Effects of macroscopic propagation on spectra of broadband supercontinuum harmonics and isolated-attosecond-pulse generation: Coherent control of the electron quantum trajectories in two-color laser fields

摘要

Recently it was shown that broadband supercontinuum harmonics can be produced from the long-trajectorynelectrons in the single-atom response by the coherent control of the electron trajectories through optimizedntwo-color laser fields. Such supercontinuum harmonics can be superposed to generate an isolated sub-30-nattosecond (as) pulse [Liu et al., Phys. Rev. A 84, 033414 (2011)]. In this paper, we investigate the effectnof macroscopic propagation on the supercontinuum harmonic spectra and the subsequent attosecond-pulsengeneration of atomic hydrogen. The time-dependent Schr¨odinger equation is solved accurately and efficientlynby means of the time-dependent generalized pseudospectral method. The effects of macroscopic propagationnare investigated in near and far field by solving Maxwell’s equation. The results show that the contributionnof short-trajectory electron emission is increased when the macroscopic propagation is considered. However,nthe characteristics of the dominant long-trajectory electron emission (in the single-atom response case) are notnchanged, and an isolated 53 as pulse can be generated in the near field.Moreover, in the far field, the contributionnof long-trajectory electron emission is still dominant for both on-axis and off-axis cases. As a result, an isolatedn42 as pulse can be generated directly. Similar results are obtained when the atomic target position is changed.nTherefore, the proposed method for the single ultrashort attosecond-pulse generation can be realized by meansnof the coherent control of the electron quantum paths in appropriately optimized two-color laser fields.