Production and spectroscopy of ultracold YbRb_1hn* molecules [Elektronische Ressource] / vorgelegt von Nils Nemitz

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• Publié par: heinrich-heine-universitat_dusseldorf
• Publié le: 01 janvier 2008
• Nombre de lectures: 10
• Langue: English
• Poids de l'ouvrage: 7 Mo

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Production and spectroscopy of
ultracold YbRb* molecules
Inaugural-Dissertation
zur
Erlangung des Doktorgrades der
Mathematisch-Naturwissenschaftlichen Fakult¨ at
der Heinrich-Heine-Universit¨ at Dusseldorf¨
vorgelegt von
Nils Nemitz
aus Wolfsburg
November 2008Aus dem Institut fur¨ Experimentalphysik
der Heinrich-Heine-Universit¨ at Dusseldorf¨
Gedruckt mit der Genehmigung der
Mathematisch-Naturwissenschaftlichen Fakult¨ at der
Heinrich-Heine-Universit¨ at Dusseldorf¨
Referent: Prof. Dr. Axel G¨ orlitz
Koreferent: Dr. Bernhard Roth
Tag der mundlic¨ hen Prufung:¨ 18.12.2008Contents
Table of Contents 3
1 Introduction 7
1.1 History ...................................... 7
1.2 Ultracold Molecules . . . ............................ 8
1.3 This Thesis .................................... 9
2 Atomic Species 11
2.1 Rubidium ..................................... 11
2.2 Ytterbium 12
2.3 Energy Levels and Wavenumbers ........................ 13
3 Review of Molecular Physics 17
3.1 Wavefunctions .................................. 17
3.1.1 Electronically Mediated Potentials ................... 20
3.1.2 Molecular Electronic States ....................... 21
3.1.3 Hund’s Cases ............................... 21
3.1.4 Nuclear Spin 24
3.1.5 Transitions between Cases and Effects on Spectra........... 24
3.1.6 Avoided Crossings and Diabatic Potential Curves 26
3.2 Vibration ..................................... 27
3.3 Rotation . . . ................................... 29
3.3.1 Rotational Constant ........................... 29
3.3.2 Rotation in Photoassociation Spectroscopy .............. 29
3.4 Photoassociation ................................. 30
3.4.1 Switching Potentials 30
3.4.2 Condon Points .............................. 31
3.4.3 Centrifugal Barriers 33
3.4.4 Shape Resonances ............................ 35
4 Experimental Setup 37
4.1 Overview ..................................... 37
4.2 Magneto-Optical Traps 37
4.2.1 Ytterbium MOT ............................. 39
4.2.2 Rubidium MOT 424 Contents
4.2.3 Forced Dark-spot MOT ......................... 43
4.3 Imaging and Trap Superposition ........................ 46
4.4 Photoassociation Laser System . 47
4.4.1 Laser ................................... 47
4.4.2 Optical Setup............................... 47
4.4.3 Short-Term Stabilization 51
4.4.4 Overlaying the Beam on the Double Trap ............... 52
4.5 Wavemeter .................................... 53
4.6 Datalogger 5
5 Trap Characterization 57
5.1 Atom Counting .................................. 57
5.1.1 Scattering Rates ............................. 57
5.1.2 Calibration ................................ 59
5.1.3 Results 61
5.2 Size and Temperature Measurements ...................... 63
5.3 Trap Interactions ................................. 67
5.3.1 Automated Measurement ........................ 68
5.4 Interpretation of Loading and Loss Rates ................... 73
5.4.1 Simple Rate Equation Model 73
5.4.2 Loss Rate from Interspecies Collisions ................. 75
5.4.3 Photoassociation Rates ......................... 77
6 Photoassociation Spectroscopy in a Cold Atomic Mixture 81
6.1 Definition of Relative Wavenumber ....................... 81
6.2 Measurement of Spectra and Wavelength Assignment . ............ 82
6.2.1 Accuracy Estimate ............................ 84
6.3 Spectra... ..................................... 88
1766.3.1 ...in Yb................................. 89
1746.3.2 ...in Yb 89
6.4 Line Assignment 92
6.4.1 Hyperfine Splitting 92
6.4.2 Rotational Structure . . . ........................ 93
6.4.3 Splitting of Rotational Lines ...................... 9
6.4.4 Vibrational Levels ............................104
6.4.5 Improved Leroy-Bernstein Equation ..................106
6.4.6 Overview of Assignment Results ....................108
6.4.7 Electronic State . . ...........................109
6.5 Saturation of the Photoassociation Rate113
6.5.1 Theoretical Predictions .........................13
6.5.2 Size Effects of the Photoassociation Beam . . . ............15
6.5.3 Application to Experimental Data . ..................18
6.5.4 Consequences for Future Experiments .................120
6.6 Line Strengths ..................................121CONTENTS 5
6.6.1 Franck-Condon Principle . .......................121
6.6.2 Application to Photoassociation ....................123
6.6.3 Reconstructing “last lobe” Positions ..................124
