Professor Simon Hooker

Abstract:

Results are presented on the ablation by 157 nm laser radiation of polytetrafluoroethylene (PTFE), polyimide, polyhydroxybutyrate (PHB), poly(methyl methacrylate) (PMMA), and poly(2-hydroxyethyl methacrylate) with 1% of ethylene glycol dimethacrylate as a crosslinking monomer. Direct photoetching of PHB and undoped PTFE is demonstrated for laser fluences ranging from 0.05 to 0.8 J/cm2. The dependence of the ablation process on the polymer structure is analyzed, and insight into the ablation mechanism is gained from an analysis of the data using Beer-Lambert's law and the kinetic model of the moving interface. Consideration of the absorbed energy density required to initiate significant ablation suggests that the photoetching mechanism is similar for all the polymers studied. © 1995 American Institute of Physics.

Abstract:

We have developed a model for the net induced gain as a function of pump fluence, based on a rate equation analysis of the populations of the 4f(n-1) 5d → 4f(n) level of the activator ions and of absorptive color centers. As an example, this has been applied to LiLuF4:Ce3+, in which we have also observed laser oscillation at 326.9 nm. The net gain is seen to rise rapidly with pump fluence before showing saturation and roll-off. This behavior can be explained by the creation of color centers that absorb strongly in the UV. We will present the results of similar measurements in the VUV on samples of LiYF4:Nd3+ and LaF3:Nd3+.