Structure study of a dielectric laser accelerator with discrete translational symmetry

The dielectric laser accelerator(DLA) is a promising technology for achieving high-gradient acceleration in a compact design. Its advantages include ease of cascading and an energy gain per unit distance which can exceed that of conventional accelerators by two orders of magnitude. This paper establishes rules for efficient particle acceleration using dielectric structures based on basic equations, proposes a design principle for DLA structures with clear physical images and verifies the accuracy of the corresponding formula for energy gain. DLA structures with different specifications, materials and geometric shapes are constructed, and the achievable acceleration gradient is calculated. Our results demonstrate that effective acceleration can be achieved when the electric field sensed by particles in the acceleration cavity has zero frequency,which provides a powerful method for designing such devices. Furthermore, we demonstrate that the simplified formula for calculating energy gain presented in this paper can accurately determine the energy gain of particles during the design of acceleration structures using a dielectric accelerator.

EAST-Educational Adaptive-optics Solar Telescope

For the public having a better understanding of solar activities,the Educational Adaptive-optics Solar Telescope(EAST)was built in July 2021 and is located at the Shanghai Astronomy Museum.The EAST consists of a 65 cm aperture solar telescope with a 177-element adaptive optics system and two-channel high resolution imaging system at the Hαand TiO bands,in addition to three full disk solar telescopes at CaK,Hαand TiO bands equipped on the tube of the main telescope.In this paper,the configuration of the EAST is described.Its performance and on-sky observational results are presented.The EAST,to our knowledge,is the most advanced solar telescope for the popularization of science in the world.Due to its excellent performance,the data acquired by the EAST can also be used for research on solar physics and space weather prediction.

Co-focus experiment of segmented mirror

In this paper, an active optics and co-focus experimental system of segmented mirror is built. Firstly, a support structure of segmented mirror is designed and it is verified by simulation to meet the requirement for the experimental system of segmented mirror. In this system, the large de-focus and tilt/tip errors of the segmented mirror are adjusted by observing the density and contrast of interference fringes based on isoclinic interference theory until the defocus and tilt/tip errors are in the detective range of the Shack–Hartmann. Then, the Shack–Hartmann is used to measure them and they are adjusted by actuators. The actuators are controlled by active optics to realize the closed-loop adjustment and maintenance for fine co-focus of segmented mirror. And the interference fringes are utilized to verify the detective precision of Shack–Hartmann. After the co-focus fine-tuning of the segmented mirror, the tilt/tip residual surface error is better than 0.01λ RMS; the defocus residual surface error is better than 0.01λ RMS.

Moderate Resolution Imaging Camera (MoRIC) of China’s First Mars Mission Tianwen-1

China's first Mars exploration mission will carry out comprehensive global surveys of the planet from data collected by instruments carried in orbit and roving on the planet itself.Goals of the mission include detailed inspections and surveys of key areas on the surface of Mars.One of the main scientific payloads installed on the orbiter is the moderate resolution camera.Its mission is to image the surface of Mars sufficiently to produce a global remote sensing image map of the planet,and to explore and record changes to the topography of Mars,including major geological structures,and to advance research on topography and geomorphology in general.The moderate resolution camera uses a lightweight and compact integrated design;its primary components are an optical module,a focal plane module,a camera control module,a power and interface module,a camera support module,a thermal control module,and a reference module.Radiometric calibration,color calibration,and geometric calibration have been carried out to ensure that the camera can acquire sufficient accurate data to complete mission goals.This paper introduces the camera's detection mission,its system composition,and its working principle;it also describes the camera's ground calibration tests and their results,and provides a reference for processing the camera's scientific data and for future applications.

Optical anisotropy of black phosphorus by total internal reflection

Although abundant research on the anisotropy of van der Waals(vd W)materials has been published,we undertake an in-depth study of their optical properties as they have an important guiding role for light control in two-dimensional(2D)nanospace.As an example,we study the reflectance of few-layered black phosphorus(BP)in the total internal reflection(TIR)mode in detail.We demonstrate that its optical anisotropy can be changed on a large scale by varying the incident angles,polarization states,and the in-plane rotation angles of the BP samples.Theoretical analysis indicates that the phenomena observed are common to all the atom-thick biaxial crystals,so these conclusions can be widely applied to other anisotropic 2D materials.This research furthers the current understanding of the properties of BP more comprehensively,and provides guidance for developing new optoelectronic applications,especially when BP and other atom-thick biaxial crystals are integrated with TIR devices.

