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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
Contributors
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
Funding Information
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Language English (EN)
Type Details URI(s) Local file(s) Year
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
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