1,298 research outputs found
Tungsten disulfide-gold nanohole hybrid metasurfaces for nonlinear metalens in the visible region
Recently, nonlinear hybrid metasurface comes into an attractive new concept
in the research of nanophotonics and nanotechnology. It is composed of
semiconductors with an intrinsically large nonlinear susceptibility and
traditional plasmonic metasurfaces, offering opportunities for efficiently
generating and manipulating nonlinear optical responses. A high second-harmonic
generation (SHG) conversion efficiency has been demonstrated in the
mid-infrared region by using multi-quantum-well (MQW) based plasmonic
metasurfaces. However, it has yet to be demonstrated in the visible region.
Here we present a new type of nonlinear hybrid metasurfaces for the visible
region, which consists of a single layer of tungsten disulfide (WS2) and a
phased gold nanohole array. The results indicate that a large SHG
susceptibility of ~0.1 nm/V at 810 nm is achieved, which is 2~3 orders of
magnitude larger than that of typical plasmonic metasurfaces. Nonlinear
metalenses with the focal lengths of 30 {\mu}m, 50 {\mu}m and 100 {\mu}m are
demonstrated experimentally, providing a direct evidence for both generating
and manipulating SH signals based on the nonlinear hybrid metasurfaces. It
shows great potential applications in designing of integrated, ultra-thin,
compacted and efficient nonlinear optical devices, such as frequency
converters, nonlinear holography and generation of nonlinear optical vortex
beam
Explaining the cosmic ray spectrum feature of Auger beyond the ankle with dip model plus the galactic propagation effect
The Auger Collaboration has recently published the energy spectrum of cosmic
rays above 1 EeV, which exhibits interesting features. These spectrum features
provide an opportunity to investigate the propagation of ultra-high-energy
cosmic rays (UHECRs). In this study, we have developed a model that
incorporates the dip model for UHECRs in the extragalactic propagation, while
accounting for the suppression due to diffusion and interactions within the
galaxy. Our model demonstrates excellent agreement with the energy spectrum
measured by Auger and supports a spectral index of 2 for the diffusion
coefficient in the galaxy starting from eV.Comment: 5 pages, 2 figure
Extremal Tri-Cyclic Graphs with respect to the First and Second Zagreb Indices
In this paper, the first and second maximum values of the first and second Zagreb indices of vertex tri-cyclic graphs are obtained
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