Search Results (208)

Miniature plasma lenses capable of withstanding high laser intensities could provide compact focusing elements for a variety of laser-plasma applications. In particular, they offer a simple route to increase ignitor beam intensity in fast ignition targets while remaining compatible with the geometric constraints of cone-in-target configurations. We report an experimental proof-of-concept demonstration of such a lens using a Ti:Sa femtosecond laser system. The lens is generated by a nanosecond laser pulse incident on a foil aperture, producing an expanding plasma with a transient radial density gradient that focuses a delayed femtosecond pulse. The resulting plasma lens focal spot is reduced to a few microns $⟨D_{\mathrm{FWHM}}⟩\approx 5.5$ $\mathsf{\mu }$m. After accounting for transmitted energy contained within the FWHM contour, the effective intensity enhancement was estimated to be ${\displaystyle \frac{I_{\mathrm{PL}}}{I_0}}\approx 47\pm 15$. Full article

Laser-induced breakdown spectroscopy (LIBS) offers rapid, in situ, and multi-element detection, and therefore shows strong potential for quality monitoring of metal powders in additive manufacturing. However, direct LIBS analysis of flowing metal powders is often affected by particle splashing, unstable laser–particle coupling, and plasma fluctuations, which reduce signal repeatability and detection reliability. To address these issues, this study developed an integrated measurement and classification framework for identifying cross-contamination in additive-manufacturing metal powders. A stable powder particle stream was generated through vibratory feeding and particle-flow focusing, while a hollow quartz tube with a side opening was introduced to provide cylindrical spatial confinement, thereby improving the stability of laser–particle interaction and enabling in situ spectral acquisition without pellet preparation. TC4 powder was used as the base material and AlSi10Mg powder as the contaminant, and samples with contamination levels of 0, 0.5, 1, 2, and 5 wt.% were prepared. Two independent batches of single-shot LIBS spectra were collected. To reduce the influence of strong spectral fluctuations, outlier spectra were removed using full-spectrum total-intensity quantile filtering, followed by asymmetric least-squares baseline correction and standard normal variate transformation. PCA combined with multiple machine-learning models was then applied for contamination identification. The results showed that LIBS spectra at different contamination levels exhibited distinguishable distributions in principal-component space, and the spectral differences between clean and contaminated powders became more pronounced with increasing contamination level. In binary classification, several models achieved high classification accuracy at medium and high contamination levels, while PCA-SVM-RBF showed the best performance at low concentrations. In five-class cross-validation, the 5 wt.% class exhibited the clearest decision boundary, whereas confusion remained among low and adjacent contamination levels, indicating that contamination-induced spectral responses followed a more continuous transition. These results demonstrate that the proposed spatially confined particle-flow LIBS framework combined with machine-learning classification can effectively achieve rapid identification of cross-contamination in additive-manufacturing metal powders and provides a feasible technical route for online powder quality monitoring. Full article

The laser irradiation effect on Charge-Coupled Devices (CCDs) has attracted wide attention in photoelectric countermeasures and imaging system hardening. This review provides a systematic analysis of the phenomena and mechanisms of laser-induced dazzling and damage effects on CCD sensors. It summarizes experimental and theoretical research progress with continuous-wave (CW), pulsed, and composite lasers, revealing distinct interaction mechanisms such as thermal effects, dielectric breakdown, and plasma ablation. The review also covers quantitative evaluation methods for assessing laser irradiation effects. This work provides a comprehensive reference for future studies. Full article

