空气中飞秒激光自聚焦等离子体通道的电导特性

 通过电学探测法，采用不同焦距的聚焦透镜，在不同激光能量、不同极性外加电压的条件下，对大气中的飞秒激光自聚焦等离子体电离通道特性进行了实验研究。发现激光脉冲经不同焦距的聚焦透镜作用后均存在较长的电离通道，通道的等效电阻率有所变化，通常电阻率的最大值出现在透镜的几何焦点附近，并且焦距越长，此电阻率的局部峰值点离几何焦点位置越近。在外加不同极性电压时，自由电子受到所加静电场作用力、洛仑兹力以及有质动力的共同作用。焦点前，通道电流变化不明显，加正向电压产生的电流略微大于加负向电压时的电流；焦点后则是加负向电压产生的电流大于加正向电压时的电流。

Conductivity of self-guided laser plasma channel produced by femtosecond laser pulses in air

The conductivity of the plasma channel are shown in detail by electrical detecting method on the conditions of different focal lengths,different laser energies and polarities of the external voltage.The experimental results show that there are long ionization channels after lens with different focal length.The equivalent resistivity of the channels change slightly,and usually the maximum value of resistivity appears near the geometric focal point.If the focal length is longer,the peak point would get closer to the geometry focal point.With voltage of different polarity,the electrostatic field force and Lorentz force as well as the ponderomotive force will together change the current of plasma channel.In front of the focal point,the variation of the current is not obvious,and the current under a positive voltage is a little bigger than that under a negative voltage;while behind the focal point,the opposite occurs.