Showing papers by "Min Gu published in 2022"

Three-dimensional direct lithography of stable perovskite nanocrystals in glass

Abstract: Material composition engineering and device fabrication of perovskite nanocrystals (PNCs) in solution can introduce organic contamination and entail several synthetic, processing, and stabilization steps. We report three-dimensional (3D) direct lithography of PNCs with tunable composition and bandgap in glass. The halide ion distribution was controlled at the nanoscale with ultrafast laser–induced liquid nanophase separation. The PNCs exhibit notable stability against ultraviolet irradiation, organic solution, and high temperatures (up to 250°C). Printed 3D structures in glass were used for optical storage, micro–light emitting diodes, and holographic displays. The proposed mechanisms of both PNC formation and composition tunability were verified. Description Perovskite nanocrystals under glass Perovskite nanocrystals (PNCs) such as cesium lead triiodide (CsPbI3) can display bright photoemission with narrow linewidths for display applications, but their long-term stability requires passivation and encapsulation steps after synthesis in solution. Sun et al. created three-dimensional arrays of PNCs in doped metal oxide glasses using ultrafast laser pulses that caused local melting and subsequent crystallization. They tuned the bandgap of PNCs and their photoluminescence between 480- and 700-nanometer wavelengths by transforming the composition from CsPb(Cl1-xBrx)3 to CsPbI3. These encapsulated PNCs exhibited long-term stability after prolonged heating or organic solvent and ultraviolet light exposure. —PDS Melting of a doped metal oxide glass with ultrafast laser pulses created perovskite nanocrystal arrays for optoelectronics.

Photonic matrix multiplication lights up photonic accelerator and beyond

Abstract: Matrix computation, as a fundamental building block of information processing in science and technology, contributes most of the computational overheads in modern signal processing and artificial intelligence algorithms. Photonic accelerators are designed to accelerate specific categories of computing in the optical domain, especially matrix multiplication, to address the growing demand for computing resources and capacity. Photonic matrix multiplication has much potential to expand the domain of telecommunication, and artificial intelligence benefiting from its superior performance. Recent research in photonic matrix multiplication has flourished and may provide opportunities to develop applications that are unachievable at present by conventional electronic processors. In this review, we first introduce the methods of photonic matrix multiplication, mainly including the plane light conversion method, Mach-Zehnder interferometer method and wavelength division multiplexing method. We also summarize the developmental milestones of photonic matrix multiplication and the related applications. Then, we review their detailed advances in applications to optical signal processing and artificial neural networks in recent years. Finally, we comment on the challenges and perspectives of photonic matrix multiplication and photonic acceleration.

Photonic matrix multiplication lights up photonic accelerator and beyond

Abstract: Matrix computation, as a fundamental building block of information processing in science and technology, contributes most of the computational overheads in modern signal processing and artificial intelligence algorithms. Photonic accelerators are designed to accelerate specific categories of computing in the optical domain, especially matrix multiplication, to address the growing demand for computing resources and capacity. Photonic matrix multiplication has much potential to expand the domain of telecommunication, and artificial intelligence benefiting from its superior performance. Recent research in photonic matrix multiplication has flourished and may provide opportunities to develop applications that are unachievable at present by conventional electronic processors. In this review, we first introduce the methods of photonic matrix multiplication, mainly including the plane light conversion method, Mach-Zehnder interferometer method and wavelength division multiplexing method. We also summarize the developmental milestones of photonic matrix multiplication and the related applications. Then, we review their detailed advances in applications to optical signal processing and artificial neural networks in recent years. Finally, we comment on the challenges and perspectives of photonic matrix multiplication and photonic acceleration.

Acoustic topological beam nonreciprocity via the rotational Doppler effect

Abstract: Reciprocity is a fundamental principle of wave physics related to time-reversal symmetry. Nonreciprocal wave behaviors have been pursued for decades because of their great scientific significance and tremendous potential applications. However, nonreciprocity devices have been based on manipulation of non-topological charge (TC) in most studies to date. Here, we introduce the rotational Doppler effect (RDE) into the acoustic system to achieve nonreciprocal control of the TC beam. We use the metasurface to generate a vortex beam with a defined TC. By rotating the metasurface with specific angular velocity, the wave vector of the transmitted wave obtains positive and negative transition flexibly due to the RDE. As a result, isolated and propagating states of the vortex beam can be realized by controlling the rotation direction, representing nonreciprocal propagation. Our work also provides an alternative method for the application of TC beams and the realization of nonreciprocity.

