Mean Transverse Energy Measurement of Negative Electron Affinity GaAs-Based Photocathode

A negative electron affinity GaAs photocathode electron source is characterized by high brightness, high quantum efficiency, and a moderate temporal response. The initial emittance depends on the mean transverse energy (MTE) of the electrons on the cathode surface. We evaluated the MTE based on emittance measurements obtained using the waist scan method with three types of cathodes: bulk GaAs, thickness-controlled samples with active-layer thicknesses of 100 and 1000 nm, and a GaAs/GaAsP superlattice sample. The dependence of the cathode quantum efficiency, the laser wavelength, and the thickness of the GaAs cathode active layer on the MTE are described. In the case of the bulk GaAs and the thickness-controlled samples, it was determined that the thickness and cathode quantum efficiency do not affect the MTE within the measurement error. The laser wavelength, on the other hand, affects the MTE of all cathodes. (C) 2012 The Japan Society of Applied Physics