A theory of two- and three-photon autoionization is presented for intermediate resonant and non-resonant cases, stressing the laser-intensity effect on the configuration mixing of the final state. Sample calculations are performed for the
5p6s1P autoionizing state. The involvement of the
5s5d intermediate state includes the effects of ac Stark shifts on the ionization rate, the line shape, and the photoelectron angular distributions.
Broadening and shift of spectral lines in dense Ba and Sr vapor have been studied below and above their first ionization limits. The latter are well-known autoionizing spectral lines that exhibit many different spectral features. However, at larger pressures of noble gases some previously unobserved or very weak spectral phenomena become visible and their studies might be also linked to energy conversion purposes. Originally, we used nanosecond laser which was scanned in a certain spectral region where the two-photon excitation of autoionization lines occurred. This pulsed laser was overlapped by a mode-locked femtosecond laser and a very sensitive thermionic detection was used to observe autoionizing spectral lines. We also presented our preliminary results with hot strontium vapor excited to the resonance level at 460.7 nm.