Third- and Second-Harmonic Generation in All-Dielectric Nanostructures: A Mini Review

Abstract: Frequency conversion such as harmonic generation is a fundamental physical process in nonlinear optics. The conventional nonlinear optical systems suffer from bulky size and cumbersome phase-matching conditions due to the inherently weak nonlinear response of natural materials. Aiming at the manipulation of nonlinear frequency conversion at the nanoscale with favorable conversion efficiencies, recent research has shifted toward the integration of nonlinear functionality into nanophotonics. Compared with plasmonic nanostructures showing high dissipative losses and thermal heating, all-dielectric nanostructures have demonstrated many excellent properties, including low loss, high damage threshold, and controllable resonant electric and magnetic optical nonlinearity. In this review, we cover the recent advances in nonlinear nanophotonics, with special emphasis on third- and second-harmonic generation from all-dielectric nanoantennas and metasurfaces. We discuss the main theoretical concepts, the design principles, and the functionalities of third- and second-harmonic generation processes from dielectric nanostructures and provide an outlook on the future directions and developments of this research field.

Beyond High-Voltage Capacitors: Supercapacitor Arrays Based on Laser-Scribed Subwavelength-Featured Graphene Patterns

Abstract: Supercapacitors are devices that instantly store and release electrical energy. However, their applications have been severely impeded by low capacitances under high operating voltages due to the surface area limit. This is why supercapacitors have not been applied for energy storage as widely as capacitors. Here, we present an innovative concept of subwavelength-featured graphene supercapacitor arrays fabricated by induction-inhibition femtosecond laser scribing. A graphene oxide film containing water is exposed to a femtosecond laser beam to create the interdigital electrodes of reduced graphene oxide. The presence of water tunes the power threshold of graphene oxide photoreduction by the generation of oxygen molecules and thus inhibits the reduction. A minimum reduced graphene oxide linewidth of 95 nm is achieved, in which the diffraction limit barrier is broken. The supercapacitor exhibits outstanding performances, including an areal capacitance of 91 mF/cm2 and a gravimetric capacitance of 384 F/g. The gravimetric capacitance value is significantly higher than those for reported sandwich-type and interdigital polyimide-reduced graphene supercapacitors. Once the subwavelength-featured supercapacitors are connected in series, 10, 25, and 50 V supercapacitor arrays demonstrate capacitances of 1.8, 0.48, and 0.17 μF, which are dramatically larger than those of capacitors (around 0.1 μF) under the same operating voltages and device areas. The retention of the areal capacitance of the 10 V supercapacitor array is 93.9% after 10,000 cycles at a current of 0.1 μA, exhibiting a considerable cycling stability. Moreover, the ultrafine structure shows a high stability to mechanical cycling. The capacitance retention is around 98.5% after 10,000 folding cycles. The capacitances beyond those of high-voltage capacitors pave the way toward the realization of supercapacitors as mainstream energy storage devices.

Direct laser writing of graphene oxide for ultra-low power consumption memristors in reservoir computing for digital recognition

Abstract: Journal: National Science Open Manuscript ID NSO20220012.R1 Manuscript Type: Research Article Date Submitted by the Author: 12-Apr-2022 Complete List of Authors: Chen, Min; University of Shanghai for Science and Technology Wan, Zhengfen; University of Shanghai for Science and Technology Dong, Hao; University of Shanghai for Science and Technology Chen, Qinyu; University of Shanghai for Science and Technology Gu, Min; University of Shanghai for Science and Technology Zhang, Qiming; University of Shanghai for Science and Technology, School of Optical-Electrical and Computer Engineering

Benchmarking calculations of wavelengths and transition rates with spectroscopic accuracy for W xlviii through W lvi tungsten ions

