Acousto-optofluidics for high-throughput laser processing (Conference Presentation)

The inherent flexibility of laser direct writing (LDW) systems is compromised by its sequential nature and consequent sacrifice in throughput. Efforts to address this use include simultaneous multi-spot processing or the generation of multi-beam interference patterns. However, these approaches are normally limited to patterning arrayed features or uniformly distributed aperiodic patterns. Even if changing the number of beams or the angles between them enables to control the distribution and periodicity of the patterns, this task typically involves the mechanical displacement of a focusing lens or the displacement of several optical elements. Other beam shaping methods, such as a spatial light modulator, offer unparalleled flexibility, but their limited refresh rate precludes the fast control of patterns. Here, we explore the unique interactions between sound, liquids, and light to split a laser beam at microsecond timescales. By using the acoustic standing waves generated in a resonant cavity filled with a liquid, we are able to split a beam into multiple spots along two orthogonal directions, namely the X and Y axis. Notably, no Doppler shifting occurs between the diffracted beams. Thus, blocking the zeroth diffraction order can be used to generate multi-beam interference patterns, with a geometry that can be user-selected by adjusting the frequency of the acoustic wave. We provide a theoretical foundation of the working principle of our acousto-optic approach, which is in good agreement with experiments, and demonstrate the myriad of possibilities it offers by laser fabrication of patterns in both subtractive as well as additive modalities.