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- 2020
- fast processes in solids
- femtosecond interferometry
- femtosecond laser radiation
- Optoelectronic Information Science and Engineering
- Prokhorov General Physics Institute, Russian Academy of Sciences; National Research Nuclear University MEPhI
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Anti-Biofouling Properties of Femtosecond Laser-Induced Submicron Topographies on Elastomeric Surfaces
摘要： Anti-bacterial coatings are often employed to elastomer surfaces to inhibit bacterial attachment. However, such approaches could lead to increased antibiotic resistance. Surface micro/nano texturing is gaining significant attention recently, as it is a passive approach to reduce bacterial adhesion to surfaces. To this end, this work aims to assess the anti-biofouling functionality of femtosecond laser-induced sub-micron topographies on biomedical elastomer surfaces. Femtosecond laser processing was employed to produce two types of topographies on stainless steel substrates. The first one was highly regular and single scale sub-micron laser-induced periodic surface structures (LIPSS) while the second one was multi-scale structures (MS) containing both sub-micron and micron-scale features. Subsequently, these topographies were replicated on Polydimethylsiloxane (PDMS) and Polyurethane (PU) elastomers to evaluate their bacterial retention characteristics. The sub-micron textured PDMS and PU surfaces exhibited long term hydrophobic durability up to 100 hours under the immersed conditions. Both LIPSS and MS topographies on PDMS and PU elastomeric surfaces were shown to substantially reduce (> 89%) the adhesion of gram-negative Escherichia coli bacteria. At the same time, the anti-biofouling performance of LIPSS and MS topographies was found to be comparable with that of lubricant-impregnated surfaces. The influence of physical defects on textured surfaces on the adhesion behaviour of bacteria was also elucidated. The results presented here are significant because the polymeric biomedical components that can be produced by replication cost-effectively, while their biocompatibility can be improved through femtosecond surface modification of the respective replication masters.
关键词： anti-biofouling,polyurethane,biomedical elastomers,PDMS,femtosecond,lubricant-impregnated surfaces,laser induced periodic surface structures
更新于2025-09-23 15:21:01
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Mechanism and Experimental Study of Femtosecond-Laser Super-Resolution Processing Based on Beam Shaping Technology
摘要： The three-dimensional microsolid can be fabricated by scanning point-by-point inside the polymer material according to the predetermined trajectory in femtosecond-laser two-photon direct writing mode. In the process of machining, the shape and intensity distribution of focus spot are changed by some processing parameters, which a?ect the processing accuracy and surface quality. Based on Fresnel di?raction theory and the intensity distribution function of focal spot, the focal spot shape is simulated and the main factors a?ecting the light intensity distribution are analyzed theoretically and simulated numerically. We propose a shaping method to improve the asymmetric shape of the facula by adding a prefocusing lens. According to the mechanism of femtosecond-laser super-resolution processing, we propose a beam shaping method using four-ring complex transmittance phase plate to achieve super-resolution processing. The phase plate was optimized on the global optimization algorithm and genetic algorithm. The validation experiment was carried out by scanning the photochromic material ?lm with pulsed laser and reading the ?uorescence signal of the photochromic point with single photon confocal. The experimental results show that the facula distribution is approximately symmetrical, and the size of facula is decreased obviously. The compression ratio is basically consistent with the theoretical calculation results. Therefore, super-resolution processing can be achieved by adding pre-focusing lens and phase plate to shaping the laser beam. The results of theoretical and experimental studies provide su?cient basis for improving the machining accuracy and surface quality of microdevices.
关键词： beam shaping,femtosecond laser,super resolution,microfabrication
更新于2025-09-23 15:21:01
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Femtosecond Lasera??Etched MXene Microsupercapacitors with Doublea??Side Configuration via Arbitrary Ona?? and Througha??Substrate Connections
摘要： The capacitance of microsupercapacitors (MSCs) can double if both sides of substrates are used to construct MSCs. Nevertheless, achieving electric connections of MSCs through substrates is a challenge due to the difficulty in precisely positioning each MSC couple that has two of the same MSCs units on two sides. In this work, taking advantage of the synchronous etching on both sides of transparent polyethylene terephthalate substrates by femtosecond laser pulses, a double-sided configuration is attained with high precision in the alignment of back-to-back MSC couples and versatile double-side MSCs are realized via arbitrary on- and through-substrate connections of MXene MSC units. The MXene double-side MSC fabricated by the series connection of 12 spiral pattern MXene MSC units with interdigital electrodes of 10 μm width interspace can output a large working voltage of 7.2 V. Additionally, femtosecond laser etching brings the transformation of MXene into titania near-etched edges with a lateral distance less than 1 μm. Such a small laser-affected area has little influence on the capacitive performance, which is one of advantages for femtosecond laser over conventional lasers. This research is valuable for one-step manufacturing of highly integrated MSCs in the field of miniaturized energy storage systems.
