Thesis (Ph.D.)--University of Melbourne, Dept. of Physics, 2005. / Typescript. Includes bibliographical references (leaves 205-223).

Thesis (M.S.)--Texas State University--San Marcos, 2008. / Vita. Includes bibliographical references (leaves 50-51). Also available on microfilm.

Thesis (Ph. D.)--University of Florida, 1981. / Description based on print version record. Typescript. Vita. Includes bibliographical references (leaves 220-224).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1984. / Typescript. Vita. Description based on print version record. Includes bibliographical references.

Th.--Sci. phys.--Grenoble 1, 1984. N°: 127.

The design, implementation and commissioning of a time-resolved electron energy spectrometer system are discussed. Since its installation at the FELIX free-electron laser user facility in Nieuwegein, The Netherlands, the spectrometer system has been in regular use as a diagnostic and investigative tool. The system provides 0.2% energy resolution with 32 channels, and time resolution of 50 ns. The spectrometer is positioned immediately following the undulator so that the gain medium—the relativistic electron beam—can be probed immediately following its interaction with the optical field in the laser cavity. The system permits real-time calculation and graphical display of key beam parameters as well as the archiving of raw data, and has been used to provide insight into the operation of an FEL in the high slippage, short pulse regime. In particular, direct measurement of the extraction efficiency is possible from macropulse to macropulse. A systematic study of efficiency as a function of wavelength and cavity desynchronisation has been undertaken. At low values of cavity desynchronisation the efficiencies measured exceed the conventional 1/2/V estimate by between 50% and 100% and these results are shown to be consistent with the formation of ultrashort optical pulses—approximately of 6 optical cycles in length. An investigation into the way in which the electron beam energy can be swept on a microsecond time scale has made it possible to produce given sweeps in wavelength—of up to 2 %, limited only by the constraints of the electron beam transport system—which have been used by molecular spectroscopists to excite target molecules through an anharmonic ladder of states. Further evidence for the recent observation of superradiance in an FEL oscillator has been provided by an investigation which shows that the efficiency and intracavity power of the radiation scale respectively as the inverse square root and the inverse square of the cavity losses, verifying the superradiant scaling laws predicted by the supermode theory. An important consequence of this observation is that it indicates that shorter and more intense optical pulses may be produced by increasing the bunch charge and reducing optical cavity losses.

No description available.

A central paradigm for classifying the phases of correlated electron systems is their symmetry. Having the ability to controllably tune symmetry-related properties of the system is therefore a powerful probe. In this thesis experiments on quasi-two-dimensional metals Sr₃Ru₂O₇ and Sr₂RuO₄ are reported, where uni-axial strain was used as a means of lifting the native tetragonal symmetry. Uni-axial strain was applied to the samples using a piezo-electric based device which can apply both positive and negative strains to the sample, to study the symmetry of the response about zero strain. Sr₃Ru₂O₇ exhibits a magnetic-field-tuned quantum critical point, in the vicinity of which a novel phase is stabilized. The transport properties of the phase were previously shown to be highly susceptible to in-plane magnetic fields. We show that resistivity inside the phase responds strongly to strain applied along one of the in-plane crystal axes, with the responses parallel and perpendicular to that of the applied strain mirroring each other about zero strain. Our results suggest that the underlying symmetry of the phase is C₄ rather than C₂ symmetric. Sr₂RuO₄ is an unconventional superconductor which was predicted to have an order parameter of the form pₓ ± ip[sub]y. This should result in a splitting of the transitions of the two components as a function of strain, with a cusp in T[sub]c versus strain at zero strain, where T[sub]c is the upper of the two transitions. We find that the response of T[sub]c to strain along [100] is large and symmetric about zero strain, whilst the response to [110] strain is weak and mostly anti-symmetric. No cusp is observed for either strain direction. We argue that although our results are in contradiction with the simplest pₓ ± ip[sub]y models, they may still be consistent with certain scenarios where the cusp would have been too small to be observed.

From Introduction: The minimum in the scalar magnitude of the geographic total field, which lies off the coast of Brazil, allows the mirror points of trapped particles to dip low into the atmosphere over the South Atlantic Ocean, resulting in two regions of maximum intensity of preciptated particles in that region, one from the inner belt and one from the outer. High charged particle fluxes have been observed at low altitudes over these regions by satellites Sputnik 5 and 6 (Ginsburg et al, 1961) and Discoverer 31 (Seward and Kornblum, 1963) amongst others. The more southerly of these two regions acts as a sink for electrons from the outer radiation belt and will be referred to in what follows as the Southern Radiation Anomaly. Gladhill and van Rooyen (1963) predicted that the energy deposited in the upper atmosphere by these charged particles would be sufficient to give rise to enhanced geophysical effects such as auroral emission, X-rays and ionization and heating of the upper atmosphere in this region. Although some of these effects have been correlated with precipitated electrons, no definite relation had until now been established between ionospheric effects and precipitated particles. The aim of this thesis was to investigate such a relationship and the results were extremely successful. It will be shown conclusively in what follows, that the precipitation of electrons can account for the ionospheric disturbances defined by a disturbance criterion at all stations around L=4. Part I describes the exploration of the radiation belts and the magnetosphere with rockets and satellites. The resulting theoretical models based on the observations are discussed. A brief review is given of the work that has been done to date to derive equations for the loss and replenishment of particles in the belts. Because of the complexity of these and the number of doubtful factors involved, a simple model of injection of electrons into the outer belt is devised, giving average values of trapped and precipitated electron fluxes at any point around L=4. In Part II, this model is employed together with the disturbance criterion of Gledhill and Torr (1965) to examine the relationship between ionospheric disturbances and electron fluxes. Also the energy range of the precipitated particles is examined.

As early as 1896, around the time of the discovery of the electron by J.J. Thompson, Birkeland was led to propose that aurorae were caused by fast moving electrons or similarly charged particles emitted by the sun and 'sucked in towards' the auroral zones by the geomagnetic field. He later supported this idea by firing electrons at a dipole field surrounding a sphere covered with a fluorescent coating. Extensive ground based observations of auroral features eventually led, in 1950, to the initial direct evidence of the fact that auroral emissions are due to energetic charged particles, consisting partly of protons, entering the earth's atmosphere (Meinel, 1951). However, it was only in 1952 and 1953 that the first measurements of what was later interpreted as bremsstrahlung X- rays from precipitating electrons were made at auroral latitudes. (Meredith et aI, 1955) During the IGY, 1957 - 1958, a number of rockets were fired through and near, visible aurorae and large fluxes of low energy electrons were detected ... Intro., p. 1.