6.6.4 Nodes of the Ground State Wavefunction ...............125
6.6.5 Wavefunction Overlap and Observed Line Strengths .........129
7 Future experiments 133
7.1 Formation of Ground States Molecules .....................133
7.2 Autler-Townes spectroscopy ...........................135
7.3 Stimulated Raman Adiabatic Passage137
7.4 Application to the Experiment .........................137
7.5 Spectroscopy with Ion Detection ........................143
7.5.1 Detector Design .............................144
7.6 Trapping Molecules................................145
7.6.1 Optical Trapping145
7.6.2 Magnetic T ............................146
7.6.3 Balancing Gravity . . ..........................146
8 Summary 149
8.1 English Version ..................................149
8.2 Deutsche Version .................................151
A Control System 155
A.1 System Overview155
A.2 Control Program156
A.3 Steady State Operation .............................157
A.4 Pattern Output Mode ..............................160
A.5 Writing Patterns .................................160
A.5.1 Analog Field Instructions ........................161
A.5.2 Function Field Commands163
A.5.3 Directives163
A.5.4 Loading and Saving Patterns ......................164
A.6 How it Works . . . ................................164
A.6.1 Steady State / Editing..........................164
A.6.2 Pattern Output..............................165
Bibliography 169
Acknowledgements 1736 ContentsChapter 1
Introduction
This chapter gives a motivation for the work presented here by outlining the history of
atomic and molecular spectroscopy and placing the experiments described in the context of
current developments. For a brief summary of the work presented, please see chapter 8,
which also provides a German version.
1.1 History
Spectroscopy is one of the oldest fields in modern science. Over the years it has provided
insight into the structure of atoms and molecules and has laid the foundations of quantum
mechanics.
As early as 1802, W. H. Wollaston found dark lines in the solar spectrum observed
through a prism. These were later rediscovered and investigated by J. Fraunhofer. In
1862 G. R. Kirchoff was awarded the Rumford medal for his work in describing the solar
spectrum and explaining why the dark absorption lines found there show the same structure
as the emission lines from hot gases.
˚In 1872 the same award was presented to A. J. Angstr¨ om, whose measurements of
the hydrogen spectrum prompted J. J. Balmer’s discovery of the underlying mathematical
progression in 1885. This was developed into a more general formalism by J. Rydberg in
1888. Rydberg was also the first to discover the mathematical advantages of working with
wavenumbers. This work led directly to N. Bohr’s theory of the atomic structure with
electrons at fixed energy levels and emission and absorption based on transitions between
them, that was presented in 1913. Bohr was awarded the 1922 Nobel Prize in physics for
his work.
This is not the only Nobel Prize awarded in this field: It was given to H. A. Lorentz
and P. Zeeman in 1902 for the discovery of what is now known as the Zeeman effect, to A.
A. Michelson in 1907 for the invention of the interferometer and its applications, and in
1911 to W. Wien for his work on thermal radiation. Between M. Planck (in 1918) and A.
Einstein (in 1921) for their respective insights into the quantized nature of radiation, the
prestigious prize went to J. Stark in 1919, for his discovery of the splitting of spectroscopic
lines in an electric field - now known as the Stark effect. The year 1930 saw the Nobel
Prize for C. V. Raman and his work on light scattering and in 1955 it was awarded to W.8 1 Introduction
E. Lamb for his investigations into the fine structure of the hydrogen spectrum.
By this time the physical principles behind atomic and molecular energy levels and the
resulting spectra were well established. G. Herzberg’s book on the “Spectra of Diatomic
Molecules” was first published in 1939 and its later editions remain definitive in many
respects even today. He, too, was awarded the Nobel Prize in 1971 for his work on the
properties of molecules.
Later surges in activity were caused by new techniques and technologies: Based on
the previous work on masers (Nobel Prize for Townes, Basov, and Prokhorov in 1964),
the first laser was built in 1960 by T. H. Maiman. In 1969 the appearance of the dye
laser with its tunable wavelength turned this into a mighty spectroscopic tool. The first
continuous-wave laser diode was built in Z. Alferov’s group in 1970 (Nobel Prize in 2000).
Modern laser diodes have turned lasers into a manageable, compact technology for a wide
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