Strong enhancement of coherent terahertz radiation by target ablation using picosecond laser pulses

Abstract

We have studied the generation of terahertz (THz) radiation via the interaction of an intense femtosecond laser pulse with aluminum (Al) and plastic targets pre-ablated by a picosecond ablation pulse. The measurements of the plasma shadowgraph and 1D-MULTI simulations show a similar micrometer density scale length of the pre-ablated plasma for the two types of targets after ablation. It is found that for the Al target, the intensity of THz radiation increased obviously under the condition of ablation, and only with the appropriate ablation delay time, the cutoff energy and charge of the accelerated protons also increased. 2D-simulations using the EPOCH program indicate that the strong enhancement of THz for the Al target is due to the increased number of energetic electrons from the interaction between the main laser and the ablated plasma. However, for the plastic targets, the intensity of THz radiation was almost vanished in the case of ablation, but the accelerated protons still existed and the cutoff energy even tended to increase. However, due to the lack of ability to simulate the molecular structure, we cannot distinguish between Al and plastic targets in the simulation. The mechanism of radiation suppression by ablation of the plastic target needs further investigation.