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Browsing by Author "Botha, LR"

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Acoustic waves in transversely excited atmospheric CO2 laser discharges: effect on performance and reduction techniques

Author: von Bergmann, HM ; Forbes, A ; Roberts, T ; Botha, LR Date: Aug 2008 Results are presented on the influence of acoustic waves on the performance of high-repetition-rate TEA CO2 lasers. It is shown that acoustic waves generated inside the laser cavity lead to nonuniform discharges, resulting in a deterioration ... Read more
Coherent excitation of vibrational levels using ultra short pulses

Author: De Clercq, LE ; Botha, LR ; Du Plessis, A ; Rohwer, EG Date: Jul 2009 The purpose of this study was to develop a model of the coherent excitation of the first few vibrational modes in the electronic ground state of the molecule. The model will be used in combination with an optimization algorithm to optimize a ... Read more
Compact fibre-laser-pumped Ho:YLF oscillator-amplifier system

Author: Bollig, C ; Strauss, Hencharl J ; Esser, MJD ; Koen, W ; Schellhorn, M ; Preussler, D ; Nyangaza, K ; Jacobs, Cobus ; Bernhardi, EH ; Botha, LR Date: Jun 2009 Ho:YLF is an attractive laser material for 2 µm high energy sources since it has a much longer upper laser level lifetime (~14 ms) and higher emission cross section than Ho:YAG. In addition, the very weak thermal lens on the polarisation helps ... Read more
Design and optimisation of a pulsed CO2 laser for laser ultrasonic applications

Author: Forbes, A ; Botha, LR ; Du Preez, N ; Drake, TE Date: Jul 2006 Laser ultrasonic is currently the optimal method for non-destructive testing of composite materials in the aerospace industry. The process is based on a laser-generated, ultrasound wave which propagates inside the composite. The response at ... Read more
Design and optimisation of a pulsed CO2 laser for laser ultrasonics

Author: Forbes, A ; Botha, LR ; du Preez, N ; Drake, T Date: Feb 2006 Laser ultrasonics is the present state-of-the art method for non-destructive testing of composite materials in the aerospace industry. The process is based on an IR laser generating an ultrasound wave that propagates inside the composite ... Read more
Efficient TEA CO2 laser based coating removal system

Author: Prinsloo, FJ ; Van Heerden, SP ; Ronander, E ; Botha, LR Date: Apr 2007 A high power 1kW pulsed transversely excited atmospheric CO2 laser that has been developed for the paint stripping of missiles was used to test paint stripping on several metallic and composite aircraft panels to determine the rate at which ... Read more
Femtosecond laser ablation of silver foil with single and double pulses

Author: Roberts, DE ; Du Plessis, A ; Botha, LR Date: 2009 The average ablation depth per pulse of silver foil by 130 fs laser pulses has been measured in vacuum over a range of three orders of magnitude of pulse fluence up to 900 J cm_2. In addition, double pulses with separations up to 3.4 ns have ... Read more
Femtosecond laser ablation of silver foil with single and double pulses

Author: Roberts, DE ; Du Plessis, A ; Botha, LR Date: 2009 The average ablation depth per pulse of silver foil by 130 fs laser pulses has been measured in vacuum over a range of three orders of magnitude of pulse fluence up to 900 J cm-2. In addition, double pulses with separations up to 3.4 ns have ... Read more
Femtosecond laser induced and controlled chemical reaction of carbon monoxide and hydrogen

Author: Du Plessis, A ; Strydom, CA ; Uys, H ; Hendriks, A ; Botha, GN ; Botha, LR Date: Jul 2011 Results from experiments aimed at bimolecular chemical reaction control of CO and H2 at room temperature and pressure, without any catalyst, using shaped femtosecond laser pulses are presented. A stable reaction product (CO2) was measured ... Read more
Femtosecond laser induced breakdown spectroscopy of silver within surrogate high temperature gas reactor fuel coated particles

Author: Roberts, DE ; Du Plessis, A ; Steyn, J ; Botha, LR ; Strydom, CA ; Van Rooyen, IJ Date: Nov 2010 The detection of metallic silver on Chemical Vapour Deposited (CVD) grown silicon carbide and in Pebble Bed Modular Reactor (PBMR) supplied tri-structural isotropic (TRISO) coated particles (with 500 µm diameter zirconium oxide surrogate ... Read more
Femtosecond pump probe spectroscopy for the study of energy transfer of light-harvesting complexes from extractions of spinach leaves

