Paulus, G.

Quint, W.

Stöhlker, T.

Vogel, M.

GSI Repository

Controlled interaction of ions with high-intensity laser lightM. Vogel1,2, W. Quint2,3, Th. Sto¨hlker2,4,5, and G. Paulus51TU Darmstadt; 2GSI, Darmstadt; 3Ruprecht Karls-Universita¨t Heidelberg; 4Helmholtz-Institut Jena; 5Universita¨t JenaWe are currently preparing an experimental setup whichfeatures a Penning trap for preparation and control of suit-able ion targets for irradiation with high-intensity laserlight and study of subsequent reactions. Of particular inter-est is the detailed investigation of multiphoton-ionisationof confined particles by highly intense laser light. One im-portant aspect is control over the confined particles’ mass,charge, density, localization and optimized overlap with thelaser light by Penning trap techniques like the use of trapelectrodes as ’electrostatic tweezers’ and by application ofa ’rotating wall’, respectively. Also, the non-destructivedetection of reaction products is a central property. ThePenning trap setup is designed in a portable fashion, suchthat it can be attached to existing laser systems easily [1].The interaction of highly intense radiation with matterand the corresponding non-linear effects have been subjectof lively research, both theoretical and experimental, es-pecially in the infrared and visible photon energy regimes.Laser systems capable of producing high intensities alsoat photon energies in the extreme ultra-violet (EUV) and(soft) X-ray regime open access to novel effects like non-linear Compton effects or simultaneous elastic and inelasticphoton scattering, and allow multiphoton-ionisation exper-iments in a new domain. However, experiments have so farnot been able to prepare and investigate well-defined parti-cle ensembles and to non-destructively analyse the reactionproducts with high accuracy, nor were they able to select orprepare products for further studies in a well-defined way.The particles (atomic or molecular ions) are confinedin the Penning trap following in-trap production or cap-ture of externally produced ions. Confined ions can becooled, compressed, positioned and selected with respectto their mass and charge prior to laser irradiation. The reac-tion products are analysed by non-destructive methods andhence remain confined for further studies. Such measure-ments are, for example, able to determine cross sections formultiphoton-ionisation in an energy- and intensity- regimeso far not or not sufficiently examined. Additionally, thecreated electrons may be extracted from the trap and anal-ysed externally. Hence, the reaction energetics may be re-constructed as completely as possible.Figure 1 shows an example of a multiphoton ionizationstudy using these techniques: ions are dynamically loadedinto the trap from external sources or produced in the trapby electron impact or laser ionization (A). One or more spe-cific ion species are selected (B), these ions are then cooled,compressed by a rotating wall and positioned. Thus, theion target is well-prepared for interaction with the high-intensity laser. During and following the laser interaction,the charge state evolution of the confined ions is monitoredion loading / productionion selection / SWIFTion coolingion cloud compressionrotating wallion positioninglaser interaction(s)...FTICR:charge stateevolutionIONTARGETPREPARATIONtime [s]products remainstored / furtherselection orpreparation orexamination...PRODUCTIONS105mass spectrometryspectroscopyreactions...PROCEDURE                          INSIDE TRAP...dP/dfX1+X2+X3+X4+m/qdP/df X3+m/q...dP/dfX7+m/qdP/dfX3+m/qX5+X4+dP/dfX3+m/qX4+X5+X6+X7+ABCDEFigure 1: Example of an experimental timing scheme for astudy of multiphoton ionization. The individual durationsare meant to reflect the typical order of magnitude. Theright hand side shows the corresponding mass-to-chargespectra of the trap content, for details see text.by FT-ICR-spectrometry (C and D). Specific product ionscan be selected and remain stored for further use (E).Ion positioning along the experimental axis has some in-teresting features when a focused laser is considered sinceit allows to determine the position of the focus with highresolution. At the same time, especially for strongly fo-cused lasers, ion positions can be chosen such that the reac-tion takes place at different field intensities and thus allowsa study of the reaction as a function of laser field intensitywithout the need to change laser parameters.References[1] M. Vogel, W. Quint, Th. Sto¨hlker and G.G. Paulus, Nucl.Inst. Meth. B 285, 65 (2012).GSI SCIENTIFIC REPORT 2012 PNI-IONS-EXP-09317

Controlled interaction of ions with high-intensity laser light

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Controlled interaction of ions with high-intensity laser light

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