The Theoretical Study Of Double Ionization Of Argon Under Elliptically Polarized Laser Fields

Understanding the interaction between light and matter is always the one of themost important tasks of physics study. Recently, with the rapid development of thelaser technology, the pulse width of laser fields was shortened gradually while thelaser intensity was increased greatly. The great development of laser technology hasmade the research of light-mater interaction extend into the domain of strong-fieldphysics. Due to the application of strong laser pulse, a series of unprecedentedstrong-field phenomena were observed. Among these novel strong-field physicalphenomena, the strong-field double ionization has attracted much attention, because itshowed us that the electron correlation can play a significant role in the light-matterinteraction at the first time. The discovery of electron correlation in the strong-fielddouble ionization greatly challenged the traditional photo-physics theory which isbased on the single electron approximation and excited a great upsurge of studyingelectron correlation under strong laser field. Most recently, with the development ofthe ultra-short laser technology and the experimental measurement methods, peoplehave had the ability to create the ultra-short near-single-cycle laser pulse and alsohave had the experiment conditions to realize effective measurement of the doubleionization process from different carrier-envelope-phases. These great advances inexperiments have promoted the study and understanding of the strong-field doubleionization under the few-cycle laser field. On the other hand, the non-sequentialdouble ionization of atom within elliptically polarized (EP) or circularly polarized (CP) laser field has also attracted much attention most recently. The electron correlationeffects under non-linearly polarized field have extended our understanding ofre-collision dynamics. Moreover, the sequential double ionization within CP and EPfields can provide us the approaches to study the new mechanisms of electroncorrelation and the potential non-adiabatic effects in the ionization process.In order to explain the strong-field double ionization phenomena in theexperiments, a lot of theoretical models or calculation methods have been invented,which can be roughly divided into three types: classical model, semi-classical model,and quantum model. All these theoretical methods have included electron correlationeffectively and have simulated the main experimental results successfully to someextent. Among these theoretical methods, the classical ensemble approach has beenwidely adopted due to its high calculation efficiency and convenient physical analysis.The classical ensemble model is an effective tool for the theoretical study of thestrong-field double ionization. In this paper, by employing the classical ensembleapproach, we carry out the theoretical study on the double ionization dynamics ofArgon atom under EP and CP fields. Here, we will discuss the non-adiabatic effects ofthe strong-field ionization of atom in CP fields and the carrier-envelope-phase effectsin few-cycle EP fields respectively.First, by using the classical ensemble model, we investigate the sensitivity ofdouble ionization in circularly polarized laser fields to the initial ensembles that aregenerated for an Ar atom with a definite total angular momentum. The numericalresults show that the double-ionization probability in the counter-rotating case, wherethe electrons initially rotate against the laser field, can be much higher than that in thecorotating case, where the electrons rotate with the laser field. By analyzing theenergy distributions of double-ionized electrons versus time, we find that, for thecounter-rotating case, the ionization of the second electron occurs much earlier than inthe corotating case, and the first ionization can leave the Ar+ion in a higher energystate, which can increase the second ionization probability. These results indicate thatnonadiabatic effects can play an important role in double-ionization dynamics.Second, by employing the classical ensemble approach, we study thenon-sequential double ionization of argon atom under few-cycle elliptically polarized laser fields. The numerical calculation results show that the carrier-envelope-phaseshave not significant influence on the curves of double ionization yield versus laserintensity but have a great influence on the electron-momentum correlation spectra. Wefind that by varying the carrier-envelope-phase of the laser fields, theelectron-momentum correlation spectra can transform from a near-axis “cross shape”distribution to a far-axis “first quadrant” distribution arbitrarily, which indicates thatin the few-cycle elliptically polarized laser fields, the double ionization process can bechanged between the recollision-excitation-subsequent-ionization channel and therecollision-impact-ionization channel by controlling the carrier-envelope-phases.Then, by analyzing the electron-energy distributions versus time and classical electrontrajectories, we confirm this conclusion and show the physical pictures for the twoionization channels. Finally, by plotting the electron-momentum correlation spectrawhich come from different ionization channels, we demonstrate the concrete processof controlling the two ionization channels by the carrier-envelope-phases.