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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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Optical and Structural Phenomena at Multipulse Interference Femtosecond Laser Fabrication of Metasurfaces on a Thin Film of Amorphous Silicon
摘要： The formation of hexagonal microarrays of nanoholes (metasurfaces) in a 50-nm hydrogenated amorphous silicon film by means of three-beam interference of femtosecond laser pulses of the visible range (wavelength 515 nm) is studied experimentally with various exposures of the film. Characterization of arrays by scanning electron and optical microscopy, as well as optical transmission and reflection microspectroscopy, shows that an increase in the number of fixed energy laser pulses leads to a gradual evaporative formation of nanoholes in the film and, overall, the metasurface. Raman microspectroscopy reveals a simultaneous growth of the volume content of the crystal phase.
关键词： nanoholes,femtosecond laser,amorphous silicon,metasurfaces,interference
更新于2025-09-23 15:19:57
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FIB-SEM Investigation of Laser-Induced Periodic Surface Structures and Conical Surface Microstructures on D16T (AA2024-T4) Alloy
摘要： The use of aluminum alloy AA2024-T4 (Russian designation D16T) in applications requiring a high strength-to-weight ratio and fatigue resistance such as aircraft fuselage often demands the control and modification of surface properties. A promising route to surface conditioning of Al alloys is laser treatment. In the present work, the formation of ripples and conical microstructures under scanning with femtosecond (fs) laser pulses was investigated. Laser treatment was performed using 250 fs pulses of a 1033 nm Yb:YAG laser. The fluence of the pulses varied from 5 to 33 J/cm2. The scanning was repeated from 1 to 5 times for different areas of the sample. Treated areas were evaluated using focused ion beam (FIB)- scanning electron microscopy (SEM) imaging and sectioning, energy-dispersive X-ray (EDX) spectroscopy, atomic force microscopy (AFM), and confocal laser profilometry. The period of laser-induced periodic surface structures (LIPSS) and the average spacing of conical microstructures were deduced from SEM images by FFT. Unevenness of the treated areas was observed that is likely to have been caused by ablation debris. The structural and elemental changes of the material inside the conical microstructures was revealed by FIB-SEM and EDX. The underlying formation mechanisms of observed structures are discussed in this paper.
关键词： femtosecond laser,LIPSS,conical microstructures,aluminum alloy 2024
更新于2025-09-23 15:19:57
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[IEEE 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Chicago, IL, USA (2019.6.16-2019.6.21)] 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Environmentally Friendly Method for Synthesizing Reduced Graphene Oxide (rGO) for Transparent Conductive Electrode (TCE) in Solar Cells
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 15:19:57
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Single-step maskless nano-lithography on glass by femtosecond laser processing
摘要： Femtosecond laser processing is widely adopted today for microfabrication because of its ability to make rapid processing on almost all types of materials in ambient environment. However, it is challenging to apply femtosecond lasers for high-speed large-scale subwavelength nanofabrication, particularly, for two-dimensional nanopatterning on transparent dielectric materials due to their low light absorption. Previous demonstrations of femtosecond laser two-dimensional nanofabrication on dielectrics typically lack structural quality and long-range uniformity. In this work, we report a maskless laser nano-lithographic technique to fabricate high-quality two-dimensional periodic nanodomes on glass. The glass sample is first coated with a thin copper film and then irradiated by femtosecond laser pulses. We show that the period and size of the nanodomes can be controlled using a multi-fluence process. More importantly, a single-fluence technique is developed here, for the first time, for high-quality nanopatterning on glass. The nanopatterning formation mechanism is studied by dynamics experiments and numerical simulations. This introduced technique will provide a simple but highly effective way for dielectrics nanofabrication.
关键词： copper film,nanofabrication,nanodomes,femtosecond laser processing,glass
更新于2025-09-23 15:19:57
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Femtosecond laser-assisted Descemeta??s stripping endothelial keratoplasty: a prospective study of 6-month visual outcomes, corneal thickness and endothelial cell loss
摘要： Purpose To report 6-month outcomes of visual acuity, the corneal thickness and endothelial cell density (ECD) in patients undergoing femtosecond laser-assisted Descemet’s stripping endothelial keratoplasty (FS-DSEK). Methods This prospective, consecutive, interventional series examined 25 eyes of 25 patients who underwent FS-DSEK for Fuchs endothelial dystrophy and bullous keratopathy. The pre-cut endothelial graft thickness (CET) was 150 lm. Best-corrected visual acuity (BCVA), central corneal thickness (CCT), donor CET, recipient corneal stromal thickness (CST) and ECD were assessed at 1 week and 1, 2, 3 and 6 months postoperatively. Results The mean BCVA at 6 months was 0.76 ± 0.35 logMAR units, improving from 1.54 ± 0.52 logMAR. CCT decreased significantly, from 759.8 ± 152.4 lm at 1 week to 631.7 ± 79.7 lm at 6 months postoperatively (P = 0.001). CET recovered to 153.4 ± 33.7 lm (P = 0.076) at 6 months as pre-cut status. The CST decreased from 561.5 ± 96.3 lm at 1 week to 479.7 ± 57.9 lm at 6 months (P < 0.001). Preoperatively, the donor ECD was 2747.6 ± 255.4 cells/mm2, and the ECD decreased to 1729.1 ± 562.9 cells/mm2 at 6 months, for a peak ECD loss of 36.86%. A greater decrease in CST observed from 1 week to 6 months postoperatively correlated with a lower ECD loss (P = 0.019) and a lower preoperative ECD (P = 0.012). However, a thinner CET correlated with a higher preoperative ECD (P = 0.028). Conclusions FS-DSEK is a safe and effective surgical alternative for corneal endothelial decompensation. The donor ECD and its changes could be used as predictive factors for the improvement of CST and CET.
