Polarization control proposal for Shanghai deep ultraviolet free electron laser

TL;DR

This paper proposes a polarization control method for the Shanghai deep ultraviolet FEL, using crossed undulators and phase-shifters to produce high-quality, circularly polarized radiation with high efficiency.

Contribution

It introduces a novel configuration of crossed undulators with phase-shifters for polarization control in deep UV FELs, supported by comprehensive start-to-end simulations.

Findings

Achieved Fourier-transform-limited output with 100 nJ pulse energy

Produced circular polarization degree above 90%

Maintained polarization performance with minimal undulator spacing

Abstract

In this paper, a fully coherent radiation option with controllable polarization is proposed for Shanghai deep ultraviolet free electron laser (FEL) test facility. Intensive start-to-end simulation suggests that, the two crossed planar undulators which generate the horizontal and vertical linear polarized FEL respectively, should be placed as close as possible for avoiding the polarization performance degradation of the final combined FEL radiation. With the existence of the phase-shifter between the two crossed radiators, Fourier-Transform-Limited output radiation with 100 nJ order pulse energy, 5 ps full pulse length and circular polarization degree above 90% could be achieved.