is desirable for lunar exploration missions, its fabrication process is complicated and time-consuming. Herein, we report a simple and fast method to fabricate a lunar dust-repellent surface by texturing on an Al substrate via nanosecond laser etching. The laser-induced photothermal effect can rapidly create hierarchical papillary structures on 25 × 25 mm Al substrates (within 30 s). Both atomic force microscopy (AFM) and in situ scanning electron microscopy (SEM) reveal that such structures enable a reduced contact area between the Al substrate and lunar dust and thus reduced adhesion. The reduced dust adhesion force of Al substrates facilitates improving their antidust performance. By optimizing processing parameters, the Al substrate etched with a laser scanning spacing of 80 μm exhibits a lower dust adhesion force (9.58 nN) due to the smallest contact area with dust. Accordingly, its static antilunar dust performance (dust coverage of 1.95%) is significantly improved compared to the pristine Al substrate (dust coverage of 12.98%). Besides, the accumulated dust on the laser-etched Al substrates with low surface adhesion force is easily cleaned up by flipping and gravity (the dust residual rates are less than 17%). The Al substrate with excellent antidust ability presents good potential for lunar exploration missions.

Optimization of nanosecond laser drilling strategy on CFRP hole quality

The drilling and cutting of carbon fiber-reinforced epoxy resin matrix composite (CFRP) structural parts is a prerequisite for one-off moulding and assembly connections. However, the thermal ablation effect observed during nanosecond laser hole-making of CFRP results in significant accuracy errors and thermal damage defects in the quality of the holes obtained from the process. To enhance the quality of laser-drilling CFRP holes, a spiral drilling path was employed in this work. The influence of diverse drilling methodologies, encompassing the trajectory of the laser beam, the spacing between scans, and the direction of the suction system's pumping, on the quality of the holes was examined. The impact of these techniques on the precision and integrity of the holes was assessed in terms of their dimensions, the quality factor, the width of the heat-affected zone (HAZ), and the prevalence of microscopic defects. The results demonstrated that when the drilling strategy involves moving the laser beam from the outside to the inside (Scheme I), a scanning spacing of 20 μm, and backward pumping, the optimal micro-hole accuracy and surface morphology, as well as minimal thermal damage defects can be achieved. This study provides a reference for further optimization of the nanosecond laser drilling process.

Nanosecond Laser Debonding Using an Ultrathin Absorber Layer in a Transparent Composite: Making a Light‐Powered Exploding Bolt

AbstractLocalized heating of an adhesive interface can separate glued substrates for recycling or reconfiguring. Light provides a way to deposit energy at this type of buried interface, but the photon energy must still be transformed into thermal energy. The deposition of an ultrathin (<1 µm) absorbing layer before gluing provides a way to build this photothermal capability into the bonded structure. To demonstrate this concept, a submicron absorbing layer composed of the dye Fluorescein 27 (F27) is applied to a poly(methyl methacrylate) (PMMA) substrate that is glued to a second PMMA piece using a commercial cyanoacrylate adhesive. The laser debonding is characterized as function of dye layer thickness, applied pressure, and laser pulse fluence. A 450 nm thick dye layer retained a high adhesive strength of 3.5 MPa but can be debonded by a single 532 nm nanosecond laser pulse with a fluence ≤ 0.7 J cm−2. Decomposition of the absorbing layer resulted in rapid gas evolution that left the micron‐scale surface morphology of the PMMA substrate intact. This system enabled the fabrication of an optical analog to the exploding bolt, where a single laser pulse can impulsively separate a structural fastener.

Numerical simulation and experiments of nano-second pulsed laser cleaning titanium alloy oxide film

Numerical simulation and experiments of nano-second pulsed laser cleaning titanium alloy oxide film

Nanosecond laser structuring for enhanced pool boiling performance of SiC surfaces

