Terahertz (THz) radiation generated from photoconductive antenna fabricated on a single crystal zinc oxide (ZnO) is presented. The THz-radiation power is saturated at bias voltages above 800V∕cm and the obtained spectrum extends up to 1 THz. Moreover, ZnO is found to be highly transparent in the visible, near-infrared, mid-infrared and THz frequency regions. The results depicted here will categorically unravel the prospects of using ZnO as a material for integrated active optics.
A new field-emission x-ray radiography system based on our design is described. The key component of the system is a triode-type x-ray source with a built-in nanostructured electron source. The electron source is comprised of palladium-induced carbon nanofibers, which continue to field-emit electrons for more than 10 h at 2×10−7 Torr with a fluctuation of ±8%. Feedback control of the potential of the electron-extracting electrode, or the gate, reduces the current fluctuation to ±0.5%, but this current regulation does little to improve the image resolution. Our system provides sharp x-ray images of both biological and nonbiological samples.
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