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Persistent URL http://purl.org/net/epubs/work/51083
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Record Id 51083
Title Cooled transmission-mode NEA-photocathode with a band-graded active layer for high-brightness electron sources
Abstract A Free-Electron Laser (FEL) places many exacting demands on a Negative Electron Affinity (NEA) photocathode, such as the need for an ultra-fast response time, low energy spread for emitted electrons, high quantum efficiency (Q.E.) and a high average photocurrent. However, these key requirements are conflicting, and cannot be fulfilled by conventional photocathode design. For example, to achieve ~ 10 ps response time, the photocathode active layer should be thinned to ~ 100 - 150 nm, but this thickness is insufficient to provide near-complete absorption of light with hv ~ eg so high Q.E. cannot be achieved. Complete optical absorption and high Q.E. can be obtained using a thin active layer at higher photon energies, but this generates photoelectrons with excess kinetic energy within the semiconductor. These photoelectrons do not thermalise in a thin active layer, so yield a broad energy distribution in the emitted electrons. Moreover, cooling of the conventional semiconductor photocathode structure is ineffective due to its fragility, so it cannot be pressed firmly to a heat sink to attain good thermal contact. Consequently, the maximum CW photocurrent is limited to a few milliamps. The goal of our work is to develop a new design of NEA-photocathode which is optimised for FEL applications.
Organisation ASTeC , ASTeC-AP , ASTeC-VS , STFC
Keywords ASTeC 2009-2010 , GaAs , Transmission mode , Physics , Reflection mode , Photoelectron , NEA , FEL , Photocathode
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Language English (EN)
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Paper In Conference Proceedings Published by the AiP with the PESP08 submissions as part of the SPIN2008 proceedings AiP Conf. Proc 1149, pp 1057-1061. Is in proceedings of: Polarised Electron Sources and Polarimetry, 2008 (PESP08), Jefferson Lab, US, 4-8 Oct 2008. 2008 Proc. PESP08…electron sources.pdf 2008