Proximate Imaging
Most of the work above focused on at least modest stand-off distances (> 1 m) with macroscopic object sizes (≥ 1 m). In addition, many proximate images have been made, often with THz-TDS systems [1].
In a typical experiment the target is placed at the focus of a pair of small f-value off-axis parabaloids that focus the radiation on a small point and collect the transmitted radiation. The sample is then raster scanned to produce an image. A particularly interesting example, perhaps the first made with THz-TDS methods, uses a leaf to show the migration of water as the leaf dries [1].
In a very different application SMM/THz imaging has been used in the study of art and archaeological objects [4]. Since many of these objects are layered and have relatively large transmission, this appears be a particularly good application of THz-TDS techniques.
The interest reader is referred to an extensive literature on this subject [5].
References
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