Reduction of thermal emittance by using p-polarized laser at oblique incidence

Abstract

High charge low emittance electron beam is crucial for the 4th generation light source. Conventionally the beam is generated by photoinjector with laser illuminating the cathode at nearly normal incidence. In this paper attention was called to the use of laser at oblique incidence, which we believe, may be more beneficial. It is found that when the laser illuminates the cathode at oblique incidence, the quantum efficiency (QE) and thermal emittance show strong dependence on incidence angle and polarization state. By using p-polarized laser at oblique incidence, surface photoemission is initiated by the presence of the normal electric field which results in a higher QE and lower thermal emittance. With this technique, the increase in QE by almost 5 times and the reduction of thermal emittance by 40% should be quite expectable for a Copper photo-cathode with atomically smooth surface.