Acceleration feedback of a current-following synchronized control algorithm for telescope elevation axis

This paper proposes a dual-motor configuration to enhance closed-loop performance of a telescope control system. Two identical motors are mounted on each side of a U-type frame to drive the telescope elevation axis instead of a single motor drive, which is usually used in a classical design. This new configuration and mechanism can reduce the motor to half the size used in the former design, and it also provides some other advantages. A master-slave current control mode is employed to synchronize the two motors. Acceleration feedback control is utilized to further enhance the servo performance. Extensive experiments are used to validate the effectiveness of the proposed control algorithm in synchronization, disturbance attenuation and low-velocity tracking.

An approach to viscoelastic c haracterization of dispersive media by inversion of a general wave propagation model

In the characterization of elastic properties of tissue using dynarmic optical coherence elasto-graphy,shear/surface waves are propagated and tracked in order to estimate speed and Y oung's modulus.However,for dispersive tssues,the displacement pulse is highly damped and distorted during propagation,diminishing the ffectiveness of peak tracking approaches,and leading to biased cstimates of wave speed.Further,plane wave propagation is sometimes assumed,which contributes to estimation erors.Therefore,we invert a wave propagation model that incorpo-rates propagation,decay,and distortion of pulses in a dispersive media in order to accurately estimate its elastic and viscous components.The model uses a general first-order approximation of dispersion,avoiding the use of any particular rheological model of tisue.Experiments are conducted in elastic and viscoelastic tissue mimicking phantoms by producing a Gaussian push using acoustic radiation force excitation and measuring the wave propagation using a Fourier domain optical coherence tomography system.Results confirmed the ffectiveness of the inversion method in est imat ing viscoelastic parameters in both the viscoelastic and elastic phantoms when compared to mechanical measurements.Finally,the viscoelastic characterization of a fresh porcine comea was conducted.Preliminary results validate this approach when compared to other methods.

Topology optimization of on-chip integrated laser-driven particle accelerator

Particle accelerators are indispensable tools in both science and industry.However,the size and cost of conventional RF accelerators limits the utility and scope of this technology.Recent research has shown that a dielectric laser accelerator(DLA)made of dielectric structures and driven at optical frequencies can generate particle beams with energies ranging from MeV to GeV at the tabletop level.To design DLA structures with a high acceleration gradient,we demonstrate topology optimization,which is a method used to optimize the material distribution in a specific area based on given load conditions,constraints,and performance indicators.To demonstrate the effectiveness of this approach,we propose two schemes and design several acceleration structures based on them.The optimization results demonstrate that the proposed method can be applied to structure optimization for on-chip integrated laser accelerators,producing manufacturable structures with significantly improved performance compared with previous size or shape optimization methods.These results provide new physical approaches to explore ultrafast dynamics in matter,with important implications for future laser particle accelerators based on photonic chips.

The Coude Echelle Spectrograph for the Lijiang 1.8 m telescope

The Coude Echelle Spectrograph(CES)was originally mounted on Xinglong 2.16 m telescope in 1994.When the High Resolution Fiber-fed Spectrograph(HRS)was commissioned at Xinglong 2.16 m telescope,the red path of CES was moved to Lijiang 1.8 m telescope,following some redesign and reinstallation.The CES of Lijiang 1.8 m telescope has the spectral resolution(R=λ/?λ)ranging from 20000 to 50000 corresponding to different slit widths.With a 2 k×2 k PI CCD,CES has a wavelength coverage between 570 nm to 1030 nm.In particular,the resolution of 37000 at 0.5 mm slit corresponds to 1.3′′on the sky.The limiting magnitude is V=11.5 with the use of the tip-tilt feedback system,and the S/N is about 40 for 1 hour exposure at 600 nm(R=37000).During the installation of CES,the tip-tilt mirror technology had successfully fulfilled high precision guiding and tracking for high resolution spectral observation and significantly improved the observation efficiency.

