eprintid: 29072
rev_number: 17
eprint_status: archive
userid: 5534
dir: disk0/00/02/90/72
datestamp: 2021-01-21 06:20:39
lastmod: 2021-02-24 08:23:27
status_changed: 2021-01-21 06:20:39
type: doctoralThesis
metadata_visibility: show
creators_name: Kurz, Niels
title: Kinematically complete multiphoton ionization studies on optically trapped 6Li and 6Li_2 created by single-color photoassociation
subjects: ddc-530
divisions: i-130001
divisions: i-741010
adv_faculty: af-13
abstract: 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 (λ = 750−820 nm, P = 10^11−10^14 W/cm2, Δt = 30 fs) and allowed to perform kinematically complete experiments, in which 6Li+ ions
as well as photoelectrons were measured coincidentically.
As a first 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 12Σg+(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 11Σg+(ν = 65) and 13Σg+(v = 57) and spectroscopically investigated. A fraction of the excited state molecules decay via fluorescence into the molecular ground state. The 11Σg+(ν = 38)(6Li2) ground state molecules created via the singlet res-
onance 11Σu+(ν = 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 identified, which leads into the continuum via
an intermediate molecular state of 6Li2∗ after photoassociation. The starting point is a pho-
toassociated excited state molecule 11Σu+(ν = 65)(6Li∗2), which absorbs two photons of the dipole trap laser (λ = 1070 nm ± 2 nm). This happens via an intermediate molecular state
31Σg+(2s + 3s), after which it leads into the 12Σg+(6Li2+) potential.
date: 2021
id_scheme: DOI
id_number: 10.11588/heidok.00029072
ppn_swb: 1747331147
own_urn: urn:nbn:de:bsz:16-heidok-290724
date_accepted: 2021-01-12
advisor: HASH(0x561a62a4e2a8)
language: eng
bibsort: KURZNIELSKINEMATICA2021
full_text_status: public
place_of_pub: Heidelberg
citation:   Kurz, Niels  (2021) Kinematically complete multiphoton ionization studies on optically trapped 6Li and 6Li_2 created by single-color photoassociation.  [Dissertation]     
document_url: https://archiv.ub.uni-heidelberg.de/volltextserver/29072/1/Dissertation_Niels_Kurz.pdf