TY  - GEN
UR  - https://archiv.ub.uni-heidelberg.de/volltextserver/29072/
AV  - public
A1  - Kurz, Niels
CY  - Heidelberg
N2  - In this work, a reaction microscope with a magneto-optical trap for 6Li atoms, was extended by an optical dipole trap in order to be able to investigate in detail laser-induced atomic and molecular ionization dynamics in a cold quantum gas.
The optical dipole trap was operated at a full trap depth of 2.3 mK for 6Li atoms and about
1% of the atoms in the MOT could be transferred into the dipole trap, with 1/e storage times
exceeding 5 s. The optically trapped ensemble of 6Li atoms was used as a target for ionisation with intensive and broadband femtosecond laser pulses (? = 750?820 nm, P = 10^11?10^14 W/cm2, ?t = 30 fs) and allowed to perform kinematically complete experiments, in which 6Li+ ions
as well as photoelectrons were measured coincidentically.
As a ?rst application, in this work, a series of association- and ionization mechanisms, which
led to production of molecular 6Li2+ ions, were investigated with trapped lithium atoms.
In photoassociative ionization, two atoms collide, which were previously lifted into the asymptotic 2p ? 3s potential energy curve by ladder excitation. During the collision the atoms autoionize into the 12?g+(6Li2+) groundstate of the molecular ion, since these two potential energy curves exhibit an avoided crossing. This process was observed when magneto-optically trapped atoms were illuminated with the femtosecond laser.
In the dipole trap, using single-color photoassociation, excited state molecules were produced
in high-lying vibrational states 11?g+(? = 65) and 13?g+(v = 57) and spectroscopically investigated. A fraction of the excited state molecules decay via ?uorescence into the molecular ground state. The 11?g+(? = 38)(6Li2) ground state molecules created via the singlet res-
onance 11?u+(? = 65)(Li?2) were detected via direct 3 photon ionisation. The momentum spectra show very low kinetic energies for the photo electrons of below 100 meV. Therefore
in the molecular ion only vibrational states of Li2+ are getting populated, which are directly below the 3-photon transition energy.
Finally, a stepwise ionization mechanism was identi?ed, which leads into the continuum via
an intermediate molecular state of 6Li2? after photoassociation. The starting point is a pho-
toassociated excited state molecule 11?u+(? = 65)(6Li?2), which absorbs two photons of the dipole trap laser (? = 1070 nm ± 2 nm). This happens via an intermediate molecular state
31?g+(2s + 3s), after which it leads into the 12?g+(6Li2+) potential.
TI  - Kinematically complete multiphoton ionization studies on optically trapped 6Li and 6Li_2 created by single-color photoassociation
Y1  - 2021///
ID  - heidok29072
ER  -