Synchrotron-laser two-color experiments: Two-photon double-resonant excitation of Ar to autoionization states between the ~2P_(3/2) and ~2P_(1/2) ionic thresholds

摘要

Two-photon double-resonant excitation of Ar to its autoionizing states lying between the ~2P_(3/2) and ~2P_(1/2) ionic thresholds was carried out with the combination of a laser system and VUV synchrotron radiation from the storage ring at NSRRC. By tuning a narrow-width synchrotron radiation to a selected Rydberg state followed by excitation to the even-parity levels of autoionization states with a tunable Ti:Sapphire laser. The experimental results show the two-photon ionization spectra of Ar with high signal-to-noise ratio. When the intermediate state 3p~5(~2P_(1/2))3d' [3/2]_1 of Ar is excited, the spectrum shows a weak continuous background and three autoionizing series 3p~5nf' [5/2]_2 (n = 9–20), 3p~5np' [3/2]_2, and 3p~5np' [1/2]_0. The latter two series were resolved for the first time partly because of improved resolution in this work, partly because their relative intensities vary with the relative polarization of two excitation sources.