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Updated: Jul 19, 2026

Characterizing Far-infrared Laser Emissions and the Measurement of Their Frequencies
Published on: December 18, 2015
Detection of broadband terahertz waves with a laser-induced plasma in gases
Jianming Dai1, Xu Xie, X-C Zhang
1Center for Terahertz Research, Rensselaer Polytechnic Institute, Troy, New York 12180, USA.
Abstract:
We report the experimental results and theoretical analysis of broadband detection of terahertz (THz) waves via electric-field-induced second-harmonic generation in laser-induced air plasma with ultrashort laser pulses. By introducing the second-harmonic component of the white light in the laser-induced plasma as a local oscillator, coherent detection of broadband THz waves with ambient air is demonstrated for the first time. Our results show that, depending on the probe intensity, detection of THz waves in air can be categorized as incoherent, hybrid, and coherent detection. Coherent detection is achieved only when the tunnel ionization process dominates in gases.
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