Contents - Max-Planck-Institut für Physik komplexer Systeme
Contents - Max-Planck-Institut für Physik komplexer Systeme
Contents - Max-Planck-Institut für Physik komplexer Systeme
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insystemsexhibitingalong-rangeinteractionofconstituentmoleculesorparticlessuchasinnematic<br />
liquidcrystalsordipolarBose-Einsteincondensates(BEC).<br />
Nonlocalityisthusafeatureofalargenumberofnonlinearsystemsleadingtonovelphenomenaofa<br />
genericnature. Forinstance,itmaypromotemodulationalinstabilityinself-defocusingmedia,aswell<br />
assuppresswavecollapseofmultidimensionalbeamsinself-focusingmedia. Nonlocalnonlinearitymay<br />
evenrepresentparametricwavemixing,bothinspatialandspatio-temporaldomainwhereitdescribes<br />
formationofthesocalledX-waves. Furthermore,nonlocalitysignificantlyaffectssolitoninteraction<br />
leadingtoformationofboundstatesofotherwiserepellingbrightordarksolitons. Ithasalsobeen<br />
shownthatnonlocalmediamaysupportformationofstablecomplexlocalizedstructures,likerotating<br />
multihumpandvortexringsolitons.<br />
Currently,weareworkingonaschemeforthecreationofthree-dimensionalbrightsolitonsinaBEC.<br />
TheapproachisbasedonopticaldressingofagroundstateatomBECtohighlyexcitedRydbergstates.<br />
WewereabletoidentifyanappropriaterangeofRydbergstatesthatprovidessign-definiteattractive<br />
nonlinearities,andthuspreventscondensatecollapseasoccurringindipolargases.Wewanttoinvestigate<br />
notonlytheexistenceofstableself-trapped”condensatebullets”,buttheintrinsicanisotropyofthe<br />
nonlocalinteractionoffersalsoanintriguingpossibilitytotransferangularmomentumtothecondensate<br />
andcreate,e.g.,vortices.<br />
Onthistopic,wecollaboratewiththegroupofThomasPohl(mpipks),WieslawKrólikowski(ANU,<br />
Canberra,Australia),andMarkSaffman(UniversityofWisconsin,USA).<br />
Laserbasedchargedparticleacceleration Highpowerlaser-pulseinteractionwithplasmasoffersa<br />
uniqueopportunitytostudymatterunderextremeconditionsoftemperatureandpressure.Currentlaser<br />
systems(withintensities > 10 18 W/cm 2 andsoonbeyond > 10 22 W/cm 2 )allowtoaccesstheso-called<br />
relativisticregimeoflaser-plasmainteraction.Thisinteractionregimeischaracterizedbytheemissionof<br />
variousenergeticparticles(electrons,ionsandalsoneutronsandpositrons)andintenseradiations(with<br />
frequenciesrangingfromTHztothegammadomain). Thesenewsourcesofparticlesandradiations<br />
offeravastrangeofapplications.<br />
Ourresearchatthe mpipksisdevotedtolaser-basedionaccelerationanditsapplications. Multi-MeV<br />
ionbeamsgeneratedduringtheinteractionofanintenselaserpulsewithaplasmacanindeedinitiate<br />
athermonuclearreactionintheso-calledfast-ignitorscenarioforinertialconfinementfusion. Dueto<br />
theirgoodlaminarity,collimationandshortduration,theyarealsousedfortime-resolvedradiographyin<br />
plasmaexperiments.Lastbutnotleast,high-qualityionbeamsmayalsobeusedformedicalapplications<br />
suchasisotopecreationandhadron-therapy.<br />
Differentmechanismsofionaccelerationhavebeenproposeddependingonwhetherionsoriginatefrom<br />
thefrontside(irradiatedbythelaser)ortherearsideofthetarget. Atthetargetrearside, ion<br />
accelerationoccursinthestrongelectrostaticfieldresultingfromchargeseparationduetohotelectrons<br />
escapingintovacuum. Thismechanism,referredtoastargetnormalsheathacceleration(TNSA),is<br />
thedominantprocessofionaccelerationforcurrentlyavailable(moderatelyrelativistic)laserintensities.<br />
TNSAprovidesionbeamswithinterestingpropertiesandrelativelylargeefficiencyofenergyconversion<br />
(afewpercent)fromthelaserpulsetotheions.However,theresultingionbeamshaveacharacteristic<br />
broadspectrumwithasharpcut-offatmaximalenergy.<br />
Multispecies(multilayeredorhomogeneous)solidtargetshaverecentlyattractedalotofattentionas<br />
theymayallowforabettercontroloftheionspectrum.Wehaveproposedanewaccelerationmechanism<br />
forthegenerationofhigh-quality(smallenergyandangulardispersion, ∆E/E 10 %and ∆θ 5 ◦ ,<br />
respectively)energetic(> 100MeV)ionbeams.Thismechanismreliesonthecompleteelectronremoval<br />
fromananometricdouble-layertargetbyanintense(> 10 21 W/cm 2 )laserpulse.Itspotentialapplication<br />
tohadron-therapyhasalsobeenconsidered. Scalinglawsderivedfromanalyticalmodelingaswellas<br />
multidimensional(1D,2Dand3D)particle-in-cell(PIC)simulationssuggestthatpetawattlaserpulses<br />
arerequiredforthisapplication.<br />
OurstudyofaccelerationmechanismsalternativetoTNSAalsoleadsustoinvestigatetheso-called<br />
radiationpressureacceleration(RPA)regime.Inthisscenario,ionsareacceleratedbydirecttransferof<br />
momentumfromthelaserphotonstotheions.Thewholetargetisacceleratedtopotentiallyrelativistic<br />
velocitiesasacompactquasi-neutralbunch.Whilethisaccelerationschememayallowforthegeneration<br />
ofintensequasi-monoenergeticionbunches,themechanismsresponsibleforenergydispersionarenot<br />
yetwellunderstoodandarecurrentlyunderinvestigation.<br />
1.9. JuniorResearchGroups 27