Abstract: Atomic properties of $n=3$ levels for ${\mathrm{W}}^{47+}\ensuremath{-}{\mathrm{W}}^{55+}$ ions ($Z=74$) are systematically calculated using two different and independent methods, namely, the second-order many-body perturbation theory and the multiconfiguration Dirac-Hartree-Fock method combined with the relativistic configuration interaction approach. Wavelengths and transition rates for electric- and magnetic-dipole transitions involving the $n=3$ levels of ${\mathrm{W}}^{47+}\ensuremath{-}{\mathrm{W}}^{55+}$ are calculated. In addition, we discuss in detail the importance of the valence and core-valence electron correlations, the Breit interaction, the higher-order frequency-dependent retardation correction, and the leading quantum electrodynamical corrections for transition wavelengths. Spectroscopic accuracy is achieved for the present calculated wavelengths, and most of them agree with experimental values within $0.05%$. Our calculated wavelengths, combined with collisional radiative model simulations, are used to identify the yet unidentified 25 observed lines in the extremely complex spectrum between $27\phantom{\rule{0.16em}{0ex}}\AA{}$ and $34\phantom{\rule{0.16em}{0ex}}\AA{}$ measured by Lennartsson $et\phantom{\rule{4pt}{0ex}}al.$ [Phys. Rev. A 87, 062505 (2013)]. We provide additional data for 472 strong electric-dipole transitions in the wavelength range of 17--50 \AA{}, and 185 strong magnetic-dipole transitions between $36\phantom{\rule{0.16em}{0ex}}\AA{}$ and $4384\phantom{\rule{0.16em}{0ex}}\AA{}$, with a line intensity greater than $1\phantom{\rule{0.16em}{0ex}}\mathrm{photon}/\mathrm{s}$. These can provide benchmark data for future experiments and theoretical calculations.

Low-Threshold Optical Bistability in the Graphene-Oxide Integrated Asymmetric Nanocavity at Visible Light Frequencies

Abstract: Here, we propose an optical bistable device structure with a few layers of graphene oxide integrated in the metal-dielectric-metal based asymmetric nanocavity. Through the light confinement in the nanocavity, the third order nonlinear absorption of graphene oxide can be significantly enhanced, which experimentally delivers low-threshold optical bistability at the visible wavelength of 532 nm with only 267 KW/cm2 intensity. In addition, the switching threshold can be further reduced via increasing the graphene oxide thickness, hence paving a new way for achieving tunable optical bistable devices at visible light frequencies.

Probing atomic physics at ultrahigh pressure using laser-driven implosions

Abstract: Spectroscopic measurements of dense plasmas at billions of atmospheres provide tests to our fundamental understanding of how matter behaves at extreme conditions. Developing reliable atomic physics models at these conditions, benchmarked by experimental data, is crucial to an improved understanding of radiation transport in both stars and inertial fusion targets. However, detailed spectroscopic measurements at these conditions are rare, and traditional collisional-radiative equilibrium models, based on isolated-atom calculations and ad hoc continuum lowering models, have proved questionable at and beyond solid density. Here we report time-integrated and time-resolved x-ray spectroscopy measurements at several billion atmospheres using laser-driven implosions of Cu-doped targets. We use the imploding shell and its hot core at stagnation to probe the spectral changes of Cu-doped witness layer. These measurements indicate the necessity and viability of modeling dense plasmas with self-consistent methods like density-functional theory, which impact the accuracy of radiation transport simulations used to describe stellar evolution and the design of inertial fusion targets.

X-ray spectra of the Fe-L complex. III. Systematic uncertainties in atomic data

Abstract: There has been a growing request from the X-ray astronomy community for a quantitative estimate of systematic uncertainties origi- nating from the atomic data used in plasma codes. Though there have been several studies looking into atomic data uncertainties using theoretical calculations, in general, there is no commonly accepted solution for this task. We present a new approach for estimating uncertainties in the line emissivities for the current models of collisional plasma, mainly based upon a dedicated analysis of observed high resolution spectra of stellar coronae and galaxy clusters. We find that the systematic uncertainties of the observed lines consistently show an anticorrelation with the model line fluxes, after properly accounting for the additional uncertainties from the ion concentration calculation. The strong lines in the spectra are in general better reproduced, indicating that the atomic data and modeling of the main transitions are more accurate than those for the minor ones. This underlying anticorrelation is found to be roughly independent of source properties, line positions, ion species, and the line formation processes. We further applied our method to the simulated XRISM and Athena observations of collisional plasma sources and discuss the impact of uncertainties on the interpretation of these spectra. The typical uncertainties are 1 − 2% on temperature and 3 − 20% on abundances of O, Ne, Fe, Mg, and Ni.

