Dokument: Frequency metrology tools for high-precision spectroscopy of molecular hydrogen ions
| Titel: | Frequency metrology tools for high-precision spectroscopy of molecular hydrogen ions | |||||||
| URL für Lesezeichen: | https://docserv.uni-duesseldorf.de/servlets/DocumentServlet?id=59794 | |||||||
| URN (NBN): | urn:nbn:de:hbz:061-20220609-110846-3 | |||||||
| Kollektion: | Dissertationen | |||||||
| Sprache: | Englisch | |||||||
| Dokumententyp: | Wissenschaftliche Abschlussarbeiten » Dissertation | |||||||
| Medientyp: | Text | |||||||
| Autor: | Hansen, Michael [Autor] | |||||||
| Dateien: |
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| Beitragende: | Prof. Dr. Schiller, Stephan [Gutachter] Prof. Dr. Görlitz, Axel [Gutachter] | |||||||
| Dewey Dezimal-Klassifikation: | 500 Naturwissenschaften und Mathematik » 530 Physik | |||||||
| Beschreibung: | The goal of this thesis is to use frequency metrology of molecular hydrogen ions to verify ab-initio calculations of molecular transition frequencies, determine fundamental constants, and to look for physics beyond the Standard Model, in particular fifth forces and extra dimensions.
To this end, a variety of high-performance laser systems and other tools for frequency metrology are required. In this thesis, some of these systems were newly developed, existing ones improved and also basic research for next-generation systems was performed. Molecular hydrogen ions, in particular the molecule HD+, were chosen as spectrosopic workhorse. They are the simplest molecules, because they have only three components. On the theoretical side, their transition frequencies can be determined very accurately. By comparison between theory and experiment, a physical constant used for the calculation of the transition frequency can be treated as a free parameter and be determined from experimentally obtained transition frequencies. Anyremaining frequency discrepancy between theory and experiment can be treated as an upper limit of the strength of hypothetical new physical effects, which are not included in the Standard Model. Spectroscopy on the HD+ ion was performed while the molecule was trapped in an ion trap and cooled to ultra-cold temperatures. This provides the advantage of long interaction times with the spectroscopy lasers as well as reduced Doppler broadening, due to lower temperatures. Rotational spectroscopy was performed using a microwave source based on frequency multipliers. Using a new Doppler-free spectroscopy technique, a transition linewidth of 1.3 kHz was obtained. From these results, the proton mass was determined. The result was consistent with the officially recommended value, but provides an independent verification, since it was determined using another method. Ro-vibrational spectroscopy was performed using a difference frequency generation system, whose frequency was measured using an optical frequency comb. The lowest observed transition linewidth of 3 MHz was still Doppler-limited, but allowed a comparison between theory and experiment at the 10^−9 level and was the first to probe QED effects at the order alpha to the power of 5. The results of these measurements were used by other researchers to set new limits on possible fifth forces. In order to further increase the measurement resolution, two new laser systems were set up. One was a quantum-cascade laser system in the mid-IR, referenced to a near-IR frequency comb in order to be able to precisely control its absolute frequency. The system reached a record linewidth. An improved version of the laser system based on difference frequency generation was also set up. Using this laser system and the new spectroscopy method demonstrated for the rotational transition, sub-Doppler transition linewidths of 0.2 kHz (3*10^−12 fractionally) were obtained. From these, an agreement between theory and experiment at the 2.9*10^−11 level was reached. Also, the proton-to-electron-mass-ratio and the ratio of the reduced nuclear mass to the electron mass were determined in an alternative way to the measurements used for previous determinations of their officially recommended values. The obtained results were consistent. Frequency metrology using lasers is always fundamentally limited by the short- and long-term performance of the reference lasers used for the spectroscopy and the optical frequency comb. To this end, research on new reference systems was performed: The long-term stability of a new material for spacers for optical resonators (NEXCERA) was studied. As an alternative to the optical resonator approach, properties of spectral holes in Europium-doped crystals at cryogenic temperatures were investigated. The obtained results demonstrate that spectroscopy of trapped molecular hydrogen ions, combined with the right tools, are now on-par with other methods for the determination of physical constants, as well as for tests of the validity of the Standard Model. Results improved by several orders of magnitude are likely to be obtained in the near future. | |||||||
| Lizenz: |  Urheberrechtsschutz | |||||||
| Fachbereich / Einrichtung: | Mathematisch- Naturwissenschaftliche Fakultät » WE Physik » Experimentalphysik | |||||||
| Dokument erstellt am: | 09.06.2022 | |||||||
| Dateien geändert am: | 09.06.2022 | |||||||
| Promotionsantrag am: | 12.08.2021 | |||||||
| Datum der Promotion: | 31.05.2022 |
