The Single Attosecond Pulse Generated By Atom Exposed To Two-color Combined Laser Fields

The attosecond pulse is a robust tool to resolve and manipulate ultrafast electronic processes. In the present years, The advent of attosecond pulses provides the possibility of probing ultrafast electron dynamics in atoms and molecules. It is well-known that the interaction of intense laser field with atoms and molecules can lead to high-order harmonic generation (HHG). A typical high-order harmonic spectrum shows that with the increase of harmonic order, the signal intensities fall off drastically for the first few low orders, then the intensities remain almost constant for many orders that form a plateau and finally the intensity drops abruptly for the highest orders, which have named the cutoff . The appearance of plateau structures from HHG power spectra make HHG possible as sources of radiation in X-ray and XUV areas, furthermore, HHG is a preferred source for the generation of attosecond pulse.In the chapter, by solving the time-dependent Schr?dinger equation with split-operator method we study the high harmonics of one dimension helium atom exposed to the two-color laser field composed of IR field and UV field and analyze the characteristics of the attosecond pulse which is produced by the high-order harmonics. It is found that the width of the attosecond pulse is shortened by increasing intensity of IR field in the combined laser field. By adjusting the time delay of two lasers, we can enhance the contribution of one electron trajectory and suppress the other electron trajectory, Then we can obtain an isolated sub-100-as pulse.Moreover, By solving the time-dependent Schrodinger equation with split-operator method, we study the high harmonics of one dimension helium atom exposed to the combined laser field composed of IR field,UV field and a static electric field, By adding a static electric field to the two-color laser field, We found the plateau of the high-order harmonics will be broaden in the presence of a static electric field. It is also found that the width of the attosecond pulse is shortened by increasing intensity of a static electric field in the combined laser field. In a word, adjusting the intensity of two-colour laser field or static electric field are all good ways to obtain ultrashort attosecond pulse.