Nanosecond Laser Micromachining Research Articles

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.

Laser-texturing of stainless steel as a corrosion mitigation strategy for high-temperature molten salts applications under dynamic conditions

Molten salts are utilized in a wide range of applications including nuclear, fuel cells, Carnot batteries, and Concentrated Solar Power (CSP). In order to enhance the profitability of next-generation CSP plants, increasing their efficiency is imperative. Ternary carbonate salts are capable of elevating the maximum CSP operating temperature, which results in improved power generation efficiency. However, higher temperatures lead to accelerated corrosion and more severe conditions for structural materials. In this study, nanosecond laser micromachining is investigated as a potential corrosion mitigation technique for molten carbonate salts in dynamic conditions. SS310 samples with laser-induced surface textures are subjected to the flow of molten Li2CO3–K2CO3–Na2CO3 at 600 °C for a period of 600 h. Laser treatment significantly impedes corrosion in SS310, as untreated samples display pitting and scaling, while minimal surface changes are noted on treated samples. Cross-sectional analysis of the samples reveals considerable peeling in the untreated samples and a 45% increase in the corrosion rate compared to the treated samples. The concentrations of Cr and Mg in the salt (determined through ICP analysis) are found to be twofold and fourfold higher than those in treated samples. Laser treatment renders Cr and Mg less accessible to the salt ions, particularly Li, which results in improved corrosion resistance.

Facile fabrication of optical diffusers by ablation-assisted nanosecond laser micromachining of glass substrates

Optical diffusers are essential components in modern technologies such as liquid crystal displays (LCDs), light emitting diodes (LEDs), imaging systems, etc., and a facile, quick, and cost effective fabrication technique is highly desired. Among the various known techniques femtosecond laser micromachining of glass substrates is known to work well for this purpose at the expense of high fabrication cost. On the other hand, low-cost nanosecond laser micromachining at 1064 nm does not always work well for most of the commonly used glass substrates. We demonstrate that this dilemma can be easily solved by ablation-assisted nanosecond laser micromachining of glass, where a metal target is placed just behind the glass substrate and the nanosecond laser is focused to the metal target through the glass so that the back surface of the glass substrate is efficiently etched by ablation fragments and plasma of the metal target. By varying the laser parameters and the gap between the glass and metal target we can control the optical properties of the fabricated diffusers. We also demonstrate that laser cleaning is an efficient way to remove all deposits after laser micromachining. All those results indicate that the demonstrated technique is a facile, quick, and cost effective fabrication method of optical diffusers.

Research on nanosecond laser processing of basic unit for ridge surface: forming condition of microgroove and micro-ridge structure on TC4 surface

Frictional resistance significantly reduces the energy efficiency of aircraft. The ridge surface has a drag reduction effect, and its processing has become one of the important ways for improving the energy efficiency of aircraft. The micro-ridge and microgroove are the basic units of the ridge surface. A nanosecond laser can prepare them. However, numerous parameters and complex laser etching mechanisms make it difficult to determine their molding conditions, the forming quality of which is difficult to guarantee. This problem restricts the high-precision preparation of the ridge surface, which inevitably affects its drag reduction performance. Therefore, it is crucial to determine the high-quality molding conditions of the microgroove and micro-ridge to ensure the drag reduction effect of the ridge surface. Here, we focus on aviation titanium alloy TC4. Through an etching experiment of the straight section, the influence of parameters on the feature size of its cross-section profile is systematically studied. The recast layer scale, symmetry, and smoothness of the cross-section profile are used to evaluate the molding quality of microgrooves. The symmetry of the cross-section profile assesses the molding quality of micro-ridges. The forming parameter range and high-quality forming condition of microgrooves and the high-quality forming parameter range of micro-ridges are determined. Finally, the morphology evolution rule and mechanism of the nanosecond laser etching TC4 is revealed based on this research. The direct molding rules and parameter range of micro-ridges on the TC4 surface are reported and show a broadening of the nanosecond laser micromachining range. Moreover, this study will provide a process window for optimizing nanosecond laser processing for microgrooves and micro-ridges on the TC4 surface.

Ablation Threshold Measurement and Chemical Modification of UV Nanosecond Laser Micromachining of Polycrystalline Diamond

Polycrystalline Diamond In article number 2100450, Jianlei Cui and co-workers study the ablation threshold and phase transition of polycrystalline diamond under the irradiation of an ultraviolet nanosecond laser with a wavelength of 355 nm. It reveals that the ablation threshold of polycrystalline diamond is approximately 3.7326 J cm−2. Furthermore, the sp3 structure of the diamond transforms into the sp2 graphite phase during the ultraviolet nanosecond laser micromachining.

