Due to the recent advancement in metamaterials for bio-sensing applications, metasurfaces are designed to enhance the chirality of the incident CP light by creating chiral hotspots formed by the interaction of electric and magnetic fields. Most of the reported works focus on induced chirality in plasmonic structures operated by shifting the molecules' circular dichroism (CD) signal to plasmonic resonance frequencies, which results in a decrease in efficiency. Moreover, chiral structures like gammadions were also reported, which can enhance the chirality. Still, the inherent chirality of the structure is much larger than the chirality of the molecules and thus overshadows it. Therefore, highly efficient planar nanomaterials with broadband uniform chirality are needed to sort and detect natural and artificially-made chiral molecules. This work presents an aluminum-based dimer structure that confines the central gap's chiral field, leading to highly uniform volumetric chirality enhancement. The proposed achiral dimer structure enhances the chirality of the incident circularly polarized light without interfering with the circular dichroism (CD) of the molecules. As a result, we report high volumetric chirality and dissymmetry factor compared to the state-of-the-art, which is the figures of merit for CD spectroscopy and separation of enantiomers, respectively. This work can be applied to distinguish molecules with CD bands in the ultraviolet and visible wavelengths.
Here in this paper, we proposed a metasurface, which consists of silicon nitride as dielectric material possessing a high transparent window in the ultraviolet regime. We designed a single-layer dual-band metasurface instead of stacking and interleaved technique to overcome noise and low resolution, which gives broadband response for UV wavelengths. The proposed spin multiplexed metasurface is capable of generating two independent holographic images for right circularly polarized (RCP) and left circularly polarized (LCP) light. We achieved maximum cross-polarization efficiency on the designed wavelength i.e. 350nm and negligible zero-order efficiency. The unit cell and the proposed metasurface are simulated using Finite Difference Time Domain-based FDTD Solution from Lumerical Inc. for the specific wavelength while it gives broadband response for the wavelength band almost covering 290nm to 390nm.
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