关键词： Visual acuity,Corneal endothelial cell density,Graft thickness,Femtosecond laser,Descemet’s stripping endothelial keratoplasty
更新于2025-09-23 15:19:57
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Temperature Effect on Capillary Flow Dynamics in 1D Array of Open Nanotextured Microchannels Produced by Femtosecond Laser on Silicon
摘要： Capillary ?ow of water in an array of open nanotextured microgrooves fabricated by femtosecond laser processing of silicon is studied as a function of temperature using high-speed video recording. In a temperature range of 23–80°C, the produced wicking material provides extremely fast liquid ?ow with a maximum velocity of 37 cm/s in the initial spreading stage prior to visco-inertial regime. The capillary performance of the material enhances with increasing temperature in the inertial, visco-inertial, and partially in Washburn ?ow regimes. The classic universal Washburn’s regime is observed at all studied temperatures, giving the evidence of its universality at high temperatures as well. The obtained results are of great signi?cance for creating capillary materials for applications in cooling of electronics, energy harvesting, enhancing the critical heat ?ux of industrial boilers, and Maisotsenko cycle technologies.
关键词： Maisotsenko cycle,cooling of electronics,silicon,open capillary microchannels,microstructures,nanostructures,femtosecond laser processing,capillary flow
更新于2025-09-23 15:19:57
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High-speed femtosecond laser plasmonic lithography and reduction of graphene oxide for anisotropic photoresponse
摘要： Micro/nanoprocessing of graphene surfaces has attracted significant interest for both science and applications due to its effective modulation of material properties, which, however, is usually restricted by the disadvantages of the current fabrication methods. Here, by exploiting cylindrical focusing of a femtosecond laser on graphene oxide (GO) films, we successfully produce uniform subwavelength grating structures at high speed along with a simultaneous in situ photoreduction process. Strikingly, the well-defined structures feature orientations parallel to the laser polarization and significant robustness against distinct perturbations. The proposed model and simulations reveal that the structure formation is based on the transverse electric (TE) surface plasmons triggered by the gradient reduction of the GO film from its surface to the interior, which eventually results in interference intensity fringes and spatially periodic interactions. Further experiments prove that such a regular structured surface can cause enhanced optical absorption (>20%) and an anisotropic photoresponse (~0.46 ratio) for the reduced GO film. Our work not only provides new insights into understanding the laser-GO interaction but also lays a solid foundation for practical usage of femtosecond laser plasmonic lithography, with the prospect of expansion to other two-dimensional materials for novel device applications.
关键词： graphene oxide,photoreduction,anisotropic photoresponse,femtosecond laser,plasmonic lithography
更新于2025-09-23 15:19:57
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Direct imaging of direction-controlled molecular rotational wave packets created by a polarization-skewed double-pulse
摘要： High‐precision, time‐resolved Coulomb explosion imaging of rotational wave packets in nitrogen molecules created with a pair of time‐delayed, polarization‐skewed femtosecond laser pulses is presented, providing insight into creation process and dynamics of direction‐controlled wave packet. To initiate unidirectional rotation, the interval of the double‐pulse was set so that the second, polarization‐tilted pulse hit the molecules at the time when molecules were aligned or antialigned along the polarization vector of the first pulse. During the revival period of the rotational wave packet, pulse intervals around both the full and half revival times were used. The observed molecular wave packet movies clearly show signatures of quantum rotation such as angular localization (alignment), dispersion, and revival phenomena during the unidirectional motion. The patterns are quite different depending on the pulse interval even when angular distribution at the second pulse irradiation is similar. The observed interval‐dependence of the dynamics was analyzed on the basis of the real‐time images, with an aid of numerical simulations, and the creation process of the packets were discussed. We show the observed image patterns can be essentially rationalized in terms of rotational period and alignment parameter. Because the double‐pulse scheme is the most fundamental in the creation of direction‐controlled rotational wave packets, this study will lead to more sophisticated control and characterization of directional molecular motions.
关键词： rotational wave packets,Coulomb explosion imaging,quantum rotation,femtosecond laser pulses,unidirectional rotation
更新于2025-09-23 15:19:57
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Femtosecond laser-induced surface structuring of the porous transport layers in proton exchange membrane water electrolysis
摘要： In proton exchange membrane water electrolysis (PEMWE) cells the performance and thus the conversion efficiency are influenced by the interface between the porous transport layer (PTL) and the catalyst layer (CL). In the following paper, this interface is modified by the use of femtosecond laser-induced surface structuring, so that the specific surface area of the titanium based fibers of the PTL is increased. The resulting morphology exhibits two roughness levels of (i) a relatively coarse structure featuring tips of a few micrometers in diameter and depth, which are each covered in turn by (ii) a substructure of smaller tips of a few to several hundred nanometers in diameter and depth. PEMWE electrochemical characterization and short-term stress tests reveal that the cell performance is increased due to the laser-structuring of the PTL surface towards the CL. For instance, the cell voltage is reduced by approximately 30 mV after 100 h at 4 A cm?2. These beneficial effects are observed over the entire current density range and thus correspond to a decreased equivalent cell resistance of at least 6 mΩ cm2 for electrical interfacial contact losses and at least 2 mΩ cm2 for mass transport losses. A physical characterization by scanning electron microscopy shows that the CL surface is much rougher and more jagged when using laser-structured fibers. Thus, the gaseous oxygen and the liquid water transport both from and to the active sites of the catalyst seem to be improved.
关键词： catalyst layer,cell performance,proton exchange membrane water electrolysis,porous transport layers,femtosecond laser-induced surface structuring
更新于2025-09-23 15:19:57