Nanoimprint replication of laser-induced ripples for encoder applications

Laser-induced periodic surface structures (LIPSS) offer unique optical properties as dark marking which is applicable for optical encoders, but their direct laser fabrication is costly and slow. This study introduces a cost-effective and scalable alternative: thermal nanoimprint replication of LIPSS onto flexible, metallized polyethylene terephthalate (PET) film. LIPSS were initially fabricated on stainless steel using picosecond laser ablation and then replicated onto aluminum-coated PET film via thermal nanoimprinting at varying temperatures. Atomic force microscopy confirmed successful replication, with optimal fidelity achieved at 180 °C, preserving the ca. 450 nm periodicity of the LIPSS while transferring ripple heights from 114 nm in steel master to 80 nm in PET replica. Reflectance measurements using UV–Vis-NIR spectroscopy and focused laser beam reflection demonstrated significant contrast between rippled and not rippled areas on the PET film, comparable to the steel master and sufficient for optical encoder applications. Frequency domain analysis of focused laser reflectance scans confirmed consistent periodicity in both master and replica. These results demonstrate that thermal nanoimprint is a viable, scalable, and cost-effective technique for replicating LIPSS onto flexible substrates, enabling the production of high-contrast optical encoder scales for various sensing and positioning applications.