Path to Increasing p-B11 Reactivity via ps and ns Lasers

Abstract: The Lawson criterion for proton-boron (p-11B) thermonuclear fusion is substantially higher than that for deuterium-tritium (DT) because the fusion cross section is lower and peaks at higher ion energies. The Maxwellian averaged p-11B reactivity peaks at several hundred keV, where bremsstrahlung radiation emission may dominate over fusion reactions if electrons and ions are in thermal equilibrium and the losses are unrestricted. Nonequilibrium burn has often been suggested to realize the benefits of this aneutronic reaction, but the predominance of elastic scattering over fusion reactivity makes this difficult to achieve. The development of ultrashort pulse lasers (USPL) has opened new possibilities for initiating nonequilibrium thermonuclear burns and significant numbers of p-11B alpha particles have been reported from several experiments. We present an analysis that shows that these significant alpha yields are the result of beam fusion reactions that do not scale to net energy gain. We further find that the yields can be explained by experimental parameters and recently updated cross sections such that a postulated avalanche mechanism is not required. We use this analysis to understand the underlying physics of USPL-driven nonequilibrium fusion reactions and whether they can be used to initiate fusion burns. We conclude by outlining a path to increasing the p-11B reactivity towards the goal of achieving ignition and describing the design principles that we will use to develop a computational point design.

Three-dimensional direct laser writing of biomimetic neuron interfaces in the era of artificial intelligence: principles, materials, and applications

Abstract: Abstract. The creation of biomimetic neuron interfaces (BNIs) has become imperative for different research fields from neural science to artificial intelligence. BNIs are two-dimensional or three-dimensional (3D) artificial interfaces mimicking the geometrical and functional characteristics of biological neural networks to rebuild, understand, and improve neuronal functions. The study of BNI holds the key for curing neuron disorder diseases and creating innovative artificial neural networks (ANNs). To achieve these goals, 3D direct laser writing (DLW) has proven to be a powerful method for BNI with complex geometries. However, the need for scaled-up, high speed fabrication of BNI demands the integration of DLW techniques with ANNs. ANNs, computing algorithms inspired by biological neurons, have shown their unprecedented ability to improve efficiency in data processing. The integration of ANNs and DLW techniques promises an innovative pathway for efficient fabrication of large-scale BNI and can also inspire the design and optimization of novel BNI for ANNs. This perspective reviews advances in DLW of BNI and discusses the role of ANNs in the design and fabrication of BNI.

New Measurement Resolves Key Astrophysical Fe XVII Oscillator Strength Problem.

Abstract: One of the most enduring and intensively studied problems of x-ray astronomy is the disagreement of state-of-the art theory and observations for the intensity ratio of two Fe XVII transitions of crucial value for plasma diagnostics, dubbed 3C and 3D. We unravel this conundrum at the PETRA III synchrotron facility by increasing the resolving power 2.5 times and the signal-to-noise ratio thousandfold compared with our previous work. The Lorentzian wings had hitherto been indistinguishable from the background and were thus not modeled, resulting in a biased line-strength estimation. The present experimental oscillator-strength ratio R_{exp}=f_{3C}/f_{3D}=3.51(2)_{stat}(7)_{sys} agrees with our state-of-the-art calculation of R_{th}=3.55(2), as well as with some previous theoretical predictions. To further rule out any uncertainties associated with the measured ratio, we also determined the individual natural linewidths and oscillator strengths of 3C and 3D transitions, which also agree well with the theory. This finally resolves the decades-old mystery of Fe XVII oscillator strengths.

High‐accuracy, direct aberration determination using self‐attention‐armed deep convolutional neural networks

Abstract: Optical microscopes have long been essential for many scientific disciplines. However, the resolution and contrast of such microscopic images are dramatically affected by aberrations. In this study, compacted with adaptive optics, we propose a machine learning technique, called the ‘phase‐retrieval deep convolutional neural networks (PRDCNNs)’. This aberration determination architecture is direct and exhibits high accuracy and certain generalisation ability. Notably, its performance surpasses those of similar, existing methods, with fewer fluctuations and greater robustness against noise. We anticipate future application of the proposed PRDCNNs to super‐resolution microscopes.

