Observation and measurement of temperature rise and distribution on GaAs photo-cathode wafer with a 532 nm drive laser and a thermal imaging camera

Significant temperature rise and gradient are observed from a GaAs photo-cathode wafer irradiated at various power density levels with over 20 W laser power at 532 nm wavelength. The laser power absorption and dissipated thermal distribution are measured. The result shows a clear indication that proper removal of laser induced heat from the cathode needs to be considered seriously when designing a high average current or low quantum efficiency photo-cathode electron gun. The measurement method presented here provides a useful way to obtain information about both temperature and thermal profiles and also applies to cathode heating study with other heating devices such as electrical heaters.