Towards recognition of energetic materials: terahertz imaging and sensing at higher frequencies

The terahertz (THz) frequency range is located between microwave and infrared radiation in the electroma¬gnetic spectrum. It spans from 300 GHz up to 10 THz. The transparency of different materials (e.g. cotton, paper, plastics, etc.) especially at lower THz frequencies opens a great variety of applications in the security sector, e.g. for the development of bodyscanners. However, in comparison to the commercially available mm-wave systems, THz systems are still at an early state of development. Most THz imaging systems still need seconds to produce an image. The THz identification of energetic materials is based on their resonant absorption, the so called spectral fingerprint. Up to a frequency of 3 THz, the resonant absorptions of many commonly used explosive materials are published. However, above 3 THz the characteristics of energetic materials are hardly known. Furthermore there is no reliable data on the precise dielectric properties of explosive materials available in literature. In this presentation, we report on a combined approach exploring the high-frequency THz recognition of energetic materials. Broadband THz time-domain spectroscopy (THz-TDS) with a bandwidth from 100 GHz to 6.5 THz is used to measure samples of different explosive materials in order determine directly the complex refractive index and the dielectric properties of a medium. Such analysis show characteristic resonances for each explosive.