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Laser-induced graphitized periodic surface structure formed on tetrahedral amorphous carbon films
摘要： Femtosecond laser-induced periodic surface structure (LIPSS), graphitization and swelling observed on ultra-hard, hydrogen-free tetrahedral amorphous carbon (ta-C) films are examined and compared with those on hydrogenated amorphous carbon (a-C:H) films, nitride films, and glassy carbon plates. The threshold fluence for LIPSS formation on ta-C is approximately twice as high as that for other specimens, and the LIPSS period Λ near the threshold is very fine at ca. 80 nm. Λ gradually increases with increasing fluence, and rapidly increases to ca. 600 nm at a high fluence. The ablation rate also increases rapidly at this fluence. In addition, ta-C and a-C:H are graphitized by irradiation and expand in volume. The surface layer of ta-C film changes to nanocrystalline graphite as the fluence increases and the crystallinity is improved; however, at higher fluence, the crystallinity deteriorates suddenly similar to that at low fluence. At high fluence, the rapid increase in Λ and the ablation rate, and the sudden deterioration in crystallinity are determined as common phenomena for these disordered carbons. LIPSS formation and swelling over a large area by scanned spot irradiation produces submicron height flat hills with conductivity and surface functionality on the insulating surface.
关键词： Graphitization,Swelling,Laser-induced periodic surface structure,Femtosecond-laser processing,Nanocrystalline graphite,Tetrahedral amorphous carbon
更新于2025-09-23 15:21:01
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Fabrication of millimeter-long structures in sapphire using femtosecond infrared laser pulses and selective etching
摘要： This paper analyzes laser and etching parameters to fabricate open and continuous microchannels and stacks of such microchannels in the bulk of crystalline sapphire (??-Al2O3). The structures are produced using a two-step method consisting of laser irradiation and selective etching. Infrared femtosecond laser pulses are focused in the bulk to locally render the crystalline material into amorphous. The amorphous material is, then, selectively etched in hydrofluoric acid. Amorphous sapphire shows a high etching selectivity in comparison to its crystalline state, which makes this material very attractive for a use with this technique. However, some of its properties make the processing challenging, especially during the laser-induced amorphization phase. This paper studies the effect of laser parameters by a step-by-step approach to fabricate long structures (longest dimensions up to millimeters) of different shapes inside the bulk of sapphire. The minimum cross-sectional dimensions of the resulting structures (microchannels) vary from few hundreds of nanometers for the smallest channels to tens of micrometers for the largest stacks of microchannels. The effect of the variation of repetition rate, pulse energy and channel-to-channel distance on the microchannels and stacks of microchannels is studied. SEM micrographs of polished cross-sections are used for performing a quantitative and qualitative analysis of the morphology of the structures after laser irradiation and, subsequently, after selective wet chemical etching.
关键词： Selective etching,Laser processing,Microchannels,Femtosecond laser,Sapphire
更新于2025-09-23 15:21:01
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Electron acceleration up to MeV level under nonlinear interaction of subterawatt femtosecond laser chirped pulses with Kr clusters
摘要： The acceleration of electrons to MeV energies from a Kr cluster jet irradiated by a relativistic (6 × 1018 W cm?2) femtosecond laser pulse is studied. For the first time, the action of transform-limited laser pulse effects on the generation of hot electrons with an effective temperature (Thot) of around 150 keV is experimentally demonstrated. The particles were accelerated in the plasma channel formed under self-focusing of the laser beam. Introducing a linear positive chirp together with pulse elongation from 50–~120 fs results in substantially enhanced hot electrons flux with a growth of Thot up to 300 keV and a maximal energy of over 2 MeV. The observed effect may be related to the strongly nonlinear propagation of the pulse through plasma, accompanied by more favorable conditions for efficient particles energy gain and pulse nonlinear compression.
