Mathematics – Logic
Scientific paper
Jan 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994phdt........33p&link_type=abstract
Thesis (PH.D.)--UNIVERSITY OF CALIFORNIA, BERKELEY, 1994.Source: Dissertation Abstracts International, Volume: 56-05, Section: B
Mathematics
Logic
2
Scientific paper
This study examines the physics of the liquid -vapor phase transition phenomenon induced by nanosecond -pulsed ultraviolet laser irradiation. This work is concerned with the science and technological applications of the phenomenon of rapid nucleation and explosive vaporization of a liquid in contact with a pulsed-laser heated solid surface. The thermodynamics of the phase transition, the kinetics of collective bubble growth and collapse, and the transient development of pressure field have been investigated experimentally by various fast optical sensing techniques. The purpose of this study is to provide new insight into the physics of the liquid-vapor transition and the interaction between laser and liquid-solid interface. A detailed study on the practical aspects of a novel technological application, the laser cleaning technology, is also included. A model system investigated throughout this work is pure water, methanol, or isopropanol in contact with a solid chromium surface that is heated by ultraviolet KrF excimer laser pulses of nanosecond duration. The dynamics of bubble nucleation, growth, and collapse is studied by optical specular reflectance and scattering probe, which isolates the onset of phase transformation with great accuracy. The thermodynamics of phase transition and metastability of liquid matter have been studied by transient photothermal reflectance probe, which monitors the transient temperature field non-intrusively with nanosecond time resolution. The transient response from the photothermal reflectance probe which utilizes temperature-dependent optical properties of an embedded thin film sensor are coupled with heat transfer modeling results in order to predict the thermodynamic condition for the vaporization in nanosecond time scale. The generation of transient pressure pulses by bubble growth and the effect of static pressure on the phase transition are studied by the piezoelectric transducer probe, photoacoustic probe beam deflection technique, and a high-pressure cell. The onset of phase change introduces a strong acoustic signal that is detected by a piezoelectric transducer and a photoacoustic probe. The information on the temperature and pressure development during the vaporization process determines the heat and momentum transfer in the explosive vaporization process. The pressure production mechanisms in the short-pulsed laser-induced vaporization are studied theoretically and experimentally. It is shown that the collective bubble growth is an effective momentum transfer mechanism to radiate acoustic energy. It is observed that the thermally driven phase change generates pressure waves in the liquid that trigger subsequent acoustic cavitation. The implications of the thermal nucleation on the following cavitation is studied. It has been found that the metastabilized microscopic bubbles can exist for much longer time than the apparent life time, subsequently enhancing the following acoustic cavitation. As an example of technological application of the phenomenon, a practical laser cleaning technique has been studied. A laser-cleaning tool capable of removing surface contaminants such as submicron-sized particulates and organic films has been constructed and implemented in practical use.
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