MEASUREMENTS OF BARIUM PHOTOCATHODE QUANTUM YIELDS AT 4 EXCIMER-LASERWAVELENGTHS

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