Ionisation of Metastable Neon with Few Cycle Laser Pulses
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This thesis describes two separate investigations into the ionisation of the 3P2 metastable state of neon (Ne) by strong-eld light pulses. The first is an investigation into the ionisation yield of Ne and the second experiment examines the electron momentum distribution of the ionised electrons. Experimental ionisation results were compared to ionisation models via a scaling fit to ion yield and laser intensity. The best laser intensity fit was provided byTDSE based theory with n = 0:82. The effect of the spin state on ionisation yield was also examined, and it was determined that there is an 15:34:6% difference in ion yield between atoms pumped into the stretched mj = 2 states compared to an atomic ensemble with a more even state population distribution. This was an unexpected result that remains unexplained. Experimental measurements of the transverse electron momentum distribution (TEMD) for Ne that is ionised well in the over-the-barrier regime are compared to the TEMD for Ar, which is ionised well in the tunnelling regime. It was observed that as the polarisation of the ionising light becomes circular, the distribution for Ne remains cusp-like, whereas the distribution for Ar broadens and becomes Gaussian. These results are predicted by a theoretical treatment of the interaction with a TDSE model and quantitatively indicate that the free electron is influenced in a non-negligible way by the ionic core in the over-the-barrier ionisation regime. This has implications for the validity of the strong field approximation in this ionisation regime.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Natural Sciences
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3P2 metastable state of neon (Ne)