Chiral nanophotonic structures can significantly enhance the chiral optical responses. However, achieving extreme chirality remains challenging. Here, chiral quasi-bound states in the continuum are realized in the visible range by controlling the etching depths in the substrate and inducing out-of-plane symmetry breaking. An extremely high level of chiral emission from a perovskite metasurface is experimentally achieved in the normal direction. Chiral emission is maximally enhanced for one helicity via critical coupling while strongly suppressed for the other helicity. Approaching the ultimate limit of chiral interactions may lead to far-reaching consequences in a variety of important applications.
Here we report a novel approach to create tunable and reconfigurable microwave metamaterials using metal ink printing on a paper. Our approach enables easy-to-fabricate but still highly functional and tunable elements. An array of asymmetric split ring resonators was printed on a photopaper to induce Fano resonances in the microwave region (~ 10 GHz). Then, the printed paper was cut line by line and folded, so that a step height between neighboring unit cells can be created and tuned. With the varying step height between neighboring cells, our sample demonstrates significant spectral shifts and resonance tuning despite its simple geometry. Depending on the cutting direction, we observe either spectral redshift or blueshift. We explain our experimental observations based on the interactions between electric/magnetic dipoles in the neighboring unit cell. Moreover, we observe phase singularity at the zero amplitude position of the Fano resonance spectrum. The spectral phase exhibits a drastic change at this singularity point, and the phase spectrum can be also largely tuned with the geometry change in our sample. The drastic changes in phase could be very useful for various applications, such as optical sensing and beam steering.
We demonstrate an efficient ENZ response in the visible spectral range using organic
molecular ultrathin films possessing a Lorentz-type dispersion. For this purpose, two
polymethine dyes: sodium [5,6-dichloro-2-[[5,6-dichloro-1-ethyl-3-(4-sulphobutyl)-
benzimidazol-2-ylidene]-propenyl]-1-ethyl-3-(4-sulphobutyl)-benzimidazolium hydroxide]
(TDBC), and [2,4-bis[8-hydroxy-1,1,7,7-tetramethyljulolidin-9-yl]squaraine]
(HTJSq) were used in spin-coated polymer films at different doping concentrations.
By varying the doping concentration in thin films, the real part of highly dispersive permittivity
ε1 can be manipulated and tuned such that the spectral width of ENZ region -1 < ε1 <1 resides
in the visible spectral range. These results are not only extremely relevant for applications
requiring a custom-tailored ENZ region in the visible but also provide important novel
information on how molecular aggregation affects the ENZ properties. In particular, based on our findings, we stress that J-aggregate is not always a mandatory molecular assembly for
obtaining a strong ENZ response. Instead, molecular aggregates with the size of a few
nanometers resulting in strong molecular interactions (i.e. Davydov splitting of the lowest
transition in energy) are required to achieve a strong ENZ response. The ENZ-enhanced optical
Kerr nonlinearity is then investigated in the optimum concentration films of TDBC and HTJSq.
Both nonlinear refractive index and nonlinear absorption coefficient are found to be strongly
enhanced in the ENZ region originating from the coupling of excitonic transition dipoles
associated with large molecular aggregates.
Nitrogen-vacancy centers in diamond are widely studied both as a testbed for solid state quantum optics and for
their applications in quantum information processing and magnetometry. Here we demonstrate coupling of the
nitrogen-vacancy centers to gap plasmons in metal nano-slits. We use diamond samples where nitrogen-vacancy
centers are implanted tens of nanometers under the surface. Silver nano-slits are patterned on the sample such
that diamond ridges tens of nanometers wide fill the slit gap. We measure enhancement of the spontaneous
emission rate of the zero photon line by a factor of 3 at a temperature of 8K.
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