The effect of pulse energy on plasma characteristics of femtosecond filament assisted ablation of soil

In this paper, the effects of pulse energy on the plasma characteristics of femtosecond filament assisted ablation of soil were experimentally studied, and the space-and time-resolved evolution processes of soil plasma parameters such as emission intensity, electron temperature and electron density were obtained. The experimental results showed that the soil plasma parameters decreased rapidly in the range of 400 ns delay time, and then decreased slowly with increasing delay time. When increasing the distance away from the soil surface, the soil plasma parameters increased firstly, and then decreased. The soil plasma parameters all increased with the pulse energy that formed the femtosecond filament and the peak position of its spatial distribution shifted from 1.5 mm to 2.0 mm away from the soil surface when the pulsed energy was increased from 2.45 mJ to 3.23 mJ. Finally, the local thermal equilibrium condition was verified based on McWhirte criterion.