Abstract
Micromachining of 1 mm thick dielectric and metallic substrates was conducted using femtosecond pulse generated filaments in water. Several hundred microjoule energy pulses were focused within a water layer covering the samples. Within this water layer, non-linear self-action mechanisms transform the beam, which enables higher quality and throughput micromachining results compared to focusing in air. Evidence of beam transformation into multiple light filaments is presented along with theoretical modeling results. In addition, multiparametric optimization of the fabrication process was performed using statistical methods and certain acquired dependencies are further explained and tested using laser shadowgraphy. We demonstrate that this micromachining process exhibits complicated dynamics within the water layer, which are influenced by the chosen parameters.
Highlights
Laser micromachining is a unique tool that has been studied for more than several decades [1]
This agreement among theoretical and experimental results demonstrates that self-actions are important when drilling materials more than 1 mm thick, since the energy distribution differs gradually in comparison to conventional focusing in air
In this study, we have presented results from a high-energy femtosecond pulse focusing within a water layer that is covering the samples
Summary
Laser micromachining is a unique tool that has been studied for more than several decades [1]. In the case of pulse propagation in transparent media, additional effects come into play: beam self-actions may lead to significant intensity profile transformations and multifilamentation [4] that affect experimental outcomes (modified shape, length, quality of micromachined grooves [5]) Such laser systems present the ability to perform a substantially higher number of micromachining tasks and are invariant to the type of material; in addition, the active non-linear phenomena provide additional degrees of freedom when optimization or delicate tailoring procedures are required. We demonstrate that the addition of a thin water layer on top of the samples results in superior micromachining quality and throughput due to additional spatial shaping of ultrashort pulses, cooling and the cleaning properties of the covering fluid This suggested approach is advantageous in various ways: e.g., axial translation is not required while several-millimeter deep structures can be fabricated, and additional cooling is provided due to the added water layer, which prevents temperature and tensile stress gradient formation. We introduced a shadowgraphic imaging system that helps explain acquired dependencies
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