利用飞秒激光脉冲分别在水平和竖直方向上进行了推进微型小球的实验。实验中首次利用毫焦量级的飞秒激光脉冲(重复频率1kHz)推进质量在毫克量级的小球,将直径0.7 mm 的铁球水平推进了65 mm,直径接近1 mm 的聚苯乙烯小球竖直推进了72 mm。实验研究发现:无论是在水平还是在竖直方向上的推进,小球离开飞秒激光聚焦区域之前与小球发生作用的脉冲个数是决定推进效果的决定性因素。通过增大脉宽、换用较长焦距的聚焦透镜增加与小球作用的脉冲个数,可以将小球推进到更远的距离或更高的高度。
Temperature dependence of the electron diffusion in metallic targets, where the electron-lectron collision is the dominant process, is investigated with the help of an extended two-temperature model. In sharp contrast to the low electron temperature case, where only the electron-phonon collisions are commonly considered, the electron diffusion process underlying the high electron temperatures evolves dramatically different in both temporal and spatial domains. Calculated results of the ablation yield at different pulse durations are presented for a copper plate impinged by ultrashort laser pulses with energy fluences ranging from 0.1 J/cm^2 to 10 J/cm^2. The excellent agreement between the simulation results and the experimental data indicates the significant role of electron-electron collisions in material ablations using intense ultrashort laser pulses.
