We experimentally demonstrate self-accelerating Bessel-like optical beams propagating along arbitrary trajectories in free space. With computer generated holography, such beams are designed to follow different controllable trajectories while their main lobe transverse profiles remain nearly invariant and symmetric. Examples include parabolic, snake-like, hyperbolic, hyperbolic secant, and even three-dimensional spiraling trajectories. The self-healing property of such beams is also demonstrated. This new class of optical beams can be considered as a hybrid between accelerating and non-accelerating nondiffracting beams that may find a variety of applications.
To develop a universal and precise detection strategy that can be applied to water contaminants of various sizes, we designed a particle-in-MoS 2 coated cavity structure of AAO/MoS 2 /Ag with a Raman internal standard. This modified particle-in-cavity structure not only successfully integrates both "surface hot spots" and "volume hot spots" via dressing and manipulating the cascaded optical-field mode inside the cavity but also introduces the chemical enhancement and internal standard attribute of MoS 2 . Because of its unique three-dimensional structure, AAO/MoS 2 /Ag accurately detects water contaminants of various sizes from ions to nanoplastics (<300 nm) for the first time. This work proposes a novel and universal surfaceenhanced Raman scattering strategy for detecting multiple-size water contaminants and demonstrates the potential to build a security line in early warning systems for the prevention of water pollution.
We investigate second harmonic generation (SHG) in all-dielectric resonance nanostructures of high-Q factors assisted by quasi-bound states in the continuum (quasi-BICs). The typical resonators, e.g., guided-mode resonance gratings and asymmetric metasurfaces, fabricated by AlGaAs were numerically studied with the consideration of nonlinear refraction of AlGaAs. The resonance peak and line-shape of linear transmission and SHG spectra in the resonators can be dramatically changed under intense pump intensities. The SHG conversion efficiency in the nanostructures working at quasi-BICs is much lower than the traditionally expected values without considering the nonlinear refraction of dielectrics. The ultimate SHG conversion efficiency is finally obtained. The investigation has the significance for the design and understanding of efficient nonlinear metasurfaces of high-Q factors.
The construction of commercial surface enhanced Raman scattering (SERS) sensors suitable for clinical applications is a pending problem, which is heavily limited by the low production of high‐performance SERS bases, because they usually require fine or complicated micro/nano structures. To solve this issue, herein, a promising mass‐productive 4‐inch ultrasensitive SERS substrate available for early lung cancer diagnosis is proposed, which is designed with a special architecture of particle in micro‐nano porous structure. Benefitting from the effective cascaded electric field coupling inside the particle‐in‐cavity structure and efficient Knudsen diffusion of molecules within the nanohole, the substrate exhibits remarkable SERS performance for gaseous malignancy biomarker, with the limit of detection is 0.1 ppb and the average relative standard deviation value at different scales (from cm2 to µm2) is ≈16.5%. In practical application, this large‐sized sensor can be further divided into small ones (1 × 1 cm2), and more than 65 chips will be obtained from just one 4‐inch wafer, greatly increasing the output of commercial SERS sensor. Further, a medical breath bag composed of this small chip is designed and studied in detail here, which suggested high‐specificity recognition for lung cancer biomarker in mixed mimetic exhalation tests.
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