Surface engineering is considered as an essential technology for many key industry sectors, e.g. automotive industry, green energy and life science. It is also connected to a variety of social themes of the 21st century like climate, energy, mobility and healthcare. In order to meet the technical requirements to succeed in a specific market, it is necessary to develop and establish new manufacturing processes to produce smaller geometric structures on large areas.
The interference of two or more coherent laser beams can be applied to produce periodic grooves, grids or dimples with pitches in the micrometer and sub-micrometer range on a variety of materials, such as metals, polymers and thin metallic films. This technique is called direct laser interference patterning (DLIP).
For nanosecond laser pulses, the primary material removal mechanism is ablation but substantial melting occurs for metallic materials. The periodic structure can be obtained only if the material at the minima positions remains thermally unaffected, a process which is controlled by FOURIER’S law of heat conduction. Thus, the minimum achievable spatial period is limited by the thermal diffusion length, which is approximately 1 µm for stainless steel and titanium, and 2 µm for copper.
When the laser pulse duration reduces to the order of picosecond or femtosecond, little thermal damage is observed and consequently feature sizes in the sub-micron range are feasible. DLIP with laser pulses < 100 ps offers therefore the possibility to fabricate precisely defined surface topographies with spatial periods bellow 1 µm.
In this study, sub-micron periodic surface pattern on stainless steel, titanium and copper are fabricated using ps-DLIP as a simple and versatile laser technique. The experimental results are compared to thermal simulations based on the two-temperature model.