FOCUS
MANUFACTURING with short pulse lasers
period value reveals that the LSFL have better regularity( smaller ratio R = ΔΛ^ / Λ^) than the HSFL. Generally, the regularity of LIPSS is better, as sharper their peaks in the Fourier domain are, i. e. as smaller R.
The technological potential of LIPSS for functional surface engineering critically depends on how regular and homogeneous these self-organized patterns are. Although many studies have shown how laser parameters, material properties, and optical effects influence LIPSS formation, assessing the quality of the resulting structures has remained a major challenge. The main reason is that suitable routines and software programs for automated evaluation were not available. Instead, evaluations were often performed purely visually or based on partly automated Fourierbased methods. Thus, the subjective influence of the person performing the analysis is a central problem, as the evaluation criteria are defined manually and the complex surface morphologies are usually reduced to a single indicator. This significantly limits the comparability between assessments and slows down systematic process optimisation.
With the introduction of ReguΛarity [ 12 ], a free, fully automated software tool developed specifically to quantify the regularity of LIPSS from microscope images, the transition from subjective, case-specific assessments to a standardised and reproducible description of LIPSS quality has been achieved. Instead of relying on a single metric, several complementary descriptors form a multi-parameter regularity tuple that is used to evaluate LIPSS. This approach considers that LIPSS regularity is multifaceted: highly functional surfaces require not only a precisely defined average period, but also low local period fluctuations, uniform alignment, spatial homogeneity and continuous phase development.
By enabling fast, objective and highthroughput regularity analysis, new perspectives are opening up for LIPSS
Figure 4. LIN of two types of LIPSS( LSFL and HSFL) on titanium featuring different spatial periods, orientations, and regularities. SEM images( left) and two-dimensional Fast Fourier Transforms( 2D-FFT, right). The double-arrows indicate the direction of the linear laser beam polarisation.
research and applications. ReguΛarity supports the data-driven optimisation of laser processes, facilitates comparisons between different materials and laboratories, and lays the foundation for machine learning-assisted design of functional laser-structured surfaces. In this sense, the software represents an important step in transforming LIPSS from a complex physical phenomenon into a reliably machinable surface technology.
CURRENT AND FUTURE TRENDS Currently, several trends are emerging in the field of LIN. One direction concerns the transfer of specific surface functionalities demonstrated in the laboratory into robust industrial and everyday applications. This includes the development of antibacterial surfaces in medical or public settings, or the development of bioactive surfaces that can improve the differentiation or enhanced / reduced growth of certain cells on medical implants. Beyond, nanostructures allow precise control over reflection, transmission, and structural coloration. Such capabilities are relevant for advanced display technologies, improved photovoltaic devices, and high-density optical data storage. The intrinsic irregularity of LIPSS, arising from self-organization processes, further enables the fabrication of non-cloneable security features for product authentication. In tribological systems, LIN can reduce friction and wear under sliding contact, lowering energy consumption and extending the operational lifetime of mechanical components.
A second trend focusses on deepening the fundamental understanding of the underlying processes. Ultrafast laser-matter interactions involve highly non-equilibrium dynamics starting already on fs to ps timescales, where nonlinear optical effects, transient electronic excitation, and rapid phase transitions interplay. Time-resolved experimental techniques are, therefore, increasingly employed to resolve ultrafast carrier dynamics, energy transfer pathways, and the onset of structure formation. In parallel, multi-scale modeling approaches are advancing, combining electrodynamics with molecular dynamics, hydrodynamic and thermomechanical descriptions to capture the coupled evolution of electromagnetic fields, electron-phonon interactions, structural changes, melt flows, pressure waves, and resolidification.
A third trend addresses scaling and manufacturing strategies required for industrial implementation [ 2 ]. Modern UPLs operating at repetition rates of several hundred kHz to several MHz along with fast beam deflection systems, such as high-speed polygon scanners, in combination with adaptive optical elements, enable largearea processing at high throughput. Optical parallelization concepts – employing diffractive optical elements or spatial light modulators – allow the simultaneous generation of multiple structured spots, significantly enhancing productivity. Automated quality assurance through in-situ monitoring and feedback control is becoming increasingly important to ensure process stability and reproducibility
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