The Generation of Ultraintense Half-Cycle Attosecond X-ray Pulse

For applications of attosecond pulse (AP), the intensity and isolation of AP are all important pursuits. We proposed a double-foil target regime to generate an ultraintense and isolated half-cycle attosecond x-ray pulse (AXP) that exhibits unipolar characteristics and an ultrahigh instantaneous electric field, which can enable more efficient directional electron acceleration and achieve superior temporal resolution to ultrafast dynamics of electrons in atoms through asymmetric manipulation. The double-foil target consists of gold foil and carbon foil. When the driving laser pulse interacts with the first gold-foil target, the electrons of the first foil are almost blown out and eventually disperse after several oscillations. Then, the laser pulse penetrates the first foil and begins to interact with the second carbon-foil target, where the electrons in the second carbon-foil target are undergoing relativistic oscillations around the ion background. Under the action of the Coulomb force from the ions of the first foil and the charge separation due to the relativistic oscillations of the electrons of the second foil, the ions of the second carbon-foil target start to expand. For moderate expansion of ions, the amplitude of the relativistic oscillations increases, and consequently, the electron sheet is formed. The electron sheet can be accelerated to ultrarelativistic velocity and emit the ultraintense AXP. However, for the large expansion of ions, it disrupts relativistic oscillations of the electrons and consequently inhibits further formation of the electron sheet and the corresponding coherent emission, which is the unique isolation regime of AXP due to the expansion dynamics of ions.