Short-pulse high-current-density photoemission in high electric fields

Presented are experimental results of photoemission studies on thin wires of gold-coated tungsten, held at surface fields in the range of 10 to the 6th to 3 x 10 to the 8th power V/m, and illuminated by 10 ps long, 4.66 eV photon laser pulses. The wire cathodes arranged coaxially in an anode experienced a surface-field enhancement of 100 to 1000 over the applied voltage. Obtained are current densities exceeding 10 kA/sqcm from a 50 micron diameter wire, from a (50 x 400) sq micron area, under partially space-change-limited conditions. The quantum efficiency for emission-limited cases was in the range of 10 to the -5 power. For these cases results using 50 micron and 4 micron diameter wires indicated linear dependence of charge density with optical energy density. The emission also scaled linearly with the emitting area. For surface fields above 3 x 10 to the 7th power V/m, a twofold enhancement of emission was observed for a tenfold increase in the field.