Electronic Stopping Power of Ions in Cold Targets and Warm Plasmas

Abstract: We report on a new wide range electronic stopping power model that builds on the random phase approximation (RPA) dielectric response formalism of Wang, et al [1] and the local density approximation (LDA) with electronic density distributions calculated in an average atom model using the Flexible Atomic Code (FAC) [2] . The accuracy of this model has been greatly improved by implementing several extensions to RPA theory including a strong collision correction based on the binary collision theory of Zwicknagel for k>kmax [3] , a static local field correction [4] , an electron binding energy correction, and the Barkas effect [5] . The combined corrections bring our RPA-LDA proton stopping power results in cold targets into close agreement with experiments across the periodic table (PSTAR database). We will also show results for the stopping of ions in warm dense plasmas as compared with the published data. We will describe our plans to implement this accurate ion stopping power model into an efficient and robust framework for computing ion energy deposition in HED plasmas spanning a wide range of temperatures and densities and to incorporate them into the HELIOS-CR hydro code (Prism) and Chicago (Voss), as well as an open source standalone code.

Application and development of fluorescence probes in MINFLUX nanoscopy

Abstract: The MINimal emission FLUXes (MINFLUX) technique in optical microscopy, widely recognized as the next innovative fluorescence microscopy method, claims a spatial resolution of 1–3[Formula: see text]nm in both dead and living cells. To make use of the full resolution of the MINFLUX microscope, it is important to select appropriate fluorescence probes and labeling strategies, especially in living-cell imaging. This paper mainly focuses on recent applications and developments of fluorescence probes and the relevant labeling strategy for MINFLUX microscopy. Moreover, we discuss the deficiencies that need to be addressed in the future and a plan for the possible progression of MINFLUX to help investigators who have been involved in or are just starting in the field of super-resolution imaging microscopy with theoretical support.

Giant Nonlinear Optical Response of Graphene Oxide Thin Films Under the Photochemical and Photothermal Reduction

Abstract: Thin graphene oxide (GO) films have been widely explored for their outstanding optical properties, especially their large optical nonlinear coefficients, and high tunability of optical nonlinear coefficients under photoreduction. In this work, an experimental observation of giant nonlinear optical response in GO films under two different photoreduction mechanisms is reported. After ultraviolet (UV) light‐induced photochemical reduction and continuous wave (CW) laser‐induced photothermal reduction, the nonlinear optical response of reduced graphene oxide (rGO) via the Z‐scan method using a femtosecond laser beam at a wavelength of 800 nm is characterized. The rGO exhibits a giant optical nonlinearity, especially two‐photon absorption (TPA). A giant TPA coefficient of rGO on the order of ≈105 cm GW−1 is obtained under two photoreduction mechanisms (photochemistry and photothermal). This is the first time that a large enhancement effect of TPA has been observed in graphene‐based materials, and the TPA coefficient is an order of magnitude higher than the highest value previously reported. The versatile optical nonlinear properties imply a huge potential of the GO film in advanced photonic and optoelectronic devices such as broadband ultrafast optical switching and optical limiting.

Topological Insulator Optoelectronic Synapses for High‐Accuracy Binary Image Recognition using Recurrent Neural Networks

Abstract: Artificial optoelectronic synapses have drawn tremendous attention in neuromorphic computing due to their exceptional properties of incorporating optical‐sensing and synaptic functions. However, the complex fabrication processes and device architectures greatly limit their applications. More importantly, artificial neural networks (ANNs) commonly implemented with optoelectronic synapses cannot take full advantage of the time‐dependent data of synaptic devices, resulting in defective accuracies. Here, facile two‐terminal optoelectronic synapses based on topological insulator Sb2Te3 films are fabricated, which exhibit significant photocurrent responses, owing to the efficient light‐matter interaction in bulk and the topological surface state of Sb2Te3. The performance of Sb2Te3 devices can be tuned both optically and electrically. Typical characteristics of synapses, such as paired‐pulse facilitation, short‐term memory, long‐term memory, and learning behavior, have been demonstrated. With the establishment of recurrent neural networks (RNNs) that are committed to processing temporal data, the as‐fabricated synapse devices are employed for binary image recognition of handwritten numbers “0” and “1”. The recognition accuracy of RNNs can reach as high as 100%, which is dramatically higher than those of ANNs. The effective employment of temporal data with RNNs ensured high recognition accuracy. These Sb2Te3 optoelectronic synapses with RNNs indicate the great potential for developing high‐performance brain‐inspired neuromorphic computing.

