Threshold effect in the photoemission of composite nanoantennas irradiated by intense femtosecond laser pulses

A new mechanism has been proposed for the formation of energy spectra of photoelectrons by above-threshold photoemission of composite nanoantennas with small gaps between elements irradiated by femtosecond laser pulses. According to this mechanism, a photoelectron can be rescattered under certain conditions not only by a “parent” element of the composite nanoantenna but also by a neighboring element. As a result, the upper edge of the plateau region in the energy spectra of photoelectrons increases strongly. Relations between the parameters determining the efficiency of the process have been found. The mechanism proposed is promising for the development of efficient compact sources of high-energy attosecond electron beams and ultrashort X-ray pulses.