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     The THz lab in the department of physics, Capital Normal University, established in 2001, boasts one of the top THz research institutions in China. It became the Beijing Key Lab of THz Spectroscopy and Imaging in 2006 and one year later the Department and Education Key Lab of THz Photonics. Its 1500 m2 campus includes two 170 m2 1000 grade clean rooms and many state-of-the-art research equipments. In the past three years, the THz lab has undertaken 23 state funded projects with grants of 1328 RMB in total. It has published over 60 SCI indexed papers including publications on Physics Review Letters, Applied Physics Letters, Optics Letters, Optics Express, Physics Letters A, Optics Communications, etc. Four patent applications have been filed with one being grated. It also has published 3 text books in THz science and technology.
     THz wave, sitting in the gap between middle infrared and millimeter wave, has been known as the last vacant area in spectrum that has not been quite understood and brought into applications. It has been the focus of research worldwide since early 1990s. Up to now there are 4 research areas in THz Lab in CNU, including THz spectroscopy, THz imaging, nondestructive evaluation using THz and infrared waves and the interaction between THz and materials.
1.THz spectroscopy. The THz domain homes to a plethora of rotational or vibrational transitions of organic compounds, including explosive chemicals, biological tissues, medical materials, and illicit drugs. These characteristic THz absorption peaks serve as spectroscopic fingerprints in identification of such materials. THz radiation is also highly transparent to a number of daily materials such as leather, wood, paper, plastic and ceramics. Furthermore, THz wave has so far proved to be noninvasive and nonionizing to biological bodies. Owning to the above advantages of THz radiation, THz spectroscopic technology has identified its potentials in a number of important applications, such as military detection, security inspection, portal screening, clinic diagnosis and biomedical research. THz spectroscopy research in CNU deals with developing a fast, accurate and convenient identification and analysis modality. This group has found distinct THz fingertips of a range of materials, such as explosive chemicals RDX, 2,4-DNT and TNT, medical chemicals Amoxicilllin, Cephalexin and Cephalexi, illicit drugs methylenedioxyamphetamine and methamphetamine, etc. Meanwhile, the THz group is equipped with Gaussion03 software for theoretical calculation and simulation of molecular structures, which has played essential roles in predict, confirm, as well as understand the THz spectroscopic responses of the above materials.
1. THz imaging. THz imaging has been envisioned as one of the most exciting applications of THz science and technology. Ever since the first THz image came into being in 1990 by B.B. Hu and J. Nuss, THz imaging has been an attraction of the most dynamic research entities all over the world. THz imaging, bearing its unique susceptibility to water content, density, thickness, absorption and scattering to the target, opened up a entire new horizon for THz technology by filling into the THz gap of the spectrum. It brought advantages over the conventional technology using X-ray, ultrasound and near infrared, in terms of its non-invasiveness, penetration and resolution. Based on two different schemes of THz generation configuration- pulsed THz wave generated by ultrafast lasers and continuous THz wave output from backward wave oscillator and Gunn diode, THz imaging research in CNU has been dynamically growing by benefiting from interdisciplinary research. It has realized real-time 2-D THz focal plane imaging, THz CT, THz DT, THz spectroscopic imaging, THz phase imaging and THz polarization imaging. Its work has been recognized by many renowned optics and physics journals such as Applied Physics Letters, Optics Letters, Optics Express, Optics Communications, etc. It is also committed to the development of faster and more powerful imaging processing algorithms and applications dealing with spectroscopic imaging data, by using state-of-the art pattern recognition technologies, such as SOM, neural networks, wavelets, etc.
3. Nondestructive evaluation using THz wave combined with thermal wave
Nondestructive evaluation using THz wave is the first THz technology that has been and is still being used in real application. Because of its excellent penetration and spectral characterization abilities, it has been pointed by NASA as one of the four nondestructive inspection modalities for insulation foam covering space shuttle vehicle. Thermal wave, which is a well-developed nondestructive imaging method, detects the defects buried inside the target by measuring the temperature response distribution of the target under heat excitations. These two technologies, by standing adjacently in the spectrum, shares many common properties in terms of propagation mechanism, hardware design, data acquisition and imaging analysis. They also compensate for each other in areas that are not covered by the other technology. For example, THz radiation doesn’t penetrate through metals while thermal wave imaging easily sees heat propagation through metal plates. The combination of the two technologies enables broader developments, finer imaging resolutions and more adaptive applications. THz lab in CNU has focused on developing THz and thermal wave nondestructive of a range of industrial materials, including aerospace microwave absorptive material, insulation foam and ceramic tile. 
4. Interaction between THz and matters
The interaction between THz and matters has been another intriguing area. The subwavelength transmission enhancement phenomena, which have been observed in microwave and near infrared, opened up the whole new horizon of surface plasma photonics. THz domain has been envisioned as a new battle field of this area by being considered easieror surface plasma stimulation. Meanwhile, the higher dielectric susceptibility in THz domain, together with its small absorption has made localization of 3-D random media much easier to detect. THz technology has provided a new platform for the research of multiple scattering and diffraction with its subwavelength spectral resolution and subcycle temporal resolution. THz research related with interaction between matters in CNU involves single cycle THz pulse and its nonlinear optical properties, femtosecond pump-THz probe carrier dynamics of semiconductors, subwavelength surface plasma and THz generated from laser induced air plasma.
Being an exuberant and dynamic research group with leading technologies, THz lab in CNU has identified its role in understanding THz mechanisms and bridging the gap between THz research and real world technologies. We have built solid connections with other THz groups in the world, such as Rensselaer Polytechnic Institute, Oklahoma State University, Rice University, Cambridge University, University of Leeds, University of Wollongong, etc. We welcome other groups sharing the same research interest to contact and join with us.

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