[en] This diploma thesis studies experimentally the long-time dynamics of laser-cooled ⁹Be⁺-beams at the TSR under different cooling conditions. The goal is to enlarge the understanding of ultra-cold, non-neutral plasma at high center-of-mass energies. By means of improved measurement capabilities one can now for the first time monitor the entire phase-space over a long time. This makes it possible to quantitatively analyse the possibilities and limitations of laser cooling at a storage ring. Under optimum cooling conditions a regime of high phase-space density is reached, close to the region where influences of Coulomb coupling are expected. Furthermore, a Monte-Carlo model is worked out that qualitatively describes the beam dynamics. The model includes the influence of transverse-longitudinal coupling due to intra beam scattering on the longitudinal phase-space distribution. At high phase-space density a sudden disappearance of intra beam collisions is observed experimentally and possible interpretations are given. (orig.)

[en] We demonstrate experimentally the guiding of cold and slow ND₃ molecules along a thin charged wire over a distance of ∼0.34 m through an entire molecular beam apparatus. Trajectory simulations confirm that both linear and quadratic high-field-seeking Stark states can be efficiently guided from the beam source up to the detector. A density enhancement up to a factor 7 is reached for beams with velocities ranging down to ∼150 m/s generated by the rotating nozzle technique.

[en] Intense beams of cold and slow molecules are produced by supersonic expansion out of a rapidly rotating nozzle, as first demonstrated by M. Gupta and D. Herschbach [J. Phys. Chem. A 103, 10670 (1999); 105, 1626 (2001)]. An improved setup is presented that is able to accelerate or decelerate cold atomic and molecular beams by up to 500 m/s. Technical improvements are discussed and beam parameters are characterized by detailed analysis of time-of-flight density distributions. The possibility of combining this beam source with electrostatic fields for guiding polar molecules is demonstrated.

[en] A new setup for doping helium nanodroplets by means of laser ablation at kilohertz repetition rate is presented. The doping process is characterized and two distinct regimes of laser ablation are identified. The setup is shown to be efficient and stable enough to be used for spectroscopy, as demonstrated on beam depletion spectra of lithium atoms attached to helium nanodroplets. For the first time, helium droplets are doped with high temperature refractory materials such as titanium and tantalum. Doping with the nonvolatile DNA basis guanine is found to be efficient and a number of oligomers are detected

No abstract available

[en] We simultaneously trap ultracold lithium and cesium atoms in an optical dipole trap formed by the focus of a CO₂ laser and study the exchange of thermal energy between the gases. The optically cooled cesium gas efficiently decreases the temperature of the lithium gas through sympathetic cooling. Equilibrium temperatures down to 25 μK have been reached. The measured cross section for thermalizing ¹³³Cs- ⁷Li collisions is 8x10^-12 cm² , for both species unpolarized in their lowest hyperfine ground state. Besides thermalization, we observe evaporation of lithium purely through elastic cesium-lithium collisions (sympathetic evaporation)

[en] We present a simple diode laser-based photoionization scheme for generating electrons and ions with well-defined spatial and energetic (≲2 eV) structures. This scheme can easily be implemented in ion or electron imaging spectrometers for the purpose of off-line characterization and calibration. The low laser power ∼1 mW needed from a passively stabilized diode laser and the low flux of potassium atoms in an effusive beam make our scheme a versatile source of ions and electrons for applications in research and education.

[en] The real-time dynamics of photoexcited and photoionized rubidium (Rb) atoms attached to helium (He) nanodroplets is studied by femtosecond pump-probe mass spectrometry. While excited Rb atoms in the perturbed 6p-state (Rb"*) desorb off the He droplets, Rb"+ photoions tend to sink into the droplet interior when created near the droplet surface. The transition from Rb"+ solvation to full Rb"* desorption is found to occur at a delay time τ ∼ 600 fs for Rb"* in the 6pΣ-state and τ ∼ 1200 fs for the 6pΠ-state. Rb"+He ions are found to be created by directly exciting bound Rb"*He exciplex states as well as by populating bound Rb"+He-states in a photoassociative ionization process

[en] Cold inelastic collisions between confined cesium (Cs) atoms and Cs₂ molecules are investigated inside a CO₂ laser dipole trap. Inelastic atom-molecule collisions can be observed and measured with a rate coefficient of ∼2.6x10^-11 cm³ s^-1, mainly independent of the molecular rovibrational state populated. Lifetimes of purely atomic and molecular samples are essentially limited by rest gas collisions. The pure molecular trap lifetime ranges 0.3-1 s, 4 times smaller than the atomic one, as is also observed in a pure magnetic trap. We give an estimation of the inelastic molecule-molecule collision rate to be ∼10^-11 cm³ s^-1

[en] We present a novel way to measure the friction force of an electron cooler in a heavy ion storage ring, which uses the counterforce provided by specially designed bunch potentials. Applying this method the friction force at small relative velocities between the electron and the ion beam has been determined with a 7.3 MeV beam of ⁹Be⁺ ions at the Heidelberg Test Storage Ring. The results are compared to a measurement performed with an alternative counterforce method using an induction accelerator