An offline system for measurement of the intrinsic emittance of photocathode

FENG Zhiwen; LI Xudong; MENG Hao; ZHOU Qin; HOU Tao; JIANG Zenggong; GU Qiang

doi:10.3724/j.0253-3219.2026.hjs.49.250042

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An offline system for measurement of the intrinsic emittance of photocathode

ACCELERATOR, RAY TECHNOLOGY AND APPLICATIONS | 更新时间：2026-02-13

- An offline system for measurement of the intrinsic emittance of photocathode
- NUCLEAR TECHNIQUES Vol. 49, Issue 2, Article number: 020202(2026)
- 作者机构：
  
  1.中国科学院上海应用物理研究所上海 201800
  2.中国科学院上海高等研究院上海 201210
  3.中国科学院大学北京 100049
  4.张江实验室上海 201210
- 作者简介：
  
  FENG Zhiwen, male, born in 1996, graduated from Nanchang University in 2019, master student, focusing on nuclear technology application
  JIANG Zenggong, E-mail: jiangzg@sari.ac.cn
  GU Qiang, E-mail: guq@sari.ac.cn
- 基金信息：
- DOI：10.3724/j.0253-3219.2026.hjs.49.250042
  CLC： TL53
- Received：25 January 2025，
  
  Revised：2025-05-05，
  
  Published：15 February 2026
- 稿件说明：
移动端阅览
冯志文,李旭东,孟浩等.光阴极本征发射度离线测量装置研制[J].核技术,2026,49(02):020202.

FENG Zhiwen,LI Xudong,MENG Hao,et al.An offline system for measurement of the intrinsic emittance of photocathode[J]. NUCLEAR TECHNIQUES,2026,49(02):020202.
冯志文,李旭东,孟浩等.光阴极本征发射度离线测量装置研制[J].核技术,2026,49(02):020202. DOI： 10.3724/j.0253-3219.2026.hjs.49.250042. CSTR： 32193.14.hjs.CN31-1342/TL.2026.49.250042.

FENG Zhiwen,LI Xudong,MENG Hao,et al.An offline system for measurement of the intrinsic emittance of photocathode[J]. NUCLEAR TECHNIQUES,2026,49(02):020202. DOI： 10.3724/j.0253-3219.2026.hjs.49.250042. CSTR： 32193.14.hjs.CN31-1342/TL.2026.49.250042.

摘要

光阴极本征发射度是光阴极电子源装置所能获得的发射度下限，对自由电子激光、超快电子衍射等装置发展具有重要意义。常用的光阴极本征发射度测量方法依赖大型加速器装置，不利于实验室环境下光阴极制备工艺的快速优化。本文基于自由空间漂移原理设计并搭建了一套光阴极离线本征发射度测量装置。该装置通过转移室实现与光阴极制备装置的兼容连接，采用5 mm阴阳极间隙、2

70 mm漂移距离和微通道板（Micro-channel Plate，MCP）探测系统，对采用Te断续、Cs持续沉积工艺制备的碲化铯（CS

Te）光阴极进行量子效率及本征发射度测量。测量结果表明，光阴极表面量子效率均大于5%，最大值达12.5%（266 nm波长）；碲化铯光阴极本征发射度为0.592 mm·mrad·mm

-1

（5 kV偏压），不同偏压下的测量结果与理论值吻合良好，验证了装置的可靠性。该离线测量系统为光阴极工艺参数优化提供了便捷高效的解决方案，测量精度通过理论对比和文献验证得到确认。

Abstract

Background

Photocathode intrinsic emittance represents the lower limit of emittance achievable by photocathode electron sources and is critical for advancing applications such as free-electron lasers and ultrafast electron diffraction. Conventional measurement methods rely on large-scale accelerator facilities

which are unsuitable for rapid laboratory-based optimization of photocathode fabrication processes.

Purpose

This study aims to develop an offline intrinsic emittance measurement system for photocathodes that enables rapid characterization and optimization of fabrication parameters in laboratory environments.

Methods

An offline intrinsic emittance measurement system was designed and constructed based on the free-space drift principle. Firstly

the system was made compatible with the photocathode preparation facility through a transfer chamber that enabled vacuum transport of photocathodes between preparation and measurement devices under ultra-high vacuum conditions (~10

-8

Pa). Then

the measurement principle utilizing cathode-anode acceleration followed by field-free drift detection was implemented with a 5 mm cathode-anode gap

270 mm drift distance

and a micro-channel plate (MCP) detector system with 10

gain factor. Finally

cesium telluride (Cs

Te) photocathodes prepared using intermittent Te and continuous Cs deposition processes were transferred to the measurement chamber and characterized for both quantum efficiency distribution and intrinsic emittance using a 266 nm ultraviolet laser with ~100 μm spot size.

Results

The measurement results of quantum efficiency show values exceeding 5% across the photocathode surface

with the maximum efficiency reaching 12.5% at 266 nm wavelength. The measured intrinsic emittance of the Cs

Te photocathode is 0.592 mm·mrad·mm

-1

under 5 kV bias voltage

aligning well with internationally reported values of 0.50~1.0 mm·mrad·mm

-1

for similar materials. Measurements under different bias voltages demonstrate good agreement with theoretical predictions. The system exhibits no space charge effects across different laser power levels

confirming the reliability of the measurement results.

Conclusions

The offline measurement system proposed in this study successfully enables rapid and reliable characterization of photocathode intrinsic emittance

providing a practical and efficient solution for photocathode fabrication process optimization in laboratory environments without requiring large accelerator facilities. The measurement accuracy validated through theoretical comparison and consistency with literature values demonstrates that this approach significantly reduces the optimization cycle time for high-quality photocathode development

making it a valuable tool for advancing high-brightness electron source technology.

关键词

Keywords

references

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