Terahertz imaging of objects in powders

The use of terahertz radiation for detecting and imaging objects hidden in powders is demonstrated. Glass, eggshell and various plastics have been imaged in powders such as wheat flour, talc and sugar. The method may have applications in quality control. The images have been compiled by making use of various features of the terahertz time-domain waveforms. Details arising from refraction and interference close to the resolution limit are discussed. A simple method is suggested for distinguishing between objects of different materials even if their thickness is unknown. The potential of THz radiation for measuring the local density profile of powders is also demonstrated