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THz Electromagnetic Wave Realizes High-resolution Imaging Technology
date£º2008-11-16 21:16:09 Click No.£º1862

Source: Tech-On!

    Japanese institutes developed a technology to shoot images with a spatial resolution exceeding the diffraction limit by using the ¡°terahertz electromagnetic wave,¡± which has a frequency of approximately 1THz (T = tera: 1012).

    By capturing the localized electromagnetic field (referred to as near-field light or evanescent light) generated behind the aperture that is smaller than the wavelength, the Japan Science and Technology Agency (JST) and Japan¡¯s Institute of Physical and Chemical Research (Riken) achieved a spatial resolution of approximately 9¦Ìm through the use of an electromagnetic wave with a wavelength of 214.6¦Ìm,

    This was enabled by fabricating a semiconductor device that integrates an opening (aperture), a near-field probe and a detector into a single chip. Two-dimensional electron gas immediately under the probe is used as a detector.

    The terahertz electromagnetic wave is positioned between light and electromagnetic waves and passes through materials that won¡¯t allow visible light to pass through. When comparing electromagnetic wave to electron, the terahertz electromagnetic wave has a photon energy on the order of milli-electron-volt. This is reportedly comparable to the electronically-excited state of a semiconductor or a superconductor.

    With such features, the terahertz electromagnetic wave is expected to be used for the food inspection, the nondestructive test of building, etc, the disconnection test for LSIs and the biological test, the institutes said.

    However, the terahertz electromagnetic wave has a long wavelength of about 100-500¦Ìm. Thus, without the near-field light technology, it can only provide a spatial resolution that is equivalent to the wavelength. In addition, there haven¡¯t been any commercial detectors that were sensitive enough until now, the institutes said.

    This time, JST and Riken designed and fabricated a device that integrates the components necessary for the near-field light measurement into a single semiconductor chip with the GaAs/AlGaAs hetero structure. In the device, a near-field probe is arranged right behind an aperture with a diameter of 8¦Ìm. With the adoption of the probe, the electromagnetic field distribution of the near-field light generated in the aperture, which is otherwise localized in one area, can be spatially expanded.

    The 2D electron gas that exists at the hetero interface between GaAs and AlGaAs, which is 60nm below the probe, is used as a detector. The detector measures the intensity distribution of electromagnetic wave based on the voltage variation of the 2D electron gas. The structure reportedly improved the detection sensitivity.

    The device also has an advantage of being unaffected by electromagnetic waves other than the near-field light (eg, background light), according to the institutes.

    A paper about this development was posted in the online advance version of a UK science journal, the ¡°Nature Photonics,¡± on Aug 10, 2008 (UK time). Further improvements will be made to achieve higher resolution and sensitivity, according to JST and Riken.

 
 

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