Staff members: CM Steenkamp, EG Rohwer
Current/recent students: CI Rigby (PhD), A de Bruyn (MSc), TB Matindi (MSc)
A wavelength tuneable vacuum ultraviolet laser source (approximately 130-160 nm) with a narrow spectral bandwidth is used to contribute to the niche research area of tuneable laser spectroscopy in the vacuum ultraviolet (VUV) spectral range. The VUV light is generated by 3rd order sum-frequency generation in a Mg vapour-Kr gas medium.
Recent applications of the VUV are spectroscopy of carbon monoxide gas and calcium fluoride crystals.
Carbon monoxide (CO) is the second most abundant molecule in space and measurements of CO spectral lines are used to map the distribution of molecular matter in stellar, planetary and cometary atmospheres and interstellar gas clouds. We are acquiring data on the weak spectral lines of forbidden transitions for which accurate laboratory measured wavelengths are not yet available. These transitions are of particular importance, since the weak lines do not saturate in astronomy measurements and can provide quantitative information.
Calcium fluoride (CaF2) is one of the most important optical materials for laser applications in the ultraviolet (UV), vacuum ultraviolet (VUV) to deep ultraviolet (DUV). However CaF2 degrades under high power UV light, causing a decrease in transmission. As optical degradation is controlled by defect generation and annealing, knowledge about defect energy levels and kinetics is needed, but basic data such as the energy levels of the self-trapped excitons (that are considered the first step in the defect formation mechanism) is still lacking. To our knowledge this is the first spectroscopic study of an alkaline-earth fluoride using tuneable VUV laser radiation. Development of proof of principle experiments is needed to establish whether absorption and laser induced fluorescence excitation spectroscopy using our source will yield new data on self-trapped exciton states and other defects.
Staff members: EG Rohwer, PH Neethling, CM Steenkamp
Current/recent students: WI Ndebeka (PhD), GO Dwapanyin (PhD)
The project involves the investigation of charge carrier dynamics across the silicon-silicon dioxide interface under femtosecond laser irradiation. This charge carrier transfer is monitored through second harmonic generation. The movement of electrons and holes across the interface establishes an interfacial electric field which significantly enhances the second harmonic signal. This phenomenon is termed electric field induced second harmonic (EFISH). This project currently focuses on measuring the EFISH signal both in a transmission and reflection geometry simultaneously. In all previous reports in literature EFISH has always been measured in a reflection geometry.
The silicon samples under investigation were manufactured at the Institute for Photonic Technology (IPHT) in Jena. Single crystalline free-standing silicon micro membranes (15-40 μm thick) were produced by chemical etching of bulk silicon.
THz source and spectroscopy
Staff members: EG Rohwer, PH Neethling
Current/recent students: S Smith (PhD)
The project entails the design, construction and evaluation of a time-domain THz ellipsommetry setup. The aim of the project is to be able to extract material parameters from samples in aqueous environments, something which is not possible with the current transmission setup due to the strong absorption by water in this frequency range. This will allow for the investigation of biological samples, which ties in with the current initiatives within the LRI towards bio-photonics.
Near IR spectroscopy and LIBS
Staff members: A du Plessis, SG le Roux
Current/recent students: Lauren Louw (MSc), Emke Hartnick (new MSc for 2017, now internship)
Applications-research driven by photonics and spectroscopy is at the heart of what we do in my group. We make use of near IR spectroscopy (NIR) and laser induced breakdown spectroscopy (LIBS) to analyse a wide range of materials and develop the application of these techniques to unravel mysteries about materials.
We have existing projects in the analysis of the geographical origins and adulteration of honey products, spectral characterization and classification of South African soil types using NIR and MIR spectroscopy, and LIBS and CT analysis of geological samples for 2D and 3D chemical imaging of mineral distributions (gold in Wits ore). Students are welcome to apply as our outputs are limited only by manpower in this group. We collaborate with departments of Food Science, Soil Science, Geology, Biology and and various engineering groups. For more information of our 3D imaging applications research see the link above. Below you will find equipment available for research in our group
- NIR spectroscopy
- UV/Vis spectroscopy
- UV diode and visible fluorescence spectroscopy
- Raman microscope
- LIBS basic custom setup (Nd YAG laser)
- FTIR (pending application for instrument, not yet available)
- Zygo interferometer (pending application for instrument, not yet available)
Access to other instruments eg. 3D X-ray microscopy (microCT/nanoCT), XRF gun, SEM, etc