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Numerically Implemented Impact of a Femtosecond Laser Pulse on Glass in the Approximation of Nonlinear Maxwell Equations
摘要： A finite-difference scheme is presented for the solution of the problem on the interaction of a femtosecond laser pulse with glass in the approximation of nonlinear Maxwell equations supplemented by equations of the hydrodynamic type for conduction electrons. The model takes into account all the basic physical processes involved in this interaction. An axially symmetric problem is considered. The construction of the scheme allows for the specifics of the problem, which ensures the efficiency of the developed method. The use of the scheme is illustrated by the results of modeling the interaction between glass and femtosecond laser pulses of an ordinary Gaussian shape with linear polarization and doughnut pulses with radial and azimuthal polarization. Significant differences in the dynamics of the interaction between glass and these three types of pulses are revealed.
关键词： aperture,nonlinear Maxwell equations,femtosecond laser pulse,Kerr effect,finite-difference scheme,implicit algorithms,plasma
更新于2025-09-23 15:19:57
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Fabrication of grooves on polymer-derived SiAlCN ceramics using femtosecond laser pulses
摘要： In this study, grooves were fabricated on the surface of fully dense polymer-derived SiAlCN ceramics. Industrial femtosecond laser source was used at wavelength of 1030 nm with pulse duration of 290 fs and repetition rate of 100 kHz. Moreover, comprehensive study was carried out to evaluate the influence of scan speed and energy fluence on grooves quality, including the heat-affected zone around the laser-machined grooves, microstructures of laser-irradiated surface, and cross-section morphology of grooves. A series of grooves with width in the range of 30–80 μm and depth below 280 μm was successfully fabricated using femtosecond laser pulse. Laser parameters were optimized to obtain grooves with satisfying surface quality. Furthermore, formation and disappearance of laser-induced periodic surface structures were systematically investigated. This study proposes fabrication of grooves on SiAlCN ceramics via laser processing, which provides precise method for fabrication of microstructure with fascinating properties.
关键词： Laser-induced periodic surface structures,Polymer-derived ceramics,Femtosecond laser pulse,Groove
更新于2025-09-19 17:13:59
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Selective excitation of one among the three peaks of tip‐enhanced Raman spectroscopy by a shaped ultrafast laser pulse
摘要： There are generally several neighboring Raman peaks that are excited simultaneously in tip‐enhanced Raman spectroscopy (TERS). A method to selectively excite a specific Raman peak and simultaneously depress the others is required for suppressing noise and improving detection sensitivity and accuracy. In this study, we demonstrate a scheme for selective excitation of one Raman peak among three excited states in TERS by properly shaping the pump and Stokes femtosecond laser pulses. The shaped pump and Stokes pulses are transformed into time domain, discretized and reconstructed; they are then used to irradiate the TERS structure obliquely. The impulse responses at five probe points of the TERS structure are calculated followed by a Fourier transform. In these cases, the probability of one selectively excited Raman transition increases by several hundreds to tens of thousands in amplitude, whereas the others are both depressed to zero. The probe points at different positions in the tip apex do not affect the enhanced and selective excitation of one Raman transition among the three excited states.
关键词： tip‐enhanced Raman spectroscopy,femtosecond laser pulse shaping,selective excitation
更新于2025-09-16 10:30:52
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SRS converter – compressor of femtosecond ytterbium laser pulses
摘要： Stimulated Raman scattering (SRS) conversion of femtosecond pulses of an ytterbium laser at a wavelength of 1.03 mm is performed in compressed hydrogen under conditions of nonlinear phase modulation. Temporal compression of frequency-chirped Stokes pulses is carried out, as a result of which 400-fs laser pulses are converted into 27-fs Stokes pulses with a wavelength of 1.8 mm. An average Stokes power of 0.6 W is implemented at an average laser power of 6.3 W and a pulse repetition rate of 20 kHz.
关键词： femtosecond laser,pulse compression,stimulated Raman scattering,nonlinear phase modulation
更新于2025-09-16 10:30:52
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[IEEE 2019 IEEE International Conference on Manipulation, Manufacturing and Measurement on the Nanoscale (3M-NANO) - Zhenjiang, China (2019.8.4-2019.8.8)] 2019 IEEE International Conference on Manipulation, Manufacturing and Measurement on the Nanoscale (3M-NANO) - Femtosecond Laser-assisted Fabrication of Fluorescent Boron Nitride Quantum Dots
摘要： As a kind of heavy metal-free quantum dot, boron nitride quantum dots (BNQDs) have attracted great interest due to their unique optical properties. Although there many synthesis methods of BNQDs, most of them require complex or time-consuming procedures, which limits the application of BNQDs. Here, we present a facile synthesizing method of few-layer BNQDs, which is based on liquid-phase ultra-short laser pulse ablation and ultrasonic-assisted exfoliation methods. The fabricated BNQDs are systematically characterized by atomic force microscope, transmission electron microscope, X-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy. The products possess an average size of about 2.1 nm with few-layer thickness. Because of the abundant surface functional groups, the BNQDs show bright luminescence emission under UV light irradiation.
