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Many non-destructive optical testing methods are currently used for material research, providing various information about material parameters. At RECENDT, a multimodal experimental setup has been designed that combines terahertz (THz) spectroscopy, optical coherence tomography (OCT), infrared (IR), and Raman spectroscopy with a tensile test stage. This setup aims to gather material information such as crystallinity and optical parameters of high-density polyethylene (HDPE) during a tensile test. The setup compares common IR and Raman spectroscopy and the less common optical methods THz and OCT. Complementarity is achieved through different frequency ranges and measurement approaches, resulting in different measured optical material parameters and depths. During tensile testing, HDPE samples with varying crystallinity were analysed, and the determined optical parameters such as refractive index, birefringence, scattering coefficient of decay, and penetration depth can be correlated with the change in crystallinity. These findings demonstrate that the optical methods and their outcomes can be interconnected. With further optimization of the experimental setup, it would be possible to observe the alignment of fibres in fibre composite panels and the stress distribution of polymers effectively. This opens interesting possibilities for polymer characterization in the future, including quality control during moulding processes and material testing.

A rugged handheld sensor for rapid in-field classification of cannabis samples based on their THC content using ultra-compact near-infrared spectrometer technology is presented. The device is designed for use by the Austrian authorities to discriminate between legal and illegal cannabis samples directly at the place of intervention. Hence, the sensor allows direct measurement through commonly encountered transparent plastic packaging made from polypropylene or polyethylene without any sample preparation. The measurement time is below 20 s. Measured spectral data are evaluated using partial least squares discriminant analysis directly on the device’s hardware, eliminating the need for internet connectivity for cloud computing. The classification result is visually indicated directly on the sensor via a colored LED. Validation of the sensor is performed on an independent data set acquired by non-expert users after a short introduction. Despite the challenging setting, the achieved classification accuracy is higher than 80%. Therefore, the handheld sensor has the potential to reduce the number of unnecessarily confiscated legal cannabis samples, which would lead to significant monetary savings for the authorities.

In this contribution, we present a high-speed, multiplex, grating spectrometer based on a spectral coding approach that is founded on principles of compressive sensing. The spectrometer employs a single-pixel InGaAs detector to measure the signals encoded by an amplitude spatial light modulator (digital micromirror device, DMD). This approach leads to a speed advantage and multiplex sensitivity advantage atypical for standard dispersive systems. Exploiting the 18.2 kHz pattern rate of the DMD, we demonstrated 4.2 ms acquisition times for full spectra with a bandwidth of 450 nm (5250–4300 cm−1; 1.9–2.33 µm). Due to the programmability of the DMD, spectral regions of interest can be chosen freely, thus reducing acquisition times further, down to the sub-millisecond regime. The adjustable resolving power of the system accessed by means of computer simulations is discussed, quantified for different measurement modes, and verified by comparison with a state-of-the-art Fourier-transform infrared spectrometer. We show measurements of characteristic polymer absorption bands in different operation regimes of the spectrometer. The theoretical multiplex advantage of 8 was experimentally verified by comparison of the noise behavior of the spectral coding approach and a standard line-scan approach.