THz near-field spectroscopic visualization of metal-hole array

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In this project, we proposed and developed a new technique which enables terahertz (THz: 0.1-10 GHz) near-field spectroscopic visualization of metal-hole array. The self-heterodyne technique and nonpolarimetric electrooptic (EO) detection technique are the key. The frequency of the optical beat for the generation is shifted by an optical frequency shifter to realize THz self-heterodyne detection. The THz signal to be detected is once up-converted by the EO phase modulation in the fiber-mounted EO crystal (ZnTe), then down converted to the intermediate frequency band by the coherent detection of the generated sideband. Our coherent technique significantly improved not only the stability and the repeatability but also the simplicity of the measurements compared with the conventional polarimetric EO detection. As a result, phase evolution of the freely propagating continuous THz wave (125 GHz) and near-field of a metal-hole array have been demonstrated, for the first time.