Optimization of the Coherent Intensity from Multi-Segment Undulators by Phase Matching

The use of inline insertion devices at third-generation synchrotron radiation sources can result in destructive interference effects if the relative phase between the devices is not properly adjusted. The destructive interference can strongly affect the emission spectrum and coherent wavefront of a compound insertion device. We simulate the photon source generated by a dual-inline elliptically polarizing undulator (EPU) situated in a low-β straight section of the planned NSLS-II storage ring and show that a magnetic chicane with adjustable field integral can be used to phase-match the devices. Furthermore, we show that the maximum coherent intensity is delivered by a focusing x-ray beamline if the chicane is adjusted to phase-match the off-axis and red-shifted radiation. Such a system will be installed at the coherent soft x-ray (CSX) beamline of the NSLS-II in order to provide the highest possible coherent flux for coherent soft x-ray scattering experiments.