“…Beam intensity and polarisation were enlarged using circularly polarised UV laser light for photoionisation of unpolarised atoms. Based on this method (Fano effect), two sources of polarised electrons were built in Bonn; one operating with caesium, the other with rubidium gas [26,27]. At the Bonn 2.5 GeV synchrotron, with the help of the rubidium source, polarised electrons were accelerated for the first time worldwide in a synchrotron [28].…”