We investigate laser induced nonsequential multiple ionization using a simple statistical model in which an electron recollides inelastically with its parent ion. In this collision, it thermalizes with the remaining $N-1$ bound electrons within a time inte

JournalofModernOptics

Vol.00,No.00,DDMonth200x,1–19

arXiv:physics/0607142v1 [physics.atom-ph] 14 Jul 2006Speed-upandslow-downcollisionsinlaser-inducednonsequentialmultipleionizationC.FigueiradeMorissonFaria 1andX.Liu21CentreforMathematicalScience,CityUniversity,NorthamptonSquare,LondonEC1VOHB,UK2DepartmentofPhysics,TexasA&MUniversity,CollegeStation,TX77843-4242,USA(Received00Month200x;In nalform00Month200x)Weinvestigatelaserinducednonsequentialmultipleionizationusingasimplestatisticalmodelinwhichanelectronrecollidesinelasticallywithitsparention.Inthiscollision,itthermalizeswiththeremainingN 1boundelectronswithinatimeinterval t.Subsequently,alltheNelectronsleave.Weaddressthequestionofhowtheabovetimedelaysin uencetheindividualcontributionsfromtheorbitsinwhichthe rstelectron,uponreturn,isacceleratedordeceleratedbythe eld,respectively,totheionmomentumdistributions.Inbothcases,thetimedelaysmodifythedriftmomentaobtainedbytheNelectronswhentheyreachthecontinuumatt+ t,bymovingsuchtimestowardsorawayfromacrossingoftheelectric eld.Thecontributionsfrombothtypesofcollisionsarein uencedindistinctways,andtheinterplaybetweensuchtrendsdeterminesthewidthsandthepeakmomentaofthedistributions.Speci callyinthefew-cyclepulsecase,wealsoshowthatsuchtimedelaysdonota ecttheshapesofthemomentumdistributionsinaradicalfashion.Hence,evenwithathermalizationtime t,nonsequentialmultipleionizationcouldinprinciplebeusedforabsolute-phasediagnosis.1IntroductionThephysicsofnon-sequentialdoubleionizationinraregasesbylow-frequency,intenselaser eldsis,toaverylargeextent,understood.Inparticularforneon,theelectronmomentumdistributionswithpeaksatnon-vanishingmomentum componentsp1||=p2||=±2Up,whereUpdenotestheponderomotiveenergy,canbeexplainedbyalaser-inducedinelasticrecollisionprocess[1–3].Speci cally,the rstelectronleavesanatombytunnelingionizationatatimet′,propagatesinthecontinuum,beingacceleratedbythe eldand,subsequently,atatimet,recollideswithitsparention.Thesecondelectronisthenfreedbyelectron-impactionization[4].