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Fabrizio Buccheri * and Xi-Cheng Zhang
The Institute of Optics, University of Rochester, 275 Hutchison Road, Rochester, NY, 14627 USA
* Email: fbuccher@ur.rochester.edu
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Abstract: Ambient air can be used as a THz wave emitter and/or THz sensor when ionized by femtosecond laser fields. The integration of such a plasma source and detector in terahertz time-domain techniques allows spectral measurements covering the elusive terahertz gap, further increasing the impact of those scientific tools in the study of the four states of matter. We report on a new paradigm for implementing THz plasma techniques. Specifically, we replace the use of elongated plasmas, with lengths ranging from a few mm to several cm, with sub-mm size plasmas, which we will refer to as microplasmas, obtained by focusing laser pulses with high numerical aperture microscope objectives (NA > 0.4). Those microplasmas have in fact unique properties compared to any other THz source and sensor, with the potential of enabling new and exciting applications. Specifically, a microplasma requires orders of magnitude less laser pulse energy to be created, enabling plasma-based terahertz technique to be implemented with low energy ultrafast lasers. Moreover, they offer a generation, or detection, volume with sub-wavelength size (1 THz = 300 μm), which could be exploited to implement near-field THz plasma techniques. In this paper we describe the experimental study of the terahertz emission from a laser-induced plasma of submillimeter size. One of the interesting phenomena is that the main direction of THz wave emission is almost orthogonal to the laser propagation direction, unlike that of elongated plasmas. Perhaps the most important achievement is that we have demonstrated that laser pulse energies lower than 1 μJ are sufficient to generate measurable terahertz pulses from ambient air. This significant decrease in the required laser energy will make plasma-based terahertz techniques more accessible to the scientific community.
Keywords: Terahertz spectroscopy, Plasmas, Photoionization, Ultrafast nonlinear optics.
Received: 2015-6-17
Published: 2015-6-30
Cite this article:
Fabrizio Buccheri and Xi-Cheng Zhang. Terahertz wave generation based on laser-induced microplasmas[J]. International Journal of Terahertz Science and Technology, 2015, Vol.8, No.2: 58-68. DOI:10.11906/TST.058-068.2015.06.07
URL: http://www.tstnetwork.org/10.11906/TST.058-068.2015.06.07
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