The role of defects in the rear side laser ablation of MgO at 308 nm

Abstract

Over a range of fluences, 308 nm pulsed laser irradiation of cleaved, single crystal MgO can produce a fluorescent plume on the side of the specimen opposite the incident light (rear side ablation). After one or two laser pulses, linear patterns of melted material are often observed. We present evidence that Fresnel diffraction from heterogeneous features on the front surface control the formation of the localized interactions on the rear side. At fluences below the threshold for plume formation on the front surface, large areas of the rear surface can be melted and ablated without fracture and pitting. At higher fluences, defect accumulation on and near the front surface eventually yields a front surface plume and eliminates the rear surface plume. Mechanical treatments strongly affect the evolution of these features due to the production of strongly absorbing point defects.