Speaker
Description
Operating photoemission electrons sources with photon energy near the work function has been shown to minimize the intrinsic emittance, but at the cost of several orders of magnitude lowered quantum efficiency. Thus, modern femtosecond photocathode electron sources would require very high intensity laser pulses to extract significant charge, which results in dynamic changes to the electronic distribution of the material during photoemission, giving rise to multiphoton photoemission and electron heating. In this work, we track the occupation function of electrons in time under high intensity laser illumination based on a Boltzmann equation to predict its dynamic effects on the quantum efficiency, mean transverse energy, and emission brightness of metal photocathodes. We find the multiphoton photoemission is significant under high intensity laser illumination resulting in an order of magnitude decrease in achievable brightness.
