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

Abstract 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.