Enhancement of material ablation using 248, 308, 532, 1064 nm laser pulse with a water film on the treated surface

Abstract

Many industrial laser processes, such as surface cleaning, require the removal of small thicknesses of matter, often on large samples. An experimental study has been performed in order to characterize and enhance the ablation of materials by means of the interaction between a pulsed laser beam and matter using common industrial laser sources, particularly at 248, 308, 532, and 1064 nm. Ablation was achieved on a static sample with one or several successive pulses and for different energy densities. These parameters enabled us to control the depth of the ablation in the micrometer range. Experiments have been carried out in ambient air, under gaseous cover, and then under a flowing water film on the material surface at atmospheric pressure. The material was a stainless-steel alloy. The experiments made it possible to determine the ablation fluence threshold for each wavelength and the alteration of the surface by the successive laser pulses. In order to avoid oxidation during the process, an argon gaseous medium was used, but peripheral oxide deposits always appeared and the efficiency of the ablation did not seem to increase. However, when the water flow on the surface was employed, the efficiency of the ablation increased by a factor of 2–15 for a certain incident power density. Peripheral oxide redeposition was absent using this method. Experiments have demonstrated that the confinement of the plasma within a transparent layer such as water at the given laser wavelength is an effective method for increasing ablation yield. This technique prevents the expansion of the plasma upstream of the target and the mechanical impulse communicated to the material increases. Calculation of ablated mass confirms that ablation yield could be increased by 15 for higher power densities. Similar results have been found using other materials such as alumina or silica. This means that this ablation technique can be employed in various types of industrial laser applications, for example, for cleaning oxidized surfaces or removing paint coatings.

Laser Beam Machining, Laser Beam Hybrid Machining, and Micro-channels Applications and Fabrication Techniques

“…[175] the authors used a 248 nm wavelength KrF excimer laser to ablate Si wafer under water thickness of 1 mm and reported the similar results. Likewise, the high ablation rate validations can be found in [160] for stainless steel, alumina, silica and in [166] for glass, stainless steel and polymers with steady results. …”

“…On the other hand, as the energy absorbance depends on the material wavelength, therefore, the selection of incident laser wavelength, preferably, be such that it should strongly be absorbed by the target matter rather than water film. Based on this statement, Dupont et al [160] claimed that a high ablation rate (2-15 times) for high laser intensities can be achieved if the laser wavelength is chosen in accordance with work material's wavelength. It has been proven that the energy absorbance does not depend on the layer thickness but the incident light wavelength.…”

“…This explosive evaporation of water molecules generates forces between substrate and the suspended melt particles. These forces are generally larger than adhesion forces thus propel the melt particles off the surface of the material [160]. Thus the mechanism changes from thermal phenomena in air to a more mechanical in water.…”

Experimental study on femtosecond laser micromachining of grooves in stainless steel

“…High aspect ratio grooves are difficult to machine mostly due to obstruction for plasma plume expansion and accordingly material removal, which then tends to stick to sidewalls. It is proposed that depending on laser parameters irradiated liquids can experience formation of the shock wave, vapour expansion, cavitations, and breakdown [30,32]. All these phenomena primarily result in disturbance of incident beam, increased laser power losses, and irregularities of machining, although values for surface roughness and cleanliness can be enhanced.…”

“…There has been done various experimental research with liquid assistance for laser machining [29][30][31]. This has motivated laser steam cleaning for the machining of rectangular grooves in steel to be examined.…”