特定参数飞秒激光制备离体牙釉质窝洞对髓腔温度的影响

目的:用特定参数飞秒激光在离体牙釉质层制备窝洞,实时监测髓腔温度(intrapulpal temperature,IPT)变化,并初步评价风冷的效果。方法:人类离体牙(前磨牙、磨牙)截根,暴露髓腔。髓腔内填入铜粉,将热电偶置于髓腔中央,将铜粉压实。用绝热胶带封闭髓室底部。室温下,用飞秒激光在离体牙颊面釉质层逐行扫描切削,以0.4 mm/s的平均速度制备边长为2.25 mm的正方形窝洞,用热电偶电子测温仪实时监测髓腔温度变化,温度升至平稳状态后加入风冷。结果:髓腔温度升高量为ΔT,前磨牙风冷前最大ΔT=12.3℃,风冷后温度下降,ΔT=3.0℃。磨牙风冷前最大ΔT=1.8℃,风冷后ΔT=-0.1℃。结论:用特定参数飞秒激光在离体牙齿釉质表面制备平均深度约为250μm窝洞时,牙髓腔温度会随着切削深度的增加而升高,风冷可有效控制温度升高程度。

Spectral absorption control of femtosecond laser-treated metals and application in solar-thermal devices

Direct femtosecond(fs)laser processing is a maskless fabrication technique that can effectively modify the optical,electrical,mechanical,and tribological properties of materials for a wide range of potential applications.However,the eventual implementation of fs-laser-treated surfaces in actual devices remains challenging because it is difficult to precisely control the surface properties.Previous studies of the morphological control of fs-laser-processed surfaces mostly focused on enhancing the uniformity of periodic microstructures.Here,guided by the plasmon hybridisation model,we control the morphology of surface nanostructures to obtain more control over spectral light absorption.We experimentally demonstrate spectral control of a variety of metals[copper(Cu),aluminium(Al),steel and tungsten(W)],resulting in the creation of broadband light absorbers and selective solar absorbers(SSAs).For the first time,we demonstrate that fs-laser-produced surfaces can be used as high-temperature SSAs.We show that a tungsten selective solar absorber(W-SSA)exhibits excellent performance as a high-temperature solar receiver.When integrated into a solar thermoelectric generation(TEG)device,W-SSA provides a 130%increase in solar TEG efficiency compared to untreated W,which is commonly used as an intrinsic selective light absorber.

Modulating the optical and electrical properties of MAPbBr_(3) single crystals via voltage regulation engineering and application in memristors

Defect density is one of the most significant characteristics of perovskite single crystals(PSCs)that determines their optical and electrical properties,but few strategies are available to tune this property.Here,we demonstrate that voltage regulation is an efficient method to tune defect density,as well as the optical and electrical properties of PSCs.A three-step carrier transport model of MAPbBr_(3) PSCs is proposed to explore the defect regulation mechanism and carrier transport dynamics via an applied bias.Dynamic and steady-state photoluminescence measurements subsequently show that the surface defect density,average carrier lifetime,and photoluminescence intensity can be efficiently tuned by the applied bias.In particular,when the regulation voltage is 20 V(electrical poling intensity is 0.167 Vμm^(−1)),the surface defect density of MAPbBr_(3) PSCs is reduced by 24.27%,the carrier lifetime is prolonged by 32.04%,and the PL intensity is increased by 112.96%.Furthermore,a voltage-regulated MAPbBr_(3) PSC memristor device shows an adjustable multiresistance,weak ion migration effect and greatly enhanced device stability.Voltage regulation is a promising engineering technique for developing advanced perovskite optoelectronic devices.

Direct visualization of the complete evolution of femtosecond laser-induced surface structural dynamics of metals

Despite extensive studies of femtosecond laser-material interactions,even the simplest morphological responses following femtosecond pulse irradiation have not been fully resolved.Past studies have revealed only partial dynamics.Here we develop a zerobackground and high-contrast scattered-light-based optical imaging technique through which we capture,for the first time,the complete temporal and spatial evolution of the femtosecond laser-induced morphological surface structural dynamics of metals from start to finish,that is,from the initial transient surface fluctuations,through melting and ablation,to the end of resolidification.We find that transient surface structures first appear at a delay time on the order of 100 ps,which is attributed to ablation driven by pressure relaxation in the surface layer.The formation dynamics of the surface structures at different length scales are individually resolved,and the sequence of their appearance changes with laser fluence is found.Cooling and complete resolidification,observed here for the first time,are shown to occur more slowly than previously predicted by two orders of magnitude.We examine and identify the mechanisms driving each of these dynamic steps.The visualization and control of morphological surface structural dynamics not only are of fundamental importance for understanding femtosecond laser-induced material responses but also pave the way for the design of new material functionalities through surface structuring.

