Short electron bunch generation using single-cycle ultrafast electron guns

We introduce a solution for producing ultrashort (~fs) high charge (~pC) from ultracompact guns utilizing single-cycle THz pulses. We show that the readily available THz pulses with energies as low as 20 μJ are sufficient to generate multi-10 keV electron bunches. Moreover, it is demonstrated that THz energies of 2 mJ are sufficient to generate relativistic electron bunches with higher than 2 MeV energy. The high acceleration gradients possible in the structures provide 30 fs electron bunches at 30 keV energy and 45 fs bunches at 2 MeV energy. These structures will underpin future devices for strong field THz physics in general and miniaturized electron guns, in which the high fields combined with the short pulse duration enable electron beams with ultrahigh brightness.