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Digitale Dissertation

Soeren Rutz :
Femtosecond Spectroscopy on the Wave Packet Dynamics in Alkali Dimers and Trimers
Femtosekundenspektroskopie zur Wellenpaketdynamik in Alkalidimeren und -trimeren

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Abstract

The wave packet dynamics in excited electronic states of diatomic and triatomic alkali molecules is investigated by means of femtosecond pump&probe techniques.

For this purpose a wave packet is prepared on a certain potential energy surface of the molecule of interest by coherently exciting several vibrational eigenstates with an ultrashort laser pulse (pump pulse). The wave packet's propagation on the potential energy surface is probed by ionizing the excited molecules with a second laser pulse (probe pulse) interacting with the molecules after a certain delay time with respect to the pump pulse. The ion signal recorded as a function of this delay time mirrors the ultrafast vibrational dynamics of the molecules in the excited state.

In the diatomic molecules K2 and Na2 the spin-orbit coupled system A 1Σu+ - b 3Πu is investigated. Energy shifts of vibrational states of the A1Σu+ state induced by spin-orbit coupling are determined by analyzing the long-time behavior of the real-time spectra and by calculating Fourier spectra and spectrograms (sliding window Fourier transforms) of the real-time data. If energy shifts are present the structure of revivals and fractional revivals in the wave packet dynamics is strongly effected compared with an unperturbed anharmonic potential. In the Na2 A state an energy shift of 0.85 cm-1 for the vibrational state |v'=8> is observed. In 39,39K2 energy shifts of up to 2.4 cm-1 are present resulting in a pronounced revival structure with a 20 ps period. Furthermore, isotopic effects in the revival structures are studied for 39,41K2 and 41,41K2. Here, the wave packet dynamics is totally different and can be regarded as a fingerprint of the excited molecules.

In the Na3 B state (32E') the symmetric stretch mode is selectively excited with femtosecond laser pulses. In former measurements the pseudorotation, the combination of the symmetric bending and the antisymmetric stretch mode, was measured time-resolved in the picosecond regime. In conclusion this demonstrates the ability of selectively exciting normal modes by judiciously chosing the duration of the laser pulses.

In K3 an excited state is detected for the first time by femtosecond spectroscopy. This excited state state can be characterized by its fragmentation times due to predissociation. The wave packet dynamics on its potential energy surface and on the potential energy surface of the K3 ground state is analyzed by comparing the related systems Na3 and K3.

Table of Contents

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Titel
Inhaltsverzeichnis 		1
1. Einleitung 3
2. Grundlagen zur Spektroskopie an Alkalidimeren und -trimeren 5
2.1Stationäre (energieaufgelöste) Spektroskopie
 5
2.1.1Spektroskopie an Alkalidimeren
 5
2.1.2Spektroskopie an Alkalitrimeren
 9
2.2Ultrakurzzeit-Spektroskopie an Alkaliaggregaten
 12
2.2.1Dynamik in Dimeren und Trimeren
 15
2.2.2Wellenpaketdynamik und Simulationen
 21
3. Experimenteller Teil 23
3.1Optischer Aufbau und Erweiterung der Lasersysteme
 25
3.1.1Der Titan:Saphir-Laser
 27
3.1.2Der regenerative Verstärker
 30
3.1.3Der synchron gepumpte optisch parametrische Oszillator
 33
3.2Überblick über die Experimentierkammer
 36
3.3Meßwerterfassung und Aufbereitung der Daten
 40
3.3.1Steuerung des Experiments und Datenaufnahme
 40
3.3.2Auswertung der Echtzeitmessungen
 41
4. Pump&Probe Spektroskopie an K2 und Na2 45
4.1Anregungsschema zu Einfarben-Pump&Probe Experimenten
 45
4.2Vibrationsdynamik in den Echtzeitspektren
 48
4.3Echtzeitspektroskopie an Na2
 50
4.3.1Zeitdomäne
 51
4.3.2Frequenzdomäne
 57
4.4Echtzeitspektroskopie an K2
 64
4.4.1Zeitdomäne
 65
4.4.2Frequenzdomäne
 71
4.5Simulationen von Wellenpaketen im K2 A Zustand
 86
4.5.1Simulation der Echtzeitspektren
 86
4.5.2Mechanismus der Störung durch den b 3Πu Zustand
 89
4.6Zweifarben-Pump&Probe Experimente am K2 A 1Σu+ Zustand
 93
4.7Pulsleistungsabhängigkeit der Echtzeitspektren an K2
 99
4.8Kurze Zusammenfassung der wichtigsten Ergebnisse an Na2 und K2
 106
5. Pump&Probe Spektroskopie an K3 und Na3 109
5.1Femtosekundenspektroskopie an Na3
 109
5.1.1Femtosekundendynamik im Na3 B Zustand
 110
5.1.2Pulsdauer und Modenselektivität
 113
5.2Femtosekundenspektroskopie an K3
 118
5.2.1Prädissoziierte Zustände in K3
 119
5.2.3Wellenpaketdynamik
 123
6. Zusammenfassung und Ausblick 131
Literatur 133
Anhang: 147
Geräteliste 147
Publikationen mit Teilen dieser Arbeit 149
Publikationsliste 151
Konferenzbeiträge 155
Lebenslauf 159
Danksagung 161

More Information:

Online available: http://www.diss.fu-berlin.de/2000/127/indexe.html
Language of PhDThesis: german
Keywords: femtosecond spectroscopy, wave packet dynamics
DNB-Sachgruppe: 29 Physik, Astronomie
Classification PACS: 33.20.Tp, 42.50.Hz, 82.20.Tr, 36.40.-c
Date of disputation: 18-Nov-1996
PhDThesis from: Fachbereich Physik, Freie Universität Berlin
First Referee: Prof. Dr. Ludger Wöste
Second Referee: Prof. Dr. Nikolaus Schwentner
Third Referee: Prof. Dr. Gustav Gerber
Contact (Author): soeren.rutz@gmx.de
Contact (Advisor): ludger.woeste@physik.fu-berlin.de
Date created:06-Nov-2000
Date available:07-Nov-2000

 

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