Surface-by-Design: From Ultrafast Laser–Matter Interactions to Functional Engineering

Ultrafast laser processing enables the creation of functional surfaces in metals, semiconductors, ceramics, polymers and other materials through spatially controlled nonequilibrium energy deposition. However, the resulting surface functionality cannot be explained solely by laser parameters or geometric features. Femtosecond irradiation induces a sequence of coupled processes, including nanoscale structuring, phase transformation, chemical modification, defect formation, and relaxation, which define the final surface state. This review introduces the Surface-by-Design concept, where functional surfaces are considered as engineered material states formed through controlled laser–matter interaction rather than as predefined patterns. Representative examples including laser-induced periodic surface structures, hierarchical micro/nanotextures, modified oxide layers, and laser-generated functional interfaces are analyzed in relation to wettability, tribological behavior, corrosion resistance, optical response, and other properties. The review further examines how advanced characterization, digital engineering, beam shaping, in situ diagnostics, and data-driven methods contribute to controlling surface evolution. Remaining challenges include reproducibility, scalability, and reliable prediction of functional behavior during service conditions. Future progress in femtosecond laser surface engineering will depend on the ability to control not only the generated morphology but also the evolving structural and physicochemical state of functional interfaces.