Plasmas formed in front of laser-targeted solids enhance electromagnetic fields

Plasma that forms in front of solid objects during ultrashort laser pulses, called pre-plasma, can boost laser energy absorption, increase terahertz radiation, and induce electromagnetic pulses (EMPs). These EMPs and transient currents can be guided and show promise in applications such as the post-acceleration of protons and the generation of strong magnetic fields.

Combining particle-in-cell simulations with experimental diagnostics, Li et al. characterized the role of pre-plasma scale lengths on EMPs created by pre-ablation laser pulses in front of targets. They found that when lasers used a target normal sheath acceleration, EMPs generated from laser-induced current increased when pre-plasma formed.

The group used a compact laser plasma accelerator platform to deliver energy to targets along with an ablation pre-pulse. Relativistic electron bunch ejections from the target led to current across its surface, which was collected by copper wires with its resulting EMP measured.

“The major challenge was synchronizing the discharging current pulse and the probe particle beam,” said author Chen Lin. “We did several experiments and set different delay times to make sure the pulse current was captured. What surprised me is that the measured discharging current is not as strong as we expected, but we managed to identify it and measure its intensity variation under different pre-plasma scale length.”

They found the intensity of the currents used to generate EMPs and the resulting magnetic fields doubled when pre-plasma was formed. When comparing their experimental results with simulations, the group found that energy absorption efficiency increased with a proper scale length of the plasma.

They plan to build on their results by further investigating proton acceleration and strong magnetic field generation using enhanced short-pulse EMP.

Source: “Enhancement of guided electromagnetic wave by preplasma formation in laser-plasma interaction,” by Yuze Li, Min Jian Wu, Dongyu Li, Tong Yang, Hao Cheng, Yadong Xia, Yang Yan, Yixing Geng, Yan Ying Zhao, X. Q. Yan, and Chen Lin, Physics of Plasmas (2023). The article can be accessed at https://doi.org/10.1063/5.0135323 .