Results of the work in the Laser4Fun project has been published as:

J. T. Cardoso, A. Garcia-Girón, J. M. Romano, D. Huerta-Murillo, R. Jagdheesh, M. Walker, S. S. Dimov and J. L. Ocaña Influence of ambient conditions on the evolution of wettability properties of an IR-, ns-laser textured aluminium alloy. RSC Advances, 63, 2017

Abstract

Micro cell structures of different sizes were patterned using a nanosecond near-infrared laser source on Al2024 aluminium alloy plates with 2 mm thickness. The influence of laser parameters on the shape and size of the produced patterns were studied together with the evolution of wettability properties over time for different storage conditions. Samples were found to be superhydrophobic from a single step laser patterning, requiring no further treatment. Exposure to ambient air was shown to be a key factor in the property changes of the samples over time. The produced surface patterns with different laser parameter settings were correlated with the contact angle measurements, revealing a great influence of the amount of recast material on the hydrophobic properties. X-Ray photoelectron spectroscopy was used to study the impact of surface chemistry changes on hydrophobicity, analysis of elemental composition proved that chemisorbed organic molecules present in the ambient air were responsible for the hydrophilic to superhydrophobic transition.

Link(s)

• http://pubs.rsc.org/en/Content/ArticleLanding/2017/RA/C7RA07421B
• doi.org/10.1039/C7RA07421B

Results of the work in the Laser4Fun project has been published as:

Fotis Fraggelakis, Girolamo Mincuzzi, John Lopez, Inka Manek-Hönninger, and Rainer Kling. Texturing metal surface with MHz ultra-short laser pulses. Optics Express 25(15), pp. 18131-18139, 2017

Abstract

We show, for the first time to our knowledge, the role the heat accumulation plays on the evolution of ultra-short pulse laser-induced surface structures morphology when varying fluence, the number of scans and the repetition rate from 100 kHz up to 2 MHz. We demonstrate how to tailor the size of micro-spikes from nearly ten microns to several tens of microns by a systematic variation of both fluence and overlap. We believe our results will contribute to an in deep understanding of the mechanisms underlying laser surface structuration at high repetition rates.

Link(s)

• https://doi.org/10.1364/OE.25.018131

Results of the work in the Laser4Fun project has been published as:

F. Fraggelakis, G. Mincuzzi, J. Lopez, I. Manek-Hönninger and R. Kling, “Controlling laser-induced features morphology on stainless steel surfaces using high average power femtosecond laser,” 2017 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), Munich, 2017, pp. 1-1.

Abstract

Ultra-short pulse (USP) Laser Induced Periodic Surface Structures (LIPSS) namely ripples, micro-grooves and spikes [1] have received considerable attention since they can modify some key surface properties like wettability, colour and tribology, increasing the material’s internal value [2]. Nevertheless, the complete understanding of the physical mechanisms leading to LIPSS formation is still under debate. Even so, at repetition rate values as high as several kHz, the fluence Φ and the overall energy irradiated over a unit surface (dose) have been identified as the physical parameters playing a major role in the structures generation process [3][4][5].
However, for a fixed Φ value, in correspondence of repetition rate as high as few MHz, the same dose value could enable the creation of surface structures having different morphologies depending on the process strategy. In fact, the latter, i.e. the combination of pulses overlap and number of scans corresponding to a given dose value has a huge bearing to determine the heat accumulated during the process which in turn will determine the final structure morphology.[6]
Here, for the first time, we report a systematic study on the influence of a comprehensive set of process parameters like Φ, pulses overlap, number of scans and cumulative dose on the induced structure over stainless steel surface for two different wavelengths and high repetition rate. An industrial USP laser (τp< 350 fs) of high power (up to 20 W) operating at a repetition rate up to 1 MHz, emitting in the near infrared at λ = 1030 nm and at λ=515 nm by second harmonic generation was used to carry out the experiment. By comparing the results for two different repetition rates (100 kHz and 1 MHz), we aim to push more in deep the understanding of the physical mechanism that leads to spike creation by verifying the role of the inter-pulse delay in heat accumulation. For both wavelengths, we demonstrate the transition from ripples to conical formation underlining the presence of groove formation as an intermediate step. Interestingly, for the first time, we demonstrate the possibility to finely tune the feature size in the case of 1 MHz. In fact, by varying the fluence between 0.22 J/cm2 and 0.65 J/cm2 feature sizes comprised between 8.3 μm ± 3 μm and 36 μm ± 10 μm. Finally, by comparing the results obtained with several Φ values we propose an effective strategy not only to overcome the heat accumulation issue in the formation of the structures, but also for scaling up the process.

References

[1] H. M. Van Driel, J. E. Sipe, and J. F. Young, “Laser-induced periodic surface structure on solids: A universal phenomenon,” Phys. Rev. Lett., vol. 49, no. 26, pp. 1955–1958, 1982.

[2] A. Y. Vorobyev and C. L. Guo, “Optical and Wetting Properties of Femtosecond Laser Nanostructured Materials,” J. Nano Res., vol. 14, pp. 57–67, 2011.

[3] G. Mincuzzi, L. Gemini, M. Faucon, and R. Kling, “Extending ultra-short pulse laser texturing over large area,” Appl. Surf. Sci., vol. 386, pp. 65–71, 2016.

[4] M. Faucon, A. Laffitte, J. Lopez, and R. Kling, “Surface blackening by laser texturing with high repetition rate femtosecond laser up to 1MHz,” Proc. SPIE, vol. 8972, no. February, p. 89721M, 2014.

[5] O. Varlamova, M. Bounhalli, and J. Reif, “Influence of irradiation dose on laser-induced surface nanostructures on silicon,” Appl. Surf. Sci., vol. 278, pp. 62–66, 2013.

[6] D.-H. Kam, J. Kim, L. Song, and J. Mazumder, “Formation mechanism of micro-spikes on AISI 4340 steel with femtosecond laser pulses at near-threshold fluence,” J. Micromechanics Microengineering, vol. 25, no. 4, p. 045007, 2015.

Link(s)

• http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=8087253&isnumber=8086161

Results of the work in the Laser4Fun project has been published as:

D. Huerta-Murillo, A.I. Aguilar-Morales, S. Alamri, J.T. Cardoso, R. Jagdheesh, A.F. Lasagni and J.L. Ocaña. Fabrication of multi-scale periodic surface structures on Ti-6Al-4V by direct laser writing and direct laser interference patterning for modified wettability applications. Optics and Lasers in Engineering, 98, 2017.

Abstract

In this work, hierarchical surface patterns fabricated on Ti-6Al-4V alloy combining two laser micro-machining techniques are presented. The used technologies are based on nanosecond Direct Laser Writing and picosecond Direct Laser Interference Patterning. Squared shape micro-cells with different hatch distances were produced by Direct Laser Writing with depths values in the micro-scale, forming a well-defined closed packet. Subsequently, cross-like periodic patterns were fabricated by means of Direct Laser Interference Patterning using a two-beam configuration, generating a dual-scale periodic surface structure in both micro- and nano-scale due to the formation of Laser-Induced Periodic Surface Structure after the picosecond process. As a result a triple hierarchical periodic surface structure was generated. The surface morphology of the irradiated area was characterized with scanning electron microscopy and confocal microscopy. Additionally, static contact angle measurements were made to analyze the wettability behavior of the structures, showing a hydrophobic behavior for the hierarchical structures.

Link(s)

• http://www.sciencedirect.com/science/article/pii/S0143816617305766