Evaluation of Resources and Environment Carrying Capacity Based on Support Pressure Coupling Mechanism: A Case Study of the Yangtze River Economic Belt

Abstract: Resource and environmental carrying capacity (RECC) is an important basis for achieving sustainable urban development, and analysis of the relationship between regional resources and human activities is of great significance for sustainable regional development. Taking the Yangtze River Economic Belt (YREB) as the study area, this study establishes a framework for analyzing RECC based on the resource and environmental support capacity (RES) and the pressure on the resource and environment (REP), calculates the RES and REP of 110 cities in the YREB from 2009 to 2018, and analyzes the main constraints on RECC. The results show that (1) there are inter-regional imbalances in RECC within the study area, with cities that are more economically developed or at a higher administrative level usually having more severe problems with RECC. (2) The RES and REP indices of cities in the YREB show an overall increasing trend, but the relative growth rates of the RES and REP indices of cities at different levels differ. (3) The built-up area, green space in built-up areas, total gas supply, and length of sewage pipes are hindering factors for most cities to improve their RES. This study contributes to a comprehensive understanding of the current situation and changing trends of RECC in the YREB and can provide a reference for decision-making on sustainable development of the region’s large river basin.

Nuclear Excitation by Muon Capture

Abstract: Efficient excitation of nuclei via exchange of a real or virtual photon has a fundamental importance for nuclear science and technology development. Here, we present a new mechanism of nuclear excitation based on the capture of a free muon into the atomic orbits (NEμC). The cross section of such a new process is evaluated using the Feshbach projection operator formalism and compared to other known excitation phenomena, i.e. photo-excitation and nuclear excitation by electron capture (NEEC), showing up to ten orders of magnitude increase in cross section. NEμC is particularly interesting for MeV excitations that become accessible thanks to the stronger binding of muons to the nucleus. The binding energies of muonic atoms have been calculated introducing a state of the art modification to the Flexible Atomic Code (FAC). An analysis of an experimental scenarios in the context of modern muon production facilities shows that the effect can be detectable for selected isotopes. The total probability of NEμC is predicted to be P ≈ 1 × 10−6 per incident muon in a beam-based scenario. Given the high transition energy provided by muons, NEμC can have important consequences for isomer feeding and particle-induced fission.

X-Ray Photoabsorption of Density-sensitive Metastable States in Ne vii, Fe xxii, and Fe xxiii

Abstract: Metastable states of ions can be sufficiently populated in absorbing and emitting astrophysical media, enabling spectroscopic plasma-density diagnostics. Long-lived states appear in many isoelectronic sequences with an even number of electrons, and can be fed at large rates by various photonic and electronic mechanisms. Here, we experimentally investigate beryllium-like and carbon-like ions of neon and iron that have been predicted to exhibit detectable features in astrophysical soft X-ray absorption spectra. An ion population generated and excited by electron impact is subjected to highly monochromatic X-rays from a synchrotron beamline, allowing us to identify Kα transitions from metastable states. We compare their energies and natural line widths with state-of-the-art theory and benchmark level population calculations at electron densities of 1010.5 cm−3.

Photopolymerization assisted by up-conversion nanoparticles for three-dimensional low-power photonics applications

Abstract: Photopolymerization assisted by up conversion nanoparticles (UCNPs) are reported to have promising potential in the biological field due to the unique fluorescent features of UCNPs. Here, we demonstrate a novel method in the fabrication of three-dimensional (3D) features at low power level with unique photo-luminescence property through the incorporation of UCNPs under a far-field direct laser writing (DLW) configuration. Equipped with long lifetime of excited energy levels, UCNPs were employed to function as the excitation light source for inducing controlled reversible deactivation radical polymerization through activating polymerization photo reagents via resonance energy transfer in the localized area surrounding the UCNPs, hence generating polymerized micro-scale features upon an incident near-infrared laser beam. UCNPs with unique emission qualities were custom-synthesized and dispersed in a monomer-based mixture containing polymerization photo-reagents to formulate a photo-sensitive nanocomposite. A thin film sample based off the nanocomposite was then placed under a DLW scheme for the fabrication of 3D micro-structures at low power level (100sW/cm2 for the writing laser beam intensity). Able to fabricate 3D micro-structures at very low power level with unique photo-luminescent properties compared to the traditional two-photon polymerization technique, this new method of laser fabrication method assisted by UCNPs has significant potential applications in research domains such as 3D low-power nanoscale optical memory, high-resolution imaging/display, functional micro-photonics devices and 3D micro-prototyping.

