Fluorescence studies of multiphoton ionization of Ca and Sr: Emission from highly excited ionic states

Multiphoton ionization of Ca and Sr was studied at a wavelength of 532 nm with optical pulses of 12-ns and 35-ps duration. Excess photon absorption followed by autoionizing decay leads to populations of excited states of singly charged ions that can be observed via their spontaneous emission. Relative measurements were performed on fluorescence from Ca+(4p), Ca+(5s), and Ca+(4d), and from Sr+(5p) and Sr+(6s). The contribution of the highly excited states was found to be favored under short-pulse (35-ps) irradiation.