We employ thickness gauging with a fast terahertz time-domain spectroscopy (TDS) system based on electronically controlled optical sampling (ECOPS) and compare the results with those of a benchmark conventional terahertz TDS system and a mechanical micrometer gauge. The results of all technologies are in good agreement. We show that the ECOPS system is suitable for fast inline thickness measurements, owing to high measurement rate of 1600 traces per second. Moreover, we characterize the system with respect to signal quality. The time-domain dynamic range is ~60 dB for a single-shot measurement, and ~90 dB with 1000 trace averages, which are completed within less than a second (i.e., 0.625 seconds). The time-domain signal-to-noise ratio amounts to ~50 dB and ~80 dB for 1 and 1000 averages, respectively.
We present an overview of current opto-electronic terahertz platforms designed for industrial applications. We discuss current and future market perspectives with respect to competing technologies and killer applications. “Make-or-break” features for industrial use are cost and volume reduction alongside with increased robustness and measurement speed. These market challenges are discussed for different technologies, and one representative industrial application is shown for each technology.
Over the last decades, scientists have paid growing attention towards the terahertz properties of liquid crystals. On the
one hand, the dielectric properties of liquid crystals are relatively unexplored at terahertz frequencies, and the observed
low-energy phenomena are not yet well understood. On the other hand, terahertz technology requires switchable devices,
in which liquid crystals could potentially serve as a base material. This paper gives an overview of the research done so
far on the properties and applications of liquid crystals in the terahertz frequency range. The path from first liquid-crystal
terahertz experiments to comprehensive studies of their structure-property relation is outlined. Furthermore, the
evolution from basic concepts to first liquid-crystal terahertz devices is sketched, and prospects as well as future
challenges are discussed. Due to the development of compact and cost-efficient components, terahertz spectrometers
matured from room-filling laboratory instruments to compact, reliable scientific tools. Modern terahertz systems are thus
also covered in this report. Liquid-crystal devices could help terahertz technology continue this trend, and pave the way
to a wider range of application.
The worldwide production volume of polymers is still rising exponentially and the number of applications for plastic
components steadily increases. Yet, many branches within the polymer industry are hardly supported by non-destructive
testing techniques. We demonstrate that terahertz (THz) spectroscopy could be the method of choice to ensure high-quality
polymer products. Applications range from the in-line monitoring of extrusion processes and the quality control
of commodities in a mass production up to a total inspection of high-tech safety relevant products. Furthermore, we
present an extension to THz time-domain spectroscopy in the form of a new data extraction algorithm, which derives the
absorption coefficient, the refractive index and the thickness of a sample with very high precision in a single pass.
Apart from that, we discuss the ability of THz systems for quality control of polymeric compounds. Here, it is essential
to monitor the additive content as well as additive inhomogeneities within the mixture. Recently, we built a fiber-coupled
THz spectrometer for in-line monitoring of compounding processes. Additionally, we demonstrate the potential of THz
systems for the non-destructive and contactless testing of structural components. THz imaging is capable of analyzing
material thicknesses, superstructures, the quality of plastic weld joints, and of detecting flaws in components.
Plastics and THz form a very fruitful symbiosis. In return, plastics industry can provide THz systems with custom-tailored
components, which have very attractive properties and extremely low costs. Examples of this development are
photonic crystals or polymeric Bragg filters, which have recently been demonstrated.
We present a compact, robust, and transportable fiber-coupled THz system for inline monitoring of polymeric
compounding processes in an industrial environment. The system is built on a 90cm x 90cm large shock absorbing
optical bench. A sealed metal box protects the system against dust and mechanical disturbances. A closed loop controller
unit is used to ensure optimum coupling of the laser beam into the fiber. In order to build efficient and stable fiber-coupled
antennas we glue the fibers directly onto photoconductive switches. Thus, the antenna performance is very
stable and it is secured from dust or misalignment by vibrations. We discuss fabrication details and antenna performance.
First spectroscopic data obtained with this system is presented.