Method and apparatus for the detection of terahertz radiation absorption

The invention is a method and apparatus for the detection of terahertz radiation. In one embodiment, frequency modulated spectroscopy is performed on a swept source of coherent far infrared electromagnetic radiation that is focused on a target. A beam of radiation passes through a cell in which the target is housed, losing energy as certain frequencies are absorbed by contaminants in the target. A detector is positioned to determine how much energy is lost by the radiation (e.g., which frequencies fail to transmit through the cell), thereby indicating the presence of contaminants in the target.