Formation of Laser-Induced Periodic Surface Structures and Ablation Patterns in Different Atmospheres on Porous Nickel by Ultrashort Laser Pulses

Controllable laser structuring of porous metallic materials demands a parameter-resolved understanding of morphology formation within complex fibrous geometries. In this work, nickel felts were structured using a 193 fs ultrashort-pulse laser at a wavelength of 1030 nm and a repetition rate of 100 kHz under air, argon, and water. Two dominant morphology regimes were identified, namely interference-driven LIPSS and ablation-dominated irregular nanostructuring, with a clear transition controlled by increasing line energy through higher fluence and lower scan speed. LIPSS were dominant at higher scan speeds and showed periodicities of about 600 to 800 nm, while decreasing scan speed promoted redeposition rich ablation morphologies and, in air, strong oxidation, and local fiber damage at high fluence. Within an optimized parameter window, the local fiber surface area was increased up to ninefold relative to the unprocessed reference area. Raman spectra of the laser-modified surfaces show bands of Ni-O compounds, which exhibit atmosphere- and fluence-dependent interactions. This manuscript demonstrates that ultrashort-pulse laser processing can be used for targeted interfacial design on porous nickel felts, extending laser nanostructuring concepts beyond well-studied planar metals to complex porous networks. The work links scan speed and fluence to the transition from LIPSS to ablation-dominated morphologies, quantifies local fiber surface-area enhancement up to ~9× while preserving felt integrity, and correlates morphology with atmosphere-dependent NiOx development by Raman spectroscopy. By combining porous geometry, processing atmosphere (air, argon, water), surface-area metrics, and Raman chemistry, the study provides a state-of-the-art framework for scalable laser functionalization of porous metallic materials.