A phase-retrieval-based 4-dimensional diagnostic method is proposed to resolve the spatial and temporal evolution of plasma in air induced by ultrafast laser. The plasma evolution dynamics (from generation to relaxation) were temporally resolved across several hundred picoseconds, spanning 3 orders of magnitude in measurable electron density (10 15 to 10 18 cm −3 ). The proposed method provides comprehensive, microscopic, and instantaneous insight into the underlying physical mechanisms of nonlinear phenomena induced by femtosecond filament.

Array detection chip is one of the key components of terahertz (THz) systems, with important applications in nondestructive testing, perspective imaging, and high-speed communication. This letter proposes an optical readout THz stacked metamaterial array chip operating at a frequency near the atmospheric window (0.22 THz). It adopts the design of upper and lower chips separation and then bonding to achieve the stacked structure. The upper chip combines with metamaterial cantilever pixels to achieve sensing and execution functions, while the lower chip undertakes auxiliary and support functions. The incident THz radiation can be absorbed and converted to mechanical energy of pixels, then read out in parallel at high speed by the optical system. The stacked mechanism reduces the size and thickness of the sensing/execution structure and improves the radiation-thermal-mechanical sensitivity of the chip. Spectral measurements show that its absorptivity is 97%. Meanwhile, the time measurement results indicate that the chip can quickly respond to THz radiation, with a response time of 1.62 ms.

Under the extreme conditions of rapid melting-solidification and complex melt pool dynamics inherent to Selective Laser Melting (SLM), achieving uniform dispersion and strong interfacial bonding of graphene within aluminum matrices remains challenging, which limits its reinforcement efficiency. To address this issue, graphene nanoplatelets (GNPs) were modified using aluminum nitrate nonahydrate (Al(NO3)3 & sdot;9H2O) to obtain Al2O3-coated GNPs (Al2O3@GNPs). Subsequently, GNPs/Al12Si and Al2O3@GNPs/Al12Si composites were fabricated via SLM. The effects of different reinforcements on microstructure, microhardness, tribological behavior, and electrochemical corrosion performance were systematically investigated. The SLM-fabricated samples exhibited relative densities exceeding 99% and a typical cellular structure with eutectic Si-enriched cell boundaries. Compared with pristine GNPs, Al2O3@GNPs showed more uniform dispersion and improved interfacial bonding within the Al12Si matrix. Consequently, the microhardness increased by 29.3%, the wear rate decreased by 52.9%, and the corrosion current density was reduced by 99.4%. The property enhancement is mainly attributed to improved interfacial wettability induced by the Al2O3 coating, which facilitates more efficient load transfer, promotes the formation of a stable tribolayer during sliding, and provides a more effective barrier against corrosive media. These results demonstrate that interfacial regulation through surface modification is an effective strategy for achieving synergistic improvements in the mechanical, tribological, and electrochemical properties of SLM-fabricated aluminum matrix composites.

High aspect ratio holes in nickel-based alloys have significant applications in the film cooling of aircraft turbine engines. The high inlet temperature (>2200 degrees C) of the next generation turbine engine imposes stringent requirements on the cooling efficiency of its hot components such that the commercial macro-hole cooling with cooling efficiency <= 60% cannot meet the requirements. Micro cooling holes with diameter of similar to 0.1 mm are proposed to generate up to 90% cooling efficiency. However, current processing techniques face challenges of inefficient debris removal and debris redeposition on the inner walls, making it difficult and inefficient to fabricate high aspect ratio holes with diameters <= 0.1 mm. In this work, an aerosol assisted laser spinning method is proposed to fabricate free tapered or reverse tapered holes with diameters <= 0.1 mm and aspect ratios >= 20 in nickel-based alloys. The aerosol modulates the laser intensity distribution and the hole's perforation time is reduced by 35.6%. This study provides a cost-effective drilling efficiency improvement method for fabricating high aspect ratio micro-holes in opaque materials with broad applicability, particularly in processing micro cooling holes in turbine engines.

