New developments on the generation of arbitrary polarized radiation from insertion devices

The availability of free straight sections on existing storage rings and the construction of new synchrotron sources that will accommodate a large number of insertion devices (ID) has motivated a worldwide effort to design and build new exotic IDs capable of generating an arbitrary state of polarization. Recent developments are reviewed. The polarization characteristics from conventional undulators and wigglers are reviewed. Some insertion devices that were proposed and/or built to generate circular polarization and more generally to improve the control of polarization are described. They are the asymmetric and elliptical wigglers and the helical and crossed undulators.<>