Cold electron beams from cryocooled, alkali antimonide photocathodes

In this paper we report on the generation of cold electron beams using a Cs₃Sb photocathode grown by codeposition of Sb and Cs. By cooling the photocathode to 90 K we demonstrate a significant reduction in the mean transverse energy validating the long-standing speculation that the lattice temperature contributes to limiting the mean transverse energy or intrinsic emittance near the photoemission threshold, opening new frontiers in generating ultrabright beams. At 90 K, we achieve a record low intrinsic emittance of 0.2 μm (rms) per mm of laser spot diameter from an ultrafast (subpicosecond) photocathode with quantum efficiency greater than 7×10^-5 using a visible laser wavelength of 690 nm.