Absolute measurement of photoionization cross sections of excited atoms: Application to determination of atomic beam densities

Near threshold photoionization of excited alkali atoms Ak(np) (Ak = Na, K, Rb, Cs; n = 3-6)

“…Effects of initial state polarization were found to be below 5% by varying the angle between the polarization directions of the two linearly-polarized pulsed lasers. The earlier result 4.8(12) Mb at ε = 0.47 eV [15] agrees with the latter [32] within the experimental errors. The comparison between theory and experiment in Figure 4A shows that the experimental uncertainties in the absolute cross-sections have to be reduced further to allow a critical test of the different theoretical results.…”

“…The cross-sections increase weakly with rising electron energy [14]. From the polarization dependence of these data and extended measurements at three photoelectron energies [32]; c: present work (CIPFCP); d: present work (photoelectron angular distribution); e: present work, using quantum defects given in [54].…”

“…These three descriptions yield similar shapes of the crosssection; near threshold the respective absolute values differ by less than 20% and are found to be in satisfactory agreement with the most recent experimental measurements. Burkhardt et al [32] used a saturation method and obtained 7.6(11) Mb at ε = 0.79 eV (open circle). Our experimental cross-sections (see Tab. 2), obtained with the procedure outlined in Section 3 and presented for the case of unpolarized K(4p 3/2 ) atoms in Figure 6A (filled dots), are in very good agreement with the CIPFCP calculations and with the value measured by Burkhardt et al [32].…”

“…Possibly the measurements were influenced by an unnoticed systematic error at the shortest wavelengths (< 240 nm). In later work [32] the same group determined an absolute cross-section of 3.7(7) Mb at the photoelectron energy ε = 0.47 eV (solid square with error bar in Fig. 4A); this value was obtained with a saturation method which does not require knowledge of the atom density.…”

Photoionization cross section measurements of the excited states of cobalt in the near-threshold region

“…The absolute photoionization cross sections from the excited states at and above the ionization threshold were measured using the saturation technique, as described previously. 1,3,4 This method has been widely used to measure the photoionization-cross sections of the excited states of alkali-metal atoms as well as for alkaline-earth-metal atoms. For the two-step photoionization of the cobalt atoms, it assumed that the ionizing laser beam is of uniform 2014) intensity and the resonance transition is saturated, the number of ions per ionizing pulse is given by…”