Terahertz waves generated and detected in ambient air

Researchers at Rensselaer Polytechnic Institute (Troy, NY) have demonstrated the use of ambient air as a sensing medium for the broadband detection of terahertz waves.

Apr 1st, 2006
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Researchers at Rensselaer Polytechnic Institute (Troy, NY) have demonstrated the use of ambient air as a sensing medium for the broadband detection of terahertz waves. Combined with terahertz-wave generation in air with femtosecond ­laser beams, the all-air and all-optical sensing approach is expected to enable remote terahertz-wave sensing and spectroscopy in high-humidity atmospheric environments.

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The terahertz wave was experimentally generated by mixing the fundamental pump beam and its second harmonic at the air-plasma point (right). A parabolic mirror (right) collimated the terahertz beam. A high-resistivity silicon filter blocked the residual pump and second-harmonic beams. A second parabolic mirror (left) focused the collimated terahertz beam. The terahertz wave was detected by the reciprocal process of its generation. A second-harmonic signal was produced by mixing the fundamental probe beam (polarization controlled by a λ/2 ­waveplate) and the terahertz field, both focused at the same point, with estimated focusing spot sizes of 800 and 20 µm for the terahertz wave and optical beam, ­respectively. By measuring the time-resolved second-harmonic signal, the amplitude and phase of the terahertz field were coherently detected using homodyne detection. Contact X.-C. Zhang at zhangxc@rpi.edu.

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