A co-axial velocity map imaging spectrometer for electrons

S Li,D Ray,Z Guo,A Natan,A Kamalov,A Marinelli,P Walter,T Osipov,K Hegazy,J O’Neal,E G Champenois,D Rich,R Coffee,J P Cryan,M Owens

doi:10.1063/1.5046192

Abstract

We present the design of an electron velocity map imaging (VMI) spectrometer where the ionizing laser source propagates along the symmetry axis of the spectrometer. The co-axial geometry is useful in a variety of experiments, because it provides a unique 2-dimensional projection of the 3-dimensional electron momentum distribution. Initial simulations show that this co-axial VMI can work with both high energy (more than 100 eV) and low energy (tens of eV) electrons. We demonstrate the performance of this co-axial VMI spectrometer at the Linac Coherent Light Source X-ray Free Electron Laser facility.

Highlights

Charged particle spectrometers that measure angle- and kinetic energy-resolved distributions of photoelectrons or photoions have become a popular tool for studying photoionization and photodetachment
Using soft X-ray pulses provided by the Linac Coherent Light Source (LCLS) X-ray free electron laser (XFEL), we studied near-edge core-level ionization of molecular CO2 near 560 eV
We demonstrated a novel co-axial velocity map imaging (c–VMI) spectrometer design

Summary

INTRODUCTION

Charged particle spectrometers that measure angle- and kinetic energy-resolved distributions of photoelectrons or photoions have become a popular tool for studying photoionization and photodetachment. This new co-axial geometry VMI is an invaluable tool for applications in attosecond experiments In addition to applications in angular streaking applications, the co-axial geometry is useful in experiments with cross-polarized laser pulses in RABBIT-like experiments,[30] extreme ultra-violet pulses from high-harmonic generation with polarization perpendicular to alignment laser axis in photoelectron angular distribution measurements,[31] and circularly polarized laser strong-field ionizations.[32,33] Overall, the c–VMI design benefits experiments that involve circularly polarized light fields with angle-resolved electron detection. In this paper we show that we are able to satisfy the VMI imaging criterion with sufficiently high resolution

INSTRUMENT DESIGN

EXPERIMENTAL DESIGN AND IMAGING PERFORMANCE

Core-level ionization of CO2 with soft x-ray FEL pulses

Findings

CONCLUSIONS