This paper is an attempt to reconstruct how C.V. Raman, a peripheral scientist in the early 20th century colonial India, managed to develop a research programme in physical optics from his remote colonial location. His attempts at self-training and self-education eventually led him to the discovery of the Raman Effect and to the Nobel Prize in Physics in 1930. In trying to re-construct an account of the ways in which Raman developed his research programme in optics by grasping various elements of a scientific practice from the Western scientific community, we see how a newcomer in science could be surprisingly creative in achieving new breakthroughs, and how through such efforts he or she can establish new trading zones with another established community that has the potential to develop into independent practices.

No description available.

Four sol-gel systems (alumina, aluminum hydroxide, zirconia, and magnesia) were investigated, primarily by laser spectroscopy, on several series of materials prepared by systematically varying the synthesis procedures. Key material phases analyzed were: (1) nanocrystalline boehmite [AlO(OH)]; (2) bayerite, nordstrandite, and gibbsite [Al(OH)₃ polymorphs]; (3) amorphous zirconia [a-ZrO₂]; and (4) magnesite [MgCO₃], hydromagnesite [4MgCO₃·Mg(OH)₂·5H₂0], and magnesia [MgO]. Crystal nucleation and crystal growth kinetics were studied in several cases, with x-ray experiments carried out to calibrate the Raman-scattering technique I developed for monitoring crystallite size. Nanocrystalline boehmite, γ-AlO(OH), was found to be the principal component in the sol-gel alumina system. Materials were prepared by the hot-water hydrolysis/condensation of Al(OC₄H₉)₃, the Yoldas process, as a function of process variables such as the time spent in the sol phase. Small but systematic changes, as a function of sol aging time, were discovered in the lineshape and position of the dominant boehmite Raman band observed in the alumina hydrogels. These spectral changes were interpreted in terms of nanocrystallinity-induced finite-size effects associated with the slow growth of AlO(OH) nanocrystals in the sol. X-ray diffraction experiments were used to determine nanocrystal sizes (as small as 3 nm for gels prepared from fresh sols) and to estimate growth kinetics from the Raman-lineshape results. These results appear to be among the first available for crystallite growth kinetics (ripening) in the near-atomic-scale nanocrystal regime. The Raman peak-position shift is proportional to L^-α, where L is the average nanocrystal size and α is a Raman-versus-size scaling exponent. For AlO(OH), I determined α to be 1.0, close to the scaling-exponent values reported for graphite and BN and different from the values (about 1.5) that describe the reported behavior of Si, Ge, and GaAs. The trihydroxide polymorph system is closely related to the sol-gel alumina system. The processing temperature and the method of hydrolysis were varied, in order to determine their effect on the trihydroxide phase mix. The trihydroxide phase mix does not change with time; it depends only on the initial hydrolysis conditions. Bayerite is the primary phase present for materials processed at 25 C, while nordstrandite is the primary phase present for materials processed at 60 C. It is shown that the trihydroxide crystal nucleation kinetics are responsible for the Al(OH)₃ phase mix. Hydroxide/oxyhydroxide phase-mix kinetics were also studied; this ratio increases with time. The associated rate constant decreases with increasing temperature. Sol-gel zirconia was prepared by using atmospheric water to hydrolyze a mixture of zirconium propoxide, acetic acid, and n-propanol. This produces a clear gel. Hydrogen peroxide was found to chemically react with the gels. Clean Raman spectra reveal a broad-band structure (the full width at half maximum is 150 cm⁻¹) centered at about 460 cm⁻¹. This band is interpreted as the signature of an amorphous phase of zirconia. Raman and luminescent spectra (both obtained on the Raman spectrometer) were used to monitor the conversion of magnesium-carbonate-based materials to magnesium oxide, as a function of temperature. This new phase-determination technique utilizes the krypton 674.1 nm laser line so that the carbonate symmetric-stretch band and the MgO:Cr⁺⁺⁺ luminescence band are readily observable on the same spectrum. / Ph. D.

No description available.

