POSIPOL: From polarized and unpolarized photons to positrons

POSIPOL represents a series of workshops dedicated, mainly, to polarized positrons for linear colliders using circularly polarized photons. Two methods were considered: the Compton backscattering of circularly polarized laser photons on electron beams and radiation from high-energy electrons in a helical undulator. The items have been progressively extended to other polarized beams and also to unpolarized positron beams generated by photons emitted by channeled electrons in oriented crystals. After a short historical survey, this article will emphasize on the last scientific and technical developments associated to the positron sources concerning the target resistance to high incident powers, the capture with magnetic lenses, the polarimetry, the emittance preservation,.... A description of the main issues and some preliminary conclusions will also be given.