Low-power nanoscale optical memory by upconversion-based photo-activation

Abstract: Far-field super-resolution optical technologies offer methods to high-capacity nanoscale optical memory. Typical approaches need high beam power and energy consumption. Because they can convert near-infrared excitation to ultraviolet and visible emission, upconversion nanoparticles show potential for photo-activation. Upconversion nanoparticles have metastable excited energy levels, enabling low-power stimulated emission depletion microscopy. We show the use of upconversion nanoparticles for low-power nanoscale photo-activation for high-capacity low-energy consumption optical memory. Upconversion nanoparticles were combined with photo-active compounds. Super-resolution irradiation excited upconversion nanoparticles for photo-activation in the nanocomposite. Written features showed nanoscale size under low-intensity irradiation and enabled multiple optical readouts.

Two-Beam Ultrafast Laser Scribing of Graphene Patterns with 90-nm Subdiffraction Feature Size

Abstract: The fabrication of high-resolution laser-scribed graphene devices is crucial to achieving large surface areas and thus performance breakthroughs. However, since the investigation mainly focuses on the laser-induced reduction of graphene oxide, the single-beam scribing provides a tremendous challenge to realizing subdiffraction features of graphene patterns. Here, we present an innovative 2-beam laser scribing pathway for the fabrication of subdiffraction graphene patterns. First, an oxidation reaction of highly reduced graphene oxide can be controllably driven by irradiation of a 532-nm femtosecond laser beam. Based on the oxidation mechanism, a 2-beam laser scribing was performed on graphene oxide thin films, in which a doughnut-shaped 375-nm beam reduces graphene oxide and a spherical 532-nm ultrafast beam induces the oxidation of laser-reduced graphene oxide. The spherical beam turns the highly reduced graphene oxide (reduced by the doughnut-shaped beam) to an oxidized state, splitting the laser-scribed graphene oxide line into 2 subdiffraction featured segments and thus forming a laser-scribed graphene/oxidized laser-scribed graphene/laser-scribed graphene line. Through the adjustment of the oxidation beam power, the minimum linewidth of laser-scribed graphene was measured to be 90 nm. Next, we fabricated patterned supercapacitor electrodes containing parallel laser-scribed graphene lines with subdiffraction widths and spacings. An outstanding gravimetric capacitance of 308 F/g, which is substantially higher than those of reported graphene-based supercapacitors, has been delivered. The results offer a broadly accessible strategy for the fabrication of high-performance graphene-based devices including high-capacity energy storage, high-resolution holograms, high-sensitivity sensors, triboelectric nanogenerators with high power densities, and artificial intelligence devices with high neuron densities.

Colorful Optical Vortices with White Light Illumination

Abstract: The orbital angular momentum (OAM) of light holds great promise for applications in optical communication, super-resolution imaging, and high-dimensional quantum computing. However, the spatio-temporal coherence of the light source has been essential for generating OAM beams, as incoherent ambient light would result in polychromatic and obscured OAM beams in the visible spectrum. Here, we extend the applications of OAM to ambient lighting conditions. By miniaturizing spiral phase plates and integrating them with structural color filters, we achieve spatio-temporal coherence using only an incoherent white light source. These optical elements act as building blocks that encode both color and OAM information in the form of colorful optical vortices. Thus, pairs of transparent substrates that contain matching positions of these vortices constitute a reciprocal optical lock and key system. Due to the multiple helical eigenstates of OAM, the pairwise coupling can be further extended to form a one-to-many matching and validation scheme. Generating and decoding colorful optical vortices with broadband white light could find potential applications in anti-counterfeiting, optical metrology, high-capacity optical encryption, and on-chip 3D photonic devices.

K-shell Emission from O vi Near 19 Å

Abstract: Laboratory measurements of O vi K-shell emission lines are presented that are situated near the O viii Lyα line at 19 Å. The data provide additional rest-frame references for velocity determinations based on absorption features in the spectra of warm absorbers in active galactic nuclei and other astrophysical objects. They also provide benchmarks for testing atomic structure calculations of energy levels with electrons in a high principal quantum number (n = 3, 4). Excellent agreement is found with our calculations using the many-body perturbation theory method, and we provide a complete listing of the O vi energy levels calculated with this approach.