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ABSTRACT:
Andreas Schmid, Uwe Weierstall and colleagues at Berkeley Lab have invented a new electron source, which has extremely high brightness, is highly monochromatic, may be pulsed, and may be used to generate spin-polarized electron beams. Electron beams are used in a wide range of applications from electron-optical analytical instruments to synchrotron storage rings and visual displays such as television, radar etc. Conventional field-emission electron sources are well-known to be among the brightest and most coherent particle sources known, but one drawback is that these conventional sources emit electrons over a relatively large energy range of about 0.3 eV. These conventional sources generate a low energy beam of free electrons in vacuum, which may readily be accelerated to higher energy using readily available accelerator techniques.
The new electron source developed at Berkeley Lab combines the field-emission effect, for high brightness and spatial coherence, with the photoelectron effect, for improved monochromaticity. The photo-field (PF) emission results from photoexcitation of sharply defined electronic states inside an emitter tip of semiconducting material. It will produce a source with millivolt energy spread while retaining the high brightness of a field-emitter. In addition, the emission can be controlled by a pulsed laser, producing pulsed electron emission. Because the new Berkeley Lab field-emission electron source is of nanometer dimensions, the resulting electron beam has very high spatial coherence in addition to monochromaticity. The source may be used for spin-polarized electron emission conditions. Potential applications include electron energy-loss spectroscopy, time-resolved diffraction, spectroscopy and imaging, and accelerator or storage-ring applications. |
