This technology relates to detecting radiation by directing an optical beam into a volume of gas, ionizing a portion of the volume of gas with the optical beam to produce a plasma, and then detecting an acoustic signal produced from an interaction of a radiation wave with the plasma. This technology relates to the phenomenon of enhanced acoustic emission from laser-induced plasma under the influence of a single-cycle terahertz pulse. Aspects of this technology bridge the unintentional gap between THz photonics and photo-acoustics. Terahertz (THz) waves occupy a segment of the electromagnetic spectrum between the infrared and microwave bands. As such, they can be used for imaging and sensing in ways not possible with conventional technologies such as X-ray and microwave. Because THz radiation transmits through almost anything that is not metal or liquid, the waves can see through most materials that might be used to conceal explosives or other materials, such as packaging, corrugated cardboard, clothing, shoes, backpacks, and book bags.