Proceedings PaperPhoto-Excited Defects In Laser-Assisted Processing, Damage And Aging
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The transfer of energy from a laser beam to a solid takes place via excitation of the electronic system. At first sight, one would expect that electronic effects might play an important role in the laser-assisted phenomena in materials. Except for very short laser pulses (in the picosecond pulse duration range), experiments show that this is rarely the case. However, evidence for nonpurely thermal effects has been obtained in some circumstances. Analysis of the microscopic mechanisms involved indicates that localised states are always present (at least at some step) in the above mentioned cases. This plus a theoretical examination of the criteria for the existence of electronic effects leads to the conclusion that electronically excited localised states are responsible for various laser-assisted phenomena. In order to arrive to a good understanding of these effects, a model for the cohesion of electronically excited localised states is first given. The theoretical model is then applied to various laser-assisted phenomena: surface reactions, oxidation, nucleation and growth, damage and aging. For surface reactions, photons may excite some reactive species selectively. This is introduced in the kinetic equations of some reaction. It is found that it is possible to describe various cases of reaction rates versus incident laser fluence by using the theory. Laser-assisted oxidation is studied in the framework of the Deal-Grove formalism, modified in order to take into account localised electronic excitation. The problem of laser-assisted damage and aging is approached theoretically via the migration of defects or impurities.