| dc.description.abstract | The goal of the presented work is to investigate double detachment of
negative ions on nano- and femtosecond time scales. I have performed
three types of experiments.
Femtosecond time resolved pump-probe experiments have been performed
on electron dynamics in the valence shell of carbon, silicon
and germanium atoms. The atom under investigation was prepared
by strong field photodetachment of its parent negative ion in a linearly
polarized femtosecond laser pulse. The detachment process coherently
populates the fine structure levels of the atomic ground state
giving rise to an electronic wave packet moving in the valence shell
of the atom. The wave packet is probed by strong field ionization at a
time delay controlled on a femtosecond time scale. The ionized electrons
are detected in an electron imaging spectrometer. The energy
and angular distribution of the ionized electrons provide information
on the phase of the wave packet. The results reveal a periodic spatial
rearrangement of the electron cloud in the atom. The experimental
procedure and detection scheme developed provide the first direct visualization
of an electronic wave packet moving in the ground state of
an atom.
The process of rescattering in strong field detachment has also been
investigated. The detached electron is accelerated in the laser field.
When the E-field changes its direction the electron follows and may
return and collide with the core. I have investigated the rescattering
effect in negative fluorine ions and compared with previous results on
bromine ions. Furthermore, strong field detachment experiments of
F
2 were conducted and the results from molecular fluorine ions are
compared to results from atomic fluorine ions.
Photodetachment cross sections and doubly excited states in K and
Cs have been investigated through double detachment. A resonant
ionization scheme was used where the ion beam and laser beams were
in a collinear configuration allowing for measurements of partial cross
section channels individually with nearly 100% detection efficiency.
A new threshold behavior has been found in photodetachment into
atomic states having a large and negative polarizability. A new model
was developed to explain the observed phenomena. Furthermore, two
new resonances stemming from doubly excited states were found below
the K(7 2P) channel opening in K and a set of new resonances
was observed in Cs below the Cs(10 2P) channel. | sv |