Silicon carbide (SiC), which has a wide bandgap and superior material properties, offers higher efficiency than conventional silicon in high-power and high-frequency semiconductor applications. In this study, the thermal management of SiC devices was explored through direct liquid cooling with laser-structured heat sinks. Pyramid-structured fin arrays were fabricated directly onto SiC substrates via laser structuring, and their boiling heat transfer performance was investigated through pool boiling experiments in a 5 °C subcooled condition. Laser structuring not only enhanced wettability due to oxidation but also facilitated nucleation through the laser-induced crevices. The oxidized surface created by the laser exhibited increased hydrophilicity, with a significant decrease in contact angle from 57° to 0°. In the pool boiling experiments, these crevices played a crucial role in enhancing the heat-transfer coefficient (HTC) at low heat fluxes (5–40 W/cm2), which promoted nucleation, resulting in the formation of very small and rapid bubbles. At heat fluxes above 180 W/cm2, the large surface area provided by the height of the fin structures further contributed to enhancing the HTC. The sample with the highest performance enhancement exhibited an 114 % increase in critical heat flux and a remarkable 393 % increase in the HTC compared to before laser structuring.

Sunflower-Inspired Superhydrophobic Surface with Composite Structured Microcone Array for Anisotropy Liquid/Ice Manipulation.

Precisely controlling the directional motion trajectories of droplets on anisotropic 3D functional surfaces has great application potential in self-cleaning, drug delivery, and droplet power generation, but it also faces huge challenges. Herein, inspired by the microcone structure in the heart of sunflowers, a nanoneedle-modified microcone array surface (NMAS)is reported. The surface is created using a combination of nanosecond laser direct engraving and electroforming and is subsequently fluorinated. Through programmable control of the laser spot, the geometric parameters and inclination angle of the microcone can be quickly and finely adjusted, thereby achieving precise control of the droplet bouncing trajectory. The results show that droplets can achieve programmable multiple bouncing behaviors on patterned functional surfaces, including gravity-defying hopping and directional water transport. It is worth noting that this functional surface has delayed freezing and anti-freezing effects. Furthermore, this functional surface has a wide range of potential applications, including surface self-cleaning, droplet capture, and droplet-based chemical microreactions, especially in the field of anti-icing operations. This opens up a new way for the directional transport of droplets on biomimetic functional surfaces.

Non-contact defect imaging of carbon fiber composites using laser excited acoustic shearography

The performance of carbon fiber reinforced polymer (CFRP) composites is significantly affected by the presence of subsurface defects, which originate from manufacturing processes or during operations. Although many non-destructive testing (NDT) methods have been employed to inspect CFRP materials and structures, the existing techniques are often time-consuming and sometimes require contact measurement. This paper presents a non-contact and rapid inspection method utilizing laser-excited acoustic shearography to detect subsurface defects in CFRP composites. In this method, a pulsed nanosecond laser is used to generate ultrasonic waves through thermoacoustic effect, and a shearography sensor is used to image the full-field wave-defect interactions. It is found that the proposed method can efficiently image various subsurface defect sizes in a non-contact way. The identified defects were validated through comparison with X-ray computed tomography (XCT).

Gold nanoparticle-mediated nanosecond laser-induced polystyrene carbonization with luminescent products

A highly soluble Au(I) gold precursor is used to produce a nanocomposite material consisting of a polystyrene matrix and gold nanoparticles. Irradiation of such a material with nanosecond laser pulses at the plasmon resonance wavelength leads to the formation of black spots containing luminescent products of carbonization. HR TEM analysis and Raman spectroscopy confirm disordered carbon. A simple model, based on laser heating of a nanoparticle to a temperature of more than 2000 K and stabilization of this temperature by the endothermic process of polystyrene carbonization, fits well with the dependence of the luminescent signal increment on the laser fluence.

Structure and optical properties laser modification of the Ag-PbSe films.

The modification of the structure and optical properties of two-layer silver-lead selenide (Ag-PbSe) films because of exposure to laser nanosecond pulses of near-infrared radiation in the scanning mode is considered. The formation of micro-sized fragments and silver nanoparticles as a result of laser irradiation, as well as their effect on the spectral transmission and reflection of the film, has been revealed. It is shown that the presence of a silver layer on a PbSe film is an effective way to improve the optical characteristics of the material, which expands the scope of possible applications of chalcogenide films of this composition.

