Mechanisms of excimer laser desorption and ablation from wide band-gap materials: the role of defects

In single crystal MgO, which is a wide bandgap, nominally transparent material, exposure to single pulses of 248 nm excimer laser radiation results in substantial interaction including extensive biaxial deformation and cleavage. We present evidence that achieving intense emission of atomic, molecular, and ionic particles depends on point defect production by laser-induced deformation and fracture. Defect production via dislocation motion yields orders of magnitude increases in laser vaporization, including neutral cluster formation. The field of moving atoms associated with a variety of dislocation structures (e.g., jogs) in turn produce point defects. We have developed new methods using the excimer laser itself to image the photoluminescence generated by these defects. In MgO, this results in a distinct 400 nm emission band which is due to clusters of oxygen vacancies occupied by electrons (F-centers)