Wavefront reconstruction algorithm for wavefront sensing based on binary aberration modes

We propose a new algorithm for wavefront sensing based on binary intensity modulation. The algorithm is based on the fact that a wavefront can be expended with a series of orthogonal and binary functions, the Walsh series. We use a spatial light modulator（SLM） to produce different binary-intensity-modulation patterns which are the simple linear transformation of the Walsh series. The optical fields under different binary-intensity-modulation patterns are detected with a photodiode.The relationships between the incident wavefront modulated with the patterns and their optical fields are built to determinate the coefficients of the Walsh series. More detailed and strict relationship equations are established with the algorithm by adding new modulation patterns according to the properties of the Walsh functions. An exact value can be acquired by solving the equations. Finally, with the help of phase unwrapping and smoothing, the wavefront can be reconstructed. The advantage of the algorithm is providing an analytical solution for the coefficients of the Walsh series to reconstruct the wavefront. The simulation experiments are presented and the effectiveness of the algorithm is demonstrated.

SERS study on the synergistic effects of electric field enhancement and charge transfer in an Ag2S quantum dots/plasmonic bowtie nanoantenna composite system

Localized surface plasmon resonance(LSPR)of nanostructures and the interfacial charge transfer(CT)of semiconductor materials play essential roles in the study of optical and photoelectronic properties.In this paper,a composite substrate of Ag2S quantum dots(QDs)coated plasmonic Au bowtie nanoantenna(BNA)arrays with a metalinsulator-metal(MIM)configuration was built to study the synergistic effect of LSPR and interfacial CT using surface-enhanced Raman scattering(SERS)in the near-infrared(NIR)region.The Au BNA array structure with a large enhancement of the localized electric field(E-field)strongly enhanced the Raman signal of adsorbed p-aminothiophenol(PATP)probe molecules.Meanwhile,the broad enhanced spectral region was achieved owing to the coupling of LSPR The as-prepared Au BNA array structure facilitated enhancements of the excitation as well as the emission of Raman signal simultaneously,which was established by finite-difference time-domain simulation.Moreover,Ag2S semiconductor QDs were introduced into the BNA/PATP system to further enhance Raman signals,which benefited from the interfacial CT resonance in the BNA/Ag2S-QDs/PATP system.As a result,the Raman signals of PATP in the BNA/Ag2S-QDs/PATP system were strongly enhanced under 785 nm laser excitation due to the synergistic effect of E-field enhancement and interfacial CT.Furthermore,the SERS polarization dependence effeas of the BNA/Ag2S-QDs/PATP system were also investigated.The SERS spectra indicated that the polarization dependence of the substrate increased with decreasing polarization angles(θpola)of excitation from p-polarized(θpola=90°)excitation to s-polarized(θpola=0°)excitation.This study provides a strategy using the synergistic effect of interfacial CT and E-field enhancement for SERS applications and provides a guidance for the development of SERS study on semiconductor QD-based plasmonic substrates,and can be farther extended to other material-nanostructure systems for various optoelectronic and sensing applications.

