The High Harmonic Generated Form Atom Irradiated By The Tera-hertz Laser Pulses

The high harmonic generation can be applied to produce XUV light source and to generate ultrashort attosecond pulse. Thus, it has been the key issue in strong field atomic and molecular physics study. There are still many restrictions on the generating attosecond pulse, such as harmonics emission intensity is too low, the phase matching condition between the harmonics inherent inappropriate and chirp effect brought about harmonic generation process. In this work, we using the numerical solution of one-dimensional theory-dependent Schr?dinger equation to study the high harmonic emission process of atom irradiated by a ultrashort laser pulse whose duration is several tens THz.In the tunneling area with same Keldysh factor, the high harmonic emission efficiency with the variation of the laser pulse frequency is investigated. It is found that the higher frequency laser pulse can obtain higher emission efficiency. The harmonic emission is study for a atom whose initial is a superposition of ground state and an excited state. It is found that the harmonic emission efficiency are largely enhanced by for the superposition state atom. One can obtaind an chirp-free harmonic emission by optimizing the intensity of main pulse and the frequency of pre-pulse which can prepared an atom in a superposition state.We also propose a optimized scheme to control the atomic high harmonic by using a combined laser pulse which include a lower frequency and higher frequency pulses. By changing the delay time of the high frequency laser pulse, the intensity and frequency of the high frequency one, the profile of high harmonic generation can be well control. By using a optimized combined pulse, one can obtain an ultrashort pulse whose duration is 191 attosecond which is close to the Fourier limit.