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.
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.
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 email@example.com.