Reproducing wrought grain structure in additive IN718 through nanosecond laser induced cavitation

Pulsed laser assisted additive manufacturing has been demonstrated as a promising technology for controlling grain structure in 3D-printing processes. The integration of a nanosecond laser onto a wire arc additive manufacturing tool has enabled the localized printing of Inconel 718 with grain sizes meeting ASTM 9 standards (average measured grain size of 13.7μm) for wrought material within a single bead under solidification conditions that would otherwise produce 340μm columnar grains. The observed grain refinement holds promise, provided scale up is possible, for overcoming the highly anisotropic mechanical properties and microcracking associated with large columnar grains of Inconel 718 that have long stood in the way of leveraging the advantages of direct energy deposition printing techniques of difficult to machine alloys. Experiments on large bead sizes allowed for decoupling surface versus bulk nanosecond laser/liquid metal interaction mechanisms to determine that the source of the observed grain refinement is the collapse of cavitation bubbles originating from acoustic waves generated by momentum transfer into the melt of an ablation plasma. Additionally, experiments that increased the cavitation bubble density within the mushy zone during solidification by tuning the nanosecond laser scan path went beyond the 25 times reduction in grain size to a 70 times factor of refinement with a minimum average grain diameter approaching 4μm.

Corrosion and tribocorrosion resistance of superhydrophobic LPBF-NiTi alloys surface fabricated by nanosecond laser and ultrasonic fluorination

NiTi alloys have been extensively studied for their excellent super-elasticity (SE) and shape memory effects (SME). With the development of laser powder bed fusion (LPBF), it is possible to process the complex structure of NiTi alloy, which results in the mechanical properties of LPBF-NiTi alloys receiving great attention. However, the processing method is different from the traditional one, which not only has an impact on the mechanical properties but also seriously affects the anti-corrosion resistance and causes a substantial deterioration. In the research work of this paper, nanosecond laser processing was used to fabricate the bionic mastoid-shaped micro-nano structure on the LPBF-NiTi alloys. An efficient and convenient ultrasonic fluorination treatment was used to achieve the full surface coverage of FAS-17 in 10 min, and the superhydrophobic LPBF-NiTi alloy surface (CA ~ 157°) was successfully achieved. The constructed superhydrophobic LPBF-NiTi alloy surface exhibits excellent anti-corrosion resistance compared with the original surface, and the icorr from (4.42 ± 0.5) × 10−7 A·cm−2 reduced to (3.21 ± 0.5) × 10−9 A·cm−2. Meanwhile, the superhydrophobic surface showed outstanding stability in the 15-day immersion test n 3.5 wt% NaCl solution. And it is also stable after the tribocorrosion tests in 3.5 wt% NaCl solution at 1 N and 5 N pressures. The remarkable anti-corrosion resistance and stability of the superhydrophobic surface can be attributed to the micro-nano structure rich in the TiO2 oxide layer, the air layer formed by the superhydrophobic surface insulates the corrosive liquid and the stable hydrophobic agent film.

Double laser two-step process for creating interconnected frame microstructures' superhydrophobic surface with dual scales

Superhydrophobic surfaces have garnered significant attention for their unique wettability and extensive applications across various critical fields. In this paper, a two-step laser processing technique, involving infrared nanosecond laser patterning and ultraviolet picosecond laser surface modification, was employed to fabricate interconnected frame surfaces with dual-scale microstructures on Ti6Al4V substrates. After that, the microstructure surface was chemically modified with 1H,1H,2H,2H-perfluorodecyl trimethoxy-silane to achieve a superhydrophobic surface. An L32 (47) orthogonal experiment was used to analyze the effect of seven main factors (including the structure size, scanning velocity and the fluence, number of scans of infrared nanosecond laser and ultraviolet picosecond laser) on the wettability of the interconnected frame microstructures surface. After optimization, the surface strongly corresponded with the Cassie-Baxter model and demonstrated a water contact angle of 153.22±1.64° and roll-off angle of 4.43±1.70°. The experiments demonstrated that the optimized surface possesses excellent mechanical stability and corrosion resistance. Additionally, the optimized surface exhibits anti-adhesion, effective self-cleaning, and anti-fouling properties, which hold promise for addressing issues of liquid adhesion and dust pollution in industrial machinery.

