Laser-induced microjet-assisted ablation for high-quality microfabrication

Abstract

Liquid-assisted laser ablation has the advantage of relieving thermal effects of common laser ablation processes, whereas the light scattering and shielding effects by laser-induced cavitation bubbles, suspended debris, and turbulent liquid flow generally deteriorate laser beam transmission stability, leading to low energy efficiency and poor surface quality. Here, we report that a continuous and directional high-speed microjet will form in the laser ablation zone if laser-induced primary cavitation bubbles asymmetrically collapse sequentially near the air-liquid interface under a critical thin liquid layer. The laser-induced microjet can instantaneously and directionally remove secondary bubbles and ablation debris around the laser ablation region, and thus a very stable material removal process can be obtained. The shadowgraphs of high-speed camera reveal that the average speed of laser-induced continuous microjet can be as high as 1.1 m/s in its initial 500 μm displacement. The coupling effect of laser ablation, mechanical impact along with the collapse of cavitation bubbles and flushing of high-speed microjet helps achieve a high material removal rate and significantly improved surface quality. We name this uncovered liquid-assisted laser ablation process as laser-induced microjet-assisted ablation (LIMJAA) based on its unique characteristics. High-quality microgrooves with a large depth-to-width ratio of 5.2 are obtained by LIMJAA with a single-pass laser scanning process in our experiments. LIMJAA is capable of machining various types of difficult-to-process materials with high-quality arrays of micro-channels, square and circle microscale through-holes. The results and disclosed mechanisms in our work provide a deep understanding of the role of laser-induced microjet in improving the processing quality of liquid-assisted laser micromachining.

Bridging the Gap between Invasive and Noninvasive Medical Care: Emerging Microneedle Approaches

“…The steps are generally laser engraving of the desired structure directly on metal and polymer materials, followed by selective plating and then corrosion removal of the original base material. 40 The disadvantage of this method is the laser cutting, the flat shape of the microneedle body, and the rough surface of the microneedle as well as the limited length of the microneedle that can be processed due to the focal length of the laser. As a result, the microneedles are often used to prepare solid microneedles, resulting in a flattened microaperture in the skin during drug delivery, which closes easily and seriously affects the efficiency of drug delivery.…”

“…Laser ablation incorporates the use of a focused optical light beam to eliminate material from a substrate and create MNAs. The steps are generally laser engraving of the desired structure directly on metal and polymer materials, followed by selective plating and then corrosion removal of the original base material . The disadvantage of this method is the laser cutting, the flat shape of the microneedle body, and the rough surface of the microneedle as well as the limited length of the microneedle that can be processed due to the focal length of the laser.…”

Femtosecond Laser Fabrication of Microchannels in Transparent Hard Materials

“…The laser‐induced microjet‐assisted ablation method invented by Guo et al. [ 50 ] is very novel. A superior quality microgroove with a depth‐to‐width ratio of 5.2 was successfully fabricated on the SiC surface with few impurities and low roughness.…”

“…However, it is difficult to obtain higher quality microgrooves with only a single method, so many new processing methods have appeared recently. The laser-induced microjet-assisted ablation method invented by Guo et al [50] is very novel. A superior quality microgroove with a depth-to-width ratio of 5.2 was successfully fabricated on the SiC surface with few impurities and low roughness.…”

Patterned Laser Ablation of Microgrooves with Controllable Cross‐Sections

“…The continuous microjet will instantaneously take ablation debris and secondary bubbles away from the ablation area, making the patterned laser ablation process much more stable. [33] Figure 1b,c shows the experimental comparison between laser micromachining in air and LIMJAA in a thin liquid film, where an asymmetrical triangular laser spot is conducted for ablation. The cross-sectional profile of the microgroove ablated in air is close to a parabolic shape instead of desired asymmetrical triangular.…”