Martin, Alexander (2017)
Laser Spectroscopic Investigation of Exotic States in Noble Gases.
Technische Universität Darmstadt
Dissertation, Erstveröffentlichung

Kurzbeschreibung (Abstract)

The focus of this thesis lies on exotic states of noble gases, in particular metastable neon (Ne*) and boron-like argon ions (Ar13+): the former shows extraordinary collisional properties due to its high internal energy compared to its low kinetic energy. On the other hand, highly charged ions, such as Ar13+, can be used to verify quantum electrodynamics with extremely high accuracy by determining their magnetic moments. These extraordinary atomic states can be probed with methods of laser spectroscopy and allow for deep insights of timely physical question.

The magnetic moment of bound electrons in Ar13+ shall be determined by the energy-splitting of the Zeeman sublevels of the fine structure transition 2P1/2 - 2P3/2 at a wavelength of 441 nm in the magnetic field of a Penning trap. For this, the transition is measured by means of microwave and fluorescence laser spectroscopy. The first part of this thesis presents the laser system for the spectroscopy of Ar13+ and tellurium 130Te2. Using a polarization stabilization scheme, a single-mode diode laser with a high long-term stability of up to two days has been developed. Using a Doppler-free 130Te2-spectroscopy, six lines close to the expected Ar13+ transitions have been characterized with an absolute frequency accuracy of 2.2 MHz. A first characterization of the Ar13+ fluorescence spectroscopy has been conducted with a dark-measurement without ions. During this process, the measured background signal was reduced by three orders of magnitude by optimizing the setup. Thus, a reliable laser system is provided for experiments with ions, as planned for the near future.

The second part of this thesis investigates the two-body collisional interactions of ultra-cold Ne* atoms. Inelastic collisions of Ne* atoms leads to losses due to Penning and associative ionization. The efficient detection of the ions produced by these processes allows for determining the collision rate. For the investigations, a laser-cooled atom cloud is prepared in a magnetic trap at 350 µK. The measurement of the inelastic collision rate in a regime between 20 µK and 350 µK confirms the theoretical predicted temperature-independent rate for 20Ne and 22Ne of mixtures of the Zeeman sublevels mJ = +2 and mJ = +1. Furthermore, the dependence of the collision rate on external magnetic fields has been measured. For fields up to 120 G, a suppression by a factor of 5.6 for 22Ne has been proved. Additionally, the so called δ-kick cooling, a method for manipulating the phase-space density of cold atom clouds, was implemented by using the magnetic trap. This allowed for a variation of the velocity distribution of the cloud over a range, which corresponds to an effective temperature between 10 µK and 460 µK.

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