Effect of tribological wear on ultraviolet laser interactions with single crystal NaNO3 and CaCO3

We report measurements of the neutral and ion emissions accompanying laser irradiation of cleaved and abraded NaNO3 and CaCO3. In both materials, abraded surfaces yield especially intense positive ion emissions during laser irradiation at low fluences (i.e., fluences well below those required for surface damage and/or the formation of a fluorescent plume). Abraded NaNO3 also yields extremely intense neutral emissions (NO, O-2) derived from NO; decomposition. Measurements of neutral molecules released during abrasion show significant anion-derived emissions from both materials (CO2 from CaCO3; NO from NaNO3). We attribute the effect of abrasion on the laser-induced emissions to the production of easily photoionized electron traps during abrasion. Such traps are expected to strongly enhance photoinduced ion emission from both materials. Because the NO3- ion undergoes dissociative electron attachment, photoionizable defects also enhance NO emission during laser irradiation. In contrast, the CO32--anion does not appear to undergo dissociative electron attachment and no enhancement of CO2 emission is observed during laser irradiation. (C) 1996 American Institute of Physics.