Ablation Threshold Measurement and Chemical Modification of UV Nanosecond Laser Micromachining of Polycrystalline Diamond

The effects of pulsed laser interaction with matter have become a center for research. The pulsed laser has become an indispensable manufacturing tool in the efficient machining of polycrystalline diamond (PCD) and other materials. Herein, the ablation threshold and chemical modification of PCD irradiated using ultraviolet (UV) nanosecond laser is scrutinized. Using a UV nanosecond laser source, a bulk of PCD is ablated in air, and multipulse processing is executed at a wavelength of 355 nm. The ablation threshold of PCD is reported to be ≈3.7326 J cm−2 based on the linear relationship between the laser pulse energy density and the crater diameter, with a Gaussian distribution of the laser intensity on the cross‐section. Furthermore, the sp3 structure transitioned to the sp2 graphite phase when the PCD is exposed to UV nanosecond laser irradiation. Consequently, this study provides a theoretical and experimental reference for UV nanosecond laser micromachining of PCD materials in the research and metal‐working industries.

Investigations in nanosecond laser micromachining on the Zr52.8Cu17.6Ni14.8Al9.9Ti4.9 bulk metallic glass: experimental and theoretical study

In addition to their attractive mechanical properties, the lack of grain boundaries and crystal defects of Bulk Metallic Glasses (BMGs) make them suitable materials for integration in micro-systems fabrication chains, either as final components or mould inserts. The application of short or ultra-short pulsed lasers has recently been demonstrated for the processing of BMGs in this context, particularly as a possible solution for machining micro-scale features on the surface of BMG workpieces. Therefore, complementary studies that consider both experimental and thermal simulation data at the same time in the context of multiple and moving pulses irradiating a BMG specimen are desirable to gain insight into micromachining phenomena. Although such models have been reported in the context of single pulse processing of BMG substrates, their extension to multiple pulse scenarios for micromachining is lacking. Thus, the overall objective of this paper is to combine both theoretical and experimental laser micromachining investigations using multiple pulses when irradiating a BMG workpiece. The specific focus is on conducting such laser operations in the nanosecond regime on a Zr-based BMG, with composition Zr52.5Cu17.9Ni14.6Al10Ti5, also known as Vitreloy 105. This combined experimental and theoretical approach enabled the identification of a suitable set of laser parameters with respect to the process efficiency over a range of pulse duration, fluence values, scanning speed and track distance between machined grooves. In addition, it was highlighted that laser micro-machining operations can lead to BMG materials experiencing thermal cycles, which are quite different from that taking place during the conventional synthesis of glassy alloys, thus complicating the further characterisation and understanding of crystallisation phenomena at play.

Manufacturing of micro-textures on metals by nanosecond laser micromachining

The advantages and disadvantages between ‘single pulse one time repeating at intervals’ (SPI) and ‘single pulse multiple times continuous’ laser micromachining technology on surface textures were experimentally investigated. The micromachining of 45 steel, GCr15 steel and grey cast iron materials were also studied using the interval manufacturing technology. The efficiency of the laser processing technologies and quality of the ablated micro-dimples such as the diameter and depth were systematically analysed. The experimental results showed that, the ‘single pulse one time repeating at intervals’ (SPI) micromachining technology produced high quality dimples with less heat affected zone, smooth dimples with little slags due to its ability to effectively alleviate the negative heat accumulation effect to produce quality dimples as compared to the ‘single pulse multiple times continuous’ micromachining technology process. The diameter and depth of the micro-dimples increased generally with an increase in the laser fluence for all materials. The grey cast iron has the smaller ablation threshold with the largest dimple geometry due to its high laser absorption rate and the presence of more sulfur (S) and phosphorus (P) in the chemical composition, while GCr15 steel exhibited the smaller geometry due to its hardness.

Laser formation of tip emitting structures with high aspect ratio on glass-carbon field-emission cathodes

Paper describes the method of creating the sharp emitting tips on the surface of a field- emission cathode. The needle-shaped structures with a high aspect ratio on the glass-carbon plate are produced by means of nanosecond laser micromachining. The operations of laser scribing, milling and cleaning were applied for fabrication of the single- and multi-tip field-emission cathode. The special technique of laser rough and fine milling provided high tips with sharp and smooth apexes. As a result we obtained the tips with aspect ratio up to 600. The tests of cathodes showed that high density of current emission and a shorter technological route of production to be reached.

