Theoretical Study Of The Above-threshold Ionization Of Hydrogen Atoms In Chirped Laser Pulses

With the emergence of laser,its development is far beyond people's expection.Now the interaction of intense femtosecond laser fields with atoms(or molecules)has became one of the research hotspots because it plays an important role.One of the most important topics is above-threshold ionization(ATI)of atoms.The main content of this paper is to study the energy spectra,the angular distributions and two-dimensional momentum spectra of photoelectron of hydrogen atom in femtosecond pulses by numerically solving the time-dependent Schr?dinger equation(TDSE).The main work is as follows.Above-threshold ionization(ATI)of hydrogen atom exposed to chirped laser fields is investigated theoretically by solving the time-dependent Schr?dinger equation.By comparing the energy spectra,the two-dimensional momentum spectra and the angular distributions of photoelectron for the laser pulses with different chirp rates,we show a very clear chirp dependence both in the multiphoton and tunneling ionization processes but no chirp dependence in the single-photon ionization.We find that the chirp dependence in the multiphoton ionization based ATI can be attributed to the excited bound states.In the single-photon and tunneling ionization regimes,the valance electrons can be removed directly from the ground state and thus the excited states may not be very important.It indicates the chirp dependence in the tunneling ionization based ATI processes is due to the different laser pulses with different chirp rates.In addition,we research the the chirp dependence in the multiphoton ionization when the 1s and 2s superposition state is the initial state.It is clear that the chirp dependence of superposition state are obviously weaker than that of 1s according to energy spectra and the angular distribution.