Heavy metal pollution, particularly in the form of airborne aerosols such as lead (Pb), cadmium (Cd), mercury (Hg), and cobalt (Co), poses serious health and environmental risks, necessitating highly sensitive remote detection techniques. In this study, Filament-Induced Fluorescence Spectroscopy (FIFS) was employed to detect ultra-trace concentrations of heavy metal aerosols with high sensitivity and stability. By systematically optimizing the balance between filament length and detection distance, the optimal detection distance under the current experimental conditions was determined. With a detection distance of 10 m, this work achieved a minimum detectable concentration of 0.47 pg m^-3 for Pb and an extrapolated limit of detection (LOD) of 0.3 pg m^-3, with excellent signal stability (RSD < 7 pg m^-3 to 0.47 g m^-3. Additionally, Cd, Hg, and Co aerosols were also successfully detected under the same conditions, with detection limits of 2 pg m^-3, 0.25 pg m^-3, and 3 pg m^-3, respectively, further confirming the versatility of FIFS in detecting diverse heavy metals. Theoretical predictions suggest that increasing laser power could further enhance the detection capability. These results highlight the ultra-sensitive remote detection capability of FIFS for heavy metal aerosol detection and provide valuable insights for optimizing system parameters to enhance its application performance in environmental monitoring.

Accidental exposure to overdose ionizing radiation will inevitably lead to severe biological damage, thus detecting and localizing radiation is essential. Traditional measurement techniques are generally restricted to the detection range of few centimeters, posing a great risk to operators. The prospect in remote sensing makes femtosecond laser filament technology a great candidate for constructively addressing this challenge. Here we propose a novel filament-based ionizing radiation sensing method, and clarify the interaction mechanism between filaments and ionizing radiation from systematic experiment to microscopic theory. Specifically, it is demonstrated that the energetic electrons produced by alpha radiation in air can be effectively accelerated within the filament, serving as seed electrons, which will enhance nitrogen fluorescence. The extended nitrogen fluorescence lifetime of similar to 1 ns is also observed. Lastly, the combined microscopic model was elaborately established to quantitatively explain the modulation of nitrogen fluorescence emission from filament by ionizing radiation. These findings provide insights into the intricate interaction among ultra-strong light field, plasma and energetic particle beam, potentially suggesting a promising novel avenue for remote sensing of ionizing radiation.

The diffraction limit of traditional millimeter-wave components makes them difficult to break through the wavelength limitation and obtain high-resolution images. Here, we propose a waveguide-metalens, which not only inherits the low loss of waveguides and the far-field imaging of a metalens but also realizes sub-wavelength super-resolution focusing. The imaging method based on a waveguide-metalens combines the integrability and flexibility of waveguides with the phase modulation characteristics of metalenses. By optimization, high-resolution focusing of less than 1/2 wavelength can be achieved at a distance of 4.7 times the wavelength. For verification, we developed a reflective imaging system operating at a frequency near the millimeter-wave atmospheric window (94 GHz), and tested the resolution plate, aerospace ceramics, industrial rubber, and aerospace honeycomb materials. The experimental results are consistent with the theoretical simulations.

Lead is a highly toxic element which poses a serious threat to human health when it dissolves in water. Laser induced breakdown spectroscopy is a simple and fast element detection method which can be used to detect liquid samples. In order to improve the limit of detection of Pb2+ in water, chelating agent assisted LIBS is investigated in this work. Sodium diethyldithiocarbamate (DDTC) is a commonly used Pb2+ chelating agent which can chelate Pb2+ bidentately. In experiments, sodium DDTC is used to chelate Pb2+ and deposits at the bottom of liquid sample by centrifugation. The precipitate is dried and concentrated on the graphite substrate. Under the optimal conditions, such as optimal concentration of sodium DDTC (0.25 mg/mL) and centrifugation time (5 min), the limits of detection of Pb2+ are 2.82 ng/mL for tap water and 3.64 ng/mL for river water are achieved. Without using sodium DDTC, the limits of detection of Pb2+ for tap water and river water are 18.20 ng/mL and 23.00 ng/mL respectively. Sodium DDTC can improve the limit of detection by more than 6 times. The work in this paper proposes a fast, simple and cost-effectively method to quantitatively measure heavy metallic elements in water samples.