We report on the generation and spectral shaping of ultrabroadband terahertz-to-infrared radiation (>119 THz) from air plasma excited by a conventional tightly focused femtosecond Ti:Sa laser pulse with a duration of 35 fs assisted by its second harmonic (SH). A controllable and large frequency detuning between the SH and blueshifted component of the fundamental spectrum was achieved by utilizing spectral broadening of the fundamental pulse under filamentation and adjusting the longitudinal separation of the two cascaded filaments. For convenience, the resulting ultrabroadband emission is divided into a low-frequency part (<30 THz), an intermediate-frequency part (~50 THz), and a high-frequency part (~100 THz) that can be optimized with the filaments’ longitudinal separation. We attribute such ultrabroadband THz radiation generation to the excitation of photocurrent from the nonlinear interaction of SH with both the field at the fundamental frequency and its blueshifted component acquired during filamentation. Theoretical calculations based on time-dependent Schrödinger equation, as well as the Maxwell–Schrödinger equation for spectral broadening dynamics, reproduced the spectral features as well as the distinct dependence of the low- and high-frequency THz components. Full article

The formation and size evolution of gas-phase nanoparticles (NPs) in laser ablation inductively coupled plasma mass spectrometry critically influence aerosol transport, plasma ionization efficiency, and ultimately analytical accuracy. Nevertheless, burst-mode laser ablation, as an efficient and versatile strategy for controlling gas-phase NP size, remains insufficiently explored. Here, we combine experimental investigations and theoretical analysis to elucidate the mechanisms of gas-phase nanoparticle formation and size control by tuning the interpulse interval in burst-mode femtosecond (fs) laser ablation. The mean nanoparticle size exhibits a non-monotonic dependence on interpulse spacing, decreasing with a narrowing size distribution as the interval increases from 0 to 300 ps, and then increasing with distribution broadening at longer delays up to 1000 ps, closely correlating with ablation-crater depth. A characteristic transition at ~300 ps is identified, where both nanoparticle size and crater depth reach a minimum, revealing a critical timescale in pulse–plume–surface interactions. Simulations show that the interpulse interval governs the redistribution of laser energy between the surface and plume, driving a transition from surface-dominated ablation to plume-dominated absorption and partial recovery of surface coupling. This delay-dependent framework provides a unified explanation for nanoparticle formation, where particle size is determined by the competition between plume-mediated fragmentation and surface-driven material supply, and offers a basis for tailoring NP size distributions via temporal pulse shaping. Full article

In this study, a femtosecond laser beam is delivered to metal wire targets to generate suprathermal electron jets reaching energies of several hundreds of keV. During the process, it is observed that the mirror-imaging distribution of the beam focus with respect to the surface of the target displays highly asymmetric features and different dynamic responses. Especially, the exterior focus exhibits an extraordinary polarity reversal of the macroscopic current, while the interior focus behaves ordinarily. The former is attributed to the strong field at the focal point outside the surface, causing the secondary ionization and driving electrons back to the target, thereby reshaping the distribution of these high-energy hot electrons and the morphology of plasma jets. A numerical model is proposed to simulate the experimental observation and interpret the unexpected phenomenon. Furthermore, the particle-in-cell algorithm is also implemented to verify the results and present more details. This study seeks to emphasize the role of focal position in regulating the photoemission process, which may offer a fresh perspective for research in laser–material interactions and dynamics. Full article

Femtosecond laser processing has become a powerful approach for high-precision micro- and nanofabrication in transparent materials, owing to its ultrashort pulse duration and minimized thermal effects. However, the limited predictability of processing depth remains a major obstacle to practical applications. Here, we present a morphology prediction framework for femtosecond Bessel laser processing of ZnS that integrates plasma physics modeling with deep learning. Through combined experimental measurements and plasma physics simulations, the influence of laser pulse energy on electron density evolution and material removal depth is systematically investigated. The results reveal the dominant roles of multiphoton ionization, avalanche ionization, and free-electron dynamics in deep-volume processing, and demonstrate the strong sensitivity of the processing morphology to the plasma distribution. Conventional plasma models can accurately reproduce the ablation diameter, yet exhibit significant limitations in predicting the processing depth. We propose a physics data-based framework for femtosecond Bessel beam processing, which integrates a depth-residual regression network conditioned on the peak electron density distribution to effectively learn and compensate for systematic modeling errors in plasma-based simulations. This strategy leads to excellent agreement between predicted and experimental processing depths and three-dimensional morphologies under various energy conditions. The model achieves a mean absolute error (MAE) of 4.9 nm at the pixel level for 3D crater reconstruction. Under rigorous crater-grouped cross-validation with Leave-One-Group-Out evaluation, the model achieves a mean R² of 0.74 across 8 independent craters, demonstrating reliable generalization to unseen energy conditions. These results demonstrate that incorporating physical priors into data-driven learning provides an effective pathway to overcoming accuracy limitations in modeling complex laser–matter interactions. This approach offers a reliable tool for quantitative prediction and parameter optimization in deep femtosecond laser processing of transparent materials and enabling highly controllable and reproducible micro- and nanofabrication for advanced photonic and three-dimensional optical applications. Full article