Droplet assisted laser micromachining of hard ceramics

Hard ceramic materials like tungsten carbide (WC) are extensively used in high value manufacturing, and micromachining of these materials with sufficient quality is essential to exploit its full potential. A new micro-machining technique called droplet assisted laser micromachining (DALM) was proposed and demonstrated as an alternative to the existing nanosecond (ns) dry pulse laser ablation (PLA). DALM involves injecting liquid micro-droplets at specific frequency during the nanosecond laser micromachining to create impulse shock pressure inside the laser irradiation zone. The impulse shock pressure is generated due to the explosive vaporisation of the droplet, during its interaction with high temperature laser irradiation zone. In this paper, the DALM uses a nanosecond pulsed Nd:YAG laser to machine tungsten carbide substrate. The results suggest that the impulse shock pressure generated during the DALM process can transform the melt ejection mechanism of the ns laser micromachining process. The change in ejection mechanism results in a 75% increase in material removal rate and 71% reduction in the spatter redeposited compared to conventional dry ns laser micromachining.

Simulation and Experimental Study of Nanosecond Laser Micromachining of Commercially Pure Titanium

Nanosecond laser machining of titanium has gained increased interest in recent years for a number of potential applications where part functionalities depend on features or surface structures with microscale dimensions. In particular, titanium is one of the materials of choice to sustain the demand for advanced and miniaturized components in the biomedical and aerospace sectors for instance. This is due to its inherent properties of high strength-to-weight ratio, corrosion resistance, and biocompatibility. However, in the nanosecond laser processing regime, the resolidification and deposition of material expelled from the generated craters can be detrimental to the achieved machined quality at such small scale. Thus, this paper focuses on the investigation of the laser–material interaction process in this pulse length regime as a function of both the delivered laser beam energy and the pulse duration in order to optimize machining quality and throughput. To achieve this, a simple theoretical model for simulating single pulse processing was developed and validated first. The model was then used to relate (1) the temperature evolution inside commercially pure titanium targets with (2) the morphology of the obtained craters. Using a single fiber laser system with a wavelength of 1064 nm, this analysis was conducted for pulse durations comprised between 25 ns and 220 ns and a range of fluence values from 14 J cm−2 and 56 J cm−2. One of the main conclusions from the study is that the generation of relatively clean single craters could be best achieved with a pulse length in the range of 85–140 ns when the delivered fluence leads to the maximum crater temperature being above but still relatively close to the vaporization threshold of the cpTi substrate. In addition, the lowest surface roughness in the case of laser milling operations could be obtained when the delivered single pulses did not lead to the vaporization threshold being reached.

Superhydrophobic Surface by Replication of Laser Micromachined Pattern in Epoxy/Alumina Nanoparticle Composite

Superhydrophobic surfaces were obtained by superposition of microstructure—defined by replication of laser micromachined masters, with nanostructure—created by durable epoxy/γ‐Al2O3 nanoparticle composite, used for replication. Hierarchical surface topography thus obtained consisted of hexagonally spaced microcavities and nanoparticle agglomerates, exposed on the replica surface by radio frequency (RF) air plasma etching. Surface topography was further enhanced by rims around the microcavity edges, resulting from nanosecond laser micromachining defects in aluminum masters. Subsequent wet chemical hydrophobization with 1H,1H,2H,2H‐perfluorotetradecyltriethoxysilane (PFTDTES) provided superhydrophobic behavior in replicas with a microcavity spacing of 30 μm, as indicated by a water contact angle of 160° and a sliding angle of 8°. The preparation method is relatively simple, inexpensive, and potentially scalable.

Compensation for time fluctuations of phase modulation in a liquid-crystal-on-silicon display by process synchronization in laser materials processing

We demonstrate the adverse influence of temporal fluctuations of the phase modulation of a spatial light modulator (SLM) display device on nanosecond laser micromachining. We show that active cooling of the display reduces the amplitude of these fluctuations, and we demonstrate a process synchronization technique developed to compensate for these fluctuations when applying the SLM to laser materials processing. For alternative SLM devices developed specifically for laser wavefront control (which do not exhibit such flickering problems), we show that our process synchronization approach is also beneficial to avoid machining glitches when switching quickly between different phase profiles (and hence beam patterns).