关键词： double-sided,microsupercapacitors,femtosecond laser etching,MXene MSCs,MSCs,high integration
更新于2025-09-23 15:21:01
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Fluorinating ??a??Extended Molecular Acceptors Yields Highly Connected Crystal Structures and Low Reorganization Energies for Efficient Solar Cells
摘要： The synthesis and characterization of new semiconducting materials is essential for developing high-efficiency organic solar cells. Here, the synthesis, physiochemical properties, thin film morphology, and photovoltaic response of ITN-F4 and ITzN-F4, the first indacenodithienothiophene nonfullerene acceptors that combine π-extension and fluorination, are reported. The neat acceptors and bulk-heterojunction blend films with fluorinated donor polymer poly{[4,8-bis[5-(2-ethylhexyl)-4-fluoro-2-thienyl]benzo[1,2-b:4,5-b′]-dithiophene-2,6-diyl]-alt-[2,5-thiophenediyl[5,7-bis(2-ethylhexyl)-4,8-dioxo-4H,8H-benzo[1,2-c:4,5-c′]dithiophene-1,3-diyl]]} (PBDB-TF, also known as PM6) are investigated using a battery of techniques, including single crystal X-ray diffraction, fs transient absorption spectroscopy (fsTA), photovoltaic response, space-charge-limited current transport, impedance spectroscopy, grazing incidence wide angle X-ray scattering, and density functional theory level computation. ITN-F4 and ITzN-F4 are found to provide power conversion efficiencies greater and internal reorganization energies less than their non-π-extended and non-fluorinated counterparts when paired with PBDB-TF. Additionally, ITN-F4 and ITzN-F4 exhibit favorable bulk-heterojunction relevant single crystal packing architectures. fsTA reveals that both ITN-F4 and ITzN-F4 undergo ultrafast hole transfer (<300 fs) in films with PBDB-TF, despite excimer state formation in both the neat and blend films. Taken together and in comparison to related structures, these results demonstrate that combined fluorination and π-extension synergistically promote crystallographic π-face-to-face packing, increase crystallinity, reduce internal reorganization energies, increase interplanar π–π electronic coupling, and increase power conversion efficiency.
关键词： impedance spectroscopy,organic solar cells,crystal structures,femtosecond transient absorption spectroscopy,computational chemistry
更新于2025-09-23 15:21:01
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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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A comprehensive approach for characterisation of the deposited energy density during laser-matter interaction in liquids and solids
摘要： We present a novel approach for characterisation of ultrafast laser-matter interaction processes both in solids and liquids under extreme conditions of microplasma generation. By combination of three-dimensional propagation imaging, absorption measurements, shadowgraphy and photoacoustic imaging we can restore plasma electron density distribution, laser pulse fluence profile and the value of deposited energy density inside the bulk of the material and characterise the regime of the laser pulse propagation. The developped concept is important to understand the physics of ultrafast laser-matter interaction with strong implications for precision control of laser micromachining, bioprocessing and biotreatment.
关键词： three-dimensional propagation imaging,photoacoustics,femtosecond filamentation,laser-matter interaction,deposited energy density,shadowgraphy
更新于2025-09-23 15:21:01
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Unseeded velocimetry in nitrogen for high-pressure, cryogenic wind tunnels: part III. Resonant femtosecond-laser tagging
摘要： Selective two-photon absorptive resonance femtosecond laser electronic excitation tagging (STARFLEET) velocimetry is characterized for the first time at high-pressure, low-temperature conditions. Studies were carried out in the NASA Langley Research Center’s 0.3 meter transonic, cryogenic wind tunnel, with flow conditions spanning the entire operational envelope of the facility; total pressures ranging from 100 kPa to 517 kPa, total temperatures from 80 K to 327 K, and Mach numbers from 0.2 to 0.85. STARFLEET signal intensity and lifetime measurements are examined for their thermodynamic dependencies since both intensity and lifetime have implications for measurement precision. Signal intensity is found to be inversely proportional to density, while lifetime scales nearly linearly with density until approaching the liquid-vapor saturation point of nitrogen. The velocity measurement accuracy and precision are assessed over the full domain of conditions, and standard error was determined to be 1.6%, while precision ranged from roughly 1.5% to 10% of the freestream velocity. The precision was also observed to have a temperature dependence, likely a result of the longer lifetimes experienced at higher densities.
关键词： femtosecond laser,resonant excitation,molecular tagging velocimetry
更新于2025-09-23 15:21:01
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The role of the femtosecond laser induced nano/micro structures on the optical features of the steel surface; experimental polarimetry study
摘要： We are witnessing that ultrashort laser material processing (ULMP) is getting an established technique to modify many characteristics of a surface. Being applicable for various materials with any geometry or physical characteristics, besides being rapid and having simple experimental set-ups makes ULMP appropriate for small and large scale controlled modifications. Using this method to adjust the optical features of a surface has been also suggested in last years. So that mimicking the functional surfaces existing in nature which have distinctive surface morphologies and thus have special optical features, efforts are going on to create similar samples using ULMP. Here in this study, the potential of ULMP technique in changing the optical properties of metallic substrates is explored. Selecting 316L stainless steel as a substrate, five samples which are irradiated in different circumstances are fabricated. The role of the laser induced nano/micro structures on the optical features of these samples are studied systematically. Visible light backscattering in the range of 0°-65° was studied at first. Extracting the Mueller matrix elements for all samples at two different incident angles of 45° and 60°, the polarimetry parameters including retardancy, depolarization and diattenuation are calculated at the next step. Due to the multi-scale nature of the morphologies, more than the illuminating light angle, dependence of the samples optical response to its orientation is also discussed in detail Results clearly reflect that the optical response of laser induced periodic surface structure (LIPSS) coated layers have an anisotropic behavior regarding the incident angle and the polarization of the illuminating light. Furthermore, the surface orientation itself can play very serious role on the final response of the sample. It comes out that the characteristics of a surface such as its morphology, roughness or the correlation of the LIPSS structures has important effect in these regards.
关键词： backscattering,structure,femtosecond laser,surface,optical features,polarimetry
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