Bibliography: p. 165-179. Electronic publication; Full text available in PDF format; abstract in HTML format. Reports on the development of a scalable high power laser for gravitational wave interferometry. Electronic reproduction.[Australia] :Australian Digital Theses Program,2001.

This thesis presents several observational studies based on radio variability and interstellar scintillation of extragalactic flat-spectrum radio sources. Such sources are commonly called blazars, a term used to describe the phenomenon observed when the jet of a radio-loud Active Galactic Nucleus (AGN) is directed towards the observer. These sources provide unique laboratories for studying the physics of relativistic jets. Observations of selected samples of blazars, made with the Australia Telescope Compact Array (ATCA) and the Australia Telescope Long Baseline Array are presented here. Statistics for long-term (months--years) and short-term (intraday) variability in both total and linearly polarized flux density at several frequencies are presented. The sensitivity and flux density measurement accuracy of the ATCA make it particularly useful for observations of intraday variability (IDV). Resolving the question of what is the mechanism for radio IDV was of great importance at the time this thesis was being undertaken, since if intrinsic, IDV implies extremely high brightness temperatures, far in excess of the Inverse Compton limit for incoherent synchrotron radiation. Most source models are fundamentally based on the assumption that the radiation from radio to optical, and sometimes soft X-ray, energies is produced by the incoherent synchrotron mechanism, so any result which challenges this has serious implications. There is now strong evidence that interstellar scintillation (ISS) is the principal cause of radio IDV, which substantially lowers the implied source brightness temperatures from those calculated assuming intrinsic variability. Some of the results presented in this thesis have made an important contribution to the paradigm shift from IDV to ISS, by showing unequivocally that the rapid IDV observed in PKS 1257-326 is a result of scintillation due to a nearby scattering screen in the ionised interstellar medium (ISM) of our Galaxy. This unusual source, serendipitously discovered during the course of my PhD, has also proved extremely valuable in showing that ISS can be used as a probe of microarcsecond-scale source structure and also of the local Galactic ISM. Such high angular resolution is not currently achievable even with space interferometer baselines. / Thesis (Ph.D.)--Physics, 2003.

Some modern laser applications require continuous wave (CW) high power (>100 W), and diffraction limited performance near 1.064 um. One such laser application with these, and additional, requirements is gravitational wave interferometry. This thesis will report the development of a scalable high power laser for this application. A high-power, single-transverse-mode laser might be produced by intensely pumping the small mode volume within a stable resonator or by using a resonator that has a large transverse mode. Intensely pumping a small volume can lead to crystal fracture and large thermally-induced wavefront aberrations. Using a large transverse mode would also be difficult if using a stable resonator as these are, in general, not suited to fundamental modes that have large cross-sectional areas. Unstable resonators, by comparison, routinely produce fundamental modes that have large cross-sectional areas. They have been used for decades with high-power, high-gain chemical or gas lasers and provide efficient energy extraction, good mode discrimination and beam quality. However, the low gain of Nd:YAG in combination with the high output coupling associated with unstable resonators would limit the efficiency of such a CW laser. One way to utilize the properties of unstable resonators while reducing the output coupling, and thus increase the efficiency, is to use a stable-unstable resonator. These resonators are stable in one plane and unstable in the orthogonal plane, rather than unstable in both planes. The required output coupling can be further reduced without degrading the beam quality by using a Graded Reflectivity Mirror (GRM) as the output coupler. The soft aperturing of the GRM also eliminates diffraction loss associated with scraper mirrors in hard-edged unstable resonators, and enhances mode discrimination. The stable-unstable resonator reported in this thesis is side-pumped by fibre-coupled diode- lasers and side-cooled. It uses a total internal reflection (TIR) zigzag slab geometry, in which the zigzag is co-planar with the pumping and cooling. The resonator is stable in the plane of the zigzag (horizontal) and unstable in the plane orthogonal to the zigzag. In this configuration the strong thermal lensing in the horizontal direction is averaged out by the zigzag. The vertical thermal lens is controlled by Thermo-Electric Coolers (TECs) which are used to adjust the temperature of the bottom and top surfaces of the slab. To test the performance of the side-pumped, side-cooled laser head it was operated initially with a stable resonator. Efficient operation was achieved and will be reported. Control of the refractive index profile (thermal lens) using the TECs on the bottom and top surfaces results in a vertical thermal lens that could be set to any value between 47 mm and 450 mm. The thermal lens encountered by the zigzag mode in the plane of pumping and cooling is weak (horizontal direction) and independent of TEC current. Thus, the thermal lensing in the horizontal and vertical directions is de-coupled, as is necessary for scalability of the mode volume in the vertical direction. A travelling-wave (for ease of injection locking) stable-unstable resonator was investigated using a Fox-Li model, which assumed a greater pump power and mode volume than used for the laser head presented in this thesis. A strip, n=2 super-Gaussian GRM is shown to be the optimum output coupler for the stable-unstable laser. Furthermore, it is shown that the output coupling loss associated with a resonator magnification of -1.3 could be sustained using pump densities below the crystal fracture limit. Useful operation over a realistic range of thermal lens focal lengths is predicted. The validity of the Fox-Li modelling is confirmed using with a standing-wave stable-unstable resonator. The standing-wave resonator was chosen as it suited the available crystal and pump power used for the work in this thesis. The GRM reflectivity profile used the minimum commercially available profile radius. The vertical thermal lens is varied by adjusting the pump power, and then by adjusting the temperature of the bottom and top surfaces at full pump power. This demonstrated CW operation of the standing-wave laser with M=1.3 and good beam quality. Good qualitative agreement with the Fox-Li model of the standing-wave resonator is thus confirmed. Finally, suppression of the multiple longitudinal modes by injection locking is reported. / Thesis (Ph.D.)--Physics and Mathematical Physics, 2001.

