Isolated Attosecond Pulse Generation Radiated By Multicolor Laser Pulse

Due to the ultrashort duration and high energy of single photon, attosecond pulse has become a powerful tool for scientists to explore the atomic internal electron dynamics process. At present, high-order harmonic generation(HHG) scheme is the only way to produce attosecond pulse, the Scientists hope to obtain supercontinuum with high emission efficiency and wide spectrum, so as to synthesize intense isolated attosecond pulse by superposing the supercontinuum. In this thesis, we adopt the strong field approximation model which is proposes by Lewenstein to simulate to HHG of helium atoms in laser pulse, investigate the generation of isolated attosecond generation by the two- and three-color field schemes, and finally we achieve an isolated attosecond pulse with high efficiency and 46 as pulse duration. The content of this thesis can be mainly divided into three parts:In the first part, We investigate the high order harmonic generation under the irradiation of a monochromic pulse with longer pulse duration. It is found that as the duration of laser pulse is relative wide, although increasing the peak amplitude of the laser can obviously increase the width of plateau area, only attosecond pulse chain can be obtained, thus failing to get isolated attosecond pulse.In the second part, We attach a low frequency pulse with long pulse duration on fundamental laser pulse. Compared with the monochromatic field with the same peak amplitude, there exists a relatively large broadening on harmonic spectrum, thus exhibiting the supercontinuum structure. By superpositing the harmonics from 200th-order to 260th-order, an isolated attosecond with duration of 73 as has been obtained. However, attaching a low frequency pulse will lower the intensity of cut-off position of the harmonics, what is worse, it will be more difficult to control the quantum path, thus limiting the further compression of the pulse duration.In the third part, we propose the three-color field scheme: by attaching two laser field which is 30 fs/532 nm and 30 fs/1330 nm pulses on the fundamental field, and adjusting the factors that affect the generation of isolated attosecond pulse at the same time: making the ionization smaller will be helpful for phase matching effect after the generation of harmonics; controlling electron trajectory, will be beneficial to the selection of the short trajectory of HHG; and controlling the maximum kinetic energy will help to achieve a wider harmonic plateau. Finally, an isolated 46-as pulse can be generated by superposing supercontinuum from the 160 th to the 210 th order harmonics.