This thesis begins with an introduction to the interaction and refraction of light in continuous media. It is shown how these properties can be exploited to achieve focusing of parallel light rays in such a medium. Past work on Gas Lenses is reviewed, highlighting the progress in design of gas lenses, leading to a justification for the research described in the rest of the chapter. Original work by the author on the subject of continuous gas lenses at low and high pressure is then presented. Experiments show that gas lenses at low pressure have stable foci, but long focal lengths, while at high pressure two foci are produced, both of unstable character. These results are explained by a simple theory, and future applications of such lensing properties are presented. Chapter two introduces the concept of the Colliding Shock Lens (CSL), and presents shallow water wave simulations, conducted by the author, as a useful analogy to the interaction of shocks in the CSL. All the properties of the CSL lensing action are reproduced in the water simulations, yielding useful insight, by means of a simple experiment, into the physics of interacting shock waves. Chapter three presents original work by the author on the subject of multiple pulse thermal lensing. A theory is developed which predicts the behaviour of thermal lenses seen in an industrial laser chain. Experiments on thermallensing, as well as some solutions, are presented and discussed. Chapter four revises the theory of Zernike Polynomials and their application to the study of aberrations. Thermal aberrations are studied, including the aberrations introduced by thermal lensing and thermal blooming. The relationship between aberrations and subsequent beam quality and beam propagation is explored. Chapter five looks at the use of adaptive mirrors for mode matching. Although the theory of adaptive systems is well known, no-one has as yet tackled the problem of correcting for mode matching changes. A new way of thinking about mode matching is proposed, and the merits of this system, called characterisation space, are explained. Chapter six comprises the theory and design of a novel vacuum chamber which has applications in gas lens designs. All the gas lenses used in pressure experiments were housed in compressional vacuum chambers. The idea of a Tensional Vacuum Vessel (TVV) is introduced, and experiments show that such chambers are very successful low vacuum chambers. The advantages and applications of TVVs are discussed, specifically those relating to gas lens applications. At the end of this thesis it was apparent that more questions had been generated than answers. This is probably true of any study. Chapter seven therefore outlines some as yet unanswered questions, and gives some suggestions for starting points. Some of this work is presently being undertaken by the author. / Thesis (Ph.D.)-University of Natal, 1997.

An experimental and a theoretical analysis for a laser beam propagating through multiple phase screens was performed. The theoretical analysis showed that the statistics for the intensity fluctuations, which can be predicted by the HK and the I-K distributions, could be derived from a multiplicative process using statistical distributions derived from Gaussian statistics. For the single phase screen experiment, the experimental normalized moments were compared with the normalized moments of both the HK and I-K distributions . In addition, the intensity data was lowpass filtered to yield moments that are predicted by the gamma distribution. The single phase screen data was segmented into small time intervals, and all time segments with approximately the same variance were grouped together into bins to yield normalized moments for each bin that are predicted by the Rician distribution. Also, the normalized moments for two and three phase screen experiments were measured. Finally, a computer program was written to simulate K distributed noise from two independent Gaussian noise sources.

