Electric field imaging using intense half-cycle terahertz pulses

Characteristics of terahertz (THz) imaging using approximately half-cycle THz pulses were studied using a large-aperture biased photoconductive antenna which emits an intense THz field with a large THz beam. Studies of the dependence of the THz image quality on delay time show that real-time imaging is possible if the probe pulse is timed appropriately. The best images were observed at a time window when the THz field had a steep transient. This allows two-dimensional imaging in a fixed-time mode, which enables observation of a nonstationary object. Using phase-sensitive electrooptic detection and scanning a delay time, not only two-dimensional time-domain spectroscopy is possible, but frequency-resolved images are also available. Depending on the frequency, we found that images of the actual shape or the edge of an object were obtained.