Researchers from the University of Science and Technology of China (USTC) have developed a powerful strategy for machining chiral microstructures in isotropic material in 3D modulated light fields, which are produced by coaxial interference of a vortex beam and a plane wave. The paper entitled “Three-dimensional chiral microstructure fabricated by structured optical vortices in isotropic material” was published in a world top journal Light: Science & Application. [6, e17011 (2017); doi:10.1038/lsa.2017.11] 

Unlike common beam, optical vortices are a kind of structured beam with helical phase wavefronts and ‘doughnut’ shape intensity distribution. As the earth rotates around the sun, the photons in the optical vortex revolve around the optical axis and carry orbital angular momentum. There are many helical structures in nature such as DNA, tendrils and spring which all have chirality. Since chiral structure of micro scale has special optical properties, it has essential significance in the research of circular dichroism and optical rotatory dispersion. However, the efficiency of the process of chiral structure of micro/nano scale is still a challenging task. And it has become a hot topic in the field of international laser processing to make use of the orbital rotation of orbital angular momentum to process chiral structures. As demonstrated in recent studies, optical vortices have been contributed to achieve complex chiral structures. But in isotropic polymer, the fabricated microstructures are typically confined to non-chiral cylindrical geometry due to 2D “doughnut" intensity profile of optical vortices.

 

Figure 1. Holographic generation of 3D spiral optical field by coaxial interference of vortex beam and a plane wave. (Image by WU Dong & HU Yanlei )

Here, the researchers developed coaxial interference of a vortex beam and a plane wave, which produces 3D optical fields. This coaxial interference beams were creatively produced by designing the contrivable holograms consisting of azimuthal phase and equiphase loaded on liquid-crystal spatial light modulator. Then, in isotropic polymer, 3D chiral microstructures were achieved under illumination of the coaxial interference femtosecond laser beams with their chirality controlled by the topological charge. Their further investigation revealed that spiral lobes and chirality were caused by the interfering patterns and helical phase wavefronts, respectively. The technique, which produced the 3D chiral microstructure, is able to control the number and direction of torsion beam with ~100nm precision. This quick, stable, easy optical modulation technique is expected to work in optical tweezers, optical communications and fast metamaterials fabrication when it

 

Figure 2. SLM-based experimental set-up for 3D chiral microstructures in isotropic material (Image by WU Dong & HU Yanlei )

In addition, CAS Key Laboratory of Mechanical Behavior and Design of Materials has been engaged in the field of holographic optical modulation with ultrafast laser micromachining for a long time, and has accumulated working experience. And it has realized the multi focus parallel laser icro device processing based on spatial light modulator as well as the rapid fabrication of the special structure based on vector beam and the algorithm optimization of digital holography. [Appl. Phys. Lett. 103, 141112; Opt. Express 22, 3983-3990; Opt. Express 25, 16739-16753; Opt. Lett.42, 2483-2486; Sci. Rep. 6, 19989; Small 2017, 1701190 etc.]

NI Jincheng, PhD candidate of Engineering Sciences, is the first author. Professor WU Dong and Associate Professor HU Yanlei are the corresponding author of the paper. This work is supported by the National Science Foundation of China, Anhui Provincial Natural Science Foundation, the Fundamental Research Funds for Central Universities and “Chinese Thousand Young Talents Programs”

The link of the paper: http://www.nature.com/lsa/journal/v6/n7/full/lsa201711a.html

Contact

Prof. WU Dong

dongwu@ustc.edu.cn

Associate Prof. HU Yanlei

huyl@ustc.edu.cn

 

（DENG Weiting, USTC News Center，School of Engineering Science）