Conveners
LOS: Lasers
- Pieter Neethling (Laser Research Institute, University of Stellenbosch)
LOS: Spectroscopy
- M J Daniel Esser (CSIR National Laser Centre)
LOS: Optics 1
- Andrew Forbes (CSIR)
LOS: Optics 2
- Patience Mthunzi (CSIR - NLC)
LOS: Femtosecond
- Hermann Uys (National Laser Centre, CSIR)
LOS: Quantum
- Venkataraman Sivakumar (CSIR-National Laser Centre)
LOS: Applications
- Hencharl Strauss (CSIR (National Laser Centre))
Description
Lasers, Optics and Spectroscopy
A dielectric barrier discharge CO2 TEA laser excited by a thyratron driven power supply has been developed and characterized. Laser output was observed at frequencies up to 25 Hz for an electrode separation of 10 mm with 1.8 mm Suprasil glass covering the electrodes. At this gap separation, pulsed power output of about 9 W was detected for gas pressures between 100 and 400 mbar. Changing...
A method of experimentally decomposing a field within an apertured plano-concave resonator cavity into a forward propagating field (plane to concave) and a backward propagating field (concave to plane) is presented. The use of an intra-cavity aperture which is a simple method of laser beam shaping is a means of mode selection as higher-order modes are actively discriminated. This apertured...
Passively Q-switched Nd:YAG lasers with Cr4+:YAG as a saturable absorber that can operate with pulse repetition frequencies(PRF) in the hundreds of kilohertz typically have problems with pulse to pulse fluctuations of pulse energy and width and the associated timing jitter as well as drift in PRF. One technique for stabilizing the PRF and reducing fluctuations is modulation of pump power....
We have previously demonstrated a novel laser pulse energy control system based on two analog controllers to control a Q-switched Nd:YLF laser. We now present the improved technique based on a custom-designed high-speed FPGA (field programmable gate array) digital logic controller, together with experimental results from controlling a high-energy Ho:YLF ring laser. Laser pulses of...
Lasers and amplifiers emitting 2µm single-frequency pulses are used for spectroscopy, remote sensing, and defence applications. The laser sources group at the CSIR National Laser Centre has developed a number of 2µm lasers and amplifiers over the course of five years. We report on three of these, all of which achieved record breaking output energies. To generate the high energy 2µm...
Optically pumped molecular lasers are attractive alternatives to generate high energy pulses in the mid-infrared wavelength range, compared to non-linear conversion that can suffer from optical damage. One such laser is based on HBr, for which it has been experimentally demonstrated to emit laser light in the 4 µm wavelength range when pumped at 1.3 µm or at 2 µm. Prior to the work...
To our knowledge, we have demonstrated the first optically pumped tunable HBr oscillator lasing on both the P- and the R-branches. Through the implementation of an intra-cavity diffractive grating, we could tune the wavelength over a range of 538 nm from 3872 nm to 4410 nm. A single-frequency Ho:YLF ring laser and amplifier system was used as pump source. The oscillator was pumped in a...
The transient absorption of Zinc phthalocyanine (ZnPc) has been studied by femtosecond pump-probe spectroscopy. We present results on the ultrafast spectroscopy of ZnPc, specifically identifying three ultrafast components observed. These are the inertial solvation dynamics (~1.8 ps), the dielectric solvation dynamics (~39 ps) and vibrational relaxation (~2.7 ps) in the electronic excited...
Understanding molecular dynamics on potential energy surfaces has been at the heart of ultrafast transient absorption in the recent years [Philipp K, etal., 2005],[Karel G, etal., 2008]. Based on the on-going experiment at our ultrafast laboratory, we ran density functional calculations on metal dithizonates, starting with their kernel molecule, formaldimine, to validate what we observe...
The Nobel prize winning technology involving a mode-locked femtosecond laser frequency comb (FLFC) has been at the epi-centre of a scientific revolution over the last two or so decades. Even though originally designed to count cycles in optical clocks, it has had a profound impact on other research areas, with a range of applications including spectroscopy, trace gas detection, signal...
Laguerre-Gaussian (LG) beams possess many interesting properties, one of which is that they carry orbital angular momentum, an extrinsic component of angular momentum, when the electric field or mode has an azimuthal angular dependence of exp(il), where l is the azimuthal mode index. These beams are easily generated using spatial light modulators (SLMs), where a Gaussian beam incident on...
In this work we propose an implementation of a new intra–cavity beam shaping technique to vary the intensity distribution of the fundamental mode in a resonator cavity while maintaining a constant intensity distribution at the output. This method can be useful for fitting a transversal intensity profile of the required mode with a pump beam profile in the region of the active medium to...
