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

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.
Comment: x-ray fel, e-TOF, position monitor, polarization