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Definitive production of intact organic pentacation radical: Octafluoronaphthalene ionized in intense femtosecond laser fields
摘要： We demonstrate the production of long-lived octafluoronaphthalene pentacation radical in gas phase by tunneling ionization using 1.4 μm femtosecond laser pulses. Multiply charged molecular cations are definitively identified by their m/z, isotopic structure, and peak shape using time-of-flight mass spectrometry. The tetracation yield relative to the trication radical yield is 0.33 that is the highest value obtained to date. The yield of pentacation radical relative to tetracation is 0.025. Our results show that the use of perfluoro-aromatics is the promising way to approach intact highly charge states.
关键词： Tunnel ionization,Time-of-flight,Mass spectrometry,Femtosecond laser
更新于2025-09-12 10:27:22
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Precession damping in [Co <sub/>60</sub> Fe <sub/>40</sub> /Pt] <sub/>5</sub> multilayers with varying magnetic homogeneity investigated with femtosecond laser pulses
摘要： We report on the ultrafast magnetization dynamics of [Co60Fe40/Pt]5 multilayers studied with femtosecond laser pulses. The samples were grown at room temperature by DC magnetron sputtering with Ta capping and Pt buffer layers and present the same thickness and perpendicular magnetic anisotropy as determined by vibrating sample magnetometry. Controlled growth rate of the Pt buffer layer modified the anisotropy fields and magnetic domain sizes as measured by magnetic force microscopy (MFM). An estimation of the average magnetic domain sizes was obtained from the profile of the self-correlation transform of the MFM images. For multilayers having an average magnetic domain size of 490 nm, we report a damped precession of the magnetization which decays with a time constant of ～100 ps and which has a frequency which varies from 8.4 GHz to 17.0 GHz as the external field increases from 192 mT to 398 mT. Fitting the precession dynamics with the Landau-Lifshitz-Gilbert equation we evaluated the damping α, which decreases from 0.18 to 0.05 with increasing magnetic domain sizes (127 nm to 490 nm). These α values are higher than for single layers suggesting an enhanced scattering and spin pumping effects from the Pt adjacent layers. In addition, the precession frequency increases from 2.04 GHz to 11.50 GHz as the anisotropy field of the multilayers increases from 6.5 kOe to 13.0 kOe. Finally, a comparative analysis between micromagnetic simulations and MFM images allowed us to determine the exchange stiffness (Aex) in the [Co60Fe40/Pt]5 multilayers.
关键词： exchange stiffness,femtosecond laser pulses,Landau-Lifshitz-Gilbert equation,[Co60Fe40/Pt]5 multilayers,damping,magnetic force microscopy,ultrafast magnetization dynamics,perpendicular magnetic anisotropy
更新于2025-09-12 10:27:22
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Analysis of physical interaction between peroxisomes and chloroplast induced by dynamic morphological changes of peroxisomes using femtosecond laser impulsive force
摘要： Plant organelles dynamically change their morphology responding to environmental signals. To investigate the correlation between the light-dependent morphological changes of peroxisomes and interaction force between peroxisomes and chloroplasts, we applied femtosecond laser to estimate the interaction force between peroxisomes and chloroplasts. Here, we introduce our studies based on resent researches about organelles interaction.
关键词： photosynthesis,photorespiration,organelle interaction,femtosecond laser,organelle morphology
更新于2025-09-12 10:27:22
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Femtosecond laser fabrication of 3D templates for mass production of artificial compound eyes
摘要： Compound eyes are unique optical imaging systems that consist of numerous separate light-sensitive units (ommatidia). Attempts have been made to produce artificial compound eyes via advanced 3D nanotechnologies. Among them, femtosecond laser direct writing (FsLDW) technology has emerged as an effective strategy due to its distinct advantages in 3D designable and high precision fabrication capability. However, the point-by-point scanning process results in a very low fabrication efficiency, limiting the practical applications of the FsLDW technology. To solve this problem, we propose a high-efficiency method for the mass production of 3D artificial compound eyes using a photopolymer template fabricated by FsLDW. The resultant 3D SU-8 compound eye templates could be used to replicate polydimethylsiloxane (PDMS) compound eyes many times (over 50 times) with a highly improved efficiency (nearly 20 times higher than the efficiency of direct fabrication using the point-by-point FsLDW). The PDMS replicas showed good focusing and imaging performances. We anticipate that this method may serve as an enabler for the mass production of 3D artificial compound eyes and promote their practical applications in the near future.
