Abstract
Due to the fast intersubband transitions, the terahertz (THz) quantum well photodetector (QWP) is supposed to work fast. Recently it has been demonstrated that the THz QWP can detect the THz light modulated at 6.2 GHz and therefore it can be used as a photomixer [H. Li et al., Sci. Rep. 7, 3452 (2017)]. In this work, the authors report a novel active THz imaging using THz QWP photomixers. The THz radiation source used for this imaging application is a multi-mode THz quantum cascade laser (QCL) operating in continuous wave mode. When the fast THz QWP is illuminated by the multi-mode THz radiation, the intermediate frequency signal that is resulted from the frequency beating between the neighbouring THz modes of the QCL can be extracted from the QWP mesa for imaging applications. Employing the technique, the frequency can be down-converted from the THz range to the microwave regime. And therefore, the signal can then be amplified, filtered, and detected using the mature microwave technology.
Highlights
The terahertz (THz) region is defined as a frequency range from 0.1 to 10 THz and lies between two well developed frequency bands: The microwave and infrared light
We just showed for the first time that the THz quantum well photodetector (QWP) can work fast and the inter-mode beat note signal at 6.2 GHz of a long cavity THz quantum cascade laser (QCL) was detected using the optimized THz QWP device.[29]
We demonstrate a terahertz imaging system taking the advantage of a novel THz fast detector (THz QWP) based on the technique of Ref. 28
Summary
The terahertz (THz) region is defined as a frequency range from 0.1 to 10 THz (wavelength from 3 mm to 30 μm) and lies between two well developed frequency bands: The microwave and infrared light. In 2005, Barbieri et al successfully demonstrated inter-mode beat note imaging with THz QCLs using a fast Schottky diode mixer.[28] Recently, we just showed for the first time that the THz quantum well photodetector (QWP) can work fast and the inter-mode beat note signal at 6.2 GHz of a long cavity THz QCL was detected using the optimized THz QWP device.[29] We demonstrate a terahertz imaging system taking the advantage of a novel THz fast detector (THz QWP) based on the technique of Ref. 28.
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