Ionization And Dissociation Of CS₂、CO₂、OCS In Femtosecond Laser Field

For decades, femtosecond laser technology has been developed enormously, theultra-short pulse with ultra-strong intensity is now a powerful tool to exploremicroscopic and ultrafast dynamics of atoms and molecular. During the last twenty-thirty years, many research of dynamics of atoms and moleculars in femtosecond laserfield have been conducted, such as ionization, dissociation, high-order harmonicgeneration, non-sequence double ionization, above-threshold ionization and coulombexplosion.In this paper, we studied the ionization and dissociation of CS2, CO2and OCS inthe femtosecond laser field with Time of Flight mass spectrum. We investigated thedependence of ion yield on laser intensity and ellipticity. The main results aresummarized below:We investigated the character of the time of flight mass spectrometry of CS2, CO2and OCS at2.0×1014W/cm2. There are many kinds of fragment ions in these threemass spectrums, such as the parent ions, diatomic molecular fragment ions and lots ofdifferent atom ions. We find that diatomic ion emerges at the laser intensity when theparent ions (CS2and CO2) or parent dications (OCS) are produced, while atomicfragments are produced from coulomb explosion which only arise at higher laserintensity. And “Knee” structure, which is the typical feature of NSDI, was founded inthe ratio of CO22+/CO2+vs laser intensity, but no structure was founded in other twomolecules.We studied dependence of fragment on the laser polarization for the threemolecules. We proved that the NSDI in CO2is a major process, because relative yieldof CO22+is completely disappeared under circular polarized light in the NSDI region,which is accordance with the prediction of three-step recollision model. The yield of CS22+do not change at all with ellipticity. For OCS2+, the relative yield of OCS2+issuppressed in the circular polarized light at low intensity, but the opposite phenomenonwill occur when the intensity is higher. The diatomic fragment ions come from thedissociative-ionization of parent divalent ions (CS2and CO2) or parent dications (OCS).The dependence of fragment ions S and O on laser polarization is similar in the threemolecules. Our results show that the higher the charge state of S or O is, the strongerdependence on the ellipticity the relative yield is. On the contrary, the trend of thefragment C is very different in the three molecules, the maximum yield of the fragmentCn+ion is observed at linear polarization for CO2, but at elliptically polarized light forOCS and circular polarized light for CS2. Our study shows that rescattering plays agreat role in dissociation, ionization and coulomb explosion of molecules.