Collisional interactions in isotope and spin mixtures of laser-cooled metastable neon atoms

Laser-cooled metastable neon atoms (Ne*) present a fascinating atomic system: The extremely low kinetic energy of the cold atoms stands in strong contrast to the large internal energy of the metastable state 3P2 and leads to unique collisional interaction properties that are dominated by ionizing collisions. In this work, experimental investigations of the collisional interactions of Ne* are presented. In particular, collisional interactions in isotope mixtures and in mixtures of different Zeeman sublevels (vertical stroke mJ right angle) are studied. With a lifetime of 14.7s, the metastable state 3P2 serves as an effective ground state for the laser manipulation. The Ne* atoms are cooled down to a temperature of several 100μK using laser cooling techniques and stored in a magneto optical or magnetic trap. The cold, trapped atoms can then be used for experiments. In order to cool and trap isotope mixtures, the isotope shift of the atomic transition 3P2 <-> 3D3 that is used for laser manipulation has to be known with high precision. In this work, the shift of the transition between the isotopes 20Ne, 21Ne, and 22Ne has been measured and, using the advantages of laser-cooled atoms, the accuracy of the measurement was improved by one order of magnitude compared to previous measurements. For 21Ne also the hyperfine interaction constants of the state 3D3 for magnetic dipole and electric quadrupole interaction have been measured. The collisional interactions of spin-polarized Ne* in all two-isotope mixtures of 20Ne, 21Ne, and 22Ne have been investigated. The investigations are focused on the question whether the heteronuclear collisional interactions are favorable for sympathetic cooling. Rate coefficients for heteronuclear ionizing collisions and upper bounds for heteronuclear thermal relaxation cross sections have been measured. In all cases, the measured ratio of elastic to inelastic collisions is not favorable for heteronuclear sympathetic cooling. For the two bosonic isotopes, 20Ne and 22Ne, experimental methods for the preparation of all 3P2 Zeeman sublevels vertical stroke mJ = +2 right angle, vertical stroke +1 right angle, vertical stroke 0 right angle, vertical stroke -1 right angle, vertical stroke -2 right angle as well as controlled spin mixtures in the five-level system vertical stroke +2 right angle,.., vertical stroke -2 right angle, in the three-level system vertical stroke +2 right angle, vertical stroke +1 right angle, vertical stroke 0 right angle, and in the two-level system vertical stroke +2 right angle, vertical stroke +1 right angle have been developed. The methods are based on different radio frequency and laser pulse sequences. The state evolution is explained quantum-mechanically and with a semi-classical model. The coherence properties of the prepared states have been studied using Ramsey and spin echo measurements. The ion rates of the spin mixtures show a pronounced mJ-state dependence. The lowest ion rates have been measured when the atoms were prepared in spin-stretched states, i.e. either all atoms in vertical stroke mJ = +2 right angle or all atoms in vertical stroke mJ = -2 right angle. For all other states larger rates of ionizing collisions have been measured. The difference between the rates is much larger for 20Ne than for 22Ne.