Time reversal three-dimensional imaging using single-cycle terahertz pulses

We demonstrate three-dimensional imaging using single-cycle terahertz electromagnetic pulses. Reflection-mode imaging is performed with a photoconductive transmitter and receiver and a reconstruction algorithm based on time reversal. A two-dimensional array is synthesized from ten concentric ring annular arrays with numerical apertures ranging from 0.27 to 0.43. The system clearly distinguishes image planes separated by 1.5 mm and achieves a −6 dB lateral resolution of 1.1 mm. In terms of the illuminating terahertz power spectrum, the lateral resolution is 38% and 81% of the peak and mean wavelengths, respectively.