Thermally assisted photoemission effect on CeB6 and LaB6 for application as photocathodes

The thermally assisted photoemission (TAPE) effect was investigated for the hexaboride thermionic cathodes (${\mathrm{LaB}}_{6}$ and ${\mathrm{CeB}}_{6}$). It was found that the quantum efficiency of these cathodes can be increased by raising the cathode temperature along with the thermionic emission. In addition both materials can emit a measurable photoemission current by being irradiated with a laser having a photon energy below the work function at sufficiently high cathode temperatures. Our measurements indicate that this process is linear. These results show the significance of the TAPE effect. An additional effect of cathode heating is surface cleaning. This effect was detected as the hysteresis of the quantum efficiency which can be observed by heating up and cooling down the cathode. This effect slightly changes the quantum efficiency but not as much as the TAPE effect.