关键词： Two-photon polymerization,Compound eyes,PDMS casting,Femtosecond laser
更新于2025-09-12 10:27:22
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Maskless Micro/Nanopatterning and Bipolar Electrical-Rectification of MoS2 Flakes Through Femtosecond Laser Direct Writing
摘要： MoS2 micro/nanostructures are desirable for tuning electronic properties, developing required functionality, and improving existing performance of multilayer MoS2 devices. This work presents a useful method to flexibly microprocess multilayer MoS2 flakes through femtosecond laser pulse direct writing, which can directly fabricate regular MoS2 nanoribbon arrays with ribbon widths of 179, 152, 116, 98, and 77 nm, and arbitrarily pattern MoS2 flakes to form micro/nanostructures such as single nanoribbon, labyrinth array, and cross structure. This method is mask-free and simple, and has high flexibility, strong controllability, and high precision. Moreover, numerous oxygen molecules are chemically and physically adsorbed on laser-processed MoS2, attributed to roughness defect-sites and edges of micro/nanostructures that contain numerous unsaturated edge-sites and highly active centres. In addition, electrical tests of the field effect transistor fabricated from prepared MoS2 nanoribbon arrays reveal new interesting features: output and transfer characteristics exhibit strong rectification (not going through zero and bipolar conduction) of drain?source current, which is supposedly attributed to the parallel structures with many edge-defects and p-type chemical doping of oxygen molecules on MoS2 nanoribbon arrays. This work demonstrates the ability of femtosecond laser pulses to directly induce micro/nanostructures, property changes, and new device-properties of two-dimension materials, which may future enable new applications at electronic devices based on MoS2 such as logic circuits, complementary circuits, chemical sensors, and p?n diodes.
关键词： micro/nanopatterning,MoS2 flakes,oxygen bonding,femtosecond laser direct writing,electrical rectification
更新于2025-09-12 10:27:22
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Carbon multicharged ions emission from femtosecond laser plume
摘要： Carbon ion emission from femtosecond laser ablation of a glassy carbon target is studied. A Ti:sapphire laser (pulse duration τ ~ 150 fs, wavelength λ = 800 nm, laser fluence F ≤ 6.4 J cm?2) is used to ablate the carbon target while ion emission is detected by a time-of-flight detector equipped with a three-grid retarding field analyzer. A strong effect of the laser pulse fluence on the yield of carbon ions is observed. Up to C6+ ions are detected. The carbon ion time-of-flight signal is fit to a shifted Maxwell-Boltzmann distribution and used to extrapolate the effective plasma ion temperature Tieff = 6.9 eV. Applying an external electric field along the plasma expansion direction increases ion extraction, possibly due to the retrograde motion of the plasma-vacuum edge.
