A Composite Velocity Map Imaging Spectrometer for Ions and 1 keV Electrons at the Shanghai Soft X-ray Free-Electron Laser

Bocheng Ding,Xiaohong Li,Zhi Liu,Weiqing Xu,Lifang Tian,Yunfei Feng,Jianye Huang,Ruichang Wu,Xiaojing Liu

doi:10.3390/app112110272

Abstract

Velocity map imaging (VMI) spectrometry is widely used to measure the momentum distribution of charged particles with the kinetic energy of a few tens of electronVolts. With the progress of femtosecond laser and X-ray free-electron laser, it becomes increasingly important to extend the electron kinetic energy to 1 keV. Here, we report on a recently built composite VMI spectrometer at the Shanghai soft X-ray free-electron laser, which can measure ion images and high-energy electron images simultaneously. In the SIMION simulation, we extended the electron kinetic energy to 1 keV with a resolution <2% while measuring the ions with the kinetic energy of 20 eV. The experimental performance is tested by measuring Ar 2p photoelectron spectra at Shanghai Synchrotron Radiation Facility, and O+ kinetic energy spectrum from dissociative ionization of O2 by 800 nm femtosecond laser. We reached a resolution of 1.5% at the electron kinetic energy of 500 eV. When the electron arm is set for 100 eV, a resolution of 4% is reached at the ion kinetic energy of 5.6 eV. This composite VMI spectrometer will support the experiment, such as X-ray multi-photon excitation/ionization, Auger electrons emission, attosecond streaking.

Highlights

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The standard velocity map imaging (VMI) spectrometer was originally designed by Eppink and Parker in 1997 [1], which consists of a repeller, an open extractor, and a flight tube
We reached a resolution of 1.5% at the electron kinetic energy of 500 eV, and the

Summary

Introduction

The velocity map imaging (VMI) spectrometer is a powerful tool to obtain a highresolution projected two-dimensional (2D) image of the three-dimensional (3D) momentum distribution of charged particles, which was widely used in atomic and molecular physics. The standard VMI spectrometer was originally designed by Eppink and Parker in 1997 [1], which consists of a repeller, an open extractor, and a flight tube. The charged particles are created at the crossing region where the light beam meets the molecular beam. They are driven towards a two-dimensional position-sensitive detector. With the well-designed electric field, the radius that the charged particle impact on the detector depends only on its initial radial momentum and is almost independent of the source position

Methods

Results

Conclusion