High harmonic generation (HHG) is a powerful and well established technique to
study ultra fast processes in atoms and molecules. Originally HHG was restricted to
the study of atomic or small molecular gases. In the last few years the use of laser
ablation to create plumes that are suitable media for HHG has gained interest due
to is ability to allow almost any solid material to be potentially studied using HHG.
Most of this thesis focuses on our advancements in this eld of ablation plume HHG
spectroscopy with a small section devoted to our continuation of work focused on
controlling electron trajectories in HHG through the use of an orthogonally polarised
second harmonic eld.
We show how through the use of a rotating target system we have been able to
stabilise the ablation process to work at 1 kHz repetition rate.
The ablation plumes of some transition metals have previously be shown to exhibit
enhancement of particular harmonic orders linked to resonances in the parent
ion. We performed investigations into tin and manganese plumes and were able to
nd good agreement between the experimental data and a theoretical model. This
showed that autoionising states in the ions of these materials were the most likely
source of the enhancements.
We present our attempts to extend the ablation plume HHG technique to work
with soft materials. It was found that graphite plumes were able to produce a very
strong harmonic response that is comparable with generation from an argon gas jet. It
was discovered that nano particles were present in the plumes and these were mostly
likely to cause of the stronger e ciency. Finally we present the rst use of laser
ablation plume HHG to study molecules of biological interest. We performed HHG
studies on uracil and thymine, a signal was obtained from former but not the latter.
Were able to determine that during ablation there was a higher degree of molecular
fragmentation from thymine molecules compared to uracil.