Terahertz radiation lies between microwaves and infrared on the electromagnetic spectrum. It has properties that make it useful for imaging, as it can penetrate materials like plastic, wood, clothes, and cardboard, while providing higher resolution than microwaves. However, there is currently a "technological terahertz gap" with no cheap and easy sources or detectors available. Terahertz imaging shows promise for applications in security, military, medicine, industry, and astronomy by allowing the detection of non-metallic objects and providing safe, non-ionizing radiation for security screening. There are two main approaches: active systems that illuminate the target, and passive systems that detect the target's natural thermal emissions from a distance without privacy

5. Why bother?