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Abstract
Abstract Metallic helical metamaterials have become the prominent candidates for circular polarizers and other optical-chiral devices as they exhibit strong circular dichroism at a broad operation bandwidth. However, the rapid fabrication of an intertwined double helix with multiple pitch numbers and excellent mechanical strength, electrical conductivity and surface smoothness remains a challenge. We propose and realize the single-exposure femtosecond laser photoreduction of a freestanding, three-dimensional silver double-helix microstructure by the double-helix focal field intensity engineered with a spatial light modulator. At the same time, the photoreduction solution and the laser repetition rate are optimized to further tackle the surface roughness and the thermal flow problems. As a result, the silver double-helix array with the enhanced quality exhibits pronounced optical chirality in a wide wavelength range from 3.5 to 8.5 μm. This technique paves a novel way to easily and rapidly fabricate metallic metamaterials for chiro-optical devices in the mid-infrared regime.
Highlights
Metallic helical metamaterials, which consist of subwavelength metallic helix unit cells, can exhibit strong circular dichroism at a broad operation bandwidth, making them prominent candidates for circular polarizers and other chiral devices [1,2,3,4]
We propose and realize the single-exposure femtosecond laser photoreduction of a freestanding, three-dimensional silver double-helix microstructure by the double-helix focal field intensity engineered with a spatial light modulator
We have demonstrated the single-exposure femtosecond laser two-photon polymerization (TPP) of a double-helix microstructure by the focal field engineering with the spatial light modulator (SLM), a 3D freestanding metallic helical metamaterial with functionality is still difficult to achieve [26]
Summary
Metallic helical metamaterials, which consist of subwavelength metallic helix unit cells, can exhibit strong circular dichroism at a broad operation bandwidth, making them prominent candidates for circular polarizers and other chiral devices [1,2,3,4]. The multi-photon-induced photoreduction of metal ions in an aqueous solution has been developed for direct writing of a 3D metal microstructure [20,21,22,23,24]. The microstructure in this single-step multiphoton photoreduction (MPR) is assembled point-by-point and formed by the nucleation of small metallic nanoparticles (NPs). The final 3D microstructures usually exhibit weak mechanical strength or poor electrical conductivity or rough surface smoothness when the height is greater than a few microns, resulting in the lack of optical function
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