Yan Xiaotian   Tang Wenxuan   Liu Junfeng   Wang Meng   Gao Xinxin   Cui Tiejun  

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The glide symmetry, which is one kind of higher symmetries, is introduced in the special type of plasmonic metamaterials, the transmission lines (TLs) of spoof surface plasmon polaritons (SSPPs), so as to control the dispersion characteristics and modal fields of the SSPPs. We show that the glide symmetric TL presents merged pass bands and mode degeneracy, which lead to broad working bandwidth and extremely low coupling between neighbouring TLs. Dual-conductor SSPP TLs with and without the glide symmetry are arranged in parallel as two channels with very deep subwavelength separation (e.g., λ0/100 at 5 GHz) for the application of integrated circuits and systems. Mutual coupling between the hybrid channels is analyzed using the coupling mode theory, and characterized in terms of scattering parameters and near-field distributions. We demonstrate theoretically and experimentally that the hybrid TL array obtains significantly suppressed crosstalks than the uniform array of two non-glide symmetric TLs. Hence, it is concluded that the glide symmetry can be adopted to flexibly design the propagation of SSPPs and benefit the development of highly-compact plasmonic circuits.

       PDF全文 (下载：0)        Advanced Photonics ，年第卷第期 pp.      

Tan Yong   Zhao Hang   Zhang Rui   Zhao Yuejin   Zhang Cunlin   Zhang XiCheng   Zhang Liangliang  

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The fundamental properties of laser-induced plasma in liquid water, such as the ultrafast electron migration and solvation, have not yet been clarified. Here, we use 1650 nm femtosecond laser pulses to induce the plasma in a stable free-flowing water film under the strong field ionization mechanism. Moreover, we adopt intense terahertz (THz) pulses to probe the ultrafast temporal evolution of quasi-free electrons of the laser-induced plasma in water on the sub-picosecond scale. For the first time, the THz wave absorption signal with a unique two-step decay characteristic in time domain is demonstrated, indicating the significance of electron solvation in water. We employ the Drude model combined with the multi-level intermediate model and particle-in-a-box model to simulate and analyze the key information of quasi-free electron, such as the frequency-domain absorption characteristics, and solvation ratio. In particular, we observe the solvation capacity of liquid water decreases with the increase of pumping energy. Up to ~50% of quasi-free electrons cannot be captured by traps associated with the bound states as the pumping energy increases to 90 μJ per pulse. The ultrafast electron evolution in liquid water revealed by the optical-pump/THz-probe experiment provides further insights into the formation and evolution mechanism of liquid plasma.

       PDF全文 (下载：0)        Advanced Photonics ，年第卷第期 pp.      

Huang Lujun   Xu Lei   Rahmani Mohsen   Neshev Dragomir   Miroshnichenko Andrey  

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High-index dielectric resonator supports different types of resonant modes. However, it is challenging to achieve high-Q factor in a single dielectric microcavity due to non-Hermitian property of the open system. Here, we present a universal approach of finding out a series of high-Q resonant modes in a single nonspherical dielectric cavity with a rectangular cross-section by exploring quasi bound-state-in-the-continuum (QBIC). Unlike conventional methods relying on heavy brutal force computations (i.e., frequency scanning by FDTD), our approach is built upon Mie mode engineering, through which many high-Q modes can be easily achieved by constructing avoid-crossing (or crossing) of the eigenvalue for pair leaky modes. The calculated Q-factor of mode TE(5,7) can be up to Qtheory =2.3*10^4 for a freestanding square nanowire (NW) (n=4), which is 64 times larger than the highest Q-factor (Qtheory=360) reported so far in single Si disk. Such high-Q modes can be attributed to suppressed radiation in the corresponding eigenchannels and simultaneously quenched electric(magnetic) field at momentum space. As a proof of concept, we experimentally demonstrate the emergence of the high-Q resonant modes (Q=211 for mode TE(3,4), Q=380 for mode TE(3,5), Q=294 for mode TM(3,5)) in the scattering spectrum of a single silicon NW.

       PDF全文 (下载：0)        Advanced Photonics ，年第卷第期 pp.      

Qiao Zhen   Gong Xuerui   Guan Peng   Yuan Zhiyi   Feng Shilun   Zhang Yiyu   Kim Munho   Chang Guo-En   Chen Yu-Cheng  

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Liquid droplets offer a great number of opportunities in biochemical and physical researches, in which droplet-based microlasers have come into play over the past decade. While the recent emergence of droplet lasers has demonstrated their powerful capabilities in amplifying subtle molecular changes inside the cavity, the optical interactions between droplet resonators and an interface remain unclear. Herein we revealed the underlying mechanism of droplet lasers when interacting with a droplet-solid interface and explored its correlation with intermolecular forces. A vertically oriented oscillation mode—arc-like mode was discovered, where the number of lasing modes and their Q-factors increase with the strength of interfacial hydrophobicity. Both experimental and theoretical results demonstrated that hydrophobicity characterized by contact angle and interfacial tension plays a significant role in the geometry of droplet cavity and laser mode characteristics. Finally, we demonstrated how tiny forces induced by proteins and peptides could strongly modulate the lasing output in droplet resonators. Our findings illustrate the potential of exploiting optical resonators to amplify intermolecular force changes, providing comprehensive insights into lasing actions modulated by interfaces and applications in biophysics.

       PDF全文 (下载：0)        Advanced Photonics ，年第卷第期 pp.      

Lan Lu   Li Yueming   Yang-Tran Tiffany   Jiang Ying   Cao Yingchun   Cheng Ji-Xin  

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Microwave, which has ~10 cm long wavelength, can penetrate deeper into tissue than photons, heralding exciting deep tissue applications such as modulation or imaging via thermo-acoustic (TA) effect. However, the TA conversion efficiency is very low even with an exogenous contrast agent. Here, we break this low conversion limit through using a split ring resonator (SRR) to effectively collect and confine the microwave into a sub-millimeter hot spot for ultrasound emission, and achieve over two thousand times higher conversion efficiency than reported TA contrast agents. Importantly, the frequency of emitted ultrasound can be precisely tuned and multiplexed by modulation of the microwave pulses. This is inaccessible by a piezoelectric-based transducer or a photoacoustic emitter and opens new opportunities to study the frequency response of cells in ultrasound bio-modulations. For applications in deep tissue localization, we further harness the SRR as a wireless, battery-free ultrasound becaon placed under a breast phantom.

       PDF全文 (下载：5)        Advanced Photonics ，年第卷第期 pp.