Laser-induced photoionization and fluorescence signals were simultaneously observed in atomic uranium using a single Nd:YAG-pumped dye laser. These signals were recorded in two specific cases. In the first case, the dye laser was resonant to the first-step transition (0–16900.38 cm−1). In the second case, the laser was near-resonant to the first-step transition with a slight detuning (0.15 cm−1) so that it became two-photon resonant at 33801.06 cm−1. The uranium atoms in the ground state were ionized by a single-color, three-photon photoionization technique resulting in the photoionization signal, and the fluorescence signal was simultaneously obtained from the first excited state involved in the photoionization process. The photoionization and the fluorescence signals in the above-mentioned cases were also estimated theoretically for several values of the photoionization cross section for the transition between the second excited state at 33801.06 cm−1 and the autoionization state at 50701.59 cm−1 using density matrix formalism. From the comparison of theoretically calculated ratios of fluorescence signals in the two specific cases with the experimentally obtained values, the photoionization cross section for the 33801.06–50701.59 cm−1 transition has been obtained, which is found to be (5±1)×10−16 cm2.
A simple technique for measuring absolute photoionization cross sections \ensuremath{\sigma} of excited atoms has been applied to the 7
D3/2 level in Cs. Past experiments on excited-state cross sections have relied on measurements of the total number of ions or photoelectrons produced by photoionization to deduce \ensuremath{\sigma}. Our technique is novel in that it utilizes the simple measurement of the reduction in the excited-atom fluorescence due to photoionization to find \ensuremath{\sigma}. We report measurements of cross sections at six different photon energies.
Two-photon absorption cross sections of ground-state xenon atoms to the 2
p5(J=0), 2
p6(J=2), and 2
p9(J=2) states in the 5${p}^{5}
6pconfigurationandphotoionizationcrosssectionsat193and248nmfromthe2{p}_{5}$ and 2
p6 states have been determined and are compared with previous experimental and theoretical values where such exist. Fluorescence depletion spectroscopy as a method for determining excited-state photoionization cross sections is described and discussed and shown to have many attractive features. Based on our cross-section measurements, we calculate that (2+1)-photon photoionization in Xe with a laser intensity of 30 MW/
cm2 during 25 ns at 249.6 nm, using the 2
p5(J=0) state as an intermediate state, can produce a fractional ionization of 10%.