Measurements of barium photocathode quantum yields at four excimer laser wavelengths

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The electron quantum yields from barium cathodes excited by excimer laser radiation at 193, 248, 308, and 351 nm have been determined. Experiments with different cathode surface preparation techniques reveal that deposition of barium film a few microns thick on a clean copper surface under moderate vacuum conditions achieves relatively high quantum efficiencies. Quantum yields measured from surfaces prepared in this manner are 2.3×10−3 at 193 nm, 7.6×10−4 at 248 nm, 6.1×10−4 at 308 nm, and 4.0×10−4 at 351 nm. Other preparation techniques, such as laser cleaning of a solid barium surface, produced quantum yields that were at least an order of magnitude lower than these values.