The Yechangping super-large porphyry–skarn deposit is a key component of the East Qinling molybdenum metallogenic belt, central China. Magnetite is widely developed across all mineralization stages of this deposit, yet its systematic geochemical evolution and prospecting significance remain poorly constrained. This study presents in situ major- and trace-element analyses of magnetite via electron probe microanalysis (EPMA), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and elemental mapping, to unravel the ore-forming hydrothermal evolution and establish reliable prospecting indicators. Four magnetite generations are identified based on petrography and paragenetic relationships: late skarn stage (Mt1), oxide stage (Mt2 and Mt3), and polymetallic sulfide stage (Mt4). Magnetite has total iron contents (TFeO, total Fe calculated as FeO) of 82.72–95.46 wt.% (values above the 93 wt.% stoichiometric limit of pure magnetite stem from minor oxidation), with dominant isovalent Fe³⁺ and Al³⁺ lattice substitution supported by a significant negative Fe–Al correlation. Systematic stage-dependent geochemical variations are observed: Mt1 has the highest Ti (mostly >1500 ppm), V and Cr, while Mt2–Mt4 show progressive Ti depletion (mostly <100 ppm), recording continuous cooling of the hydro-thermal system. V and Cr contents decrease markedly from Mt1 to Mt3, with secondary enrichment in Mt4; Mo concentrations peak in Mt2 (average 5.06 ppm), coupled with elevated chalcophile metalloid Te, As, Pb and Bi. Elemental mapping results show that K occurs as discrete hotspots, which may be mainly derived from feldspar microinclusions, rather than lattice substitution in magnetite. These geochemical fingerprints record a transition from high-temperature magmatic–hydrothermal fluids to late contact-metasomatic fluids, with evolving fluid–rock interaction and oxygen fugacity. Our results demonstrate that magnetite chemistry is a reliable tool for discriminating mineralization stages and vectoring prospecting targets in porphyry–skarn Mo–W systems. Full article

The performance of a four-frequency differential laser gyroscope (FFDLG) is severely affected by the magnetic field. In this paper, the following conclusions are discussed through theoretical analyses and experimental data: First of all, the Zeeman effect cannot fully explain the magnetic effect on the gain region due to the plasma movement. Secondly, an FFDLG does not have a unique optimal operating point where the gyroscope is not affected by any magnetic field. Plasma movement driven by Lorentz force induces a Fresnel drag effect, leading to a frequency imbalance and magnetic error in the ring laser gyroscope (RLG). This mechanism, involving the interaction between moving gain media and the counter-propagating beams, was missed in previous research. Full article

Combined pulse laser systems combining continuous-wave (CW) lasers and nanosecond pulsed lasers have shown clear advantages in metal ablation and surface modification. However, the plasma shielding effect induced by nanosecond pulses and the associated shock-wave phenomena in hybrid laser systems remain insufficiently investigated, particularly regarding their influence on CW laser energy coupling. In this study, the ablation behavior of metal targets under the combined irradiation of a 500 W CW laser and nanosecond pulsed lasers with pulse energies ranging from 0.4 J to 1.0 J was investigated. High-speed plasma imaging was employed to analyze laser–material interaction characteristics, including absorption behavior and molten material ejection, while high-speed infrared thermography was used to monitor transient temperature evolution during combined pulse laser processing. Macroscopic and microscopic analyses were conducted to characterize damage morphology, and a three-dimensional surface profilometer was used to quantitatively evaluate ablation efficiency. The results show that, under combined pulse laser irradiation, the removed volume increased from 0.05 mm³ to 0.618 mm³ and the ablation depth increased from 0.136 mm to 0.776 mm. Compared with CW laser processing alone, the ablation efficiency was markedly enhanced. This improvement is attributed to the combined effects of optimized energy deposition, thermal distribution, and material response. In addition, the plasma shielding effect was observed to vary with nanosecond pulse energy, indicating that precise energy control is critical for performance enhancement. This study demonstrates the potential of combined pulse laser technology for high-efficiency and high-precision metal surface processing and micro–nano fabrication. Full article

