Wood, J.; (2009) Atoms, ions and molecules in intense ultrafast laser fields. Doctoral thesis , UCL (University College London).

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Abstract

The dynamics of atoms and hydrogen molecules in ultrafast intense laser pulses are studied experimentally using time of flight mass spectroscopy and fast ion beam techniques. The content of the study can be split naturally into two parts; the first dealing with the interaction of noble gas atoms and ions with laser pulses of between 40 and 50 fs in duration and around 20 mJ of energy per pulse, the second dealing with a time-resolved investigation of the nuclear dynamics of hydrogen molecules and their corresponding molecular ions with laser pulses of approximately 10 fs duration and an energy per pulse of 50 μJ. Within the first section of the study the technique of Intensity Selective Scanning with Effective Intensity Matching (ISS-EIM) has been used to observe Multi Electron Tunnelling Ionisation (METI) for the first time. These experiments were conducted with laser pulses focussed on neutral targets of argon and krypton. Also within the first section, the recombination of ionised electrons with their residual atomic cores has been observed for the first time in the atomic channel. This recombination occurs in the metastable ion population of singly charged ion beams of krypton and argon, provided by a fast ion beam apparatus. In the second section of the study, a pump-probe technique is employed using few cycle laser pulses to initiate (pump) and then image (probe) the nuclear dynamics of hydrogenic molecules and their molecular ions. In the ions, vibrational wavepackets have been studied and the phenomena of dephasing and revival observed. Additionally signatures of rotational wavepacket dynamics have been isolated in the neutral molecules. A technique to verify the laser pulse duration at the focus has also been introduced using xenon atoms and the same pump-probe technique.

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