Application of cooled spatial light modulator for high power nanosecond laser micromachining

The application of a commercially available spatial light modulator (SLM) to control the spatial intensity distribution of a nanosecond pulsed laser for micromachining is described for the first time. Heat sinking is introduced to increase the average power handling capabilities of the SLM beyond recommended limits by the manufacturer. Complex intensity patterns are generated, using the Inverse Fourier Transform Algorithm, and example laser machining is demonstrated. The SLM enables both complex beam shaping and also beam steering.

Design and performance of LEDs with circular geometry

AbstractInGaN light‐emitting diodes (LEDs) on sapphire substrate in the shape of cuboid and circular disk are diced via ultraviolet nanosecond laser micromachining. The geometrical influence on light extraction and emission pattern are evaluated. Our postulation on the optical characteristics of circular LEDs is qualitatively confirmed according to ray‐tracing simulation. The enhancement in light extraction over conventional cuboid chips is more than 10% according to measurements of our fabricated devices. The fair consistency between the simulation result and measurements indicates that the circular design is indeed effective for improving light extraction from InGaN LEDs. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Numerical and Experimental Study of Interference Based Micromachining of Stainless Steel

An interference based nanosecond laser micromachining method for stainless steel has been investigated. Predictive mathematical modeling was carried out using MATLAB to identify the optimum laser parameters for the micromachining of stainless steel. Experiments on machining of stainless steel sample plates were then performed with a nanosecond pulse length laser beam of central wavelength 1064nm. Marking of the material was achieved at different power levels, pulse repetition rates and machining times. The modeling and experimental results were compared, with proper justification.

Numerical Simulation of Laser Surface Micro-Texturing

In order to predict the geometry character of laser surface micro-texturing, the finite element analyzing software ANSYS is used to simulate temperature field and crater on the laser ablation. The influence and change regulation of laser intensity, laser pulse number and pulse duration in laser surface texturing are analyzed in detail. The simulation results conclude the best laser intensity in laser-pulse and materials interactions on certain conditions, and the best pulse duration in nanosecond laser micromachining. This research establishes the foundation for laser machining regular non-smooth surface in a rapid and effective way.

Femtosecond versus nanosecond laser micro-machining of InP: a nondestructive three-dimensional analysis of strain

Ultra-fast femtosecond laser micro-machining can lead to improved surface morphology and a reduction in the heat-affected zone. In this paper, synchrotron x-ray topography (SXRT) and micro-Raman spectroscopy have been used as nondestructive tools to compare the residual strain in InP substrates after femtosecond (fs) and nanosecond (ns) laser processing. Two-dimensional stain distributions with varying probing depth and cross-section images across the four laser machined grooves were obtained. The recrystallized poly-InP layer on the laser machined groove surface has been found to be highly strained in tension, and the stress magnitude is much bigger than the shear stress introduced by crystal distortion underneath. After comparing the simulation results of SXRT orientation contrast with the topography images, the nature of the crystal plane distortion induced by both fs and ns laser machining methods was elucidated.

Comparative analysis of microactuators fabricated by femtosecond and nanosecond laser micromachining

Laser micromachining technology is a cost-effective microfabrication technique for prototyping and in some cases batch production of miniature components and microdevices with complex geometries requiring high accuracy and precision. The objective of this paper is to analyze experimentally the effect of the laser micromachining process and its parameters, particularly, the pulse duration, on the characteristics of the fabricated functional microdevices. This was achieved through the microfabrication of two electro-thermally driven in-plane microactuators using a femtosecond and a nanosecond pulse laser. The dynamic/static performance of the microactuators was compared with respect to the required current/power and generated actuation force/displacement and the geometric quality of the machining.

Rear surface spallation on single-crystal silicon in nanosecond laser micromachining

Rear surface spallation of single-crystal silicon under 5-ns laser pulse ablation at intensities of 0.6–60GW∕cm2 is studied through postablation examination of the ablated samples. The spallation threshold energy and the spallation depth’s dependences on the energy and target thickness are measured. From the linear relation between the spallation threshold energy and the target thickness, an estimation of the material spall strength around 1.4GPa is obtained, in reasonable agreement with the spall strength estimation of 0.8–1.2GPa at a strain rate of 107s−1 using Grady’s model for brittle materials. The experiment reveals the internal fracturing process over an extended zone in silicon, which is controlled by the competition between the shock pressure load and the laser ablation rate. The qualities of the laser microstructuring and micromachining results are greatly improved by using an acoustic impedance matching approach.