Flexible Gray-Scale Surface Patterning Through Spatiotemporal-Interference-Based Femtosecond Laser Shaping

The function of a laser-shaped material depends on the geometrical morphology of its laser-induced surface structures, which is mainly determined by the spatial intensity distribution of the laser. However, conventional patterning methods based on laser shaping techniques have shortcomings in efficiency or flexibility. A novel patterning method is developed in the present study for mask-free and flexible fabrication of surface structures through a time-saving spatiotemporal-interference-based femtosecond laser shaping technique that is based on a Michelson interferometer. The phase-difference distribution is controlled by a spatial light modulator so that the interference intensity distribution can be modulated to user-designed shapes. The congruence between the interference intensity distribution and the geometries on phase holograms enables the generation of phase holograms without complicated algorithms and time-consuming calculations. This uniquely simple technique realizes flexible gray-scale patterning on bulk material surfaces with a single femtosecond laser pulse. Thus, by using the on-the-fly technique, fabrication of large-area surface structures is realized. Moreover, this technique is applied to fabricate complex structures through splicing. As an application example, three types of terahertz filters, including band-stop and band-pass filters, are fabricated successfully; their transmittance is in good agreement with the finite-difference time-domain simulation results.