Efficient three-step, two-color ionization of plutonium using a resonance enhanced 2-photon transition into an autoionizing state

Resonance ionization mass spectrometry (RIMS) has proven to be a powerful method for isotope selective ultra-trace analysis of long-lived radioisotopes. For plutonium detection limits of 10(6) to 10(7) atoms have been achieved for various types of samples. So far a three-step, three-color laser excitation scheme was applied for efficient ionization. In this work, a two-photon transition from an excited state into a high-lying autoionizing state, will be presented, yielding a similar overall efficiency as the three-step, three-color ionization scheme. In this way, only two tunable lasers are needed, while the advantages of a three-step, three-color excitation (high selectivity, good efficiency and low non-resonant background) are preserved. The two-photon transition has been characterized with respect to saturation behavior and line width. The three-step, two-color ionization is a possibility for an improved RIMS procedure.