Uniform LIPSS on copper created using zeroth-order femtosecond Bessel beam for SERS-based applications

We present results from the studies on the generation of laser-induced periodic surface structures (LIPSS) during the interaction of femtosecond (fs) amplifier pulses (1 kHz, 800 nm) with a copper target in the form of a non-diffracting, propagation invariant, zeroth-order Bessel beam. We performed laser ablation in the air (LAA) with the focused, axicongenerated Bessel beam (~50 fs). We have investigated the novel, highly uniform, large-area, ladder-step-like nanostructures formed through laser-matter interaction. The target material used was copper (Cu) and the experimental process involved imprinting the beam profile on a single spot of the Cu surface, followed by overlapping two ablation zones (achieved through scanning the sample). Nanoscale topographical developments were extensively characterised using field emission scanning electron microscopy (FESEM). The investigation focused primarily on the central lobe ablated region and concentric rings-ablated exciting patterns. Remarkably, the raster scan ablation created ladder-like periodic surface structures with sub-15 nm spherical and aspherical nano growths. Energy dispersive X-ray (EDX) mapping confirmed the elemental distribution and surface oxidation in the engineered areas. Subsequently, the laser-engineered plasmonic surface was engaged as a surface-enhanced Raman scattering (SERS) substrate to detect traces of secondary explosives [e.g., Tetryl (TL) - 2,4,6-Trinitrophenylmethylnitramine and pentaerythritol tetranitrate (PETN)] in real-time. The obtained SERS spectra of TL and PETN unveiled signature Raman modes/peaks at 1357 cm⁻¹ and 1292 cm¹, with the lowest possible detectable traces of 5 µM and 1 mM concentrations, respectively. © The author(s).