Papers by Keyword: Picosecond Laser

Abstract: One of the most important and widely visualized process taking place in nature is condensation. Superhydrophobic surfaces, which facilitates dropwise condensation has been the principal area of research in the last decade or so. Fabrication of superhydrophobic surface can be achieved by either surface modification using mechanical process, surface treatment like coating or by the combination of both. But, the major drawback of coating is its durability and vulnerability. So, in this work we have fabricated a robust surface by means of picosecond laser machining. Apart from being a simple process, this method has an advantage of cutting down the surface fabrication time by several hours as compared to other methods like one-step immersion, electro-deposition, top-down fabrication method, etc. In our work three different work specimens irradiated with different laser power were studied for its surface morphologies by scanning electron microscope (SEM) images and its wettability was measured using contact angle meter. It is found that the wettability of surface changes with different laser power and hence it is possible to control the wettability by adjusting the laser parameters. Condensation experiment was carried out on these different surfaces and its performance was compared with plain surface.

Abstract: Conditioning challenges of superabrasive grinding wheels cause a barrier to the extensive applications of these tools. These concerns are more pronounced in the case of conditioning of metal-bonded superabrasive grinding wheels owing to their high bond hardness. Laser ablation has been used as a promising method for conditioning of such tools. In this research an ultrashort pulsed laser was used for efficient profiling of metal-bonded diamond grinding wheels. In order to assess the laser-profiling technique, the experiments were aimed to generate precise profiles which are rather too difficult or impossible to generate with conventional methods. Convex and concave profiles with minimum radius of about 20 μm and 40 μm, respectively are produced successfully via laser conditioning.

Abstract: A laser drilling technique named the nested-circle method is introduced in this work, in the respect of short-pulse laser processing.it is found that, as the power increases, the depth to diameter ratio of the hole will increase and the minimum number of circles can be set drilled hole reliably is reduced. Further studies have been carried out on the effect of the number of circles in the nested-circle method. Keys of settings the nested-circle method parameters—Outer circle diameter ‘D1’, Inner circle diameter ‘D2’, The Number of circles ‘R’—have been found out.

Abstract: In this paper, the technique of drilling process with picosecond(ps) laser is studiedinAl2O3 ceramics. The defocus method is used to drill the ceramic slice, which is able to improve thedrilling ratio of depth to diameter.It is found out that the best location ofthis ps-laser is about0.15mm under the lower surface of workpiece,demonstrating the difference from nanosecond(ns)-laser machinein the respective ofdefocusing.The impact of the power and the processing speed isinvestigated on the quality of the drilling. For ps-laser machine,a smaller and high qualitythrough-holeis achievable by increasing the power of laser and reducing the speed of process, withthe ratio of depth to diameter from 3.12 to 4.27.The ratio can be further increased upto 6.25,throughoptimization of these three parameters: defocusing amount, laser power and laser processing speed.

Abstract: The laser welding can provide flexible processing, and ultrashort pulsed laser with high pulse repetition rates enabled locally selective welding of monocrystalline silicon and glass with comparable processing performance to anodic bonding method. The 20ps laser pulse of 1060nm was absorbed at monocrystalline silicon through glass plate, and its surface temperature reached its boiling temperature. In addition, it was considered that the absorption of laser energy to glass was occurred, and the temperature of glass increased more than the forming temperature. Thus the convection of silicon and glass was caused by the recoil pressure of evaporation, which led to mild mixture of silicon and glass. This phenomenon produced anchor geometry at the interface between silicon and glass without gap generation. The number of laser shot in the laser spot had an influence on shearing strength of weld joint, and higher shearing strength of weld joint could be performed at proper number of laser shot in the laser spot.

Abstract: Ultra-hard AlMgB₁₄ (30-50 GPa) thin films were deposited on silicon substrate for a nominal thickness of 100 nm using a pulsed excimer laser and then subjected to direct micromachining using a 532 nm, 30 picosecond pulsed Nd:YAG laser. The application is targeted towards synthesizing an artificial nacre material composed of hexagonal bricks and particle bridges of superhard AlMgB₁₄ thin film and mortars of Ti thin film that biomimic the hierarchical architecture of natural nacre. The effects of pulse energy (0.1 to 1 μJ) and laser scanning speed (0.5 to 1.5 m/sec) on ablation depth and quality of scribed channels were evaluated. The morphology of the channels was characterized using confocal microscope and optical profilometer. Results indicated a clean material removal process characterized by absence of heat affected zone, high-speed scribing and small feature size. The energy fluence for the removal of 100 nm thin film without affecting the silicon substrate was 0.3 J/cm². An interesting observation is that particulate matter present in the thin film was not ablated suggesting a size effect. Analysis of thermal transport reveals that the material removal has occurred via spallation and phase explosion mechanisms. The picosecond laser thus offers a high-speed energy source for precisely ablating ultra-hard thin films that in turn will allow the potential for fabrication of novel artificial nacre with exceptional strength and toughness.

Abstract: Elastomeric polymers have been used as moulds for fabricating micro structures in the soft lithography technology due to their elastic features and unstickiness to polymer features. Previously, the micro moulds were normally produced by imprinting on micro prototypes, which are fabricated using deep reactive etching or photolithography. In this paper, we introduce a direct mould fabrication method, which uses pulsed laser drilling technology to directly generate high aspect ratio patterns in elastomeric polymers. The effects of laser parameters such as pulse repetition rate and average power on the drilling qualities are systematically studied. The techniques presented in this paper would provide a more flexible way to fabricate high aspect ratio micro features on elastomer mould efficiently.

Abstract: Detailed studies on the ablation threshold of Mo with picosecond laser pulses are reported in this paper. The laser pulses used for the research were 1064 nm in wave length and 15 ps in pulse duration. Scanning electronic microscope (SEM) and optical surface analyzer were used to analyze the ablation sample, and by analyzing the linear relationship between the squared diameter of ablation crater and pulses energy we obtained the ablation threshold of Mo with single- and multi-pulses. Influence factors of ablation threshold were observed while analyzing machining process. Finally, the shape and topography of holes drilled by percussion with ablation regularity in Mo were studied, which provided an important guidance for the following applications on picosecond micro-machining.

Abstract: The interest in laser material processing of Carbon Fibre Reinforced Plastic (CFRP) over the past few years has increased, especially in the aerospace industry. A number of different laser groups around the world are investigating different laser sources for the express reason of developing a laser material processing centre for machining CFRP for the aerospace and automotive industry. This paper reports on the work of two such groups, in the UK and Germany, who are using fibre laser technology and a diode pumped solid state laser system. The initial results from the two studies are reported and show that these two very different laser systems offer processing capability with respect to machining CFRP.

Abstract: The microstructured samples were prepared by irradiating silicon surface with picosecond laser pulses in SF6. The surface morphology of microstructured samples irradiated at different laser fluence was characterized by SEM. The samples exhibited high optical absorptance over a wide wavelength range between 300 and 2700 nm. The absorptance of samples irradiated with the fluence of 1.0 J/cm² was measured to be up to 95% between 1100 and 2700 nm. The infared absorptance of the surface-structured samples increased with increasing fluence. Whereas, as the annealing temperature was increased, the infared absorptance of the samples irradiated at the same fluence decreased. A tentative explanation for the effects of laser fluence and annealing temperature on the infared absorptance has been proposed based on the formation of mid-band gap impurity bands and the multiple reflections of light between microstructures.