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Nanobubbles are typical nanodefects commonly existing in two-dimensional (2D) van der Waals materials such as transition metal dioxides, especially after their transfer from growth substrate to target substrates. These nanobubbles, though tiny, may significantly alter the local electric, optoelectronic, thermal, or mechanical properties of 2D materials and therefore are rather detrimental to the constructed devices. However, there is no post-processing method so far that can effectively eliminate nanobubbles in 2D materials after their fabrication and transfer, which has been a major obstacle in the development of 2D material based devices. Here, we propose a principle, called laser optothermal nanobomb (LOTB), that can effectively flatten nanobubbles in 2D materials through a dynamic process of optothermally induced phase transition and stress-pulling effect in nanobubbles. Operation of LOTB on monolayer molybdenum disulfide (1L-MoS2) films shows that the surface roughness can be reduced by more than 70% on a time scale of ~50 ms, without damage to the intrinsic property of 1L-MoS2 as validated by micro-nano photoluminescence and Raman spectroscopy. Moreover, a dual-beam cascaded LOTB and a multi-shot LOTB strategies are proposed to increase the flattened area and processing effect, showing the potential of LOTB for fast nanodefect repairing in the mass production of van der Waals materials and devices., Comment: 20 pages, 4 figures, research article

The stability and emissivity of the online calibration blackbody used in high-precision infrared remote sensing detectors in extreme environments are the primary limiting factors for their measurement accuracy. Due to the limitations of microstructure size effects, traditional calibration extended area blackbody cannot achieve an optimal balance between emissivity and stability, thus hindering further improvement in infrared remote sensing accuracy. This work proposes a new method that utilize suppressing near-field backscattering to control far-field reflectance. Specifically, through simultaneously reducing backscattering intensity and the backscattering solid angle, the reflectance is significantly reduced to an extremely low limit, which is validated through numerical simulations. Additionally, by combining the femtosecond laser self-convergent processing technique, the spontaneous energy negative feedback mechanism during femtosecond laser processing is utilized to achieve the fabrication of a high emissivity, thermally stable, mechanically stable, and highly uniform extended area blackbody. The blackbody fabricated using this technique can be applied for online calibration in various extreme environments, significantly improving measurement accuracy and service life.

Plasmonic vortex lenses (PVLs), producing vortex modes, known as plasmonic vortices (PVs), in the process of plasmonic spin-orbit coupling, provide a promising platform for the realization of many optical vortex-based applications. Very recently, it has been reported that a single PVL can generate multiple PVs. This work exploits the representation theory of finite groups, reveals the symmetry origin of the generated PVs, and derives a new conservation relation based on symmetry principles. Specifically, the symmetry principles divide the near field of the PVL into regions, designate integers, which are the topological charges, to the regions, and, particularly, give an upper bound to the topological charge of the PV at the center of the PVL. Further application of the symmetry principles to the spin-orbit coupling process leads to a new conservation relation. Based on this relation, a two-step procedure is suggested to link the angular momentum of the incident field with the one of the generated PVs through the symmetries of the PVL. This theory is well demonstrated by numerical calculations. This work provides an alternative but essential symmetry perspective on the dynamics of spin-orbit coupling in PVLs, forms a strong complement for the physical investigations performed before, and therefore lays down a solid foundation for flexibly manipulating the PVs for emerging vortex-based nanophotonic applications., Comment: 23 pages and 3 figures

Fourier-based optical computing operations, such as spatial differentiation, have recently been realized in compact form factors using flat optics. Experimental demonstrations, however, have been limited to coherent light requiring laser illumination and leading to speckle noise and unwanted interference fringes. Here, we demonstrate the use of optimized multilayer films, combined with dual color image subtraction, to realize differentiation with unpolarized incoherent light. Global optimization is achieved by employing neural networks combined with the reconciled level set method to optimize the optical transfer functions of multilayer films at wavelengths of 532 nm and 633 nm. Spatial differentiation is then achieved by subtracting the normalized incoherent images at these two wavelengths. The optimized multilayer films are experimentally demonstrated to achieve incoherent differentiation with a numerical aperture up to 0.8 and a resolution of 6.2 {\mu}m. The use of multilayer films allows for lithography-free fabrication and is easily combined with existing imaging systems opening the door to applications in microscopy, machine vision and other image processing applications., Comment: 16 pages,5 figures

Near-field microscopy is widely used for characterizing electromagnetic fields at nanoscale, where nanoprobes afford the opportunity to extract subwavelength optical quantities, including the amplitude, phase, polarization and chirality. However, owing to the complexity of various nanoprobes, a general and intuitive theory is highly needed to assess the vectorial field response of the nanoprobes and interpret the mechanism of the probe-field interaction. Here, we develop a general imaging theory based on the reciprocity of electromagnetism and multipole expansion analysis. The proposed theory closely resembles the multipolar Hamiltonian for light-matter interaction energy, revealing the coupling mechanism of the probe-field interaction. Based on this theory, we introduce a new paradigm for the design of functional nanoprobes by analyzing the reciprocal dipole moments, and establish effective design principles for the imaging of vectorial near fields. Moreover, we numerically analyze the responses of two typical probes, which can quantitatively reproduce and well explain the experimental results of previously reported measurements of optical magnetism and transverse spin angular momentum. Our work provides a powerful tool for the design and analysis of new functional probes that may enable the probing of various physical quantities of the vectorial near field., Comment: 13 pages, 5 figures, revised contents and styles of references

Cascaded optical field enhancement (CFE) can be realized in some specially designed multiscale plasmonic nanostructures, where the generation of extremely strong field at nanoscale volume is crucial for many applications, for example, surface enhanced Raman spectroscopy (SERS). Here, we propose a strategy of realizing a high-quality plasmonic nanoparticle-in-cavity (PIC) nanoantenna array, where strong coupling between a nanoparticle dark mode with a high order nanocavity bright mode can produce Fano resonance at a target wavelength. The Fano resonance can effectively boost the CFE in the PIC, with a field enhancement factor up to 5X10^2. A cost-effective and reliable nanofabrication method is developed with room temperature nanoimprinting lithography to manufacture high-quality PIC arrays. This technique guarantees the generation of only one gold nanoparticle at the bottom of each nanocavity, which is crucial for the generation of the expected CFE. As a demonstration of the performance and application of the PIC array, it is used as active SERS substrate for detecting 4-aminothiophenol molecules. The SERS enhancement factor up to 2X10^7 is obtained experimentally, verifying the field enhancement and potential of this device., Comment: 19 pages and 4 figures

Surface plasmon polaritons (SPPs) have been widely exploited in various scientific communities, ranging from physics, chemistry to biology, due to the strong confinement of light to the metal surface. For many applications it is important that the free space photon can be coupled to SPPs in a controllable manner. In this Letter, we apply the concept of interfacial phase discontinuity for circularly polarizations on a metasurface to the design of a novel type of polarization dependent SPP unidirectional excitation at normal incidence. Selective unidirectional excitation of SPPs along opposite directions is experimentally demonstrated at optical frequencies by simply switching the helicity of the incident light. This approach, in conjunction with dynamic polarization modulation techniques, opens gateway towards integrated plasmonic circuits with electrically reconfigurable functionalities., Comment: 17 pages, 5 figures. Published on