The Research Of Attosecond Ultrafast Manipulation For The XUV Photoabsorption Spectrum Of Atom

Recently, with the rapid development of laser technology, especially the attosecond pulse technology, the extreme ultraviolet(XUV) photoabsorption spectrum has become an interesting research area and some dramatic results are obtained by the recent study. The XUV photoabsorption spectrum is based on the all-optical detection scheme which brings with it a number of benefits compared to the previously existing techniques based on electron and ion detection, and overcomes several of the limitations, the transient absorption spectroscopy can provide information that is fundamentally inaccessible to the techniques based on ionisation, namely dynamics occurring well below the ionisation threshold, which makes the method attractive for fundamental studies. In the paper, based on the different models, we investigate the transient absorption spectroscopy, and provide some methods for the manipulation of the electron dynamics occurred in the attosecond time scale.In Chapter 1, the development of laser technology is introduced in brief, mainly covering the high order harmonic generation(HHG), its features, attosecond pulse generation and its application. Especially, the development of the transient absorption spectroscopy is presented and the current research situation of XUV photoabsorption spectrum is introduced.In Chapter 2, we investigate the XUV photoabsorption spectrum of atom by numerically solving the time-dependent one-dimensional(1D) two-electron Schrodinger equation and some different three-level models. The helium atoms are subjected to a XUV attosecond pulse and a time-delayed infrared(IR) few-cycle laser pulse. The excited states are populated by the XUV pulse, and probed by the time-delayed IR laser. The time-resolved transient absorption spectroscopy demonstrates that three-level model can show most of the features observed in that obtained from TDSE, but the photoabsorption spectrum based on three-level model with rotating-wave approximation(RWA) can not repeat the fast oscillation structure observed from TDSE, and the photoabsorption spectrum based on our modified three-level model agrees very well with that observed from TDSE. By compare different level models, we show that different energy style may result the asymmetry between the stripes and fast oscillations above and blow the main absorbtion line in attosecond transient absorption spectroscopy. The stripes and fast oscillations above and blow the main absorbtion line become fainter when the IR laser intensity is decreased.In Chapter 3, we investigate the time-resolved transient absorption spectroscopy of doubly-excited states of helium atoms by solving the time-dependent two-electron Schrodinger equation numerically based on a one-dimensional model. The helium atoms are subjected to an extreme ultraviolet(XUV) attosecond pulse and a time-delayed infrared(IR) few-cycle laser pulse. A superposition of doubly excited states populated by the XUV pulse is identified, which interferes with the direct ionization pathway leading to Fano resonance profiles in the photoabsorption spectrum. In the presence of an IR laser, however, the Fano line profiles are strongly modified: A shifting, splitting, and broadening of the original absorption lines is observed when the XUV attosecond pulse and infrared few-cycle laser pulse overlap in time, which is in good agreement with recent experimental results. At certain time delays, we observe symmetric Lorentz, inverted Fano profiles, and even negative absorption cross sections indicating that the XUV light can be amplified during the interaction with atoms. We further prove that the above pictures are general for different doubly excited states by suitably varying the frequency of the IR field to coherently couple the corresponding states.In Chapter 4, we investigate the time-resolved transient absorption spectroscopy of doubly-excited states,the quantum control of the XUV photoabsorption spectrum of helium atoms via the carrier-envelope-phase(CEP) of an infrared(IR) laser pulse by numerically solving the time-dependent one-dimensional(1D) two-electron Schrodinger equation. The time-resolved transient absorption spectroscopy varies as a function of the CEP periodically. We fit the absorption spectra with the Fano line profiles giving rise to the CEP-dependent Fano q parameters, which are modulated from extremely large positive value to extremely large negative value. These results indicate that the quantum interference between two ionization paths can be efficiently controlled by the CEP of an ultrashort laser pulse, and thus offering another possibility, in addition to the laser intensity and the time delay between the XUV pulse and the IR laser, of manipulating the extreme ultrafast electronic motion in atoms. Our predictions can be experimentally verified at ease with the present experimental technique.In Chapter 5, we investigate the time-resolved transient absorption spectroscopy of singly-excited states of He atom by solving the time-dependent one-dimensional(1D) Schrodinger equation based on single electron model and two correlated electron model. It is demonstrated that the transient absorption spectroscopy are similar with each other, both the models can destrible the basic structure of the absorption spectroscopy, in the presence of an IR laser, the main sbsorbtion line is strongly modified: the shifting, splitting, and broadening of the original absorption lines is observed, all of this is in good agreement with the previously observations. However, there is a time delay in the sidebad of the main sbsorbtion line between the results based on the single electron model and two correlated electron model, which manifest that the electron correlation plays an important role in the interation of atom and XUV pulse.