Ion dynamics in ultrafast laser ablation of copper target
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摘要:
We investigate the angular distribution and average kinetic energy of ions produced during ultrafast laser ablation (ULA) of a copper target in high vacuum.Laser produced plasma (LPP) is induced by irradiating the target with Ti:Sapphire laser pulses of ~50 fs and 800 nm at an angle of incidence of 45°.An ion probe is moved along a circular path around the ablation spot,thereby allowing characterization of the time-of-flight (TOF) of ions at different angles relative to the normal target.The angular distribution of the ion flux is well-described by an adiabatic and isentropic expansion model of a plume produced by solid-target laser ablation (LA).The angular width of the ion flux becomes narrower with increasing laser fluence.Moreover,the ion average kinetic energy is forward-peaked and shows a stronger dependence on the laser pulse fluence than on the ion flux.Such results can be ascribed to space charge effects that occur during the early stages of LPP formation.