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19 th International Symposium on Space Terahertz Technology P1-2 Progress of Space Terahertz Technology in China * Cunlin Zhang and Guozhong Zhao Department of Physics, Capital Normal University, Beijing 100037, China Cunlin_zhang@mail.cnu.edu.cn Terahertz science and technology attract more and more attentions of scientists and techniques in the recent years. The space terahertz technology is becoming into a hot spot in the field of the space research and the space application. We present the progress of space terahertz technology in china in this paper. Except for the exploring the application of terahertz technology on the space positioning, the remote sensing, and the monitoring of cosmic rays, and so on, we are focusing on the application of the new technologies of terahertz imaging on the space technology. Instead of the point-by-point scanning of terahertz imaging, we have developed the two-demission quasi-real time of terahertz imaging technology. The infrared CCD with the operating wavelength of around 800 nm is used for the imaging of terahertz field by the electro-optic sampling. The scope of imaging depends on the size of the electro-optic crystal. The corresponding software is explored based on the LabVIEW programming. The stand-off terahertz imaging by the CCD detection is going on the development based on the cooperation between the Institute of Space Technology of China and the key lab of Terahertz Optoelectronics of Education Committee in the Capital Normal University. We also present the future trend of space technology of china including the terahertz imaging technology. Finally the cooperation between China and Europe is suggested with concerning on the basis of technology cooperation of other field. It is helpful for all us to exchange the idea on the application of terahertz technology on the space research. * This work is supported by the Basic Research Program of China (973, Grant No. 2007CB310408 and 2006CB302901) and Natural Science Foundation of Beijing (Grant No. 4073030)). 110
19 th International Symposium on Space Terahertz Technology P2-1 Superconducting contacts and NbN HEB mixers performance T. Bansal 1,2 , P. Khosropanah 2 , W. Zhang 2,3 , J.R. Gao 1,2 , T.M. Klapwijk 1 , 1 Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands 2 SRON Netherlands Institute for Space Research, Utrecht/Groningen, The Netherlands 3 Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing, P.R. China email:T.bansal@tudelft.nl Phonon-cooled superconducting NbN hot electron bolometer (HEB) mixers are so far the only sensitive heterodyne detector at high frequencies beyond 1.5 THz. It is known that under operating conditions the parabolic electron temperature set up due to the absorbed LO power depends on the boundary conditions, related to the contact pads. 1 Earlier, we have reported that the sensitivity of such a mixer can depend on contact materials. The best sensitivities have been obtained by using a NbTiN superconductor layer between thin NbN and Au in the contacts. 2,3 In this work we replace the 10nm thick NbTiN with 10 nm thick Nb. The motivations are: a) Gain a new insight of the role of the contacts and ultimately the physics; b) Nb process is much more widely available; c) Establish a more reproducible fabrication process. We have succeeded in realizing HEB mixers using both contacting materials on a single wafer with the same fabrication steps except for the contacting materials. The bolometer is based on a typical thin NbN film 4 grown on a Si substrate with a critical temperature of 9.5 K. The bolometer has a dimension of 0.2 μm×2 μm and is terminated by a spiral antenna with an upper cut-off frequency of ~6 THz. We are currently evaluating the heterodyne performances of both types of mixers. The first device of HEBs with Nb contacts has demonstrated a DSB receiver noise temperature of 1230 K at 2.5 THz at the optimal LO power (190 nW) and bias and using an uncoated Si lens. This value was measured directly by recording the output noise power responding to hot/cold loads at the same bias current 5 . If we correct the loss due to the absence of the antireflection coating, we expect to reduce this noise temperature to 980 K, which is practically same as the best performance reported at this frequency from a NbTiN contacted HEB previously 2 . References: 1. R. Barends, M. Hajenius, J. R. Gao, T.M. Klapwijk, “Current inducd vortex unbinding in bolometer mixers”, Appl. Phys. Lett, 87, 263506 (2005). 2. M. Hajenius, J. J. A. Baselmans, J. R. Gao, T.M. Klapwijk, P. A. J. de Korte, B. Voronov and G. Gol’tsman, “Low noise NbN superconducting hot electron bolometer mixers at 1.9 and 2.5 THz”, Supercond. Sci. Technol. 17, S224– S228 (2004). 3. J. J. A. Baselmansa, M. Hajenius, J. R. Gao, T. M. Klapwijk, P. A. J. de Korte, B. Voronov and G. Gol’tsman “Doubling of sensitivity and bandwidth in phonon cooled hot electron bolometer mixers” Appl. Phys. Lett, 84, 1958- 1961 (2004). 4. The NbN thin film was provided by SCONTEL, Moscow, Russia ( http:/www.scontel.ru). 5. P. Khosropanah, J. R. Gao, W. M. Laauwen, M. Hajenius, and T. M. Klapwijk, “ Low noise NbN hot electron bolometer mixer at 4.3 THz”, Appl. Phys. Lett. 91, 221111 (2007). 111
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