The detection of explosives carried about the person is an important current security concern. Explosives absorb high frequency waves in a characteristic manner, depending on the frequency of those waves. The frequencies of interest are in the teraHertz (THz) range, about a thousand times as high as the frequency range used by mobile phones. Signals at these frequencies can pass through clothes with little absorption, so that concealed explosives can be detected.Generating signals at such extremely high frequencies is difficult and usually requires a large and expensive laser having power consumption similar to an electric oven. Such a system is not very practical for checking whether people are carrying explosives.We have developed very efficient converters of light to THz signals which can be used with very small semiconductor lasers, requiring a total power of about 1 W, about the same as a small torch. In this project we propose to use these converters with a new and very sensitive detection scheme to create a system for detecting concealed explosives.In addition this type of technology could be used in a compact scanning system to identify concealed weapons and other items of security interest.