Analysis of photocurrent measurements from LaB6 and CeB6 at high temperatures

Thermally assisted photoemission (TAPE) has emerged as a promising approach to enhance the quantum efficiency (QE) of electron sources. Notably, measurements at Kyoto University’s Free-Electron Laser (KUFEL) in 2017 revealed significantly enhanced photoemission even below the work function of the LaB6 and CeB6 cathodes, an observation that has remained unexplained. In this paper, we analyze their measurements using a model that accounts for heating of the electron gas due to photon absorption, originally developed to analyze the thermal photoemission from a dispenser cathode. Our results show excellent agreement with the experimental data for the LaB6 cathode. For the CeB6 cathode, the fit is good at higher temperatures and shows minor discrepancies at lower temperatures. This work demonstrates that the thermal photoemission model has the potential to describe the observed TAPE enhancement in QE and offers a framework for understanding and optimizing TAPE in electron sources.