Appl. Phys. Lett. 99, 103504 (2011)
The laser-induced field emission of electrons from sharp metallic tips could lead to the development of ultrafast electron microscopy and compact free-electron lasers. So far, however, the maximum electron bunch charge from such tips has been around 103 electrons per laser pulse, and this must be increased to 107 before practical applications can be realized. Anna Mustonen and co-workers from the Paul Scherrer Institut and University of Bern in Switzerland have now achieved this level of electron bunch charge by fabricating large-area metallic field emitter array cathodes. Their field emitter array comprised 1.5-μm-base and 5-μm-pitch emitters with a tip apex radius of 10 nm. They arranged a total of 1.2 × 105 emitter tips in a 2.2-mm-diameter circle and installed the array in a vacuum chamber. Using a polarized laser beam with a central wavelength of 800 nm and a pulse duration of 50 fs, the researchers illuminated the field emitter array at an incident angle of 60° normal to the chip surface. They found that the electron emission from the field emitter array rose dramatically when a gate voltage of larger than 70 V was applied and the incident light was p-polarized and had an intensity of 72 GW cm−2. Under the optimum conditions of a laser intensity of 86 GW cm−2 and a gate voltage of 92 V, the laser-induced charge generated was 5.2 pC, which corresponds to 107 electrons per laser pulse.
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