Generation of isolated ultraintense half-cycle attosecond pulse in coherent bremsstrahlung regime by double-foil target mechanism
L. Q. Qin, Ze Chen, Meiqi Sun, Jin Yan, Yanfei Tian, Zhongyi Chen, Yan Wang, Xingqiao Ma, Xueqing Yan, Yunliang Wang
Abstract
A unique coherent bremsstrahlung (CB) regime is proposed for the generation of an isolated half-cycle attosecond pulse (AP), even for the case of a multicycle driving laser pulse, which is realized by the laser pulse interacting with the double-foil target. When the rising edge of the laser pulse interacts with the double-foil target, the AP train is generated in the reflected direction due to the fact that the relativistic electron sheet (RES) is generated periodically twice per cycle of the laser pulse. While the peak cycle of the laser pulse interacts with the target, the electrons of the second foil target were nearly completely removed, which leads to the formation of an electrostatic potential well, and then the double-foil target becomes an electrostatic storage target (EST) that can capture and store electrons coming from the second foil target. Accordingly, only one RES can be generated by the peak cycle of the laser pulse interacting with those electrons stored in the EST, and is accelerated to ultra-relativistic velocity in the transmission direction, which emits the isolated AP by the CB regime. The isolation regime of AP can be determined by the scaling law of the depletion of electrons, which is described by the ratio of the areal charge density of the double-foil target and the amplitude of the peak-cycle laser pulse. The ratio is called the generalized similarity parameter. The generalized similarity parameter is about 2/π, which is predicted by the theoretical model and confirmed by the simulation results. The robustness of the isolation regime of AP is confirmed by considering different parameters of the laser pulse and plasmas, and by considering the presence of preplasma and two-dimensional effects.