＜正＞During the past few years,the terahertz（THz）frequency regime has had renewed scientific and technological interest because of recent breakthroughs in the areas of high power sources,sensitive detectors,novel materials,and high resolution video imaging.Because it lies between the radio frequencies and infrared wavelengths,the terahertz electromagnetic region was thought to be promising for practical applications（300 micrometers wavelength corresponds to 1 THz frequency）,but it suffered from very high attenuation through the atmosphere（above 1 dB/meter）,and was found to be difficult to generate,modulate,and detect.On the other hand,many non-polar dielectric materials are transparent to THz waves,allowing the detection of inclusions,internal in homogeneities,or materials behind dielectric obstacles for
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