Numerical study of transverse position monitor and compensation for x-ray polarization diagnosis

TL;DR

This paper presents a numerical approach to monitor and compensate for transverse position errors in x-ray FEL polarization diagnostics, improving measurement accuracy and polarization fidelity.

Contribution

It introduces a novel method to monitor transverse FEL pulse position using an eTOF polarimeter and demonstrates effective compensation through comprehensive numerical modeling.

Findings

Achieved 20 μm spatial resolution in position monitoring.

Improved polarization measurement accuracy by 0.5%.

Validated the compensation method via numerical simulations.

Abstract

Diagnosing free electron laser (FEL) polarization is critical for polarization-modulated research such as x-ray free electron laser (XFEL) diffraction imaging and probing material magnetism. In an electron time-of-flight (eTOF)\ polarimeter, the flight time and angular distribution of photoelectrons were designed based on x-ray polarimetry for on-site diagnosis. However, the transverse position of x-ray FEL pulses introduces error into the measured photoelectron angular distribution. This work thus proposes a method to monitor the transverse position using an eTOF polarimeter and explains how to compensate for the error due to transverse position. A comprehensive numerical model is developed to demonstrate the feasibility of the compensation method, and the results reveal that a spatial resolution of 20 \(\mu\)m and a polarity improved by 0.5\% is possible with fully polarized FEL pulses. The impact of FEL\ pulses and a method to calibrate their linearity is also discussed.