3. Industrial control

3.1 Imaging

For industrial applications, the appeal of terahertz technologies lies in their ability to observe objects, or defects in them, through materials that are opaque in other spectral ranges (visible and infrared), while being less dangerous and therefore easier to use than X-rays, or better spatially resolved than microwaves. Terahertz images can be acquired in several different ways: mainly by amplitude or phase contrast in transmission or reflection configurations.

• By transmission amplitude contrast

  The more or less opaque regions of the object are, for example, those that are damp or electrically charged. In the case of heterogeneous objects, regions with different chemical compositions can also...