Formation and evolution of vortex ring induced by laser ablation on carbon particle

• Main Authors: Shang-Bin Lin, 林上斌
• Other Authors: Hong-Yu Chu
• Format: Others
• Language: en_US
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/94545792641593374297

碩士 === 國立中正大學 === 物理所 === 98 === We ablated a suspended micrometer-size carbon particle at 460 torr N2 gas environment by nanosecond laser pulsed. The evolution of carbon particle explosion is investigated. Rarefaction wave is suspected to be responsible for the cause of the hot gas deformation. After 70 μs, the jet stretches out of the body of the hot gas. A vortex ring is formed. About 250 μs, the ripple-type structure is produced. We show that Rayleigh-Taylor instability and Kelvin-Helmholtz instability are not the causes of the growth of the wavy vortex. We further guess that the growth of the ripple-type perturbation is led by free diffusion. Through a quick estimation, R = nh, measurements show the consistent scaling relations. We further show that the comatic aberration is suspected to be responsible for the asymmetric rarefaction wave, which triggers Kelvin-Helmholtz instability and induces the wavy vortex and the spiral jet. If without comatic aberration, the vortex and the jet are still with smooth boundary at late stage. About 500 μs, the second vortex ring is produced due to Kelvin-Helmholtz instability. Finally, at 1 ms, it can also explain that the expension of ripple structure is caused not because of instabilities since the turbulence-type structure is not produced at late stage. Therefore, our proposed model is demonstrated again.