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The scattering of laser light by laboratory plasmas has been observed. When the scattering was from a plasma formed in a θ-pinch, with scattering angle of 90° , a nearly Gaussian profile of the scattered intensity as a function of wavelengths was observed, corresponding to scattering by non-interacting electrons. When the scattering was from a plasma jet, with scattering angle of 45° from the forward direction distinct satellite peaks were observed on both sides of a narrow central peak at the laser frequency as predicted by theory, 1,2,3,4 indicating a strong collective scattering effect between the electrons and the ions. The widths of the satellite lines were greater than the values predicted by theory. The discrepancy is ascribed to spatial variations in the electron density in the volume of the observed plasma. The intensities and frequencies at-which they occur these peaks also vary with the current of the plasma jet in a manner consistent with theory. The scattered intensity of the central peak was measured approximately and it agrees with theoretical prediction. Some indication of perturbation of the plasma by the incident laser light has also been observed. 1. E.E; Salpeter, Phys. Rev. 120, 1528(1960). 2. J.A. Fejer, Can. J. Phys. 38, 1114(1960). 3. J.P, Dougherty and D.T. Farley, Pro. Roy. Soc. (London) A259, 79(1960). 4. M.N. Rosenbluth and N. Rostoker, Phys. Fluids 5., 776(1962). / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The enhancement of the scattered light signal due to the mixing of two optical beams in a plasma has been observed. The two beams are produced in a dual-cavity organic dye laser pumped by a Q-switched ruby laser. The plasma is generated by a Helium plasma jet. In normal scattering a distinct satellite is observed on either side of the incident ruby wavelength 6943Å. The presence of enhanced oscillations is demonstrated by a significant increase in the intensity of one of these satellites when the dye lasers are tuned such that the difference in their frequencies is equal to the normally-observed resonant frequency of the plasma. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1995.

Carbon nanotubes, and particularly single wall carbon nanotubes (SWNTs) have attracted much attention for their unique structure, as well as for their excellent mechanical, electrical and thermal properties. Most properties of carbon nanotubs are closely related with its anisotropic structure and geometry factor. Characterization of carbon nanotube length is critical for understanding their behavior in solutions as well as in polymer composites. Microscopy, particularly atomic force microscopy, has been used for their length measurement. Microscopy, though straightforward, is quite laborious, particularly for statistically meaningful sampling. Light scattering can be used to measure particle dimensions. In this study, light scattering has been used to study polyvinyl pyrrolidone (PVP) wrapped SWNTs surfactant assisted aqueous dispersion and SWNT dispersion in oleum. To determine the length of SWNTs, Stokes - Mueller formalism was used, which is a universal model for particles with any size and shape. The Mueller matrix for an ensemble of long, thin cylinders proposed by McClain et al. was used in this study. This Mueller matrix includes the information of size (length and radius) and optical constants (refractive index and extinction coefficient) of cylinders. In this matrix, extinction coefficient, radius and length of SWNTs are unknown. By normalizing scattering intensity I(theta) (theta from 30 to 155 degree) to that at 30degree , the effects of radius and extinction coefficient were cancelled out. Thus, the effect of SWNT length on scattering intensity could be studied independently. A series of curves of normalized scattering intensity of SWNTs (I(theta) /I(30degree)) with varied length as a function of wave vector were predicted. A curve of normalized scattering intensity of SWNT as a function of wave vector was also obtained experimentally. By comparing experimental and predicted curves, average SWNT length in the dispersion has been determined. Scattering intensity at a given angle initially increases with concentration, and then reaches a critical concentration(C*), above which the scattering intensity decreases. This phenomenon has been attributed to the competition between scattering and absorption of light by the presence of SWNT. By using Beer-Lambert law, this phenomenon has been used to determine the molar absorption coefficient of SWNTs.

No description available.

No description available.

No description available.

The distribution of particles in the Eastern Pacific Ocean was investigated from 2 January to 14 February, l969, on the YALOC-69 cruise of Oregon State University. The size distributions were well fitted by the two-parameter Weibull distribution function, with a predominant number of them nearly exponential in distributional shape. Although particles smaller in diameter than 1i could not be measured, extrapolation of the Weibull distribution into the small particle range indicated the median particle diameter was smaller than 1μ. Measurements of light scattering were taken simultaneously with the particle size determinations. A linear relationship between the total particulate surface area and the volume scattering function, β(45°) was indicated, as well as between β(45°)/β(135°) and the mean particle diameter of distributions sharing a common shape parameter. Five different characteristic distributional shapes were found which typified all but a few of the distributions. No direct relationship was found between the distributional shapes and the water types encountered on the cruise. The first-order exponential shapes of the size distributions suggest that a detrital decay mechanism of the larger particles (i. e. phytoplankton) could be a dominant factor in determining the small particle end of oceanic particle distributions. / Graduation date: 1970