Abstract
There is a growing interest in producing intense, coherent x-ray radiation with an adjustable and arbitrary polarization state. In this paper, we study the crossed-undulator scheme [K.-J. Kim, Nucl. Instrum. Methods Phys. Res., Sect. A 445, 329 (2000)] for rapid polarization control in a self-amplified spontaneous emission (SASE) free electron laser (FEL). Because a SASE source is a temporally chaotic light, we perform a statistical analysis on the state of polarization using FEL theory and simulations. We show that, by adding a small phase shifter and a short (about 1.3 times the FEL power gain length), 90\ifmmode^\circ\else\textdegree\fi{} rotated planar undulator after the main SASE planar undulator, one can obtain circularly polarized light---with over 80% polarization---near the FEL saturation.
Highlights
Several x-ray free electron lasers (FELs) based on selfamplified spontaneous emission (SASE) are being developed worldwide as next-generation light sources [1,2,3]
The x-ray FEL is normally linearly polarized based on planar undulators
An alternative approach for polarization control is the socalled ‘‘crossed undulator’’, which is the subject of this paper
Summary
Several x-ray free electron lasers (FELs) based on selfamplified spontaneous emission (SASE) are being developed worldwide as next-generation light sources [1,2,3]. The crossed-planar undulator was proposed by Kim to generate arbitrarily polarized light in synchrotron radiation [5] and FEL sources [6]. It is based on the interference of horizontal and vertical radiation fields generated by two adjacent planar undulators in a crossed configuration The radiation pulses generated in two adjacent undulators by each electron do not overlap in time. Three-dimensional (3D) effects and simulation results are discussed
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