Can nonresonant multiphoton ionization be ultrasensitive?

A method of surface analysis by nonresonant multiphoton ionization is described and illustrated with an example of analysis consuming ~10−15 gram of a uranium compound (~10−17 mole). The method is chemically general and quantitative for elemental analysis without specially prepared standards. In this method desorbed, sputtered, or evaporated neutral species are photoionized above the surface for subsequent time-of-flight mass spectrometry. Examples are also presented for several atoms of laser-power dependencies of atomic multiphoton ionization including double ionization. Comparisons are made between this analytical approach and resonantly enhanced multiphoton ionization for mass-spectrometric surface analysis.