Generation of Polarization-direction-controllable Attosecond Pulses with Twisting Double Laser Pulses(Invited)
Strong field physics has evolved throughout the decades,and numerous unprecedented physical phenomena have been observed.High order harmonics generation,as an essential phenomenon in strong-field physics,has resulted in significant improvements in related research and applications since their first experimental discovery in 1987.After the first experimental observation of attosecond bursts from gas harmonic generation in 2001,a variety of gating techniques were used to obtain shorter and shorter isolated attosecond pulses,and attosecond pulses provide an important tool for observing ultrafast electron dynamics in matter on the atom's time scale.In addition to the intensity and width of the attosecond pulses,the research also focuses on the modulation of their polarization state.Because polarization-state controllable attosecond pulses can provide more degrees of freedom for manipulating ultrafast processes,they have important applications in chiral identification,magnetic circular dichroism,and spin currents.Two-color ω+2ω laser is a very common type of driving field used in the harmonic and attosecond pulse generation.The intensity of harmonics can be improved and the harmonic cut-off can be extended effectively by using linear polarization two laser pulses with parallel polarization direction.The elliptically polarized attosecond pulse can be generated by using two pulses with orthogonal polarization or with a certain angle.In recent years,homochromatic dual laser pulses(ω+ω)have attracted attention in the study of molecules and atoms in the strong laser fields.The two laser beams are obtained by splitting a linearly polarised laser beam into two by means of a commonly used interferometer or waveplate.The time delay,phase delay,intensity ratio and the polarization angle between two beams can be easily modulated by additional optical elements such as waveplates and irises.When two laser pulses are polarized in parallel directions,the central frequency of the synthesized laser electric field changes with time delay,which can be used to control the photon energy of the harmonics.When the polarization directions of the two pulses have an angle of entrainment,the polarization state of the combined laser field changes as the time delay changes.The polarization direction of the laser electric field changes continuously with time every half cycle at specific time delays.In this work,the possibility of using homochromatic twisted double laser pulses to generate twisted linearly polarized attosecond pulse trains with controllable time-dependent polarization directions is discussed theoretically,by means of a strong-field approximation model.The results show that when two beams of same-frequency linearly polarized laser pulses are polarized in orthogonal directions with suitable time delays(correspond to a phase difference of nπ,n is an integer),linearly polarized attosecond pulse trains in the entire x-y plane can be generated from high order harmonics,by varying the intensity ratios between two laser pulses.The laser carrier envelope phase,on the other hand,the laser carrier envelope phase does not significantly affect this modulation,the polarization direction of the attosecond pulse change no more than 7 degrees at all phases for all intensity ratios.In addition,we find that under appropriate laser intensity ratio,polarization angle between two laser pulses laser polarization can also be used as an effective parameter to control the polarization of attosecond pulses.Compared with the intensity ratio,the laser polarization angle between two laser pulses should be easier to accurately control in the experiment,so it can be used as a supplementary parameter of the intensity ratio to fine-tune the time-dependent polarization direction of the attosecond pulse.The present work provides a simple and easy-to-use scheme for generating controllable twisting attosecond pulses in the direction of polarization.
万方数据
维普
