INTERACTIONS OF WIDE BAND-GAP SINGLE-CRYSTALS WITH 248 NM EXCIMER-LASER RADIATION .1. MGO

The emission of charged and neutral particles from single-crystal MgO irradiated with pulsed 248 nm excimer laser light is studied by means of quadrupole mass spectrometry, time-resolved emission spectroscopy, luminescence spectroscopy, and scanning electron microscopy (SEM) obse rvations. The role of the initial distribution of near-surface defects plus defects which result from repeated application of laser pulses i s explored. This increase in defect density eventually leads to format ion of a visible plume and rapid material vaporization. SEM observatio ns after irradiation indicate that substantial surface fracture is pre sent prior to the onset of rapid vaporization. Defect production durin g irradiation is attributed to mechanical processes involving deformat ion and fracture with accompanying dislocation motion. The accumulatio n of these defects increases laser absorption in the near-surface regi on resulting in rapid thermal etching and cluster emission.