Generation of Bessel-beam arrays for parallel fabrication in two-photon polymerization

Microfabrication based on two-photon polymerization (TPP) is typically achieved by scanning a focal spot point-by-point. This is a type of serial processing that significantly limits fabrication speed. Bessel beams known for their nondiffracting property are suitable for the fabrication of high-aspect-ratio microstructures without scanning the beams. The zero-order Bessel beam generated by an axicon or a spatial light modulator (SLM) has been used to fabricate such structures as polymer fibers with an aspect ratio exceeding 500:1. However, the fabrication speed is still limited by the serial exposure of a single Bessel beam. In this paper, the authors explore a method for parallel fabrication of high-aspect-ratio microstructures using an array of high-order Bessel beams. An optics system is built in which high-order and superposed high-order Bessel beams generated by an SLM are demagnified and relayed to the photopolymer. These beams retain the same nondiffracting property as the zero-order beam while expanding the exposure light field to arrays of beams. Beam profiles are characterized and compared with theoretical predictions. The power efficiency of the system is measured and analyzed. The influence of off-axis illumination on the SLM is studied. Combined with suitable photopolymer and exposure parameters, this method could be useful for high-speed, volumetric fabrication in TPP.