Effect of Background Signal on Momentum Imaging

TL;DR

This paper investigates how background signals affect momentum imaging in electron-molecule interaction studies and proposes solutions like background subtraction and using supersonic beams to improve image accuracy.

Contribution

It provides a systematic analysis of background artefacts in momentum imaging and demonstrates effective methods to mitigate these effects for enhanced experimental precision.

Findings

Background signals cause artefacts in momentum images at high magnification.

Background subtraction with suitable magnification reduces artefacts.

Supersonic molecular beams minimize background signals, improving image quality.

Abstract

The velocity Slice Imaging technique has revolutionised electron molecule interaction studies. Multiple electrostatic lens assemblies are often used in spectrometers for resolving low kinetic energy fragments. However, in a crossed-beam experiment with an effusive molecular beam, the extended source of ion generation due to the presence of the background gas creates artefacts on the momentum images as we try to magnify them beyond a certain size. Here, we present a systematic study of this effect on momentum imaging and the solutions to address this issue by background subtraction with suitable magnification. Additionally, we demonstrated that a supersonic molecular beam target helps minimise these artefacts in the image magnification by reducing the background signal. These systematic findings may bring valuable insight into the investigation of low kinetic energy release processes involving electron impact, ion impact, and merge beam experiments with large interaction volumes where high magnification is needed.