Fluorescence studies of multiphoton ionization of Sr: Production of excited ionic states

Multiphoton ionization of strontium in the wavelength range of Å558-590 nm is studied via the fluorescence from excited Sr+(5pP32,122) ions. The fine-structure sublevels in the singly charged ion are fully resolved and are found to be nonstatistically populated. Four- and five- (or more) photon processes are observed to populate Sr+(5pP2) in the intensity regime of I∼1-50 GW/cm2, but no emission is detected from higher-lying states of Sr+.