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1. Ballistic supercavitating nanoparticles driven by single Gaussian beam optical pushing and pulling forces

   https://doi.org/10.1038/s41467-020-16267-9  

   Lee, Eungkyu ; Huang, Dezhao ; Luo, Tengfei ( May 2020 , Nature Communications)

   Directed high-speed motion of nanoscale objects in fluids can have a wide range of applications like molecular machinery, nano robotics, and material assembly. Here, we report ballistic plasmonic Au nanoparticle (NP) swimmers with unprecedented speeds (~336,000 μm s⁻¹) realized by not only optical pushing but also pulling forces from a single Gaussian laser beam. Both the optical pulling and high speeds are made possible by a unique NP-laser interaction. The Au NP excited by the laser at the surface plasmon resonance peak can generate a nanoscale bubble, which can encapsulate the NP (i.e., supercavitation) to create a virtually frictionlessmore »environment for it to move, like the Leidenfrost effect. Certain NP-in-bubble configurations can lead to the optical pulling of NP against the photon stream. The demonstrated ultra-fast, light-driven NP movement may benefit a wide range of nano- and bio-applications and provide new insights to the field of optical pulling force.

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2. An optical slot-antenna-coupled cavity (SAC) framework towards tunable free-space graphene photonic surfaces

   https://doi.org/10.1007/s12274-020-3184-z  

   Fu, Sidan ; Wang, Xiaoxin ; Wang, Haozhe ; Gao, Xiaoxue ; Broderick, Kurt ; Kong, Jing ; Liu, Jifeng ( November 2020 , Nano Research)

   The optical conductivity of single layer graphene (SLG) can be significantly and reversibly modified when the Fermi level is tuned by electrical gating. However, so far this interesting property has rarely been applied to free-space two-dimensional (2D) photonic devices because the surface-incident absolute absorption of SLG is limited to 1%–2%. No significant change in either reflectance or transmittance would be observed even if SLG is made transparent upon gating. To achieve significantly enhanced surface-incident optical absorption in SLG in a device structure that also allows gating, here we embed SLG in an optical slot-antenna-coupled cavity (SAC) framework, simultaneously enhancing SLGmore »absorption by up to 20 times and potentially enabling electrical gating of SLG as a step towards tunable 2D photonic surfaces. This framework synergistically integrates near-field enhancement induced by ultrahigh refractive index semimetal slot-antenna with broadband resonances in visible and infrared regimes, ~ 3 times more effective than a vertical cavity structure alone. An example of this framework consists of self-assembled, close-packed Sn nanodots separated by ~ 10 nm nanogaps on a SLG/SiO2/Al stack, which dramatically increases SLG optical absorption to 10%-25% at λ = 600–1,900 nm. The enhanced SLG absorption spectrum can also be controlled by the insulator thickness. For example, SLG embedded in this framework with a 150 nm-thick SiO2 insulating layer displays a distinctive red color in contrast to its surrounding regions without SLG on the same sample under white light illumination. This opens a potential path towards gate-tunable spectral reflectors. Overall, this work initiates a new approach towards tunable 2D photonic surfaces.« less
3. Annular substructures in the transition disks around LkCa 15 and J1610

   https://doi.org/10.1051/0004-6361/202038027  

   Facchini, S. ; Benisty, M. ; Bae, J. ; Loomis, R. ; Perez, L. ; Ansdell, M. ; Mayama, S. ; Pinilla, P. ; Teague, R. ; Isella, A. ; et al ( July 2020 , Astronomy & Astrophysics)

