This thesis details the design and construction of an experiment to measure the radial distribution of laser gain in a cylindrical Helium-Neon laser gain tube. This distribution is important as it can effect the transverse mode structure of a running ring laser. Earlier theoretical models of the distribution were not supported by high quality experimental data and fail to take into account some physical processes. A resolution of 8 parts per million in gain and 50 μm in radial position has been achieved. Gain distributions have been measured and are shown to be well modeled by a 0th order Bessel function with first roots at the tube walls and a central dip depending on excitation power; except for the region very near to the tube walls where a very rapid increase in gain has been observed. Hydrogen has been identified by spectroscopic analysis as the primary constituent of gas contamination and cause of the long term reduction in gain of large ring lasers. Additional work has been done to detect a proposed non-classical Lense-Thirring field around a spinning lead superconductor. It was found that any effect is at least 20 times smaller than predicted. Techniques and tools for data acquisition programming have been reviewed focusing on difficulties with coupling of user interface and application logic, monolithicity, difficulties with scripting and algorithm implementation.

The emergence of Cantilever Neon Signage has accompanied with the grown-up of Hong Kong urban development after World War II. This enormous steel frame covered with bent neon lights has been erected onto the external wall over the streets of Hong Kong city in the past few decades. Its image has been firmly imprinted on every citizen’s memory by its multi-colored and eye-catching gesture. The signal itself embodies part of the social and urban development history of Hong Kong. However, its role in this city has been fading out following with the city’s renewal and advancement in information technology. It is afraid that the Cantilever Neon Signage will end up with a calamitous fate one day as all of them will be eradicated from our city. Throughout this dissertation, we tried to unveil some hidden stories behind this mysterious mask by unravelling the development history and exploring this fading industry in person throughout face-face site visits. The results were astonishing as less people would commit to this handicraft driven industry and it coupled with austere statutory controls which have inevitably halted further potential successors to enter into the industry. / published_or_final_version / Conservation / Master / Master of Science in Conservation

Atomic lifetimes of selected levels in Neon I and Argon I were measured using a method of delayed coincidence. Pulsed rf was used to excite a discharge tube containing the neon and argon gas. The radiation emitted from the excited atoms of the gas was passed through a monochromator so only the desired wavelength would be observed. Each time an excitation pulse ended, the decay of light intensity was detected by a photomultiplier tube. By measuring the decay time of the light intensity using the delayed coincidence technique, the average lifetime of the desired level was determined. The values of lifetimes determined in this study were found to contain considerable error. Several factors contributing to these errors were thought to be the shape of the rf pulses and an effort known as cascading which was caused by the use of rf for excitation of the gas.

The development and implementation of a high resolution, direct absorption, rapidscanning infrared diode laser spectrometer incorporating a supersonic jet expansion source is described. High sensitivity is achieved by directly modulating absorption signals at frequencies in excess of 50 kHz, enabling their separation from lower frequency mechanical and diode 1/f noise. This is accomplished by rapidly scanning the diode laser across a small frequency window (~0.5-1.5cm^-1) synchronously with a pulsed supersonic expansion in a time period of 1 or 2 ms. Absorptions appear as small attenuations in the overall variation of the laser mode power across the scan window. This background profile is removed by recording the laser power without gas pulsing and subtracting. Relative frequency calibration is effected by simultaneously recording the spectrum of a reference gas and the interference fringes of an etalon. Absorption signals are recorded by means of a fast 12-bit analog-to-digital converter operating at 1 MHz. This is housed within a dedicated PC microprocessor which performs spectrometer control, data coaddition, signal processing and spectrum calibration functions. The spectrometer has been used to measure the infrared spectra of two weakly bound complexes, CO-OCS and Ne-SiH₄. The infrared absorption spectrum of CO-OCS was measured in the 5μm region of the OCS ν₃ asymmetric stretch. In addition microwave spectra of CO-OCS and two isotopomers ¹³CO-OCS and CO-OC³⁴S have been recorded using a pulsed nozzle microwave Fourier transform spectrometer. The lines have been fitted to a Watson S reduction Hamiltonian yielding rotational, quartic and (for the ground states) sextic centrifugal distortion constants. A T-shaped structure is determined and this is rationalised by a simple potential model incorporating a distributed multipole analysis of the electrostatic charge distribution, distributed dispersion contribution and a cylindrical hard-core repulsion. The infrared spectrum of Ne-SiH4 was recorded in the vicinity of the SiH₄ ν₃ triply degenerate stretching vibration centred at 2189.19 cm^-1. Ne-SiH₄ is only the second atomspherical top complex to be successfully recorded and analysed. The complex exhibits an intermolecular potential with considerably smaller anisotropy than its argon analogue Ar-SiH₄. Consequently the SiH₄ unit is almost free to rotate within the complex, resulting in novel Coriolis interaction between the angular momentum of the SiH₄ unit and that of the overall complex. Individual bands are fitted to Coriolis interaction Hamiltonians, and the band centres for all the transitions of the complex are fitted to an anisotropic intermolecular potential. Finally, applications of the spectrometer to the study of air sensitive compounds and species generated by electric discharge sources are considered.

This thesis details the design and construction of an experiment to measure the radial distribution of laser gain in a cylindrical Helium-Neon laser gain tube. This distribution is important as it can effect the transverse mode structure of a running ring laser. Earlier theoretical models of the distribution were not supported by high quality experimental data and fail to take into account some physical processes. A resolution of 8 parts per million in gain and 50 μm in radial position has been achieved. Gain distributions have been measured and are shown to be well modeled by a 0th order Bessel function with first roots at the tube walls and a central dip depending on excitation power; except for the region very near to the tube walls where a very rapid increase in gain has been observed. Hydrogen has been identified by spectroscopic analysis as the primary constituent of gas contamination and cause of the long term reduction in gain of large ring lasers. Additional work has been done to detect a proposed non-classical Lense-Thirring field around a spinning lead superconductor. It was found that any effect is at least 20 times smaller than predicted. Techniques and tools for data acquisition programming have been reviewed focusing on difficulties with coupling of user interface and application logic, monolithicity, difficulties with scripting and algorithm implementation.

Thesis (Ph.D.)--Ohio University, March, 2009. / Title from PDF t.p. Includes bibliographical references.

Thesis (Ph. D.)--University of Michigan, 1934. / Cover title. "Reprinted from the Physical review, vol. 47, no. 1, January, 1935."

Thesis (Ph. D.)--University of Michigan, 1936. / Cover title. Running title: Impacts of the second kind. "Reprinted from the Physical review, vol. 51, no. 10, May 15, 1937."

Thesis (Ph. D.)--Ohio University, June, 2004. / Includes bibliographical references (leaves 194-200).

Thesis (Ph. D.)--University of Michigan, 1934. / Cover title. "Reprinted from the Physical review, vol. 47, no. 1, January, 1935."