Hyperdoping of germanium with argon toward strain-doping-induced indirect-to-direct bandgap transition in Ge

The first-principles calculations have recently shown that implanting sufficient noble gas atoms into germanium (Ge) can expand its lattice to achieve the desired tensile strain for indirect-to-direct bandgap transition to develop the on-chip high-efficient light emitter. Here, to experimentally prove this strain-doping concept, we implant argon (Ar) ions into Ge and then recrystallize the Ar-doped amorphous Ge (a-Ge) layer using nanosecond laser annealing (NLA) and furnace thermal annealing (FTA), respectively. The NLA effectively recrystallizes the 12 nm thick a-Ge layer with minimal loss of Ar dopants, while FTA fails to fully recrystallize it and results in significant loss of Ar dopants. The regrown Ge layer with Ar concentration above the critical value (0.8%) for bandgap transition is 3.8 nm thick, making it a challenge to distinguish the photoluminescence signal of strain-doped layer from the substrate. To overcome this, increasing the implantation energy and adding a capping layer may be necessary to further prevent Ar loss and achieve a strain-doped layer with sufficient depth. These findings provide promising view of the strain-doping concept for direct-bandgap emission from Ge.

Analysis method of point defects evolution in fused silica under multi-pulse nanosecond laser irradiation

Although no optically visible damage is produced in the fused silica under laser irradiation below its laser-induced damage threshold (LIDT), defect proliferation may occur due to the evolution of its internal atomic structure. The escalation in defect content leads to heightened absorption, and resulting in the degradation of the optical performance of the optics. In recent decades, there have been a lot of experimental studies on laser-induced damage and laser conditioning, but there is still a great lack of in-depth understanding and theoretical analysis of the evolution process of point defects in fused silica. In this study, the emphasis is on the evolution of point defects and fatigue damage in fused silica under multi-pulse nanosecond laser irradiation. To address this, a point-defect evolution model is developed, and the coupled evolution law of temperature and defect during laser irradiation is derived by integrating it with a numerical model. The results demonstrate that the model effectively predicts the defect evolution of fused silica under laser irradiation and facilitates the prediction of fatigue damage. It is revealed that the rate of defect evolution in fused silica is more influenced by temperature than stress, and a temperature threshold can be used to judge the condition of damage occurrence. Furthermore, through an analysis of the effect of laser fluence on defect relaxation rate, a defect relaxation method employing variable laser fluence was proposed. This study provides a reliable theoretical analysis method for understanding the fatigue damage induced by multi-pulse laser irradiation in fused silica and offers a new perspective for the annealing treatment of point defects in fused silica.

Laser Treatment of Central Serous Chorioretinopathy - An Update.

Laser treatment has been a mainstay for management of central serous chorioretinopathy for a few decades. Different types of lasers have been used and non-damaging retinal laser is the most recent option. The aim of this review is to provide an update on this form of treatment, based on the research published during last 5 years, in comparison with earlier studies published. A MEDLINE database search was performed with a combination of the following terms: central serous chorioretinopathy and laser photocoagulation or subthreshold laser or subthreshold micropulse laser or nanosecond laser or microsecond laser or end-point management or photodynamic therapy. Results were analyzed separately for each modality of laser treatment. Reports published in recent years confirm findings of previous research and do not distinguish treatments of this clinical entity. Among all analyzed laser options, photodynamic therapy provides the fastest and most prominent morphological improvements, including subretinal fluid resorption and reduction of choroidal thickness. This modality is also associated with fewer recurrences than with other treatments. Subthreshold micropulse laser allows the physician to maintain and, in selected cases, improve the patient's vision. Conventional photocoagulation is still effective, especially with the introduction of navigated laser systems. Despite the availability of variable laser treatment options, long-term functional improvements in chronic cases are minor for each modality. Long-lasting central serous chorioretinopathy cases with significantly altered retinal morphology do not usually present with functional improvement, despite satisfactory morphological outcomes. Early initiation of treatment has the potential to prevent visual loss and to improve the patient's quality of life.

Nanosecond laser micromachining of graphene nanoplatelets reinforced ZK60 matrix composites

AbstractIn this paper, a nanosecond laser was used to etch the surface of graphene nanoplatelets reinforced ZK60 (GNPs/ZK60) matrix composites, and the effects of different scanning speeds, pulse repetition frequency and laser power on the etched morphology of the machined surface were investigated. The experimental results show that the etched groove width and heat affected zone width of GNPs/ZK60 composites are significantly increased compared with ZK60 material due to the influence of graphene, and the growth rate of the difference in heat affected zone width between GNPs/ZK60 composites and ZK60 materials is most significantly affected by the pulse repetition frequency. In addition, the dross height increases with the increase of laser power, while the scaly dross structure becomes increasingly clear.