Browsing by Author "Botha, L. R."

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    Femtosecond pump probe spectroscopy for the study of energy transfer of light-harvesting complexes from extractions of spinach leaves
    (Academy of Science of South Africa (ASSAf), 2009-10) Ombinda-Lemboumba, S.; Du Plessis, A.; Sparrow, R. W.; Molukanele, P.; Botha, L. R.; Rohwer, E. G.; Steenkamp, C. M.; Van Rensburg, L.
    Measurements of ultrafast transient processes, of temporal durations in the picosecond and femtosecond regime, are made possible by femtosecond pump probe transient absorption spectroscopy. Such an ultrafast pump probe transient absorption setup has been implemented at the CSIR National Laser Centre and has been applied to investigate energy transfer processes in different parts of photosynthetic systems. in this paper we report on our first results obtained with Malachite green as a benchmark. Malachite green was chosen because the lifetime of its excited state is well known. We also present experimental results of the ultrafast energy transfer of light-harvesting complexes in samples prepared from spinach leaves. Various pump wavelengths in the range 600-680 nm were used; the probe was a white light continuum spanning 420-700 nm. The experimental setup is described in detail in this paper. Results obtained with these samples are consistent with those expected and achieved by other researchers in this field.
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    A single-element plane-wave solid-state laser rate equation model
    (Academy of Science of South Africa, 2008) Bernhardi, E. H.; Bollig, C.; Esser, M. J. D.; Forbes, A.; Botha, L. R.; Jacobs, C.
    A numerical rate equation model has been developed to describe the dynamics of a solid-state laser during continuous wave or Q-switched operation. The model allows the optimization of parameters such as the output coupler transmission percentage, crystal length and beam diameters, with the aim of improving the laser output performance. To validate the model, it was applied to a Nd:YLF laser, and proved successful in predicting and explaining the laser dynamics. It also satisfied our objective of creating a useful laser design tool.