Selection and Enhancement of the Single Harmonic Emission Event in the Water Window Region

The control of the high-order harmonic generation in the half-cycle region has been investigated by using the improved polarization gating (PG) technology. It is found that by properly controlling the delay time of the PG pulse, the contribution of the harmonic plateau is nearly coming from the single harmonic emission event, which is much better for producing the single attosecond pulses (SAPs). Further, by properly adding an ultraviolet pulse and a half-cycle pulse in the driven laser polarization direction, the harmonic yield can be enhanced and the harmonic cutoff can be extended, showing a high-intensity harmonic plateau covering the whole water window region. Finally, through the Fourier transformation of some selected harmonics, a 35 as SAP in the water window region can be obtained.

Single attosecond pulse generation by using plasmon-driven double optical gating technology in crossed metal nanostructures

An effective method to obtain the single attosecond pulses (SAPs) by using the multi-cycle plasmon-driven double optical gating (DOG) technology in the specifically designed metal nanostructures has been proposed and investigated. It is found that with the introduction of the crossed metal nanostructures along the driven and the gating polarization directions, not only the harmonic cutoff can be extended, but also the efficient high-order harmonic generation (HHG) at the very highest orders occurs only at one side of the region inside the nanostructure. As a result, a 93 eV supercontinuum with the near stable phase can be found. Further, by properly introducing an ultraviolet (UV) pulse into the driven laser polarization direction (which is defined as the DOG), the harmonic yield can be enhanced by two orders of magnitude in comparison with the singe polarization gating (PG) technology. However, as the polarized angle or the ellipticity of the UV pulse increase, the enhancement of the harmonic yield is slightly reduced. Finally, by superposing the selected harmonics from the DOG scheme, a 30 as SAP with intensity enhancement of two orders of magnitude can be obtained.