Dark-lifetime degradation of GaAs photo-cathode at higher temperature
Dark-lifetime degradation of GaAs photo-cathode at higher temperature
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DOI：
10.1016/j.nima.2010.02.029
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发表时间：
2011-05
影响因子：
1.4
通讯作者：
M. Kuriki;C. Shonaka;H. Iijima;D. Kubo;H. Okamoto;H. Higaki;Katsuhide Ito;M. Yamamoto;T. Konomi;S. Okumi;M. Kuwahara;T. Nakanishi
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文献类型：
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作者：
M. Kuriki;C. Shonaka;H. Iijima;D. Kubo;H. Okamoto;H. Higaki;Katsuhide Ito;M. Yamamoto;T. Konomi;S. Okumi;M. Kuwahara;T. Nakanishi
ERL 被认为是未来光源之一，其工作平均电流高达 100mA，发射度极低，低至 0.1mm-mrad。它还适用于通过束压缩产生低至 100fs 的短电子束。超短光子脉冲可以通过逆激光康普顿散射或FEL与ERL的短脉冲产生。在 ERL 中，最关键的设备之一是电子枪。电子束由高平均功率激光器驱动的砷化镓光电阴极产生。需要足够的量子效率和相当长的工作寿命。 GaAs晶体经过人工处理而产生的负电子亲和力（NEA）表面对于产生高亮度电子束具有重要的作用。在实际操作中，15W 激光以小光斑尺寸（通常为几毫米）照射在 GaAs 阴极上，并且该驱动激光会提高阴极温度。在如此恶劣的条件下，砷化镓阴极的使用寿命是一个重要问题。在本文中，我们研究了 GaAs 寿命与温度的关系，以评估加热的影响。根据我们的估计，5mm 激光半径的温升为 60K。我们观察到加热导致寿命显着缩短。通过分析解吸过程的寿命，发现GaAs表面“NEA分子”的结合能为1.20eV。根据结果，加热导致的寿命下降是 ERL 枪最关键的问题之一，应该解决它以开发坚固的阴极，否则我们应该考虑对阴极进行主动冷却。
ERL is considered to be one of the future light source, which is operated in a high average current up to 100mA with an extremely low emittance down to 0.1mm-mrad. It is also applicable to generate short electron bunch down to 100fs with a bunch compression. Ultra-short photon pulse can be generated by the inverse laser Compton scattering or FEL with the short pulse from ERL. In ERL, one of the most critical device is the electron gun. The electron beam is generated by GaAs photo-cathode driven by a high-average power laser. Enough quantum efficiency and a reasonably long operational lifetime are required. The Negative Electron Affinity (NEA) surface, which is generated by artificial treatments on GaAs crystal, has an important roll to generate the high brightness electron beam. In a real operation, 15W laser is illuminated on the GaAs cathode in a small spot size (typically a few mm) and the cathode temperature is increased by this drive laser. The operational lifetime of GaAs cathode is an important issue in such tough condition. In this article, we examine GaAs lifetime as a function of temperature to evaluate effects of heating. In our estimation, temperature rise is 60K for 5mm laser radius. We observed a significant degradation of the lifetime by heating. By analyzing the lifetime as desorption process, the binding energy of “NEA molecule” on the GaAs surface is found to be 1.20eV. According to the result, the lifetime degradation by heating is one of the most critical problem on the ERL gun and should be solved to develop a robust cathode, otherwise we should consider an active cooling of the cathode.