Thesis (MSc)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: The efficient manipulation of various nonlinear optical processes frequently requires the shaping of the laser beams used for these processes. Three beam shaping techniques were investigated in this thesis. The focussing of Gaussian laser beams was investigated analytically, in order to efficiently manipulate the focussed beam characteristics. The beam-shaping characteristics of a diffractive optical element (DOE) was investigated numerically, which illustrates the beamshaping capability of the DOE, and identifies the critical parameters in experimental situations. The use of a waveguide as beam shaping device was investigated analytically and experimentally, and characterized for use with the available tunable laser sources. A Raman laser, or Raman shifter, employs stimulated vibrational Raman scattering to generate laser radiation at shifted frequencies. The waveguide was successfully applied as a beam shaping device in the Raman laser system, for optimisation of the process. The Raman laser system was investigated experimentally and characterized for use with the available tunable laser sources. The successful generation of laser radiation at shifted frequencies illustrates the usefulness of the system for generating tunable red-shifted frequencies. The results of this work allow the simple and efficient application of the Raman laser to generate laser radiation at shifted frequencies, in particular tunable infrared laser radiation which is desirable for molecular spectroscopy. / AFRIKAANSE OPSOMMING: Nie-liniêre optiese prosesse kan meer effektief benut word deur die vervorming van die laserbundels wat gebruik word in die prosesse. In hierdie tesis word drie laserbundel-vervormings tegnieke ondersoek. Die fokussering van Gaussiese laserbundels word analities ondersoek, om die gefokusseerde bundel se eienskappe effektief te manipuleer. Die bundel-vervormings eienskappe van ’n diffraktiewe optiese element word numeries ondersoek, wat die effektiwiteit van die bundelvervorming en die sensitiewe parameters in die sisteem uitwys. Die gebruik van ’n golfgeleier as ’n bundel-vervormings tegniek word ook analities en eksperimenteel ondersoek, en gekarakteriseer vir gebruik met die gegewe golflengte-verstelbare laser sisteme. ’n Raman laser, wat gestimuleerde vibrasionele Raman verstrooiing gebruik om laser lig te genereer by Stokes-verskuifde frekwensies, word ondersoek. Die golfgeleier word effektief gebruik as ’n bundel-vervormings tegniek in die Raman laser, om die bogenoemde nie-liniêre proses te optimeer. Die Raman laser was eksperimenteel ondersoek en gekarakteriseer vir gebruik met die gegewe golflengte-verstelbare lasers. Laser lig by verskuifde golflengtes is suksesvol gegenereer, wat die bruikbaarheid van die sisteem illustreer. Van belang is spesifiek verstelbare infrarooi laser lig, wat gebruik kan word in die laser-spektroskopie van molekules. Die resultate van hierdie werk lei tot die eenvoudige en effektiewe gebruik van die Raman laser, om langer golflengtes in die infrarooi gebied te genereer met ’n gegewe laser in die sigbare gebied.

published_or_final_version / abstract / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Master / Master of Philosophy

Medidas eletroquímicas, incluindo cronoamperometria, voltametria cíclica, procedimentos eletroquímicos de envelhecimento de filmes superficiais, espectroscopia de absorção no infravermelho, espectroscopia Raman in situ e ex situ, incluindo o efeito SERS, foram empregados no estudo da redução eletroquímica de íons perclorato a cloreto sobre eletrodo de estanho. Solução de perclorato de sódio 0,5 mol L-1 foi utilizada como eletrólito. Observou-se que a concentração máxima de cloreto produzida em decorrência da redução de íons perclorato (5,0 x 10-5 mol L-1) ocorre na região de potenciais localizada no final da contribuição de corrente da dupla camada elétrica e início da região de desprendimento de hidrogênio. A concentração limite de cloreto é decorrente do estabelecimento de um equilíbrio entre os íons cloreto na solução e cloreto adsorvido que inativa os sítios na superfície, impedindo a continuidade do processo. Programas de perturbação de potencial visando a eletromodificação da superfície do estanho foram aplicados, com o objetivo de verificar a ocorrência de mudanças das propriedades eletrocatalíticas dessas superfícies. A influência das variáveis, velocidade da perturbação, tempo de duração e limites de potencial na cinética de redução de perclorato e na concentração máxima de cloreto foi estudada. Em todos os casos a concentração máxima de cloreto detectada na solução foi de 2,0 x 10-5 mol L-1, exceto no tratamento de ativação eletroquímica quando essa concentração atinge 5,0 x 10-5 mol L-1. A influência da presença de óxidos superficiais, temperatura e agitação da solução, pH, e tempo de polarização no processo de redução de perclorato também foi avaliada. Concluiu-se que (i) a presença de óxidos catalisa o processo de redução; (ii) a influência da temperatura é significativa a 70 °C; (iii) a agitação e o pH da solução não exercem influência na concentração máxima de cloreto produzida e (iv) a concentração máxima de cloreto estabiliza-se após cerca de 150 minutos de polarização. / Electrochemical measurements including chronoamperometry, cyclic voltammetry, film surface electrochemical ageing procedures, FTIR and Raman spectroscopy including the SERS effect were carried out in order to study the electrochemical reduction of perchlorate ions at tin electrodes. Sodium perchlorate solution 0.5 mol L-1 was employed as electrolyte. It was observed that maximum chloride concentration produced by the perchlorate reduction (5.0 x 10-5 mol L-1), takes place within a potential range comprising the negative side of de double layer region and the positive side of the hydrogen evolution region. The upper limit of chloride concentration occurs due to the establishment of an equilibrium between the chloride ions in solution and the adsorbed chloride ions that blocks the surface sites where the reduction process takes place. In order to electromodify the tin surface, the electrode was subjected to perturbing potential programs, aiming to evaluate changes in the electrocatalytic properties of the modified sufaces. The influence of the experimental variables perturbation sweep rate as well as perturbation time and potential limits on the perchrolate reduction kinetic and on the maximum chloride concentration was studied. Except to the activation treatment, the maximum chloride concentration was 2.0 x 10-5 mol L-1 for all the applied perturbation programs. The influence of the oxides on the electrode surface, stirring, temperature, pH and polarization time on the reduction process was evaluated too. It was shown that (i) the presence of oxides on the electrode surface favors the reduction reaction; (ii) there is significant influence of temperature at 70 °C; (iii) pH and stirring the solution exerts no influence on the maximum chloride concentration produced and (iv) the maximum chloride concentration produced by electroreduction is reached after 150 minutes.