Surface Analysis with 1014-1015 W cm2 Laser Intensities

Very high laser intensities (1014–1015 W cm-2) have been used to photoionize both sputtered and gaseous samples. The cross-sectional spatial intensity distributions of a 35 ps, 532 nm laser beam have been analyzed by direct optical imaging and show near-diffraction limited and near-Gaussian profiles at and near focus. Experimental results from sputtered atoms and gaseous atoms and molecules demonstrate that the high laser beam quality combined with the high power density leads both to the saturation of photoionization of species with very different ionization potentials and to a sharply defined ionization volume with well-characterized spatial distributions. It is possible not only to make a quantitative surface composition analysis under high sensitivity conditions using high-intensity multiphoton ionization but also to drive the relative sensitivity factors towards unity. This work demonstrates the feasibility of performing quantitative surface and material analysis under high sensitivity conditions by using very high-intensity non-resonant multiphoton ionization.