A Crossed undulator system for a variable polarization synchrotron radiation source

A crossed undulator system can produce synchotron radiation whose polarization is abitrary and adjustable. The polarization can be linear and modulated between two mutually perpendicular directions, or it can be circular and can be modulated between right and left circular polarizations. The system works on low emittance electron storage rings and can cover a wide spectral range. Topics discussed include the basic principle of the system, the design equations and the limitations in performance