- Material inspection, non-destructive testing, security applications
- Non-ionizing radiation – no health risks for humans or animals
- Imaging systems benefit from powerful all-electronic sources
Many plastic compounds and synthetics are transparent for terahertz light. This has been used for non-contact analysis and imaging of hidden objects. Researchers at Braunschweig University have used TOPTICA’s DFB lasers to examine the safety covers of airbags , demonstrating that terahertz imaging provides an alternative to conventional - destructive - testing methods. In a feasibility study that aimed at security-related applications, researchers at TeraView Ltd. (Cambridge, UK) employed terahertz radiation to depict a ceramic knife blade hidden behind black denim. Other imaging applications include the examination of the water content of foodstuffs inside their air-tight packaging, or the structure of pharmaceuticals.
Compared to X-rays, a distinct advantage of terahertz radiation is its non-ionizing nature. X-rays, due to their high photon energy, are ionizing and therefore pose significant health risks for humans and animals. With terahertz radiation, by contrast, there is no danger of chemical bonds being broken up or the examined material being modified in any way. Terahertz radiation is generally considered biologically innocuous.
A limitation of opto-electronic imaging systems is the long acquisition time: An image has to be created in a pixel-by-pixel scan, with integration times in the order of seconds for each pixel. Thus, total imaging time ranges from tens of minutes to many hours. Much faster imaging is feasible with all-electronic systems, at millimeter-wavelengths (e.g., 100 GHz or 300 GHz). Frequency-modulation continuous-wave (FMCW) techniques even provide three-dimensional information: A 2D translation stage moves the measurement head across the sample, and additional depth information is gathered by scanning the emission frequency of the electronic emitter. Modern systems generate a 3D image within a few minutes, yet achieve a dynamic range of 50 dB.
 R. Wilk et al., Appl. Optics 47, 3023 (2008).