Research On Generation Of High-order Harmonic And Isolated Attosecond Pulse With Two-color Laser Field

When intense lasers interact with atoms and molecules, a coherent wave whose frequency is an integral times of that of the driving laser pulse is radiated, due to the highly nonlinear response, which is called as high-order harmonic generation (HHG). Since it is found that it covers the spectral range from the infrared to xuv and even to soft x-rays regions, it is quickly becoming a candidate to break femtosecond limit and realizing attosecond pulse generation, which opens the door of the attosecond science. In a few years, the generation of high-order harmonic and attosecond pulse generation has been a focus of world attention. Moreover, scientists have obtained a series of great achievements in atomic and molecular physics, material science, condensed physics, and so on. Therefore, attosecond pulse with shorter duration and higher intensity has been a worthwhile goal of more and more people. In this paper, on the basics of single-active electron approximation, we numerically solve the one-dimensional time-dependent Schrodinger equation (TDSE) for interaction between intense laser and atoms or molecules to investigate the improvement of high-order harmonic and attosecond pulse generation efficiency.Firstly, the importance of interaction between intense laser and atoms, molecules is described briefly. And we discuss the characteristics of HHG next, which are well understood by the semiclassical three-step model. Moreover, we discuss two forms of TDSE in the velocity gauge and length gauge.Secondly, the generation of high-order harmonic and attosecond pulse is investigated. And the results reveals that we can extend the cut-off of HHG greatly and synthetize attosecond pulses with different central frequencies with two-color laser pulse. A scheme to improve high-order harmonic efficiency with UV is also proposed, which can further compress the width and enhance the intensity of the attosecond pulse successfully.Finally, a new scheme for producing attosecond pulse with large ellipticity is presented. It is found that the high-order harmonic with large ellipticity is obtained successfully with the extended Lewenstein model, according to the interaction between intense laser and CO molecule. In addition, the stability of the supercontinuum ellipticity is also discussed under different conditions then, and the ultra-short attosecond pulse can be generated.