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Title: Studies of plasmas produced by picosecond laser pulses
Author: Devlin-Hill, P. M.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1995
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This thesis contains a study into plasmas created by the interaction of 35ps laser pulses, of energy ≃ 100mJ and wavelength 1064nm, with planar gold and carbon targets mounted in a vacuum chamber. A time-of-flight mass spectrometer, employing electrostatic separation of particles, was used as the plasma diagnostic. A detailed analysis of the ion spectrometer showed how its performance depended on the characteristics of the plasma flowing through its entrance aperture. The flow was approximated by a displaced Maxwellian, i.e. a velocity of mass motion with a super-imposed random component of velocity, the latter being associated with a kinetic ion temperature Ti. Using this model it was found that the signal pulses were broadened and shifted in time by an amount determined by Ti, these features influencing resolution and the accuracy of particle identification and time-of-flight analyses. Conversely, the signal broadening and time shift can be used to estimate the temperature Ti (values of ≃ 1 eV were obtained) of the expanded plasma. The observation of what are believed to be small multiply charged cluster ions is reported. Homonuclear gold cluster ions comprising of three atoms and carrying charges of up to +5, and of four atoms carrying charges of up to +3, or possibly +4, were observed. Carbon cluster ions carrying charges up to +6 and of mass slightly greater than that of four carbon atoms were also observed. The observation of such non-integer cluster ion to single atom ion mass ratios may indicate the generation of heteronuclear cluster ions formed between the atoms of the target material and vacuum contamination. Non-integer mass ratios were also obtained for gold. It is proposed that the cluster ions form through the influence of a small background gas pressure which enables neutrals, generated through recombination, to aggregate on to single atom ions. The observation of Au32+ and Au43+ in the present work has also been reported by other workers, as well as that of small multiply charged homonuclear carbon cluster ions. However the observation of Au34+ and Au35+, and of what appears to be small multiply charged heteronuclear carbon cluster ions is new.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available