  Polarisation analysis of synchrotron THz radiation was carried out with a
standard stretched polyethylene polariser and revealed that the linearly
polarised (horizontal) component contributes up to 22 +/- 5% to the circular
polarised synchrotron emission extracted by a gold-coated mirror with a
horizontal slit inserted near a bending magnet edge. Comparison with
theoretical predictions shows a qualitative match with dominance of the edge
radiation. Grid polarisers 3D-printed out of commercial acrilic resin were
tested for the polariser function and showed spectral regions where the
dichroic ratio DR > 1 and < 1 implying importance of molecular and/or stress
induced anisotropy. Metal-coated 3D-printed THz optical elements can find a
range of applications in intensity and polarisation control of THz beams.
