Made available in DSpace on 2014-10-09T12:46:03Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:05:30Z (GMT). No. of bitstreams: 1 07494.pdf: 2575009 bytes, checksum: ef57996bcc391004d1ab919499f11556 (MD5) / Dissertacao (Mestrado Profissionalizante em Lasers em Odontologia) / IPEN/D-MPLO / Instituto de Pesquisas Energeticas e Nucleares, IPEN/CNEN-SP; Faculdade de Odontologia, Universidade de Sao Paulo

Made available in DSpace on 2014-10-09T12:27:31Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:08:09Z (GMT). No. of bitstreams: 0 / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Neste trabalho s€o apresentadas as medidas do coeficiente de multiplica€o gasosa (α) no isobutano puro obtidas com uma cƒmara de placas paralelas protegida contra descargas por um eletrodo de vidro (anodo) de elevada resistividade (ρ = 2 x 1012.cm). O m†todo empregado foi o de Townsend pulsado, onde a ioniza€o prim‡ria † produzida pela incidˆncia de um feixe de laser de nitrogˆnio em um eletrodo met‡lico (catodo). As correntes el†tricas medidas com a cƒmara operando em regime de ioniza€o e de avalanche foram utilizadas para o c‡lculo do coeficiente de multiplica€o gasosa pela solu€o da equa€o de Townsend para campos el†tricos uniformes. A t†cnica utilizada foi validada pelas medidas do coeficiente de multiplica€o gasosa no nitrogˆnio, um g‡s amplamente estudado, e para o qual se tem dados bem estabelecidos na literatura. Os coeficientes de multiplica€o gasosa do isobutano foram medidos em fun€o do campo el†trico reduzido no intervalo de 139Td a 208Td. Os valores obtidos foram comparados com os simulados pelo programa Imonte (vers€o 4.5) e com os ‰nicos dados existentes na literatura, recentemente obtidos pelo nosso grupo. Esta compara€o demonstrou que os resultados s€o concordantes dentro dos erros experimentais. / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP / FAPESP:07/06773-0

The effect of the refraction of a laser beam propagating through three different phase objects, i.e. a laser produced plasma and two different gas media, is investigated in this thesis. It is shown that these effects have useful applications. As an introduction to the work performed, a basic discussion of the theory of light is given. In the first experimental study, the accuracy of using the Refractive Fringe Diagnostic, as a tool to determine the electron density profiles of laser produced plasmas, is investigated [Buccellato et al. (1992)]. A comparative study is performed between an established method of determining the electron density profiles of laser produced plasmas, i.e. Nomarski interferometry, and the Refractive Fringe Diagnostic, by comparing experimental data obtained from the same laser shot. For the electron density profiles investigated, it is shown that the Refractive Fringe Diagnostic over-estimates the electron density by an order of magnitude. It is suggested that the electron density errors are due to the inherent assumptions of the Refractive Fringe Diagnostic. To verify this, a numerical simulation into the accuracy of the RFD is performed on a mathematically modelled plasma. The discrepancy in the numerical results are consistent with those of the experimental results and these can be attributed to the assumptions made by the Refractive Fringe Diagnostic. Laser light refracted by a gas medium, with a specific density profile, may produce a near diffraction limited focal spot. The remaining two experimental investigations deal with two novel gas lenses: the Pulsed Gas Lens and the Colliding Shock Lens. A radially expanding cylinder of gas produces a suitable density structure to focus laser light. A design of a gas lens, the Pulsed Gas Lens, using this principle is proposed as a final focusing lens for a laser fusion power station [Buccellato et al. (1993a)]. To establish the feasibility of such a lens a proof-of- principle design for the lens is given. A numerical simulation of this lens is performed by modelling the gas flow from the lens and raytracing through the determined density profiles inside the lens. It is found that this lens can be used as a focusing element. To establish certain practical aspects of the proof-of- principle design, a beam deflection device was constructed and tested. This beam deflection device models the lensing principle of the proposed lens. The laser beam deflection observed did not match the computed deflection. The opening mechanism for the proof-of-principle design did not produce an instantaneous opening of the chamber as was assumed in the simulation. The opening mechanism must be modified to decrease the opening time. Diverging spherical shock waves, produced by pairs of opposing electrodes evenly spaced on a circumference, produce a converging cylindrically symmetric shock wave. After convergence a suitable density structure exists for near diffraction li.mited focusing to occur. It is found that the Colliding Shock Lens is a varifocal lens: the focal length and lens diameter increase with time [Buccellato et al. (1993b)]. A numerical simulation is performed to model the operation of the Colliding Shock Lens. The numerical results compare favourably with the experimental results. From the simulation it is established that the lens diameter can be scaled up by increasing the physical size of the lens and the input energy to the lens. Potential applications of the colliding shock lens are discussed. To conclude this thesis, the results of the separate investigations are summarised. / Thesis (Ph.D.)-University of Natal, 1994.

Research towards the development of a gas-discharge fibre laser using noble gases, with target emission wavelengths in the mid-IR. Additional and separate work on gas treatment methods for managing the formation of photo-induced defects in silica glass.

No description available.