Papers by Keyword: Femtosecond Laser

Abstract: Steel 1.7220 is widely used in mechanical engineering for heavily loaded components operating at temperatures up to 450 °C. Femtosecond laser processing enables the formation of controlled microstructures without overheating or deformation, reducing the contact area and serving as reservoirs for lubricants. This study aims to evaluate the effect of laser microstructuring (Mesh and LIPSS types) on the tribological properties of steel, particularly under dry lubrication with powder. Micro- and nanostructures were analyzed using optical and scanning electron microscopy. Tribological tests were conducted using the ball-on-plate reciprocating method, with a load of 200 g, a frequency of 2 Hz, and a stroke amplitude of 1 cm for 30 minutes. For LIPSS structures, the influence of the friction direction relative to the orientation of the surface structures was investigated. The change in surface morphology after laser texturing was investigated. The effects of lubrication and surface structuring on tribological properties were analyzed, and the role of periodic structures in enhancing tribofilm stability was demonstrated.

Abstract: The morphology of laser-induced periodic surface structures (LIPSS) and micro/nanostructures may be influenced by laser optics or process parameters. This study focused on two beam profiles, Gaussian and vector beams. Vector beam is an annular beam with a null intensity at its center. Radial and azimuthal polarization are the common states of polarization. We investigated Gaussian and vector femtosecond laser beams with the wavelength of 515 nm irradiated on titanium to analyze the ablation crater characterization and the ablation threshold of titanium. Finally, we conducted an experiment on the fabrication of the hybrid micro/nanostructures via spot-by-spot vector beam.

Abstract: The work is devoted to the problem of controlled laser micromachining of materials surface layers. The problem of ablation products reverse deposition near the laser processing region is considered. Laser ablation products, in addition to direct interaction with laser radiation, significantly increase lifetime and temperature of laser-induced plasma torch, which leads to decrease in energy entering processing area, as a result of which not removal, but heating of coating material occurs. Ablated particles can be deposited on the processed samples surface, which causes distortions in recorded structure spatial geometry. The possibility of using an electrostatic filtration system is considered as a method for protecting treated surface.

Abstract: The work is devoted to the problem of thin metal coatings deposition on dielectric substrates using the method of target material pulsed laser evaporation. The main advantage of laser ablation over other methods of coating deposition is the possibility of using practically any material as a target, while the resulting films are characterized by a high correspondence of the phase and chemical composition to the target material. The possibility of using an electrostatic field to improve the efficiency of coating deposition process is considered. Under the action of an electric field formed between the plates of high-voltage electrodes, the ablation products leave the treatment area and settle on the substrate surface. Examples of coatings deposited under various ablation conditions are shown.

Abstract: The work is devoted to the problem of synthesis of highly dispersed spherical powder granules by laser ablation. The formation of microspheres is carried out by the action of femtosecond laser radiation on the surface of a titanium target in a two-component reaction medium. The process of titanium treatment in n-hexane by ultrashort laser pulses is investigated. It is shown that the use of n-hexane as a working medium component allows the synthesis of micro-and nanopowders containing titanium carbide, which are resistant to atmospheric environment during prolonged exposure. The presented method provides the possibility of synthesis of high-purity powder materials with typical sizes from 1 to 3 microns.

Abstract: The thermal conductivity of suspended graphene varies greatly under light, but the thermal conductivity of supported graphene does not change as much as that of suspended graphene. This is due to the fact that all of the loaded graphene is placed on the substrate and the thermal diffusivity of the loaded graphene is very good. In this paper, the ultrafast properties of supported graphene and suspended graphene have been studied. Suspended graphene has unique thermal conductivity, and its thermal conductivity will change greatly with the increase of temperature. Because of graphene has no band gap, the photon emission of supported graphene cannot be realized by electron hole recombination as in direct band gap materials. Optical emission of hot carriers is possible in graphene, but usually inefficient. That’s because most materials have much faster thermal carrier relaxation time than radiation lifetime. Herein, the hot carrier emission of suspended graphene and supported graphene are studied by femtosecond laser. It is found that the hot carrier can reduce the relaxation time of hot carrier in suspended structure. The suspension structure does increase the intensity of photon emission.

Abstract: In the present work, the surface of Ti-6Al-7Nb samples was patterned with Laser Induced Periodic Surface Structures in order to improve biocompatibility, increase tissue ingrowth and decrease bacterial adhesion and inflammatory response for applications in dental and orthopedic implants. Polished and sandblasted disks 10 mm in diameter were treated generating LIPSS under two different sets of parameters. The surface morphology and chemistry were investigated both by secondary electrons imaging, EDS analysis and Atomic Force Microscopy. Primary rat osteoblast culture (passage 2) was used to assess cell toxicity and biocompatibility. Alamar Blue assay was used to access cell viability and proliferation on day 1, 3 and 7. The difference between cell adhesion on polished and sandblasted surface as well as between polished and LIPSS-modified surface are described and discussed.

Abstract: We made the protoplast cell of red cabbage. And we irradiated to the protoplast cell with continues-wave laser. It is impossible to break down the protoplast cell. On the other hand we use the slide evaporated gold thin film, it is possible to break down a few protoplast cell. We use the femtosecond laser, it is possible to break down almost protoplast cell. The femtosecond laser used in experiment is mode-locked fiber ring laser. It also has 300fs pulse width, 52kW peak power and 4.773MHz pulse repetition frequency. Experiments show it is possible to break down the protoplast cell on an electrode.

Abstract: We presented a new method to fabricate gold nanoparticles resistance using the deposition technique of Laser Induced Backward Transfer (LIBT). The femtosecond laser was focused on the surface of the gold film covered by a receiving substrate. The ablation was carried out by scanning the laser beam and the expanded plasma can be transferred to the receiving substrate, which forms nanoscale resistance composed of gold nanoparticles lines. Gold nanoparticles were characterized by optical microscope, scanning electron microscope (SEM) and atomic force microscope (AFM). Femtosecond laser fluence, scanning speed, and the space between the scanned lines can influence gold nanoresistance. The resistance of gold nanoparticles with different parameters varied from ~ 8 GΩ to ~ 40 GΩ, which was measured by the picoammeter. Linetype resistance with nanostructured particles can be widely used in the field of microelectronics and optoelectronic devices.

Abstract: An experimental study is reported to characterise the femtosecond (FS) laser grooving process for Germanium (Ge) substrates. The effects of process parameters, including laser fluence, pulse repetition rate and scan speed, on the groove characteristics, material removal rate (MRR) and heat affected zone (HAZ) size are discussed. It is shown that with properly selected process parameters, high quality micro-grooves can be obtained on Ge wafers. Recommendations are finally made on the selection of the most appropriate process parameters for FS micro-grooving of Ge substrates.