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Construction and demolition waste are one of the largest waste streams generated in the EU by volume. They consist of materials such as concrete, bricks, gypsum, wood, glass, metals, foams, plastics, solvents, asbestos, asphalt, and excavated soil. Nowadays, many of them can be recycled, some even endlessly. This research attempts to contribute to the non-destructive characterization of such a waste with a novel method using terahertz radiation. By combining terahertz imaging and spectroscopy, we performed analytical characterization of selected building materials. The results demonstrate that terahertz technology allows an inside view into some of the non-conducting building materials. THz imaging can detect and visualize the organic solvents in the insulation material, which are often disposed of together with construction and demolition waste. It can also visualize the content of foreign objects or hazardous and toxic substances, which is important for their separation in the recyclate according to the type of the material. Furthermore, THz spectra reveal some spectral lines that can differentiate between different plastics and polymers within the frequency range of 1.0-4.5 THz due to different material structures and chemical compositions. Such results significantly contribute to the decision of which product meets all the standards, which can be returned to the production process due to irregularities or may be disposed of as waste. The only way to reduce construction and demolition waste in the future is to encourage the adoption of innovative technologies like terahertz spectroscopy in combination with traditional methods. This approach can bring some changes also to the construction design philosophy toward more sustainable buildings with minimum end-of-life demolition.

The terahertz range of the electromagnetic spectrum reveals important insights when studying material properties. An ultra-broadband terahertz time-domain spectroscopy system based on state-of-the-art, high-stability organic nonlinear optical crystals used as both THz wave generator and detector is presented. In transmission geometry, a broad spectrum exceeding 20 THz and a high dynamic range of more than 80 dB is achieved using a compact 100 MHz femtosecond laser working at telecom wavelength 1560 nm. In the normal-incidence reflection geometry, a similar bandwidth with a dynamic range surpassing 60 dB is reported. The experimental results are supported by a complete theoretical model, which includes the pump pulse duration, THz phonon/vibrational modes of the organic crystals and optical/THz beam path optimizations. The effectiveness of the newly developed system is demonstrated by measuring pharmaceutical samples with distinct THz features in the ultra-broadband THz range and by measuring narrow water vapor lines at a spectral resolution of 2.7 GHz (0.090 cm−1), resulting in an excellent accuracy with a frequency deviation of less than 0.05% from the reference values.

Organic π-conjugated crystals with second-order optical nonlinearity are considerably attractive materials for diverse terahertz (THz) wave photonics. An overview of the research of organic nonlinear optical (NLO) crystals for THz wave generation, detection, and applications is provided here. First, the status of organic NLO crystals compared to other alternative THz materials is described. Second, the basic theory and requirements for organic THz generators and detectors are explained. Third, with a primary focus on the organic NLO crystals that have been developed during the last decade, various molecular engineering approaches are discussed from the perspective of THz photonics. Finally, various types of high-power broadband coherent THz sources and their applications in THz nonlinear optics are discussed.

DSTMS organic electro-optic crystal is a very promising and efficient THz-wave generation material. It allows for both very high THz electric fields generation, exceeding several GV/m using optical rectification of femtosecond laser pulses, as well as the possibility for extremely broad bandwidth extending well beyond 10 THz [1]. However, the usual laboratory THz systems based on these crystals exploit very bulky and expensive fs laser systems [2], which are not desired for industrial THz imaging and spectroscopy applications [3,4]. Recently, some compact system employing organic crystals were demonstrated [5], however they use a conventional photoconductive antenna as a THz-wave detector. Here we present a compact THz time-domain spectroscopy system based on a relatively low-cost and small-size femtosecond fiber lasers operating at 1560 nm. As the THz generation and detection material, we choose the organic crystal DSTMS (4-N,N-dimethylamino-4‘-N‘-methyl-stilbazolium 2,4,6-trimethylbenzenesulfonate), since it reaches the highest overall efficiency and the flattest spectrum among the presently known state-of-the-art organic crystals (Figure 1).

Ultra-broadband THz photonics covering the 0.3–20 THz range provides a very attractive foundation for a wide range of basic research and industrial applications. However, the lack of ultra-broadband THz devices has yet to be overcome. In this work, high-density organic electro-optic crystals are newly developed for efficient THz wave generation in a very broad THz spectral range and are successfully used for a broadband THz time-domain spectroscopy. The new organic THz generator crystals, namely the OHP-TFS crystals, have very low void volume, high density, and are shown to cover the ultra-broadband THz spectrum up to about 15 THz, which cannot be easily accessed with the more widely used inorganic-based THz generators. In addition to the very favorable broadband properties, the generated THz electric-field amplitude at the pump wavelength of 1560 nm is about 40 times higher than that generated by a commercial inorganic THz generator (ZnTe crystal). By using the newly developed OHP-TFS as generation crystal in a compact table-top all-organic THz time-domain spectrometer based on a low-cost telecom fiber laser, the optical characteristics of a model material are successfully determined in the broad 1.5–12.5 THz range with high accuracy.