Femtosecond laser filamentation has attracted significant attention due to its applications in remote sensing of atmospheric pollutants and artificial weather intervention.Nitrogen is the most abundant gas in the atmosphere,and its stimulated ultraviolet emission is remarkably clean,distinctly different from the fluorescence obtained through electron impact or laser breakdown.While numerous experiments and mechanism analyses have been con-ducted on its characteristic fluorescence excited by laser filamentation,they predominantly focused on short-distance filamentation(less than 1 m).Contrary to previous reports,we find that at long distances(30 m),the fluorescence intensity of neutral nitrogen molecules excited by linearly polarized laser pulses is approximately 7 times that excited by circularly polarized pulses with the same energy.This enhancement is caused by the enhanced tunneling ioniza-tion rate,3.7 times that under circular polarization,and the elongated filament length,1.85 times that under circular polarization,when using linear polarization.Additionally,after comparing existing theories for N2(C3Πu))exci-tation,the dissociation-recombination model is found to be more appropriate for explaining the formation of N2(C3Πu))excited states during long-distance filamentation.

The temperature distribution of both the nanotip and the substrate during thermal scanning probe lithography processing is a critical factor that significantly influences the processing outcomes. The nanotip and the contact area both exhibit a relatively small spatial scale, which presents a significant challenge in accurately measuring the temperature distribution during thermal processing. In this study, finite element simulations are carried out to investigate the thermophysical process between the laser-irradiated nanotip and the PMMA substrate. The temperature distributions of the nanotip and substrate at different contact thermal resistances, apex radii, and vertical loads are investigated. The findings reveal that as the thermal contact resistance rises, the average temperature of the interface between the nanotip and the PMMA substrate diminishes, while it increases with the rise in the vertical load. The maximum average temperature reaches 669.51 K when the laser power and apex radius are 20 mW and 20 nm, respectively. Furthermore, the effective area of heat conduction, delineated by temperatures surpassing the glass transition temperature of PMMA, exhibits a similar trend to the average temperature. The results obtained under various conditions provide theoretical insights for optimizing the process settings of laser-assisted precise fabrication.

Ultrashort terahertz (THz) pulse has a broad spectral bandwidth and essential applications in material identification and disease diagnosis. In this work, the cascaded Fabry-Perot interferometer is proposed to construct a Fabry-Perot cavity based first-order autocorrelator(FPAC) for measuring the spectrum of the ultrashort THz pulse. The FPAC is made up of two pieces of uncoated high resistivity float zone silicon wafers and can be regarded as three tandem Fabry-Perot interferometers/etalons. It can be demonstrated numerically that without any coating process to measure the spectrum of the THz pulse. Using the home-built FPAC, the spectrum of THz pulses generated by dual-color femtosecond laser filament and the THz transmission spectrum of the penicillin sodium tablet is measured, experimentally demonstrating the validity of the FPAC in THz spectrum detection. Compared to other THz spectrum detection methods, such as the Fourier transform spectrometer and THz time-domain spectral system, the FPAC has a more compact structure due to the utilization of the common-path interference setup, which can be used in narrow space for in situ detection.

We present a dual -comb fiber laser in the wavelength range of 2.1 mu m from an all -polarization -maintaining holmium -doped fiber laser based on a reflective nonlinear amplifying loop mirror (Figure- 9) scheme. The dynamics of the laser, where net cavity dispersion is controlled by varying the length of the intra-cavity dispersioncompensating fiber (DCF), has been fully investigated. The laser is found capable of mode -locking with a net cavity dispersion value ranging from net anomalous (-0.19 ps 2 ) to net normal (0.11 ps 2 ). More interestingly, without any intentional design, dual -comb operation with a relatively small offset frequency, down to a few Hertz, is observed in the system. The dual -comb operation is believed to arise from direction multiplexing in the loop cavity and polarization multiplexing in the linear arm, and is likely to be a generic solution for Figure- 9 lasers. Such a dual -comb system with a characteristic small frequency difference can provide sample interval with higher precision in asynchronous optical sampling (ASOP) applications.

