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Broadband terahertz wave remote sensing using coherent manipulation of fluorescence from asymmetrically ionized gases


Terahertz wave sensing and imaging have received a great deal of attention because of their significant scientific and technological potential in multidisciplinary fields1,2,3. However, owing to the challenge of dealing with high ambient moisture absorption, the development of remote open-air broadband terahertz spectroscopy is lagging behind the urgent need for the technology that exists in homeland security and the fields of astronomy and environmental monitoring3,4. The requirement for on-site bias or forward collection of the optical signal in conventional terahertz detection techniques has inevitably prohibited their use in remote sensing5,6,7. We introduce an ‘all-optical’ technique of broadband terahertz wave detection by coherently manipulating the fluorescence emission from asymmetrically ionized gas plasma interacting with terahertz waves. Owing to the high atmospheric transparency and omnidirectional emission pattern of the fluorescence, this technique can be used to measure terahertz pulses at standoff distances with minimal water vapour absorption and unlimited directionality for optical signal collection. We demonstrate coherent terahertz wave detection at a distance of 10 m.

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Figure 1: Schematic of the terahertz wave remote sensing technique.
Figure 2: The terahertz wave assisted electron impact ionization of high-lying states in plasma.
Figure 3: Differential THz-REEF, coherent terahertz detection and simulation.
Figure 4: Broadband terahertz wave remote sensing.
Figure 5: Two-colour phase dependence of fluorescence and terahertz wave emission.

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The authors thank N. Karpowicz for technical assistance and scientific discussions. We also gratefully acknowledge support from the National Science Foundation, Defense Threat Reduction Agency and the Department of Homeland Security through the DHS-ALERT Center under award no. 2008-ST-061-ED0001. The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. Department of Homeland Security.

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J.L. designed the experiment and performed the simulation. J.D. designed the phase compensator and performed remote terahertz sensing. X.-C.Z. and S.L.C. provided theoretical analysis and guidance. X.-C.Z. initiated and supervised the project. All authors contributed to the final manuscript.

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Correspondence to X.-C. Zhang.

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Liu, J., Dai, J., Chin, S. et al. Broadband terahertz wave remote sensing using coherent manipulation of fluorescence from asymmetrically ionized gases. Nature Photon 4, 627–631 (2010).

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