Fast Active THz Cameras with Ranging Capabilities
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Fast Active THz Cameras with Ranging Capabilities Christian am Weg & Wolff von Spiegel & Ralf Henneberger & Ralf Zimmermann & Torsten Loeffler & Hartmut G. Roskos
Received: 24 March 2009 / Accepted: 5 August 2009 / Published online: 26 August 2009 # Springer Science + Business Media, LLC 2009
Abstract We report on the realization of two active, fully electronic THz cameras, both operating at room temperature, but at different frequencies (645 GHz and 300 GHz, respectively). Active illumination together with the frequency-modulated-continuous-wave (FMCW) approach allows us to implement unique features such as phase-sensitive detection, suppression of spurious reflections and high resolution ranging. The measuring of the phase of the THz wave allows for sub-wavelength depth resolution while the ranging capabilities enable us to acquire an absolute depth map of objects under test with accuracy in the mm range. With both systems, we are able to acquire images with more than 55,000 pixels (phase and amplitude) in 9 seconds and the dynamic range exceeds 35 dB. The typical object distance is about 75–150 cm and the image size is in the order of hundreds of cm2 suitable for stand off detection of concealed weapons. Keywords Active illumination . THz camera . Frequency sweeping . Quasioptical system . FMCW . Ranging . Multi view
1 Introduction Many interesting ways of applying THz imaging [1–20] have been demonstrated in the last years. Slow image acquisition speeds prevent practical usage for many of them. On the way to a fast, room-temperature THz camera with high reliability, we present two different active systems with fast scanning optics and fully electronic detection. With both systems, C. am Weg (*) : W. von Spiegel : H. G. Roskos Physikalisches Institut, Johann Wolfgang Goethe-Universität, 60438 Frankfurt, Germany e-mail: [email protected] URL: http://www.uni-frankfurt.de R. Henneberger : R. Zimmermann RPG Radiometer Physics GmbH, Birkenmaarstraße 10, 53340 Meckenheim, Germany T. Loeffler SynView GmbH, Glaskopfweg 17, 61479 Glashütten, Germany
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J Infrared Milli Terahz Waves (2009) 30:1281–1296
we are able to acquire images (amplitude and phase) in a few seconds [4]. They are based on the same modular design, which allows setting up various configurations with different characteristics. Application of the FMCW concept of radar technology allows us to implement helpful properties, such as THz ranging, and working-distance selection. The setup for the 645-GHz System is shown in Fig. 1 while the setup for the 300-GHz system is shown in Fig. 2. A CAD drawing of the general setup for the active THz-cameras is shown in Fig. 1, the diagrams in Fig. 2; the 645-GHz system is shown in frame A, while the setup for the 300-GHz system is shown in frame B. The performance specifications for both systems are listed in Table 1 and Table 2 respectively. In the next section, we explain the general setup of the 645-GHz system and introduce the 300-GHz ranging-camera. Section 3 shows experimental data acquired w
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