Terahertz radiation penetrates a variety of materials that are traditionally considered opaque, such as paper, cardboard, plastics, or clothing. Terahertz imaging might thus be employed to detect concealed weapons, or hazardous substances in parcels and envelopes. In a feasibility study, researchers at TeraView Ltd. (Cambridge, UK) employed TOPTICA's DFB lasers to image a ceramic scalpel blade, hidden behind a layer of black denim cloth. At 0.5 THz the blade was clearly discernible (see figure above). The experiment proved the ability of terahertz imaging to reveal non-metallic objects, which present a particular challenge for traditional detection techniques.

Identifying the individual compounds in a mixture of gases by their spectral "fingerprint" calls for a spectroscopic approach. As gas absorption lines can be very narrow (∼ 10 MHz), a cw terahertz spectrometer with a high bandwidth (e.g. 50 .. 1500 GHz), yet with precise frequency resolution is required. TOPTICA’s laser technology is already employed in a prototype spectrometer, that aims at the detection of trace gases even in a cluttered environment. The envisaged application is the control of the air quality in public institutions, including a correct identification of potential threat chemicals against a background of e.g. cleaning agents, glues, perfumes and paint [1]. This scenario is particularly challenging as a complete library of terahertz spectral signatures does not yet exist. The high-resolution spectrometer thus also helps to augment existing spectral libraries.