Quantum efficiency mapping of the GaAs photocathode
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摘要: 基于负电子亲和势GaAs光阴极直流高压注入器,设计并搭建了国内首套光阴极量子效率分布测量系统。该系统利用单透镜实现逐点扫描,并采用LabVIEW进行控制和数据读写。实验表明,该系统单点采样时间小于2.3 s,分辨率优于0.32 mm。初步测量了GaAs阴极的量子效率分布,观察到量子效率分布及其衰减的不均匀性,量子效率较高区域的衰减速率更低。Abstract: An accurate quantum efficiency (QE) map is very important in characterizing the performances of semiconductor photocathodes. This paper presents the study of a QE mapping system built on a DC high-voltage GaAs photocathode injector. A focusing lens is used to move the laser spot to different locations on the photocathode and to map the quantum efficiency. The control system and the data acquisition are established by LabVIEW. With a single sampling time of 2.3 s and a resolution of 0.32 mm, several quantum efficiency maps of the GaAs photocathode have been measured during 330 h. Both the distribution and the decay of the quantum efficiency have been observed from these maps as non-uniform. The quantum efficiency in the high quantum efficiency region decays slower than that in other regions. This QE mapping system is critically useful in improving the preparation technique of the photocathode.
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Key words:
- NEA-GaAs photocathode /
- quantum efficiency /
- photo-injector /
- cathode lifetime
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