   We present high-resolution millimeter continuum ALMA observations of the disks around the T Tauri stars LkCa 15 and 2MASS J16100501-2132318 (hereafter, J1610). These transition disks host dust-depleted inner regions, which have possibly been carved by massive planets, and they are of prime interest to the study of the imprints of planet-disk interactions. While at moderate angular resolution, they appear as a broad ring surrounding a cavity, the continuum emission resolves into multiple rings at a resolution of ~60 × 40 mas (~7.5 au for LkCa 15, ~6 au for J1610) and ~7 μ Jy beam −1 rms at 1.3 mm.more »In addition to a broad extended component, LkCa 15 and J1610 host three and two narrow rings, respectively, with two bright rings in LkCa 15 being radially resolved. LkCa 15 possibly hosts another faint ring close to the outer edge of the mm emission. The rings look marginally optically thick, with peak optical depths of ~0.5 (neglecting scattering), in agreement with high angular resolution observations of full disks. We performed hydrodynamical simulations with an embedded, sub-Jovian-mass planet and show that the observed multi-ringed substructure can be qualitatively explained as the outcome of the planet-disk interaction. We note, however, that the choice of the disk cooling timescale alone can significantly impact the resulting gas and dust distributions around the planet, leading to different numbers of rings and gaps and different spacings between them. We propose that the massive outer disk regions of transition disks are favorable places for planetesimals, and possibly second-generation planet formation of objects with a lower mass than the planets carving the inner cavity (typically few M Jup ), and that the annular substructures observed in LkCa 15 and J1610 may be indicative of planetary core formation within dust-rich pressure traps. Current observations are compatible with other mechanisms contributing to the origin of the observed substructures, in particular with regard to narrow rings generated (or facilitated) at the edge of the CO and N 2 snowlines.« less
4. Quasi-continuous wavelength tuning of single-mode interband cascade lasers based on V-coupled cavity

   https://doi.org/10.1117/12.2575270  

   Jingli, Gong ; Yang, Hanting ; Yang, Rui Q. ; He, Jian-Jun ( October 2020 , Semiconductor Lasers and Applications X)

   Zhu, Ning Hua ; Hofmann, Werner H. ; He, Jian-Jun (Ed.)

   Mid-infrared semiconductor lasers have a wide range of applications in gas sensing, environmental monitoring, medical diagnosis and other fields. The V-coupled cavity laser (VCCL) approach has been successfully applied in the communication band to achieve single-mode operation with a wide tuning range because of its advantages of no grating, compact structure and simple wavelength control. In this paper, the concept of V-coupled cavity is introduced to the interband cascaded lasers, and a monolithically integrated mid-infrared widely tunable single-mode laser is developed. In addition, we experimentally demonstrated a simple and general algorithm for wavelength tuning controlled by two electrodes synchronously, andmore »realized quasi-continuous tuning of single-mode wavelength in mid-infrared interband cascade laser based on the V-coupled cavity configuration for the first time. In the tuning process, the injection current of the short cavity remains unchanged, and the stepped increase of the long cavity current is equivalent to the realization of discrete tuning with the channel spacing of 1.1 nm determined by the short cavity. With the increase of the injection current of the coupler electrode while fixing the long cavity current, the thermo-optic effect caused by the coupler current will cause the refractive index of the two FP cavities to change together, thus realizing the fine tuning of the laser wavelength. A total tuning range of 53.2 nm has been achieved, from 2.8244 μm to 2.8776 μm, with the temperature adjusted from 110K to 120K.« less
5. A global algorithm for AC optimal power flow based on successive linear conic optimization

   https://doi.org/10.1109/PESGM.2017.8273957  

   Barati, Masoud ; Kargarian, Amin ( July 2017 , 2017 IEEE Power & Energy Society General Meeting)

   Newly, there has been significant research interest in the exact solution of the AC optimal power flow (AC-OPF) problem. A semideflnite relaxation solves many OPF problems globally. However, the real problem exists in which the semidefinite relaxation fails to yield the global solution. The appropriation of relaxation for AC-OPF depends on the success or unfulflllment of the SDP relaxation. This paper demonstrates a quadratic AC-OPF problem with a single negative eigenvalue in objective function subject to linear and conic constraints. The proposed solution method for AC-OPF model covers the classical AC economic dispatch problem that is known to be NP-hard.more »In this paper, by combining successive linear conic optimization (SLCO), convex relaxation and line search technique, we present a global algorithm for AC-OPF which can locate a globally optimal solution to the underlying AC-OPF within given tolerance of global optimum solution via solving linear conic optimization problems. The proposed algorithm is examined on modified IEEE 6-bus test system. The promising numerical results are described.« less