  The present work reports on the generation of short-pulse coherent extreme
ultraviolet radiation of controlled polarization. The proposed strategy is
based on high-order harmonics generated in pre-aligned molecules. Field-free
molecular alignment produced by a short linearly-polarized infrared laser pulse
is used to break the isotropy of a gas medium. Driving the aligned molecules by
a circularly-polarized infrared pulse allows to transfer the anisotropy of the
medium to the polarization of the generated harmonic light. The ellipticity of
the latter is controlled by adjusting the angular distribution of the molecules
at the time they interact with the driving pulse. Extreme ultraviolet radiation
produced with high degree of ellipticity (close to circular) is demonstrated.
