Imaging technology has a rich history that began thousands of years ago. The reflection from a pool of still water or a shiny metal surface was arguably the first imaging method routinely used by mankind. With the advent of lenses, many other novel forms of optical imaging emerged, including telescopes and microscopes. Using a lens, a pinhole camera, and a sensitized pewter plate, Niépce was the first person to permanently record an image. Optical photography and other forms of optical imaging have since become commonplace.
Of course, imaging has not been constrained to optical frequencies. In 1895 Roentgen discovered X-rays. As with X-rays, whenever a portion of the electromagnetic (EM) spectrum became practically usable, it wasn’t long before it was adapted to an imaging configuration. Therefore, it is not surprising that many types of imaging systems exist today and utilize the radio, microwave, infrared (IR), visible, ultraviolet, X-ray, and gamma ray portions of the EM spectrum. Pressure waves have also been adapted to imaging and are manifest in the various forms of ultrasonic and sonographic imaging systems.
Terahertz (THz) radiation (0.1 THz to 10 THz, 1 THz = 1012 Hz) lies between the infrared (night vision cameras) and microwave (operating range of mobile phones) region of the electromagnetic spectrum. What makes these waves so fascinating to scientists is their ability to penetrate materials that are usually opaque to both visible and infrared radiation. For example, terahertz waves can pass through fog, fabrics, plastic, wood, ceramics and even a few centimeters of brick - although a metal object or a thin layer of water can block them. The way in which terahertz waves interact with living matter has potential for highlighting the early signs of tooth decay and skin or breast cancer, or understanding cell dynamics.