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Science 23 November 2007:
Vol. 318. no. 5854, pp. 1291 - 1293
DOI: 10.1126/science.1149802
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Reports
Emission of Coherent THz Radiation from Superconductors
L. Ozyuzer,1,2
A. E. Koshelev,2
C. Kurter,2,3
N. Gopalsami,4
Q. Li,2
M. Tachiki,5
K. Kadowaki,6
T. Yamamoto,6
H. Minami,6
H. Yamaguchi,6
T. Tachiki,7
K. E. Gray,2
W.-K. Kwok,2
U. Welp2*
Compact solid-state sources of terahertz (THz) radiation are being sought for sensing, imaging, and spectroscopy applications across the physical and biological sciences. We demonstrate that coherent continuous-wave THz radiation of sizable power can be extracted from intrinsic Josephson junctions in the layered high-temperature superconductor Bi 2Sr 2CaCu 2O 8. In analogy to a laser cavity, the excitation of an electromagnetic cavity resonance inside the sample generates a macroscopic coherent state in which a large number of junctions are synchronized to oscillate in phase. The emission power is found to increase as the square of the number of junctions reaching values of 0.5 microwatt at frequencies up to 0.85 THz, and persists up to  50 kelvin. These results should stimulate the development of superconducting compact sources of THz radiation.
2 Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, USA.
3 Physics Division, Illinois Institute of Technology, Chicago, IL 60616, USA.
4 Nuclear Engineering Division, Argonne National Laboratory, Argonne, IL 60439, USA.
5 Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa 277-8568, Japan.
6 Institute of Materials Science, University of Tsukuba, 1-1-1 Tennodai, Tsukuba-shi, Ibaraki-ken 305-8577, Japan.
7 Department of Electrical and Electronic Engineering, National Defence Academy, Hashirimizu 1-10-20, Yokosuka, Kanagawa 239-8686, Japan.
* To whom correspondence should be addressed. E-mail: welp{at}anl.gov
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