Femtosecond laser filament-induced plasma spectroscopy (FIPS) demonstrates great potential in remote sensing for identifying atmospheric pollutant molecules. Due to the widespread aerosols in the atmosphere, remote detection based on FIPS would be affected by both the excitation and the propagation of fingerprint fluorescence, which still remain elusive. Here the physical model of filament-induced aerosol fluorescence is established to reveal the combined effect of Mie scattering and amplification spontaneous emission, which is subsequently proven by experimental results, the dependence of the backward fluorescence on the interaction length between filaments and aerosols. These findings provide an insight into the complicated aerosol effect in the overall physical process of FIPS including propagation, excitation, and emission, paving the way to its practical application in atmospheric remote sensing.

Remote spectral detection is an important way to explore large-scale space and matter,which plays critical roles in astronomy,meteorology,and the deep sea.However,detecting remote and often weak spectra poses high requirements for the performance of spectrometers.According to the spectral performance evaluation standard proposed by Jacquinot,compared with other spectral systems(grating spectrometer,prism spectrometer,etc.),the Fabry Perot(F-P)interferometer has a large aperture and high spectral resolution,which possesses the intrinsic advantage in the field of remote weak light detection.Since Fabry first used the F-P interferometer for astronomical observation in 1914,the F-P interferometer has been widely used in remote spectral measurement,and various improved F-P interferometers have been developed in recent years.Traditional F-P interferometers mainly face three problems when used in remote spectral detection:narrow free spectral range,difficult installation and adjustment of large aperture F-P interferometers,and unconcentrated spectral energy induced by the circular interference structures.This article introduces three typical improved F-P interferometers,including the cascaded F-P interferometer that greatly extends the free spectral range,the rotating scanning F-P interferometer that eases the adjustment and is suitable for extreme environments,and the circle-to-line interferometer optical system(CLIO)that converts interference rings to interference lines with improved energy concentration.This article provides a systematic summary of the important applications of the F-P interferometer in meteorology,astronomy,and the deep sea.In meteorology,a large-aperture F-P interferometer for measuring wind speeds in the atmosphere's mesosphere and thermosphere was introduced,and a German Heisenberg high-precision F-P interferometer for measuring trace gases and their isotopes in the atmosphere was also presented.In astronomy,a cascaded F-P interferometer designed by the University of Wisconsin in the United States for studying interstellar material emission lines was introduced.In the field of oceanography,the main application examples of domestic F-P interferometers for measuring Brillouin scattering were introduced,including the underwater Brillouin scattering system designed by Beijing Normal University in 2004 and the spaceborne Brillouin scattering system designed by Shanghai Jiao Tong University in 2021.Finally,this article proposes that spectral recognition accuracy and thermal stability are difficulties that need to be solved in the future applications of F-P interferometers in remote spectral measurement.

Based on Look Ahead Orthogonal Matching Pursuit (LAMOP), which is an excellent sparse decomposition method, an improved thin coating thickness measurement method with terahertz time-domain spectroscopy is proposed. Suffering from uneven coating, interlayer and noise in samples, it is difficult to locate the interfaces of thin coatings after decomposing the terahertz reflection signal with sparse decomposition. To address the challenge, through minimizing reconstruction error of the reflected signal, not only the number of nonzero pulses in LAMOP is determined, but also the interfaces of the coatings are accurately located. This method is validated on the coated carbon-fiber reinforced polymers (CFRP) samples with two coating layers successfully.

