Laser-Power Dependency of Resonant Two-Photon Ionization in Flames

Resonant two-photon ionization competes with laser-enhanced collisional ionization (LEI) in flames to ionize analyte atoms. The predominance of either mechanism for a given element depends on the excitation scheme as well as the level of irradiance. Optical saturation of the resonant transition through which the two-photon mechanism proceeds precludes observation of a second-order dependence of ionization signal on laser power. The laser power dependency of resonant two-photon ionization for a series of elements is examined, and results of diagnostic value regarding the probable ionization mechanisms are obtained.