Abstract
Direct laser Interference Patterning (DLIP) with ultrashort laser pulses (ULP) represents a precise and fast technique to produce tailored periodic sub-micrometer structures on various materials. In this work, an experimental and theoretical approach is presented to investigate the previously unexplored fundamental mechanisms for the formation of unprecedented laser-induced topographies on stainless steel following proper combinations of DLIP with ULP. DLIP is aimed to determine the initial conditions of the laser-matter interaction by defining an ablated region while double ULP are used to control the reorganisation of the self-assembled laser induced sub-micrometer sized structures by exploiting the interplay of different absorption and excitation levels coupled with the melt hydrodynamics induced by the first of the double pulses. A multiscale physical model is presented to correlate the interference period, polarization orientation and number of incident pulses with the induced morphologies. Special emphasis is given to electron excitation, relaxation processes and hydrodynamical effects that are crucial to the production of complex morphologies. Results are expected to derive new knowledge of laser-matter interaction in combined DLIP and ULP conditions and enable enhanced fabrication capabilities of complex hierarchical sub-micrometer sized structures for a variety of applications.
Highlights
Laser surface processing has emerged as a fast, chemicalfree technology for surface functionalization
The impact of the Double Pulse (DP) and the fact that the second constituent pulse of DP irradiates molten material, simulations results show [70] that the first of the two pulses for number of pulses (NP)=1 leads to a maximum depression of the surface equal to ~24 nm due to ablation; By contrast, as the second of DP irradiates a material in molten phase and given the significantly reduced reflectivity of the fluid [70], the energy which is absorbed is enhanced which subsequently leads to accumulative ablated region equal to ~34 nm
An improved theoretical model can lead to a finer control of feature modulation. Despite these limitations that can be the objective of a future work, the present study demonstrates the capability to control laser matter interaction through tailoring the coupling of DP and DLIP characteristic parameters to enable a novel surface engineering tool for advanced laser processing applications)
Summary
Laser surface processing has emerged as a fast, chemicalfree technology for surface functionalization. The use of femtosecond (fs) pulsed laser sources for material processing and associated laser driven physical phenomena have received considerable attention due to the important technological applications [1,2,3,4,5,6]. These abundant applications require a precise knowledge of the fundamentals of laser interaction with the target material for enhanced controllability of the resulting modification of the irradiated target. The features of the induced periodic structures are related to the laser parameters while a series of multiscale phenomena such as energy absorption, excitation, relaxation phenomena, phase transitions and melt fluid dynamics upon resolidification determine the final relief
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