Laser-induced periodic surface structured electrodes with 45% energy saving in electrochemical fuel generation through field localization

Electrochemical oxidation/reduction of radicals is a green and environmentally friendly approach to generating fuels.These reactions,however,suffer from sluggish kinetics due to a low local concentration of radicals around the electrocatalyst.A large applied electrode potential can enhance the fuel generation efficiency via enhancing the radical concentration around the electrocatalyst sites,but this comes at the cost of electricity.Here,we report about a~45%saving in energy to achieve an electrochemical hydrogen generation rate of 3×10^(16) molecules cm^(–2)s^(–1)(current density:10 mA/cm^(2))through localized electric field-induced enhancement in the reagent concentration(LEFIRC)at laser-induced periodic surface structured(LIPSS)electrodes.The finite element model is used to simulate the spatial distribution of the electric field to understand the effects of LIPSS geometric parameters in field localization.When the LIPSS patterned electrodes are used as substrates to support Pt/C and RuO_(2) electrocatalysts,the η_(10) overpotentials for HER and OER are decreased by 40.4 and 25%,respectively.Moreover,the capability of the LIPSS-patterned electrodes to operate at significantly reduced energy is also demonstrated in a range of electrolytes,including alkaline,acidic,neutral,and seawater.Importantly,when two LIPSS patterned electrodes were assembled as the anode and cathode into a cell,it requires 330 mVs of lower electric potential with enhanced stability over a similar cell made of pristine electrodes to drive a current density of 10 mA/cm^(2).This work demonstrates a physical and versatile approach of electrode surface patterning to boost electrocatalytic fuel generation performance and can be applied to any metal and semiconductor catalysts for a range of electrochemical reactions.

A sodium laser guide star coupling efficiency measurement method

A large telescope＇s adaptive optics （AO） system requires one or more bright artificial laser guide stars to improve its sky coverage. The recent advent of a high power sodium laser is perfect for such application. However, besides the output power, other parameters of the laser also have a significant impact on the brightness of the generated sodium laser guide star, mostly in non-linear relationships. When tuning and optimizing these parameters it is necessary to tune based on a laser guide star generation performance metric. Although return photon fluxis widely used, variability of the atmosphere and sodium layer makes it difficult to compare results from different sites or even within a short time period for the same site. A new metric, coupling efficiency, is adopted in our field tests. In this paper, we will introduce our method for measuring the coupling efficiency of a 20W class pulse sodium laser for AO application during field tests that were conducted during 2013-2015.

Degradation of platinum electrocatalysts for methanol oxidation by lead contamination

Platinum exhibits high electrocatalytic activity toward various reactions but might be poisoned by some species. This communication reports a new finding that the electrocatalytic activity of platinum for methanol oxidation will be largely lost in a lead-contaminated environment. This activity loss is demonstrated in an electrochemical cell using a lead counter electrode for measuring the activity of platinum electrode towards methanol oxidation. The recorded methanol oxidation current in this cell is significantly decreased compared with that using a platinum counter electrode. The possible mechanism is related to the adsorption of trace lead ions from the lead counter electrode, as confirmed by comparing the calculated binding energies of platinum and lead ions with oxygen ion. This report is of great importance for reliably designing and efficiently managing direct methanol fuel cells, because trace lead might be present in various components in the fuel cell systems or in air and attention should be paid to its negative effect.

Local measurement of terahertz field-induced second harmonic generation in plasma filaments

The concept of Terahertz Field-Induced Second Harmonic(TFISH)Generation is revisited to introduce a single-shot detection scheme based on third order nonlinearities.Focused specifcally on the further development of THz plasma-based sources,we begin our research by reimagining the TFISH system to serve as a direct plasma diagnostic.In this work,an optical probe beam is used to mix directly with the strong ponderomotive current associated with laser-induced ionization.A four-wave mixing(FWM)process then generates a strong second-harmonic optical wave because of the mixing of the probe beam with the nonlinear current components oscillating at THz frequencies.The observed conversion efciency is high enough that for the frst time,the TFISH signal appears visible to the human eye.We perform spectral,spatial,and temporal analysis on the detected second-harmonic frequency and show its direct relationship to the nonlinear current.Further,a method to detect incoherent and coherent THz inside plasma flaments is devised using spatio-temporal couplings.The single-shot detection confgurations are theoretically described using a combination of expanded FWM models with Kostenbauder and Gaussian Q-matrices.We show that the retrieved temporal traces for THz radiation from single-and twocolor laser-induced air-plasma sources match theoretical descriptions very well.High temporal resolution is shown with a detection bandwidth limited only by the spatial extent of the probe laser beam.Large detection bandwidth and temporal characterization is shown for THz radiation confned to under-dense plasma flaments induced by<100 fs lasers below the relativistic intensity limit.