Two important applications of the fiber Fabry-Perot Interferometer (FFPI) sensor are investigated: (1) an optical binary switch for aerospace application, and (2) an FFPI weigh-in-motion sensor for measuring the weight of trucks traveling down a highway. In the fiber optical switch, the FFPI sensor is bonded to a copper cantilever to sense the elongation of cavity length induced by force applied to the end of the cantilever via a pushed button. Light from a superluminescent diode light source passes through a scanned Michelson interferometer and is reflected from a sensing FFPI and a reference FFPI to produce a fringe pattern. A secondary interferometer uses a distributed feedback laser light source to compensate for irregularities in the mechanical scanning rate of the moving stage to achieve precision measurement of the optical path difference. The system is calibrated by applying known weights to the cantilever. The elongation measured by the FFPI sensor shows excellent linearity as a function of the force applied, and little hysteresis was observed. By comparing the measured force to a threshold, the system produces a binary signal that indicates the state of the pilotactuated system; i. e., whether or not the button has been pushed. In FFPI weigh-in-motion sensors system, the FFPI sensors are installed in metal bars so that they will experience the strain induced by applied loads and are connected to the Signal Conditioning Unit (SCU). The SCU determines the induced phase shift in the FFPI and produces voltage outputs proportional to the phase shifts. Laboratory Material Testing System tests show that the fiber optic sensor response is a fairly linear function of the axial displacement. In highway tests the FFPI sensors showed strong responses and consistently reproduced the expected characteristics of truck wheel crossings. A falling weight deflectometer was used to calibrate the sensor response and predict unknown loads. All sensors in steel bars and aluminum bars showed excellent repeatability and accurate predictions, with an average relative percentage error within 2%. The study on sensor response variation with applied load positions shows a bell shaped distribution. Truck tests on the road sensors indicate that the repeatability of wheel crossings at similar position is good. The sensor can accurately measure axle spacing, speed, and truck class.

This study is focus on solute concentration ahead of solidification front and base on holographic method by using holographic interferometry. Heterogeneous nucleation of bubbles on an advancing solidification front during freezing of water containing a dissolved gas has been experimentally and analytically studied. The formation of bubbles resulting from supersaturation of liquids is commonly encountered in different fields such as heat transfer, manufacturing, and bioscience.

Thesis (M. Phil.)--University of Hong Kong, 2010. / Includes bibliographical references (p. 65-69). Also available in print.

Thesis (Ph. D.)--University of Queensland, 2002. / Includes bibliographical references.

Thesis (M.S.)--West Virginia University, 2004. / Title from document title page. Document formatted into pages; contains x, 132 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 131).

The concept of using an interferometric process to reduce scattered light in optical systems has been examined from a physical optics viewpoint. An experiment is described which illustrates the basic concepts of a particular scheme addressing the important case of a telescope viewing a distant point object whose image is degraded by scattering from dust on the primary lens. A basic conceptual scheme is described, utilizing a modified Twyman-Green interferometer, which introduces a π phase shift and a focal power difference between the arms. The interferometer is inserted into the optical train of an elementary telescope to null the scattered energy while preserving the image intensity associated with the distant point object, thereby enhancing the signal-to-noise ratio. The effect of this interferometer on the image of a distant point object is examined in detail. Computer techniques were used to solve Lommel function based series representations of the diffraction integral, and generate the intensity distributions which are presented as a series of iso-intensity contour maps. The results indicate that a distant point object could be reimaged successfully. Further analytic evaluations reveal specific operating conditions for the interferometer that optimize the peak intensity at the focal plane. A wavefront model was used to derive the radially dependent intensity distribution at the focal plane from the single on-axis scattering point. To evaluate the effectiveness of the scatter-nulling interferometric technique, an analytic expression for the gain in signal-to-noise ratio was developed, utilizing elementary models of a reimaging system with and without the inclusion of a nulling interferometer. Gains up to a factor of 10⁸ were observed with the assumption of a reasonable set of system parameters and for the limited set of conditions employed. Results imply that the interferometric approach could be successful and effective under restricted conditions. Imagery from the experimental arrangement is presented showing a projection of the concentrated distant source image along with the broad null field from the scattering source.

published_or_final_version / Mechanical Engineering / Master / Master of Philosophy