Author: Ombinda-Lemboumba, Saturnin ; Du Plessis, A ; Sparrow, RW ; Molukanele, P ; Botha, LR ; Rohwer, EG ; Steenkamp, CM ; Van Rensburg, L Date: Sep 2009 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 ... Read more
Femtosecond pump-probe studies of zinc phthalocynine in DMSO

Author: Ombinda-Lemboumba, Saturnin ; du Plessis, A ; Botha, LR ; Rohwer, EG ; Steenkanp, CM Date: 01 Sep 2010 Phthalocyanines are new class of photosensitiser used for photodynamic therapy. These drugs are used to treat small and superficial tumours. In recent years, a particular attention has been given to phthalocyanine in order to search suitable ... Read more
Generation and application of high power flattened Gaussian beams

Author: Forbes, A ; Du Preez, N ; Litvin, IA ; Botha, LR Date: Jul 2009 Generation and application of high power flattened Gaussian beams. Presented at the 54th Annual Conference of the South African Institute of Physics (SAIP) 2009. Read more
High power infrared super-Gaussian beams: generation, propagation and application

Author: Du Preez, NC ; Forbes, A ; Botha, LR Date: Sep 2009 In this paper researchers present the design of a CO2 laser resonator that produces as the stable transverse mode a super–Gaussian laser beam. The resonator makes use of an intra–cavity diffractive mirror and a flat output coupler, generating ... Read more
Ho:YLF pumped HBr laser

Author: Botha, LR ; Bollig, C ; Esser, MJD ; Campbell, RN ; Jacobs, Cobus ; Preussler, DR Date: Oct 2009 A Ho:YLF laser pumped HBr molecular laser was developed that produced up to 2.5mJ of energy in the 4 micron wavelength region. The Ho:YLF laser was fiber pumped using a commercial Tm:fibre laser. The Ho:YLF laser was operated in a single ... Read more
Influence of amplification on pulse shaping for coherent control applications

Author: Du Plessis, A ; Botha, GN ; Botha, LR Date: Jul 2011 Results from experiments aimed at bimolecular chemical reaction control of CO and H2 at room temperature and pressure, without any catalyst, using shaped femtosecond laser pulses are presented. A stable reaction product (CO2) was measured ... Read more
An investigation of Laser Induced Breakdown Spectroscopy for use as a control in the laser removal of rock from fossils found at the Malapa hominin site, South Africa

Author: Roberts, DE ; Du Plessis, A ; Steyn, J ; Botha, LR ; Pityana, Sisa L ; Berger, LR Date: Jul 2012 Laser Induced Breakdown Spectroscopy (LIBS) was used to study the spectra from fossils and surrounding rock recovered from the Cradle of Mankind site at Malapa, South Africa. The objective was to find a suitable spectral line(s), specific to ... Read more
Mathematical model of an optically pumped molecular laser

Author: Botha, LR ; Bollig, C ; Esser, D ; Jacobs, Cobus ; Preussler, D Date: Jul 2009 A mathematical model was developed that accurately predicts the performance of an optically pumped HBr laser. Relatively high conversion efficiency was achieved. Tm pumped Ho:YLF is a viable source for pumping HBr laser, while HBr can be ... Read more
Optically pumped tunable HBr laser in the mid-infrared region

Author: Koen, W ; Jacobs, Cobus ; Bollig, C ; Strauss, Hencharl J ; Esser, MJD ; Botha, LR Date: Jun 2014 An optically pumped tunable HBr laser has been demonstrated for the first time. The pump source was a single-frequency Ho:YLF laser and amplifier system, which was locked to the 2064 nm absorption line of HBr. Laser oscillation was demonstrated ... Read more
Paint stripping with high power flattened Gaussian beams

Author: Forbes, A ; Du Preez, NC ; Belyi, VN ; Botha, LR Date: Aug 2009 In this paper the researchers present results on improved paint stripping performance with an intra-cavity generated Flattened Gaussian Beam (FGB). A resonator with suitable diffractive optical elements was designed in order to produce a ... Read more

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