关键词： Femtosecond laser ablation,Time-of-flight,Plasma ion temperature,Carbon multicharged ions,Shifted Maxwell-Boltzmann distribution
更新于2025-09-12 10:27:22
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Comparison of Perioperative Parameters in Femtosecond Laser-assisted Cataract Surgery using Three Nuclear Fragmentation Patterns
摘要： Purpose: To compare the perioperative parameters of quadrant, sextant, and grid lens fragmentation patterns in femtosecond laser-assisted cataract surgery (FLACS). Design: Prospective randomized clinical trial. Methods: Setting: Eye Center of the Second Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, China. Patient or Study Population: A total of 894 eyes in 661 patients with cataracts were enrolled. Intervention or Observation Procedures: The nuclear density was graded according to the Emery-Little classification. Patients received lens fragmentation using a quadrant, sextant, or grid pattern after random allocation. Evaluations included intraoperative parameters, complications, and postoperative outcomes. Main Outcome Measure(s): Effective phacoemulsification time (EPT), intraoperative complications, visual acuity and intraocular pressure (IOP) at one day postoperatively, as well as endothelial cell density (ECD), endothelial cell loss (ECL) and central corneal thickness (CCT) at one week postoperatively. Results: In grade 1 nuclei, the mean EPT in the grid group was the shortest compared to those in the quadrant (P = 0.011) and sextant (P = 0.001) groups. In grade 2 nuclei, all three patterns showed no significant difference in the mean EPT (p > 0.05). In grade 3 nuclei, the sextant group revealed shorter mean EPT compared to the grid (P = 0.017) and quadrant (P > 0.05) groups. In grade 4 & 5 nuclei, the quadrant pattern had the shortest mean EPT among all three patterns (P < 0.05). The grid pattern is associated with higher IOP in hard nuclei (grade 4 & 5) than the other two patterns (P < 0.05). Conclusions: The grid and quadrant patterns allow for shorter EPT in soft (grade 1) and hard (grade 4 & 5) nuclei, respectively. All three patterns can be selected for treating grade 2 nuclei. The sextant pattern may be the best option when treating grade 3 nuclei. The grid pattern should be avoided in hard nuclei combined with glaucoma or glaucoma suspect.
关键词： nuclear fragmentation patterns,Femtosecond laser-assisted cataract surgery,Emery-Little classification,perioperative parameters,FLACS
更新于2025-09-12 10:27:22
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Heat accumulation effects in laser processing of diamond-like nanocomposite films with bursts of femtosecond pulses
摘要： In this paper, we have investigated the burst mode (BM) ablation and surface structuring of diamondlike nanocomposite (DLN) a-C:H:Si:O films with femtosecond laser pulses (wavelength λ = 515 nm, pulse duration τ = 320 fs, and pulse repetition rate f = 100 kHz) under different scanning conditions (single spots and linear structures). The pulse separation in the bursts is 25 ns (intraburst frequency f = 40 MHz), and the pulse number is varied from 1 to 8. The ablation depth and specific ablation rates (μm3/μJ) are found to be higher for the burst mode compared to single-pulse irradiation, increasing with the pulse number in the burst. The obtained experimental data of the higher ablation efficiency are shown to correlate with computer simulations of the BM ablation. In correlation with the ablation findings, Raman spectra of single spots and microgrooves have evidenced a growing graphitization of the amorphous film structure with the pulse number in the bursts (at an equal energy deposited into the films). Contact-mode atomic force microscopy (AFM) is applied to reveal an influence of the BM processing on the surface properties (nanoscale relief, friction) of laser-structured films. Based on the ablation and Raman data analysis, AFM examination of ablated/redeposited layers, and computer simulations of the burst mode ablation, the heat accumulation is identified as the main factor responsible for the enhanced ablation efficiency during the BM processing of DLN films. In addition, results of the high precision surface microstructuring of DLN films in the burst mode are presented.
关键词： heat accumulation,diamondlike nanocomposite films,surface structuring,femtosecond laser pulses,burst mode ablation
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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High-precision femtosecond laser beam shaping in material processing
摘要： Laser beam shaping is the process of modulating the amplitude and phase of a laser beam. With the development of the spatial light modulator, laser beam shaping can modulate the light field to arbitrary pattern dynamically via the computer-generated hologram (CGH). Otherwise, femtosecond laser is widely used in material processing owing to its high peak power, low hot effect and nonlinear effects. However, femtosecond laser is not strictly monochromatic, which will introduce dispersion when femtosecond laser diffracted by a spatial light modulator, and deteriorate the effect of beam shaping. Here we present a method of high-precision femtosecond laser beam shaping. Experimental results confirm that the proposed method can be used to shape femtosecond laser beams into arbitrary patterns in the whole field of view (FOV) with the resolution near the optical diffraction limit.
关键词： spatial light modulator,beam shaping,dispersion compensation,femtosecond laser,material processing
更新于2025-09-12 10:27:22