We outline an approach for the calculation of the mean focal length of an aberrated lens, and provide closed form solutions that show that the focal length of the lens is dependent on the presence of defocus, x-astigmatism and spherical aberration. The results are applicable to Gaussian beams in the presence of arbitrary sized apertures. The theoretical results are confirmed experimentally,...
Due to their self-renewal and pluripotency characteristics, stem cells possess the potential to dramatically advance current therapies in tissue regeneration and engineering. Nonetheless, there still remains a pressing necessity to answer the biological questions concerning how stem cell renewal and differentiation programs are operated and regulated at the genetic level. Genetic...
Since its inception, optical trapping has found its place in the field of physics, biology and recently in micro-fluidics. To a physicist, this technique opens up avenues to carry out force measurement with utmost accuracy and precision on the micro-scale level. This is attained by measuring the magnitude of the trapping force required to restrain a trapped particle to its equilibrium...
With modern liquid crystal devices it is possible to implement digital holograms for the modulation in amplitude and phase of light: so called 'structured light'. In this non-specialist talk, we will introduce the concept of complex amplitude modulation, and show how light can be tailored to have interesting properties: defying diffraction, twisted like a spring in intensity and phase, and...
In this work we investigate the behavior of an instantaneous Poynting vector for different types of cylindrical symmetric beams such Gaussian beams, Bessel beams and so on. In most investigations for energy flow in real laser beams, the oscillation component of the Poynting vector is not considered. However this component of the Poynting vector carries useful information regarding beam...
The transformation of a Gaussian beam into a symmetrical TEMp0 Laguerre Gaussian beam (LGB) intensity distribution which has transverse superresolution properties is very useful in improving the spatial resolution of optical imaging microscopes by making the central diffractive spot smaller than the Airy spot. The beam shaping is achieved by using an annular binary Diffractive Optical...
The phase measurements of a Shack-Hartmann wavefront sensor are calibrated. The process involves creating holograms of known amounts of individual phase aberrations on a spatial light modulator and reflects an aberration free laser beam off of the modulator’s liquid crystal display thereby giving the beam that aberration. The beam is then relayed onto the sensor for direct measurement. The...
Time-domain terahertz (TD-THz) spectroscopy has emerged as a valuable tool for studying material properties in the THz region of the electromagnetic spectrum. Many classes of materials exhibit characteristic absorption signatures in this previously unstudied portion of the electromagnetic spectrum. This opens up the possibility for non-destructive and non-invasive testing and analysis of...
We observe ultrafast structural dynamics in crystals. For that, we use the 'Pump Probe Technique': The 'Pump' triggers a fast process, the 'Probe' takes a snapshot of it at a specific time. We are interested in observing processes, which happen on a picosecond timescale. That means, the duration of our 'Probe' must be in the order of ~ 100 fs. The only source of a 100 fs short signal,...
Obtaining single shot electron diffraction patterns is highly desirable when dealing with samples that are either destroyed or display irreversible structural changes upon photo-excitation. Such single shot measurements demand highly charged pulses that contain in the order of 105 – 106 electrons. Maintaining femtosecond pulse duration in the presence of the inevitably...
Quantum key distribution (QKD) is a secure method of transferring encryption keys between two distant parties. It provides a physical layer of security rather than a mathematical algorithm used in conventional encryption systems. As QKD is of paramount importance in the future ICT landscape, various innovative solutions have been developed and tested to expand the spatial coverage of these...
The orbital angular momentum (OAM) state of light has been the object of much interest within the quantum information community lately mainly because it can be used to implement higher dimensional entanglement. Unfortunately, the OAM cannot be used for quantum communication through optical fibers in use today because these fibers support only modes with zero OAM values. One can...
We simulate real-time quantum state estimation due to a sequence of so-called "unsharp" measurements applied to a two-level system undergoing Rabi oscillations. These measurements allow an experimentalist to extract information about the system without destroying the quantum state. They can be realized physically through the use of auxilary quantum states in addition to the quantum state...
The growing social concern for environmental protection and human health has driven widespread interest in analysis of heavy metals in the various environmental compartments including soil. Soil is unanimously considered as one of the recipients of heavy metals released by several human activities. Rapid analysis of heavy metals in soil is an important factor in modelling the effect of...
Maintaining, monitoring and safeguarding South Africa’s oceans and dams is a multifaceted project requiring the skills and expertise from several scientific domains-.The radiometric study and spectral characterization through in situ measurements of these water systems is critical to such a project. The objective is to develop and subsequently test 2 prototype radiometers for their...
Light Detection and Ranging (LIDAR) studies on particulate matter (Aerosols) and pollutants; elucidate their distribution and concentration in the atmosphere. Particulate matter plays a key role in atmospheric physical and chemical processes from local to global scale. The complexity of these processes have been largely reviewed in literatures and LIDAR measurements have mostly...
