No abstract

No abstract

No abstract

A new regime in the interaction of a two-colour (ω,2ω) laser with a nanometre-scale foil is identified, resulting in the emission of extremely intense, isolated attosecond pulses -even in the case of multi-cycle lasers. For foils irradiated by lasers exceeding the blow-out field strength (i.e. capable of fully separating electrons from the ion background), the addition of a second harmonic field results in the stabilization of the foil up to the blow-out intensity. This is then followed by a sharp transition to transparency that essentially occurs in a single optical cycle. During the transition cycle, a dense, nanometre-scale electron bunch is accelerated to relativistic velocities and emits a single, strong attosecond pulse with a peak intensity approaching that of the laser field.

The Daqingshan area is located in the Khondalite belt in the northern margin of the North China Craton. It has the best-preserved Mesozoic basin and is an ideal area for research on Jurassic strata. Sandstones mainly contain quartz and feldspar, with significantly less debris content. In addition, petrography and geochemical classifications have revealed the presence of arkose and wacke. Chondrite-normalized rare earth element patterns of samples are characterized by the enrichment of light rare elements and the flat trend toward heavy rare earth elements. Petrography and source rock discrimination diagrams of geochemical data suggest the presence of felsic rock and Precambrian basement in the northern and southern parts of the basin, which are crucial source areas; however, few mafic materials occur in the Wudanggou Formation. Tectonic discrimination diagrams of geochemical data show that the source materials were deposited on an active continental margin and/or continental island arc. Petrological and geochemical data from the Wudanggou Formation and Changhangou Formation samples suggest that the Yanshan movement influenced the formation of the Changhangou Formation.