Thesis (MSc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: This study involved the analysis of crystallization kinetics by means of a unique and newly developed Solution crystallization analysis by laser light scattering (Scalls) technique. In the main study we compared two commercial linear low-density polyethylene (LLDPE) polymers (PE-1- octene and PE-1-hexene) and studied the effect of short-chain branching on the solution crystallization of these complex polymer systems. Characterization of the polymers was done by nuclear magnetic resonance spectroscopy (NMR) and high-temperature gel permeation chromatography (HT-GPC). The second study involved the fractionation of a PE-1-hexene copolymer by temperature rising elution fractionation (Tref) and analyzing the solution crystallization of the different temperature fractions. This resulted in important details on the different molecular regions present in the polymer. A third additional study was done on the compatibility in polyolefin blends. Two different blends were prepared: isotactic polypropylene (iPP) – low density polyethylene (LDPE) blend and iPP – polypropylene impact copolymer (PPIC) blend. It was found that co-crystallization only occurred for the iPP - PPIC blends. Phase separation occurred for the iPP – LDPE blends, resulting in the formation of two phases for all blend compositions. Solution crystallization analysis is usually measured by the conventional Crystallization Analysis Fractionation (Crystaf) technique. In this study all crystallization data were compared with Crystaf results and a good correlation was found between the results obtained by Crystaf and Scalls. The major advantages of the Scalls technique are that, results similar to that of Crystaf can be acquired with much shorter analysis times and Scalls also allows for the measurement of solution melting of the crystallized polymer solutions. / AFRIKAANSE OPSOMMING: Hierdie studie het die analise van kristallisasie kinetika behels met behulp van die unieke en nuut ontwikkelde oplossing kristallisasie analise deur laser lig verstrooiing (Scalls) tegniek. In die hoof studie het ons twee kommersïele liniêre lae-digtheid polietileen (LLDPE) polimere (PE-1-okteen en PE-1-hekseen) vergelyk en die effek van kort-ketting vertakking op kristallisasie in oplossing van hierdie komplekse polimeer sisteme bestudeer. Karakterisering van die polimere was gedoen met kern magnetiese resonans spektroskopie (KMR) en hoë-temperatuur gel permeasie kromatografie (HT-GPC). Die tweede studie het die fraksionering van ‘n PE-1-hekseen ko-polieer met behulp van temperatuurstyging eluering fraksionering (Tref) behels asook die analisering van kristallisasie in oplossing van die verskillende temperatuur fraksies. Belangrike informasie oor die verskillende molekulêre areas teenwoordig in die polimeer was verkry. ‘n Derde addisionele studie was gedoen op die versoenbaarheid in poliolefin mengsels. Twee verskillende mengsels was voorberei: isotaktiese polipropileen (iPP) – lae digtheid polietileen (LDPE) mengsel en iPP – polipropileen impak ko-polimeer (PPIC) mengsel. Daar was gevind dat ko-kristallisasie slegs in die iPP – PPIC mengsel plaasgevind het. Fase skeiding het plaasgevind in die iPP – LDPE mengsels wat tot twee fases gelei het vir alle mengsel komposisies. Kristallisasie in oplossing word gewoonlik gemeet met die konvensionele kristallisasie analise fraksionering (Crystaf) tegniek. In hierdie studie was al die kristallisasie data met Crystaf resultate vergelyk en ‘n goeie korrelasie was gevind tussen die resultate van Crystaf en Scalls. Die grootste voordele van die Scalls tegniek is dat resultate soortgelyk aan diè van Crystaf kan verkry word met baie korter analises en Scalls laat ook toe vir die meting van smeltpunt van die gekristalliseerde polimeer oplossings.

Thesis. 1977. M.S.--Massachusetts Institute of Technology. Dept. of Electrical Engineering and Computer Science. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / M.S.

LIDAR, an acronym for LIght Detection And Ranging, is a system used for studying the scattering of laser light incident on a parcel of air. This thesis investigates the atmosphere above the Durban region using two atmospheric LIDARs, referred to, in this study, as the "old LIDAR" and the "new LIDAR". The old LIDAR was used in a campaign of observation from July to October 1997 in a study of aerosol concentrations over Durban. This thesis will focus on, among other things, the local aerosol profiles for low altitude (0 to 10 km) and high altitude (10 to 35 km). In particular, the focus will shift on any long persistence in this region (it was found that the aerosol layer observed by M. Kuppen (1996) on June 1994 at 25 km may have moved to the higher altitude of 28 km in October 1997. This may be explained by stratospheric upwelling, carrying the layer to higher altitude. These aerosols are known to influence the local climate). This investigation will give some useful insight into the local atmospheric dynamics. The new LIDAR system (Rayleigh-Mie LIDAR) has been used to measure atmospheric temperatures from 20 to 60 km as well as aerosol extinction coefficients from 15 to 40 km. Height profiles of temperature have been measured by assuming that the LIDAR returns are solely due to Rayleigh scattering by molecular species and that the atmosphere obeys the perfect gas law and is in hydrostatic equilibrium (Hauchecorne and Chanin 1980). Since its installation in April 1999, the new LIDAR has been used to monitor stratospheric temperatures and aerosol concentrations from 10 to 40 km. In this study, we discuss in chapter 7 the results of a validation campaign conducted during the period of April 1999 to December 2000. Average monthly LIDAR temperatures are computed from April 1999 to December 1999 and compared with radiosonde temperatures obtained from the South African Weather Service (SAWS) at Durban. The monthly LIDAR temperature profiles over two years (1999 and 2000) were also computed and compared with the climatological model Cospar International Reference Atmosphere (CIRA)-1986 and with the average monthly European Centre for Medium Range Weather Forecast (ECMWF) temperatures . The results show that there is good agreement between LIDAR and SAWS radiosonde temperatures in the 20 and 30 km altitude range. Between 20 and 40 km, the monthly LIDAR temperatures agree closely with the CIRA-86 and ECMWF profiles. However, during winter, in the altitude range 40 to 60 km, LIDAR temperatures are warmer than CIRA-1986 and ECMWF temperatures, and they show large variability. These variations could be due to relatively fast transient phenomena like gravity waves or planetary waves propagating vertically in the stratosphere. As part of the validation process, the aerosol extinction coefficients retrieved from the LIDAR data have also been compared with the extinction coefficients measured by Stratospheric Aerosol and Gas Experiment (SAGE) II close to the LIDAR location and on coincident days. Appendix E of this thesis also investigates the concept of refraction by atmospheric gases as applied to gas lenses. A simple spinning pipe gas lens (SPGL) has been used as the objective lens of a camera to take pictures of the moon and sun spots. The SPGL is a varifocal length lens which depends on the temperature of the pipe and the angular velocity at which it spins. For our purpose a focal length of 8 m has been used. The moon pictures are compared with a lunar map so as to identify the maria. / Thesis (Ph.D.)-University of Natal, Durban, 2002.

