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We theoretically investigate the illusion device designed by a conformal transformation that can render an elliptic defect behave like a flat mirror. Different from illusion devices consisting of the complementary medium and anti-object with negative permittivity and permeability, our proposed illusion device requires only isotropic positive permittivity medium. It offers a possible route to eliminate the lateral shift in the conventional quasi-conformal carpet cloak. Interestingly, with the same conformal transformation, we can achieve an impedance-matched flat absorber by simply varying the shape and the refractive index of the defects. Both the illumination device and the absorber in our design have broad bandwidth, wide-illumination range and polarization-insensitive performance.

We report the generation of high energy 2 μm picosecond pulses from a thulium-doped fiber master oscillator power amplifier system. The all-fiber configuration was realized by a flexible large-mode area photonic crystal fiber (LMA-PCF). The amplifier output is a linearly-polarized 1.5 ns, 100 kHz pulse train with a pulse energy of up to 250 μJ. Pulse compression was achieved with (2+2)-pass chirped volume Bragg grating (CVBG) to obtain a 2.8 ps pulse width with a total pulse energy of 46 μJ. The overall system compactness was enabled by the all-fiber amplifier design and the multi-pass CVBG-based compressor. The laser output was then used to demonstrate high-speed direct-writing capability on a temperature-sensitive biomaterial to change its topography (i.e. fabricate microchannels, foams and pores). The topographical modifications of biomaterials are known to influence cell behavior and fate which is potentially useful in many cell and tissue engineering applications.

Hardware implementation of reconfigurable and nonvolatile photoresponsivity is essential for advancing in-sensor computing for machine vision applications. However, existing reconfigurable photoresponsivity essentially depends on the photovoltaic effect of p-n junctions, which photoelectric efficiency is constrained by Shockley-Queisser limit and hinders the achievement of high-performance nonvolatile photoresponsivity. Here, we employ bulk photovoltaic effect of rhombohedral (3R) stacked/interlayer sliding tungsten disulfide (WS2) to surpass this limit and realize highly reconfigurable, nonvolatile photoresponsivity with a retinomorphic photovoltaic device. The device is composed of graphene/3R-WS2/graphene all van der Waals layered structure, demonstrating a wide range of nonvolatile reconfigurable photoresponsivity from positive to negative (± 0.92 A W−1) modulated by the polarization of 3R-WS2. Further, we integrate this system with a convolutional neural network to achieve high-accuracy (100%) color image recognition at σ = 0.3 noise level within six epochs. Our findings highlight the transformative potential of bulk photovoltaic effect-based devices for efficient machine vision systems. Gong et al. report bulk photovoltaic effect in rhombohedral stacked/interlayer sliding WS2 with reconfigurable and nonvolatile photoresponsivity and develop a convolutional neural network for image processing based on two-terminal all 2D van der Waals layers vertical retinomorphic device. [ABSTRACT FROM AUTHOR]

Monitoring and modelling surface deformation are crucial components of understanding the freeze‒thaw process and preventing disasters in permafrost regions. However, previous methods had limitations that inhibited the interpretation of freeze‒thaw deformation, such as a lack of physical meaning, an inability to reflect the physical freeze–thaw process and consideration of only a single external factor's impact on permafrost deformation. This study proposes an improved degree-day model (IDM) for quantitatively isolating surface deformation using interferometric synthetic aperture radar (InSAR) technology over permafrost. We considered the effect of soil moisture variation on permafrost deformation and incorporated interannual variation in the freeze‒thaw process due to climate change. By applying small baseline subset (SBAS) technology to Sentinel-1 InSAR measurements over the Wudaoliang permafrost region on the Qinghai‒Tibet Plateau from 2018 to 2019, we estimated long-term and seasonal permafrost deformation. The reliability of InSAR results was validated using in situ measurements, with root mean square errors (RMSEs) less than 10 mm. The results showed that the average linear deformation rates in 2018 and 2019 were −3.8 mm a−1 and −11.0 mm a−1, respectively, and the maximum seasonal deformations were 15.7 mm and 13.2 mm, respectively. Compared with the original degree-day model (ODM), the method used in this study produced smaller residual deformations of 6.9 mm and 6.4 mm, highlighting its ability to improve a quantitative description of permafrost deformation. [ABSTRACT FROM AUTHOR]

