One of the most fascinating spectroscopic techniques, the terahertz time-domain spectroscopy (TDS) is now barely 25 years old. It appeared in the mid 80s in the pioneering works of D.H. Auston and had become a technique applicable to materials research in early 90s. Now, terahertz time-domain technique is a rapidly emerging measurement technique constantly finding new applications in various areas as diverse as the semiconductor, medical, manufacturing, space, and defense industries.
Terahertz time-domain systems allow for 3-D imaging with a high degree of precision. This 3-D imaging approach takes advantage of the fact that it takes longer for terahertz pulses to reflect off of a surface that is farther away than one which is closer. This provides the exact distance to the target as well as the thickness and density information. In addition, different materials absorb different terahertz frequencies, providing a unique fingerprint. As a result, terahertz time-domain systems can identify the chemical composition of the materials. This is what provides the spectroscopic aspect of terahertz radiation, the unique absorption of certain terahertz frequencies. Terahertz time-domain system is also able to sort and differentiate various materials which are not sortable using other competitive techniques. This is done based on different absorption characteristics of materials in terahertz frequency range.
Since many materials are transparent to terahertz radiation, the items of interest can be observed through visually opaque intervening layers, such as packaging and clothing. Moreover, reflections from buried interfaces and defects can be found and precisely imaged. This technology is the best performing for subsurface imaging, uniquely identifying subsurface material and identifying on surface and subsurface feature defects.
A rugged and compact terahertz time-domain system can be the powerful measurement and sensing tool of many scientific and industrial applications.