Advances in bright electron sources

In this paper, we review the status of bright electron sources. High peak current (up to kA) low emittance (<1 mm rad) electron beams have been one of the critical components in the development of XFELs. The outlook for the field is even more promising as progress in the understanding of photoemission physics, development of novel photocathode materials, gun and laser technology, enable further progress in advanced light sources as well as novel applications such as ultrafast electron diffraction and microscopy. We outline here the more recent research trends which pave the way for potentially orders of magnitude brightness improvements with respect to the current state-of-the-art.