Magnetic fields, either imposed externally or produced spontaneously, are often present in laser-driven high-energy-density systems. In addition to changing plasma conditions, magnetic fields also directly modify laser–plasma interactions (LPI) by changing the participating waves and their nonlinear interactions. In this paper, we use two-dimensional particle-in-cell (PIC) simulations to investigate how magnetic fields directly affect crossbeam energy transfer (CBET) from a pump to a seed laser beam when the transfer is mediated by the ion-acoustic wave (IAW) quasimode. Our simulations are performed in the parameter space where CBET is the dominant process and in a linear regime, where pump depletion, distribution function evolution, and secondary instabilities are insignificant. We use a Fourier filter to separate out the seed signal and project the seed fields onto two electromagnetic eigenmodes, which become nondegenerate in magnetized plasmas. By comparing the seed energy before CBET occurs and after CBET reaches quasi-steady state, we extract the CBET energy gains for both eigenmodes in lasers that are initially linearly polarized. Our simulations reveal that, starting from a few MG fields, the two eigenmodes have different gains, and magnetization alters the dependence of the gains on laser detuning. The overall gain decreases with magnetization when the laser polarizations are initially parallel, while a nonzero gain becomes allowed when the laser polarizations are initially orthogonal. These findings qualitatively agree with theoretical expectations. Full article

Background: Plasma fibrinogen (FIB) levels exhibit a significant elevation during the acute phase of ischemic stroke (IS), and their dynamic fluctuations serve as important biomarkers for stroke onset, disease progression, and long-term prognosis. Tong-Qiao-Huo-Xue Decoction (TQHXD) is highly effective in treating blood stasis syndromes affecting the head and face. Nevertheless, the association between TQHXD and FIB in the underlying mechanism of treating IS warrants further investigation. Methods: Proteomics analysis predicted the potential therapeutic targets of TQHXD for IS. An in vivo model of middle cerebral artery occlusion followed by reperfusion (MCAO/R) was created in mice. To explore the interaction between FIB and NLRP3, as well as to verify the particular healing outcomes of TQHXD. Results: An increased blood–brain barrier (BBB) permeability was observed after MCAO/R, accompanied by substantial accumulation of FIB in the brain. In vivo experiments demonstrated that FIB triggered the activation of the NLRP3 inflammasome in microglia. Proteomic analysis revealed a significant increase in FIB levels following model induction, which were markedly reduced after treatment with TQHXD; KEGG pathway enrichment analysis indicated that these changes were primarily associated with the NOD-like receptor signaling pathway. Laser speckle contrast imaging showed that TQHXD treatment significantly improved cerebral blood flow and attenuated brain injury in mice. Fluorescence imaging, ELISA, and Western blotting results collectively demonstrated that TQHXD effectively reduced FIB accumulation and suppressed NLRP3 inflammasome activation. MD and pull-down experiments further demonstrated a strong interaction strength between FIB and NLRP3. Conclusions: FIB accumulates in the ischemic penumbra following CIRI, while TQHXD can effectively down-regulate FIB expression and inhibit NLRP3 inflammasome activation to mitigate CIRI. These findings provide a novel theoretical foundation and treatment direction for stroke management in clinical settings. Full article

