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Versatile high-repetition-rate phase-locked chopper system for fast timing experiments in the vacuum ultraviolet and x-ray spectral region
Stockholm University, Faculty of Science, Department of Physics.
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2012 (English)In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 83, no 1, 013115- p.Article in journal (Refereed) Published
Abstract [en]

A novel light chopper system for fast timing experiments in the vacuum-ultraviolet (VUV) and x-ray spectral region has been developed. It can be phase-locked and synchronized with a synchrotron radiation storage ring, accommodating repetition rates in the range of similar to 8 to similar to 120 kHz by choosing different sets of apertures and subharmonics of the ring frequency (MHz range). Also the opening time of the system can be varied from some nanoseconds to several microseconds to meet the needs of a broad range of applications. Adjusting these parameters, the device can be used either for the generation of single light pulses or pulse packages from a microwave driven, continuous He gas discharge lamp or from storage rings which are otherwise often considered as quasi-continuous light sources. This chopper can be utilized for many different kinds of experiments enabling, for example, unambiguous time-of-flight (TOF) multi-electron coincidence studies of atoms and molecules excited by a single light pulse as well as time-resolved visible laser pump x-ray probe electron spectroscopy of condensed matter in the valence and core level region.

Place, publisher, year, edition, pages
2012. Vol. 83, no 1, 013115- p.
National Category
Physical Sciences
Research subject
Physics
Identifiers
URN: urn:nbn:se:su:diva-76763DOI: 10.1063/1.3677329ISI: 000300594900016OAI: oai:DiVA.org:su-76763DiVA: diva2:527125
Note

8

Available from: 2012-05-16 Created: 2012-05-16 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Single-photon multiple ionization processes studied by electron coincidence spectroscopy
Open this publication in new window or tab >>Single-photon multiple ionization processes studied by electron coincidence spectroscopy
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is based on studies of multiple ionization of atoms and molecules induced by the absorption of a single photon. For the experimental investigations a time-of-flight magnetic bottle spectrometer has been used to detect the emitted electrons in coincidence. The method of coincidence time-of-flight spectroscopy and the experimental setup used is described. Experimental and theoretical results on molecular double core holes (DCHs) and multiple ionization of atoms are presented.

Molecular DCHs are of considerable interest, as their chemical shifts are predicted to be more sensitive than their single core hole counterparts. Using CH4 and NH3 as examples, it is shown that molecules with two vacancies in the innermost shell can be studied using synchrotron light in combination with our coincidence technique. The chemical shifts of S 2p DCHs are investigated for the molecules CS2, H2S and SO2 and the influence of relaxation effects on the shifts are estimated. In the studies of atoms, the main focus is on the processes leading to double and higher degrees of ionization, and the final state populations. In cadmium double photoionization in the photon energy region 40-200 eV occurs mainly by indirect ionization via valence ionized satellite states and through Coster-Kronig decay of inner shell hole states. In valence-valence ionization of krypton by 88 eV photons both direct and indirect ionization processes are found to be important. For the indirect pathways strong final state selectivity in the autoionization decays of the intermediate states is observed. Triple ionization of krypton via intermediate core-valence doubly ionized states is investigated. The intermediate states are observed in the energy region 120-125 eV, and their decay to states of the triply charged ion is mapped. Experimental and theoretical results on the formation of 2p double hole states in argon are presented.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2013. 61 p.
Keyword
photoionization, multiple ionization, autoionization, synchrotron radiation, electron coincidence spectroscopy
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-89601 (URN)978-91-7447-710-8 (ISBN)
Public defence
2013-06-07, Lecture Hall FB42, AlbaNova University Center, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.

Available from: 2013-05-16 Created: 2013-05-01 Last updated: 2013-05-13Bibliographically approved

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