Optical constants of harmful and highly energetic liquids for application to THz screening systems
(2016)
The far-infrared (IR) optical constants of a set of hazardous and flammable liquids have been obtained by means of spectroscopic ellipsometry in attenuated total reflection configuration over a broad spectral range. Such liquids recently became of considerable concern for transportation security measures worldwide. Their optical identification at check-in gates can only become possible if the characteristic spectra are already known. The refractive indices and the extinction coefficients reported here contribute to a spectroscopic data base in the far-IR and terahertz (THz) spectral regions and may support modeling the performance of THz screening systems on liquids for airports and other security sensitive areas. Examples of several container material/liquid systems are discussed. From the measured optical constants typical THz waveforms are calculated and discussed.
We present a handheld fiber-coupled terahertz spectrometer operating at a center wavelength of 1550 nm. The key elements are a fs-fiber laser, a fiber stretcher delay line and fiber-coupled antennas, which contain novel InAlAs-InGaAs multi layer chips. First experimental data obtained with this system demonstrates its great potential and robustness. In addition, we investigate different hazardous and harmless liquids in reflection geometry. These experiments show that liquids are in principle distinguishable by terahertz spectroscopy. Finally, first steps towards an algorithm that allows for an extraction of the liquids dielectric properties are discussed. The algorithm works for the analysis of reflection data even if the liquid is located inside a container.