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Femtosecond molecular dynamics driven by extreme ultra violet radiation
Scientists have always been interested in the various motions, dynamics and reactions
of the world around them. The understanding of chemical reactions, which often
proceed through many intermediate states, has been of particular interest. An essential
step toward a better understanding of chemical reactions is the study of electronic,
atomic and molecular dynamics.
This work demonstrates a novel spectroscopic method with femtosecond resolution,
giving it the capability to directly observe molecular dissociation dynamics. This
is made possible by combining a number of recently developed source and detector technologies.
EUV light is created by upconverting ultrashort, high intensity, infrared laser
pulses through the mechanism of high-harmonic generation. It is then used to initiate
dynamics in molecules through valence ionization, inner-valence ionization and shake-up
processes. The dynamics are then probed by time-delayed infrared pulses. An ion and
electron coincident momentum imaging detector is used to study the dynamics.
This combination of high-harmonic generation and momentum imaging technologies
has permitted us to observe, for the first time, the dissociation dynamics of shake-up
states of nitrogen (N2) molecules. Additional molecules (D2, O2 and CO) have also been
studied and preliminary analysis points to very interesting dynamics occurring in each
This work also presents the first demonstration of a carrier-envelope phase stabilized,
chirped pulse amplifier system using diffraction gratings in the stretcher and
compressor, a potentially useful tool for molecular reaction imaging. The amplifier system
is cryogenically cooled and exhibits intrinsic long term phase stability. The results
represent a significant improvement over previously demonstrated phase coherence for
grating-based, femtosecond laser amplifier system.