Terahertz (THz) radiation is electromagnetic radiation with wavelengths are in the range of 0.03 mm to 3 mm. It has frequencies are higher than those of radio waves and microwaves, but lower than those of infrared light. THz radiation thus lies well outside the visible range and can penetrate materials such as plastic, cardboard, wood and composite materials. This makes it a valuable and desirable alternative to harmful x-rays for medical imaging and security applications.