Lights is almost always detected by its interaction with matter. One of these interaction phenomena is the scattering of light by small particles. A model is developed that estimates the amount of energy that is scattered towards a detector from a beam given the locations of the source, detector and particle. This collection of particles is allowed to be very dense so that a photon scattered from the beam can be scattered several times before leaving the scattering medium. By considering the single-scatter component and multiple-scatter component separately, the model retains the characteristics of both types.

Thesis (PhD)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: An instrument, named solution crystallization analysis by laser light scattering (SCALLS), that measures the solution melting and crystallization of polymers in solution was developed further in this study. The instrument was tested in a theoretical study to evaluate the Flory-Huggins relationship of melting point depression in solution of copolymers. It was found that the solvent interaction parameter for propylene/higher 1-alkene copolymers, with low comonomer content is dependent on the comonomer type. It was also showed that the melting point depression is dependent on both the type and amount of comonomer included in the copolymer. The instrument was further developed to include a total of three lasers with different wavelengths. Initial problems with laser interference was rectified by the introduction of dichroic mirrors to direct the laser light to the relevant detectors and broad pass filters in front of the the detectors to ensure that only the relevant laser light passes through. For homogenous polypropylene samples it was found that even though a slower cooling rate increases the relative peak temperatures as well as the relative temperature differences between the peaks, detail in the peak profiles is the same for the faster cooling rate. The subsequent heating analysis does show that there is a definite dependence on the cooling rate. The ZNPP-4 sample shows that the appearance of a shoulder in the heating analysis becomes more defined as a peak if the preceding cooling analysis is slower. Complex impact-polypropylene samples, differing only in the amount of ethylene were analysed and even small differences between samples were detected. The possible application of the SCALLS instrument was investigated. It was proven that the instrument can be used as a screening method for prep-TREF to determine the fractionation temperatures. / AFRIKAANSE OPSOMMING: 'n Instrument, genoem oplossing kristallisasie-analise deur laser lig verstrooiing (SCALLS), wat die smeltpunt asook die kristallisasie temperatuur in oplossing kan meet is verder ontwikkel in hierdie studie. Die Flory-Huggins verhouding oor die smeltpunt depressie in oplossing van ko-polimere is ondersoek in ‘n teoretiese studie. Daar is bevind dat die oplossing interaksie parameter vir propileen/hoër 1-alkeen kopolimere, met lae ko-monomeer inhoud is afhanklik op die ko-monomeer tipe. Dit is ook getoon dat die smeltpunt depressie afhanklik is van beide die tipe en hoeveelheid ko-monomeer in die ko-polimeer. Die instrument is verder ontwikkel om 'n totaal van drie lasers met verskillende golflengtes in te sluit. Aanvanklike probleme met laser inmenging is reggestel deur die bekendstelling van dichromatiese spieëls wat die laser lig na die regte ooreenstemmende detektor rig en filters voor die detektors verseker dat net die relevante laser lig die detektor bereik. Vir homogene polipropileen monsters is dit bevind dat selfs al is die analises gedoen teen ‘n stadiger afkoelings tempo wat lei tot ‘n verhoging in die piek kristallisasie temperatuur asook die relatiewe temperatuur verskille tussen die lasers, bly die detail in die piek profiele dieselfde as wat gesien word met ‘n vinniger afkoelings tempo. Die daaropvolgende verhitting analise toon dat die analise definitief afhanklik is op die voorafgaande afkoelings analise. Die ZNPP-4 monster toon dat die voorkoms van 'n skouer in die verwarming-analise word meer gedefinieerd en ‘n piek word gevorm soos die voorafgaande afkoelings tempo verlaag. Komplekse impak-polipropileen monsters, wat net verskil in die hoeveelheid etileen inhoud is geanaliseer en verskille is bepaal. Moontlike toepassings van die SCALLS instrument is ondersoek. Dit is bewys dat die instrument gebruik kan word om die fraksionering temperature vooraf te bepaal vir prep-TREF.