Browsing by Author "Ndebeka, Wilfrid Innocent"
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- ItemCharacterization of thulium doped fiber for mid infrared laser applications(Stellenbosch : University of Stellenbosch, 2011-03) Ndebeka, Wilfrid Innocent; Rohwer, Erich G.; Schwoerer, Heinrich; University of Stellenbosch. Faculty of Science. Dept. of Physics.Please refer to full text to view abstract.
- ItemCharge carrier effects in free standing Si membranes investigated by linear and second harmonic optical techniques(Stellenbosch : Stellenbosch University, 2016-12) Ndebeka, Wilfrid Innocent; Rohwer, Erich G.; Neethling, Pieter N.; Steenkamp, Christine M.; Stafast, Herbert; Stellenbosch University. Faculty of Science. Dept. of PhysicsENGLISH ABSTRACT : Silicon (Si) based materials have been of technological importance throughout the years and today silicon remains a leading material in microelectronics industries. The silicon/silicon dioxide (Si/SiO2) interface has been one of the most studied systems in the realms of material and condensed matter physics. Despite the great outpouring research and huge technological success, there has been little effort to construct a comprehensive, unified microphysical model of the Si/SiO2 interface. The optical properties, both linear and nonlinear, of the interface region are of interest since they vary considerably from those of the adjacent bulk phases. Second harmonic generation is used as a versatile tool to investigate surfaces and buried interfaces of centrosymmetric materials such as Si. Specifically, the electric field induced second harmonic (EFISH) generation process is used as a valuable technique to investigate the mechanisms of charge transfer and trap generation and population, both by electrons and holes being pumped across the interface. In this work, the transmission of the fundamental laser beam (90 fs pulse trains at 80MHz repetition rate, 800 nm) through 10 m to 30 m thick silicon (Si) membranes as well as simultaneous measurements of the electric field induced second harmonic (EFISH) generated in reflection from and transmission through the Si membranes are reported for the first time. The transmission of the laser power through Si membranes, irradiated at an incident angle of 45 , shows an increase with increased power, then reaches a maximum, and finally continues to decrease considerably as the incident power is increased. A similar behavior is observed with the EFISH signals in transmission of the Si membranes. The nonlinear behavior of the fundamental transmitted signal is attributed to free charge carrier absorption (FCA) in Si. The experimental setup and these results are discussed in this thesis.
- ItemEfficiency of Tm3+ -doped silica triple clad fiber laser(Optical Society of America, 2011) Ndebeka, Wilfrid Innocent; Heidt, A.; Schwoerer, Heinrich; Rohwer, Erich G.We present measurements of the slope efficiency and the pump power at threshold of a Tm3+ -doped silica triple clad fiber laser emitting at 2.02 μm using different cooling techniques. The slope efficiency of 53.6 % was obtained at a temperature of 25oC with a maximum output power of 5 W for 19 W of absorbed power at the pump wavelength of 800 nm and 9.9 W threshold. In a slightly different setup, the output power could be increased to 10 W for an absorbed pump power of 32 W.