Advantages of THz Radiation
THz radiation has several distinct advantages over other forms of spectroscopy: many materials are transparent to THz, THz radiation is safe for biological tissues because it is non-ionizing (unlike for example X-rays), and images formed with terahertz radiation can have relatively good resolution (less than 1 mm). Also, many interesting materials have unique spectral fingerprints in the terahertz range, which means that terahertz radiation can be used to identify them. Examples which have been demonstrated include several different types of explosives, polymorphic forms of many compounds used as Active Pharmaceutical Ingredients (API) in commercial medications as well as several illegal narcotic substances. Since many materials are transparent to THz radiation, these items of interest can be observed through visually opaque intervening layers, such as packaging and clothing. Though not strictly a spectroscopic technique, the ultrashort width of the THz radiation pulses allows for measurements (e.g., thickness, density, defect location) on difficult to probe materials (e.g., foam). The measurement capability shares many similarities to that observed with pulsed ultrasonic systems. Reflections from buried interfaces and defects can be found and precisely imaged. THz measurements are non-contact however.
Read more about this topic: Terahertz Time-domain Spectroscopy, Explanation
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