Time reversal and object reconstruction using single-cycle terahertz pulses

Developments in optoelectronics for the generation and detection of singleand few-cycle terahertz pulses over the past 10 years have resulted in a heightened understanding of the diffraction and propagation of ultrashort electromagnetic transients. Particularly, the spatiotemporal shaping of singleand few-cycle THz pulses, as investigated by Bromage et al. and Budiarto et al. (1998), has served to verify the effects that diffraction through conductive apertures impose on such pulses. These same developments in optoelectronics have also resulted in numerous inventive applications for this radiation, whereby THz imaging technology has opened new applications in medical and industrial settings. We present novel form of imaging using mathematically reversed scattered fields to reconstruct objects under test. Similar to the innovations pioneered by Cheville et al. (1995) in impulse ranging with single-cycle THz pulses, we have performed an experiment that can serve as a scaled model for the diffraction of single-cycle pulses in other systems. For the two-fold study presented, the reconstruction of the electric field amplitude at any position on an object in one dimension was achieved by measuring the diffracted fields at several off-axis positions (with one object orientation). For a two-dimensional object, the reconstruction was accomplished by rotating the object about its central normal and measuring the scattered radiation at one off-axis position; consequently in both case, we are able to ascertain the shape of the diffracting object