scholarly journals Influence of Sulphur Content on Structuring Dynamics during Nanosecond Pulsed Direct Laser Interference Patterning

Nanomaterials ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 855
Author(s):  
Theresa Jähnig ◽  
Cornelius Demuth ◽  
Andrés Fabián Lasagni
Keyword(s):  
Sulphur Content ◽  
Surface Tension Gradient ◽  
Laser Interference ◽  
Surface Active Element ◽  
Direct Laser ◽  
Particle Hydrodynamics ◽  
Sph Model ◽  
Surface Active ◽  
Melt Penetration ◽  
Direct Laser Interference Patterning

The formation of melt and its spread in materials is the focus of many high temperature processes, for example, in laser welding and cutting. Surface active elements alter the surface tension gradient and therefore influence melt penetration depth and pool width. This study describes the application of direct laser interference patterning (DLIP) for structuring steel surfaces with diverse contents of the surface active element sulphur, which affects the melt convection pattern and the pool shape during the process. The laser fluence used is varied to analyse the different topographic features that can be produced depending on the absorbed laser intensity and the sulphur concentration. The results show that single peak geometries can be produced on substrates with sulphur contents lower than 300 ppm, while structures with split peaks form on higher sulphur content steels. The peak formation is explained using related conceptions of thermocapillary convection in weld pools. Numerical simulations based on a smoothed particle hydrodynamics (SPH) model are employed to further investigate the influence of the sulphur content in steel on the melt pool convection during nanosecond single-pulsed DLIP.

scholarly journals An Incompressible Smoothed Particle Hydrodynamics (ISPH) Model of Direct Laser Interference Patterning

Computation ◽  
2020 ◽  
Vol 8 (1) ◽  
pp. 9
Author(s):  
Cornelius Demuth ◽  
Andrés Fabián Lasagni
Keyword(s):  
Stainless Steel ◽  
Smoothed Particle Hydrodynamics ◽  
Shear Stresses ◽  
Laser Interference ◽  
Melt Pool ◽  
Direct Laser ◽  
Particle Hydrodynamics ◽  
Smoothed Particle ◽  
Periodic Microstructures ◽  
Direct Laser Interference Patterning

Functional surfaces characterised by periodic microstructures are sought in numerous technological applications. Direct laser interference patterning (DLIP) is a technique that allows the fabrication of microscopic periodic features on different materials, e.g., metals. The mechanisms effective during nanosecond pulsed DLIP of metal surfaces are not yet fully understood. In the present investigation, the heat transfer and fluid flow occurring in the metal substrate during the DLIP process are simulated using a smoothed particle hydrodynamics (SPH) methodology. The melt pool convection, driven by surface tension gradients constituting shear stresses according to the Marangoni boundary condition, is solved by an incompressible SPH (ISPH) method. The DLIP simulations reveal a distinct behaviour of the considered substrate materials stainless steel and high-purity aluminium. In particular, the aluminium substrate exhibits a considerably deeper melt pool and remarkable velocity magnitudes of the thermocapillary flow during the patterning process. On the other hand, convection is less pronounced in the processing of stainless steel, whereas the surface temperature is consistently higher. Marangoni convection is therefore a conceivable effective mechanism in the structuring of aluminium at moderate fluences. The different character of the melt pool flow during DLIP of stainless steel and aluminium is confirmed by experimental observations.

In-Depth Investigation of Copper Surface Chemistry Modification by Ultrashort Pulsed Direct Laser Interference Patterning

Langmuir ◽  
2020 ◽  
Vol 36 (45) ◽  
pp. 13415-13425 ◽  
Author(s):  
Daniel W. Müller ◽  
Anne Holtsch ◽  
Sarah Lößlein ◽  
Christoph Pauly ◽  
Christian Spengler ◽  
...  
Keyword(s):  
Surface Chemistry ◽  
Copper Surface ◽  
Laser Interference ◽  
Direct Laser ◽  
Surface Chemistry Modification ◽  
Direct Laser Interference Patterning

scholarly journals Direct Laser Interference Patterning of Diffraction Gratings in Safrofilcon-A Hydrogel: Fabrication and Hydration Assessment

Polymers ◽  
2021 ◽  
Vol 13 (5) ◽  
pp. 679
Author(s):  
Daniel Sola ◽  
Stephan Milles ◽  
Andrés F. Lasagni
Keyword(s):  
Laser Fluence ◽  
Contact Lenses ◽  
Laser Source ◽  
Spatial Period ◽  
Laser Interference ◽  
Periodic Patterns ◽  
Hydration Properties ◽  
Water Contact ◽  
Direct Laser ◽  
Direct Laser Interference Patterning

Refractive index modification by laser micro-structuration of diffractive optical devices in ophthalmic polymers has recently been applied for refractive correction in the fields of optics and ophthalmology. In this work, Safrofilcon-A hydrogel, used as soft contact lenses, was processed by direct laser interference patterning (DLIP) to fabricate linear periodic patterns on the surface of the samples. Periodic modulation of the surface was attained under two-beam interference by using a Q-switched laser source with emission at 263 nm and 4 ns pulse duration. Features of processed areas were studied as a function of both the interference spatial period and the laser fluence. Optical confocal microscopy used to evaluate the topography of the processed samples showed that both structured height and surface roughness increased with laser fluence. Static water contact angle (WCA) measurements were carried out with deionized water droplets on the structured areas to evaluate the hydration properties of DLIP structures. It was observed that the laser structured areas induced a delay in the hydration process. Finally, microstructural changes induced in the structured areas were assessed by confocal micro-Raman spectroscopy showing that at low laser fluences the polymer structure remained almost unaltered. In addition, Raman spectra of hydrated samples recovered the original shape of areas structured at low laser fluence.

scholarly journals Improving Throughput and Microstructure Uniformity in Direct Laser Interference Patterning Utilizing Top-Hat Shaped Beams

2021 ◽  
Author(s):  
Mikhael El-Khoury ◽  
Bogdan Voisiat ◽  
Tim Kunze ◽  
Andrés Fabián Lasagni
Keyword(s):  
Intensity Distribution ◽  
Laser Interference ◽  
Gaussian Laser Beam ◽  
Laser Beam Intensity ◽  
Direct Laser ◽  
Standard Configuration ◽  
Laser Sources ◽  
Periodic Microstructures ◽  
Direct Laser Interference Patterning ◽  
The Impact

Abstract Uniform periodic microstructures formation over large areas is generally challenging in Direct Laser Interference Patterning (DLIP) due to the Gaussian laser beam intensity distribution inherent to most commercial laser sources. In this work, a diffractive fundamental beam-mode shaper (FBS) element is implemented in a four-beam DLIP optical setup to generate a square-shaped top-hat intensity distribution in the interference volume. The interference patterns produced by a standard configuration and the developed setup are measured and compared. In particular, the impact of both laser intensity distributions on process throughput as well as fill-factor is investigated by measuring the resulting microstructure height with height error over the structured surface. It is demonstrated that by utilizing top-hat-shaped interference patterns, it is possible to produce on average 44.8 % deeper structures with up to 60 % higher homogeneity at the same throughput. Moreover, the presented approach allows the production of microstructures with comparable height and homogeneity compared to the Gaussian intensity distribution with increased throughput of 53%.

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