Photo-emission studies from Zn cathodes under plasma phase

Abstract

In this paper, we report investigations of the electron emission from pure Zn cathodes irradiated by UV laser pulses of 23 ns (full-width at half-maximum) at a wavelength of 248 nm (5 eV). The metal cathodes were tested in a vacuum photodiode chamber at 10 −5 Pa. They were irradiated at normal incidence and the anode-cathode distance was set at 3 mm. The maximum applied accelerating voltage was 18 kV, limited by the electrical breakdown of the photodiode gap. Under the above experimental conditions, a maximum applied electric field of 6 MV/m resulted. In the saturation regime, the measured quantum efficiency value increased with the accelerating voltage due to the plasma formation. The highest output current was achieved with 14 mJ laser energy, 18 kV accelerating voltage and its value was 12 A, corresponding to a global quantum efficiency (GQE) approximately of 1 × 10 −4 . The temporal quantum efficiency was 1.0 × 10 −4 at the laser pulse onset time and 1.4 × 10 −4 at the pulse tail. We calculated the target temperature at the maximum laser energy. Its value allowed us to obtain output pulses of the same laser temporal profile. Tests performed with a lower laser photon energy (4.02 eV) demonstrated a GQE of two orders of magnitude lower.

Electron beams produced by innovative photocathodes based on nanodiamond layers

“…5, it is seen that at low accelerating voltage, the charge extracted from the NDbased photocathodes exceeds the predictions of the Child-Langmuir law. This peculiar result is due to the plasma formation near the cathode surface [33,36]. Although the utilized laser energies are lower than the ablation threshold, the emitted electrons can ionize the atoms of contaminants and adsorbates, forming a plasma layer on the diamond surface.…”

“…where x is the depth from the surface. The TðtÞ solution is expressed in terms of the following integral [32][33][34],…”