The effect of target thickness on the efficiency of high-order harmonics generated from laser-driven overdense plasma target**

Abstract

In this paper, we analytically and numerically studied the impact of the target thickness on the efficiency of laser-plasma based high-order harmonics generation (HHG). The optimal parametric region is acquired where the laser normalized amplitude a 0, the target density n e and thickness d 0 satisfy the relation: for . In this region, the laser can partially penetrate the target, leading to efficient acceleration of the target. Meanwhile, the target is thick enough to oscillate along the rising edge of the laser without being broken, which guarantees the occurrence of HHG. Both one-dimensional and two-dimensional particle-in-cell simulation results verify our optimal target thickness theory, and a single attosecond pulse with I = 3.0 1020 W cm-2 is generated under the driving of 8.6 1020 W cm-2, which is several hundred times more intense than that from a thick target.