This award will support a long-term visit of nine months by Professor M. Quinn Brewster, Department of Mechanical and Industrial Engineering, University of Illinois at Urbana- Champaign, to Japan for a cooperative research project with Professor Yukio Yamada at the Mechanical Engineering Laboratory (MEL), Agency for Industrial Science and Technology, Ministry of International Trade and Industry. The research will include a study of the picosecond time-resolved spectroscopy of laser plumes. A major problem associated with laser material processing is achieving efficient coupling of laser energy into the workplace. This coupling is governed by complicated, non- linear mechanisms at the target and above the target surface in a plume/plasma/shock wave generated by laser-material interaction. Various studies have shown sharp decreases in the transmissivity and/or thermal coupling coefficients associated with plume formation. Characteristics of the plume are largely unknown, but are known to depend upon incident laser flux level. This research addresses the difficult problem of shedding more light on the structure of, and heat transfer mechanisms in, the plume formed above Al targets when irradiated by high power lasers. This research supports a companion NSF-sponsored study which has as a primary objective the development of techniques which can be used to determine the relative importance of plume absorption, scattering, and emission on coupling of laser energy into metal targets. Results of the research have the potential of optimizing and expanding the use of lasers in materials processing. The facilities at MEL are state-of-the-art and include high power processing lasers, rapid scan spectrometers, and picosecond, pulsed dye lasers and photo-oscilloscopes. This type of equipment is found in only a few laboratories in the world. The combination of modern experimental facilities and experience in application of picosecond time-resolved spectroscopy on the part of the Japanese host researcher and experience in high-power laser-material interaction on the part of the U.S. principal investigator offers a unique opportunity to expand the knowledge- base of a technology which is of critical importance to U.S. industrial competitiveness.