We demonstrate ultrabroadband THz-wave generation and detection in a compact system based on a femtosecond fiber laser at 1560 nm and optical rectification in organic electro-optic crystals DSTMS. Terahertz time-domain spectroscopy with a spectrum extending up to 20 THz with a maximum bandwidth exceeding 70 dB is possible with this system.

There is a need for fast and reliable quality and authenticity control tools of pharmaceutical ingredients. Among others, hormone containing drugs and foods are subject to scrutiny. In this study, terahertz (THz) spectroscopy and THz imaging are applied for the first time to analyze melatonin and its pharmaceutical product Circadin. Melatonin is a hormone found naturally in the human body, which is responsible for the regulation of sleep-wake cycles. In the THz frequency region between 1.5 THz and 4.5 THz, characteristic melatonin spectral features at 3.21 THz, and a weaker one at 4.20 THz, are observed allowing for a quantitative analysis within the final products. Spectroscopic THz imaging of different concentrations of Circadin and melatonin as an active pharmaceutical ingredient in prepared pellets is also performed, which permits spatial recognition of these different substances. These results indicate that THz spectroscopy and imaging can be an indispensable tool, complementing Raman and Fourier transform infrared spectroscopies, in order to provide quality control of dietary supplements and other pharmaceutical products.

Terahertz (THz) spectroscopy and imaging is used to analyse different types of thermal building insulation materials. First, the absorption coefficients of polymer foams are calculated, showing an inverse relationship with thermal conductivity. In addition, manufacturing imperfections and internal structures within the foams are clearly visualized with THz amplitude imaging. Secondly, different fibre orientations within aerogel composite blanket are recognized in THz spectra and amplitude images. Lastly, the phase transition of microencapsulated phase-change material is indicated by occurrence of spectral peaks in THz spectrum. The selected method is promising for a non-destructive testing of the thermal insulation material properties and structure.

In different industrial applications, several strictly defined parameters of calcium-based microfillers such as average particle size, particle size distribution, morphology, specific surface area, polymorphism and chemical purity, play a key role in the determination of its usefulness and effectiveness. Therefore, an analytical tool is required for rapid and non-destructive characterization of calcium-based microfillers during the synthesis process or before its use in a further manufacturing process. Since spectroscopic techniques are preferred over microscopy and thermogravimetry, particularly due to its non-destructive nature and short analysis time, we applied terahertz (THz) spectroscopy to analyse calcite microfillers concentration in polymer matrix, its granulation and chemical treatment. Based on the analysis of peak absorbance amplitude, peak frequency position, and the appearance of additional spectral features, quantitative and qualitative analysis was successfully achieved. In addition, THz imaging was also applied for both quantitative and qualitative analysis of calcium-based microfillers. By using spatial distribution map, the inhomogeneity in concentration of calcium carbonate in polymer matrix was characterized. Moreover, by THz spectroscopy and imaging different calcium compounds were detected in binary mixtures. Finally, we demonstrated that the applied spectroscopic technique offers valuable results and can be, in combination with other spectroscopic and microscopic techniques, converted to a powerful rapid analytical tool.

We study the impact of anisotropic nanoparticles (NPs) on the nematic liquid crystal (LC) order. Within a mesoscopic Flory–Huggins-type approach we have estimated regimes where LC–NP mixtures are essentially homogenous. Using a lattice Lebwohl–Lasher type approach we have also studied the impact of anisotropic NPs on LC ordering. We analysed the cases where the orientations of NPs are either frozen-in or could be varied, to which we refer as random field mixtures and annealed mixtures, respectively. In the latter case we have demonstrated the existence of qualitatively different regimes. In particular, we determined the concentration regime, where LC configurations resembling a transparent nematic phase could be observed. Such domain patterns are stabilised by NPs hindering the annihilation of topological defects in LC order.

In last two decades, rapid development in the field of terahertz (THz) technology has opened new possibilities for creating innovative imaging and sensing systems. Although the applications of THz technology in different sectors constantly increase, the construction industry lags behind them. The aim of this article is to review the current applications of THz spectroscopy in research and industry related to construction and building materials, along with the key drawbacks of technology and recommendations for future use. The review concludes that THz spectroscopy and imaging have promising potential and provide many opportunities for applications in construction and building materials characterization.

