Abstract

Recently laser induced electron emission from metallic nanotip arrays (Figure 1) has been investigated for a purpose of generating high charge ultrafast electron pulses [1, 2]. In particular, short electron bunches up to 10⁷ electrons were successfully generated by near-infrared laser pulses with 50 fs pulse duration, showing feasibility of high bunch charge generation by laser induced field emission for application in accelerators such as, for example, SwissFEL free electron laser facility. The experiments also showed the importance of the laser incident angle and polarization for efficient electron generation. The laser induced charge was more efficiently generated when the laser electric field was enhanced at tip apex, the effect known as formation of “hot spot” at the sharp end of a metallic wedge. Therefore, we propose to further optimize light coupling to field emitter nanotips (Figure 1) by integrating gate electrodes that support excitation of surface plasmon polaritons at wavelengths of interest (schematically shown on Figure 2) [3]. The study indicates that the submicron arrays with the plasmonic gate electrodes can increase electron yield by 30 times and simplify experimental setup by allowing efficient excitation at normal incidence. By using an advantage of SPP generated on gate surface, optical excitation of the emitter tips is also possible for double gate field emitter arrays [4], where the second gate is used for electron beam collimation (Figure 4). This should create opportunities for development high charge ultrafast electron sources with superior brightness.

© 2013 IEEE