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FU Berlin
Digitale Dissertation

Kay Hoffmann :
Femtosecond Laser Spectroscopy of Fullerenes
Femtosekunden-Laserspektroskopie an Fullerenen

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Abstract

The subject of this thesis is the study of the ionization and fragmentation behavior of C60 in short laser pulses. The interaction is analyzed here for first time monitoring the resultant photoions and photoelectrons with systematic variation of wavelength, intensity and pulse duration. Furthermore, it was possible to vary the pulse polarization and pulse spacing in a pump probe configuration.
Based on the performed experiments, three different ionization mechanisms depending on the pulse duration were identified.
For pulse durations in the sub-50 fs domain, the ionization mechanism is direct multiphoton ionization shown by clear observation of an ATI structure in the photoelectron spectra.
As the pulse duration is increased beyond 50 fs, the dominant mechanism is statistical ionization due to energy equilibration among the electronic degrees of freedom. Statistical electron emission causes the loss of the ATI structure in the electron spectra. This is the case for pulse durations up to 500 fs.
For pulse durations on the order of one ps, there is time for statistical energy redistribution also among vibrational degrees of freedom. Detailed measurements in this time domain show that the coupling from electronic to vibrational degrees of freedom occurs around 700 fs. This third process is characterized by an onset of delayed ionization on the µs time scale in the ion spectra.

Table of Contents

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Titel und Inhalt
1 Einleitung 1
2 Grundlagen 5
2.1 Kohlenstoffcluster 5
2.2 Direkte und statistische Ionisationsmechanismen 11
2.3 Fragmentationsmechanismen 31
3 Das Experiment 39
3.1 Molekularstrahlerzeugung 40
3.2 Die Laserquellen 41
3.3 Charakterisierung des Reßektron-TOF 44
3.4 Das Elektronenspektromete 46
3.5 Meßverfahren und Meßelektronik 48
3.6 Intensitätsbestimmung 54
4 Meßergebnisse 59
4.1 C60 im sub-50-fs-Laserfeld 59
4.2 Die Laserpulslängenabhängigkeit 89
4.3 Resonanzstrukturen in den Elektronenspektren 102
4.4 Verzögerte Fragmentation 114
4.5 Pump-Probe-Messungen 126
5 Zusammenfassung und Ausblick 131
A Anhang 135
Literaturverzeichnis  147

More Information:

Online available: http://www.diss.fu-berlin.de/2001/180/indexe.html
Language of PhDThesis: german
Keywords: fullerene, intensive laserfields, femtosecond laser spectroscopy, photoelectron spectroscopy, rydberg states
DNB-Sachgruppe: 29 Physik, Astronomie
Date of disputation: 19-Dec-2000
PhDThesis from: Fachbereich Physik, Freie Universität Berlin
First Referee: Prof. Dr. Ingolf Hertel
Second Referee: Prof. Dr. Ludger Wöste
Contact (Author): kay@physics.utexas.edu
Contact (Advisor): f3aec@fy.chalmers.se
Date created:09-Sep-2001
Date available:26-Oct-2001

 

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