  We have developed a detector which records the full polarisation state of a
terahertz (THz) pulse propagating in free space. The three-electrode
photoconductive receiver simultaneously records the electric field of an
electromagnetic pulse in two orthogonal directions as a function of time. A
prototype device fabricated on Fe+ ion implanted InP exhibited a cross
polarised extinction ratio better than 390:1. The design and optimisation of
this device are discussed along with its significance for the development of
new forms of polarisation sensitive time domain spectroscopy, including THz
circular dichroism spectroscopy.