In the past, most of the introduced ultrafast pulse lasers have primarily focused on shortening cavity lengths or employing harmonic mode‐locking methods to achieve megahertz and gigahertz coherent pulses. In contrast, lasers generating pulses at terahertz repetition rates seemed to have received less attention. These pulses are crucial for applications in fields such as biological imaging, quantum computing, and atmospheric earth sciences, requiring ultra‐high repetition rates and ultrafast pulses. Here, an all‐fiber laser system is presented that generates ultra‐high repetition rate pulses. It relies on the comb‐like filtering effect of a microfiber resonator and the interaction with high birefringence. This enables the production of terahertz‐class pulses with a pulse interval of ≈290 fs, achieving a remarkable maximum repetition rate of about ≈3.448 THz. To the authors' knowledge, this stands as the highest pulse repetition rate achievable in an all‐fiber laser. By contrast experiment, the terahertz repetition rate produced by this system is related to the length of the high‐birefringence fiber; the shorter the length, the wider the filtering spacing, and the higher the achievable repetition rate. The overall system's birefringence effect can be adjusted by two polarization controllers, allowing for a wide range of tunability in pulse repetition rates. [ABSTRACT FROM AUTHOR]

Epitaxy-enabled bottom-up synthesis of self-assembled planar nanowires via the vapor-liquid-solid mechanism is an emerging and promising approach toward large-scale direct integration of nanowire-based devices without postgrowth alignment. Here, by examining large assemblies of indium tin oxide nanowires on yttria-stabilized zirconia substrate, we demonstrate for the first time that the growth dynamics of planar nanowires follows a modified version of the Gibbs-Thomson mechanism, which has been known for the past decades to govern the correlations between thermodynamic supersaturation, growth speed, and nanowire morphology. Furthermore, the substrate orientation strongly influences the growth characteristics of epitaxial planar nanowires as opposed to impact at only the initial nucleation stage in the growth of vertical nanowires. The rich nanowire morphology can be described by a surface-energy-dependent growth model within the Gibbs-Thomson framework, which is further modulated by the tin doping concentration. Our experiments also reveal that the cutoff nanowire diameter depends on the substrate orientation and decreases with increasing tin doping concentration. These results enable a deeper understanding and control over the growth of planar nanowires, and the insights will help advance the fabrication of self-assembled nanowire devices.

Manipulators applied to polishing can avoid the harm of dust and noise to workers' health in manual polishing, and can significantly increase productivity. The degrees of freedom (DOF) of the existing end-effector for manipulator polishing is insufficient, and then it is difficult to adapt to complex surfaces. A passive compliant end-effector (PCEE) with 4-DOF employing pneumatic floating was designed to solve that problem in this article. According to the included angle between the floating spindle and the plunger, the supporting force functions of floating amount were constructed. Considering the characteristics of the supporting force and the operating modes comprehensively, an appropriate number of plungers was selected. Based on the equilibrium principle of spatial force system, a PCEE was designed by using the floating scheme at both ends, and then a physical model and a simplified model were provided. Eventually, the performances of 4-DOF PCEE are compared with those of the existing 2-DOF compliant end-effector (CEE). The results show that The PCEE can float with 4-DOF; when the number of plungers is 9, all performances meet the design requirements; the polishing force can adapt to the local bulges and overcome the error reflection; the 4-DOF PCEE can adaptively fit the surface to reduce its geometric error. [ABSTRACT FROM AUTHOR]

Nonlinear pulse compression techniques have been applied widely in the pursuit of ultra‐intense laser pulse with extremely high pulse energy (≈mJ) and extremely short pulse duration (≈sub‐10 fs). Although postcompression techniques using dispersive gratings or chirped mirrors have achieved 1 TW few‐cycle pulses, further increasing of the pulse intensity is limited by the damage threshold of dispersive optics, especially when self‐focusing and ionization in the propagation medium are considered. To overcome such limitations, ultrashort pulses self‐compression techniques without vulnerable dispersive optics have been explored in the past two decades. In this paper, the latest advances in these techniques will be reviewed with a discussion on the progress of various experimental approaches as well as their potential applications and roles in generating extremely intense optical fields for strong‐field physics research. [ABSTRACT FROM AUTHOR]