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.
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