Terahertz measurement system based on frequency-selective detector chips for inline industrial monitoring

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The project aims at the development of a THz measurement system based on frequency-selective detector chips, the system targeting inline industrial monitoring applications. The fact that many dielectric materials have characteristic spectral features at THz frequencies and simultaneously are transparent, holds much potential for applications such as product control and authentication, biomedical analysis and material identification. Until now, the lack of fast frequency-resolved measurement techniques, or their price tag, have prevented such applications to be addressed in a satisfactory manner.The product “TeraSpeed” of the project partner Toptica Photonics AG represents a step in this direction, but has the shortcoming that it doesn’t utilize the available spectral information. The system works with spectrally broad THz pulses generated with advanced photoconductive emitters in combination with a mature optical fiber technology. Rectifying Schottky diodes (SDs) are employed for signal detection, averaging over several THz pulses. The spectral information is lost in the detection process and the detectors suffer from the strong intrinsic frequency roll-off of the sensitivity of the SDs notably above 1 THz.With the view towards the target application fields mentioned above, fast frequency-selective data acquisition especially in the frequency regime above 1 THz and over a large spectral range is a requirement. This is the pivotal point of this project. We aim to bring THz detectors based on antenna-coupled semiconductor field-effect transistors (so-called TeraFETs) into the measurement systems. In a number of the applicant’s projects such as the preceding DFG-funded project, TeraFETs have proven to be highly efficient THz detectors. While SDs represent the state-of-the-art below 1 THz, this role has gone to TeraFETs above 1 THz. TeraFETs have a much weaker frequency role-off and are superior in sensitivity to SDs above 1 THz, with a sensitivity range reaching multiple THz.The existing TeraSpeed platform with its optoelectronic source will be expanded by the use of TeraFET detectors, the frequency selectivity either being incorporated intrinsically in the narrowband, resonant antenna design of the TeraFETs, or extrinsically by the use of narrow-band filter structures made from frequency-selective surfaces to be used in combination with broadband TeraFETs. The system concept of the TeraSpeed will thus be extended into that of a multispectral THz measurement system. Its functionality will be demonstrated by application-relevant spectroscopic measurements, among which will be the rapid recording of security features for product authentication in an inline situation.