In this work, double orthogonally polarized femtosecond laser beams with picosecond time delay are employed to irradiate the silicon wafer. The scanning speed of the silicon wafer is 10 mm/s, which is kept constant during the experiment. Taking account of the focal spot size (25 mu m) and the laser repetition rate (1 kHz), only 2.5 pulses on average strike on a single spot of the silicon wafer. It is found that periodic ripples with different morphologies are respectively formed in the middle part and periphery of the etching line. These two types of periodic ripples have nearly identical periods, but have a spatial phase difference of pi and different morphologies. The spatial phase difference and the different patterns of the ripples infer that ripples ' coalescence occurs in the middle part of the etching line, leading to the dislocation of the periodic ripples. It is considered that the recoil pressure due to the material ejection mainly induced by the subsequently incident laser beam plays a critical role in the coalescence and dislocation of the laser induced periodic ripples. It is well known that the period and orientation of the ripples can be controlled respectively by the wavelength and the polarization of femtosecond laser, furthermore this work demonstrates that the spatial phase of the periodic ripples also can be adjusted which may find important applications in fabricating the metasurface optical elements.

Silver nanoparticles (AgNPs) are widely used as nanoagents in biomedical fields, while it is still challenging to improve their loading capacity and biocompatibility in microcarrier delivering systems. Herein, the physicochemical properties of AgNPs were manipulated by forming biomolecular corona derived from bovine serum albumin (AC), and three organisms at various trophic levels: Chlorella sp. (BC1), Daphnia magna (BC2), and zebrafish (BC3). Proteins were identified by chemical composition analysis as the dominant components adsorbed on the surface of AgNPs. Proteomics indicated that AgNPs preferred to bind with low molecular weight (<50 kDa) and hydrophobic proteins with more positively charged residues. Consequently, AC and BC3 displayed stronger adsorption affinity on the surface of AgNPs than BC1 and BC2. Modifications by AC and BC3 effectively alleviated the oxidative stress and cell cycle arrest of AgNPs due to their superior antioxidative ability. However, BC3 with lower hydrophobicity enabled AgNPs to be more biocompatible than AC at subcellular level. Moreover, AC could significantly improve the loading capacity of AgNPs by Chlorella through enhancing caveolin-mediated endocytosis. Notably, owing to the adsorption of abundant Ca2+-binding proteins, BC3-AgNPs could also be internalized by microalgae via Ca2+-dependent clathrin-mediated endocytosis, which makes it a promising approach to deliver AgNPs. The results of this study would provide insights into the development of an efficient strategy to deliver AgNPs based on the microalgae carrier without altering its original properties and functionality.

The TC4 (Ti6Al4V) titanium alloy fabricated by Selective Laser Melting (SLM) has gained significant attention in recent years due to its exceptional properties, including high strength-toweight ratio, excellent corrosion resistance, and biocompatibility. This study examines the effect of heat treatment on the microstructure, phase composition, and mechanical properties of SLMfabricated TC4 alloy, to provide a more comprehensive understanding of the material's behavior under varying thermal conditions. Experimental results demonstrated that the as-deposited TC4 alloy has a relative density above 0.99. The as-deposited TC4 alloy was mainly composed of closepacked hexagonal structure α/ α′ phases. In addition, a small amount of β-phase was also detected. After annealing treatment, the TC4 alloy showed a similar phase composition. The microstructure of the as-deposited TC4 alloy was composed of acicular martensite a′phase accompanied by α-phase in β-matrix. After annealing treatment, the acicular α′ martensite decomposed, transforming the microstructure into a lamellar structure consisting of α- and β-phases. The microhardness was to 351.7 HV0.2, the tensile strength was approximately 1,120 MPa, and the yield strength comprised approximately 1,080 MPa of the TC4 alloy fabricated by SLM. The tensile fracture surface of the asdeposited alloy demonstrated a mixture of brittle and ductile fracture. A quasi-cleavage river pattern and a small amount of irregular dimples can be observed. After annealing treatment, the elongation increased to 16.5