关键词： femtosecond laser pulse ablation,ultrasonic-assisted exfoliation,boron nitride quantum dots
更新于2025-09-16 10:30:52
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Ultrafast electron transfer through silicon-vacuum interface induced by the action of intense femtosecond laser pulse
摘要： A theoretical study of the influence of a quasistationary electric field formed during emission separation of charges on ultrafast electron transfer near the silicon-vacuum interface irradiated by femtosecond laser pulses was carried out. The values of the strength of the arising quasistationary field during irradiation by femtosecond pulses with fluences near and above the silicon damage thresholds were estimated. The possibility of the formation of a dynamic optically layered structure in the near-surface layers of silicon irradiated by a femtosecond pulse resulting from a modification of its optical properties due to the depletion of electrons in the surface layer was studied. It is suggested that the time-depending dipole moment induced by the emission separation of charges should lead to the generation of electromagnetic radiation from the terahertz frequency range. The basic properties of this radiation were theoretically investigated.
关键词： Coulomb explosion,silicon,ultrafast heating,terahertz radiation,electron emission,electron transfer,femtosecond laser pulse
更新于2025-09-12 10:27:22
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Femtosecond laser pulse ablation characteristics of polymer-derived SiAlCN ceramics
摘要： Polymer-derived ceramics (PDCs) are promising high-performance materials for various applications, yet their brittleness represents major drawback in their machining. Femtosecond laser pulse ablation is non-contact rapid processing method used in precision machining of PDCs. Herein, two laser parameters (laser energy fluence and rotational speed) were investigated to achieve laser–material interactions and machining characteristics via machine single circular lines, blind holes, and through-holes in polymer-derived SiAlCN ceramics. With the decrease in rotational speed, the morphology of single circular lines gradually roughened and heat-affected zone was produced. Varying ablation rates were obtained at different energy fluences. For blind holes, three different ablation regions were observed. As the energy fluence increased, blind holes gradually transformed into through-holes. Through-holes with near-cylindrical profiles and minimal collateral damage were obtained. Ablation debris deposited around through-holes were indicative of N release, breaking of Si-N and C-C bonds, and formation of SiOx. Laser ablation of PDCs led to the formation of laser-induced surface structures, bubble pits, stripe structures, molten materials, and sphere-like particles.
关键词： femtosecond laser pulse,ablation characteristics,polymer-derived ceramics,energy fluence
更新于2025-09-12 10:27:22
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Cylindrical and plane surface electromagnetic waves in laser technology of silicon surface texturing with a double femtosecond pulse
摘要： This paper presents experimental results of laser modification of the surface of monocrystalline silicon under the influence of a double femtosecond laser pulse with varying delays less than or close to the electron–phonon interaction time, as well as the results of numerical simulation of the photoexcitation of a semiconductor in the approximation of dielectric constant. It is shown that the excitation of cylindrical surface waves not only precedes the excitation of plane surface electromagnetic waves, but is also a determining factor in the cumulative change in the dielectric constant of the medium and the creation of conditions for the excitation of plane surface electromagnetic waves.
关键词： Femtosecond texturing of the surface,Cylindrical surface electromagnetic waves,Monocrystalline silicon,Surface electromagnetic waves,Double femtosecond laser pulse
更新于2025-09-11 14:15:04
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Robust Remote Sensing of Trace-Level Heavy-Metal Contaminants in Water Using Laser Filaments
摘要： Water is the major natural resource that enables life on our planet. Rapid detection of water pollution that occurs due to both human activity and natural cataclysms is imperative for environmental protection. Analytical chemistry–based techniques are generally not suitable for rapid monitoring because they involve collection of water samples and analysis in a laboratory. Laser-based approaches such as laser-induced breakdown spectroscopy (LIBS) may offer a powerful alternative, yet conventional LIBS relies on the use of tightly focused laser beams, requiring a stable air–water interface in a controlled environment. Reported here is a proof-of-principle, quantitative, simultaneous measurement of several representative heavy-metal contaminants in water, at ppm-level concentrations, using ultraintense femtosecond laser pulses propagating in air in the filamentation regime. This approach is straightforwardly extendable to kilometer-scale standoff distances, under adverse atmospheric conditions and is insensitive to the movements of the water surface due to the topography and water waves.
关键词： filamentation,heavy-metal pollution,femtosecond laser pulse,remote sensing
更新于2025-09-11 14:15:04
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Using a Polarization-Skewed Femtosecond Laser Pulse
摘要： We experimentally observe the bond stretching time of one-photon and net-two-photon dissociation pathways of singly ionized H2 molecules driven by a polarization-skewed femtosecond laser pulse. By measuring the angular distributions of the ejected photoelectron and nuclear fragments in coincidence, the cycle-changing polarization of the laser field enables us to clock the photon-ionization starting time and photon-dissociation stopping time, analogous to a stopwatch. After the single ionization of H2, our results show that the produced H+2 takes almost the same time in the one-photon and net-two-photon dissociation pathways to stretch to the internuclear distance of the one-photon coupled dipole-transition between the ground and excited electronic states. The spatiotemporal mapping character of the polarization-skewed laser field provides us a straightforward route to clock the ultrafast dynamics of molecules with sub-optical-cycle time resolution.
关键词： femtosecond laser pulse,H2 molecules,bond stretching time,sub-optical-cycle time resolution,dissociative ionization
更新于2025-09-11 14:15:04