Two-color photoionization of noble gases using laser and VUV synchrotron radiation

Two-photon double-resonant photoionization of Ar and Xe to their autoionizing states lying between the 2P3/2 and 2P1/2 ionic thresholds was carried out with the combination of a laser system and VUV synchrotron radiation from the storage ring at NSRRC. Tuning this radiation of narrow width to a selected Rydberg state was followed by excitation to even-parity levels of autoionization states with a tunable Ti:sapphire laser. The experimental results show two-photon ionization spectra of argon with a large ratio of signal to noise. When the intermediate state 3p5(2P1/2)3d′ [3/2]1 of argon is excited, the spectrum shows a weak continuous background and three autoionizing series 3p5nf′[5/2]2 (n = 9-20), 3p5np′ [3/2]2 and 3p5np′ [1/2]0. The latter two series were resolved partly because of improved resolution in this work and partly because their relative intensities vary with the relative polarization of two excitation sources.