Simulation studies on overdense plasmas from laser-solid target interactions

Abstract

The chirped-pulse amplification (CPA) technique for ultrashort and high-intensity lasers can be used in diverse research applications such as the laser wakefield acceleration, the laser fusion, the nonlinear quantum electrodynamics research, etc. However, the conventional CPA scheme has fundamental limitations. For example, the final compression grating can be easily damaged. The overdense plasma with a ramped density can be used for chirped-pulse compression. As a plasma is already ionized, it can be a promising robust medium for such compression. In this study, the laser-ablated plasma is regarded as the source of an overdense plasma. The laser-induced ablation was simulated with a radiation hydrodynamics code called FLASH. For a high pulse compression ratio, a longer length of a critical-density plasma is required. A typical laser-ablated plasma has a very short length of critical-density region. Thus, the simulations with pump lasers with various pulse widths were performed to maximize the plasma length of the critical density region. Moreover, several methods for extension of the overdense plasma length were attempted. One method involves utilizing targets with varying materials and mass densities, while the other entails introducing micro-structures on the target. Eventually, it is revealed that using a truncated conical cavity in the planar target extended the critical-density plasma length by approximately 100 microns. Therefore, this type of target can produce overdense plasma, which can be experimentally demonstrated. Subsequent research in the future will explore the implementation of a plasma-based pulse compression scheme through experiments.