关键词： femtosecond laser,nonlinear phenomena,krypton,clusters,laser-driven electron acceleration
更新于2025-09-23 15:21:01
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Beam optimization in a 25 TW femtosecond laser system for high harmonic generation
摘要： It has been demonstrated in the past that high fluxes of extreme ultraviolet (XUV) light could be obtained by driving high harmonic generation (HHG) with high energy lasers. However, the peak intensity at the focal point of a femtosecond laser with more than 100 mJ can be too high for phase-matched HHG in gases. We propose a method to optimize the spatial profile at focus by adding customized wavefront terms. An XUV pulse energy of 5.6 μJ was obtained from HHG when a larger off-focus spot of a 500 mJ Ti: Sapphire laser beam was applied in an argon gas cell.
关键词： wavefront correction,extreme ultraviolet,femtosecond laser,high harmonic generation,Ti: Sapphire laser
更新于2025-09-23 15:21:01
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Atomic simulation of irradiation of Cu film using femtosecond laser with different pulse durations
摘要： It is necessary to understand the light-matter interaction for application of femtosecond laser micro/nanoprocessing. In this work, the authors investigated the melting and disintegration behavior of a Cu film irradiated by a femtosecond laser with different pulse durations in the range of 35–500 fs by using a combined two temperature model (TTM) and molecular dynamics (MD) method. On the basis of TTM-MD, the temperature and stress evolution of the Cu film were analyzed. The result indicated that the Cu film disintegrates when the pulse duration is shorter than 100 fs but melts at a pulse duration of 200 fs. The photomechanical and thermomechanical evolutions induced by the femtosecond laser were also analyzed. The stress wave and increasing temperature were the main reasons for film disintegration and vibration. The snapshots of the Cu film indicate the melting and disintegration processes on an atomic scale. It shows that the melting occurs homogeneously, whereas the disintegration occurs at the center of the film. These results are helpful to understand the mechanism of femtosecond laser materials ablation.
关键词： TTM-MD simulation,Cu film,pulse durations,femtosecond laser,irradiation
更新于2025-09-23 15:21:01
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[IEEE 2019 IEEE International Electron Devices Meeting (IEDM) - San Francisco, CA, USA (2019.12.7-2019.12.11)] 2019 IEEE International Electron Devices Meeting (IEDM) - Demonstration of BEOL-compatible ferroelectric Hf <sub/>0.5</sub> Zr <sub/>0.5</sub> O <sub/>2</sub> scaled FeRAM co-integrated with 130nm CMOS for embedded NVM applications
摘要： We present a phase mask inscription technique with two beam interferometry using a lateral nonhomogeneous beam splitter to create gratings with nonhomogeneous periods, the so-called chirped fiber Bragg gratings. Inscription experiments with deep ultraviolet excimer and femtosecond laser sources reveal how this inscription method depends on the coherence properties of the inscription laser. Nonhomogeneous beam splitters are shown to provide a method to generate chirped fiber Bragg gratings with great wavelength versatility, even with the ultraviolet femtosecond laser.
关键词： Femtosecond laser,optical fiber filters,two-beam interferometry,fiber Bragg gratings
更新于2025-09-23 15:21:01
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Tm-doped all-fiber structured femtosecond laser mode-locked by a novel Chem-Te saturable absorber
摘要： We succeed in developing a chemically synthesized tellurium nanocrystals (Chem-Te) thin film by liquid phase peeling technique, and demonstrate this material is an effective saturable absorber (SA) for realization of stable mode-locking in an all-fiber structured thulium-doped laser cavity. By integrating this SA into an all-fiber structured ring laser cavity, we obtained the mode-locked pulses at the repetition rate of 11.17 MHz, the achieved pulses spectral bandwidth FWHM (full width at half maximum) of 5.26 nm and the pulses duration of 890 fs with 620 mW pump power at 1560 nm, the fundamental mode-locked laser output power as high as 5.35 mW. In addition, by further increasing the pump power, the second-order and third-order harmonic mode-locked pulses train of this fiber laser were also observed. To the best of our knowledge, this is the first report on the novel Chem-Te material saturable absorption property realization in 2 μm-band fiber laser system.
