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

Abstract

We have measured the effect of 445 nm, high power diode laser, directed on the cathode of a SNICS ion source on the extracted beam currents of Cl-, Br- and I- ion beams. Beam current enhancement factors up to 9 were observed in Cs-depleted operation mode of the ion source. The photo-assisted enhancement is shown to scale with the laser power and depend strongly on the neutral Cs flux into the ion source. The effect of the laser diminishes with increasing Cs oven temperature. We present a qualitative model, supported by cathode current measurement, arguing that photoelectron emission and Cs coverage of the cathode surface could explain the observations.