Realization of Single Attosecond Pulse Generation in Multi-Cycle Regime   through Modulation of Carrier Wave
  An intuitive physical mechanism for single attosecond pulse generation in multi-cycle pulse regime is proposed. We suggest that the continuum spectra of HHG can be controlled through the modulation of carrier wave, while keeping the multi-cycle envelope unchanged approximately. By increasing the time interval between the adjacent maximum return kinetic energy peaks, the kinetic energy of the side peaks will be apparently suppressed by the multi-cycle envelope. The photons with energies near the cutoff burst only at the pulse center with high coherence, which contribute to the generation of single attosecond pulse. We verify this mechanism by using a multi-cycle tri-color pulse as driver field. 
Xiang Yang, Yueping Niu, and Shangqing Gong
physics.optics