关键词： Femtosecond laser,Saturable absorber,Chem-Te,Mode-locked
更新于2025-09-23 15:21:01
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Neue Intraokularlinsendesigns f??r die Femtosekundenlaser-assistierte Kataraktoperation; New intraocular lens designs for femtosecond laser-assisted cataract operations;
摘要： The perfection and high reproducibility of capsulotomy in femtosecond laser-assisted cataract surgery (FLACS) lead to the possibility of new intraocular lens (IOL) designs for capsulotomy fixed implantation. Currently four different types of femtolenses for capsulotomy fixation are described in the literature or are commercially available. The first described was the lens in the bag or Tassignon IOL, which was developed for secondary cataract prevention, the second was the Masket IOL for reduction of negative dysphotopsia and third the 90F designed by Dick. All three types are or will be produced by Morcher. The fourth lens is the Femtis from Oculentis. All lenses are characterized by a high level of safety during implantation, The Tassignon lens leads to reduction of secondary cataract, especially in juvenile cataract because of the additional posterior capsulotomy. In studies the Masket IOL could show a decrease of negative dysphotopsia. In comparison to standard lenses, the 90F and Femtis in particular showed better results with respect to tilt, rotation and decentration. The new IOL designs for capsulotomy fixation show a safe implantation procedure and indications for a very stable position in the capsular sac. Further studies must be carried out to confirm the possible advantages in comparison to standard IOL with respect to postoperative results for refraction, tilt, rotation and decentration and possible induction of aberrations.
关键词： Femtolens,Femtosecond laser-assisted cataract surgery,Capsulotomy,Decentration,Tilt
更新于2025-09-23 15:21:01
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Zircon fissiona??track and Ua??Pb double dating using femtosecond laser ablationa??inductively coupled plasmaa??mass spectrometry: A technical note
摘要： We present a new LA–ICP–MS system for zircon fission-track (FT) and U–Pb double dating, whereby a femtosecond laser combined with galvanometric optics simultaneously ablates multiple spots to measure average surface U contents. The U contents of zircon measured by LA–ICP–MS and standardized with the NIST SRM610 glass are comparable to those measured by the induced fission track method, and have smaller analytical errors. LA–ICP–MS FT dating of seven zircon samples including three IUGS age standards is as accurate as the external detector method, but can give a higher-precision age depending on the counting statistics of the U content measurement. Double dating of the IUGS age standards gives FT and U–Pb ages that are in agreement. A chip of the Nancy 91500 zircon has a homogeneous U content of 84 ppm, suggesting the possibility of using this zircon as a matrix-matched U standard for FT dating. When using the Nancy 91500 zircon as a U standard, a zeta calibration value of 42–43 yr cm?2 for LA–ICP–MS FT dating is obtained. While this value is strictly only valid for the particular session, it can serve as a reference for other studies.
关键词： dating,femtosecond laser,U–Pb,fission track,zircon,LA–ICP–MS
更新于2025-09-23 15:21:01
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THz Wave Emission From ZnTe Nano-Colloidal Aqueous Dispersion Irradiated by Femtosecond Laser
摘要： THz wave emission from ZnTe nano-colloidal aqueous dispersion flow (the particle size is 5-nm in diameter, the flow thickness is 17 μm) with two different particle densities (1.60 mmol/L and 1.07 mmol/L) was measured by time-domain spectroscopy (TDS) under femtosecond laser irradiation (>35 fs/transform-limited, 800 nm, horizontally-polarized, 0.5 kHz) in air. Intensity increase and peak shift in the TDS signal wave-form if compared with distilled water indicate that THz wave emission is induced in ZnTe nano-particles in the aqueous dispersion.
关键词： Terahertz,femtosecond laser,ZnTe nano-colloid
更新于2025-09-23 15:21:01