Browsing by Author "Steenkamp, C. M."
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- ItemAccurate laboratory wavelengths of the e 3 Σ–(ν' = 5) – X 1 Σ+(ν'' = 0) band of 12C16O(IOP Science, 2010) Dickenson, G. D.; Nortje, A. C.; Steenkamp, C. M.; Rohwer, E. G.; Du Plessis, A.The forbidden singlet-triplet transitions of carbon monoxide (CO) are important in the interpretation of vacuum ultraviolet interstellar absorption spectra and in particular for the measurement of large CO column densities. Twenty rovibronic lines of the e 3Σ–(ν' = 5) – X 1Σ+(ν'' = 0) band of 12 C 16O for which laboratory wavelengths were previously unavailable were identified in laser-induced fluorescence excitation spectra. Wavelengths were assigned to five rovibronic transitions to an average accuracy of 0.0028 Å. A further 15 lines could not be fully resolved and average wavelengths were measured for these groups of closely spaced lines. A wavelength difference of 0.011 ± 0.0028 Å between the measured wavelengths and the calculated wavelengths in the atlas of Eidelsberg & Rostas demonstrates the need for more experimental data on CO.
- ItemFemtosecond 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.
- ItemFirst comparison of electric field induced second harmonic of NIR femtosecond laser pulses in reflection and transmission generated from Si/SiO2 interfaces of a silicon membrane(Springer, 2011) Nyamuda, G. P.; Rohwer, E. G.; Steenkamp, C. M.; Stafast, H.For the first time electric field induced second harmonic (EFISH) generation of femtosecond (fs) laser pulses (λ=800 nm, τ=75±5 fs, rep. rate=80 MHz, Epulse≤10 nJ) is observed in transmission through a thin free-standing silicon (Si) membrane of 10-μm thickness and compared to the well-known EFISH results in reflection by use of the z-scan technique. EFISH in reflection and transmission unequivocally originate from the front and rear Si/SiO2 interfaces, respectively, with SiO2 being the natural oxide on the Si surfaces. Frequency conversion is enhanced by photoinduced electric fields across the Si/SiO2 interfaces caused by charge-carrier injection from Si into the oxide. The z-scan results and time-dependent measurements allow comparison of the EFISH signal amplitudes and time constants detected in transmission and reflection, demonstrating the need for further investigation. © 2011 Springer-Verlag.
- ItemFree charge carrier absorption in silicon at 800 nm(Springer, 2016) Heisel, P.-C.; Ndebeka, W. I.; Neethling, P. H.; Paa, W.; Rohwer, E. G.; Steenkamp, C. M.; Stafast, H.The transmission of a Ti:sapphire laser beam (c.w. and fs pulsed operation at 800 nm) through a 10-μm-thin oxidized silicon membrane at 45° angle of incidence at first increases with the incident laser power, then shows a maximum, and finally decreases considerably. This nonlinear transmission behavior is the same for c.w. and pulsed laser operation and mainly attributed to free charge carrier absorption (FCA) in Si. A simple FCA model is developed and tested.
- ItemAn improved experimental setup for high-resolution vacuum ultraviolet laser spectroscopy(Academy of Science for South Africa, 2005) Steenkamp, C. M.; Du Plessis, A.; Rohwer, E. G.The experimental setup for vacuum ultraviolet (VUV) laser spectroscopy at Stellenbosch University's Laser Research Institute, has been improved by the addition of a VUV monochromator. The VUV source has been characterized over the extended wavelength range 144.2-157.7 nm, and simultaneous measurement of laser-induced fluorescence and absorption spectra has been achieved. We discuss current investigations of carbon monoxide molecules and complexes, facilitated by the narrow bandwidth of the VUV light and the low temperature collision-free conditions in a supersonic jet.