We carried out a comparative study on ablation threshold behavior of femtosecond laser twin double-pulse processing of typical transparent material, semiconductors and metallic materials. Based on the change of ablation area with pulse temporal separation (100 fs-15ps) under the same spatially distributed Gaussian beam, influence of pulse-separation on normalized double-pulse ablation threshold (which is normalized to the single-pulse ablation threshold) was demonstrated qualitatively. Special attention paid on the variation characteristics of normalized double-pulse ablation threshold in the sub-picosecond pulse-separation range, as well as its value in pulse-separations comparable or larger than the electron-phonon (or ion) coupling time. We show that the ablation threshold behavior of femtosecond laser twin double-pulse is strongly material-specie dependent, however, can be summarized in to several ones. The difference in ionization and/or deionization mechanisms for the non-metal compared is possibly the physical origins for the contrasted behavior of double-pulse ablation threshold.
Carbon fiber reinforced polymer(CFRP) is a typical hard to machine material. High modulus CFRP is one of the most widely used types in spacecraft structures. In this paper, the ultrafast laser precision cutting technology for two kinds of high modulus materials with different thermal conductivity is studied. The single factor ablation experiments are carried out on two kinds of plates with the thickness of 1mm. The threshold value of the two materials and the influence law of different laser fluence and scanning speed parameters on the entrance cutting size and heat-affected zone are obtained, and the physical mechanism of the above laws is described. The results show that the huge difference in the thermal conductivity of the two materials has a certain influence on the difficulty of processing the material and the selection of process parameters.
High-volume SiCp/Al materials were processed by Laser-induced Oxidation assisted machining technology.We obtained the laser induced oxidation process and oxidation mechanism, through the analysis of the average laser power, scanning speed, scanning distance and other factors on the oxidation effect.The results show that:1) In an oxygen-rich environment, the oxide layer will eventually exist as mullite(2 Al2O3·SiO2)after sufficient reaction of the surface material. 2) When the average laser power is 6W, the laser scanning speed is 1 mm/s, and the laser scanning distance is 10 μm, the optimal combination of parameters is obtained. The results show that the thermal hardening layer and dense layer are the least and the hardness is low, which is suitable for high efficiency and precision milling; 3)The laser induced oxidation assisted milling technology can significantly improve the processing efficiency, the material removal rate is greater than 3000 mm3 /min, the surface roughness value after Precision machining is better than Ra0.4 μm.
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