In this thesis I present the results of photoassociation measurements in ensembles of
atomic calcium over an intensity range of below 1 W/cm2 up to 600 W/cm2. The temperature
of the atoms was reduced to 1 μK by laser and evaporative cooling. Afterwards
the two most-weakly bound states in the excited molecular potentials that dissociate
to the asymtote 3P1+1S0 have been investigated regarding the shape and absolute rate
of the resonances. The investigation showed that the measured rates differ by more
than an order of magnitude compared to theoretical calculations. The predictions are
based on a scattering formalism by Bohn & Julienne and wave functions derived from
coupled-channel calculations. The shape of the resonances, the width in particular,
agrees well with the numerical calculations. Especially the power broadening at high
intensity is reproduced by the experiment. Further the light shift introduced by the
photoassociation laser has been measured which also differs from the predictions.
In the further course of the thesis the numerical simulations were improved by considering
additional influences like the exact dependence of the Franck-Condon density and
the light shift of the photoassociation laser as a function of the collision energy. Additionally
the modeling of the experimental setup with a special emphasis on the volume
of the optical trap and thus the density of the atomic ensemble was improved and the
influence of varying trap depth and photoassociation duration has been studied. Investigating
possible explanations for the discrepancy of the measured rates compared to
theory, I show that by a modification of the coupling parameter and the spontaneous
decay rate of the molecular state the rates measured in the experiment can be reproduced
theoretically, with the restriction that at high intensity the calculated line shape
no longer agrees with the measurement. In the last chapter an improved experimental
apparatus is presented that by using an optical lattice suppresses thermal broadening
and thus simplifies the analysis substantially.
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