A coherent detection technique via optically biased field for broadband terahertz radiation.

We demonstrate theoretically and experimentally a coherent terahertz detection technique based on an optically biased field functioning as a local oscillator and a second harmonic induced by the terahertz electric field in the air sensor working in free space. After optimizing the polarization angle and the energy of the probe pulse, and filling the system with dry nitrogen, the terahertz radiation generated from a two-color-femtosecond-laser-pulses induced plasma filament is measured by this technique with a bandwidth of 0.1-10 THz and a signal-to-noise ratio of 48 dB.

[Progress of Detection Technology of Ultra-Broadband THz Time-Domain Spectroscopy].

Terahertz Time-Domain Spectroscopy (THz-TDS) is one of the effective coherent detection techniques. It has been widely applied in materials, chemistry, biology, security and other fields due to its capabilities such as high signal-to-noise ratio (SNR), broadband detection, working at room temperature, time resolved measurement and others. Limited by the spectrum bandwidth of THz radiation and detection techniques, the measuring range of the traditional THz-TDS system is generally less than several THz, thus the spectral information of high frequencies cannot be obtained.