Structural analysis of polymer foams for insulation enables manufacturers and research facilities to optimise their products and production processes for applications such as building construction. Therefore, two- and three-dimensional investigation of the macro- and microstructure of these materials is important in order to characterize their physical and mechanical properties. In this paper, we present terahertz time-domain spectroscopy and pulsed imaging method to analyse the macroscopic structure of foamed polymers including analysis of voids, inclusions and bead distribution. By measuring the difference between the terahertz waveforms and by calculating the spectroscopic constants we analyse certain material characteristics such as foam density and infrared radiation absorption. Furthermore, we demonstrate that terahertz techniques have several advantages over other technologies, in particular as a non-ionizing alternative to X-ray tomography, and a complementary imaging method to optical or electron microscopy enabling chemical and structural characterization of foamed polymers.

Several pharmaceutical drugs, such as alprazolam, ibuprofen, acetaminophen, activated carbon and others, and caffeine-containing foods were tested using terahertz (THz) time domain spectroscopy in the range from 0.3 to 2 THz. The dry powder of pharmaceutical drugs was mixed with HDPE and pressed into the pellets using hydraulic press. The coffee grounds were also pressed into the pellets after ball-milling and mixing with HDPE. The caffeine containing liquid foods were dried out on the paper strips of various stacking. Experiments allow one to determine characteristic spectral signatures of the investigated substances within THz range caused by active pharmaceutical ingredients, like in the case of caffeine, as well as supporting pharmaceutical ingredients. Spectroscopic THz imaging approach is considered as a possible option to identify packaged pharmaceutical drugs. The caffeine spectral features in the tested caffeine containing foods are difficult to observed due to the low caffeine concentration and complex caffeine chemical surrounding.

Terahertz time-domain spectroscopy and imaging is used to study the effects of various hiding techniques of spectral features of drug and explosive simulants in combination with different paper and textile barriers. Results show that rapid detection and identification of concealed simulants is possible in the frequency range from 1.5 to 4.0 THz by using an organic-crystal-based terahertz time-domain system and the spectral peak analysis method.

A new polymorphic crystal form of piroxicam was discovered while preparing crystalline samples of piroxicam for 14 N nuclear quadrupole resonance (NQR) analysis. The new crystal form, designated as V, was prepared by evaporative recrystallization from dichloromethane. Three known polymorphic forms (I, II, and III) were also prepared. Our aim was to apply 14 N NQR to characterize the new polymorphic form of piroxicam and compare the results with those of the other known polymorphic forms. Additional analytical methods used for characterization were X-ray powder diffraction (XRPD), thermal analysis, and vibrational spectroscopy. For the first time, a complete set of nine characteristic 14 N NQR frequencies was found for each prepared polymorph of piroxicam. The consistent set of measured frequencies and calculated characteristic quadrupole parameters found for the new polymorphic form V is a convincing evidence that we are dealing with a new form. The already known piroxicam polymorphic forms were characterized similarly. The XRPD results were in accordance with the conclusions of 14 N NQR analysis. The performed study clearly demonstrates a strong potential of 14 N NQR method to be applied as a highly discriminative spectroscopic analytical tool to characterize polymorphic forms.

Date of Conference: 5-9 May 2014 Conference name: SPIE Sensing Technology + Applications, 2014 - Proceedings - Terahertz Physics, Devices, and Systems VIII: Advanced Applications in Industry and Defense We present results on the comparison of different THz technologies for the detection and identification of a variety of explosives from our laboratory tests that were carried out in the framework of NATO SET-193 THz technology for stand-off detection of explosives: from laboratory spectroscopy to detection in the field under the same controlled conditions. Several laser-pumped pulsed broadband THz time-domain spectroscopy (TDS) systems as well as one electronic frequency-modulated continuous wave (FMCW) device recorded THz spectra in transmission and/or reflection. © 2014 SPIE.

We report on measurements of the refractive indices and the absorption in bulk single crystals of aluminum nitride, in the region from 1 to 8 THz. The birefringence is approximately 0.2 and is larger than in the optical frequency range. Both indices exhibit normal dispersion with no pronounced absorption resonances. Optical power loss coefficients are approximately 2 cm−1 and 4 cm−1 and the estimated static dielectric constants are 7.84 and 9.22, for the ordinary and extraordinary polarization, respectively.