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

Abstract

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.

Nanosecond Laser Fabrication of Dammann Grating-like Structure on Glass for Bessel-Beam Array Generation

“…The FWHM central core and non-diffracting length of zero-order Bessel beams in both isolated and array formats were 0.9 µm and 220 µm, respectively. There are several beam-array configurations reported in the literature [17][18][19][20]. The present study deals with the generation of diverging Bessel beam array configurations.…”

“…Indeed, they have obtained arrayed zero-order Bessel beams of 7.6 µm full width half maxima (FWHM) central core and successfully drilled 5 µm diameter holes on aluminium foil using such beams. Using a spatial light modulator, Cheng et al [18] have exploited the superposition of high-order Bessel beams to obtain tightly packed foci, retaining the non-diffractive length of 1 mm, and resembling an array of zero-order Bessel beams. Schwarz et al [19] have generated an array of parallel zero-order Bessel beams using fused silica axicon lenslets in hexagonal arrangements by exploiting laser manufacturing techniques.…”

A conceptual review on Bessel beams

“…In the presence of two-photon polymerization, flexible fabrication of flowerlike microstructures and micro-tubes with slits are created by illuminating the material with superposed higher order BBs [346]. Further, multiple photo-polymerization structures can be created in a single shot by using a BB array [347].…”

Combination of an axicon and a spatial light modulator for the generation of multiBessel beams for microdrilling using ultrashort pulsed laser

“…Spatial light modulators are variable optical elements that can be used for a variety of beam shaping applications, such as spherical aberration correction 24 and multi-spot material processing 25 . Multi-Bessel beam generation using a SLM is also possible by combining an axicon phase mask and a beam splitting function [26][27][28] . The period length of the axicon function determines the transmitted angle, with a reduced period resulting in a larger angle, but at the same time the diffraction efficiency decreases significantly above a certain threshold.…”