Experimental evidence on photo-assisted O− ion production from Al2O3 cathode in cesium sputter negative ion source

Abstract

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Photo-assisted O− and Al− production with a cesium sputter ion source

“…The experiments described above and in Ref. [11] have confirmed the existence of a photo-assisted enhancement of negative ion production in cesium sputter ion sources, first noted by Vogel [5]. The insensitivity of the prompt effect on the laser wavelength and the fact that both, O − and Al − exhibit a similar enhancement, questions the hypothesis of resonant ion pair production explaining the observed photo-assisted beam current gain.…”

“…The extracted beam currents are only modest as the ionizer temperature controlling the Cs + ion flux incident on the cathode was deliberately maintained low to observe the photo-assisted contribution superimposed on the continuous beam current. The magnitude of the prompt effect was observed to depend linearly on the laser power in the 320-1600 mW range accessible with the 450 nm diode [11]. In order to gain understanding on the observed photo-assisted negative ion production, we measured the O − beam current gain by the 450 nm laser exposure as a function of the beamline dipole magnet field strength at B < B optimum .…”

“…The 5d excited states of Cs that are expected to be in pair production of O − ions are not populated with the 405, 520 and 638 nm lasers (see Ref. [11] for further details). Nevertheless, a prompt enhancement of the O − beam current is observed with the 405 nm laser, which together with Fig.…”

“…We have recently reported experimental results on photo-assisted O − ion production with a cesium sputter ion source [11]. In this paper, we expand on that work e.g.…”

Photo-assisted Cl-, Br- and I- production in caesium sputter ion source

“…In a recent paper [3] Vogel introduced a hypothesis based on resonant ion pair production [4][5][6][7] where the negative ion yield could be enhanced by exposing the cathode to a laser beam resonantly exciting neutral caesium atoms to 7p electronic states, followed by an electron transfer to the affinity levels of the anions. The resonant ion pair production model was later questioned by demonstrating that the laser-assisted production of negative ions can be provoked equally with off-resonance laser [8,9]. The laser-induced ion pair production scheme in direct laser exposure of the cathode surface was conclusively disputed in a recent experiment [10] with an adjustable high-precision wavelength laser.…”