Study On Single Attosecond Pulse Generated By Atom Exposed To Two Laser Pulses With The Same Color And Other Pulse

Attosecond extreme ultraviolet pulses is a novel tool for studying basic ultrafast electronic processes and electronic dynamics in the scale of atoms and molecules. Attosecond pulses can be used for imaging ultrashort pulse of 2.5 fs of the time width and tracking the inner-shell Auger processes in atomic, so that people are interested in the study of attosecond. It is well-known that the interaction of intense laser field with atoms can lead to high-order harmonic generation (HHG). HHG is a preferred source for the generation of attosecond pulse. Therefore, HHG has been a subject of great interest owing to these potential applications in recent years and in the future. Presently there are many ways to produce such a single attosecond pulse, polarization gating, two-color laser field, three-color laser field, multicolor laser field, a combination of a laser pulse and a half cycle pluses, a combination of a chirped laser and static electric field.By solving numerically the time-dependent Schr?dinger equation with the split-operator method, we investigate the characteristic of the high-order harmonic of one-dimensional helium atom exposed to two laser pulses with the same color and half cycle pulses. It is shown that the harmonic spectrum is extended to IP+9.6UP in the case of the combined fields, and an isolated 63 as pulse can be obtained by superposing around the cut-off position of the high-order harmonic generation spectrum. By analyzing, we found that the plateau of the high-order harmonic generation spectrum is extended greatly and the contribution of the long electron trajectory is suppressed by adding the half cycle pulses.We propose a method to generate single attosecond pulse when one-dimensional helium atom is exposed to the combination of two laser pulses with the same color and a midinfrared laser pulse. We investigate the characteristic of the high-order harmonic by numerical simulation. It is shown that the harmonic spectrum is extended to IP+12.6UP. By superimposing some orders harmonics on different region for the second plateau, all of the pulses obtained are single attosecond ones. Minimum pulse achieves 42 as. Especially, by superimposing the lower order harmonics of the second plateau, one can not only obtain single attosecond pulse, but also the intensity of the single pulse is three order of magnitude higher, compared to the attosecond pulse obtained near cut-off of harmonics. By analyzing, we found that the plateau of the high-order harmonic generation spectrum is extended greatly and the contribution of the long electron trajectory is suppressed by adding the midinfrared laser pulse.