The High-order Harmonic Generated From An Atom Irradiated By Shaped Femtosecond Pulse

Many nonlinear phenomena come from the interaction between the ultrashort intense laser with matter.Such as above threshold ionization,high order harmonic generation,etc.High order harmonic radiation from gas atom irradiated by strong laser pulse can be used to generate ultrashort attosecond pulses,which is an important tool fordetecting electronic dynamic.Therefore,for the high harmonic generation,the analysisof the generation processes,improvement of harmonicefficiency and the control of harmonic field waveform have gradually become the focus of research.In this paper,the effects of laser field strength and potential function on harmonic generation are studied by numerically solving the time-dependent Schr?dinger equation.At the same time,we systematically explored the high order harmonic generation from atom irradiated by Sin shaping pulse.For linearly polarized laser pulse,the efficiency of each harmonics rises linearly with the increase of the amplitude of the electric field.When a certain amplitude intensity is reached,the harmonic intensity exhibits an oscillating structure.By selecting a separate analysis of the long and short trajectory contribution in the dipole moment,it is found that the oscillation of the harmonic intensity results from the phasedifference between the two trajectories generated by the subharmonic.The effects of the shaping parameters A and T of the Sin phase shaping pulse on the harmonic generation of the atom are systematically studied.The parameter A can adjustthe amplitude of the laser field and the number of sub-pulses after shaping.When the value of A is increased,the intensity of the high order harmonic is lowered,and the cut-off energy is decreased.The parameter T can change the time delay between the main pulse and the sub-pulse of the laser field.Increasing T reduces the overlap asymmetry of the different sub-pulses of the laser field and makes the harmonic spectrum red-shift.The phase offset Φ can adjust thephase between the sub-pulses,theasymmetry of the rising and falling edges of the laser pulse,and further the frequency peak position movement of the harmonic generation.