We present a systematic study on the optical response of plasma mirrors generated in polymer foils under ultrashort laser pulse irradiation within the non-relativistic intensity regime, reaching up to $2\times {10}^{17}$ W/cm². Using a Ti:sapphire system that delivers 50 fs pulses, we simultaneously measured reflection, transmission, and diffuse scattering with three energy meters for single-shot laser energies of 5, 10, 15, and 20 mJ as a function of the laser spot size on the target. The results reveal intensity-dependent variations in reflectivity, accompanied by simultaneous changes in transmission and scattering, allowing to estimate laser energy absorption by the polymer. Morphological analysis of the plasma surface suggests a significant role in modifying energy absorption, with implications for the efficiency of processes such as laser particle acceleration, nuclear fusion, and attosecond pulse generation. These findings provide critical insights into plasma mirror formation, absorption dynamics in polymers, and the potential of nanostructured polymer targets in high-intensity laser–matter interaction applications. Full article

The northern segment of the Great Xing’an Range, northeastern China, hosts a previously unrecognized near-E–W-trending rhyolite belt in the Tulihe area. We conducted systematic geochronological and geochemical investigations to constrain its formation age, petrogenesis, and regional tectonic significance. Field investigation, petrographic observation, and zircon laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) U–Pb dating indicate that the rhyolite belt was formed during the Early Cretaceous, with emplacement ages directly determined from three samples ranging from 143.8 to 131.5 Ma. Geochemically, the rhyolites yielded high SiO₂ contents (74.44–75.88 wt.%), high total alkalis (K₂O + Na₂O = 8.50–8.99 wt.%), and low MgO contents (0.16–0.55 wt.%). They displayed strong enrichment in light rare earth elements and depletion in high field strength elements, weakly negative Eu anomalies, A/CNK ratios near unity, and relatively high Nb/Ta ratios. Trace element signatures and incompatible element abundances (Zr + Nb + Ce + Y = 193.2–338.3 × 10⁻⁶) are mostly consistent with highly fractionated I-type volcanic rocks, rather than S-type or M-type affinities. The geochemical data suggest that the rhyolites were mainly generated by partial melting of a medium- to high-K basaltic lower crust, with minor crustal assimilation and limited mantle input. Tectonically, Early Cretaceous magmatism in the northern Great Xing’an Range was governed by flat-slab subduction and subsequent rollback of the Paleo-Pacific (Izanagi) plate, while the local E–W-trending rhyolite belt was controlled by pre-existing faults, reflecting localized post-orogenic extension consistent with regional NE-trending volcanic belts. The northwest-to-southeast younging trend records asthenospheric upwelling and enhanced crust–mantle interaction induced by slab rollback. These results highlight the petrogenetic and tectonic evolution of medium- to high-K magmatism along the NE Asian continental margin and improve our understanding of Mesozoic volcanism in the Great Xing’an Range. Full article

In this work we report the results of analysis of the acoustic signal generated by the interaction of a nanosecond laser pulse (30 mJ, 1064 nm) with various residues placed on a silica wafer. The signal was captured by a unidirectional microphone placed 30 mm from the laser-generated plasma. The examined sample classes, other than the clean wafer, included particles from soils and rocks, carbonates, nitro precursors, ash, coal, smeared diesel, and particles of explosives. We tested three types of explosives, namely PETN, RDX, and HMX, having different origins. For the explosives, the acoustic signal showed a faster rise, larger amplitude, different width, and attenuation compared with the other sample classes. By subtracting the acoustic signal from the wafer at the same position, obtained after four cleaning laser pulses, the contribution of echoes was eliminated and true differences between the residue and substrate became evident. Through four different features in the subtracted signal, it was possible to classify explosives without the presence of false positives; the estimated limit of detection was 15 ng, 9.6 ng, and 18 ng for PETN, RDX, and HMX, respectively, where the mass was extrapolated from nano-printed samples and LIBS spectra acquired simultaneously. Furthermore, HMX was distinguished from the other two explosives in 90% of the cases; diesel and coal were also recognized. We also found that explosives deposited through wet transfer behaved as inert substances for the tested masses up to 30 ng. Full article