Chiral metasurfaces can exhibit a strong circular dichroism, but it is limited by the complicated fabrication procedure and alignment errors. Here, a new type of self‐aligned suspended chiral bilayer metasurface with only one‐step electron beam lithography exposure is demonstrated. A significant optical chirality of 221° µm−1 can be realized using suspended metasurfaces with a thickness of 100 nm. Furthermore, this study experimentally demonstrates that such a structure is capable of label‐free discrimination of the chiral molecules at zeptomole level, exhibiting a much higher sensitivity (orders of magnitude) compared to the conventional circular dichroism spectroscopy. The fundamental principles for chiral sensing using molecules–metasurfaces interactions are explored. Benefiting from the giant chiroptical response, the proposed metadevice may offer promising applications for ultrathin circular polarizers, chiral molecular detectors, and asymmetry information processing.
Auxetic materials exhibit a negative Poisson’s ratio, i.e., they become thicker rather than thinner in at least one dimension when strained. Recently, a nematic liquid crystal elastomer (LCE) was shown to be the first synthetic auxetic material at a molecular level. Understanding the mechanism of the auxetic response in LCEs is clearly important, and it has been suggested through detailed Raman scattering studies that it is related to the reduction of uniaxial order and emergence of biaxial order on strain. In this paper, we demonstrate direct observation of the biaxial order in an auxetic LCE under strain. We fabricated ~100 μm thick LCE strips with complementary geometries, exhibiting either planar or homeotropic alignment, in which the auxetic response is seen in the thickness or width of the sample, respectively. Polarized Raman scattering measurements on the planar sample show directly the reduction in the uniaxial order parameters on strain and suggest the emergence of biaxial order to mediate the auxetic response in the sample thickness. The homeotropic sample is studied via conoscopy, allowing direct observation of both the auxetic response in the width of the sample and increasing biaxiality in the LCE as it is strained. We verified that the mechanism of the auxetic response in auxetic LCEs is due to the emergence of the biaxial order and conclude such materials can be added to the small number of biaxial nematic systems that have been observed. Importantly, we also show that the mechanical Frèedericksz transition seen in some LCEs is consistent with a strain-induced transition from an optically positive to an optically negative biaxial system under strain, rather than a director rotation in a uniaxial system.
A lightweight and portable spectrometer is desirable for miniaturization and integration. The unprecedented capability of optical metasurfaces has shown much promise to perform such a task. We propose and experimentally demonstrate a compact high-resolution spectrometer with a multi-foci metalens. The novel metalens is designed based on wavelength and phase multiplexing, which can accurately map the wavelength information into its focal points located on the same plane. The measured wavelengths in the light spectra agree with simulation results upon the illumination of various incident light spectra. The uniqueness of this technique lies in the novel metalens that can simultaneously realize wavelength splitting and light focusing. The compactness and ultrathin nature of the metalens spectrometer render this technology have potential applications in on-chip integrated photonics where spectral analysis and information processing can be performed in a compact platform.
Bulk photovoltaic effect (BPVE), a second-order nonlinear optical effect governed by the quantum geometric properties of materials, offers a promising approach to overcome the Shockley-Quiesser limit of traditional photovoltaic effect and further improve the efficiency of energy harvesting. Here, we propose an effective platform, the nano edges embedded in assembled van der Waals (vdW) homo- or hetero-structures with strong symmetry breaking, low dimensionality and abundant species, for BPVE investigations. The BPVE-induced photocurrents strongly depend on the orientation of edge-embedded structures and polarization of incident light. Reversed photocurrent polarity can be observed at left and right edge-embedded structures. Our work not only visualizes the unique optoelectronic effect in vdW nano edges, but also provides an effective strategy for achieving BPVE in engineered vdW structures.
Chirality induction, transfer, and manipulation have aroused great interest in achiral nanomaterials. Here, we demonstrate strong upconverted circularly polarized luminescence from achiral core–shell upconversion nanoparticles (UCNPs) via a plasmonic chiral metasurface-induced optical chirality transfer. The Yb3+-sensitized core–shell UCNPs with good dispersity exhibit intense upconversion luminescence of Tm3+ and Nd3+ through the energy transfer process. By spin-coating the core–shell UCNPs on this chiral metasurface, strong enhancement and circular polarization modulation of upconversion luminescence can be achieved due to resonant coupling between surface plasmons and upconversion nanoparticles. In the UCNPs-on-metasurface composite, a significant upconversion luminescence enhancement can be achieved with a maximum enhancement factor of 32.63 at 878 nm and an overall enhancement factor of 11.61. The luminescence dissymmetry factor of the induced upconverted circularly polarized luminescence can reach 0.95 at the emission wavelength of 895 nm. The UCNPs-on-metasurface composite yields efficient modulation for the emission intensity and polarization of UCNPs, paving new pathways to many potential applications in imaging, sensing, and anticounterfeiting fields.
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