A terahertz ray (T-ray) is an electromagnetic wave that has a frequency measured in trillions of cycles per second. Experimental imaging systems utilizing T-rays have been found to produce pictures with resolutions down to 150 micrometers. Thus, T-ray systems have a potentially wide range of applications in medicine and industry. For instance, they could be used to check the integrity of computer chip circuitry, monitor the freshness of foods, and look for defects in building materials such as plastics.