岩石特性的编码激励超声参数表征及分析

编码激励技术是提高超声穿透能力和分辨率的有效手段。为分析岩石特性对编码信号脉冲压缩性能的影响,通过数值模拟以及不同岩石的超声检测实验,研究并比较了几类编码信号的检测效果。结果表明幅度加权线性调频信号(TLFM)调制的Barker码信号(BTL)受到的信噪比损失低于正弦调制Barker码信号(BS),而分辨率损失要低于TLFM信号。实验结果验证了编码激励技术的有效性,为岩石超声检测中编码参数的设置提供了依据。      

Asymmetrical photonic spin Hall effect based on dielectric metasurfaces

The photonic spin Hall effect has attracted considerable research interest due to its potential applications in spin-controlled nanophotonic devices. However, realization of the asymmetrical photonic spin Hall effect with a single optical element is still a challenge due to the conjugation of the Pancharatnam-Berry phase, which reduces the flexibility in various applications. Here, we demonstrate an asymmetrical spin-dependent beam splitter based on a single-layer dielectric metasurface exhibiting strong and controllable optical response. The metasurface consists of an array of dielectric nanofins, where both varying rotation angles and feature sizes of the unit cells are utilized to create high-efficiency dielectric metasurfaces, which enables to break the conjugated characteristic of phase gradient. Thanks to the superiority of the phase modulation ability, when the fabricated metasurface is under normal incidence with a wavelength of 1550 nm, the left-handed circular polarization (LCP) light exhibits an anomalous refraction angle of 28.9°, while the right-handed circular polarization (RCP) light transmits directly. The method we proposed can be used for the flexible manipulation of spin photons and has potentials in high efficiency metasurfaces with versatile functionalities, especially with metasurfaces in a compact space.