Papers by Keyword: Ablation Threshold

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: A novel two-stage technique to fabricate silicon nanoparticles is reported. At the first stage, silicon nanowire arrays are formed by metal-assisted chemical etching. At the second stage, the nanoparticles are produced by pulsed laser ablation of the silicon nanowire targets in water and ethanol. The fabricated particles have relatively small mean size in the range of 24 – 45 nm depending on the used buffer liquid. The ablation threshold of the silicon nanowire arrays is 2 – 11 times smaller than that for crystalline silicon targets. Owing to the achieved parameters, the proposed technique is more efficient in comparison with traditional approaches of mechanical milling of silicon nanowires and laser ablation of crystalline silicon. Raman spectroscopy study revealed crystalline structure of the fabricated silicon nanoparticles. The properties of the produced nanoparticles indicate their high potential in biophotonics.

Abstract: This paper presents a theoretical and experimental investigation into the ablation threshold of nickel template by femtosecond laser in air at atmospheric pressure. The laser pulses used for the study are 800 nm in wavelength, 100fs in pulse duration, and 1KHz in repetition rate. The two-temperature model is used to predict the single-pulse ablation threshold for nickel theoretically. Micro-hole ablation experiments are carried out in air by focusing the femtosecond laser beam on the nickel target surface at normal incidence with the long-focus objective lens of enlargement factor 50 and NA=0.7 to determine the single-pulse and multi-pulse ablation thresholds for nickel by setting up the relationship between the measured hole diameters and the pulse energies. The single pulse ablation threshold of 4132.98 Jm^-2 obtained experimentally is very close to that of 3907.99 Jm^-2 predicted by two-temperature model. The incubation factor ξ, which describes the changes of the multi-pulse ablation thresholds with the number of pulses, is determined to be 0.812 for nickel.

Abstract: Experiment on ablation of silicon wafer on different crystallographic facet planes by single laser pulse irradiation was carried out with a femtosecond pulsed laser operating at a wavelength of 780 nm and a pulse width of 160 fs. The quality and morphology of the laser ablated silicon surface were evaluated by atomic force microscopy. The ablation threshold fluences on different crystallographic facet planes were obtained through the relationship between the squared diameter of the craters and pulse energy. The effects of different crystallographic facet planes of silicon wafer on the process of femtosecond laser ablation of silicon wafer were studied.

Abstract: To establish the green laser ablation process more accurately, a detailed knowledge of the exact value of ablation threshold is of great importance. Therefore, the presented paper has investigated the single pulse ablation threshold using four different methods, namely, fitting method via diameter square, fitting method via depth, micro-topography method and the one-dimensional heat conduction model. Through this research, the well-defined threshold in term of laser fluence (J/cm2) is obtained, and the comparison among different methods casts a light on the effective way to determine the ablation threshold. Also, the underlying laser-material interaction mechanism is analyzed.

Abstract: Short pulse lasers, including picosecond laser and femtosecond laser are involved to investigate the ablation characteristics of processing carbon fiber reinforced plastics (CFRPs). The ablation threshold of the femtosecond laser, 0.453 J/cm², is twice higher than that of the picosecond laser 0.867 J/cm², since the former generates an intense and shorter pulse and the atoms excitation and multi-photon absorption may occur as short as 10 ps or less. The ablation test also describes the processing qualities, where the femtosecond laser has processing abilities without visible thermal defects or charring over the picosecond laser.

Abstract: We demonstrated an experiment of femtosecond-laser damage threshold on GaAs wafer, the damage threshold was measured from 50 to 400fs. The mechanism was discussed through injection power, pulse duration and ablation profile. The results showed that the damage threshold increased with the pulse duration, the relationship between diameter of ablation hole and laser power density was also analyzed. It was concluded that the main factor affecting the damage threshold was photon ionization and collision ionization.